Photosensitivity of the central nervous system of Limulus polyphemus

The photosensitivity of the central nervous system (CNS) of the horseshoe crab, Limulus polyphemus, was investigated by analyzing changes in motor nerve activity in the segmental nerves of prosomal and opisthosomal ganglia. Spontaneous efferent impulses were recorded in the dark from all the investigated segmental nerves. Impulse trains from the 7th dorsal nerve in the prosomal CNS were inhibited in response to illumination of the whole CNS. Impulse trains from each of the 9-13th dorsal nerves in the isolated opisthosomal CNS were inhibited, and the impulse train from each the 14-16th dorsal nerve was elicited or inhibited upon illuminating the whole CNS. Spontaneous rhythmic bursts at 20-80 s intervals were recorded in the dark from the ventral nerves of the isolated opisthosomal CNS. In the presence of light, the rhythmicity of spontaneous bursts disappeared and other species of impulse trains were elicited. In single ganglion preparations, isolated from the rest of the CNS by surgically severing the connectives, similar photoresponses were recorded before and after isolation. These results demonstrate that the CNS of Limulus is a photosensitive organ.     

Serotonin modulation of caudal photoreceptor in crayfish

The sixth abdominal ganglion (6th AG) of the crayfish contains two photosensitive neurons. This caudal photoreceptor (CPR) displays spontaneous electrical activity and phasic-tonic responses to light pulses. In this paper, we analyzed the presence of serotonin in the 6th AG and its effects in the modulation of the activity of CPR. In the first part of our study, we identified serotonergic neurons in the 6th AG by immunostaining using an antibody against serotonin. Next, we quantified the serotonin contents in the 6th AG by using liquid chromatography. Finally, we searched for serotonergic modulation of the CPR electrical activity by using conventional extracellular recordings. We found 13 immunopositive neurons located in the ventral side of the 6th AG. The mean diameter of their somata was 23+/-9 microm. In addition, there was immunopositive staining in neuropilar fibers and varicosities. The contents of serotonin and its precursors in the 6th AG varied along the 24-h cycle. Its maximum value was reached by midday. Topic application of serotonin to ganglia kept in darkness increased the CPR spontaneous firing rate and reduced its light responsiveness. Both effects were dose-dependent within ED(50) approximately 1 microM and were blocked by the 5-HT antagonist methysergide. These observations support the role of serotonin as a neurotransmitter or neuromodulator in the CPR of the two species of crayfish Procambarus clarkii and Cherax quadricarinatus.     

Widespread distribution of a unique marine protistan lineage

Unicellular eukaryotes (protists) are key components of marine food webs, yet knowledge of their diversity, distributions and respective ecologies is limited. We investigated uncultured protists using 18S rRNA gene sequencing, phylogenetic analyses, specific fluorescence in situ hybridization (FISH) probes and other methods. Because few studies have been conducted in warm water systems, we focused on two Atlantic subtropical regions, the Sargasso Sea and the Florida Current. Cold temperate waters were also sampled. Gene sequences comprising a unique eukaryotic lineage, herein termed 'biliphytes', were identified in most samples, whether from high- (30 degrees C) or from low- (5 degrees C) temperature waters. Sequences within this uncultured group have previously been retrieved from high latitudes. Phylogenetic analyses suggest biliphytes are a sister group to the cryptophytes and katablepharids, although the relationship is not statistically supported. Bootstrap-supported subclades were delineated but coherence was not obvious with respect to geography or physicochemical parameters. Unlike results from the initial publication on these organisms (therein 'picobiliphytes'), we could not detect a nucleomorph, either visually, or by targeted primers. Phycobilin-like fluorescence associated with biliphyte-specific FISH-probed cells supports the hypothesis that they are photosynthetic. Our data indicate the biliphytes are nanoplanktonic in size, averaging 4.1 +/- 1.0 x 3.5 +/- 0.8 microm (+/-SD) for one probed group, and 3.5 +/- 0.9 x 3.0 +/- 0.9 microm (+/-SD) for another. We estimate biliphytes contributed 28 (+/-6)% of the phytoplanktonic biomass in tropical eddy-influenced surface waters. Given their broad thermal and geographic distribution, understanding the role these protists play in biogeochemical cycling within different habitats is essential.     

