Cholecystokinin octapeptide depolarizes guinea pig inferior mesenteric ganglion cells and facilitates nicotinic transmission

Systemic cholecystokinin differentially affects baro-activated GABAergic neurons in rat caudal ventrolateral medulla

Cholecystokinin (CCK) is released after a meal to promote digestion and satiety. Circulating CCK inhibits splanchnic sympathetic nerve activity (sSNA), which may contribute to postprandial increases in mesenteric blood flow. The CCK-induced sympathoinhibition occurs by activation of vagal afferent nerves and inhibition of a subset of presympathetic rostral ventrolateral medullary (RVLM) neurons. The present study sought to determine whether the caudal ventrolateral medulla (CVLM) may also play a role in the CCK-induced changes in sSNA. Rats were anesthetized with chloralose, artificially ventilated, paralyzed, and prepared for recording arterial pressure (AP), heart rate (HR), sSNA, and activity of individual CVLM neurons. Injection of CCK-8 (8-10 microg/kg, iv) decreased sSNA, AP, and HR. Most baro-activated CVLM neurons were excited by CCK (n = 25, 3.4-fold increase), whereas other baro-activated CVLM neurons were not affected (n = 7) or were inhibited (n = 3). A subset of baro-activated CVLM neurons that were activated (n = 8) or unaffected (n = 2) was confirmed to be GABAergic by the presence of GAD67 mRNA. Bilateral inhibition of the CVLM by microinjections of muscimol reversed the decreases in sSNA and AP to a prominent sympathoactivation and increase in AP (n = 18). These data suggest that systemic injection of CCK leads to the activation of most baro-activated GABAergic CVLM neurons and that the CVLM is essential for the production of CCK-induced inhibition of sSNA. The differential responses of baro-activated GABAergic CVLM neurons to CCK may contribute to the diverse responses of presympathetic RVLM neurons and sympathetic outflows observed with systemic CCK.

Chemical sympathectomy attenuates myenteric but not dorsal vagal complex Fos-like immunoreactivity induced by cholecystokinin-8 in the rat

Vagotomy and capsaicin treatment attenuate dorsal vagal complex (DVC) but not myenteric Fos-like immunoreactivity (Fos-LI) induced by cholecystokinin-8 (CCK-8). The goal of this experiment is to test the role of the sympathetic nervous system in the pathway by which CCK-8 increases myenteric Fos-LI. Adult male Sprague-Dawley rats were pretreated with guanethidine sulfate (40 mg/kg daily for 5 weeks) or vehicle intraperitoneally (IP), and injected with CCK-8 (40 microg/kg) or saline IP. Fos-LI was then quantified in the DVC and the myenteric neurons of the duodenum and jejunum using a diaminobenzidine reaction. Guanethidine pretreatment attenuated myenteric but not DVC Fos-LI induced by CCK-8. These findings demonstrate that sympathetic neurons play a role in mediating the myenteric Fos-LI response to CCK. They also suggest differential mediation of myenteric and DVC responses to CCK.

Cholinergic modulation of neuronal responses to cholecystokinin in anesthetized rats

The aim of this study was to investigate whether the effects of the neuropeptide cholecystokinin on neuronal firing can be changed by acetylcholine in various structures of the brain. Single unit activity was extracellularly recorded in rats anesthetized with urethane. The neurons were located in several nuclei of the thalamus, the basal ganglia and the cerebral cortex. Neurons responding to the sulfated octapeptide of cholecystokinin (CCK-8S) were mainly activated by the drug [Wilcoxon test (Wt) p < 0.0001, n=113]. Thalamic neurons could also increase the number of burst discharges (Wt p < 0.005, n=39). Iontophoretically administered acetylcholine could reduce the activating effects of CCK-8S on firing and burst discharges. In its presence, even inhibitory effects of CCK-8S predominated (Wt p < 0.0001, n=113). The suppressive action seemed not to depend on the direction of the effect of acetylcholine itself and concerned neurons of all locations studied. Atropine could diminish or block the suppressive action of acetylcholine. In the presence of both drugs, CCK-8S mainly activated the neurons (Wt p < 0.005, n=43). Atropine itself did not significantly change the responses to CCK-8S (Wt p > 0.05). It can be concluded that cholecystokinin may reduce neuronal firing instead of increasing it during activation of the cholinergic system.

