Localization of dopamine in the endocrine hypothalamus of the rat

Summary Microspectrofluorometry, fluorescence histochemistry and light and electron microscopic autoradiography have established the presence of sub-populations of neurons in the arcuate-periventricular region of the rat hypothalamus that sequester both radiolabeled dopamine and demonstrate formaldehyde-induced fluorescence. These characteristics are consistent with a catecholaminergic function. Selective sequestration of ³H-dopamine at the light and ultrastructural level is discussed in the context of an ultrashort loop autoregulatory mechanism for this neuronal population.Supported by USPHS Program Project Grants NS-11642, RR-05403USPHS Career Development Awardee K04 GM 70001.     

Terminal synthesis of xanthommatin in Drosophila melanogaster. II. Enzymatic formation of the phenoxazinone nucleus

Xanthommatin, the brown eye pigment of Drosophila melanogaster is a phenoxazinone compound formed by the bimolecular oxidative condensation of 3-hydroxykynurenine. Evidence is presented in this report for an enzyme system in drosophila which catalyzes the formation of the phenoxazinone chromophore of xanthommatin. This enzyme system, which is separable from the interfering activities of phenol oxidase and cytochrome oxidase, is relatively inactive in crude extracts but can be activated either by heat treatment or by passage through Sephadex G-50. The preliminary characterization of several properties of the enzyme-catalyzed reaction and their biological significance are discussed.Supported by USPHS grant GM12323 and by the Robert A. Welch Foundation, Houston, Texas.Postdoctoral Fellow supported by USPHS (1 FO2 GM44, 562-01) and the Rosalie B. Hite Memorial Fund.     

Organization of the stomatogastric ganglion of the spiny lobster

Summary The Stomatogastric ganglion ofPanulirus interruptus contains about 30 neurons, and controls the movements of the lobster's stomach. When experimentally isolated, the ganglion continues to generate complex rhythmic patterns of activity in its motor neurons which are similar to those seen in intact animals.In this paper, we describe the synaptic organization of a group of six neurons which drive the stomach's lateral teeth (Figs. 2, 6). This group includes four motor neurons and two interneurons, all but one of which were recorded and stimulated with intracellular microelectrodes.One pair of synergistic motor neurons, LGN and MGN, are electrotonically coupled and reciprocally inhibitory (Figs. 9, 12). A second pair of synergistic motor neurons, the LPGNs, are antagonists of LGN and MGN. The LPGNs are electrotonically coupled (Fig. 14), and are both inhibited by LGN and MGN (Figs. 8, 11). The LPGNs inhibit MGN (Fig. 15) but not LGN. One of the two interneurons in the ganglion, Int 1, reciprocally inhibits both LGN and MGN (Figs. 10, 13). The other interneuron, Int 2, excites Int 1 and inhibits the LPGNs (Fig. 16). The synaptic connections observed in the ganglion are reflected in the spontaneous activity recorded from the isolated ganglion and from intact animals.From the known synaptic organization and observations on the physiological properties of each of the neurons, we have formulated some hypotheses about the pattern-generating mechanism. We found no evidence that any of the neurons are endogenous bursters.We thank D. Kennedy, Eve Marder, and D. Russell for criticizing early drafts of these papers, Nina Pollack and Betty Jorgensen for expert technical assistance, Diane Newsome, SanDee Newcomb, and Pattie Macpherson for typing the many drafts. The authors' research is supported by grant number NS-09322 from N.I.H. and by the Alfred P. Sloan Foundation. B. M. is an NINDS-NIH postdoctoral fellow.     

Electrical characteristics of granule cells of the carp olfactory bulb

Intracellular responses of granule cells and secondary neurons of the carp olfactory bulb to electrical stimulation of the olfactory nerve and olfactory tract were investigated. Synaptic responses of granule cells to both types of stimuli consisted of an early and late EPSP and IPSP. Comparison of responses of the secondary and granule neurons indicated that the granule cells are interneurons of postsynaptic inhibition of secondary neurons. The results suggest that dendro-dendritic and recurrent collateral pathways exist for the activation of granule cells and that inhibitory synapses are located on those dendrites of the secondary neurons that are in contact with endings of olfactory nerve fibers.M. V. Lomonosov State University, Moscow. Translated from Neirofiziologiya, Vol. 7, No. 6, pp. 597–602, November–December, 1975.     

