Double labeling of the paravertebral sympathetic C system in the bullfrog with antisera to LHRH and NPY

In Adult Rats With Polycystic Ovarian Syndrome, Unilateral or Bilateral Vagotomy Modifies the Noradrenergic Concentration in the Ovaries and the Celiac Superior Mesenteric Ganglia in Different Ways

In rats with polycystic ovarian syndrome (PCOS) induced by estradiol valerate (EV) injection, sectioning of the vagus nerve in the juvenile stage restores ovulatory function, suggesting that the vagus nerve stimulates the onset and development of PCOS. We analyzed whether in adult rats, the role played by the vagus nerve in PCOS development is associated with the nerve’s regulation of noradrenergic activity in the celiac superior mesenteric ganglion (CSMG). Ten-day-old rats were injected with corn oil [vehicle (Vh)] or EV (2 mg). At 76 days of age, rats injected with Vh or EV were subjected to sham surgery or the sectioning of one or both vagus nerves (vagotomy). The animals were sacrificed at 80–82 days of age at vaginal estrus smear. Compared to Vh-treated animals, EV-induced PCOS rats showed a lack of ovulation, the presence of follicular cysts, and a high concentration of testosterone, without changes in noradrenaline concentrations in the CSMG or ovaries. In PCOS rats, sham surgery lowered serum testosterone and noradrenaline concentrations in the CSMG but did not restore ovulation. In animals with PCOS, vagotomy lowered testosterone concentrations to a larger degree than in sham-surgery animals. The ovaries of rats with PCOS and vagotomy showed fresh corpora lutea, indicating ovulation. In EV-treated rats with unilateral vagotomy, the concentration of noradrenaline in the CSMG was similar to that in rats with PCOS and sham surgery, which did not ovulate, while in the ovaries of PCOS rats with left or bilateral vagotomy, the noradrenaline concentration was lower than that in sham-surgery-treated animals. Our results suggest that the vagus nerve regulates PCOS development through a different mechanism than the increase in the noradrenergic activity in the CSMG; however, in ovaries, the restoration of ovulation is associated with a decrease in ovarian noradrenaline.

Noradrenaline modulates the presence of gonadotropin-releasing hormone in ovary. The importance of its interrelation on the ovarian steroidogenesis and apoptosis on dioestrus II in rat

The aim of this work was to investigate if noradrenaline (NA), added in the coeliac ganglion -superior ovarian nerve- ovary system (CG-SON-O) and in ovary incubation, modifies the release of ovarian progesterone (P4), gonadotropin-releasing hormone (GnRH) and oestradiol (E2), and the expression of 3β-HSD and 20α-HSD and proapoptotic bax and antiapoptotic bcl-2 on dioestrus II in the rat. The CG-SON-O system and the ovary were removed and placed in one cuvette containing Krebs-Ringer solution (control groups), and NA was added to the ganglion compartment in the ex vivo system and in the ovary compartment in the ovary incubation (experimental groups). P4, GnRH and E2 were measured by RIA, and gene expression was measured by RT-PCR. In the ex-vivo system, the release of ovarian P4 and GnRH and the expression of 3β-HSD and bax decreased; E2 and bcl-2 increased, and the bax/bcl-2 ratio decreased. However, in the ovary incubation, P4, GnRH, the expression of 3β-HSD and bax increased; E2, the expression of 20α-HSD and bcl-2 decreased while the bax/bcl-2 ratio increased, thus favoring apoptosis. The peripheral nervous system protected the ovary from the apoptotic mechanisms while in the ovary incubation the effect was reverted. Our results indicate that NA regulates ovarian steroidogenesis and apoptosis by modulating GnRH release from the coeliac ganglion and ovary, being NA a possible generator of a GnRH-gonadotropins axis in the ovary. This work is expected to contribute with new evidence of the clinical importance of catecholamines and GnRH in therapy and prevention of ovarian pathologies.

Autonomic control of the urogenital tract

The urogenital tract houses many of the organs that play a major role in homeostasis, in particular those that control water and salt balance, and reproductive function. This review focuses on the anatomical and functional innervation of the kidneys, urinary ducts and bladders of the urinary system, and the gonads, gonadal ducts, and intromittent organs of the reproductive tract. The literature, especially in recent years, is overwhelmingly skewed toward the situation in mammals. Nevertheless, where specific neurochemical markers have been investigated, common patterns of innervation can be found in representatives from most vertebrate classes. Not surprisingly the vasculature, epithelia and smooth muscle of all urogenital organs receives adrenergic innervation. These nerves may contain non-adrenergic non-cholinergic (NANC) neurotransmitters such as ATP and NPY. Cholinergic nerves increase motility in most urogenital organs with the exception of the kidney. The major NANC nerves found to influence urogenital organs include those containing VIP/PACAP, galanin and neuronal nitric oxide synthase. These can be found associated with both smooth muscle and epithelia. The role these nerves play, and the circumstances where they are activated are for the most part unknown.

