Co-localization of vasoactive intestinal polypeptide and neuropeptide Y immunoreactivities in the nerve fibers of the rat adrenal gland

3D organization of the rat adrenal medulla

Without knowledge of the spatial [three-dimensional, (3D)] organization of an organ at the tissue and cellular levels, it is impossible to form a complete picture of its structure and function. At the same time, tissue components hidden in the thickness of the organ are the most difficult to study. The rapid development of computer technologies has contributed both to the development and implementation of new methods for studying 3D microstructures of organs, and the improvement of classical ones but the most complete picture can still be obtained only by recreating 3D models from serial histological sections. This fully applies to the important, but hidden in the thickness of the organ, and difficult to study 3D organization of the adrenal medulla. Only 3D reconstruction from serial sections makes it possible to identify all the main tissue components of the adrenal medulla simultaneously and with good resolution. Of particular importance to this method is the ability to reliably differentiate and study separately the 3D organization of the two main subpopulations of medulla endocrinocytes: adrenaline-storing (A-) cells and noradrenaline-storing (NA-) cells. In this chapter, we discuss the 3D organization of the adrenal medulla based on these original serial section 3D reconstructions and correlating them with data obtained by other methods.

Adaptive remodeling of the stimulus-secretion coupling: Lessons from the 'stressed' adrenal medulla

Stress is part of our daily lives and good health in the modern world is offset by unhealthy lifestyle factors, including the deleterious consequences of stress and associated pathologies. Repeated and/or prolonged stress may disrupt the body homeostasis and thus threatens our lives. Adaptive processes that allow the organism to adapt to new environmental conditions and maintain its homeostasis are therefore crucial. The adrenal glands are major endocrine/neuroendocrine organs involved in the adaptive response of the body facing stressful situations. Upon stress episodes and in response to activation of the sympathetic nervous system, the first adrenal cells to be activated are the neuroendocrine chromaffin cells located in the medullary tissue of the adrenal gland. By releasing catecholamines (mainly epinephrine and to a lesser extent norepinephrine), adrenal chromaffin cells actively contribute to the development of adaptive mechanisms, in particular targeting the cardiovascular system and leading to appropriate adjustments of blood pressure and heart rate, as well as energy metabolism. Specifically, this chapter covers the current knowledge as to how the adrenal medullary tissue remodels in response to stress episodes, with special attention paid to chromaffin cell stimulus-secretion coupling. Adrenal stimulus-secretion coupling encompasses various elements taking place at both the molecular/cellular and tissular levels. Here, I focus on stress-driven changes in catecholamine biosynthesis, chromaffin cell excitability, synaptic neurotransmission and gap junctional communication. These signaling pathways undergo a collective and finely-tuned remodeling, contributing to appropriate catecholamine secretion and maintenance of body homeostasis in response to stress.

Stem cells, evolutionary aspects and pathology of the adrenal medulla: A new developmental paradigm

The mammalian adrenal gland is composed of two main components; the catecholaminergic neural crest-derived medulla, found in the center of the gland, and the mesoderm-derived cortex producing steroidogenic hormones. The medulla is composed of neuroendocrine chromaffin cells with oxygen-sensing properties and is dependent on tissue interactions with the overlying cortex, both during development and in adulthood. Other relevant organs include the Zuckerkandl organ containing extra-adrenal chromaffin cells, and carotid oxygen-sensing bodies containing glomus cells. Chromaffin and glomus cells reveal a number of important similarities and are derived from the multipotent nerve-associated descendants of the neural crest, or Schwann cell precursors. Abnormalities in complex developmental processes during differentiation of nerve-associated and other progenitors into chromaffin and oxygen-sensing populations may result in different subtypes of paraganglioma, neuroblastoma and pheochromocytoma. Here, we summarize recent findings explaining the development of chromaffin and oxygen-sensing cells, as well as the potential mechanisms driving neuroendocrine tumor initiation.

Gap junction-mediated intercellular communication in the adrenal medulla: an additional ingredient of stimulus-secretion coupling regulation

The traditional understanding of stimulus-secretion coupling in adrenal neuroendocrine chromaffin cells states that catecholamines are released upon trans-synaptic sympathetic stimulation mediated by acetylcholine released from the splanchnic nerve terminals. Although this statement remains largely true, it deserves to be tempered. In addition to its neurogenic control, catecholamine secretion also depends on a local gap junction-mediated communication between chromaffin cells. We review here the insights gained since the first description of gap junctions in the adrenal medullary tissue. Adrenal stimulus-secretion coupling now appears far more intricate than was previously envisioned and its deciphering represents a challenge for neurobiologists engaged in the study of the regulation of neuroendocrine secretion. This article is part of a Special Issue entitled: The Communicating junctions, composition, structure and characteristics.

Enhanced neuropeptide Y synthesis during intermittent hypoxia in the rat adrenal medulla: role of reactive oxygen species-dependent alterations in precursor peptide processing

Intermittent hypoxia (IH) associated with recurrent apneas often leads to cardiovascular abnormalities. Previously, we showed that IH treatment elevates blood pressure and increases plasma catecholamines (CAs) in rats via reactive oxygen species (ROS)-dependent enhanced synthesis and secretion from the adrenal medulla (AM). Neuropeptide Y (NPY), a sympathetic neurotransmitter that colocalizes with CA in the AM, has been implicated in blood pressure regulation during persistent stress. Here, we investigated whether IH facilitates NPY synthesis in the rat AM and assessed the role of ROS signaling. IH increased NPY-like immunoreactivity in many dopamine-β-hydroxylase-expressing chromaffin cells with a parallel increase in preproNPY mRNA and protein. IH increased the activities of proNPY-processing enzymes, which were due, in part, to elevated protein expression and increased proteolytic processing. IH increased ROS generation, and antioxidants reversed IH-induced increases in ROS, preproNPY, and its processing to bioactive NPY in the AM. IH treatment increased blood pressure and antioxidants and inhibition of NPY amidation prevented this response. These findings suggest that IH-induced elevation in NPY expression in the rat AM is mediated by ROS-dependent augmentation of preproNPY mRNA expression and proNPY-processing enzyme activities and contributes to IH-induced elevation of blood pressure.