Postsynaptic inhibition in the general cortex of the turtle forebrain

Postsynaptic inhibition in the general cortex of the turtle forebrain was investigated by recording unit activity intracellularly. Depending on the type of IPSPs recorded in response to electrical stimulation of the contralateral optic nerve and cortical surface the neurons were subdivided into three groups: 1) with long direct IPSPs, 2) with long and short direct, and also recurrent IPSPs, 3) with short direct and recurrent IPSPs. It is concluded that inhibitory pathways of the short direct and recurrent IPSPs have a common final component, a stellate interneuron. Compared with the recurrent collaterals of the principal neurons, the direct afferents make contact with more distal portions of the dendrites of this cell. Synapses formed on dendrites of the principal neurons by axons of the stellate cells are nearer to the soma than synapses responsible for generation of the long direct IPSP.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 5, No. 4, pp. 375–383, July–August, 1973.     

Motor pattern generation of the posterior cardiac plate-pyloric system in the stomatogastric ganglion of the mantis shrimp Squilla oratoria

Activity patterns of the constituent neurons of the posterior cardiac plate-pyloric system in the stomatogastric ganglion of the mantis shrimp Squilla oratoria were studied by recording spontaneous burst discharges intracellularly from neuronal somata. These neurons were identified electrophysiologically, and synaptic connections among them were qualitatively analysed. The posterior cardiac plate constrictor, pyloric constrictor, pyloric dilator and ventricular dilator motoneurons, and the pyloric interneuron were involved in the posterior cardiac plate-pyloric system. All the cell types could produce slow burst-forming potentials which led to repetitive spike discharges. These neurons generated sequentially patterned outputs. Most commonly, the posterior cardiac plate neuron activity was followed by the activity of pyloric constrictor neurons, and then by the activity of pyloric dilator/pyloric interneuron, and ventricular dilator neurons. The motoneurons and interneuron in the posterior cardiac plate-pyloric system were connected to each other either by electrical or by inhibitory chemical synapses, and thus constructed the neural circuit characterized by a wiring diagram which was structurally similar to the pyloric circuit of decapods. The circuitry in the stomatogastric ganglion was strongly conserved during evolution between stomatopods and decapods, despite significant changes in the peripheral structure of the foregut. There were more electrical synapses in stomatopods, and more reciprocal inhibitory synapses in decapods.Abbreviations EJP excitatory junctional potential - IPSP inhibitory postsynaptic potential - CoG commissural ganglion - CPG central pattern generator - ion inferior oesophageal nerve - OG oesophageal ganglion - pcp posterior cardiac plate - son superior oesophageal nerve - STG stomatogastric ganglion - stn stomatogastric nerve - PY pyloric constrictor - PD pyloric dilator - VD ventricular dilator - AB pyloric interneuron - lvn lateral ventricular nerves - tcpm transverse cardiac plate muscle     

Mathematical model of memory trace and forgetfulness

A mathematical model of a memory trace and forgetfulness is proposed here based on an improved version of our previous work (Harth et al., 1970; Anninos et al., 1970). Thus it was shown that the trace of a stimulus pattern presented to a subject decays with time due to the interference theory which assumes that competition among different associations leads to losses of retention. Such interference theory has been tested in this model by assuming that the retention of a first learned item followed by the learning of other successive tasks, depends on the inhibitory effect induced by them on the first item.This research has been supported by NIH grants NS-8012 and NS-8498, and NSP grant GB-30498. Computation assistance was provided by the Health Sciences Computing Facility, UCLA, sponsored by NIH Special Research Resources grant RR-3.     