CCKA and CCKB receptor subtypes both mediate the effects of CCK-8 on myenteric neurons in the guinea-pig ileum

The effects of cholecystokinin (CCK-8) on myenteric S neurons were investigated by intracellular recording techniques, with the aim to determine the CCK receptor subtypes involved. CCK-8 (1-1000 nM) evoked concentration-dependent long-lasting excitatory responses in 45 of 54 neurons. CCK receptor antagonists were applied to 15 neurons in which CCK-8 evoked an excitatory response. In 5 of these neurons, application of the CCKA antagonist L-364,718 (100-500 nM) antagonized the action of CCK-8 and the CCKB antagonist L-365,260 (500 nM) had no effect. L-365,260 (100-500 nM) antagonized the CCK-8 induced response in 5 neurons, on which L-364,718 had no effect. In the other 5 neurons each antagonist (500 nM) partly inhibited the CCK-8 evoked excitation and application of both antagonists (500 nM) caused a complete blockade of the response to CCK-8. The selective CCKB receptor agonist CCK-8NS had similar excitatory effects as CCK-8, but only on the neurons in which CCK-8 evoked effects were antagonized by L-365,260. The results demonstrate that the excitatory effects of CCK-8 are mediated by both CCKA and CCKB receptor subtypes. Further, the results indicate that some neurons possess exclusively the CCKA or the CCKB receptor subtype, but others possess both subtypes.

The mammalian sympathetic prevertebral ganglia: integrative properties and role in the nervous control of digestive tract motility

The prevertebral ganglia which are a constitutive part of the sympathetic system have long been considered as a simple relay on this efferent pathway. In fact, these ganglia must be considered as true peripheral nervous centres. They possess various integrative properties, such as projections of central and peripheral inputs onto the ganglionic neurones, gating of these projections and pacemaker activity of the ganglionic neurones. These properties explain the ability of these ganglia to participate in the regulation of various visceral functions, including digestive tract motility.

Modulation by opioid peptides of mechanosensory pathways supplying the guinea-pig inferior mesenteric ganglion

1. Radioimmunological techniques were used in isolated guinea-pig inferior mesenteric ganglion (IMG)-colon preparations to determine whether opioid peptides and neurotensin8-13 (NT8-13), the C-terminal region of NT1-13 recognized by neurotensin receptors, modulate distension-induced release of substance P (SP)- and vasoactive intestinal polypeptide (VIP)-like immunoreactive (LI) material. 2. Colonic distension significantly increased the amount of SP- and VIP-LI material released in the ganglionic superfusate. A low-Ca2+ (0.1 mM), high-Mg2+ (15 mM) solution blocked their release. 3. In vivo capsaicin pretreatment abolished release of SP-LI material during colonic distension but had no significant effect on distension-induced release of VIP-LI material. 4. The addition of [Leu5]enkephalin, [Met5]enkephalin, PL017 (a mu-receptor agonist) and DPDPE (a delta-receptor agonist) to the ganglion side of a two-compartment chamber blocked distension-induced release of SP-LI material. The addition of naloxone and ICI-174,864 (a delta-receptor antagonist) to the ganglion compartment reversed the inhibitory effect of the mu- and delta-receptor agonists. 5. Addition of [Leu5]enkephalin and [Met5]enkephalin to the ganglion compartment had no significant effect on release of VIP-LI material during colonic distension. 6. Addition of NT8-13 to the ganglion compartment significantly increased in the amount of SP-LI material released during colonic distension but had no affect on distension-induced release of VIP-LI material. 7. The results suggest the hypothesis that under in vivo conditions, enkephalinergic nerves decrease and neurotensinergic nerves increase the release of SP from peripheral branches of primary afferent sensory nerves.

