Superior Cervical Ganglion Of Cat Research Articles

Rapid structural remodeling of shaft synapses associated with long-term potentiation in the cat superior cervical ganglion in situ.

Synaptic plasticity associated with long-term potentiation was studied electrophysiologically and ultrastructurally in the cat superior cervical ganglion in situ. The preganglionic nerve fiber was stimulated at 10 Hz for 50 s for conditioning and then at 1 Hz for 1-3 h to monitor changes in the postganglionic compound action potential (PGP). The present material has shown the long-term potentiation (LTP), around 120% of the control, which lasted for up to 3 h. Fifteen of 18 ganglia (83%) have shown LTP. Ultrastructural studies demonstrated the synaptic structural remodeling: (1) The preganglionic nerve terminals ordinarily made mainly asymmetrical type of shaft synapses directly with dendrites of the ganglion cells that lacked dendritic spines; (2) conditioning tetanus rapidly remodeled simple shaft synapses into perforated ones characterized by perforations in the postsynaptic density (PSD), some of which had synaptic spinules associated with the perforated PSDs, i.e. spinule-synapses; (3) a rapid increase in the number of both structures was detected immediately after the tetanus. Perforated synapses and the spinule-synapses increased from 5% and 0% in the control to 27 and 9% at 0 min, respectively. Spinule-synapses occurred about one-third of the perforated shaft synapses; (4) Increased numbers of restructured shaft synapses was maintained for 15 min in ganglia expressing LTP; (5) Remodeled synapses did not increase in ganglia that did not express LTP or ganglia that were activated at 0.5 or 1 Hz. It was suggested a rapid increase in the number of remodeled synapses associated with the onset of LTP and its durability at its earlier phases in the cat SCG.

Morphological correlate of the post-tetanic potentiation in the cat superior cervical ganglion in situ

Morphological correlate of the post-tetanic potentiation in the cat superior cervical ganglion in situ

Effect of hypoxia and dopamine on arachidonic acid metabolism in superior cervical ganglion.

Superior cervical ganglion (SCG) may play a modulatory role on ventilatory control through its efferent sympathetic fibres, which innervate cells in the carotid bodies. In this study the in vivo effect of acute hypoxia versus normoxia on arachidonic acid (AA) metabolism was investigated in cat SCG. Using SCG homogenate AA was incorporated into glycerolipids of normoxic SCG in the following order: neutral glycerolipids > phosphatidylcholine (PtdCh) > phosphatidylinositol (PtdIns) > phosphatidylethanolamine (PtdE) > phosphatidylserine (PtdS) > and phosphatidic acid (PA). In vivo hypoxic treatment caused a significant decrease in incorporation of [1-14C]AA into PtdIns. Hypoxia had no significant effect on the level of AA radioactivity in diacylglycerol (DAG) as compared to control but significantly enhanced the level of arachidonoyl-CoA (AA-CoA) radioactivity. It was observed that dopamine (DA) one of the most important neurotransmitter in SCG decreases AA uptake into phospholipids of normoxic SCG. In normoxic SCG, DA significantly decreased, AA incorporation into PtdCh, PtdIns and DAG. Moreover, DA decreased the level of AA-CoA radioactivity. Hypoxia and dopamine has no effect on AA metabolism in medulla oblongata isolated from the same animals. These results indicate that arachidonic acid metabolism in SCG is sensitive to hypoxia and dopamine action. Moreover, these results indicate that hypoxia inhibits selectively AA incorporation on the level of acylCoA-lysophosphatidylinositol-acyltransferase.

Synaptic Spinules Attendant on Post-tetanic Potentiation in Cat Sympathetic Ganglion.

A synaptic spinule formed on the postsynaptic membrane in the cat superior cervical ganglion (SCG) in vivo was electron microscopically studied. When the preganglionic nerve fiber was tetanically stimulated at 10Hz for more than 10 seconds, a post-tetanic potentiation (PTP) was electrophysiologically detected and maintained up to 30min. Concurrently with PTP, a small process, termed as synaptic spinule, was generated as a small projection standing out from the postsynaptic dendritic membrane with a straightly extended contour. The spinule produced a break at about a middle point of the postsynaptic density (PSD) and divided it into two parts forming a perforated synapse. Then, the spinule increased in size, invaginated into the cytoplasm of the nerve terminal, and subdivided the presynaptic terminal bag into two compartments. Each of the compartments retained a morphology of an active synaptic site with a cluster of synaptic vesicles associated with a presynaptic active zone standing opposite to the one part of the subdivided PSD. The longer the tetanic stimulation in period, the more the synapses with the spinule increased in number. In addition to this, a few spinules (multiple type of spinule) were often formed after the stimulation of 1min and more than two compartments were generated in a single nerve ending. The present observations have suggested that the synaptic spinule is a morphological representation of the “synaptic plasticity” which is electrophysiologically displayed as the PTP in cat SCG in vivo.