Somatostatin interneurons delineate the inner part of the external plexiform layer in the mouse main olfactory bulb

Neuropeptides play a major role in the modulation of information processing in neural networks. Somatostatin, one of the most concentrated neuropeptides in the brain, is found in many sensory systems including the olfactory pathway. However, its cellular distribution in the mouse main olfactory bulb (MOB) is yet to be characterized. Here we show that approximately 95% of mouse bulbar somatostatin-immunoreactive (SRIF-ir) cells describe a homogeneous population of interneurons. These are restricted to the inner lamina of the external plexiform layer (iEPL) with dendritic field strictly confined to the region. iEPL SRIF-ir neurons share some morphological features of Van Gehuchten short-axon cells, and always express glutamic acid decarboxylase, calretinin, and vasoactive intestinal peptide. One-half of SRIF-ir neurons are parvalbumin-ir, revealing an atypical neurochemical profile when compared to SRIF-ir interneurons of other forebrain regions such as cortex or hippocampus. Somatostatin is also present in fibers and in a few sparse presumptive deep short-axon cells in the granule cell layer (GCL), which were previously reported in other mammalian species. The spatial distribution of somatostatin interneurons in the MOB iEPL clearly outlines the region where lateral dendrites of mitral cells interact with GCL inhibitory interneurons through dendrodendritic reciprocal synapses. Symmetrical and asymmetrical synaptic contacts occur between SRIF-ir dendrites and mitral cell dendrites. Such restricted localization of somatostatin interneurons and connectivity in the bulbar synaptic network strongly suggest that the peptide plays a functional role in the modulation of olfactory processing.

Revisiting the stimulus-secretion coupling in the adrenal medulla: role of gap junction-mediated intercellular communication

The current view of stimulation-secretion coupling in adrenal neuroendocrine chromaffin cells holds that catecholamines are released upon transsynaptic sympathetic stimulation mediated by acetylcholine released from the splanchnic nerve terminals. However, this traditional vertical scheme would merit to be revisited in the light of recent data. Although electrical discharges invading the splanchnic nerve endings are the major physiological stimulus to trigger catecholamine release in vivo, growing evidence indicates that intercellular chromaffin cell communication mediated by gap junctions represents an additional route by which biological signals (electrical activity, changes in intracellular Ca(2+) concentration,...) propagate between adjacent cells and trigger subsequent catecholamine exocytosis. Accordingly, it has been proposed that gap junctional communication efficiently helps synapses to lead chromaffin cell function and, in particular, hormone secretion. The experimental clues supporting this hypothesis are presented and discussed with regards to both interaction with the excitatory cholinergic synaptic transmission and physiopathology of the adrenal medulla.

Histogenesis and morphofunctional characteristics of chromaffin cells

This article reviews the current status of research about the histogenesis and morphofunctional characteristics of chromaffin cells in the adrenal medulla. First, this study reports the selective migration, transcription and activation factors, and the morphological events of the chromaffin cell precursors during adrenal medulla development. Subsequently, the morphofunctional characteristics of adrenergic and non-adrenergic cells are considered, with particular reference to the characteristics of chromaffin granules and their biological steps, including their formation, traffic (storage, targeting and docking), exocytosis in the strict sense and recapture. Moreover, the relationship of chromaffin cells with other tissue components of the adrenal medulla is also revised, comprising the ganglion cells, sustentacular cells, nerves and connective-vascular tissue.

Endogenous Ligands of PACAP/VIP Receptors in the Autocrine–Paracrine Regulation of the Adrenal Gland

Vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) are the main endogenous ligands of a class of G protein-coupled receptors (Rs). Three subtypes of PACAP/VIP Rs have been identified and named PAC(1)-Rs, VPAC(1)-Rs, and VPAC(2)-Rs. The PAC(1)-R almost exclusively binds PACAP, while the other two subtypes bind with about equal efficiency VIP and PACAP. VIP, PACAP, and their receptors are widely distributed in the body tissues, including the adrenal gland. VIP and PACAP are synthesized in adrenomedullary chromaffin cells, and are released in the adrenal cortex and medulla by VIPergic and PACAPergic nerve fibers. PAC(1)-Rs are almost exclusively present in the adrenal medulla, while VPAC(1)-Rs and VPAC(2)-Rs are expressed in both the adrenal cortex and medulla. Evidence indicates that VIP and PACAP, acting via VPAC(1)-Rs and VPAC(2)-Rs coupled to adenylate cyclase (AC)- and phospholipase C (PLC)-dependent cascades, stimulate aldosterone secretion from zona glomerulosa (ZG) cells. There is also proof that they can also enhance aldosterone secretion indirectly, by eliciting the release from medullary chromaffin cells of catecholamines and adrenocorticotropic hormone (ACTH), which in turn may act on the cortical cells in a paracrine manner. The involvement of VIP and PACAP in the regulation of glucocorticoid secretion from inner adrenocortical cells is doubtful and surely of minor relevance. VIP and PACAP stimulate the synthesis and release of adrenomedullary catecholamines, and all three subtypes of PACAP/VIP Rs mediate this effect, PAC(1)-Rs being coupled to AC, VPAC(1)-Rs to both AC and PLC, and VPAC(2)-Rs only to PLC. A privotal role in the catecholamine secretagogue action of VIP and PACAP is played by Ca(2+). VIP and PACAP may also modulate the growth of the adrenal cortex and medulla. The concentrations attained by VIP and PACAP in the blood rule out the possibility that they act as true circulating hormones. Conversely, their adrenal content is consistent with a local autocrine-paracrine mechanism of action.

A new focus on interoceptive properties of adrenal medulla

The adrenal medulla is an important part of the sympathoadrenal system. Chromaffin cells of the adrenal medulla respond to a broad spectrum of stressful situations by releasing epinephrine and norepinephrine. Originally, it was accepted that this response is controlled exclusively by central nervous system structures. However, it was also demonstrated that a surgically denervated adrenal medulla can respond directly by secreting epinephrine and norepinephrine during an imbalance of internal environment (hypoglycemia, asphyxia). Published data had documented the innervation of the adrenal medulla by sensory neurons of spinal dorsal root ganglia. In addition, recent data showed that ganglion cells of the adrenal medulla project ascending axons. These data suggested potential transmission of information from the adrenal medulla to the central nervous system regarding metabolic changes in the blood. This paper presents an overview of possible involvement of adrenal medullary chromaffin cells in the detection of changes in the internal environment and in the transmission of this information to the central nervous system.

Corticosterone-dependent driving influence of the suprachiasmatic nucleus on adrenal sensitivity to ACTH

We investigated the effects of ablation of the suprachiasmatic nucleus (SCN) on corticosterone (CORT) responses to synthetic ACTH given in either the morning or evening. After dexamethasone treatment, evening ACTH injections in intact rats produced a significantly larger increase in plasma CORT compared with morning ones. In rats with SCN lesions, the ACTH-induced CORT secretion was independent of time of day, providing direct evidence for a driving influence of the SCN on the diurnal rhythm of adrenal sensitivity to ACTH. In the absence of dexamethasone treatment, the SCN-lesioned rats were selected for morning-like (ML) or evening-like (EL) basal levels of CORT. Responses to ACTH were not different in ML rats compared with sham-lesioned morning controls. In contrast, EL rats compared with sham-lesioned evening controls showed an approximately 60% decrease in increment of CORT levels within the first 15 min postinjection. These results indicate that the SCN upregulates ACTH sensitivity of the adrenal cortex during the ascending phase of the daily CORT secretion and point to a critical role of glucocorticoids in determining SCN action.

