Retrograde transport of horseradish peroxidase in the magnocellular neurosecretory system of the rat

Central and peripheral roles of vasopressin in the circadian defense of body hydration

Vasopressin is a neuropeptide synthesized by specific subsets of neurons within the eye and brain. Studies in rats and mice have shown that vasopressin produced by magnocellular neurosecretory cells (MNCs) that project to the neurohypophysis is released into the blood circulation where it serves as an antidiuretic hormone to promote water reabsorption from the kidney. Moreover vasopressin is a neurotransmitter and neuromodulator that contributes to time-keeping within the master circadian clock (i.e. the suprachiasmatic nucleus, SCN) and is also used as an output signal by SCN neurons to direct centrally mediated circadian rhythms. In this chapter, we review recent cellular and network level studies in rodents that have provided insight into how circadian rhythms in vasopressin mediate changes in water intake behavior and renal water conservation that protect the body against dehydration during sleep.

Role of Vasopressin in Rat Models of Salt-Dependent Hypertension

PURPOSE OF REVIEW

Dietary salt intake increases both plasma sodium and osmolality and therefore increases vasopressin (VP) release from the neurohypophysis. Although this effect could increase blood pressure by inducing fluid reabsorption and vasoconstriction, acute activation of arterial baroreceptors inhibits VP neurons via GABA_A receptors to oppose high blood pressure. Here we review recent findings demonstrating that this protective mechanism fails during chronic high salt intake in rats.

RECENT FINDINGS

Two recent studies showed that chronic high sodium intake causes an increase in intracellular chloride concentration in VP neurons. This effect causes GABA_A receptors to become excitatory and leads to the emergence of VP-dependent hypertension. One study showed that the increase in intracellular chloride was provoked by a decrease in the expression of the chloride exporter KCC2 mediated by local secretion of brain-derived neurotrophic factor and activation of TrkB receptors. Prolonged high dietary salt intake can cause pathological plasticity in a central homeostatic circuit that controls VP secretion and thereby contribute to peripheral vasoconstriction and hypertension.

Mechanical basis of osmosensory transduction in magnocellular neurosecretory neurones of the rat supraoptic nucleus

Rat magnocellular neurosecretory cells (MNCs) release vasopressin and oxytocin to promote antidiuresis and natriuresis at the kidney. The osmotic control of oxytocin and vasopressin release at the neurohypophysis is required for osmoregulation in these animals, and this release is mediated by a modulation of the action potential firing rate by the MNCs. Under basal (isotonic) conditions, MNCs fire action potentials at a slow rate, and this activity is inhibited by hypo-osmotic conditions and enhanced by hypertonicity. The effects of changes in osmolality on MNCs are mediated by a number of different factors, including the involvement of synaptic inputs, the release of taurine by local glial cells and regulation of ion channels expressed within the neurosecretory neurones themselves. We review recent findings that have clarified our understanding of how osmotic stimuli modulate the activity of nonselective cation channels in MNCs. Previous studies have shown that osmotically-evoked changes in membrane potential and action potential firing rate in acutely isolated MNCs are provoked mainly by a modulation of nonselective cation channels. Notably, the excitation of isolated MNCs during hypertonicity is mediated by the activation of a capsaicin-insensitive cation channel that MNCs express as an N-terminal variant of the transient receptor potential vanilloid 1 (Trpv1) channel. The activation of this channel during hypertonicity is a mechanical process associated with cell shrinking. The effectiveness of this mechanical process depends on the presence of a thin layer of actin filaments (F-actin) beneath the plasma membrane, as well as a densely interweaved network of microtubules (MTs) occupying the bulk of the cytoplasm of MNCs. Although the mechanism by which F-actin contributes to Trpv1 activation remains unknown, recent data have shown that MTs interact with Trpv1 channels via binding sites on the C-terminus, and that the force mediated through this complex is required for channel gating during osmosensory transduction. Indeed, displacement of this interaction prevents channel activation during shrinking, whereas increasing the density of these interaction sites potentiates shrinking-induced activation of Trpv1. Therefore, the gain of the osmosensory transduction process can be regulated bi-directionally through changes in the organisation of F-actin and MTs.

Cells of origin of hypothalamo-spinal projections in the rat

The retrograde transport of horseradish peroxidase (HRP) was used to determine the distribution of hypothalamic neurons which send axonal projections to the spinal cord. Labeled cells were observed in the paraventricular nucleus (PV) and in the lateral hypothalamic area following HRP injections into the lower thoracic and upper lumbar spinal cords of rats. In PV, the HRP-labeled cells were located in the parvocellular portion of the nucleus. Hypothalamo-spinal projections are predominantly uncrossed.

Vesicle degradation in dendrites of magnocellular neurones of the rat supraoptic nucleus

The magnocellular neurones of the supraoptic nucleus (SON) and paraventricular nucleus release neuropeptide from their axon terminals and also from their dendrites. In the axon terminals, swellings known as Herring bodies are responsible for the degradation of aged, unreleased large dense-cored vesicles (LDCVs) by lysosomes. Dendrites of magnocellular neurones also contain a large number of LDCVs but specialised areas of vesicle degradation have yet to be discovered. Using immunofluorescence labelling for lysosomes in vasopressin-enhanced green fluorescent protein (vasopressin-eGFP) transgenic rats, we found that lysosomes are preferentially located in the centre of the dendrites where there was a high density of vasopressin-eGFP expression. These data suggest that there are local "hot spots", but not specific compartments for vesicle degradation in magnocellular dendrites.

Effects of ciliary neurotrophic factor and leukemia inhibiting factor on oxytocin and vasopressin magnocellular neuron survival in rat and mouse hypothalamic organotypic cultures

Organotypic cultures of mouse and rat magnocellular neurons (MCNs) in the hypothalamo-neurohypophysial system (HNS) have served as important experimental models for the molecular and physiological study of this neuronal phenotype. However, it has been difficult to maintain significant numbers of the MCNs, particularly vasopressin MCNs, in these cultures for long periods. In this paper, we describe the use of the neurotrophic factors, leukemia inhibiting factor (LIF) and ciliary neurotrophic factor (CNTF) to rescue rat vasopressin (Avp)- and oxytocin (Oxt)-MCNs from axotomy-induced, programmed cell death in vitro. Quantitative data are presented for the efficacy of the LIF family of neurotrophic factors on the survival of MCNs in three nuclei, the paraventricular (PVN), supraoptic (SON), and accessory (ACC) nuclei in the mouse and rat hypothalamus.