The site of inhibitory action of endogenous opioids in the superior cervical ganglion of the cat

A low-frequency stimulus train to the preganglionic input inhibits synaptic transmission in the superior cervical ganglion (SCG) of the cat. The inhibition is blocked by naloxone as well as by selective antagonists at mu and delta opiate receptors, which suggests that the mediator is an endogenous opioid [27, 29]. Exogenous opioid peptides, including methionine-enkephalin (Met-Enk), which is present in preganglionic axons of the SCG, inhibit ganglionic transmission by a naloxone-sensitive mechanism. In the present study we test, in the anesthetized cat, whether the naloxone-sensitive synaptic inhibition is mediated by a pre- and/or post-synaptic mechanism. As a test of presynaptic inhibition, we measured the acetylcholine (ACh) released by preganglionic stimulation into the venous effluent of the perfused SCG. As a test of post-synaptic inhibition, we measured the effect of a preganglionic conditioning train on the ganglion cell firing evoked by ganglion-stimulant drugs injected into the arterial supply of the ganglion. In presence of naloxone (3 μM), which blocked the synaptic inhibition, the amount of ACh released by stimulated preganglionic axons did not change. Thus, the endogenous opioid which mediates the naloxone-sensitive inhibition does not act by depressing ACh release. In contrast, the ganglion cell firing evoked by ganglion-stimulant drugs was markedly depressed by a conditioning train, and naloxone blocked the depression, which suggests that the endogenous mediator of the naloxone-sensitive inhibition acts postsynaptically to decrease the excitability of ganglion cells. Exogenous Met-Enk depressed both ACh release by preganglionic stimulation and the firing of ganglion cells evoked by ganglion-stimulant drugs. These findings suggest that although opiate receptors in the cat SCG are present at both pre- and post-synaptic sites, under the conditions of the present experiment the naloxone-sensitive, synaptically mediated inhibition is mediated exclusively by activation of post-synaptic opiate receptors.

Lack of long-term potentiation, non-cholinergic transmission and muscarinic inhibition in cat superior cervical ganglia innervated by nodose ganglion cells

In anesthetized cats, in which a nodose-superior cervical ganglion (SCG) anastomosis had been performed 6–9 months earlier, the nictitating membrane contraction evoked by electrical stimulation of the cervical vagus nerve ipsilateral to the anastomosis was recorded. The competence of nodose neurons in regulating the multiple synaptic mechanisms of the sympathetic ganglion was tested by comparing this response with the responses to stimulation of the intact cervical sympathetic trunk (CST) or of the CST that had been transected and sutured 6–9 months earlier (self-reinnervated SCG). The response of the nictitating membrane ipsilateral to the anastomosis was smaller and had a lower EC50 for hexamethonium (C6) than the responses of the nictitating membrane ipsilateral to the intact or sutured CST. A 40 Hz 10s stimulus train to the intact or sutured CST produced potentiation of ganglionic transmission lasting 1 hour or longer, while a similar stimulus train to the anastomosed cervical vagus nerve produced no potentiation. During block of ganglionic nicotinic transmission with C6, CST or vagus nerve stimulation evoked responses which increased in amplitude with increasing stimulus frequency and were blocked by the selective muscarinic receptor antagonist pirenzepine. When the anticholinesterase eserine was added, the responses evoked by preganglionic stimulation decreased in amplitude in the intact SCG, as previously shown [7], and in the self-reinnervated SCG. This effect, which is due to inhibition mediated by muscarinic receptors selectively blocked by AF-DX116, was absent in the anastomosed SCG. During block of ganglionic transmission with C6 and atropine, a 40 Hz stimulus train to the intact or to the sutured CST evoked a slow, small amplitude contraction that was enhanced by naloxone. This response, most likely mediated by peptides [6], was absent in the anastomosed SCG. The present study confirms the previous finding of decreased efficacy of nicotinic transmission in the SCG innervated by nodose ganglion cells, and contributes the new finding that this synapse lacks long-term potentiation, excitation mediated by non-cholinergic receptors and inhibition mediated by muscarinic receptors. This absence suggests lack of appropriate co-transmitters and/or trophic factors required for the expression of these responses.