The fine structure of polychaete septate junctions

Summary Epidermal septate junctions of Nereis sp. and Cirriformia sp. fixed with OsO₄ or glutaraldehyde/OsO₄ display variable structure in electron micrographs. In transverse section the septa are often indistinct and obscured by opaque material that fills the junctional cleft. Septa (spaced at 180–280 Å) are more clearly defined in slightly oblique transverse section; they exhibit an electron lucent center and appear to be linked by arms. En face views of the junction show a honeycomb pattern. Cytoplasmic faces of junctional membranes are backed with plaques opposite the septa. Lanthanum used as a tracer delineates junctional structure in negative contrast. In transverse section a chain-like lattice is present in the junctional cleft. En face views show parallel rows of pleated elements often linked by arms into honeycomb arrays. Oblique sections demonstrate that these pleated elements are continuous with the chain-like lattice seen in transverse sections. Lanthanum does not pass entirely through the junction. Lanthanum reveals that the septa have a very intricate substructure, but it is difficult to visualize the architecture that could generate the various images presented by these junctions when seen in different orientations. However, it is clear that these junctions possess some features that are diagnostic of several supposedly different types of septate junctions in invertebrates.Supported by USPHS grants NIH 5 P01 NS-07512, NIH 2701 GM-00102, and NB-00840, and by a grant from the Pomona College Research CommitteeI thank Sarah Wurzelmann, Stanley Brown, Nancy Kelly, and Gerhard Ott for excellent technical assistance. Portions of this study were carried out while I was a Postdoctoral Fellow in the Department of Anatomy, Albert Einstein College of Medicine. I dedicate this article to Berta Scharrer as a token of appreciation and affection for her guidance, encouragement, inspiration, and example of excellence     

Expression of nerve growth factor and its receptors in the somatosensory-motor cortex of Macaca nemestrina

The present study was designed to examine the nerve growth factor (NGF) system (ligand and receptor-expressing neurons) in the somatosensory (areas 1, 3a, and 3b) and motor (area 4) cortices of the mature macaque. Light and electron microscope immunohistochemistry was used to assess the distribution and identity of NGF-, p75-, and trk-expressing elements. In each cortical area examined, NGF-positive neuronal somata were distributed through all laminae; most immunolabeled neurons were in layers II, III, and V. Based upon light microscope criteria (e.g., the morphology of proximal dendrites), both pyramidal and stellate neurons expressed NGF. Of the identifiable NGF- immunoreactive cells, 92% were pyramidal neurons and the remainder was stellate neurons. The electron microscope study showed that most (88%) NGF-positive somata formed symmetric synapses, whereas the others formed both symmetric and asymmetric synapses. As the somata of pyramidal neurons form only symmetric synapses and those of inhibitory stellate neurons form both symmetric and asymmetric somatic synapses, the ultrastructural data support the light microscopic analyses. In contrast, neurotrophin receptors, p75 and trk, were expressed chiefly by the cell bodies of layer V pyramidal neurons and the supragranular neuropil. At the ultrastructural level, receptor-positive profiles were post-synaptic elements (e.g., dendritic shafts and spines) and the concentration of immunoreactivity was greatest in the vicinity of post-synaptic densities. Thus, NGF regulatory systems parallel excitatory and inhibitory neurotransmitter systems. Cortex contains the morphological framework by which pyramidal and/or inhibitory stellate neurons can affect the activity of post-synaptic pyramidal neurons via anterograde and autocrine/paracrine NGF systems.     

Pattern of synaptic connections in the pineal organ of the ayu,Plecoglossus altivelis (Teleostei)

