Morphology and synaptic connectivity of nitric oxide synthase-immunoreactive neurons in the guinea pig retina

Immunocytochemical methods with an antiserum against neuronal nitric oxide synthase (NOS) were applied to identify the morphology and synaptic connectivity of NOS-like immunoreactive neurons in the guinea pig retina. In the present study, two types of amacrine cells were labeled with anti-NOS antisera. Type 1 cells had large somata located in the inner nuclear layer (INL) with long, sparsely branched processes ramifying mainly in stratum 3 of the inner plexiform layer (IPL). The somata of type 2 cells (smaller diameters) were located in the INL. Some displaced amacrine cells in the ganglion cell layer were labeled. The soma size of the displaced amacrine cells was similar to that of the type 2 amacrine cells. However, processes originating from type 2 amacrine cells and displaced amacrine cells stratified mainly in strata 1 and 5, respectively. Some cone bipolar cells were weakly NOS-immunoreactive. The synaptic connectivity of NOS-like immunoreactive amacrine cells was identified in the IPL by electron microscopy. NOS-labeled amacrine cell processes received synaptic input from other amacrine cell processes and bipolar cell axon terminals in all strata of the IPL. The most frequent postsynaptic targets of NOS-immunoreactive amacrine cells were other amacrine cell processes. Cone bipolar cells were postsynaptic to NOS-labeled amacrine cells in all strata of the IPL. Labeled amacrine cells synapsing onto ganglion cells were found only in sublamina b. A few synaptic contacts were observed between labeled cell processes. In the outer plexiform layer, dendrites of labeled bipolar cells made basal contact with cone pedicles or formed a synaptic triad opposed to a synaptic ribbon of cone pedicles.     

Intracellular activity of morphologically identified neurons of the grass frog's optic tectum in response to moving configurational visual stimuli

Summary In the grass frogRana temporaria, various classes of tectal neurons were identified by means of intracellular recording and iontophoretic staining using potassium-citrate/Co³⁺-lysine-filled micropipettes, which have been defined previously by extracellular recording methods. Class T5(1) neurons had receptive fields (RF) of 33°±5° diameter. In response to a moving 8°×8° square (S), a 2°×16° worm-like (W), or a 16°×2° antiworm-like (A) moving stripe, these cells showed excitatory postsynaptic potentials (EPSPs) and spikes which were interrupted occasionally by small inhibitory postsynaptic potentials (IPSPs). The excitatory responses (R) were strongest towards the square (R_S) and less to the worm (R_W). For the antiworm (R_A) the responses were smallest or equal to the worm stimulus yielding the relationship R_S>R_WR_A. Some of these cells were identified as pear-shaped or large ganglionic neurons, whose somata were located in the tectal cell layer 8. The somata of other large ganglionic neurons were found in layer 7 and the somata of other pear-shaped neurons at the top of layer 6, both displaying T5(1) properties. Class T5(2) neurons (RF=34°±3°) responded with large EPSPs and spikes, often interrupted by small IPSPs, when their RF was traversed by the square stimulus. The excitatory activity was somewhat less to the worm stimulus, whereas no activity at all, or only IPSPs, were recorded in response to the antiworm-stimulus; thus yielding the relationship for the excitatory activity R_S>R_W>R_A 0. Such a cell was identified as pyramidal neuron; the soma was located at the top of layer 6, with the long axon travelling into layer 7 to the medulla oblongata. Class T5(3) neurons (RF=29°±6°) showing EPSPs and spikes according to the relationship R_S>R_A>R_W have been identified as large ganglionic neurons. Their somata were located in layer 8. Class T5(4) neurons (RF=24±7°) responded only to the square stimulus with EPSPs and spikes, sometimes interrupted by IPSPs and yielding the relationship R_S>R_AR_W0. The somata of these large ganglionic or pear-shaped neurons were located in layer 8. Class T1(1) neurons (RF=30°–40°) were most responsive to stimuli moving at a relatively long distance in the binocular visual field, and have been identified as pear-shaped neurons. Their somata were located in layer 6.Further neurons are described and morphologically identified which have not yet been classified by extracellular recording methods. For example,IPSP neurons (RF=20°–30°) responded (R) with IPSPs only according to the relationship R_S>R_A R_W. The somata of these pear-shaped neurons were located in layer 6.The properties of tectal cells in response to electrical stimulation of the optic tract and to brisk changes of diffuse illumination suggest certain neuronal connectivity patterns. The results support the idea ofintegrative functional units (assemblies) of connected cells which are involved in various perceptual processes, such as configurational prey selection expressed by T5(2) prey-selective neurons.Abbreviations A antiworm-like 16°×2° stripe stimulus with long axis perpendicular to the direction of movement - W wormlike 2°×16° stripe stimulus with long axis oriented parallel to the direction of movement - S square 8°×8° moving stimulus - ERF excitatory receptive field - IRF inhibitory receptive field - RF receptive field - EPSP excitatory postsynaptic potential - IPSP inhibitory postsynaptic potential     