The role of tonic preganglionic neuron firing in the turnover of the large dense-cored vesicle store in sympathetic preganglionic nerve terminals

Large dense-cored vesicles are transported centrifugally in the cervical sympathetic trunk and are depleted in a calcium-dependent manner from synaptic boutons of the cat superior cervical ganglion during orthodromic stimulation at 20–40 Hz [P. Weldon et al. (1993) Neuroscience 55, 1045–1054]. In the present study, we tested in awake cats whether the normal tonic firing of the sympathetic preganglionic neuron contributes to the turnover of large dense-cored vesicles in synaptic boutons of the superior cervical ganglion. Tetrodotoxin was applied with a mini-osmotic pump to one cervical sympathetic trunk, while vehicle alone was applied to the contralateral cervical sympathetic trunk, for two, four or seven days. The appearance of Horner syndrome ipsilateral to the tetrodotoxin application demonstrated block of action potential propagation. Both superior cervical ganglia were excised and processed for electron microscopy. The number of large dense-cored vesicles per bouton cross-section was higher in the ganglion with tetrodoxin-treated input than in the control. The content at four days was higher than at two days; the content at seven days was similar to that at four days. The number of lysosomes per bouton profile also increased in the ganglion with tetrodotoxin-treated input. No changes were observed in size of bouton profiles, number of boutons or of synapses per grid square and length of the presynaptic densities in the ganglion with tetrodotoxin-treated input. The increased large dense-cored vesicle content of the boutons in the ganglion with tetrodotoxin-treated input is likely the result of lack of release while supply is maintained and suggests that under normal conditions there is a steady turnover of large dense-cored vesicles by an action potential-dependent mechanism, presumably involving exocytosis. The lack of a further increase in large dense-cored vesicle content after four days of tetrodotoxin block may be the result of action potential-independent release and/or decreased supply and/or increased intraterminal breakdown. These observations are consistent with the hypothesis that, in sympathetic preganglionic axon terminals, the components of large, dense-cored vesicle turnover are supplied from the soma and released by the neuron tonic firing which, in this preparation, has a mean rate of 1–2 Hz.

Dynamics of Presynaptic Endosomes Produced during Transmitter Release

The movements of the presynaptic endocytotic structures produced during tetanic stimulation at 10 Hz were examined morphometrically and cytochemically in the cat superior cervical ganglion in vivo. The longitudinal profiles of the axon terminal and preterminal area were subdivided into five zones, I-V. Zone I, the area adjacent to the active zone, was assigned a hemicircle with a diameter equivalent to the active zone width (2R). Zones II-IV were defined by subdividing successively the presynaptic and preterminal areas within hemicircles with diameters equivalent to three-, five-, and sevenfold of 2R, respectively. Zone V was composed of the rest of the preterminal profile. The endocytotic structures, macropinocytotic endosomes and coated vesicles, observed in each zone were morphometrically analyzed with the time course of stimulation. The lateral surface of zone II was shown to be the main site for internalization of the terminal surface membrane during transmitter release. A large amount of the plasmalemma of zone II was rapidly retrieved by macropinocytosis to produce early endosomes at an increased rate of about three times that at rest. The population of coated vesicles, few in number at rest, increased to two- to threefold in zones II-V following the stimulation. Cytochemical examinations showed the incorporation of HRP into synaptic vesicles, endosomes and multivesicular bodies. An antibody against synaptophysin labeled the presynaptic endosomes, multivesicular bodies, coated vesicles as well as synaptic vesicles. The results have suggested that a considerable part of these endosomes was transported retrogradely at an increasing rate from zone II to zone V via zones III and IV. On the other hand, synaptophysin was observed to be distributed on the tubular protrusions of the presynaptic endosomes, suggesting the segregation and recycling of a part of synaptic vesicle proteins from the early endosomes in the nerve endings of the cat superior cervical ganglion.