Peripheral nerve lesion-induced uptake and transport of choleragenoid by capsaicin-sensitive c-fibre spinal ganglion neurons

In the present experiments the effect of systemic capsaicin treatment on the retrograde labelling of sensory ganglion cells was studied following the injection of choleratoxin B subunit-horseradish peroxidase conjugate (CTX-HRP) into intact and chronically transected peripheral nerves. In the control rats CTX-HRP injected into intact sciatic nerves labelled medium and large neurons with a mean cross-sectional area of 1,041 +/- 39 gm2. However, after injection of the conjugate into chronically transected sciatic nerves of the control rats, many small cells were also labelled, shifting the mean cross-sectional area of the labelled cells to 632 +/- 118 microm2. Capsaicin pretreatment per se induced a moderate but significant decrease in the mean cross-sectional area of the labelled neurons (879 +/- 79 microm2). More importantly, systemic pretreatment with capsaicin prevented the peripheral nerve lesion-induced labelling of small cells. Thus, the mean cross-sectional areas of labelled neurons relating to the intact and transected sciatic nerves, respectively, did not differ significantly. These findings provide direct evidence for a phenotypic switch of capsaicin-sensitive nociceptive neurons after peripheral nerve injury, and suggest that lesion-induced morphological changes in the spinal cord may be related to specific alterations in the chemistry of C-fibre afferent neurons rather than to a sprouting response of A-fibre afferents.     

ErbB transmembrane tyrosine kinase receptors are expressed by sensory and motor neurons projecting into sciatic nerve.

Adult spinal cord motor and dorsal root ganglion (DRG) sensory neurons express multiple neuregulin-1 (NRG-1) isoforms that act as axon-associated factors promoting neuromuscular junction formation and Schwann cell proliferation and differentiation. NRG-1 isoforms are also expressed by muscle and Schwann cells, suggesting that motor and sensory neurons are themselves acted on by NRG-1 isoforms produced by their peripheral targets. To test this hypothesis, we examined the expression of the NRG-1 receptor subunits erbB2, erbB3, and erbB4 in rat lumbar DRG and spinal cord. All three erbB receptors are expressed in these tissues. Sciatic nerve transection, an injury that induces Schwann cell expression of NRG-1, alters erbB expression in DRG and cord. Virtually all DRG neurons are erbB2- and erbB3-immunoreactive, with erbB4 also detectable in many neurons. In spinal cord white matter, erbB2 and erbB4 antibodies produce dense punctate staining, whereas the erbB3 antibody primarily labels glial cell bodies. Spinal cord dorsal and ventral horn neurons, including alpha-motor neurons, exhibit erbB2, erbB3, and erbB4 immunoreactivity. Spinal cord ventral horn also contains a population of small erbB3+/S100beta+/GFAP- cells (GFAP-negative astrocytes or oligodendrocytes). We conclude that sensory and motor neurons projecting into sciatic nerve express multiple erbB receptors and are potentially NRG-1 responsive.     

Fictive locomotion and scratching inhibit dorsal horn neurons receiving thin fiber afferent input