Immunochemical and electrophysiological analyses of magnetically responsive neurons in the mollusc Tritonia diomedea

Tritonia diomedea uses the Earth’s magnetic field as an orientation cue, but little is known about the neural mechanisms that underlie magnetic orientation behavior in this or other animals. Six large, individually identifiable neurons in the brain of Tritonia (left and right Pd5, Pd6, Pd7) are known to respond with altered electrical activity to changes in earth-strength magnetic fields. In this study we used immunochemical, electrophysiological, and neuroanatomical techniques to investigate the function of the Pd5 neurons, the largest magnetically responsive cells. Immunocytochemical studies localized TPeps, neuropeptides isolated from Pd5, to dense-cored vesicles within the Pd5 somata and within neurites adjacent to ciliated foot epithelial cells. Anatomical analyses revealed that neurites from Pd5 are located within nerves innervating the ipsilateral foot and body wall. These results imply that Pd5 project to the foot and regulate ciliary beating through paracrine release. Electrophysiological recordings indicated that, although both LPd5 and RPd5 responded to the same magnetic stimuli, the pattern of spiking in the two cells differed. Given that TPeps increase ciliary beating and Tritonia locomotes using pedal cilia, our results are consistent with the hypothesis that Pd5 neurons control or modulate the ciliary activity involved in crawling during orientation behavior.     

Patch-clamp analysis of voltage- and ligand-activated whole-cell currents in freshly dissociated neurons of the locust optic lobe

Whole-cell patch-clamp recordings were obtained from 116 freshly dissociated neuronal somata from the optic lobe of adult locusts (Schistocerca gregaria). Prerequisites were a papain treatment and the directed transfer of somata to the recording chamber by dabbing. Of the recorded somata, 65 were from lamina and 51 from other optic lobe neurons. All somata supported voltage-activated outward currents and some (24% of optic lobe, 3% of lamina neurons) also fast inward currents. Most lamina neurons supported an outward current that activated (V _1/2=−8.5 mV) and inactivated rapidly and a sustained outward current. Some lamina and most optic lobe neurons expressed only a sustained outward current (V _1/2=−9.4 mV). GABA and histamine elicited inward currents at negative holding potentials. Most optic lobe (95%) but only 18% of lamina neurons showed a γ-aminobutyric acid (GABA) current, whereas a similar percentage of optic lobe (50%) and lamina neurons (67%) expressed a histamine current. Both currents reversed near the chloride equilibrium potential, were reversibly reduced by picrotoxin, and did not show rundown. Thus, they likely represent chloride currents mediated by ionotropic receptors. Our data indicate that the lamina neurons recorded mainly represent monopolar cells postsynaptic to histaminergic photoreceptors. The optic lobe neurons, on which GABA and histamine apparently act as inhibitory neurotransmitters, are more heterogeneous. Accepted: 30 November 1997     