Neuropeptide Y gene expression in the jerboa arcuate nucleus: modulation by food deprivation and relationship with hibernation

Using in situ hybridization, the mRNA levels encoding neuropeptide Y (NPY) was investigated in the arcuate nucleus (ARC) of jerboas under three different states of energy balance. (1) normally feeding animals, (2) hibernating animals and finally (3) animals food deprived for 5 days. The hibernating and food deprived jerboas exhibited a significant increase (130%; P < 0.05 and 210%; P < 0.01, respectively) of mRNA expression as compared with controls. This elevated NPY mRNA expression supports the hypothesis that NPY may be implicated in abnormal feeding behaviour associated with eating deprivation. The stimulation of NPY gene expression in hibernating jerboas may be related to food deprivation and / or cold exposure since NPY is known to be an hypothermiant factor. It is thus envisaged that NPY within neurons of the ARC plays an integrative role in the control of energy metabolism.

Neuropeptide Y gene expression in the jerboa arcuate nucleus: modulation by food deprivation and relationship with hibernation

Using in situ hybridization, the mRNA levels encoding neuropeptide Y (NPY) was investigated in the arcuate nucleus (ARC) of jerboas under three different states of energy balance. (1) normally feeding animals, (2) hibernating animals and finally (3) animals food deprived for 5 days. The hibernating and food deprived jerboas exhibited a significant increase (130%; P<0.05 and 210%; P<0.01, respectively) of mRNA expression as compared with controls. This elevated NPY mRNA expression supports the hypothesis that NPY may be implicated in abnormal feeding behaviour associated with eating deprivation. The stimulation of NPY gene expression in hibernating jerboas may be related to food deprivation and / or cold exposure since NPY is known to be a hypothermiant factor. It is thus envisaged that NPY within neurons of the ARC plays an integrative role in the control of energy metabolism.

Pathway specific expression of neuropeptides and autonomic control of the vasculature

In this article, we review the immunohistochemical evidence for the pathway-specific expression of co-existing neuropeptides in autonomic vasomotor neurons, and examine the functional significance of these expression patterns for the autonomic regulation of the vasculature. Most final motor neurons in autonomic vasomotor pathways contain neuropeptides in addition to non-peptide co-transmitters such as catecholamines, acetylcholine and nitric oxide. Neuropeptides also occur in preganglionic vasomotor neurons. The precise combinations of neuropeptides expressed by neurons in vasomotor pathways vary with species, vascular bed, and the level within the vascular bed. This applies to both vasoconstrictor and vasodilator pathways. There is a similar degree of variation in the expression of neuropeptide receptors in the vasculature. Consequently, the contributions of different peptides to autonomic vasomotor control are closely matched to the functional requirements of specific vascular beds. This arrangement allows for a high degree of precision in vascular control in normal conditions and has the potential for considerable plasticity under pathophysiological conditions.

Neuronal morphology and the synaptic organisation of sympathetic ganglia

In this article, we provide a short review of the structure and synaptic organisation of the final motor neurons in the sympathetic ganglia of mammals. Combinations of pathway tracing, multiple-labelling immunofluorescence and intracellular dye injection have shown that neurons in different functional pathways differ not only in their patterns of neuropeptide expression, but also in the size of their cell bodies and dendritic fields. Thus, vasoconstrictor neurons consistently are smaller than any other major functional class of neurons. Serial section ultrastructural analysis of dye filled neurons, together with electron microscopic and confocal microscopic analysis of immunolabelled synaptic inputs to sympathetic final motor neurons indicate that synapses are rare and randomly distributed over the surface of the neurons. The total number of synapses is simply proportional to the total surface area of the neurons. Many terminal boutons of peptide-containing preganglionic neurons do not make conventional synapses with target neurons. Furthermore, there is a spatial mismatch in the distribution of peptide-containing terminals and neurons expressing receptors for the corresponding peptides. Together, these results suggest that there are likely to be significant differences in the ways that the final sympathetic motor neurons in distinct functional pathways integrate their synaptic inputs. In at least some pathways, heterosynaptic actions of neuropeptides probably contribute to subtle modulation of ganglionic transmission.