Neuropeptide Y and the adrenal gland: a review

This paper sets out to review several aspects of NPY and adrenal function, starting with the localisation of NPY in the adrenal, then describing the regulation of NPY release and considering whether the adrenal is a significant source of circulating NPY. The review then describes the regulation of adrenal content of peptide, and finally covers the actions of NPY on the adrenal gland, and the receptor subtypes thought to mediate these effects. The regulation and actions of NPY are discussed with reference to both the adrenal cortex and the medulla.

Stress induces zinc finger immediate early genes in the rat adrenal gland

The secretion of steroid hormones from the adrenal cortex as well as cathecolamines from the adrenal medulla is stimulated by stress. In this study, we studied the effect of capsaicin-induced stress on the expression of the immediate-early genes (IEGs) NGFI-A, -B, -C, egr-2, -3 and Nurr1 in the rat adrenal gland using in situ hybridization. All of these IEGs except egr-2 were rapidly induced in the adrenal cortex and medulla. The temporal patterns of the IEG induction in medulla varied significantly. NGFI-A was induced in medulla within 15 min after stress, NGFI-B, egr-3 and Nurr1 were induced by 30 min, whereas NGFI-C was induced by 2 h. Surprisingly, only NGFI-B and Nurr1 were induced in the glucocorticoid secreting regions of zonae reticularis and fasciculata of the cortex, starting 15 min after the stress. All of the inducible IEGs were induced in the aldosterone secreting zona glomerulosa 15-30 min after the capsaicin injection. NGFI-A, NGFI-B and Nurr1 expression persisted for 6 h. Since the IEGs studied had major differences in their temporospatial induction pattern, they are likely to be induced by distinct stress-elicited factors and have separate target genes and roles in stress-induced glucocorticoid and catecholamine secretion.

Hypothalamic-pituitary-adrenocortical and gonadal axes and sympathoadrenal activity of adult male rats prenatally exposed to morphine

The present investigation concerns 80-90 day-old male rats born from morphine-exposed mothers (2 x 10 mg/kg per day from days 11 to 18 of gestation which showed at birth reduced size and activity of the adrenals). This prenatal treatment did not significantly disturb under resting conditions: (1) the postnatal body growth up to week 10 after birth, (2) the activity of the pituitary gonadal axis (circulating luteinizing hormone (LH) and testosterone (T), weight of the testicles and seminal vesicles), (3) the activity of the hypothalamo-pituitary-adrenal axis (HPA) (hypothalamic corticoliberin (CRF) content, plasma adrenocorticotrophic hormone (ACTH) level, adrenal weight and corticosterone (B) content, plasma B level) as well as Bmax and Kd of mineralocorticoid (type I) and glucocorticoid (type II) receptors to B in both the hippocampus and the hypothalamus. In contrast these rats showed reduced content of adrenals in noradrenaline (NA) and adrenaline (A) but increased circulating levels of A.

Circulating neuropeptide Y (NPY) and catecholamines in rat under resting and stress conditions. Arguments for extra-adrenal origin of NPY, adrenal and extra-adrenal sources of catecholamines

Neuropeptide Y (NPY) is found in cell bodies of neurons in the brain and co-localized with noradrenaline (NA) in sympathetic nerves as well as with NA and adrenaline (A) in the adrenal chromaffin cells. The purpose of the present work is to determine whether NPY and catecholamines found in the plasma of the rat under resting and stress conditions (ether inhalation, restraint) arise from the adrenals or from extra-adrenal sites. We used adrenalectomized (adx) rats and sham-adx ones. Adrenalectomy increased plasma adrenocorticotrophic hormone (ACTH) levels but decreased drastically circulating corticosterone (B) and A (-97%). However, resting NA was slightly but not significantly decreased and NPY not affected. Ether inhalation (3 min) increased plasma levels of ACTH, B, NA and A in sham-adx rats, ACTH, NA and, weakly, A in adx ones. Restraint (30 min) increased B, NA and A in sham-adx rats, NA and, poorly, A, in adx ones. In contrast, plasma levels of NPY were not significantly affected by these stress conditions. The present data suggest that NA found in rat plasma at rest and during ether or restraint stress could arise from both adrenal medulla and noradrenergic nerve endings while A arises mainly from the adrenergic chromaffin cells of the adrenals. In contrast, NPY found in the circulation, at rest and under stress conditions, is not derived from the adrenals but emanates mainly from an extra-adrenal source.

Uptake of [3H]dopamine in isolated chromaffin cells of the mouse: modulation by intra- and extra-adrenal peptides and other secretagogues

The effects of intra- and extra-adrenal peptides on [3H]dopamine uptake in adrenal chromaffin cells of the mouse were examined in vitro. Dopamine uptake was inhibited by acetylcholine, high potassium, reserpine, imipramine and desmethylimipramine as was in noradrenaline uptake. Among the intra-adrenal peptides, vasoactive intestinal peptide (VIP, 100 pmol/l) and neurotensin inhibited [3H]dopamine uptake by approximately 25%. Somatostatin, enkephalin, and neuropeptide Y did not cause any significant inhibition. An extra-adrenal peptide, bradykinin, inhibited the uptake while angiotensin II showed no significant effect. Intra-adrenal peptides which cause catecholamine secretion inhibit catecholamine uptake probably to extend its effect. Extra-adrenal peptide which causes catecholamine secretion also inhibits catecholamine uptake.

An adrenal slice preparation for the study of chromaffin cells and their cholinergic innervation

Thin slices (200-300 microm) of adrenal glands were prepared from Wistar rats. Patch-clamp recordings were made from visually identified chromaffin cells using the whole-cell and amphotericin B perforated-patch techniques. Electrophysiological properties of chromaffin cells in slices were similar to those in cultured cells. Catecholamine release from single chromaffin cells or cell clusters in slices was also measured by amperometry. Immunostaining of slices with an antineurofilament antibody revealed the presence of neuronal fibers. Acetylcholine release was stimulated either by raising external [K+] or by focally applying voltage pulses. Nicotinic excitatory postsynaptic currents (EPSCs) were detected, ranging from 20 pA to several hundreds of pA. Amplitude distributions of spontaneous EPSCs revealed clear equidistant peaks, supporting a quantal model for acetylcholine release onto chromaffin cells. The adrenal slice preparation therefore appears to be an excellent model for studying both the cholinergic innervation of chromaffin cells as well as catecholamine release from these cells.