In decerebrate paralyzed cats, we examined the effects of two central motor commands (fictive locomotion and scratching) on the discharge of dorsal horn neurons receiving input from group III and IV tibial nerve afferents. We recorded the impulse activity of 74 dorsal horn neurons, each of which received group III input from the tibial nerve. Electrical stimulation of the mesencephalic locomotor region (MLR), which evoked fictive static contraction or fictive locomotion, inhibited the discharge of 44 of the 64 dorsal horn neurons tested. The mean depth from the dorsal surface of the spinal cord of the 44 neurons whose discharge was inhibited by MLR stimulation was 1.77 +/- 0.04 mm. Fictive scratching, evoked by topical application of bicuculline to the cervical spinal cord and irritation of the ear, inhibited the discharge of 22 of the 29 dorsal horn neurons tested. Fourteen of the twenty-two neurons whose discharge was inhibited by fictive scratching were found to be inhibited by MLR stimulation as well. The mean depth from the dorsal surface of the cord of the 22 neurons whose discharge was inhibited by fictive scratching was 1.77 +/- 0.06 mm. Stimulation of the MLR or the elicitation of fictive scratching had no effect on the activity of 22 dorsal horn neurons receiving input from group III and IV tibial nerve afferents. The mean depth from the dorsal surface of the cord was 1.17 +/- 0.07 mm, a value that was significantly (P < 0.05) less than that for the neurons whose discharge was inhibited by either MLR stimulation or fictive scratching. We conclude that centrally evoked motor commands can inhibit the discharge of dorsal horn neurons receiving thin fiber input from the periphery.     

Right ventricular systolic pressure load alters myocyte maturation in fetal sheep

The effects of right ventricular (RV) systolic pressure (RVSP) load on fetal myocyte size and maturation were studied. Pulmonary artery (PA) pressure was increased by PA occlusion from mean 47.4 +/- 5.0 (+/-SD) to 71 +/- 13.6 mmHg (P < 0.0001) in eight RVSP-loaded near-term fetal sheep for 10 days. The maximal pressure generated by the RV with acute PA occlusion increased after RVSP load: 78 +/- 7 to 101 +/- 15 mmHg (P < 0.005). RVSP-load hearts were heavier (44.7 +/- 8.4 g) than five nonloaded hearts (31.8 +/- 0.2 g; P < 0.03); heart-to-body weight ratio (10.9 +/- 1.1 and 6.5 +/- 0.9 g/kg, respectively; P < 0.0001). RVSP-RV myocytes were longer (101.3 +/- 10.2 microm) than nonloaded RV myocytes (88.2 +/- 8.1 microm; P < 0. 02) and were more often binucleated (82 +/- 13%) than nonloaded myocytes (63 +/- 7%; P < 0.02). RVSP-loaded myocytes had less myofibrillar volume than did nonloaded hearts (44.1 +/- 4.4% and 56. 1 +/- 2.6%; P < 0.002). We conclude that RV systolic load 1) leads to RV myocyte enlargement, 2) has minor effects on left ventricular myocyte size, and 3) stimulates maturation (increased RV myocyte binucleation). Myocyte volume data suggest that RV systolic loading stimulates both hyperplastic and hypertrophic growth.     

Nerve growth factor-induced stimulation of dorsal root ganglion/spinal cord co-grafts in oculo: enhanced survival and growth of CGRP-immunoreactive sensory neurons

Intraocular co-grafts of rat fetal spinal cord and dorsal root ganglia were used to examine the enhanced survival, growth, and differentiation of sensory neurons by nerve growth factor. E14 lumbar spinal segments were implanted into the anterior eye chamber of capsaicin-pretreated rats. Two weeks later, an E14 dorsal root ganglion was implanted beside the spinal cord graft. Nerve growth factor or vehicle was injected weekly for 4 weeks into the anterior eye chamber. Co-grafts were examined weekly and, at 6 weeks, processed for calcitonin gene-related peptide (CGRP) immunofluorescence. No differences in overall size were determined for the grafts. Co-grafts treated with nerve growth factor contained many more CGRP neurons (19.4 cells/20 microm) that were significantly larger (mean 764 microm2) than neurons from control co-grafts (8.6 cells/20 microm; mean 373 microm2). In co-grafts treated with nerve growth factor, CGRP-immunoreactive fibers were extensive in the dorsal root ganglion, adjacent iris, and spinal cord compared to control co-grafts. A few CGRP-positive motoneurons were observed in the spinal cord, but no differences in number or size of motoneurons were found. The current report demonstrates that spinal cord and dorsal root ganglia can be co-grafted in oculo for long periods of time. Many dorsal root ganglion neurons survive and send peripheral processes into the iris and central processes into the spinal cord under the influence of exogenous nerve growth factor. The intraocular graft paradigm can be of use to further examine the role of neurotrophic factors in regulating or modulating dorsal root ganglion and spinal cord neurons.     