Responses of medullary neurons to moving visual stimuli in the common toad

Summary Intracellular recording and labeling of cells from the toad's (Bufo bufo spinosus) medulla oblongata in response to moving visual (and tactual) stimuli yield the following results. (i) Various response types characterized by extracellular recording in medullary neurons were also identified intracellularly and thus assigned to properties of medullary cell somata. (ii) Focussing on monocular small-field and cyclic bursting properties, somata of such neurons were recorded most frequently in the medial reticular formation and in the branchiomotor column but less often in the lateral reticular formation. (iii) Visual object disrimination established in pretectal/tectal networks is increased in its acuity in 4 types of medullary small-field neurons. The excitatory and inhibitory inputs to these neurons evoked by moving visual objects suggest special convergence likely to increase the filter properties. (iv) Releasing conditions, temporal pattern, and refractoriness of cyclic bursting neurons resemble membrane characteristics of vertebrate and invertebrate neurons known to play a role in premotor/motor activity. (v) Integrating functions of medullary cells have an anatomical correlate in the extensive arborizations of their dendritic trees; 5 morphological types of medullary neurons have been distinguished.Abbreviations A stripe moving in antiworm configuration - (W) moving in worm configuration - S square - BMC branchiomotor column - EPSP excitatory postsynaptic potential - IPSP inhibitory postsynaptic potential - RetF medullary reticular formation - RF receptive field - M neurons response properties of medullary neurons - T neurons classes of tectal neurons - TH neurons classes of thalamic/pretectal neurons - tr.tb.d. tractus tecto-bulbaris directus - tr.tbs.c. tractus tecto-bulbaris et spinalis cruciatus     

Properties of central motor neurons exciting locomotory cilia inTritonia diomedea

Summary A pair of large, identifiable neurons (Pd 21), one in each pedal ganglion, can excite previously inactive locomotory cilia on the sole of the foot ofTritonia diomedea (Audesirk, 1978; Fig. 3). These neurons exert their effect via axons which innervate the foot and are probably central motor neurons for pedal cilia. IntactTritonia are stimulated to crawl by the application of 1.5 M NaCl to the tail, and conversely usually stop crawling when the chemosensitive oral veil is touched with food (sea whip,Virgularia sp.). The Pd 21 neurons are excited by 1.5 M NaCl applied externally to the tail, and are inhibited by sea whip touch to the oral veil (Figs. 4 and 5). When aTritonia performs its escape swim, the cilia move strongly, and the Pd 21 neurons fire bursts of spikes in phase with dorsal flexions (Figs. 6 and 7). After a swim, aTritonia rapidly crawls along the substrate; during this time the spiking rate of the Pd 21s is greatly accelerated. Interneurons thought to drive swim bursts produce monosynaptic EPSPs in the Pd 21s (Fig. 8). The Pd 21s are coordinated in their spike activity by synaptic activity which is synchronous in the two neurons regardless of the site of external stimulation, and by electrical coupling between the two cells via axons in a pedal commissure (Figs. 9 and 10). The coupling coefficient for passively conducted potentials is quite high, about 0.15, despite an axon 8 to 12 mm long separating the two cells.Abbreviations BPSP biphasic postsynaptic potential - SW sea water     

Organization of efferent extraspinal sympathetic pathways in Rana esculenta

Origin and distribution of pre- and postsynaptic fibres in the sympathetic trunk of Rana esculenta (from ganglion 3 to ganglion 10) have been investigated by means of extracellular recordings. Two systems conducting efferent information appear to exist: 1) a system made of faster conducting fibres (B group pre- and postsynaptic fibres); presynaptic fibres originating from a very high monosegmental source (4th spinal root); postsynaptic fibres leave the sympathetic chain plurisegmentally (rami communicantes 5-10); 2) a system made of slower conducting fibres (C group pre- and postsynaptic fibres) originating plurisegmentally from spinal roots 5-8. Intracellular recordings have shown that: 1) integrative processes take place in the amphibian sympathetic trunk, as in the mammalian one, but are quantitatively lesser. Homonomous (B-B) and heteronomous (B-C) convergence has been observed in B neurons, and also the convergence of a collateral of a C postsynaptic axon on B neurons. 2) posthumous depolarizations are present: these are events modulating the activity of sympathetic neurons. In B neurons posthumous depolarization follows orthodromic responses, and a late posthumous depolarization can be seen in B and C neurons following either ortho- or antidromic stimulation.     