Caffeine and carbonyl cyanide m-chlorophenylhydrazone increased evoked and spontaneous release of luteinizing hormone-releasing hormone from intact presynaptic terminals

In bullfrog sympathetic ganglia, the ryanodine-sensitive Ca2+ store and mitochondria modulate [Ca2+] within nerve terminals. We used caffeine (10 mM) and carbonyl cyanide m-chlorophenylhydrazone (10 microM) to assess how these Ca2+ stores affect release of a neuropeptide, luteinizing hormone-releasing hormone, from these nerve terminals. Release of luteinizing hormone-releasing hormone was evoked by electrical stimulation to presynaptic nerves and was monitored as a late slow excitatory postsynaptic potential in ganglionic neurons. Caffeine increased release of luteinizing hormone-releasing hormone similarly whether the release was evoked by 4 or 20 Hz stimulations (by 2.7 +/- 1.1- and 3.2 +/- 0.9-fold, mean +/- S.E.M., n = 27, respectively). Carbonyl cyanide m-chlorophenylhydrazone augmented release of luteinizing hormone-releasing hormone evoked by 4 Hz stimulation much more strongly (by 11.8 +/- 1.8-fold) than it increased the release evoked by 20 Hz stimulation (by 3.6 +/- 1.3-fold, n = 25). We detected spontaneous release of luteinizing hormone-releasing hormone as a slow hyperpolarization in response to a brief application of an antagonist to the receptors for luteinizing hormone-releasing hormone in 65% (34 of 52) and 39% (11 of 28) of the ganglionic B and C neurons, respectively. Caffeine increased spontaneous release of luteinizing hormone-releasing hormone by 2.3 +/- 0.7-fold (n = 6) whereas carbonyl cyanide m-chlorophenylhydrazone increased this release by 4.27- and 1.76-fold (n = 2). Facilitation of Ca2+ release from the intracellular store by caffeine and inhibition of mitochondrial Ca2+ removal by carbonyl cyanide m-chlorophenylhydrazone increased spontaneous as well as evoked release of luteinizing hormone-releasing hormone. Moreover, caffeine increments of evoked release did not depend on the firing frequency of the nerve whereas carbonyl cyanide m-chlorophenylhydrazone augmentations of evoked release strongly depended on the firing frequency.

Synaptic organisation of neuropeptide-containing preganglionic boutons in lumbar sympathetic ganglia of guinea pigs

Within the lumbar sympathetic ganglia of guinea pigs, the endings of different populations of neuropeptide-containing preganglionic neurons form well-defined pericellular baskets of boutons around target neurons in specific functional pathways. We have used multiple-labelling immunofluorescence, confocal microscopy, and ultrastructural immunocytochemistry to investigate synaptic organisation within pericellular baskets labelled for immunoreactivity to calcitonin gene-related peptide (CGRP), substance P (SP), or the pro-enkephalin-derived peptide, met-enkephalin-arg-gly-leu (MERGL) in relation to their target neurons. Different functional populations of neurons, identified by their neurochemical profile, showed a significant degree of spatial clustering and predicted well the distribution of specific classes of pericellular baskets. Most of the boutons in a basket were completely surrounded by Schwann cell processes and did not form synapses. The synapses that were present were made mostly onto dendrites enclosed by the Schwann cell sheath surrounding the neuron within the basket. These dendrites probably originated from neurochemically similar neighbouring neurons. Nevertheless, some of the boutons in the baskets did form synapses with the cell body or proximal dendrites of the neuron they surrounded. Occasionally, cell bodies received a relatively high number of synapses and close appositions from boutons in a pericellular basket. Synaptic convergence of two immunohistochemically distinct types of preganglionic inputs was found in baskets of SP-immunoreactive or MERGL-immunoreactive, but not CGRP-immunoreactive, boutons. Taken together, our results show that the appearance of pericellular baskets is primarily due to the packing of the target neurons. The grouping of functionally similar classes of neurons with their pathway-specific projections of peptide-containing preganglionic neurons suggests that peptides could exert their effects in relatively well-defined zones within the ganglia.