The hypothalamic supraoptic and paraventricular nuclei of the echidna and platypus

The monotremes are an intriguing group of mammals that have major differences in their reproductive physiology and lactation from therian mammals. Monotreme young hatch from leathery skinned eggs and are nourished by milk secreted onto areolae rather than through nipples. Parturition and lactation are in part controlled through the paraventricular and supraoptic nuclei of the hypothalamus. We have used Nissl staining, enzyme histochemistry, immunohistochemistry for tyrosine hydroxylase, calbindin, oxytocin, neurophysin and non-phosphorylated neurofilament protein, and carbocyanine dye tracing techniques to examine the supraoptic and paraventricular nuclei and the course of the hypothalamo-neurohypophysial tract in two monotremes: the short-beaked echidna (Tachyglossus aculeatus) and the platypus (Ornithorhynchus anatinus). In both monotremes, the supraoptic nucleus consisted of loosely packed neurons, mainly in the retrochiasmatic position. In the echidna, the paraventricular nucleus was quite small, but had similar chemoarchitectural features to therians. In the platypus, the paraventricular nucleus was larger and appeared to be part of a stream of magnocellular neurons extending from the paraventricular nucleus to the retrochiasmatic supraoptic nucleus. Immunohistochemistry for non-phosphorylated neurofilament protein and carbocyanine dye tracing suggested that hypothalamo-neurohypophysial tract neurons in the echidna lie mainly in the retrochiasmatic supraoptic and lateral hypothalamic regions, but most neurophysin and oxytocin immunoreactive neurons in the echidna were found in the paraventricular, lateral hypothalamus and supraoptic nuclei and most oxytocinergic neurons in the platypus were distributed in a band from the paraventricular nucleus to the retrochiasmatic supraoptic nucleus. The small size of the supraoptic nucleus in the two monotremes might reflect functional aspects of monotreme lactation.

A rat brain slice preserving synaptic connections between neurons of the suprachiasmatic nucleus, organum vasculosum lamina terminalis and supraoptic nucleus

The organum vasculosum lamina terminalis (OVLT), the suprachiasmatic nucleus (SCN) and the supraoptic nucleus (SON) are three hypothalamic structures involved in the osmotic and circadian control of neurohypophysial secretion. Recent experiments have suggested that interactions between osmotic and circadian factors may be important for homeostasis. The existence of an in vitro slice preparation retaining these nuclei and their interconnections would therefore be useful for the analysis of synaptic interactions. In the rat, the OVLT, SCN and SON are found at increasingly ventral and lateral positions along the rostro-caudal axis, such that conventional 400 microm slices taken in the pure coronal or horizontal planes do not retain all three nuclei. Here we show that horizontal slices cut at angles of 38-42 degrees relative to the dorsal surface of the cortex retain large fractions of the three nuclei. Intracellular recordings revealed membrane properties consistent with those previously published for OVLT, SCN and SON neurons. Moreover, antidromic and synaptic responses evoked by electrical stimulation revealed that extensive axonal projections are retained between these nuclei. Finally, chemical and osmotic stimulation of the OVLT exerted powerful influences on the rate of spontaneous synaptic events in SON neurons. We therefore conclude that angled horizontal hypothalamic slices represent a useful preparation for the analysis of physiological interactions between the OVLT, SCN and SON.

Suckling and genital stroking induces Fos expression in hypothalamic oxytocinergic neurons of rabbit pups

Maternal behaviour in the rabbit is unusual among mammals because the doe visits her litter to nurse once every 24 h. In the present study we examined the consequences of milk intake on oxytocinergic (OT) and vasopressinergic (AVP) neurons of the supraoptic (SON) and paraventricular (PVN) nuclei of 7-day-old pups before suckling, after suckling and following anogenital stroking in un-nursed pups. To determine neuronal activation we assessed the expression of the Fos protein combined with antibodies against OT and AVP at two levels in the SON (supraoptic rostral, SOr, and supraoptic retrochiasmatic, SOrch), and three levels in the PVN (anterior, PVab; medial PVm and caudal, PVc). Daily nursing bouts lasted only 228+/-6 s throughout the observed 7 days, and pups ingested up to 34.95+/-9.0% of their body weight in milk on day 7, the day of perfusion. Suckling induced a significant increase in the number of double-labeled Fos/OT cells in both subdivisions of the SON (P<0.01) and in PVab and PVm (P<0.01). The effect in the SON was related to suckling, as it was not seen in stroked, un-nursed pups, which showed Fos increases only in PVab and PVm. All regions in the SON and PVN showed significant increases in the number of Fos/AVP neurons after suckling or stroking but, contrary to OT, the number of double-labeled Fos/AVP cells was very low. In conclusion, our results show that the oxytocinergic system of the SON and PVN is differentially activated by suckling of milk and anogenital stroking, and that the vagal-hypothalamic axis is mature in 7-day-old rabbits.

Inter- and intra-nuclear differences in galanin expression between the hypothalamic paraventricular and supraoptic nuclei in colchicine-untreated rats

Not much is known of the topography of galanin expression in the hypothalamic supraoptic (SON) and paraventricular (PVN) nuclei neurons in colchicine (an axoplasmic inhibitor)-untreated animals. Insight into the biological implication(s) of galanin expression in the PVN and SON will depend, at least in part, on the nature of its distribution in colchicine-untreated animals. In this study therefore, the topographical distribution of galaninergic profiles was examined in the PVN and SON of colchicine-untreated rats. Staining in the parvocellular PVN (PVN(p)) was predominantly as varicose thin galanin fiber processes while the magnocellular PVN (PVN(m)) contained large cell soma and fiber processes. The relative fiber density was higher in the anterior, periventricular and medial PVN(p) than in the dorsal, lateral and posterior subdivisions. Large-sized cells and thick fibers were limited to the posterior PVN(m) while the anterior and medial PVN(m) contained varicose profiles. Light- and intensely-stained galanin-positive cells as well as large- and small-diameter (varicose or non-varicose) fibers were observed in the SON. The large and thin fibers exhibit preferential ventral and dorsal distribution, respectively. Together with the complexity of specific afferent and efferent connections within the PVN and SON, these observations underscore heterogeneous galanin expression and raise potential implications for understanding the biological role of galanin by physiologically challenging stimuli.

Colocalization of estrogen beta-receptor messenger RNA with orphanin FQ, vasopressin and oxytocin in the rat hypothalamic paraventricular and supraoptic nuclei

The functional significance of the novel estrogen receptor beta in brain areas that exclusively contain the ERbeta receptor subtype such as the paraventricular (PVN) and the supraoptic (SON) nuclei of the hypothalamus is not yet fully understood. The present study attempts to characterize the peptidergic nature of the ERbeta-containing neuronal population in the PVN and the SON using the double in situ histochemistry method in the female rat. Using this method, the ERbeta mRNA coexpressions with the novel opioid neuropeptide (orphanin FQ and its receptor ORL1) mRNA in addition to the previously reported neuropeptide (arginine vasopressin-AVP, oxytocin-OXY, corticotropin releasing hormone-CRH, enkephalin-ENK) mRNAs were assessed. In the PVN, roughly half of the ERbeta expression was colocalized with the prepro-orphanin FQ mRNA, which was comparable to the colocalization observed between the ERbeta and AVP mRNAs in the same region. In addition, there was 20% overlap between the ERbeta and ORL1 receptor mRNAs, and 10% overlap between the ERbeta and OXY mRNAs in the PVN. By contrast, the coexpression between the prepro-orphanin FQ and ERbeta mRNAs was less striking in the SON. Potential interactions between the ERbeta and the well-characterized AVP-OXY neurosecretory system as well as the novel OFQ-ORL1 opioid neuropeptide system may provide new leads for the functional significance of ERbeta, specifically in stress/autonomic responses.