Characterization of the synaptic actions of an interneuron in the central nervous system of Tritonia

The motor program that drives the swimming behavior of the marine mollusk Tritonia diomedea is generated by three interneuronal populations in the cerebral ganglia. One of these populations, the pair of C2 neurons, is shown to also exert powerful synaptic actions upon most cells in the contralateral pedal ganglion. Intracellular staining with Co²⁺ showed that the C2 neurons projected to the contralateral pedal ganglion as a single unbranched axon, and nearly all contralateral pedal neurons received monosynaptic input from C2. Orthodromic stimulation of most peripheral nerves caused monosynaptic excitation of C2 by afferent sensory cells and, in some cases, monosynaptic inhibition from an unidentified source. C2 neurons produced four types of postsynaptic potential (PSP) on pedal neurons: (1) a fast, Cl^?-mediated inhibition (FIPSP); (2) a fast, Na⁺-mediated excitation (FEPSP); (3) a slow, K⁺-mediated inhibition (SIPSP); and (4) a slow, conductance-decrease excitation (SEPSP). All four could be recorded simultaneously in some pedal neurons. The C2 neurons appear to be high-order, multiaction neurons involved in both the generation of a complex motor program and the coordination of ancillary neuronal activity.     

Distribution of inhibitory synapses on the somata of pyramidal neurons in cat motor cortex

The mechanisms by which cortical neurons perform spatial and temporal integration of synaptic inputs are dependent, in large part, on the numbers, types, and distributions of their synapses. To further our understanding of these integrative mechanisms, we examined the distribution of synapses on identified classes of cortical neurons. Pyramidal cells in the cat motor cortex projecting either to the ipsilateral somatosensory cortex or to the spinal cord were labeled by the retrograde transport of horseradish peroxidase. Entire soma of selected corticocortical and corticospinal cells were examined using serial-section electron microscopy. The profiles of these somata and the synapses formed with each of these profiles were reconstructed from each thin section with a computer-aided morphometry system. All somatic synapses were of the symmetrical, presumably inhibitory type. For both cell types, these synapses were not homogeneously distributed over the somatic membrane, but were clustered at several discrete zones. The number and density of synapses on the somata of different corticocortical and corticospinal neurons were not significantly different. However, the density of these synapses was inversely correlated with the size of their postsynaptic somata. We discuss the significance of these findings to the integrative properties of cortical neurons.     

Light- and electron-microscopic study of substance P-immunoreactive neurons in the guinea pig retina

Substance P (SP) immunoreactivity in the guinea pig retina was studied by light and electron microscopy. The morphology and distribution of SP-immunoreactive neurons was defined by light microscopy. The SP-immunoreactive neurons formed one population of amacrine cells whose cell bodies were located in the proximal row of the inner nuclear layer. A single dendrite emerged from each soma and descended through the inner plexiform layer toward the ganglion cell layer. SP-immunoreactive processes ramified mainly in strata 4 and 5 of the inner plexiform layer. SP-immunoreactive amacrine cells were present at a higher density in the central region around the optic nerve head and at a lower density in the peripheral region of the retina. The synaptic connectivity of SP-immunoreactive amacrine cells was identified by electron microscopy. SP-labeled amacrine cell processes received synaptic inputs from other amacrine cell processes in all strata of the inner plexiform layer and from bipolar cell axon terminals in sublamina b of the same layer. The most frequent postsynaptic targets of SP-immunoreactive amacrine cells were the somata of ganglion cells and their dendrites in sublamina b of the inner plexiform layer. Amacrine cell processes were also postsynaptic to SP-immunoreactive neurons in this sublamina. No synaptic outputs onto the bipolar cells were observed.     