Immunohistochemical and in situ hybridization studies of choline acetyltransferase in large motor neurons of the human spinal cord

The localization of choline acetyltransferase (ChAT) protein and mRNA was investigated in large motor neurons of the lumbar spinal cord of 10 autopsied individuals without neurological diseases, by immunohistochemistry and in situ hybridization. In the immunohistochemistry using 20 serial tissue sections with a total thickness of 80 microm, about approximately 58-85% (average 67%) of the large motor neurons (30 microm and more in somal minimal diameter) in the ventral horn were stained with the anti-human ChAT antibody. In the positive neurons, most immunoreactive products were observed focally in the perikarya. Occasionally, the perikarya of some neurons were stained diffusely. In situ hybridization with a single 4 microm-thick tissue section showed that almost all large motor neurons had positive signals (approximately 93-100%, average 98%), which were distributed diffusely in the perikarya. The positivity rate in the in situ hybridization was higher than that in the immunohistochemistry for all 10 cases. These results indicate that ChAT mRNA is transcribed in almost all large motor neurons in the ventral horn of the human spinal cord, but ChAT protein cannot always be detected in the cytoplasm by immunohistochemistry.     

Brain stem mechanisms underlying acupuncture modality-related modulation of cardiovascular responses in rats.

The present study was designed to investigate brain stem responses to manual acupuncture (MA) and electroacupuncture (EA) at different frequencies at pericardial P (5-6) acupoints located over the median nerve. Activity of premotor sympathetic cardiovascular neurons in the rostral ventral lateral medulla (rVLM) was recorded during stimulation of visceral and somatic afferents in ventilated anesthetized rats. We stimulated either the splanchnic nerve at 2 Hz (0.1-0.4 mA, 0.5 ms) or the median nerve for 30 s at 2, 10, 20, 40, or 100 Hz using EA (0.3-0.5 mA, 0.5 ms) or at approximately 2 Hz with MA. Twelve of 18 cells responsive to splanchnic and median nerve stimulation could be antidromically driven from the intermediolateral columns of the thoracic spinal cord, T2-T4, indicating that they were premotor sympathetic neurons. All 18 neurons received baroreceptor input, providing evidence of their cardiovascular sympathoexcitatory function. Evoked responses during stimulation of the splanchnic nerve were inhibited by 49 +/- 6% (n = 7) with EA and by 46 +/- 4% (n = 6) with MA, indicating that the extent of inhibitory effects of the two modalities were similar. Inhibition lasted for 20 min after termination of EA or MA. Cardiovascular premotor rVLM neurons responded to 2-Hz electrical stimulation at P 5-6 and to a lesser extent to 10-, 20-, 40-, and 100-Hz stimulation (53 +/- 10, 16 +/- 2, 8 +/- 2, 2 +/- 1, and 0 +/- 0 impulses/30 stimulations, n = 7). These results indicate that rVLM premotor sympathetic cardiovascular neurons that receive convergent input from the splanchnic and median nerves during low-frequency EA and MA are inhibited similarly for prolonged periods by low-frequency MA and EA.     