Role of VIP, PACAP, and related peptides in the regulation of the hypothalamo-pituitary-adrenal axis

Vasoactive intestinal polypeptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) are members of a family of regulatory peptides that are widely distributed in the body and share numerous biologic actions. The two peptides display a remarkable amino acid-sequence homology, and bind to a class of G protein-coupled receptors, named PACAP/VIP receptors (PVRs), whose signaling mechanism mainly involves the activation of adenylate-cyclase and phospholipase-C cascades. A large body of evidence suggests that VIP and PACAP play a role in the control of the hypothalamo--pituitary-adrenal (HPA) axis, almost exclusively acting in a paracrine manner, since their blood concentration is very low. VIP and PACAP are contained in both nerve fibers and neurons of the hypothalamus, and VIP, but not PACAP, is also synthesized in the pituitary gland. Both peptides are expressed in the adrenal gland, and especially in medullary chromaffin cells. All the components of the HPA axis are provided with PVRs. VIP and PACAP enhance pituitary ACTH secretion, VIP by eliciting the hypothalamic release of CRH and potentiating its secretagogue action, and PACAP by directly stimulating pituitary corticotropes. Through this central mechanism, VIP and PACAP may increase mineralo- and glucocorticoid secretion of the adrenal cortex. VIP but not PACAP also exerts a weak direct secretagogue action on adrenocortical cells by activating both PVRs and probably a subtype of ACTH receptors. VIP and PACAP raise aldosterone production via a paracrine indirect mechanism involving the stimulation of medullary chromaffin cells to release catecholamines, which in turn enhance the secretion of zona glomerulosa cells via a beta-adrenoceptor-mediated mechanism. PACAP appears to be able to evoke a glucocorticoid response through the activation, at least in the rat, of the intramedullary CRH/ACTH system. The relevance of these effects of VIP and PACAP under basal conditions is questionable, although there are indications that endogenous VIP is involved in the maintenance of the normal growth and steroidogenic capacity of rat adrenal cortex. However, indirect evidence suggests that these peptides might play a relevant role under paraphysiological conditions (e.g., in the mediation of HPA axis responses to cold and inflammatory stresses) or may be somehow involved in the pathogenesis of Cushing disease or some case of hyperaldosteronism associated with secreting pheochromocytomas.

Innervation of the adrenal cortex, its physiological relevance, with primary focus on the noradrenergic transmission

The current knowledge of the catecholaminergic innervation of the mammalian adrenal cortex is summarized, and macro- and microscopic neuromorphology, including the central nervous system connections of the adrenal cortex, is briefly discussed. Morphological and functional data on the catecholaminergic (i.e., noradrenergic) innervation of the adrenal cortex are reviewed. Experimental data suggest that in addition to the regulation of adrenal blood flow, the noradrenergic innervation has a primary influence on zona glomerulosa cells possibly via beta 1 adrenergic and dopaminergic receptors (DA2 subtype via inhibiting T-type Ca2+ channels) It is concluded that the local, modulatory effect of noradrenergic nerve fibres, terminating in the close vicinity of the zona glomerulosa cells, on the systemic renin-angiotensin-aldosterone and other peptide cascade may be influenced by neuropeptides, particularly neuropeptide Y and vasoactive intestinal peptide.

Vascularization of the adrenal cortex: its possible involvement in the regulation of steroid hormone release

This review examines the morphology of the adrenal gland with particular reference to the adrenal vasculature. It examines the possibility that variability in adrenal gland responsiveness may be attributable to neural or hormonal modulation of adrenal blood flow. Changes in the rate of blood flow through the adrenal cortex would be expected to play an important role in the regulation of steroid hormone release. It would affect both the delivery of the major stimulant (ACTH) and the removal of the end product from the steroidogenic cells (the glucocorticoids). In the past, interest in this area has concentrated on the regulation of arterial blood flow, rather than the regulation of venous drainage. The current review examines the concept of vascular damming, and attempts to link the morphological features of the gland with experimental data associated with glucocorticoid release. It is postulated that regulation of venous drainage, via the vascular dam, plays an important role in the storage of the secretory product during the animals' inactive phase, and in the initial rapid rise in plasma levels of the glucocorticoids seen in response to stress or injection of ACTH.

Neuropeptide Y receptor gene regulation in mouse adrenocortical Y-1 cells

The mouse adrenocortical Y-1 cell line expresses a high level of neuropeptide Y1 receptor (NPY-Y1). Moreover the receptor density can be up-regulated by dexamethasone or down-regulated by cAMP. To determine whether such regulation occurs at the level of gene expression, Y1 receptor mRNA was measured using a reverse transcriptase-competitive PCR method. Dexamethasone treatment increased Y1 mRNA in Y-1 cells, whereas the cAMP and ACTH decreased it. We also observed that the amount of Y1 receptor RNA was unaffected by phorbol 12-myristate 13-acetate, a protein kinase C stimulator, but was abolished in a cell line expressing apolipoprotein E (apoE). The results indicated that NPY-Y1 receptor mRNA in Y-1 cells is highly regulated by several intracellular messengers. The role of apoE in such regulation is of particular interest in view of evidence that the isoform of the molecule is highly correlated to the age of onset of Alzheimer's disease. The effect observed in the Y-1 cell line which expresses apoE may implicate a possible role of this protein in the process of neuronal death that occurred in the Alzheimer's disease.

A non-cholinergic transmitter, pituitary adenylate cyclase-activating polypeptide, utilizes a novel mechanism to evoke catecholamine secretion in rat adrenal chromaffin cells

Pituitary adenylate cyclase-activating polypeptide (PACAP) is the most potent non-cholinergic neurotransmitter to stimulate catecholamine secretion from rat chromaffin cells; however, the mechanism of action is not clear. We used amperometric detection of exocytosis and indo-1 monitoring of [Ca2+]i to identify PACAP actions in cultured chromaffin cells. PACAP (100 nM) required external Ca2+ to evoke secretion. However, unlike nicotine and KCl which caused immediate and relatively brief secretion, PACAP has a latency of 6.8 +/- 0.96 s to the first secretory response and secretion continued for up to 2 min. PACAP elevation of [Ca2+]i showed similar latency and often remained above base line for several minutes following a brief exposure. ZnCl2 (100 microM) selectively inhibited PACAP-stimulated secretion and [Ca2+]i with little effect on nicotine-evoked responses. Nifedipine (10 microM) had little effect on PACAP-evoked secretion but inhibited nicotine-evoked secretion by more than 80%, while omega-conotoxin (100 nM) failed to affect either agonist. PACAP-stimulated cAMP levels required 5 s to significantly increase, consistent with the latency of exocytotic and Ca2+ responses. Forskolin (10 microM) caused responses similar to PACAP. PACAP-evoked exocytosis was blocked by the protein kinase A inhibitor adenosine 3'5'-cyclic monophosphorothioate Rp-diastereomer (Rp-cAMPS). These data showed that PACAP stimulates exocytosis by a mechanism distinctly different from cholinergic transmitters that appears to involve cAMP-mediated Ca2+ influx. Differences in receptor coupling mechanisms and pharmacology of Ca2+ entry stimulated by cholinergic and peptidergic agonists support the idea that the peptidergic system maintains catecholamine secretion under conditions where the cholinergic system desensitizes or otherwise fails.