Opposite effects of PSD-95 and MPP3 PDZ proteins on serotonin 5-hydroxytryptamine2C receptor desensitization and membrane stability

PSD-95/Disc large/Zonula occludens 1 (PDZ) domain-containing proteins (PDZ proteins) play an important role in the targeting and the trafficking of transmembrane proteins. Our previous studies identified a set of PDZ proteins that interact with the C terminus of the serotonin 5-hydroxytryptamine (5-HT)(2C) receptor. Here, we show that the prototypic scaffolding protein postsynaptic density-95 (PSD-95) and another membrane-associated guanylate kinase, MAGUK p55 subfamily member 3 (MPP3), oppositely regulate desensitization of the receptor response in both heterologous cells and mice cortical neurons in primary culture. PSD-95 increased desensitization of the 5-HT(2C) receptor-mediated Ca(2+) response, whereas MPP3 prevented desensitization of the Ca(2+) response. The effects of the PDZ proteins on the desensitization of the Ca(2+) response were correlated with a differential regulation of cell surface expression of the receptor. Additional experiments were performed to assess how PDZ proteins globally modulate desensitization of the 5-HT(2C) receptor response in neurons, by using a peptidyl mimetic of the 5-HT(2C) receptor C terminus fused to the human immunodeficiency virus type-1 Tat protein transduction domain, which disrupts interaction between the 5-HT(2C) receptor and PDZ proteins. Transduction of this peptide inhibitor into cultured cortical neurons increased the desensitization of the 5-HT(2C) receptor-mediated Ca(2+) response. This indicates that, overall, interaction of 5-HT(2C) receptors with PDZ proteins inhibits receptor desensitization in cortical neurons.     

Target cell contact suppresses neurite outgrowth from soma-soma paired Lymnaea neurons

Neurite extension from developing and/or regenerating neurons is terminated on contact with their specific synaptic partner cells. However, a direct relationship between the effects of target cell contact on neurite outgrowth suppression and synapse formation has not yet been demonstrated. To determine whether physical/synaptic contacts affect neurite extension from cultured cells, we utilized soma-soma synapses between the identified Lymnaea neurons. A presynaptic cell (right pedal dorsal 1, RPeD1) was paired either with its postsynaptic partner cells (visceral dorsal 4, VD4, and Visceral dorsal 2, VD2) or with a non-target cell (visceral dorsal 1, VD1), and the interactions between their neurite outgrowth patterns and synapse formation were examined. Specifically, when cultured in brain conditioned medium (CM, contains growth-promoting factors), RPeD1, VD4, and VD2 exhibited robust neurite outgrowth within 12-24 h of their isolation. Synapses, similar to those seen in vivo, developed between the neurites of these cells. RPeD1 did not, however, synapse with its non-target cell VD1, despite extensive neuritic overlap between the cells. When placed in a soma-soma configuration (somata juxtaposed against each other), appropriate synapses developed between the somata of RPeD1 and VD4 (inhibitory) and between RPeD1 and VD2 (excitatory). Interestingly, pairing RPeD1 with either of its synaptic partner (VD4 or VD2) resulted in a complete suppression of neurite outgrowth from both pre- and postsynaptic neurons, even though the cells were cultured in CM. A single cell in the same dish, however, extended elaborate neurites. Similarly, a postsynaptic cell (VD4) contact suppressed the rate of neurite extension from a previously sprouted RPeD1. This suppression of the presynaptic growth cone motility was also target cell contact specific. The neurite suppression from soma-soma paired cells was transient, and neuronal sprouting began after a delay of 48-72 h. In contrast, when paired with VD1, both RPeD1 and this non-target cell exhibited robust neurite outgrowth. We demonstrate that this neurite suppression from soma-soma paired cells was target cell contact/synapse specific and Ca(2+) dependent. Specifically, soma-soma pairing in CM containing either lower external Ca(2+) concentration (50% of its control level) or Cd(2+) resulted in robust neurite outgrowth from both cells; however, the incidence of synapse formation between the paired cells was significantly reduced. Taken together, our data show that contact (physical and/or synaptic) between synaptic partners strongly influence neurite outgrowth patterns of both pre- and postsynaptic neurons in a time-dependent and cell-specific manner. Moreover, our data also suggest that neurite outgrowth and synapse formation are differentially regulated by external Ca(2+) concentration.     