Rapid recovery of structure and function of the cholinergic synapses in the cat superior cervical ganglionin vivo following stimulation-induced exhaustion

Cat superior cervical ganglia (SCG) were tetanically stimulated in vivo at 30-100 Hz until neural transmission was exhausted, and then were allowed to rest and recover. Changes in their cholinergic synapses were examined electrophysiologically and morphologically during the time of tetanic stimulation and during recovery. For morphometric analysis the presynaptic terminal was subdivided into two areas: an area directly over the active zone, termed zone-I, (bounded by a hemicircle with a diameter equivalent to the active zone length), and the remaining preterminal area, termed zone-II. In control ganglia before stimulation synaptic vesicle density in zone-I (SVD-I) averaged 90 microns-2 and the number of vesicles actually attached to the active zone (SVA) averaged about 2.5 per single profile of nerve terminal. Upon stimulation, the postganglionic potential immediately began to decline in amplitude and disappeared after 1 min of stimulation. Simultaneously, SVD-I declined to less than 35 microns-2 and SVA declined to less than 1 per section. Thereafter, stimulation was terminated and the ganglion was allowed to rest. Recovery of the postganglionic potential was monitored by stimulation at 1 Hz. The postganglionic potential reached control levels after only 1 min of rest. Likewise, the structural parameters, SVD-I and SVA, also rapidly recovered, reaching control levels after only 30 sec of rest, slightly faster than the postganglionic potential. This illustrates that stimulation-induced fatigue of transmitter output and depletion of synaptic vesicles recover to the control level at a high rate in synapses of the cat SCG with a normal supply of blood. In fact, morphological recovery may be slightly faster than electrophysiological recovery. Mechanisms of vesicle formation and migration to the presynaptic area are discussed in light of these observations.

Dynamics of large dense-cored vesicles in synaptic boutons of the cat superior cervical ganglion

We have shown previously that stimulation of the cat cervical sympathetic trunk for 2 h at 40 Hz Depletes the large Dense-cored vesicle Store in synaptic boutons of the superior cervical ganglion and that post-depletion recovery of the store takes several days. In the present study, we examine the properties of the depletion and recovery mechanisms. Invaginations of the plasmalemma suggestive of the exocytosis of dense cores were seen frequently in boutons from stimulated ganglia. The depletion process is calcium dependent: in ganglia perfused with calcium-free Krebs solution no depletion was produced by 40 Hz preganglionic stimulation. The depletion process is rapid: during continuous stimulation of the cervical sympathetic trunk with 40 Hz, depletion observed by the end of 2 h was similar to depletion by the end of the initial 5 min of stimulation. The depletion process is frequency dependent: when the cervical sympathetic trunk was stimulated with a constant number of stimuli, no depletion occurred at the frequency of 2 or 10 Hz, while the frequencies of 20 and 40 Hz produced depletion, which was greater at 40 Hz. Recovery of the large dense-cored vesicle store during the initial 24 h after 10 min of 40 Hz stimulation was faster, and of approximately the same magnitude, than during the succeeding five days. Recovery of the store after stimulus-evoked depletion was prevented by application of colchicine to the cervical sympathetic trunk, which suggests dependence of recovery on fast axonal transport. Large dense-cored vesicles accumulated in the colchicine-treated segment of cervical sympathetic trunk axons. In conclusion, these observations suggest that the stimulus-evoked depletion of large dense-cored vesicle stores in synaptic boutons of the cat superior cervical ganglion is the result of calcium-dependent exocytosis of the large dense-cored vesicle core and that the post-stimulus recovery is critically dependent on microtubule-mediated axonal transport.

Mobilization of a vesamicol-insensitive pool of acetylcholine from a sympathetic ganglion by ouabain.