Distribution of fluorescence following injection of recombinant adeno-associated virus encoding green fluorescent protein into the paraventricular nucleus

We have used recombinant type 2 adeno-associated virus to deliver the gene encoding green fluorescent protein into the central nervous system of adult rats. Gene expression, determined by fluorescent microscopy, was observed not only at the site of injection but also in axons following known neuroanatomical pathways. We have demonstrated a spread of enhanced green fluorescent protein from the paraventricular nucleus of the hypothalamus into the median eminence and neurohypophysis. Cell bodies containing enhanced green fluorescent protein were also visualized in the paraventricular nucleus contralateral to the side of injection. These findings suggest that gene transfer by recombinant adeno-associated virus could be used as a tool to investigate hypothalamic-pituitary interactions and, elsewhere in the central nervous system, to trace axonal pathways.

Gene regulation in the magnocellular hypothalamo-neurohypophysial system

The hypothalamo-neurohypophysial system (HNS) is the major peptidergic neurosecretory system through which the brain controls peripheral physiology. The hormones vasopressin and oxytocin released from the HNS at the neurohypophysis serve homeostatic functions of water balance and reproduction. From a physiological viewpoint, the core question on the HNS has always been, "How is the rate of hormone production controlled?" Despite a clear description of the physiology, anatomy, cell biology, and biochemistry of the HNS gained over the last 100 years, this question has remained largely unanswered. However, recently, significant progress has been made through studies of gene identity and gene expression in the magnocellular neurons (MCNs) that constitute the HNS. These are keys to mechanisms and events that exist in the HNS. This review is an inventory of what we know about genes expressed in the HNS, about the regulation of their expression in response to physiological stimuli, and about their function. Genes relevant to the central question include receptors and signal transduction components that receive and process the message that the organism is in demand of a neurohypophysial hormone. The key players in gene regulatory events, the transcription factors, deserve special attention. They do not only control rates of hormone production at the level of the gene, but also determine the molecular make-up of the cell essential for appropriate development and physiological functioning. Finally, the HNS neurons are equipped with a machinery to produce and secrete hormones in a regulated manner. With the availability of several gene transfer approaches applicable to the HNS, it is anticipated that new insights will be obtained on how the HNS is able to respond to the physiological demands for its hormones.

Galanin immunoreactivity in mouse basal forebrain: sex differences and discrete projections of galanin-containing cells beyond the blood-brain barrier

The distribution of galanin-immunoreactive (GAL-IR) cell bodies in the basal forebrain of mice was investigated. The overall pattern of staining for GAL in the area of brain analyzed was similar to that reported in other species with noticeable variations. Distinctive groups of GAL-IR cells were present in the bed nucleus of stria terminalis (BNST), supraoptic nucleus, retrochiasmatic supraoptic nucleus (SOR), magnocellular paraventricular nucleus, arcuate nucleus (ARC) and the nucleus circularis which is one of the cell groups belonging to the accessory magnocellular system. Comparison of the number of GAL-IR cells between the sexes indicated sexual dimorphism in the BNST, SOR and the ARC. As compared with female mice, the mean number of GAL-IR cells/section in the BNST and the SOR was higher and that in the ARC was lower in the males. Unlike in rats, the preoptic area contained mostly scattered GAL-IR cell bodies. Intraperitoneal injection of the retrograde tracer fluoro-gold in male mice resulted in uptake of fluoro-gold by selective GAL-IR cell groups in the basal forebrain suggesting that only some of these cell groups may project outside the blood-brain barrier whereas others may be involved in intracerebral neural transmission.

Extrinsic modulation of spike afterpotentials in rat hypothalamoneurohypophysial neurons

1. Magnocellular neurosecretory cells (MNCs) in the rat hypothalamus adopt a phasic pattern of spike discharge under conditions demanding enhanced vasopressin release, such as during dehydration or hemorrhage. The emergence of phasic firing minimizes the occurrence of secretory fatigue from the axon terminals of MNCs, thereby maximizing vasopressin release from the neurohypophysis. 2. Intracellular and whole-cell recordings from hypothalamic slices or explants in vitro have shown that phasic firing is supported by the presence of a plateau potential which arises from the summation of spike depolarizing afterpotentials (DAPs). Modulatory actions of neurotransmitters on the amplitude of the DAP, therefore, represent possible mechanisms by which the expression of phasic firing may be regulated in vivo. 3. Here we review the basis for phasic firing in MNCs of the rat supraoptic nucleus and present recent findings concerning the direct and indirect mechanisms through which selected neurotransmitters have been found to regulate the amplitude of DAPs.

Expression of nitric oxide synthase in hypothalamic nuclei following axonal injury or colchicine treatment

Nitric oxide (NO) has recently gained much attention due to its apparently double-edged role in neuronal injury. This study was aimed at elucidating neuronal nitric oxide synthase (nNOS) expression in the brain after two types of injury, namely axonal transection and colchicine treatment. The neurosecretory hypothalamo-pituitary pathway served as a model for the reaction of central neurons to these two types of injury. Axonal transection, i.e., pituitary stalk section, resulted in a qualitative increase in NOS content in the supraoptic and paraventricular nuclei. In these nuclei, there was also an increase in the number of NOS-expressing neurons after the operation. Surprisingly, in the periventricular nucleus, a strong decrease in the number of NOS-positive magnocellular neurons was observed in the anterior part of the nucleus. Intracerebroventricular injection of colchicine resulted in an increase in the cell count in the paraventricular nucleus, while the other nuclei remained unchanged. Our results suggest that axonal injury results in an increase in nNOS expression in the major neurosecretory nuclei, while the periventricular nucleus shows the opposite reaction. Colchicine treatment has an effect similar to that of axotomy in the major neurosecretory nuclei, suggesting that an increase in NOS expression may be induced by interrupted axonal transport. In the periventricular nucleus, the decrease in the number of NOS-containing neurons suggests differences among hypothalamic NOS-containing neuron groups in response to neuronal injury.