Distribution of motor cortical neuron synaptic terminals on monkey parvocellular red nucleus neurons.

We determined the location of 54 horseradish peroxidase (HRP)-labeled motor cortical neuron synaptic terminals on 17 parvocellular neurons in the monkey red nucleus. Synaptic terminals and their postsynaptic elements were identified and reconstructed, using light- and electron-microscopic techniques, from serial thick and thin sections. Terminals were found on proximal and distal dendrites of small and medium-sized parvocellular neurons, where they formed excitatory synapses. Some were 180 microns from cell somata. Approximately half of the labeled terminals, aside from those located at dendritic origins, were situated strategically at or near dendritic branch points. Since monkey parvocellular neurons show little activity during movement, the obvious next question is this: How and in what way does motor cortex influence these cells?     

The GTPase dMiro is required for axonal transport of mitochondria to Drosophila synapses

We have identified EMS-induced mutations in Drosophila Miro (dMiro), an atypical mitochondrial GTPase that is orthologous to human Miro (hMiro). Mutant dmiro animals exhibit defects in locomotion and die prematurely. Mitochondria in dmiro mutant muscles and neurons are abnormally distributed. Instead of being transported into axons and dendrites, mitochondria accumulate in parallel rows in neuronal somata. Mutant neuromuscular junctions (NMJs) lack presynaptic mitochondria, but neurotransmitter release and acute Ca2+ buffering is only impaired during prolonged stimulation. Neuronal, but not muscular, expression of dMiro in dmiro mutants restored viability, transport of mitochondria to NMJs, the structure of synaptic boutons, the organization of presynaptic microtubules, and the size of postsynaptic muscles. In addition, gain of dMiro function causes an abnormal accumulation of mitochondria in distal synaptic boutons of NMJs. Together, our findings suggest that dMiro is required for controlling anterograde transport of mitochondria and their proper distribution within nerve terminals.     

Characteristics of GABAergic neurons and their synaptic relationships with intrinsic axons in the cat motor cortex

The intrinsic circuitry of the motor cortex comprises a complex network of connections whose synaptic relationships are poorly understood. This study was designed to determine the characteristics of subsets of GABAergic neurons containing the calcium-binding proteins parvalbumin (PV) and calbindin (CB), and their relationships with intrinsic axons in motor cortex. Immunohistochemically identified PV-containing neuronal profiles were more evenly distributed across cortical laminae (38% in II-III, 32% inV, 30% in VI) and more numerous (2.1/1) than CB-containing neuronal profiles (71% in II-III, 17% in V, 12% in VI). Relationships between neurons and axons intrinsic to motor cortex were visualized with fluorescent markers using the laser scanning confocal microscope. Similar percentages of PV (43%) and CB-immunoreactive (IR) (40%) neurons formed sparsely distributed appositions (1-5/neuron) with anterogradely labeled axons. The mean distances of such appositions from the somata were significantly different for the two groups (PV, mean = 22 microm, range = 1.6-93 microm; CB, mean = 32 microm, range = 6.2-132 microm). PV-IR neurons had a lower ratio of axosomatic/axodendritic appositions (1/99) compared with CB-IR neurons (14/86). Ultrastructural studies confirmed these findings. Fifty-seven percent of CB-IR neurons and 38% of PV-IR neurons formed synapses with intrinsic axons. Both populations received sparse input (1-6 synapses/neuron). Nearly all appositions between labeled terminals and postsynaptic profiles formed one synapse. Postsynaptic dendrites of PV-IR neurons (mean = 1.4 microm diameter) were larger than those of CB-IR neurons (mean = 1.1 microm), indicating more proximal synapses. Distinct input patterns of intrinsic axons to the two populations of neurons suggest unique roles in cortical processing.     