Tapering of human nerve fibres

To determine the tapering of human nerve fibres, rostral and caudal root pieces of cauda equina nerve roots were removed and nerve fibre diameter distributions were constructed for 4 myelin sheath thickness ranges for the two sites, and compared with each other. The reduction of the group diameter in the different alpha-motoneuron groups was 0.2 % per 13 cm. Accounting for systematic errors, there may be even less tapering. An identified single nerve fibre showed no tapering. Further, there is indication that gamma-motoneurons, preganglionic sympathetic and parasympathetic fibres and skin afferents also reduce their fibre diameter by 0.2 % per 13 cm or less. Consequently, a nerve fibre with a diameter of 10 microm would be reduced to approximately 9.8 microm at 1m from the cell soma. Preganglionic parasympathetic fibres were found to be represented in roots S1 to S5. At similar distances from the spinal cord, the mean diameter of ventral root alpha1-motoneuron (FF) axons increased from the thoracic towards the lumbo-sacral region before decreasing again in the lower sacral region. Usually no alpha1-motoneuron axons were found in S5 roots. The diameter distribution of unmyelinated nerve fibres of a ventral S5 root showed three peaks at 0.25, 0.95 and 1.2 microm. The unmyelinated fibres with diameters around 0.25 microm may represent parasympathetic fibres. In six selected areas of the ventral S5 root, 6.6 times more unmyelinated nerve fibres than myelinated fibres were found on the average.     

Characterization and subcellular targeting of GCaMP-type genetically-encoded calcium indicators

Genetically-encoded calcium indicators (GECIs) hold the promise of monitoring [Ca(2+)] in selected populations of neurons and in specific cellular compartments. Relating GECI fluorescence to neuronal activity requires quantitative characterization. We have characterized a promising new genetically-encoded calcium indicator-GCaMP2-in mammalian pyramidal neurons. Fluorescence changes in response to single action potentials (17+/-10% DeltaF/F [mean+/-SD]) could be detected in some, but not all, neurons. Trains of high-frequency action potentials yielded robust responses (302+/-50% for trains of 40 action potentials at 83 Hz). Responses were similar in acute brain slices from in utero electroporated mice, indicating that long-term expression did not interfere with GCaMP2 function. Membrane-targeted versions of GCaMP2 did not yield larger signals than their non-targeted counterparts. We further targeted GCaMP2 to dendritic spines to monitor Ca(2+) accumulations evoked by activation of synaptic NMDA receptors. We observed robust DeltaF/F responses (range: 37%-264%) to single spine uncaging stimuli that were correlated with NMDA receptor currents measured through a somatic patch pipette. One major drawback of GCaMP2 was its low baseline fluorescence. Our results show that GCaMP2 is improved from the previous versions of GCaMP and may be suited to detect bursts of high-frequency action potentials and synaptic currents in vivo.     

Activation of slowly conducting medullary raphe-spinal neurons, including serotonergic neurons, increases cutaneous sympathetic vasomotor discharge in rabbit

Neurons in the rostral medullary raphe/parapyramidal region regulate cutaneous sympathetic nerve discharge. Using focal electrical stimulation at different dorsoventral raphe/parapyramidal sites in anesthetized rabbits, we have now demonstrated that increases in ear pinna cutaneous sympathetic nerve discharge can be elicited only from sites within 1 mm of the ventral surface of the medulla. By comparing the latency to sympathetic discharge following stimulation at the ventral raphe site with the corresponding latency following stimulation of the spinal cord [third thoracic (T3) dorsolateral funiculus] we determined that the axonal conduction velocity of raphe-spinal neurons exciting ear pinna sympathetic vasomotor nerves is 0.8 +/- 0.1 m/s (n = 6, range 0.6-1.1 m/s). Applications of the 5-hydroxytryptamine (HT)(2A) antagonist trans-4-((3Z)3-[(2-dimethylaminoethyl)oxyimino]-3-(2-fluorophenyl)propen-1-yl)-phenol, hemifumarate (SR-46349B, 80 microg/kg in 0.8 ml) to the cerebrospinal fluid above thoracic spinal cord (T1-T7), but not the lumbar spinal cord (L2-L4), reduced raphe-evoked increases in ear pinna sympathetic vasomotor discharge from 43 +/- 9 to 16 +/- 6% (P < 0.01, n = 8). Subsequent application of the excitatory amino acid (EAA) antagonist kynurenic acid (25 micromol in 0.5 ml) substantially reduced the remaining evoked discharge (22 +/- 8 to 6 +/- 6%, P < 0.05, n = 5). Our conduction velocity data demonstrate that only slowly conducting raphe-spinal axons, in the unmyelinated range, contribute to sympathetic cutaneous vasomotor discharge evoked by electrical stimulation of the medullary raphe/parapyramidal region. Our pharmacological data provide evidence that raphe-spinal neurons using 5-HT as a neurotransmitter contribute to excitation of sympathetic preganglionic neurons regulating cutaneous vasomotor discharge. Raphe-spinal neurons using an EAA, perhaps glutamate, make a substantial contribution to the ear sympathetic nerve discharge evoked by raphe stimulation.     