CCKA receptors mediate slow depolarizations in cultured mammalian sympathetic neurons

The effect of cholecystokinin octapeptide (CCK-8) was examined in guinea-pig celiac ganglion (CG) neurons in primary culture using standard intracellular recording techniques. Sulfated CCK-8 (CCK-8S; 1 microM) evoked slow depolarizing responses in 94% of CG neurons tested. In contrast, membrane potential was not affected by nonsulfated CCK-8 (CCK-8NS; 1 microM), CCK tetrapeptide (CCK-4; 1 microM), or gastrin (1 microM). The selective CCKA receptor antagonist L 364,718 potently inhibited CCK-8S-induced slow depolarizations (IC50 2.9 pM). In contrast, the selective CCKB receptor antagonist L 365,260 was a weak inhibitor of CCK-8S-induced slow depolarizations (IC50 1.3 microM). The depolarizing responses to CCK-8S were associated with an average increase in cell input resistance of 61%. Single electrode voltage clamp experiments indicated that CCK-8S-induced depolarizations were associated with a slow inward shift in holding current. Thus, the present findings indicate that guinea-pig cultured CG neurons are endowed with excitatory CCKA receptors the activation of which elicits a decrease in membrane conductance, thereby resulting in slow depolarizations.

Modulation of the transient potassium current in rat hippocampal neurones by cholecystokinin

Cholecystokinin (CCK) affects neuronal excitability in a variety of in vivo and in vitro preparations, apparently by modulating a resting potassium conductance. The data presented here show that CCK (applied as CCK8-S) also affects the transient potassium current in hippocampal neurones, by changing the voltage dependence of the inactivation and activation of the current. The way in which the voltage dependence is changed can lead to either an enhancement of the current or an attenuation, depending upon the voltage protocol used. This effect of CCK does not desensitise over a time period of minutes, and may therefore be important in controlling neuronal excitability in the CNS.

Excitatory effects of cholecystokinin octapeptide on rat nodose ganglion cells in vitro

Cholecystokinin octapeptide (CCK-8) applied by pressure evoked in the majority of rat nodose ganglion cells a rapid depolarization associated with a fall of membrane resistance and in a few cells a slow depolarization accompanied by an increase of membrane resistance. The fast depolarizations were increased and decreased by membrane hyperpolarization and depolarization; the extrapolated reversal potential was about -10 mV. The response was depressed in a Na-free solution and by d-tubocurarine (10-100 microM) but not in a Cl-deficient solution. It is concluded that CCK-8 depolarized the nodose ganglion cells by increasing cation conductances and in a few cells it also produced a slow excitation, the mechanism of which remains to be established.

The role of cholecystokinin in ganglionic transmission in the guinea-pig gall-bladder

1. The effects of cholecystokinin (CCK) on intact guinea-pig gall-bladder ganglia were investigated with intracellular, single-electrode current- and voltage-clamp recording techniques. 2. Cholecystokinin octapeptide (CCK-8; 0.01-100 nM) increased the amplitude of the fast excitatory postsynaptic potential (EPSP) that was evoked by stimulation of interganglionic fibre tracts. In most cases, neurones that exhibited subthreshold EPSPs in normal Krebs solution fired action potentials in the presence of CCK-8. In a low Ca2+/high Mg2+ solution, CCK-8 caused a 3-fold increase in the amplitude of fast EPSPs. 3. The amplitude of the evoked excitatory postsynaptic current (EPSC) was increased by CCK-8 (0.01-100 nM) in a concentration-dependent manner. The effect was maximal at 1.0 nM. 4. Cholecystokinin octapeptide caused a 3-fold increase in the quantal content of the EPSP in a low Ca2+/high Mg2+ solution, but had no effect on the quantal size. 5. The specific CCK-A receptor antagonist, MK-329 (formerly L-364,718; 1.0 nM), reversibly blocked the facilitatory effect of CCK-8 on ganglionic transmission. However, the specific CCK-B receptor antagonist, L-365,260 (10 nM), did not alter the presynaptic facilitatory effect of CCK-8. 6. The response of gall-bladder neurones to exogenously applied ACh was not modified by CCK-8. 7. Application of CCK-8, by superfusion (0.001-100 nM) or by pressure microejection (100 microM), had no effect on the membrane potential, membrane conductance, action potential, or threshold of gall-bladder neurones. 8. Immunohistochemistry was employed to determine whether the actions of CCK could be elicited by release of the peptide from nerve terminals within the ganglionated plexus of the gall-bladder. Immunoreactivity for CCK was not detected in the ganglionated plexus of the gall-bladder, but CCK immunoreactivity was plentiful in control preparations of intestinal myenteric and submucosal plexuses. 9. These results show that CCK has a presynaptic facilitatory effect on fast synaptic transmission in guinea-pig gall-bladder ganglia, and that this effect is mediated by presynaptic CCK-A receptors. Furthermore, it appears that such an effect would normally occur in response to hormonal CCK, rather than CCK that is released from nerve terminals.