Summary Synaptic connections were studied by means of electron microscopy in the sensory pineal organ of the ayu, Plecoglossus altivelis, a highly photosensitive teleost species. Three types of specific contacts were observed in the pineal end-vesicle: 1) symmetrically organized gap junctions between the basal processes of adjacent photoreceptor cells; 2) sensory synapses endowed with synaptic ribbons, formed by basal processes of photoreceptor cells and dendrites of pineal neurons; 3) conventional synapses between pineal neurons, containing both clear and dense-core vesicles at the presynaptic site. Based on these findings, the following interpretations are given: (i) The gap junctions may be involved in an enhancement of electric communication and signal encoding between pineal photoreceptor cells. (ii) The sensory synapses transmit photic signals from the photoreceptor cells to pineal nerve cells. (iii) The conventional synapses are assumed to be involved in a lateral interaction and/or summation of information in the sensory pineal organ. A concept of synaptic relationships among the sensory and neuronal elements in the pineal organ of the ayu is presented.Fellow of the Alexander von Humboldt Foundation, Federal Republic of Germany     

Synaptogenesis in Co-Culture of Neurons of Dorsal Root Ganglia and Spinal Cord

In co-culture of spinal cord and dorsal root ganglion (DRG) neurons, we studied at different terms of culturing postsynaptic currents in DRG neurons evoked by direct electrical stimulation of single spinal neurons using a voltage-clamp technique in the whole-cell configuration. According to the reversal potential and sensitivity to bicuculline, these currents were classified as inhibitory postsynaptic currents (IPSC) carried by Cl^- ions through GABA_A receptors. During neuronal development in dissociated co-culture, the amplitude of evoked IPSC and their time to peak significantly increased. The time to peak of spontaneous IPSC (sIPSC) in DRG neurons remained unchanged, while the frequency of these currents increased with increasing culturing time. It is concluded that under culturing conditions spinal neurons establish inhibitory synaptic contacts with the somata of DRG neurons, and the number of such functional contacts increases in the course of culturing. Our findings show that in dissociated co-culture the process of formation of inhibitory synapses on the axon terminals of primary afferent neurons is akin to that realized in vivo, but with dissimilar topography of distribution of such synapses.     

On the dynamics of electrically-coupled neurons with inhibitory synapses

We study the dynamics and bifurcations of noise-free neurons coupled by gap junctions and inhibitory synapses, using both delayed delta functions and alpha functions to model the latter. We focus on the case of two cells, as in the studies of Chow and Kopell (2000) and Lewis and Rinzel (2003), but also show that stable asynchronous splay states exist for globally coupled networks of N cells dominated by subthreshold electrical coupling. Our results agree with those of Lewis and Rinzel (2003) in the weak coupling range, but our Poincaré map analysis yields more information about global behavior and domains of attraction, and we show that the explicit discontinuous maps derived using delayed delta functions compare well with the continuous history-dependent, implicitly-defined maps derived from alpha functions. We find that increased bias currents, super-threshold electrical coupling and synaptic delays promote synchrony, while sub-threshold electrical coupling and fast synapses promote asynchrony. We compare our analytical results with simulations of an ionic current model of spiking cells, and briefly discuss implications for stimulus response modes of locus coeruleus and for central pattern generators. Action Editor: F. Skinner     

Ultrastructure and morphometric parameters of glutamatergic synapses on nigrothalamic and unidentified neurons of the reticular zone of theSubstantia nigra in cats

Nigrothalamic neurons were identified into thesubstantia nigra by their retrograde labelling with horseradish peroxidase. Axon terminals that contain glutamate (the excitatory transmitter) were revealed immunocytochemically with an immunogold electron microscopic technique. Ultrastructural parameters (the large and small diameters of axon terminals, area of their profiles, coefficient of form of profiles, large and small diameters of synaptic vesicles) were analyzed in all 240 synapses under study. Synaptic contacts localized on both nigrothalamic and unidentified neurons belonged to three morphologically specific groups. Synapses of the groups I and III, according to classification by Rinvik and Grofova, were characterized by a symmetric type of synaptic contact and contained polymorphic synaptic vesicles. Contacts in group-II synapses were asymmetric, and respective terminals contained round vesicles. Among the studied synapses, 65.8% were classified as group-I contacts, 25.0% belonged to group II, and 9.2% belonged to group III. Glutamate-positive axon terminals formed predominantly group-II synapses; such connections constituted 70% of this group's synapses. Sixty percent of glutamate-positive synapses were localized on the distal dendrites and 23% on the proximal dendrites, while 17% of such synapses were distributed on the somata of nigral neurons. Such a pattern of distribution of glutamate-positive synapses was observed on both nigrothalamic and unidentified nigral neurons. About 7% of glutamate-positive synapses were formed by very large axon terminals containing round synaptic vesicles; yet, the contacts of these terminals were of a symmetric type. Twenty percent of group-I synapses, i.e., synapses considered inhibitory connections, were found to manifest a weak immune reaction to glutamate.Neirofiziologiya/Neurophysiology, Vol. 28, No. 6, pp. 285–295, November–December, 1996.     