Nitric oxide inhibits neuronal activity in the supraoptic nucleus of the rat hypothalamic slices

The presence of abundant nitric oxide synthase (NOS) in magnocellular neurons of the rat hypothalamus suggests that nitric oxide (NO) may be involved in controlling the release of oxytocin and vasopressin. To test this possibility, we examined the effect of NO-related drugs on extracellular discharges of 124 supraoptic nucleus (SON) neurons from slices of rat hypothalamus in vitro. Twenty-three (43%) of 53 neurons were inhibited by sodium nitroprusside (SNP), a spontaneous releaser of NO, at 1-3 mM. This inhibition was prevented by preincubation of the slices with 1 microM hemoglobin, an inactivator of NO (n = 14), whereas hemoglobin alone enhanced neuronal activity in seven (35%) of 20 neurons. L-Arginine (1 mM), a precursor of NO, inhibited neuronal activity in five (36%) of 14 neurons, while D-arginine (1 mM), the inactive counterpart of L-arginine, was ineffective (n = 12). N-omega-nitro-L-arginine methyl ester (L-NAME, 10 microM), an inhibitor of NOS, also enhanced neuronal activity in five (29%) of 17 neurons, while N-omega-nitro-D-arginine methyl ester (DNAME, 10 microM), the inactive enantiomer of L-NAME, was without effect (n = 11). Together, our data show that NO exerts predominantly an inhibitory effect on SON neurons and may serve as a negative feedback loop in controlling release of oxytocin and vasopressin.

Distribution of small vasopressinergic neurons in golden hamsters

In rats, small (diameter: ca. 10 micrograms) vasopressinergic neurons have been localized in the forebrain, including extrahypothalamic sites, such as the bed nucleus of the stria terminalis (BST) and the medial amygdala (MeA). In golden hamsters, no such neurons have ever been described in extrahypothalamic sites, while their presence in some hypothalamic sites, such as the paraventricular nucleus (PVN), remains controversial. The present studies were carried out to confirm the existence of small vasopressinergic neurons in the forebrain of golden hamsters, using rats as a positive control. The presence of small vasopressinergic neurons in these sites was first tested by immunocytochemistry in colchicine-treated animals. The resulting distribution was corroborated by in situ hybridization for vasopressin (AVP) mRNA. While a large number of small AVP-immunoreactive (AVP-ir) neurons was found in the BST and MeA of colchicine-treated rats, none was found in the same locations in hamsters. Interestingly, as a few large (diameter: 20-25 micrograms) AVP-ir neurons were found in the BST just medial to the small neurons in rats, the same area contained a few large and small AVP-ir neurons in hamsters. In the PVN, large and small AVP-ir neurons were found in rats and hamsters. However, three to four times more neurons were counted in rats. These data were confirmed by in situ hybridization. Indeed, in hamsters, no labelling for AVP mRNA was detected in small neurons within the BST and MeA. Furthermore, the PVN of rats contained more labelling for AVP mRNA, as compared to hamsters. These results confirm that the distribution of vasopressinergic neurons in rats cannot be generalized to other species without a detailed analysis.

Sexual differences in the magnocellular vasopressinergic system in golden hamsters

Golden hamsters, as compared to rats, lack several parvicellular vasopressinergic cell groups, particularly sexually dimorphic populations. We decided to test the possibility that magnocellular vasopressinergic neurons are subjected to sexual differences in hamsters, as they are known to display vasopressin (AVP)-dependent sexually dimorphic behaviors. The distribution of magnocellular vasopressinergic neurons was mapped and compared between males and females. Approximately 50% more vasopressin-immunoreactive (AVP-ir) neurons were counted in males within the medial and lateral divisions of the supraoptic nucleus. Furthermore, levels of AVP extracted from the hypothalamus and the pituitary gland were three to four times higher in males than in females. Finally, hypothalamic extracts from a male and a female hypothalamus were fractionated by HPLC and assayed for AVP immunoreactivity. Immunoreactivity from each extract had the same retention time as synthetic AVP standards; and the levels were twice as high in the male. These results support the existence of sexual differences in the magnocellular vasopressinergic system in golden hamsters. These differences appear to be related to previously reported sexual differences in AVP secretion from the neurohypophysis.

Organization of the hamster paraventricular hypothalamic nucleus

The hamster periventricular hypothalamic area has been the focus of functional research concerning photoperiodic time measurement. These studies have relied upon the extensive analysis of rat paraventricular nucleus because there has been a general absence of anatomical description in the hamster. The present work sought to remedy this problem by investigating the structure of the hamster paraventricular nucleus with respect to the localization of cells immunoreactive to vasopressin, oxytocin, or corticotropin-releasing factor and of cells projecting to the spinal cord or to vascular sites outside the blood-brain barrier. The hamster paraventricular nucleus includes the medial, lateral, and posterior magnocellular divisions, the main parvicellular division, as well as the periventricular area and dorsal cap, which are also parvicellular. The magnocellular divisions are characterized by many large neurons immunoreactive to oxytocin and vasopressin, which are generally absent from the parvicellular divisions. In contrast, corticotrophin-releasing hormone-immunoreactive cells are plentiful in most of the parvicellular areas. Spinally projecting cells are found in two rostral areas, one dorsally and a second, more ventral area. More caudally, the two regions merge within the posterior magnocellular division. Cells of the ventral group are frequently immunoreactive for one of the three peptides. Cells identified by peripheral injection of retrograde label are found in the rostral magnocellular divisions but not in the caudal posterior magnocellular division. Areas in which these cells also contain peptide are also described. The features of the hamster paraventricular nucleus are compared to those in the rat and apparent species differences are discussed.

Distribution of nerve growth factor-like immunoreactive neurons in the adult rat brain following colchicine treatment

Using immunohistochemical techniques, we have previously localized nerve growth factor (NGF)-like immunoreactivity in the normal adult rat central nervous system (CNS) exclusively in the hippocampal mossy fiber region and within basal forebrain cholinergic neurons--a cell population believed to be primary NGF consumers within the CNS. In the present investigation, we have attempted to identify potential producers of NGF by pretreating animals with colchicine. Such a treatment would be expected to block microtubule-assisted neuritic transport mechanisms, thus preventing the accumulation of antigens normally obtained by retrograde transport and forcing the accumulation of cell products normally exported anterogradely. Forty-eight hours after colchicine administration within their innervation territories, basal forebrain cholinergic neurons showed a marked loss of NGF-like immunoreactivity. Conversely, following colchicine treatment, many new populations of NGF-like immunoreactive cells were detected, several of which have been previously observed with in situ hybridization techniques for NGF mRNA. Many NGF-like immunoreactive populations, however, were not previously recognized by in situ hybridization methods, including cells of the striatum, reticular thalamic nucleus, paraventricular hypothalamic nucleus, supraoptic nucleus, lateral and medial septum, substantia innominata, and nucleus basalis. Furthermore, evidence is provided that colchicine-blocked, NGF-like immunoreactive neurons within the basal forebrain are not cholinergic, thus reinforcing the hypothesis that trophic support for these NGF-dependent neurons may be derived from distant and local sources. The distinctive distribution of NGF-like immunoreactive cells observed in this study strongly correlates with the reported distribution of NGF mRNA in CNS neurons, thus suggesting that our antibodies are uniquely recognizing NGF and not other related neurotrophins.