Cholecystokinin modulates voltage dependent K+ currents in cultured rat hippocampal neurones

Much interest has been focussed recently on neuroactive peptides originally found in the peripheral nervous system, but now, increasingly, being shown to be present in considerable amounts in the mammalian CNS. One of these peptides, cholecystokinin (CCK), is present in large amounts in higher brain areas. Immunoreactivity to CCK has been demonstrated in the mammalian hippocampus and dentate gyrus, localised in nerve terminals, and increasingly this peptide is being suggested as having a role as a transmitter in the CNS. Generally, CCK appears to produce depolarisations of neurones: e.g. mesenteric ganglion cells, and hippocampal neurones [5], although the mechanism by which it does so remains unclear, there being reports of either a decrease in input resistance, an increase, or both.

Central neurotensin nerves modulate colo-colonic reflex activity in the guinea-pig inferior mesenteric ganglion

1. The effects of neurotensin and of stimulation of preganglionic nerves on peripheral afferent synaptic input from segments of distal colon to neurones in the inferior mesenteric ganglia of guinea-pigs were studied using intracellular recording techniques in vitro. 2. Electrical stimulation of colonic afferent nerve fibres evoked fast, nicotinic synaptic responses (fast EPSPs or action potentials) followed by a slow depolarizing response (slow EPSP). 3. Neurotensin (1 microM) increased the amplitude and duration of slow EPSPs evoked by stimulation of colonic afferents. 4. Distention of a segment of distal colon left attached to an inferior mesenteric ganglion evoked a slow depolarization. Neurotensin (1 microM) increased the amplitude and duration of distention-induced depolarizations. 5. Electrical stimulation of central preganglionic nerve fibres present in the third and fourth lumbar ventral roots increased the amplitude and duration of slow EPSPs evoked by electrical stimulation of colonic afferent nerves. This facilitatory effect was abolished after desensitization to neurotensin. 6. Slow depolarizations evoked by neurotensin and by stimulation of central preganglionic nerves converted subthreshold fast EPSPs due to mechanosensory synaptic input from an attached segment of distal colon to action potentials. This increase in firing rate of sympathetic ganglion cells led to a decrease in colonic intraluminal pressure. 7. Taken together these data support the hypothesis that neurotensin or a closely related substance contained in central preganglionic nerves facilitated release of a non-cholinergic excitatory transmitter from colonic mechanosensory nerves. The slow depolarization evoked by the non-cholinergic transmitter converted on-going subthreshold fast EPSPs to action potentials thereby increasing sympathetic output to the colon. 8. It is suggested that under normal in vivo conditions, central preganglionic fibres containing neurotensin or a closely related peptide modulate peripheral reflex activity through prevertebral ganglia in guinea-pigs.