Characteristics of GABAergic neurons and their synaptic relationships with intrinsic axons in the cat motor cortex

The intrinsic circuitry of the motor cortex comprises a complex network of connections whose synaptic relationships are poorly understood. This study was designed to determine the characteristics of subsets of GABAergic neurons containing the calcium-binding proteins parvalbumin (PV) and calbindin (CB), and their relationships with intrinsic axons in motor cortex. Immunohistochemically identified PV-containing neuronal profiles were more evenly distributed across cortical laminae (38% in II-III, 32% in V, 30% in VI) and more numerous (2.1/1) than CB-containing neuronal profiles (71% in II-III, 17% in V, 12% in VI). Relationships between neurons and axons intrinsic to motor cortex were visualized with fluorescent markers using the laser scanning confocal microscope. Similar percentages of PV (43%) and CBimmunoreactive (IR) (40%) neurons formed sparsely distributed appositions (1-5/neuron) with anterogradely labeled axons. The mean distances of such appositions from the somata were significantly different for the two groups (PV, mean =22 mum, range = 1.6-93 mum; CB, mean = 32 mum, range = 6.2-132 mum). PV-IR neurons had a lower ratio of axosomatic/ axodendritic appositions (1/99) compared with CB-IR neurons (14/86). Ultrastructural studies confirmed these findings. Fifty-seven percent of CB-IR neurons and 38% of PV-IR neurons formed synapses with intrinsic axons. Both populations received sparse input (1-6 synapses/neuron). Nearly all appositions between labeled terminals and postsynaptic profiles formed one synapse. Postsynaptic dendrites of PV-IR neurons (mean = 1.4 mum diameter) were larger than those of CB-IR neurons (mean = 1.1 mum), indicating more proximal synapses. Distinct input patterns of intrinsic axons to the two populations of neurons suggest unique roles in cortical processing.     

Octopamine-like immunoreactivity in the dorsal unpaired median (DUM) neurons innervating the accessory gland of the male cockroach Periplaneta americana

The musculature of the mushroom-shaped accessory gland receives innervation from trunks 5C1 of the phallic nerves, which arise from the posterior part of the terminal abdominal ganglion of the male cockroach Periplaneta americana. Anterograde cobalt filling through trunks 5C1 with the subsequent precipitating procedure has shown the fine innervation of the accessory gland. By retrograde cobalt filling through the same trunks, different types of cells have been mapped in the terminal abdominal ganglion. About 25 dorsal unpaired median (DUM) neurons have been identified among them. About 36 octopamine-like immunoreactive DUM neurons with large somata have been characterized in whole-mount preparations of the terminal abdominal ganglion. The combination of the cobalt-filling technique with immunohistochemical mapping of cells suggests an octopaminergic innervation of the musculature of the accessory gland by DUM neurons.     

Morphology and electrophysiological properties of neurons projecting to the retrocerebral complex in the blow fly, <Emphasis Type="Italic">Protophormia terraenovae</Emphasis>

Morphological and electrical properties of neurons with somata in the pars intercerebralis (PI) and pars lateralis (PL) were examined by intracellular recording and staining in the adult blow fly, Protophormia terraenovae. According to the location of somata and fiber distribution, two types of PI neurons (PIa and PIb) and two types of PL neurons (PLa and PLb) were identified. PIb neurons were further divided into two subgroups of PIb₁ and PIb₂ depending on fiber branching patterns in the retrocerebral complex. PIa neurons projected axons to the contralateral nervi corporis cardiaci, whereas PLa and PLb neurons projected axons to the ipsilateral nervi corporis cardiaci. PIb neurons characteristically showed symmetrical morphology with their somata along the midline. PLb neurons had a large branching area in the subesophageal ganglion. In the retrocerebral complex, PIb₂ and PLa neurons sent fibers into the corpus allatum. PIa, PIb₁ and PLb neurons projected not to the corpus allatum but to the corpus cardiacum–hypocerebral complex or visceral muscles in their vicinity. PIa, PIb and PLa neurons showed long spike durations (3–10 ms). PLb neurons were immunoreactive with antisera against corazonin, FMRFamide, or -pigment-dispersing hormone. This is the first report revealing the morphology of individual neurons with somata residing in PI and PL in the adult fly.The authors acknowledge a research grant from the Naito Foundation, a Grant-in-Aid for Scientific Research C (13640686) from the Japan Society for the Promotion of Science, and a Grant-in-Aid for Young Scientists B (15770050) from the Ministry of Education, Culture, Sports, Science, and Technology of Japan     