Further investigations on the effects of neuropeptide Y on the secretion and growth of rat adrenal zona glomerulosa

NPY is a regulatory peptide, high levels of which are contained in adrenal glands of several mammals and which is co-released with catecholamines during various stressful conditions. The acute and chronic effects of NPY on adrenocortical secretion and growth were studied in the rat. NPY concentration-dependently increased aldosterone (ALDO), but not corticosterone (B) secretion of adrenal slices (maximal effective concentration was 10(-7) M). Two competitive inhibitors of NPY receptors, named PYX-1 and PYX-2, were found to dose-dependently inhibit ALDO response of adrenal preparations to 10(-7) M NPY; PYX-2 was more efficient than PYX-1, and at a concentration of 10(-5) M completely annulled the effect of 10(-7) M NPY. The acute bolus intraperitoneal (i.p.) injection of NPY (3 nmol/kg) raised plasma ALDO concentration (PAC), but not that of B (PBC); this effect of NPY was blocked by the simultaneous injection of PYX-2 (300 nmol/kg). The prolonged i.p. infusion with NPY (3 nmol/kg/h for 7 days) increased PAC (but not PBC) and induced a marked hypertrophy of the zona glomerulosa (ZG) and its parenchymal cells; dispersed ZG cells obtained from NPY-infused rats displayed a significantly enhanced basal and maximally agonist-stimulated ALDO production. The simultaneous infusion with PYX-2 (300 nmol/kg/h) completely annulled all these effects of NPY. The acute or chronic administration of PYX-2 alone did not evoke any apparent effect on the ZG secretion and growth. In light of these findings the following conclusions can be drawn: (i) NPY is able to stimulate not only the secretion, but also the growth of adrenal ZG in rats, via a receptor-mediated mechanism (since this effect is blocked by PYX-2); (ii) endogenous NPY does not play a prominent role in the physiological maintenance of secretion and growth of rat ZG (since PYX-2 alone is ineffective); (iii) NPY may play a crucial role in the fine tuning of the ZG functions in conditions requiring an increased release of mineralocorticoid hormones.

Adrenal medullary ganglion neurons project into the splanchnic nerve

Retrograde tract-tracing was used to study the projections of adrenal medullary ganglion neurons. The splanchnic nerve was cut close to the suprarenal ganglia and the retrograde tracer FluoroGold was applied at the site of nerve transection. Groups of adrenal medullary ganglion neurons exhibited FlurorGold- or Fast Blue-induced fluorescence restricted to the perikarya. Using immunohistochemistry most retrogradely labelled ganglion neurons showed immunoreactivity for neuropeptide Y. In addition, after splanchnicotomy most ganglion neurons expressed galanin and galanin message-associated peptide immunoreactivities which could not be observed in control adrenals. Taken together, the present results strongly indicate that adrenal medullary ganglion neurons project back into the splanchnic nerve perhaps representing feedback system modulating the preganglionic innervation of the adrenal gland.

A confocal approach to the morphofunctional characterization of the transient tyrosine hydroxylase system in the rat suprachiasmatic nucleus

The suprachiasmatic nucleus (SCN) of the neonatal rat is transiently innervated by tyrosine hydroxylase (TH) fibers of unknown origin and whose catecholaminergic nature is rather doubtful. In order to characterize this system morphofunctionally, immunocytochemical double labelling and confocal laser scanning microscopy analysis were employed on cryostat brain sections of 10-day-old rats. Simultaneous stainings for neuropeptide Y (NPY) and tyrosine hydroxylase (TH) immunoreactivity showed that they are not colocalized, neither in the SCN fibers nor in the intergeniculate leaflet (IGL) neurons, site of origin of the NPY projection to the SCN. Therefore, the possibility that SCN transient TH fiber system originates from the IGL could be excluded. Double labelling for TH and aromatic L-aminoacid decarboxylase (AADC) demonstrated that transient SCN TH immunoreactive (IR) fibers are AADC negative, thus supporting the hypothesis of their non-catecholaminergic nature. Moreover two new group of cells which are TH positive and AADC negative were found: one in the SCN and the other in the periventricular hypothalamic nucleus (PHN). The presence of somatostatin (SRIF) and TH in PHN neurons and SCN fibers suggested their possible colocalization, but double immunolabellings gave negative results. Simultaneous immunocytochemical staining for vasoactive intestinal polypeptide (VIP) and TH showed that TH fibers may interact with ventrolateral SCN VIP neurons. This result suggests a possible involvement of TH fibers in regulating VIP cells activity in the entrainment of circadian rhythms.

Immunocytochemical localization of the renal neutral and basic amino acid transporter in rat adrenal gland, brainstem, and spinal cord

A neutral and basic amino acid transporter (NBAT) cloned from rat kidney was recently localized to enteroendocrine cells and enteric neurons. We used an antibody directed against a synthetic peptide representing a putative extracellular domain of NBAT to determine whether this transporter was also present in other endocrine and neural tissues, including rat adrenal gland, brainstem, and spinal cord. Abundant, highly granular labeling for NBAT was observed in the cytoplasm of chromaffin and ganglion cells in the adrenal medulla. A small population of intensely labeled varicose processes was also seen in both the cortex and the medulla of the adrenal gland. More numerous, intensely labeled varicose processes were detected in brainstem and spinal cord nuclei, including the locus coeruleus, rostral ventrolateral medulla, nuclei of the solitary tract, dorsal motor nucleus of the vagus, and intermediolateral cell column of the thoracic spinal cord. Significant perikaryal labeling for NBAT was only detected in brainstem and spinal cord following intraventricular colchicine treatment, which increased the number, distribution, and intensity of NBAT-immunolabeled cells. These NBAT-immunoreactive perikarya were most numerous in the locus coeruleus, rostral ventrolateral medulla, nuclei of the solitary tract, and raphe nuclei. Ultrastructural examination of the nuclei of the solitary tract of normal rats showed that NBAT was localized predominantly to axon terminals. Within these labeled terminals, NBAT was associated with large dense core vesicles and discrete segments of plasma membrane. The observed localization of NBAT suggests that this renal specific amino acid transporter subserves a role as a vesicular or plasmalemmal transporter in monoamine-containing cells, including chromaffin cells and autonomic neurons.