Neurotensin facilitates release of substance P in the guinea-pig inferior mesenteric ganglion

1. Intracellular, electrophysiological techniques were combined with radio-immunological, chromatographic and pharmacological techniques to determine if nerve terminals containing substance P mediated transient depolarizing responses of principal ganglion cells induced by neurotensin. Experiments were performed in vitro on guinea-pig inferior mesenteric ganglia. 2. In 61% of principal ganglion cells tested in normal ganglia, neurotensin caused a transient membrane depolarization. In ganglia which were removed from animals which had been pre-treated with capsaicin, transient responses to neurotensin were virtually abolished. 3. In normal ganglia, neurotensin increased the amplitude and duration of noncholinergic slow EPSPs evoked by electrical stimulation of the lumbar colonic nerve. Such increases were absent in ganglia obtained from animals pre-treated with capsaicin. 4. In guinea-pigs pre-treated with capsaicin, the content of substance P-like material was significantly reduced in inferior mesenteric and coeliac ganglia, dorsal root ganglia and lumbar spinal cord, compared to control animals. The content of substance P-like material in segments of distal colon was slightly reduced. The content of vasoactive intestinal polypeptide-, cholecystokinin- and bombesin-like material in the same tissues from animals pre-treated with capsaicin was not significantly different from control animals. 5. Chromatographic analysis using HPLC (high-performance liquid chromatography) techniques revealed that the material depleted from inferior mesenteric and coeliac ganglia, dorsal root ganglia and lumbar spinal cord by capsaicin pre-treatment co-eluted with synthetic substance P. 6. Electrical stimulation of the lumbar colonic nerve released substance P-like material from isolated inferior mesenteric ganglia as determined by radioimmunoassay of samples of superfusate. Exogenous administration of neurotensin caused a significant increase in the amount of substance P-like material released during nerve stimulation. 7. Transient depolarizing responses evoked by neurotensin were markedly attenuated when ganglion cells were postsynaptically desensitized to exogenously administered substance P. 8. Taken together, these findings suggest that transient depolarizations mediated by an indirect action of neurotensin and facilitation of electrically evoked non-cholinergic slow EPSPs by neurotensin involved presynaptic release of substance P from collateral nerve terminals of primary afferent nerve fibres in the inferior mesenteric ganglion. 9. It was suggested that under normal in vivo conditions, neurotensin or a C-terminal-related peptide contained in central preganglionic nerve endings might function as an excitatory neuromodulator to enhance the release of substance P from primary afferent nerve terminals thereby facilitating non-cholinergic peripheral afferent synaptic input to prevertebral ganglion cells.

The electrophysiological effects of neurotensin on neurones of guinea-pig prevertebral sympathetic ganglia

1. The membrane effects of neurotensin on neurons of guinea-pig prevertebral ganglia were investigated by means of intracellular recording techniques in vitro. 2. Neurotensin (2-5 microM) applied by superfusion caused depolarizing responses in fifty-seven of seventy-four neurones tested in the inferior mesenteric ganglion and thirty-seven of forty-seven neurones tested in the coeliac plexus. The remaining neurones tested showed no membrane response. 3. Responses to neurotensin could be discriminated into two different types of membrane depolarizations on the basis of their different time courses and pharmacological characteristics: a steady-state type of depolarization and a transient type of depolarization. Seven of fifty-seven responsive neurones tested in the inferior mesenteric ganglion and ten of thirty-seven responsive neurones tested in the coeliac plexus responded to neurotensin with a depolarization which was maintained constant as long as neurotensin was superfused over the preparation (steady-state type). Forty-eight of fifty-seven responsive neurones tested in the inferior mesenteric ganglion and twenty of thirty-seven responsive neurones tested in the coeliac plexus responded with a transient depolarization which was followed by a repolarization in the maintained presence of neurotensin (transient type). A combination of both types of responses was observed in two neurones tested in the inferior mesenteric ganglion and in seven neurones tested in the coeliac plexus. 4. Steady-state type responses were characterized by a slowly developing membrane depolarization which reached a plateau and lasted throughout the presence of neurotensin. Amplitude and time course of this response were not altered in a solution containing hexamethonium (10 microM) and atropine (10 microM) or by a solution low in calcium (1 mM) and high in magnesium (15 mM). 5. Transient type depolarizations evoked by neurotensin were faster in reaching their maximum and were followed by a repolarization during the maintained presence of neurotensin. Responses similar in time course and amplitude were obtained in solutions containing hexamethonium (10-100 microM) and atropine (10 microM). However, transient responses were abolished in a solution low in calcium (1 mM) and high in magnesium (15 mM) and were markedly attenuated in ganglia treated with capsaicin (3 microM). 6. Both types of depolarizations were associated with increases in membrane input resistance. Both responses converted subthreshold depolarizing electrotonic potentials and subthreshold fast EPSPs to action potentials. 7. Both types of depolarizations were observed when the C-terminal hexapeptide fragment neurotensin 8-13 was used.(ABSTRACT TRUNCATED AT 400 WORDS)