These experiments investigate the release of transmitter from the perfused superior cervical ganglia of cats induced by ouabain in the absence or presence of 2-(4-phenylpiperidino)cyclohexanol (vesamicol), a blocker of acetylcholine (ACh) uptake. Ouabain, perfused through the ganglia, released ACh in a Ca(2+)-dependent way. Vesamicol caused some inhibition of the release of ACh by ouabain; however, under this condition, the Na+,K(+)-ATPase inhibitor released five times more transmitter than did preganglionic stimulation at 5 Hz. Also, when ganglia exposed to vesamicol were depleted of the impulse-releasable pool of ACh, subsequent perfusion with ouabain released ACh, and this included ACh newly synthesized in the presence of vesamicol; this phenomenon could be inhibited by the lack of Ca2+ and presence of EGTA, and was completely abolished by perfusion with a medium containing 18 mM Mg2+. To test whether the release of this vesamicol-insensitive Ca(2+)-dependent pool by ouabain is associated with a decrease in the number of synaptic vesicles, ganglia treated with the ATPase inhibitor after the depletion of the impulse-releasable pool of ACh were fixed for electron microscopy. In the presence of Ca2+, coincident with the release of the vesamicol-insensitive pool of ACh, nerve terminals were almost depleted of synaptic vesicles; ganglia treated similarly, but with medium containing 18 mM Mg2+ instead of Ca2+, were not depleted of synaptic vesicles. These results suggest that ouabain releases a vesamicol-insensitive pool of ACh from the sympathetic ganglion and also support the notion that this compartment is vesicular and its exocytosis depends on extracellular Ca2+. It is suggested that empty-vesicle recycling in the presence of vesamicol restricts mobilization of full vesicles to release sites.

Use-dependent fade and two-rate recovery of a naloxone-sensitive inhibition in the cat superior cervical ganglion

In anaesthetized cats, a short train to the cervical sympathetic trunk (CST), of frequency between 0.5 and 5.0 Hz, inhibited the postganglionic compound action potential (CAP) evoked by a test shock to the CST. When the CST was split into two bundles, the inhibition was obtained both homosynaptically and heterosynaptically. The inhibition was antagonized by naloxone and enhanced by peptidase inhibitors. Leu-enkephalin (ENK), injected into the arterial supply of the superior cervical ganglion (SCG) depressed the CAP. The ENK-evoked inhibition was antagonized by naloxone, enhanced by peptidase inhibitors and was occluded by the train-evoked inhibition. After prolonged stimulation of the CST (5–20 min at 5 Hz), the inhibition produced by a short train was depressed (faded). The fade was greater the longer the stimulation. After 20 min of stimulation the inhibition was absent. At this time the depressant effect of ENK was unchanged. When only one bundle of the split CST was stimulated at 5 Hz for 20 min, only the inhibition produced by that bundle faded, although both bundles converged onto a common set of ganglion cells. Thus, the fade is not due to receptor desensitization but more likely to failure to release the inhibitory mediator by the overstimulated axons. When, after 20 min of 5 Hz stimulation, no further stimuli were applied, the inhibition recovered in 60 min (fast recovery). However, recovery was slower when stimulation lasted longer than 20 min. Recovery took three days when stimulation lasted 80 min (slow recovery). The inhibition was markedly depressed after application of colchicine to the CST three days earlier. This suggests significant spontaneous release of the endogenous opioid. This treatment also prevented the slow recovery from the fade. The fast recovery from the fade was not prevented by protein synthesis inhibitors nor by a colchicine block of the CST. The data are consistent with the hypothesis that the transmitter mediating the naloxone-sensitive inhibition in the SCG of the cat is present in the preganglionic axon terminals in a small, readily releasable, pool which is exhausted by 20 min stimulation at 5 Hz. A presumably local mechanism, which is exhausted by 80 min of stimulation at 5 Hz, is responsible for the fast recovery. The slow recovery presumably involves protein synthesis and axonal transport.

An AF-DX 116 sensitive inhibitory mechanism modulates nicotinic and muscarinic transmission in cat superior cervical ganglion in the presence of anticholinesterase.

The effect of the muscarinic receptor antagonist AF-DX 116 on the inhibitory action of muscarinic agonists and on responses mediated by nicotinic or muscarinic ganglionic transmission was studied in the superior cervical ganglion of the anesthetized cat. The postganglionic compound action potential evoked by cervical sympathetic trunk stimulation was depressed by methacholine or acetylcholine (ACh) injected into the ganglionic arterial supply. The depression was blocked by AF-DX 116. The compound action potentials evoked by preganglionic stimulus trains were also depressed when the intratrain frequency was 2 Hz or greater. This intratrain depression was, however, insensitive to AF-DX 116. The anticholinesterase drug physostigmine markedly enhanced the intratrain depression of the compound action potential. This effect was reversed by AF-DX 116. During nicotinic receptor block with hexamethonium, preganglionic stimulus trains with intratrain frequencies of 5 Hz or greater produced nicitating membrane contractions that could be blocked by the M1 muscarinic receptor antagonist pirenzepine. The amplitude of the contractions increased with frequency and reached a maximum at 20-40 Hz. AF-DX 116 had no effect on these responses. After administration of physostigmine, the amplitude of the nictitating membrane responses decreased with increasing intratrain frequency. AF-DX 116 reversed this effect. The data suggest that, in the superior cervical ganglion, AF-DX 116 sensitive muscarinic receptors which depress synaptic transmission are activated by exogenous agonists but not by the ACh released by the preganglionic axon terminals unless cholinesterase activity is inhibited.(ABSTRACT TRUNCATED AT 250 WORDS)