Responses of neurons in the rat anterior hypothalamic periventricular zone to osmotic stimulation and angiotensin II in vitro

Extracellular recordings were made in vitro from neurons in slices of the rat periventricular zone surrounding the anterior portion of the third ventricle. Spontaneous unit activity of these neurons was decreased in 39.5% of the neurons tested, increased in 32.9%, and biphasically changed (i.e., excitation-inhibition) in 10.5%, in response to bath application of hypertonic artificial cerebrospinal fluid (aCSF) containing elevated levels of NaCl (330 mOsm). Similar responses were observed following bath application of hypertonic aCSF prepared with additional mannitol. Angiotensin II in the perfusion medium dramatically increased spontaneous unit activity in 73.7% of neurons tested, while, unexpectedly, 5.3% were inhibited. These results suggest that some neurons in the periventricular zone are themselves osmosensitive, and may be involved in the regulation of water balance.

NMDA receptor-mediated rhythmic bursting activity in rat supraoptic nucleus neurones in vitro

1. Intracellular recordings were obtained from 112 supraoptic nucleus magnocellular neurosecretory cells (MNCs) in superfused explants of rat hypothalamus maintained in vitro. The effects of glutamate receptor agonists and antagonists were examined at 32-34 degrees C. 2. In control solutions, spontaneously active (> 5 Hz) phasic or continuous neurones showed interspike interval distributions slightly skewed toward short intervals, but did not feature pauses in the 0.4-2 s range. Current injection to alter the rate of cell discharge shifted the histograms according to the mean firing rate, but failed to induce intermittent pauses in the 0.4-2 s range. 3. Application of N-methyl-D-aspartate (NMDA) induced a mode of firing in which bimodal interspike interval distributions reflected a high incidence of clusters of short interspike intervals (0.5-1.5 s) recurring every 1-3 s. In contrast, firing evoked by application of D,L-alpha-amino-3-hydroxy-5-methyl-4-isoxalone propionic acid (AMPA) was not associated with a clustering of impulse discharge. 4. The putative endogenous excitatory amino acid transmitters L-glutamate, L-aspartate and quinolinate all mimicked the effects of NMDA. Clustered spiking responses to these agents were reversibly blocked by D,L-2-amino-5-phosphono-valerate (APV), but not by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). In contrast, the non-NMDA receptor ligands kainate and quisqualate caused CNQX-sensitive increases in firing rate, but these responses were not associated with the appearance of clustered activity. 5. When applied to cells showing negative resting potentials (< -70 mV), or to neurones hyperpolarized by current injection, responses to NMDA consisted of rhythmic (approximately 1 Hz) voltage oscillations associated with bursts of spike discharge. In the presence of TTX, NMDA could induce subthreshold voltage oscillations in the absence of action potentials. 6. Application of a voltage clamp to potentials between -75 and -55 mV during rhythmic bursting responses failed to reveal any rhythmic oscillation of the membrane current. In all cases, rhythmic bursting activity resumed upon returning to the current-clamp mode. 7. Rhythmic bursting responses to NMDA application were abolished in Mg(2+)-free solutions, suggesting that the voltage dependence of NMDA channels served to promote regenerative voltage changes throughout the cycle. The NMDA-induced current itself, however, did not appear to decrease with time, suggesting that a distinct, outward current, was necessary to initiate the repolarizing phase of each cycle.(ABSTRACT TRUNCATED AT 400 WORDS)

Distribution of corticotropin-releasing hormone immunoreactivity in golden hamster brain

The distribution of corticotropin-releasing hormone-immunoreactive (CRH-IR) neurons and fibers was observed in golden hamsters. CRH-IR neurons and fibers were observed within the hypothalamus, thalamus, amygdala, cortex, midbrain, and hindbrain. The largest numbers of CRH-IR neurons were seen within the magno- and parvocellular divisions of the paraventricular nucleus of the hypothalamus and within the septum, bed nucleus of the stria terminalis, preoptic area continuum. The highest density of immunoreactive fibers was observed in the external zone of the median eminence. In addition, many immunoreactive fibers were observed within the bed nucleus of the stria terminalis and the preoptic area. The distribution obtained in hamsters was compared with previously reported distributions from rats, and both were generally similar.

Intravenous injection of Evans Blue labels magnocellular neuroendocrine cells of the rat supraoptic nucleus in situ and after dissociation

Previous work has demonstrated that intravenous injection of neuronal tracers, e.g. horseradish peroxidase or Fast Blue, can retrogradely label neurons in brain areas that project outside the blood-brain barrier, e.g. magnocellular neuroendocrine neurons of the hypothalamus. Here we have shown that 24 h after intravenous injection of the fluorescent retrograde tracer Evans Blue, the same population of magnocellular neuroendocrine neurons is labeled in the paraventricular, supraoptic and accessory magnocellular nuclei. Parvicellular neuroendocrine cells in the paraventricular nuclei are also labeled. Most Evans Blue-labeled magnocellular neuroendocrine cells in the supraoptic nucleus could be stained immunocytochemically for neurophysins, suggesting that these neurons continue to produce their peptide hormones after taking up the fluorescent dye. Ultrastructural observation of supraoptic cells retrogradely labeled with Evans Blue shows that 95% of the neurons appeared healthy. There was no ultrastructural evidence of degeneration, hyperstimulation, or interruption of the axoplasmic flow. Labeling the neuroendocrine cells with Evans Blue did not alter the size of magnocellular cells, the animal's fluid balance or ingestive behavior. Following enzymatic/mechanical dissociation of the supraoptic nucleus from animals that had been injected with Evans Blue 24 h previously, phase-bright neurons that often contained fluorescent material were observed, thus identifying these neurons as neuroendocrine. Recording from identified neuroendocrine cells showed that these neurons generated spontaneous or current-evoked overshooting action potentials with an afterhyperpolarization and had negative resting membrane potentials. Action potential broadening, a feature of magnocellular neurons, was observed during bursts of action potentials elicited by depolarizing current injection. Taken together, this work would suggest that Evans Blue is non-toxic at the doses used and that it provides a method to identify single neuroendocrine cells in primary cell cultures made from adult hypothalamus for voltage-clamp recordings.

Functionally and anatomically distinct populations of vasopressinergic magnocellular neurons in the female golden hamster

The present study was done to determine whether the vasopressinergic neurons in the hypothalamus controlling flank marking behavior are distinct from the magnocellular neurons comprising the hypothalamo-neurohypophysial system. Animals were either hypophysectomized or injected with a suicide transport lectin, volkensin, into the neurohypophysis. Both procedures resulted in a pronounced loss of vasopressin-immunoreactive perikarya throughout the hypothalamus concomitant with increases in water intake and urine output and decreases in circulating levels of vasopressin. The loss of the hypothalamo-neurohypophysial system was most pronounced in volkensin-treated animals that presented with frank diabetes insipidus and exceedingly low levels of plasma vasopressin. However, the vasopressinergic fibers and magnocellular neurons in and around the anterior hypothalamus implicated in the control of flank marking survived the volkensin treatment. Volkensin-treated animals exhibited levels of flank marking typical of untreated animals. These data suggest the presence of anatomically and functionally distinct populations of vasopressinergic magnocellular neurons in the hypothalamus of the golden hamster.