Differential modulation of chemical and electrical components of mixed synapses in the lobster stomatogastric ganglion

1. Two pairs of neurons in the pyloric network of the spiny lobster, Panulirus interruptus, communicate through mixed graded chemical and rectifying electrical synapses. The anterior burster (AB) chemically inhibits and is electrically coupled to the ventricular dilator (VD); the lateral pyloric (LP) and pyloric (PY) neurons show reciprocal chemical inhibition and electrical coupling. We examined the effects of dopamine (DA), serotonin (5HT) and octopamine (Oct) on these mixed synapses to determine the plasticity possible with opposing modes of synaptic interaction.
2. Dopamine increased net inhibition at all three pyloric mixed synapses by both reducing electrical coupling and increasing chemical inhibition. This reversed the sign of the net synaptic interaction when electrotonic coupling dominated some mixed synapses, and activated silent chemical components of other mixed synapses.
3. Serofonin weakly enhanced LP → PY net inhibition, by reducing electrical coupling without altering chemical inhibition. Serotonin reduced AB→ VD electrical coupling, but variability in its effect on the chemical component made the net effect non-significant.
4. Octopamine enhanced LP→ PY and PY→ LP net inhibition by enhancing the chemical inhibitory component without altering electrical coupling.
5. Differential modulation of chemical and electrical components of mixed synapses markedly changes the net synaptic interactions. This contributes to the flexible outputs that modulators evoke from anatomically defined neural networks.

     

Neural control of the pyloric region in the foregut of the shrimp Penaeus (Decapoda: Penaeidae)

Pyloric pattern-generating neurons that control the pyloric region of the foregut were identified in the stomatogastric ganglion of the most primitive decapod genus Penaeus. Five types of motor neurons and one interneuron are involved in generation of pyloric motor pattern. One cell type of motor neurons innervates muscles of both the gastric mill and the pylorus like the gastric motor neurons in Cancer, but unlike those in Panulirus. These identified neurons are connected to each other either by electrical or inhibitory chemical synapses to construct the neural circuit. This pyloric circuit is similar to the homologous circuit of other crustacean species though some differences are seen in synaptic connections, supporting the hypothesis that the basic design of the neural circuit has been conserved during evolution of the Malacostraca, and that differences have occurred in the synaptic connectivity as the foregut structure has become complex. The motor neurons use either acetylcholine or glutamate as a neurotransmitter like in reptantians. The foregut structure, the number of the pyloric cells, muscle innervation, neurotransmitters, and circuitry are compared among malacostracan crustaceans to provide insight into how the neural circuits change and evolve to produce the motor patterns mediating behaviour. Accepted: 18 April 1997     

Cellular mechanisms governing synapse formation: lessons from identified neurons in culture

The accessibility of embryonic and adult neurons within invertebrate nervous systems has made them excellent subjects for neurobiological study. The ability to readily identify individual neurons, together with their great capacity for regeneration, has been especially beneficial to investigations of synapse formation and the specificity of neuronal connectivity. Many invertebrate neurons survive for long periods following isolation into primary cell culture. In addition, they readily extend new neuritic arbors and form electrical and chemical connections at sites of contact. Thus, cell culture approaches have allowed neuroscientists greater access to, and resolution of, events underlying neurite outgrowth and synaptogenesis. Studies of identified neuromuscular synapses ofHelisoma have determined a number of signaling mechanisms involved in transsynaptic communication at sites of neuron-target contact. At these sites, both anterograde and retrograde signals regulate the transformation of growth cones into functional presynaptic terminals. We have found that specific muscle targets induce both global and local changes in neurotransmitter secretion and intracellular calcium handling. Here we review recent studies of culturedHelisoma synapses and discuss the mechanisms thought to govern chemical synapse formation in these identified neurons and those of other invertebrate species.     