Calcitonin gene-related peptide evokes distinct types of excitatory response in guinea pig coeliac ganglion cells

Pressure application of calcitonin gene-related peptide (CGRP) evoked in a population of guinea pig coeliac neurons 3 types of response: a fast, a slow and a biphasic depolarization. The responses were not appreciably affected in low Ca/high Mg or tetrodotoxin-containing Krebs solution. The fast depolarization was associated with a fall in membrane resistance; it was made larger on hyperpolarization and the estimated reversal potential was -24 mV. The fast response was reversibly blocked in a Na-free medium as well as by relatively high concentrations of d-tubocurarine (50-100 microM) but not by hexamethonium. The slow, CGRP-induced depolarization resistant to nicotinic and muscarinic antagonists, was associated with either a small increase or decrease of input resistance. Membrane hyperpolarization increased the slow response in the majority of coeliac neurons, with an estimated reversal potential of -44 mV. The biphasic depolarization displayed electrophysiological and pharmacological characteristics resembling the fast and slow responses. These results raise the possibility that CGRP acting via two distinct types of receptor elicits, respectively, a fast, Na-dependent excitatory response and a slow response, the mechanism of which remains to be established.

Neuroneuronal interconnections in the rat superior cervical ganglion; possible anatomical bases for modulatory interactions revealed by intracellular horseradish peroxidase labelling

Electrophysiologically identified neurons of rat superior cervical ganglion were intracellularly injected with horseradish peroxidase and processed for light and electron microscopic observation. At light microscope level, neurons could be classified according to their dendritic arborization pattern in the vicinity of the soma into radiate, tufted and intermediate types. Upon electrical stimulation of the internal and external carotid nerves it was observed that radiate and intermediate neurons sent their axons into one or the other of these nerve trunks, whereas a majority of tufted neurons gave no response to stimulation of either of these postganglionic nerves. Electron microscopic exploration of horseradish peroxidase-labelled neurons revealed a surprisingly high prevalence of interconnectivity between ganglionic neurons. These contacts were both dendrosomatic and dendrodendritic, and were a universal feature of the labelled neurons explored. Twenty-two of the 23 labelled cells were found to receive direct dendritic appositions on their somata, and 13 of these 23 cells were seen each to send their dendrites into contact with at least one unlabelled neuronal soma. Dendrodendritic contacts were observed for 87% of the labelled neurons, and most of the cells (80%) were seen to form triadic contacts which included two dendrites and a preganglionic nerve ending. All these figures represent minimum incidences. None of the dendrosomatic or dendrodendritic appositions observed was overtly synaptic although several morphological features indicated the possibility of somatic and or dendritic release and uptake at sites of apposition. It is suggested that the observed appositions provide anatomical substrates for modulatory interactions between the ganglionic neurons, possibly involving slow potentials or the switching of metabolic pathways.

Non-cholinergic synaptic potentials mediated by lumbar colonic nerve in the guinea-pig inferior mesenteric ganglion in vitro