Colocalization of neuropeptides and NADPH-diaphorase in the intra-adrenal neuronal cell bodies and fibres of the rat

Colocalization of vasoactive intestinal peptide, neuropeptide Y, calcitonin gene-related peptide, substance P, and tyrosine hydroxylase, respectively, with NADPH-diaphorase staining in rat adrenal gland was investigated using the double labelling technique. All vasoactive intestinal peptide- and some neuropeptide Y-immunoreactive intrinsic neuronal cell bodies seen in the gland were double stained with NADPH-diaphorase. Double labelling also occurred in some nerve fibres immunoreactive to vasoactive intestinal peptide and neuropeptide Y in the medulla and cortex. No colocalization of calcitonin gene-related peptide, substance P or tyrosine hydroxylase immunoreactivity with NADPH-diaphorase staining was observed. However, nerve fibres with varicosities immunoreactive for all the neuropeptides examined were closely associated with some of the NADPH-diaphorase-stained neuronal cell bodies. Thus, in rat adrenal gland, nitric oxide is synthesized in all ganglion cells containing vasoactive intestinal peptide and in some containing neuropeptide Y, but not in those containing calcitonin gene-related peptide, substance P or tyrosine hydroxylase.

Neuropeptides in the adrenal gland: distribution, localization of receptors, and effects on steroid hormone synthesis

In this review we defined and classified the neuropeptides (NPs) related to the adrenal gland, according to Palkovits (Frontiers Neuroendocrinol 10:1 1988). The concentration (RIA) and distribution (immunohistochemistry) of NPs, as well as the localization of the receptors (radioligand studies) were summarized. Direct effects of NPs on aldosterone and corticosterone synthesis obtained by in vivo, in situ perfusion, and in vitro experimental approaches were reviewed. Data (from different rat strains and genders) for 35 NPs are presented.

Evidence that endogenous vasoactive intestinal peptide (VIP) is involved in the regulation of rat pituitary-adrenocortical function: in vivo studies with a VIP antagonist

The effect of a subcutaneous bolus injection of 2 micrograms magnitude of Ac,Tyr1,D-Phe2-GRF(1-29) amide, a specific VIP antagonist (VIP-A), on the hypothalamo-pituitary-adrenocortical (HPA) axis were investigated in both normal and ether- or cold-stressed rats. Blood concentrations of ACTH, aldosterone (ALDO) and corticosterone (B) were measured by specific RIA 1, 2 or 4 h after VIP-A injection. VIP-A administration to normal rats strikingly lowered the plasma concentration of ALDO, without significantly affecting those of ACTH and B. Ether and cold stresses notably raised the blood levels of ACTH, ALDO and B, and these rises lasted unchanged until 4 h. VIP-A did not affect the response of HPA axis to ether stress, but provoked a marked depression of that to cold stress. In light of these findings the following conclusions can be drawn: (i) endogenous VIP does not regulate HPA-axis function under basal conditions, but it plays a pivotal role in the mechanisms involved in the activation of HPA axis induced by cold exposure; and (ii) endogenous VIP exerts a tonic stimulatory action on ALDO secretion, probably by acting directly on the adrenal zona glomerulosa.

Evidence that endogenous vasoactive intestinal peptide (VIP) plays a role in the maintenance of the growth and steroidogenic capacity of rat adrenal zona glomerulosa

The effects of a 7-day intraperitoneal infusion with VIP (0.03 nmol.kg-1.min-1) and its antagonist [4-Cl-D-Phe6,Leu17]-VIP (VIP-A; 3 nmol.kg-1.min-1) were studied in sham and bilaterally adrenalectomized rats bearing ACTH and angiotensin II (ANG-II)-responsive adrenocortical autotransplants. VIP significantly increased plasma aldosterone (ALDO) concentration (PAC) and lowered plasma renin activity (PRA) in both groups of animals, without affecting plasma levels of ACTH and corticosterone. This treatment caused a marked hypertrophy of adrenal zona glomerulosa (ZG) and its parenchymal cells (without inducing any significant change in the zona-fasciculata morphology), as well as of ZG-like cells of autotransplants. Isolated ZG cells and autotransplant quarters obtained from VIP-infused rats evidenced a notable increase in both their basal and maximally ACTH- or ANG-II-stimulated ALDO secretion. The simultaneous infusion of rats with VIP-A completely reversed all these effects of VIP. The infusion with VIP-A alone caused, in sham-operated rats, a net decrease in PAC, coupled with a rise in PRA, and a marked atrophy of ZG and ZG cells; basal and maximally stimulated ALDO secretion of dispersed ZG cells was also significantly lowered. Conversely, VIP-A did not evoke any appreciable effect in autotransplanted rats. These findings suggest that endogenous VIP is specifically involved in the maintenance of the growth and secretory capacity of rat adrenal ZG. Since regenerated adrenocortical autotransplants, which are responsive to VIP but not to VIP-A infusion, are completely deprived of chromaffin cells, the hypothesis is advanced that adrenal medulla may be the source of endogenous VIP regulating ZG function.

In vitro steroidogenic effects of neuropeptide Y (NPY1-36), Y1 and Y2 receptor agonists (Leu31-Pro34 NPY, NPY18-36) and peptide YY (PYY) on rat adrenal capsule/zona glomerulosa

The effects of neuropeptide Y (NPY1-36), of two analogs (Leu31-Pro34 NPY and NPY18-36) and of Peptide YY (PYY) on aldosterone and corticosterone secretions by freshly isolated rat adrenal capsule/zona glomerulosa preparations were investigated in vitro. NPY-related peptides (NPY1-36, Leu31-Pro34 NPY, NPY18-36), but not PYY, induced a dose-dependent release of aldosterone at concentrations ranging from 10(-8) to 10(-6) M. All the investigated peptides failed to significantly affect corticosterone secretion in concentrations ranging from 10(-10) to 10(-6) M (NPY1-36, NPY18-36), 10(-11) to 10(-6) M (Leu31-Pro34 NPY) or 10(-9) to 10(-6) M (PYY). Aldosterone secretion by this preparation of isolated adrenal capsule/zona glomerulosa was also significantly stimulated by high potassium levels (55 mEq) or by angiotensin II (AII) in concentrations ranging from 10(-8) to 10(-6) M. Moreover, NPY and Y1 or Y2 receptor agonists were positive aldosterone releasing agents as potent as AII. The present data support the existence of: (1) NPY binding sites of the Y3-like subtype, on rat adrenal capsule/zona glomerulosa. (2) A stimulatory effect of NPY on aldosterone production. So that the NPYergic innervation of the rat adrenal capsule/zona glomerulosa could be implicated in the multifactorial control of aldosterone production.

Multiple mitogenic signalling pathways in chromaffin cells: a model for cell cycle regulation in the nervous system

Adult rat chromaffin cells proliferate in vivo in response to neurally derived signals. Their proliferation in vitro is stimulated either by peptide growth factors or by activators of adenylate cyclase or protein kinase C that mimic the effects of neurotransmitters in adrenal medullary nerve endings. Differing susceptibilities to inhibitors and potentiators suggest that growth factors, cyclic AMP-dependent protein kinases and protein kinase C act via partially distinct and partially overlapping signalling pathways. Depolarization inhibits the mitogenic response to NGF, through a mechanism that apparently involves activation of voltage-gated calcium channels, while sparing the response to phorbol esters that activate PKC. Activators of adenylate cyclase also inhibit the response to NGF. The findings suggest that during normal development, neurally derived signals supersede growth factors in regulating proliferation of chromaffin cells by selectively inhibiting or co-opting portions of growth factor signalling pathways. This model might be generally applicable to the development of the nervous system.