Functional and morphometric evaluation of end-to-side neurorrhaphy for muscle reinnervation

This study was undertaken to quantify the effect of motor collateral sprouting in an end-to-side repair model allowing end organ contact. Besides documentation of the functional outcome of muscle reinnervation by end-to-side neurorrhaphy, this experimental work was performed to determine possible downgrading effects to the donor nerve at end organ level. In 24 female New Zealand White rabbits, the motor nerve branch to the rectus femoris muscle of the right hindlimb was dissected, cut, and sutured end-to-side to the motor branch to the vastus medialis muscle after creating an epineural window. The 24 rabbits were divided into two groups of 12 each, with the second group receiving additional crush injury of the vastus branch. After a period of 8 months, maximum tetanic tension in the reinnervated rectus femoris and the vastus medialis muscles was determined. The contralateral healthy side served as control. The reinnervated rectus femoris muscle showed an average maximum tetanic force of 24.9 N (control 26.2 N, p = 0.7827), and the donor- vastus medialis muscle 11.0 N (control 7.3 N, p = 0.0223). There were no statistically significant differences between the two experimental groups (p = 0.9914). The average number of regenerated myelinated nerve fibers in the rectus femoris motor branch was 1,185 +/- 342 (control, 806 +/- 166), and the mean diameter was 4.6 +/- 0.6 microm (control, 9.4 +/- 1.0 microm). In the motor branch to the vastus medialis muscle, the mean fiber number proximal to the coaptation site was 1227 (+/-441), and decreased distal to the coaptation site to 795 (+/-270). The average difference of axon counts in the donor nerve proximal to distal regarding the repair site was 483.7 +/- 264.2. In the contralateral motor branch to the vastus medialis muscle, 540 (+/- 175) myelinated nerve fibers were counted. In nearly all cross-section specimens of the motor branch to the vastus medialis muscle, altered nerve fibers could be identified in one fascicle distal and proximal to the repair site. The results show a relevant functional reinnervation by end-to-side neurorrhaphy without functional impairment of the donor muscle. It seems to be evident that most axons in the attached segment were derived from collateral sprouts. Nonetheless, the present study confirms that end-to-side neurorrhaphy is a reliable method of reconstruction for damaged nerves, which should be applied clinically in a more extended manner.     

Octopamine Uptake and Metabolism in the Insect Nervous System

Several insect tissues were examined for their ability to take up octopamine in the presence and absence of sodium ions. The cockroach Malpighian tubules, ovary, and ventral nerve cord showed the highest level of sodium-dependent uptake. The adult firefly lantern exhibited substantial sodium-independent uptake. Some of these tissues were also examined for their ability to metabolize octopamine by N-acetylation. Measurable N-acetyltransferase activity was present in the cockroach ventral nerve cord, tobacco hornworm CNS, and firefly light organ. N-Acetylation is proposed to be the major metabolic pathway for octopamine in the cockroach (Periplaneta americana) nervous system. Several classes of compounds, including octopamine receptor agonists, tricyclic antidepressants, amphetamines, chloroethylbenzylamines, and some experimental insecticides, were tested for their ability to inhibit octopamine uptake and metabolism. The sodium-insensitive component of uptake was not inhibited by most compounds tested, but the sodium-sensitive component was strongly inhibited by xylamine, N-ethyl-N-chloroethyl-o-bromobenzylamine, and their aziridinium ions (60-100%). These compounds also effectively inhibited N-acetyl-transferase (IC50 values at or below 1 microM). Other good inhibitors of N-acetyltransferase included desipramine, synephrine, and an experimental insecticide, CGA 132427. Formamidine pesticides had limited effect on both processes, and neither action seems likely to be involved in their octopaminergic actions in vivo. Cocaine was unique in stimulating N-acetyltransferase activity. When inhibition of sodium-sensitive uptake is compared with inhibition of N-acetyltransferase in the cockroach ventral nerve cord, two groups of inhibitors are discernible. Type 1 compounds inhibit uptake without an effect on N-acetyltransferase, whereas type 2 compounds inhibit both processes. These results suggest a functional linkage between the uptake and acetylation of octopamine.     