Mobilization of the readily releasable pool of acetylcholine from a sympathetic ganglion by tityustoxin in the presence of vesamicol.

The present experiments tested whether preganglionic stimulation and direct depolarization of nerve terminals by tityustoxin could mobilize similar or different pools of acetylcholine (ACh) from the cat superior cervical ganglia in the presence of 2-(4-phenylpiperidino)cyclohexanol (vesamicol, AH5183), an inhibitor of ACh uptake into synaptic vesicles. In the absence of vesamicol, both nerve stimulation and tityustoxin increased ACh release. In the presence of vesamicol, the release of ACh induced by tityustoxin was inhibited, and just 16% of the initial tissue content could be released, a result similar to that obtained with electrical stimulation under the same condition. When the impulse-releasable pool of ACh had been depleted, tityustoxin still could release transmitter, amounting to some 10% of the ganglion's initial content. This pool of transmitter seemed to be preformed in the synaptic vesicles, rather than synthesized in response to stimuli, as tityustoxin could not release newly synthesized [3H]ACh formed in the presence of vesamicol, and hemicholinium-3 did not prevent the toxin-induced release. In contrast to the results with tityustoxin, preganglionic stimulation could not release transmitter when impulse-releasable or toxin-releasable compartments had been depleted. Our results confirm that vesamicol inhibits the mobilization of transmitter from a reserve to a more readily releasable pool, and they also suggest that, under these experimental conditions, there might be some futile transmitter mobilization, apparently to sites other than nerve terminal active zones.

Synaptic Vesicle Increase Correlated to Potentiation of Transmission at the Synapse of the Cat Superior Cervical Ganglion <italic>In Vivo</italic>

Changes in the pattern, number and size of synaptic vesicles during transmitter release were examined in the synapses of the cat superior cervical ganglion (SCG) in vivo in relation to alteration in the amplitude of postganglionic compound action potential (PGP). Stimulation of the preganglionic nerve fibers at 10 Hz caused an increase in the mean amplitude of PGP. It became augmented by approximately 30% compared to control 10-30 sec after starting the stimulation, and then gradually declined to reach a plateau after 4-6 min. This level, about 20% higher in value than control, was sustained until the end of 30 min of stimulation. The nerve terminal was divided into two areas to examine topographically the numerical changes in synaptic vesicles (SVs): zone I on the presynaptic membrane encircled with a diameter equivalent to the active zone length, and zone II occupying the remaining area outside zone I. The synaptic vesicle density in zone I (vesicle number/microns 2) was 96.9 +/- 4.8 (mean +/- S.E.M.) in the unstimulated control ganglia and 128.8 +/- 9.4 (mean +/- S.E.M.) in the ganglia stimulated for 10-30 sec, which was 30% higher in value than control. Then, it decreased slightly reaching a plateau, 20% higher in value than control. The diameter distribution of the SVs showed that their diameters in zone I (56.6 nm mean) were larger than those (51.6 nm mean) in zone II, and that prolonged stimulation induced smaller vesicles in both areas. The results showed that the increase in SV number in zone I correlated well with the elevation of PGP.(ABSTRACT TRUNCATED AT 250 WORDS)

Cytochemistry of 5′-nucleotidase in the superior cervical ganglion of cat and guinea pig

The localization of 5′-nucleotidase, an adenosine-producing ectoenzyme, was studied by a cytochemical method in the superior cervical ganglion of the adult cat and guinea pig. The following subcellular sites of enzymatic activity were detected: (1) the surface of Schwann and satellite cells including the extracellular space between these cells and neuronal profiles; (2) the plasmalemma and pinocytotic vesicles of capillary endothelial cells; and (3) the synaptic clefts between cholinergic preganglionic axon terminals and sympathetic neurons. The simultaneous presence of 5′-nucleotidase at both glial elements and synapses within the adult peripheral nervous system (PNS) constitutes a novel distribution pattern for this enzyme which does not apply to the mature central nervous system (CNS), but which is rather typical for the developing CNS. These distributions of 5′-nucleotidase activity may reflect specific cellular requirements for nucleosides involved in parenchymal metabolism, in vascular transport processes and, possibly, in synaptic plasticity.