Synaptic organization of amphibian sympathetic ganglia

The synaptic organization of the amphibian sympathetic ganglia was studied, especially in the last two abdominal paravertebral ganglia of the frog. These ganglia appear to form a monosynaptic relay, not containing interneurons. They consist of two systems working in parallel: the principal neurons, by far the most numerous, and a small number of chromaffin (i.e., SIF) cells, usually arranged in clusters. Each principal neuron is innervated by a preganglionic branch forming a set of cholinergic synapses which exhibit classical ultrastructure. The only peculiarity is the presence of a subsynaptic apparatus in a variable percentage of synaptic complexes. Electrophysiological studies have demonstrated that synaptic transmission is due to ACh release and involves several postsynaptic potentials. Moreover, the principal neurons are of two types, B and C, whose preganglionic axons and their own axons have different conduction velocities. C neurons tend to be small in diameter, and B neurons are larger, but the size distribution of the two populations overlaps. More recently, it was demonstrated that these two neuronal systems have different immunocytochemical features. The C preganglionic fibers contain an LHRH-like peptide, which is responsible for late synaptic events. The B preganglionic fibers contain CGRP, whose role has not yet been established. The principal neurons all contain adrenaline, but neuropeptide Y is also present in C neurons and could be a second transmitter at peripheral junctions. SP-containing fibers also pass through the ganglia, but give rise to intraganglionic synapses only rarely, except in the celiac plexus. Galanin can coexist with neuropeptide Y in certain C neurons. Numerous principal neurons are immunoreactive for VIP. Chromaffin cells contain noradrenaline and metenkephalin, and some contain SP or LHRH; they are endocrine cells controlled by preganglionic fibers and can have a modulatory effect on principal neurons endowed with appropriate receptors. The accessibility of frog abdominal ganglia and the anatomical separation of B and C preganglionic fiber pathways provide interesting systems in which to carry out experimentation on the stability and specificity of synaptic contacts. After postganglionic axotomy, the majority of synapses disappear by disruption of synaptic contacts. There is a certain discrepancy between the recovery of synaptic transmission and the reappearance of morphologically identifiable synapses, suggesting that a certain amount of transmission is possible at contacts devoid of synaptic complexes. The selective deafferentation of B or C neurons showed that the subsynaptic apparati are mainly found at B neuron synapses. The course of reinnervation following selective deafferentation reveals the existence of different specificities at B and C synapses: C neurons are easily reinnervated by B preganglionic fibers, whereas C fibers appear fairly ineffective at reinnervating B neurons, even after a long interval. Attempts were made to reinnervate ganglionic neurons with somatic motor nerve fibers. Reinnervation was achieved only rarely, and it is concluded that the ganglionic synapses in the frog have a higher specificity and lower plasticity than in mammals.

Dendritic morphology of presumptive vasoconstrictor and pilomotor neurons and their relations with neuropeptide-containing preganglionic fibres in lumbar sympathetic ganglia of guinea-pigs

We have used intracellular dye-filling combined with multiple-labelling immunofluorescence to examine the dendritic morphology of neurons and their relations with neuropeptide-containing preganglionic terminals in the lumbar sympathetic chain of guinea-pigs. Presumptive vasoconstrictor neurons with immunoreactivity for both tyrosine hydroxylase and neuropeptide Y dendritic fields that were significantly smaller, on average, than those of presumptive pilomotor neurons containing immunoreactivity to tyrosine hydroxylase but not to neuropeptide Y. However, there was considerable variation in the sizes of the dendritic fields of the vasoconstrictor neurons. Preganglionic nerve terminals containing immunoreactivity to calcitonin gene-related peptide, but not to substance P, only surrounded cell bodies of vasoconstrictor neurons containing immunoreactivity to tyrosine hydroxylase and neuropeptide Y. In most cases, the neuropeptide-containing preganglionic terminals were not associated closely with the distal dendrites of these neurons. Few neuropeptide-containing terminals were associated closely with either the cell bodies or dendrites of the pilomotor neurons. These results show that there is a considerable range in the size of dendritic trees of sympathetic final motor neurons. Some of this variation is related to the pathways within which the neurons lie, so that presumptive pilomotor neurons generally are larger than presumptive vasoconstrictor neurons. The marked variation in size of vasoconstrictor neurons raises the possibility that there may be a size dependent recruitment of these neurons, similar to that seen in pools of spinal motor neurons. The distribution of the peptide-containing preganglionic endings suggests that they would act predominantly at the cell body and proximal dendrites of the final motor neurons.