Cerebral metabolic and vasopressin and oxytocin responses during osmotic stimulation in conscious rats

Intravenous infusion of hypertonic saline increased plasma [Na (+) ] and osmolality and induced a short-latency drinking response. These changes were associated with increased glucose utilization in the supraoptic and paraventricular nuclei and neural lobe, and decreases in the medial septum and nucleus ambiguus. The increases in glucose utilization were more accentuated in the supraoptic nuclei than in paraventricular nuclei, indicating that they are more sensitive to osmotic stimulation than the paraventricular nuclei. In association with enhanced activity in the hypothalamo-neurohypophysial system, plasma vasopressin and oxytocin concentrations increased, with a preferential increase of oxytocin over vasopressin. The hormonal contents in the neural lobe were not depleted by the osmotic stimulus despite the large increases of their concentrations in the plasma.

Regional haemodynamic effects of noradrenaline injected into the hypothalamic paraventricular nuclei of conscious, unrestrained rats: possible mechanisms of action

The cardiovascular effects of noradrenaline bilaterally injected into the hypothalamic paraventricular nuclei were investigated in conscious, unrestrained Long-Evans rats and homozygous, vasopressin-deficient Brattleboro rats, chronically instrumented with pulsed Doppler probes for measurement of regional haemodynamics. In Long-Evans rats, incremental doses of noradrenaline (0.01-10 nmol) caused dose-related increases in blood pressure and a substantial, dose-related, superior mesenteric vasoconstriction. These changes were accompanied by bradycardia and reductions in renal and hind-quarter vascular conductances. In Brattleboro rats, noradrenaline (10 nmol) had no effect on blood pressure, heart rate, or renal or superior mesenteric vascular conductances. However, there was a slight vasodilatation in the vascular bed of the hindquarters. In Long-Evans rats, intravenous pretreatment with phentolamine had no effect on the bradycardia but partly inhibited the pressor response to noradrenaline injected into the paraventricular nuclei. These effects were associated with a smaller superior mesenteric vasoconstriction and an abolition of the vasoconstriction in the hindquarters. Combined intravenous pretreatment with phentolamine and propranolol had no effect on the heart rate or pressor responses to noradrenaline injected into the paraventricular nuclei, but reduced the superior mesenteric vasoconstriction, potentiated the vasoconstriction in the hindquarters and eliminated the renal vasoconstriction. These results suggest that, in untreated Long-Evans rats, alpha-adrenoceptor-mediated constriction in the mesenteric vascular bed and beta-adrenoceptor-mediated dilatation in the vascular bed of the hindquarters have important influences on the pressor response to noradrenaline injected into the paraventricular nuclei. In the presence of the vasopressin V1-receptor antagonist, d(CH2)5[Tyr(Et)]DAVP, the pressor and heart rate responses to noradrenaline injected into the paraventricular nuclei were abolished, as were the vasoconstrictions in the renal, superior mesenteric and hindquarter vascular beds. Together these results suggest an interaction between the sympathoadrenal system and vasopressin-mediated mechanisms in the cardiovascular responses to noradrenaline injected bilaterally into the paraventricular nuclei of conscious, untreated rats.

The distribution of pituitary adenylate cyclase-activating polypeptide-like immunoreactivity is distinct from helodermin- and helospectin-like immunoreactivities in the rat brain

Pituitary adenylate cyclase-activating polypeptide (PACAP) is an amidated 38-residue polypeptide isolated from the ovine hypothalamus. Helodermin, a 35-amino acid peptide, and helospectins, peptides of 38 and 37 amino acid residues, have been isolated from lizard venom. PACAP, helodermin and helospectins share structural features and have a similar profile of pharmacological effects: they stimulate adenylate cyclase. We studied the distribution and characteristics of PACAP-like immunoreactivity in the rat brain with immunochemical and immunohistochemical methods and compared its distribution with that of helodermin- and helospectin-like immunoreactivities. With radioimmunoassay, the highest concentrations of PACAP-like immunoreactivity were found in the hypothalamus and cerebellum. PACAP-immunoreactive cell bodies were located immunohistochemically in the supraoptic nucleus, paraventricular and periventricular hypothalamic nuclei, and in the central grey. PACAP-immunoreactive fibres and terminals were detected in the medial part of the central nucleus of amygdala, in the median eminence and neurohypophysis, and in the central grey. No PACAP-immunoreactive structures were observed in areas such as the cerebral cortex, hippocampus, or cerebellum. The distribution of PACAP-like immunoreactivity differed considerably from the distribution of helodermin- and helospectin-like immunoreactivities. The results of this study suggest that PACAP is a neuropeptide with a role in the regulation of endocrine function in the hypothalamo-hypophyseal axis.

Ultrastructural localization of neuropeptide FF, a new neuropeptide in the brain and pituitary of rats

The octapeptide FLFQPQRF-NH2 or neuropeptide FF ('F8Famide'; FMRFamide-like peptide'; 'morphine-modulating peptide') has been isolated from the bovine brain. In this study, the ultrastructural localization of neuropeptide FF-like immunoreactivity was examined with pre-embedding immuno-electron microscopy in the nucleus of the solitary tract and in the posterior lobe of the pituitary gland of an adult rat. Neuropeptide FF-like immunoreactivity was detected only in neuronal structures of the medial and commissural nuclei of the solitary tract and in the neurohypophysis. In the medulla, the peroxidase-antiperoxidase reaction product was localized in large (100 nm) dense-cored vesicles and in the cytoplasm of the neuronal perikarya, dendrites and axon terminals. In the labeled terminals, small (50 nm) clear vesicles rimmed with the peroxidase-antiperoxidase reaction product were seen. Synaptic contacts of labeled perikarya and dendrites with unlabeled axon terminals were observed. Labeled axon terminals formed contacts with unlabeled dendrites and perikarya. In the posterior lobe of the pituitary gland, neuropeptide FF-like immunoreactivity was localized in nerve terminals frequently associated with blood vessels. The results suggest that neuropeptide FF-like peptides are localized exclusively in neuronal structures and that they are synthesized in cell somata and released from axon terminals. In the brain, neuropeptide FF-like peptides may act as neuromodulators involved in the regulation of autonomic functions. The localization of neuropeptide FF-like immunoreactivity in the neurohypophysis suggests endocrine regulatory functions of these peptides.