Modulated long-term potentiation in the cat superior cervical ganglion in vivo

In the sympathetic ganglion a high frequency conditioning train produces a post-train potentiation (PTrP) which decays with a temporal course that can be described by two components: an early faster component known as post-tetanic potentiation (PTP), and a long-lasting one which is known as long-term potentiation (LTP). The magnitude of PTP and LTP is thought to be a function of the subliminal fringe size. Moreover, under full activation of ganglion cells LTP does not appear due to the saturation conditions. LTP emerges only when the subliminal fringe is increased, and to achieve this, a low-level tetanization must be performed. However, another possibility, explored in this paper, is that in addition to the desaturation effect of the low-level conditions of tetanization, a different mechanism, responsible for the LTP appearence, may be introduced by these low-level conditions of tetanization. This possibility implies a variable LTP according to the input conditions; accordingly, the shape of LTP was compared in 4 experimental conditions in which the input to the ganglion cells was different: (1) supramaximal activation of the intact cervical sympathetic trunk (CST), (SPM); (2) submaximal activation of the intact CST, (SBM); (3) supramaximal activation of the partially transected CST, (TRN); and (4) supramaximal activation of the intact CST under partial nicotinic block with hexamethonium, (BLK). Even when PTrP was evoked with the same subliminal fringe obtained under the 3 low-level conditions of tetanization, the degree of potentiation and the proportion of PTP and LTP were different. After either SPM or SBM conditions LTP was negligible, though PTP developed to a certain degree. LTP emerged to a large degree in TRN experiments and particularly under BLK conditions, though PTP remained nearly constant under these and SPM, and SBM conditions. These different degrees and shapes of PTrP attained with similar subliminal fringe cannot be explained only by a desaturation effect, therefore a different mechanism must be involved. Furthermore, the fact that the changes were mainly at the expense of the growth of LTP, suggests the presence of a specific mechanism for this phenomenon, which it manifested particularly upon blockade conditions.

Continuous retrograde migration of macropinocytotic vacuoles produced in the presynaptic terminal during tetanic stimulation in the cat superior cervical ganglion in vivo

Continuous retrograde migration of macropinocytotic vacuoles produced in the presynaptic terminal during tetanic stimulation in the cat superior cervical ganglion in vivo

Depletion by preganglionic stimulation and post-stimulus recovery of large dense core vesicles in synaptic boutons of the cat superior cervical ganglion

Large dense core vesicles (LDCV), a possible site for neuropeptide storage, were counted within synaptic boutons of the superior cervical ganglion of anaesthetized cats in the unstimulated condition and 2 h, 1 day or 10 days after 40 Hz 2 h stimulation of the cervical sympathetic trunk. The number of LDCV decreased markedly after stimulation. It was lowest at 2 h and then recovered slowly. Ten days post-train the number was close to, but still significantly lower than, control. This time course of recovery is much longer than for agranular vesicles number, which is known to be back to normal within 2 h of the end of a comparable stimulus train. The post-stimulus loss of LDCVs is consistent with the hypothesis that LDCVs are released by the nerve terminal. The slow recovery is consistent with the hypothesis of replenishment by axoplasmic transport.

Glycyl-L-glutamine opposes the fall in choline acetyltransferase in the denervated superior cervical ganglion of the cat.

Intracarotid infusion of 3 microM glycyl-L-glutamine was found to oppose the fall in the choline acetyl-transferase content of the preganglionically denervated cat superior cervical ganglion; this same effect has been demonstrated previously for acetylcholinesterase content. Because choline acetyltransferase, in contrast to acetylcholinesterase, occurs exclusively in the preganglionic axons and their terminals, this finding raises the possibility that glycyl-L-glutamine opposes postsectional axonal degeneration.