Ganglion cells immunoreactive for catecholamine-synthesizing enzymes, neuropeptide Y and vasoactive intestinal polypeptide in the rat adrenal gland

Immunohistochemistry has been used to demonstrate tyrosine hydroxylase (TH), dopamine-beta-hydroxylase (DBH), phenylethanolamine N-methyltransferase (PNMT), neuropeptide Y (NPY) and vasoactive intestinal polypeptide (VIP) immunoreactivities, and acetylcholinesterase (AChE) activity was demonstrated in rat adrenal glands. The TH, DBH, NPY and VIP immunoreactivities and AChE activity were observed in both the large ganglion cells and the small chromaffin cells whereas PNMT immunoreactivity was found only in chromaffin cells, and not in ganglion cells. Most intra-adrenal ganglion cells showed NPY immunoreactivity and a few were VIP immunoreactive. Numerous NPY-immunoreactive ganglion cells were also immunoreactive for TH and DBH; these cells were localized as single cells or groups of several cells in the adrenal cortex and medulla. Use of serial sections, or double and triple staining techniques, showed that all TH- and DBH-immunoreactive ganglion cells also showed NPY immunoreactivity, whereas some NPY-immunoreactive ganglion cells were TH and DBH immunonegative. NPY-immunoreactive ganglion cells showed no VIP immunoreactivity. AChE activity was seen in VIP-immunopositive and VIP-immunonegative ganglion cells. These results suggest that ganglion cells containing noradrenaline and NPY, or NPY only, or VIP and acetylcholine occur in the rat adrenal gland; they may project within the adrenal gland or to other target organs. TH, DBH, NPY, and VIP were colocalized in numerous immunoreactive nerve fibres, which were distributed in the superficial adrenal cortex, while TH-, DBH- and NPY-immunoreactive ganglion cells and nerve fibres were different from VIP-immunoreactive ganglion cells and nerve fibres in the medulla. This suggests that the immunoreactive nerve fibres in the superficial cortex may be mainly extrinsic in origin and may be different from those in the medulla.

Neuropeptide Y (NPY)- and vasoactive intestinal peptide (VIP)-induced aldosterone secretion by rat capsule/glomerular zone could be mediated by catecholamines via beta 1 adrenergic receptors

The effects of two Neuropeptide Y (NPY) analogs (Y1- and Y2-type) and vasoactive intestinal peptide (VIP) on both catecholamine (adrenaline and noradrenaline) release and aldosterone production by rat adrenal capsule/glomerular zone, have been investigated in vitro. The adrenal capsule/glomerular zones, collected from adult male rats, were incubated in a medium (Krebs-Ringer bicarbonate buffer supplemented with glucose and bovine serum albumin) containing or not one of the following synthetic peptides: human Leu31,Pro34-NPY (an agonist of the Y1-type receptors), human/porcine NPY18-36 (an agonist of the Y2-type receptors) and VIP at the concentration of 10(-7) M, associated or not with 10(-7) M atenolol (a beta 1 adrenergic antagonist) or ICI-118,551 hydrochloride (a beta 2 adrenergic antagonist). The two NPY analogs as well as the VIP stimulated the release of catecholamines and of aldosterone. The beta 1 adrenergic antagonist, but not the beta 2 one, which failed to affect basal aldosterone production when given alone, prevented NPY18-36-, Leu31,Pro34-NPY- or VlP-induced aldosterone secretion. Present data support the hypothesis that adrenaline and/or noradrenaline could mediate the effects of both NPY and VIP on aldosterone secretion via beta 1 adrenergic receptors; alternatively, the steroidogenic effect of NPY or VIP could be related to direct interaction between NPY- or VIP-specific binding sites, present on the capsule/glomerular zone of the rat adrenal cortex, and beta 1 adrenergic receptors. Then the NPYergic, VIPergic and catecholaminergic innervation of the adrenal cortex, previously characterized by immunohistochemistry, may be a potent stimulatory element in the nervous control of the aldosterone secretion.

Unusual effect of prolonged vasoactive intestinal peptide (VIP) administration on the adrenal growth and corticosterone secretion in the rat

VIP is widely distributed in the body, and among others is present within the hypothalamo-pituitary-adrenal axis. The aim of this study was to investigate the effect of prolonged VIP administration on the structure and function of the rat adrenal cortex. Adult female rats were treated for 7 or 14 days with VIP (1.5 micrograms/100 g/day). This treatment did not change adrenal weight and evoked only slight changes in the stereologic parameters of adrenal cortex (volume of adrenocortical zones, average cell volume and number of cells in the gland). On the contrary, basal plasma corticosterone levels were markedly lowered (44% and 26% of control values in 7- and 14-day experiments, respectively), an effect accompanied by a significant decrease in corticosterone output by adrenal slices. After standardized ether stress, blood corticosterone concentration was similar in control and 14-day VIP-treated rats, while corticosterone secretion by adrenal quarters was higher in VIP-administered animals. Thus, prolonged VIP administration results in an unusual inhibition of corticosterone secretion in the rat, which is not coupled with a compensatory hypertrophy of the rat adrenal cortex. Such changes may depend on a modulatory action of VIP on the hypothalamo-pituitary-adrenal axis, and its possible mechanism is discussed.

Effect of adrenal demedullation on neuropeptide Y content of the capsule/glomerulosa zone of the rat adrenal gland

The capsule/glomerulosa zone of the adrenal gland is richly innervated by neuropeptide Y (NPY)-containing nerve fibers. The content and concentration of NPY in the capsule/glomerulosa zone of the female rat adrenal were determined by radioimmunoassay both in unoperated females (controls) and in operated ones, a week after in situ unilateral demedullation which excludes both the medulla and the fasciculata/reticularis zones. Demedullation induced a significant weight increase of the capsule/glomerulosa zone of the operated gland (compared to contralateral intact one) as well as of the medulla/fasciculata-reticularis zone of the contralateral intact one (compared to the corresponding part of the gland of controls). Both NPY content and concentration in the capsule/glomerulosa zone of the demedullated adrenal were significantly reduced in comparison with those in the corresponding part of the contralateral intact gland. NPY immunoreactive fibers, revealed by immunofluorescence, were present in the capsule/glomerular zone of both intact and contralateral demedullated adrenal gland. In the former, NPY fibers were regularly distributed in this part of the gland, while in the latter, some areas were devoid of immunoreactive fibers. NPY content, but not concentration, was increased in the medulla/fasciculata-reticularis zone of the contralateral intact gland. Present data support a dual origin for the NPY nerves present in the capsule/glomerulosa zone of the adrenal cortex: one part could arise from extra-adrenal site possibly the suprarenal ganglia while the other part could arise from intra adrenal ganglia cells which also contain NPY.