Genomic effects of cold and isolation stress on magnocellular vasopressin mRNA-containing cells in the hypothalamus of the rat

We assessed the effects of cold and isolation stress on arginine vasopressin (AVP) mRNA in the paraventricular (PVN) and supraoptic (SON) nuclei of the hypothalamus. Vasopressin mRNA levels were determined by in situ hybridization histochemistry at the cellular level. In posterior magnocellular neurons of the PVN isolation stress for 7 or 14 days increased vasopressin mRNA levels 28 and 29%, respectively, compared to group-housed controls. No significant alterations in vasopressin gene expression were observed in the SON after 7 or 14 days of isolation stress. Scattered magnocellular AVP mRNA-expressing cells of the medial parvocellular PVN showed increases of 19 and 34% after 7 and 14 days of isolation, respectively. We also studied the effect of cold or combined cold and isolation stress on vasopressin gene expression in the PVN and SON. Cold stress for 3 h daily for 4 consecutive days increased AVP mRNA levels in the posterior magnocellular PVN by 15%. Cold-isolated animals showed an increase of 21%. No significant effect on AVP mRNA levels in the SON was observed. In contrast to the posterior magnocellular PVN, cold or cold-isolation stress increased AVP mRNA in magnocellular neurons of the medial parvocellular region of the PVN by 25 and 43%, respectively, relative to control rats. These results suggest that psychological and metabolic stress may be added to the list of stressors that activate the hypothalamo-neurohypophysial system.

Efferent projections from the periventricular and medial parvicellular subnuclei of the hypothalamic paraventricular nucleus to circumventricular organs of the rat: a Phaseolus vulgaris-leucoagglutinin (PHA-L) tracing study

The heterogeneous hypothalamic paraventricular nucleus (PVN) is intimately involved in the regulation of several homeostatic functions. These regulations might, at least partly, be mediated via neuronal projections from the PVN to circumventricular organs outside the blood-brain barrier. To study the efferent projections of the medial and periventricular parvicellular subnuclei of the PVN with particular emphasis on the projections to the circumventricular organs, anterograde tracing with Phaseolus vulgaris leucoagglutinin (PHA-L) was applied. Three major efferent pathways and one minor one coursed from the medial and periventricular parvicellular subnuclei to the circumventricular organs. The major fiber projections included a rostral, a lateral, and a dorsocaudal projection tract, whereas the minor projection coursed ventrally. Fibers of the rostral projection were followed to the preoptic area and along the fornix to the subfornical organ. Single fibers originating from this projection coursed further rostrally to the organum vasculosum laminae terminalis. The lateral projection equivalent to the hypothalamo-pituitary tract passed through the lateral hypothalamic area to the median eminence, and nerve terminals were observed throughout the rostrocaudal extent of this structure. A few fibers of this bundle continued into the infundibular stalk and some terminated in the posterior pituitary lobe. Few fibers of the lateral projection descended to caudal pontine levels, where they reached descending fibers of the dorsocaudal projection. The dorsocaudal projection was essentially restricted to midline structures. Along the midline, fibers were followed from the hypothalamus either dorsally through the thalamus to the dorsal part of the third ventricle or caudally alongside the ventricular wall to the mesencephalic periaqueductal grey. The density of fibers decreased along the caudal direction of the neuraxis. The dorsal part of this projection gave rise to terminals in the deep pineal gland and pineal stalk, whereas the caudal part of this projection sent terminating fibers into the area postrema. The minor ventrally directed projection could be followed through the periventricular region to the rostral part of the median eminence. The number of terminals in the circumventricular organs varied. Within the median eminence, a high density of afferents was observed in the entire rostrocaudal extent of the external zone, whereas a low density of fibers was seen in the internal zone. A medium density of afferents was observed in the organum vasculosum laminae terminalis, whereas a relative low density of nerve terminals was observed in the posterior pituitary, the deep pineal gland, the subfornical organ, and the area postrema.(ABSTRACT TRUNCATED AT 400 WORDS)

Neurons with access to the general circulation in the central nervous system of the rat: a retrograde tracing study with fluoro-gold

Central nervous system neurons which have access to the general circulation were identified by injecting the retrograde tracer Fluoro-Gold peripherally. Fluoro-Gold does not penetrate the blood-brain barrier but is taken up by nerve terminals which project to areas supplied by fenestrated capillaries or to the periphery. Fluoro-Gold-accumulating neurons were present in the following regions or cell groups of the central nervous system: diagonal band of Broca; medial preoptic area; organum vasculosum of the lamina terminalis; subfornical organ; anterior periventricular area; paraventricular nucleus; arcuate nucleus; accessory magnocellular nuclei of the hypothalamus; motor neurons of cranial nerves III-VII, and IX-XII in the brainstem and spinal cord; autonomic ganglionic cells of cranial nerve III (Westphal-Edinger nucleus) in the mesencephalon and the intermediolateral column of the spinal cord; sensory ganglia of the cranial nerve V (mesencephalic trigeminal nucleus); and the C1-C2 and A2 adrenergic cell groups in the medulla. In addition, Fluoro-Gold-accumulating neurons were seen in the sensory ganglia of cranial and spinal nerves. Retrograde labeling with Fluoro-Gold can be combined with immunocytochemistry to identify the chemical messengers within Fluoro-Gold-labeled perikarya. Although a large number of neurons are labeled in the central nervous system with Fluoro-Gold when it is administered peripherally, this technique in combination with immunocytochemistry can be a powerful tool to identify selected neuronal systems in the central nervous system.

Central neuronal pathways containing FLFQPQRFamide-like (morphine-modulating) peptides in the rat brain

Octapeptide FLFQPQRFamide (FMRFamide-like peptide; morphine-modulating peptide), isolated from bovine brain, has some opiate analgesia modulating effects. Octapeptide FLFQPQRFamide-like immunoreactivity is found in high concentrations in the posterior pituitary, hypothalamus, pons-medulla, and dorsal spinal cord. Octapeptide FLFQPQRFamide-immunoreactive neurons of the brain are localized in the medial hypothalamus and in the nucleus of the solitary tract. High densities of octapeptide FLFQPQRFamide-immunoreactive nerve terminals are found in the median eminence, lateral parabrachial nucleus, and nucleus of the solitary tract. By using the retrograde tract tracing method combined with immunohistochemistry, we studied the central pathways interconnecting the octapeptide FLFQPQRFamide-immunoreactive structures. The octapeptide FLFQPQRFamide-immunoreactive neurons of the hypothalamus sent projections bilaterally to the nucleus of the solitary tract. The octapeptide FLFQPQRFamide-immunoreactive neurons of the nucleus of the solitary tract projected to the contralateral side of the same nucleus, to the lateral parabrachial nuclei bilaterally, and to the ipsilateral periambigual region. The results give neuroanatomical evidence of interacerebral pathways containing recently identified FLFQPQRFamide-like peptides, which may belong to a larger family of peptides. These neuroanatomical findings support the previous pharmacological studies, suggesting that the mammalian FMRFamide-like peptides may, in addition to modulatory effects on nociceptive mechanisms, participate in the regulation of blood pressure, feeding behaviour and endocrine functions.