NO inhibits supraoptic oxytocin and vasopressin neurons via activation of GABAergic synaptic inputs

To study modulatory actions of nitric oxide (NO) on GABAergic synaptic activity in hypothalamic magnocellular neurons in the supraoptic nucleus (SON), in vitro and in vivo electrophysiological recordings were obtained from identified oxytocin and vasopressin neurons. Whole cell patch-clamp recordings were obtained in vitro from immunochemically identified oxytocin and vasopressin neurons. GABAergic synaptic activity was assessed in vitro by measuring GABA(A) miniature inhibitory postsynaptic currents (mIPSCs). The NO donor and precursor sodium nitroprusside (SNP) and L-arginine, respectively, increased the frequency and amplitude of GABA(A) mIPSCs in both cell types (P < or = 0.001). Retrodialysis of SNP (50 mM) onto the SON in vivo inhibited the activity of both neuronal types (P < or = 0.002), an effect that was reduced by retrodialysis of the GABA(A)-receptor antagonist bicuculline (2 mM, P < or = 0.001). Neurons activated by intravenous infusion of 2 M NaCl were still strongly inhibited by SNP. These results suggest that NO inhibition of neuronal excitability in oxytocin and vasopressin neurons involves pre- and postsynaptic potentiation of GABAergic synaptic activity in the SON.     

Identification of 5-HT receptor subtypes enhancing inhibitory transmission in the rat spinal dorsal horn in vitro

ABSTRACT: BACKGROUND: 5-hydroxytryptamine (5-HT) is one of the major neurotransmitters widely distributed in the CNS. Several 5-HT receptor subtypes have been identified in the spinal dorsal horn which act on both pre- and postsynaptic sites of excitatory and inhibitory neurons. However, the receptor subtypes and sites of actions as well as underlying mechanism are not clarified rigorously. Several electrophysiological studies have been performed to investigate the effects of 5-HT on excitatory transmission in substantia gelatinosa (SG) of the spinal cord. In the present study, to understand the effects of 5-HT on the inhibitory synaptic transmission and to identify receptor subtypes, the blind whole cell recordings were performed from SG neurons of rat spinal cord slices. RESULTS: Bath applied 5-HT (50 microM) increased the frequency but not amplitudes of spontaneous inhibitory postsynaptic currents (sIPSCs) in 58% of neurons, and both amplitude and frequency in 23 % of neurons. The frequencies of GABAergic and glycinergic mIPSCs were both enhanced. TTX (0.5 microM) had no effect on the increasing frequency, while the enhancement of amplitude of IPSCs was eliminated. Evoked-IPSCs (eIPSCs) induced by focal stimulation near the recording neurons in the presence of CNQX and APV were enhanced in both amplitude by 5-HT. In the presence of Ba2+ (1 mM), a potassium channel blocker, 5-HT had no effect on both frequency and amplitude. A 5-HT2Areceptor agonist, TCB-2 mimicked the 5-HT effect, and ketanserin, an antagonist of 5-HT2A receptor, inhibited the effect of 5-HT partially and TCB-2 almost completely. A 5-HT2C receptor agonist WAY 161503 mimicked the 5-HT effect and this effect was blocked by a 5-HT2C receptor antagonist, N-desmethylclozapine. The amplitude of sIPSCs were unaffected by both agonists. A 5-HT3 receptor agonist mCPBG enhanced both amplitude and frequency of sIPSCs. This effect was blocked by a 5-HT3 receptor antagonist ICS-205,930. The perfusion of 5-HT2B receptor agonist had no effect on sIPSCs. CONCLUSIONS: Our results demonstrated that 5-HT modulated the inhibitory transmission in SG by the activation of 5-HT2A and 5-HT2C receptors subtypes located predominantly at inhibitory interneuron terminals, and 5-HT3 receptors located at inhibitory interneuron terminals and soma-dendrites, consequently enhanced both frequency and amplitude.