Dorsal horn administration of muscimol abolishes the muscle pressor reflex.

The purpose of this study was to determine the effect of blocking synaptic transmission in the dorsal horn on the cardiovascular responses produced by activation of muscle afferent neurons. Synaptic transmission was blocked by applying the GABA(A) agonist muscimol to the dorsal surface of the spinal cord. Cats were anesthetized with alpha-chloralose and urethane, and a laminectomy was performed. With the exception of the L(7) dorsal root, the dorsal and ventral roots from L(5) to S(2) were sectioned on one side, and static contraction of the ipsilateral triceps surae muscle was evoked by electrically stimulating the peripheral ends of the L(7) and S(1) ventral roots. The dorsal surface of the L(4)--S(3) segments of the spinal cord were enclosed within a "well" created by applying layers of vinyl polysiloxane. Administration of a 1 mM solution of muscimol (based on dose-response data) into this well abolished the reflex pressor response to contraction (change in mean arterial blood pressure before was 47 +/- 7 mmHg and after muscimol was 3 +/- 2 mmHg). Muscle stretch increased mean arterial blood pressure by 30 +/- 8 mmHg before muscimol, but after drug application stretch increased MAP by only 3 +/- 2 mmHg. Limiting muscimol to the L(7) segment attenuated the pressor responses to contraction (37 +/- 7 to 24 +/- 11 mmHg) and stretch (28 +/- 2 to 16 +/- 8 mmHg). These data suggest that the dorsal horn of the spinal cord contains an obligatory synapse for the pressor reflex. Furthermore, these data support the hypothesis that branches of primary afferent neurons, not intraspinal pathways, are responsible for the multisegmental integration of the pressor reflex.     

Respiratory resetting induced by spinal cord stimulation in the cat

Electrical stimulation (50-150 microA, 0.5-ms duration, 3-300 Hz) was performed within three different regions (lateral, ventrolateral, and ventral) of the C2-C3 spinal cord of decerebrate, vagotomized, paralyzed, and artificially ventilated cats. Spinal cord stimulation sites were located by inserting monopolar or bipolar stimulating electrodes either at the dorsolateral sulcus or at least 1 mm medial or lateral to the sulcus. With stimulation at each site, alterations in respiratory rhythm, orthodromic phrenic nerve responses, and antidromic activation of medullary respiratory-modulated neurons were examined. Phrenic nerve responses to cervical spinal cord stimulation consisted of an early excitation (2-4 ms) and/or a late excitation (4-8 ms). Stimulation of the lateral region evoked the greatest amplitude early response and stimulation of the ventrolateral region produced the greatest late excitation. All three stimulus sites elicited antidromic activation of some respiratory-modulated neurons in the dorsal (DRG) and ventral respiratory groups (VRG). The lateral region was the least effective resetting site, and it had the highest incidence of antidromic activation of both DRG and VRG neurons. The ventrolateral region of the cervical spinal cord was the most effective resetting site, but it had the lowest incidence of antidromic activation of DRG respiratory-modulated neurons. In addition, resetting responses were observed with spinal cord stimulation at similar sites in the thoracic and lumbar spinal cord regions thought to be devoid of inspiratory bulbospinal axons.(ABSTRACT TRUNCATED AT 250 WORDS)     

Characterization of pancreas-projecting rat dorsal motor nucleus of vagus neurons