Neuropeptides in the human celiac/superior mesenteric ganglionic complex: an immunohistochemical study

The occurrence of vasoactive intestinal polypeptide (VIP), peptide histidine-isoleucine (PHI), calcitonin gene-related peptide (CGRP), substance P (SP), somatostatin (SOM), galanin (GAL) and enkephalins (ENK) is studied in the human celiac/superior mesenteric ganglionic complex of pre- and full-term newborns, and adult subjects by means of immunohistochemistry. The antisera used labelled nerve fibres and terminal-like networks for each examined peptide, as well as VIP- and SOM-positive postganglionic neurons. Differences in the relative amount and density of the structures immunoreactive to the various peptides were observed. Moreover, variations in the amount and type of labelled elements were appreciable for each peptide when specimens from subjects at perinatal and adult ages were compared. Double-labelling immunofluorescence for SP and each other peptide showed that co-localization with SP is very frequent for CGRP, moderate to scarce for GAL and SOM, and rare to absent for PHI, VIP and ENK. VIP-, ENK- and CGRP-immunolabeled perikarya bearing the morphological features of the small intensely fluorescent (SIF) cells occurred in the organ. The presence of a paraganglion in one of the specimens examined allowed the detection of VIP- and ENK-positive cell bodies and VIP-, ENK-, SP- and GAL-like immunoreactive varicose nerve fibres in it. The results obtained provide substantial morphological data in support of the involvement of the examined peptides in the chemical interneuronal signalling in the human celiac/superior mesenteric ganglia.

Neuroendocrine regulatory mechanisms in the choroid plexus-cerebrospinal fluid system

The CSF is often regarded as merely a mechanical support for the brain, as well as an unspecific sink for waste products from the CNS. New methodology in receptor autoradiography, immunohistochemistry and molecular biology has revealed the presence of many different neuroendocrine substances or their corresponding receptors in the main CSF-forming structure, the choroid plexus. Both older research on the sympathetic nerves and recent studies of peptide neurotransmitters in the choroid plexus support a neurogenic regulation of choroid plexus CSF production and other transport functions. Among the endocrine substances present in blood and CSF, 5-HT, ANP, vasopressin and the IGFs have high receptor concentrations in the choroid plexus and have been shown to influence choroid plexus function. Finally, the choroid plexus produces the growth factor IGF-II and a number of transport proteins, most importantly transthyretin, that might regulate hormone transport from blood to brain. These studies suggest that the choroid plexus-CSF system could constitute an important pathway for neuroendocrine signalling in the brain, although clearcut evidence for such a role is still largely lacking.

Reflex changes in post- and preganglionic sympathetic adrenal nerve activity and postganglionic sympathetic renal nerve activity upon arterial baroreceptor activation and during severe haemorrhage in the rat

The aim of the study was to compare pre- (pre-aSNA) and postganglionic adrenal sympathetic nerve activity (post-aSNA) and postganglionic renal sympathetic nerve activity (rSNA) in rats during arterial baroreceptor activation and haemorrhage. Adrenal multifibre nerve activity was recorded in chloralose-anaesthetized Wistar rats. To test for pre-aSNA or post-aSNA in adrenal nerves, a ganglionic blocker, trimethaphan (10 mg kg-1), was administered i.v. If the nerve activity in the adrenal nerve decreased or increased the nerve was considered to contain predominantly post- or preganglionic fibres, respectively. In contrast, the renal nerves exhibit an almost pure postganglionic activity. Baroreceptor activity was tested by activation of baroreceptors, with an alpha-receptor agonist, phenylephrine, which was slowly infused (0.5-2 micrograms kg-1 min-1), and to deactivate the baroreceptors the rats were bled down to 50 mmHg for 8 min. The experiments showed that all tested nerve types were baroreceptor dependent. There were no significant differences between the slopes relating nerve activity inhibition to increase in blood pressure (infusion of phenylephrine). During maximal inhibition there was a difference between the rSNA and pre-aSNA, 87 +/- 4%, n = 6, and 68 +/- 6%, n = 10 (P less than 0.01) of the control value, respectively. The maximal inhibition of post-aSNA was 80 +/- 3%, n = 7, of the control value. During haemorrhage there was a difference between the nerve populations. Pre-aSNA responded with a marked increase within 1.5 min (159 +/- 29% of control, n = 7) and was then maintained at that level until retransfusion.(ABSTRACT TRUNCATED AT 250 WORDS)

The peptide VIP is a neurotransmitter in rat adrenal medulla: physiological role in controlling catecholamine secretion

1. The perfused adrenal gland of the rat was used to establish the identity of a non-cholinergic substance involved in splanchnic nerve-mediated secretion of catecholamines. 2. The perfused adrenal medulla was rich in vasoactive intestinal polypeptide (VIP) content (28 pmol g-1 of wet tissue). VIP-immunoreactive nerve fibres were present in the adrenal medulla and the adrenal cortex. 3. Field stimulation (10 Hz for 15 min plus 1 Hz for 15 min) caused a large increase in the output of VIP in the perfusate over the spontaneous release of VIP. Secretion of catecholamines was also greatly elevated by field stimulation. Field stimulation-evoked output of VIP and catecholamines was abolished after chronic denervation of the adrenal glands. 4. Infusion of acetylcholine (ACh) did not increase the output of VIP but caused a robust secretion of catecholamines. 5. The VIP output declined when the stimulation frequency was increased (8.6 x 10(-3) fmol pulse-1 at 1 Hz and 4.0 x 10(-3) fmol pulse-1 at 10 Hz). 6. In contrast, the output of 3H-acetylcholine (3H-ACh, expressed as a fraction of tissue 3H-ACh content) increased from 7.0 x 10(-2) pulse-1 at 1 Hz to 16.3 x 10(-2) pulse-1 at 10 Hz. 7. Secretion of catecholamines evoked by low-frequency stimulation (1 Hz) was reduced by 40% in the presence of cholinergic receptor antagonists (atropine plus hexamethonium). Inclusion of a VIP receptor antagonist ([Ac-Tyr1, D-Phe2]-GRF 1-29 amide) caused about 75% inhibition. 8. The VIP receptor antagonist inhibited VIP-evoked secretion of catecholamines without affecting ACh-evoked secretion. 9. In conclusion, VIP satisfies all the essential criteria to assume the role of a neurotransmitter in the rat adrenal medulla. The contribution of VIP to the secretion of adrenal medullary hormones is more prominent at low rates of neuronal activity whereas ACh is the major contributor at higher activity.