NPY- and CGRP-like immunoreactive nerve fibers in the testis and mesorchium of the toad (Bufo arenarum)

The presence and distribution of peptidergic nerve fibers were studied in the testis and mesorchium of the toad by means of immunohistochemistry. Cryostat sections of the testis and whole-mount preparations of mesorchia were immunostained with antisera to calcitonin gene-related peptide (CGRP) and neuropeptide tyrosine (NPY). After leaving the mesorchium CGRP-immunoreactive (IR) fibers were seen predominantly running in between the seminiferous tubules. In addition, a small population of CGRP-IR nerve fibers formed thin plexuses around blood vessels. Conversely, NPY-like immunoreactivity predominated in nerve fibers that formed dense plexuses around vessels both in the mesorchium and testis. Additionally, some single NPY-IR nerve fibers could be seen in both structures studied. The functional significance of these peptidergic systems in the testis of the toad remains to be analyzed.

Segmental restriction and target specificity of bullfrog preganglionic neurons that exhibit galanin-like immunoreactivity

These experiments were designed to examine the distribution of galanin-like peptide immunoreactivity (GAL-IR) in bullfrog sympathetic preganglionic neurons and to identify the peripheral target organs affected by these neurons. Cells expressing GAL-IR were observed in the intermediolateral column of segments 7 and 8 only. Apparent GAL-IR innervation is present, but rare, in sympathetic chain ganglia. Double-labelling with retrogradely transported fast blue and galanin antiserum demonstrated that most GAL-IR neurons project via splanchnic nerves to innervate the adrenal gland, which receives a dense plexus of GAL-IR fibers surrounding chromaffin cells. The adrenal gland is also innervated by preganglionic neurons in segments 5 and 6 that do not express GAL-IR. Because nitric oxide is expressed in sympathoadrenal preganglionic neurons in mammals (Anderson, C.R., Neurosci. Lett., 139 (1992) 280), we examined whether it is expressed in bullfrog preganglionic neurons. Nicotinamide adenine dinucleotide phosphate-diaphorase positive neurons are present in bullfrog spinal grey at segments 5 through 8. These neurons were not double-labelled with fast blue retrogradely transported from the sympathetic chain, celiac ganglion, or adrenal gland; nor were they double-labelled with GAL-antiserum. Thus nitric oxide is apparently not expressed in bullfrog sympathetic preganglionic neurons.

Neuronal specificity and plasticity in the autonomic nervous system

The autonomic nervous system is divided into the sympathetic, parasympathetic and enteric subdivisions. The present review is focussed upon the highly specialized reflex organization and neurochemistry of sympathetic parasympathetic neurons. The currently available informations allow to conclude that autonomic control of each peripheral target tissue is specifically regulated under normal conditions but nevertheless able to respond to altered conditions by changes in neural activity and mediator expression.

Ganglionic and arterial release of neuropeptide Y by bullfrog sympathetic neurons

Sympathetic C neurons in lumbar paravertebral ganglia of the bullfrog have previously been shown to be vasomotor in function and to express neuropeptide Y (NPY). In the present experiments, a sensitive radioimmunoassay was used to measure the NPY content of ganglia and the descending abdominal aorta and to measure the overflow of NPY evoked by depolarizing concentrations of K+. Paravertebral ganglia 9 and 10 contain 3.1 pg NPY/micrograms protein and the aorta contains 0.18 pg NPY/micrograms protein. During 20-min depolarizations in high K+ (58 mM) Ringer, the ganglia released approximately 5% of their NPY content and the aorta released approximately 2% of its NPY content. Pretreatment of the tissues with Ringer containing 0.18 mM Ca2+, 8 mM Mg2+, and 1 mM Co2+ blocked the NPY release elicited by high K+. These findings provide further evidence that NPY is a postganglionic co-transmitter in sympathetic C neurons of the bullfrog.

Vasoconstrictor, vasodilator and pilomotor pathways in sympathetic ganglia of guinea-pigs

Triple-labelling immunofluorescence and retrograde axonal tracing with fluorescent dyes have been combined to identify and characterize the neuropeptide content of vasoconstrictor, vasodilator and pilomotor neurons in the lumbar sympathetic ganglia of guinea-pigs. Postganglionic noradrenergic pilomotor neurons lacked immunoreactivity to neuropeptide Y and comprised up to about 30% of postganglionic neurons. Most post-ganglionic noradrenergic neurons that contained neuropeptide Y immunoreactivity were likely to be vasoconstrictor neurons, although some noradrenergic neurons containing neuropeptide Y projected to pelvic viscera. Vasoconstrictor neurons comprised up to about 60% of postganglionic neurons. About 15% of postganglionic neurons were non-noradrenergic and contained immunoreactivity to vasoactive intestinal peptide, neuropeptide Y and dynorphin. They mostly innervated blood vessels supplying skeletal muscles and were likely to be vasodilator neurons. Endings of presumed preganglionic neurons containing immunoreactivity to substance P were exclusively associated with vasodilator neurons. Conversely, presumed preganglionic endings containing immunoreactivity to calcitonin gene-related peptide were exclusively associated with vasoconstrictor neurons, although not all vasoconstrictor neurons had such endings associated with them. Presumed preganglionic terminals containing immunoreactivity to enkephalin were associated with some postganglionic neurons in each functional class. These results show that preganglionic and postganglionic sympathetic neurons lying in different functional pathways can be distinguished by their neuropeptide content as well as their projections. The identification of neurochemically distinct functional pathways begins to explain how the sympathetic nervous system is organized to allow the precise control of discrete target tissues.