Synchronous activity of inhibitory networks in neocortex requires electrical synapses containing connexin36

Inhibitory interneurons often generate synchronous activity as an emergent property of their interconnections. To determine the role of electrical synapses in such activity, we constructed mice expressing histochemical reporters in place of the gap junction protein Cx36. Localization of the reporter with somatostatin and parvalbumin suggested that Cx36 was expressed largely by interneurons. Electrical synapses were common among cortical interneurons in controls but were nearly absent in knockouts. A metabotropic glutamate receptor agonist excited LTS interneurons, generating rhythmic inhibitory potentials in surrounding neurons of both wild-type and knockout animals. However, the synchrony of these rhythms was weaker and more spatially restricted in the knockout. We conclude that electrical synapses containing Cx36 are critical for the generation of widespread, synchronous inhibitory activity.     

Connexin36 is essential for transmission of rod-mediated visual signals in the mammalian retina

To examine the functions of electrical synapses in the transmission of signals from rod photoreceptors to ganglion cells, we generated connexin36 knockout mice. Reporter expression indicated that connexin36 was present in multiple retinal neurons including rod photoreceptors, cone bipolar cells, and AII amacrine cells. Disruption of electrical synapses between adjacent AIIs and between AIIs and ON cone bipolars was demonstrated by intracellular injection of Neurobiotin. In addition, extracellular recording in the knockout revealed the complete elimination of rod-mediated, on-center responses at the ganglion cell level. These data represent direct proof that electrical synapses are critical for the propagation of rod signals across the mammalian retina, and they demonstrate the existence of multiple rod pathways, each of which is dependent on electrical synapses.     

The anatomy and motor nerve distribution of the eye muscles in the crayfish

Summary The gross anatomy of the muscles in the crayfish compound eye and the distribution of brain oculomotor neurons were studied by a variety of anatomical and physiological techniques. There are 11 major muscles in each eye. These vary considerably in size and influence upon eye movements and in their source of motor innervation. Muscles that cause defensive eyestalk withdrawal are controlled by axons of a giant motor neuron cluster. Muscles that move the eyecup in vertical planes are innervated by cells of an anterior motor cluster, as well as by cells in the medulla terminalis. Muscles which move the eyecup horizontally are supplied by neurons of the lateral motor cluster. The separation of the oculomotor system into different neuronal groups that supply different sets of muscles thus reflects functional specializations of the component divisions.I am grateful to Mr. Gene Lorton for his technical assistance with some phases of this work. I also thank Sharon Greene for executing the illustration in Figure 1 and Susan Suarez for illustrating Figure 2. This work was supported by USPHS research grant NS04989.     

Dynamics of spiking neurons connected by both inhibitory and electrical coupling

We study the dynamics of a pair of intrinsically oscillating leaky integrate-and-fire neurons (identical and noise-free) connected by combinations of electrical and inhibitory coupling. We use the theory of weakly coupled oscillators to examine how synchronization patterns are influenced by cellular properties (intrinsic frequency and the strength of spikes) and coupling parameters (speed of synapses and coupling strengths). We find that, when inhibitory synapses are fast and the electrotonic effect of the suprathreshold portion of the spike is large, increasing the strength of weak electrical coupling promotes synchrony. Conversely, when inhibitory synapses are slow and the electrotonic effect of the suprathreshold portion of the spike is small, increasing the strength of weak electrical coupling promotes antisynchrony (see Fig. 10). Furthermore, our results indicate that, given a fixed total coupling strength, either electrical coupling alone or inhibition alone is better at enhancing neural synchrony than a combination of electrical and inhibitory coupling. We also show that these results extend to moderate coupling strengths.