Non-cholinergic slow synaptic potentials mediated by the lumbar colonic nerve have been investigated using an in vitro preparation of the guinea-pig inferior mesenteric ganglion attached to a distal colonic segment. Non-cholinergic potential responses to colonic nerve stimulation, colonic distension and chemical activation of sensory afferents were recorded intracellularly from neurons in the inferior mesenteric ganglion. Electrical stimulation of the lumbar colonic nerve produced either a slow excitatory postsynaptic potential, or a slow inhibitory postsynaptic potential followed by a slow excitatory postsynaptic potential. The extrapolated reversal potential of the slow excitatory postsynaptic potential was in the range of 0 to -20 mV and that of the slow inhibitory postsynaptic potential was -90 to 110 mV. The slow excitatory postsynaptic potential and the slow inhibitory postsynaptic potential were reversibly abolished by perfusion of the ganglion with tetrodotoxin (1 microM), or perfusion with low calcium (200 microM), high magnesium (12 mM) containing solution. Capsaicin (1 microM) evoked a reversible depolarization of inferior mesenteric ganglion cells after which desensitization occurred and the slow excitatory postsynaptic potential was abolished but the slow inhibitory postsynaptic potential was enhanced in amplitude and prolonged in duration. Bath application of substance P (2 microM) evoked a prolonged depolarization of inferior mesenteric ganglion neurons, during which the slow excitatory postsynaptic potential but not the slow inhibitory postsynaptic potential was abolished. Distensions of the colon to pressures in the range of 2-25 cm of water produced a stimulus graded non-cholinergic slow depolarization which was occasionally followed by a late slow hyperpolarization. Both types of response were abolished by tetrodotoxin.(ABSTRACT TRUNCATED AT 250 WORDS)

Neuropeptides in pelvic afferent pathways

Neurochemical and pharmacological experiments have raised the possibility that several neuropeptides including, vasoactive intestinal polypeptide (VIP), peptide histidine isoleucine amide (PHI), substance P, calcitonin gene-related peptide (CGRP), neurokinin A, cholecystokinin (CCK) and opioid peptides may be transmitters in afferent pathways to the pelvic viscera. These substances are widely distributed in: 1) nerve fibers in the pelvic organs, 2) visceral afferent neurons in the lumbosacral dorsal root ganglia and 3) at sites of afferent termination in the spinal cord. Double staining immunocytochemical techniques have shown that more than one peptide can be localized in individual visceral afferent neurons and that neuronal excitatory (VIP, substance P, CCK) and inhibitory peptides (leucine enkephalin) can coexist in the same afferent cell. Studies with the neurotoxin, capsaicin, indicate that peptidergic afferent pathways are involved in the initiation of central autonomic reflexes as well as peripheral axon reflexes which modulate smooth muscle activity, facilitate transmission in automatic ganglia and trigger local inflammatory responses.

Paracervical ganglia of the female rat: histochemistry and immunohistochemistry of neurons, SIF cells, and nerve terminals

The paracervical ganglia of the female rat were studied to elucidate the variety of neural elements in the ganglia. Light and electron microscopy, histochemistry, and immunohistochemistry were employed to reveal subtypes of neurons; small, intensely fluorescent (SIF) cells; and nerve terminals and to examine the relationships between these elements. On the basis of their histochemical markers, four subtypes of principal neurons were identified: acetylcholinesterase (ACHE)-positive, noradrenergic, neuropeptide tyrosine-immunoreactive (NPY-I), and vasoactive intestinal polypeptide-immunoreactive (VIP-I). The NPY-I neurons appeared to be the most numerous and the noradrenergic the least common type of neuron. Four subtypes of chemically coded SIF cells were revealed: catecholamine-containing, NPY-I, and those immunoreactive for calcitonin-gene-related peptide (CGRP-I) and cholecystokinin-octapeptide (CCK-8-I). The SIF cells were present as single cells among and adjacent to principal neurons and as large clusters near the edges of the ganglia or in nearby nerve trunks. Synaptic contacts on SIF cells, or between SIF-cell processes and neurons, were not observed. Seven subtypes of nerve terminals were stained: ACHE-positive, CGRP-I, CCK-8-I, VIP-I, substance P-I, enkephalin-I, and atrial natriuretic factor-I. Nerve terminals enwrapped the neurons as perineuronal plexuses in synaptic-like relationships. These results demonstrate that the paracervical ganglia of the female rat are a complex system of neural elements. For example, several classes of chemically coded neurons, SIF cells, and terminals exist in the ganglia. Each of these components contains a number of substances, some of which are putative neurotransmitters, which could influence activity in the ganglia or in the effector organs innervated by the ganglia.