Preganglionic and sensory axons in developing bullfrog sympathetic ganglia express three neuropeptides during early tadpole stages

Retrograde tracing in fixed tissue with the fluorescent carbocyanine dye, DiI, was used to identify neurons that project to paravertebral sympathetic ganglia 9 and 10 in bullfrog tadpoles. Applying DiI to ganglion 9 at stage II labelled spinal preganglionic neurons and sensory neurons in dorsal root ganglia. When examined in a stage V tadpole, the segmental boundaries of the preganglionic cell column which supply the lumbar chain ganglia were identical to that in the adult. Using immunocytochemistry, luteinizing hormone releasing hormone-like immunoreactivity, calcitonin gene-related peptide-like immunoreactivity, and substance P-like immunoreactivity were localized at stage III in axons within sympathetic ganglia 9 and 10. During subsequent stages, the density of fibers containing these peptides increased and it became easier to identify synaptic boutons in contact with postganglionic neurons. These observations demonstrate that projections to the lumbar sympathetic ganglia are already formed by the earliest tadpole stages, they are consistent with the previous physiological observation of nicotinic synapses in stage III ganglia, and they suggest that neuropeptide function may also begin during early stages.

Ontogeny of immunoreactive gonadotropin-releasing hormone neuronal systems in amphibians

The ontogeny of gonadotropin-releasing hormone (GnRH) systems was investigated in 3 anuran amphibians (genus Rana) by means of immunocytochemical (ICC) techniques and antibodies generated against 3 different forms of GnRH. Antisera that recognize primarily chicken II and mammalian GnRHs revealed two anatomically and developmentally distinct GnRH systems. One system, referred to here as the forebrain-spinal cord system, contained GnRH immunoreactive (ir) fibers extending from the rostral diencephalon through the ventromedial brainstem to the spinal cord. Intensity of labeling was robust in the youngest, premetamorphic tadpoles, but decreased with age. GnRH immunolabeling in the hypothalamic-pituitary tract was not detected until late prometamorphosis and increased with age. Development of GnRHir in the hypothalamic-pituitary tract coincided with first appearance of GnRHir in the terminal nerve in R. catesbeiana, but not in R. cascadae or R. aurora, suggesting species differences. Comparisons of results obtained with antisera to different forms of GnRH support the interpretation that the forebrain-spinal cord system, hitherto undescribed in amphibians, develops first and synthesizes a non-mammalian, chicken II-like GnRH, and that the hypothalamic-pituitary system develops later and synthesizes primarily mammalian GnRH. We speculate that the forebrain-spinal cord system may represent a GnRH innervation of frog sympathetic ganglia, and that the two GnRH systems are chemically and embryonically distinct.

Neuropeptide Y mimics a non-adrenergic component of sympathetic vasoconstriction in the bullfrog

The effects of preganglionic sympathetic nerve stimulation and exogenous agents upon vascular tone were observed in hindlimb preparations of pithed adult bullfrogs. Repetitive electrical stimulation of the sympathetic C, but not the B, system elicited arterial vasoconstriction and reduced blood flow in vascular beds supplying the sartorius muscle and the skin. Close-arterial injections of epinephrine and neuropeptide Y each mimicked neurogenic vasoconstriction. After close-arterial injection of phentolamine, an alpha-adrenergic antagonist, the maximal effects of nerve stimulation were delayed in onset and reduced in magnitude, but not eliminated. Pretreatment with phentolamine blocked the vasoconstriction caused by injection of epinephrine, and produced a mild reduction in responses to neuropeptide Y. These observations demonstrate the vasomotor function of the sympathetic C system and they support the hypothesis that neuropeptide Y and epinephrine function as cotransmitters in postganglionic C neurons.