The electrophysiological and morphological properties of rat dorsal motor nucleus of the vagus (DMV) neurons innervating the pancreas were examined by using whole cell patch clamp recordings from brain stem slices and postfixation morphological reconstructions of Neurobiotin-filled neurons. Recordings were made from 178 DMV neurons whose projections had been identified by previous apposition of the fluorescent neuronal tracer DiI to the body of the pancreas. DMV neurons projecting to the pancreas had an input resistance of 434 +/- 14 M omega, an action potential duration of 3 +/- 0.1 ms, and an afterhyperpolarization of 18 +/- 0.4 mV amplitude and 108 +/- 7 ms time constant of decay; these electrophysiological properties resembled those of gastric-projecting neurons but were significantly different from those of intestinal-projecting neurons. Interestingly, 14 of 178 pancreas-projecting neurons showed the presence of a slowly developing afterhyperpolarization whose presence was not reported in DMV neurons projecting to any other gastrointestinal area. The morphological characteristics of pancreas-projecting neurons (soma area 274 +/- 12 microm2; soma diameter of 25 +/- 0.7 microm; soma form factor 0.74 +/- 0.01; segments 9.7 +/- 0.41), however, were similar to those of intestinal- but differed from those of gastric-projecting neurons. In summary, these results suggest that pancreas-projecting rat DMV neurons are heterogeneous with respect to some electrophysiological and morphological properties. These differences might underlie functional differences in the vagal modulation of pancreatic functions.     

PS-100 and NF 70-200 double immunolabeling for human digital skin meissner corpuscle 3D imaging.

For detailed study of complex structures such as corpuscular mechanoreceptors, confocal microscopy can be used with multiple immunolabeling that identifies specifically different subcomponents. In addition, anatomic interpretation is enhanced by three-dimensional reconstruction. Confocal laser micrographs, reconstructed from serial images 1 microm thick of human skin Meissner corpuscles simultaneously immunostained for neurofilaments (NF 70-200) and protein S-100 (PS-100), clearly reveal the complex 3D relationship between Schwann-related lamellar cells immunoreactive for PS-100 and the nerve fibers marked by NF 70-200. The nerve fiber, after branching into the corpuscle, divides into several ramifications, presenting discoidal expansions and flattened fringed sections. The mean nerve diameter was 4 microm +/- 1 (2-5 microm) and the mean size of the discoidal expansions was 15 microm +/- 1 (7-30 microm). Corpuscle size varied from 30-140 +/- 1 microm in length and from 20-60 +/- 1 microm in diameter. This study confirms the presence of neural discoidal areas in Meissner's corpuscles, which are probably involved to some extent with the transduction process. Despite the accuracy of immunolabeling and imaging, an extracorpuscular neural network was never observed in the vicinity of corpuscles, thus giving doubt as to their existence. (J Histochem Cytochem 48:295-302, 2000)     

Anatomy and in vivo activity of neurons connecting the crustacean stomatogastric nervous system to the brain

In decapod crustaceans, the inferior ventricular nerve connects the cerebral ganglia (brain) with the stomatogastric nervous system (STNS). In the ivn of the crayfish, eight axons with diameters between 3.5 microm and 10 microm were found in close proximity to the oesophageal ganglion. Two of these axons terminate with their cell body within the ivn. The projections of the other six axons spread inside many neuropiles of the brain, mainly within the protocerebrum and the neuropils of the first and second antennae. Several fibers also send neurites via the circumoesophageal connectives toward the paired commissural ganglia and further down to the ventral nerve cord. The activity of motoneurons within the STNS and of axons in the ivn was recorded with implanted electrodes before, during and after times of feeding. At the beginning of feeding all tonically active ivn neurons accelerated their discharge rate and initially silent neurons also started to fire. Spike frequency was correlated with the quantity of food consumed. The ivn response was accompanied by a corresponding increase in pyloric frequency and an initiation of a gastric rhythm. The two motor rhythms showed a strong phasic interaction, but there was no phase coupling to the ivn activity.