Non-phasic discharge and osmoresponsiveness of cat magnocellular neuroendocrine cells

Abstract Repetitive bursting (phasic firing) generated endogenously by magnocellular neuroendocrine cells (MNCs) in the rat facilitates systemic release of vasopressin from axon terminals in the neurophypophysis. However, little is known of how MNCs function in other mammals. Using coronal slices of hypothalamus we studied the firing behaviour and intrinsic membrane properties of homologous neurons in the cat supraoptic nucleus where vasopressinergic MNCs outnumber oxytocinergic cells. Less than 1% of units recorded in cat supraoptic nuclei (2 of 270) spontaneously fired in a phasic mode compared to 39% in the rat (90 of 230). A discrete level of steady current across the extracellular recording micropipette promoted phasic firing in 66 of 152 non-phasic units tested in rat supraoptic nuclei, but no phasic activity in 189 units from the cat. One or several stimuli applied dorsal to supraoptic nuclei triggered a single burst (afterdischarge) in 115 of 180 MNC units from the rat, whereas none of 173 MNC units tested in the cat fired an afterdischarge. Intracellular recordings from 56 feline MNCs revealed that unlike the rat, spike depolarizing afterpotentials were absent in all cells. This explains both the absence of phasic firing and the inability to trigger regenerative bursts in the intact cat. The possible Osmoresponsiveness of cat MNCs was examined using unit recording. These units reversibly increased their firing rate as osmolality was elevated with mannitol or NaCl (10 to 100 mOsm/kg), comparable to rat units. However, in no case did hyperosmotic conditions elicit phasic firing. We conclude that cat MNCs lack a regenerative burst capability but that unit Osmoresponsiveness is comparable to rat MNC units. We hypothesize that since the kidney of the cat normally functions at high efficiency in terms of water resorption, there may be little need for the rapid and pronounced elevation in vasopressin release evoked by phasic firing.

Hypothalamic galanin-immunoreactive neurons projecting to the posterior lobe of the rat pituitary: a combined retrograde tracing and immunohistochemical study

To identify the galanin-immunoreactive neurons projecting to the posterior lobe of the pituitary in the rat hypothalamus, a retrograde tracer (complex of wheat germ agglutinin-enzymatically inactive horseradish peroxidase-colloidal gold) was injected into the posterior lobe of the pituitary. Sections of the hypothalamus were treated with a combination of silver enhancement of retrogradely transported tracer and immunohistochemistry of galanin. Of the total number of hypothalamic cells doubly labeled with retrograde tracing and galanin-immunostaining, 56-60% were found in the supraoptic nucleus, 18-23% in the retrochiasmatic nucleus, 8-10% in the lateral magnocellular portion of the paraventricular nucleus. The ratio of (number of doubly labeled cells/number of galanin-immunoreactive cells) in each of the above regions was similar to the ratio of (number of retrogradely labeled cells/number of Nissl-stained cells) in the supraoptic nucleus. Of all retrogradely labeled cells in the hypothalamus, 51-56% also contained galaninlike immunoreactivity.

IN CONCLUSION

(1) galanin-immunoreactive fibers in the posterior lobe of the pituitary originate mainly in the supraoptic nucleus, retrochiasmatic nucleus, and lateral magnocellular portion of the paraventricular nucleus, (2) most of galanin-immunoreactive cells in these regions project to the posterior lobe of the pituitary, and (3) about half the neurons constituting the hypothalamo-neurohypophyseal system contain galaninlike immunoreactivity.

Appearance of neurons with glucocorticoid receptors and neurovascular links in the embryonal rat hypothalamus grafted in the third ventricle

We have investigated the appearance of the transmitter phenotypes of hypothalamic neurons in grafts transplanted into the third ventricle of adult female rats. The grafts were the mediobasal hypothalamus and the preoptic area of 12.5-day-old rat embryos, and were examined 40-100 days later. Wheat germ agglutinin (WGA) was injected into the jugular vein of several animals for the examination of the existence of neurovascular associations. Three days after the injection, WGA appeared to have been incorporated into the neurons in the paraventricular, periventricular, and arcuate nuclei of the host animals. In the grafts, WGA was also seen incorporated in certain neurons which were found immunoreactive for tyrosine hydroxylase (TH), rat corticotropin-releasing factor (rCRF), substance P (SP), or somatostatin (SRIH). Neurons immunoreactive for neuropeptide Y (NPY) and ACTH did not seem to incorporate WGA. These findings suggest that the neurons containing TH, rCRF, SP, or SRIH link with fenestrated capillaries developed in the grafts. The immunoreactivity for glucocorticoid receptor (GR) was detected mainly in the nucleus of certain neurons and glial cells in the grafts as well as in the host hypothalamic neurons. In the grafts, strong GR immunoreactivity was detected in the cells immunoreactive for TH, NPY, and rCRF as in the host animals. It is concluded that the undifferentiated hypothalamic neurons differentiate to synthesize GR as well as definitive peptides and TH in the grafts.

Emerging concepts of structure-function dynamics in adult brain: the hypothalamo-neurohypophysial system

As the first known of the mammalian brain's neuropeptide systems, the magnocellular hypothalamo-neurohypophysial system has become a model. A great deal is known about the stimulus conditions that activate or inactivate the elements of this system, as well as about many of the actions of its peptidergic outputs upon peripheral tissues. The well-characterized actions of two of its products, oxytocin and vasopressin, on mammary, uterine, kidney and vascular tissues have facilitated the integration of newly discovered, often initially puzzling, information into the existing body of knowledge of this important regulatory system. At the same time, new conceptions of the ways in which neuropeptidergic neurons, or groups of neurons, participate in information flow have emerged from studies of the hypothalamo-neurohypophysial system. Early views of the SON and PVN nuclei, the neurons of which make up approximately one-half of this system, did not even associate these interesting, darkly staining anterior hypothalamic cells with hormone secretion from the posterior pituitary. Secretion from this part of the pituitary, it was thought, was neurally evoked from the pituicytes that made the oxytocic and antidiuretic "principles" and then released them upon command. When these views were dispelled by the demonstration that the hormones released from the posterior pituitary were synthesized in the interesting cells of the hypothalamus, the era of mammalian central neural peptidergic systems was born. Progress in developing an ever more complete structural and functional picture of this system has been closely tied to advancements in technology, specifically in the areas of radioimmunoassay, immunocytochemistry, anatomical tracing methods at the light and electron microscopic levels, and sophisticated preparations for electrophysiological investigation. Through the judicious use of these techniques, much has been learned that has led to revision of the earlier held views of this system. In a larger context, much has been learned that is likely to be of general application in understanding the fundamental processes and principles by which the mammalian nervous system works.(ABSTRACT TRUNCATED AT 400 WORDS)

Catecholaminergic afferents to the cat median eminence as determined by double-labelling methods

The localization of dopaminergic and non-dopaminergic neuronal perikarya sending axons to the median eminence was investigated in the cat by using two colour double-immunostaining techniques. Unconjugated cholera toxin and wheat germ agglutinin were used as retrograde tracers and injected respectively into the median eminence and the neuro-intermediate pituitary of the same animal. As controls, cholera toxin was also injected into the arcuate (infundibular) nucleus or third ventricle. The retrograde labelling of one of the tracers was combined with tyrosine hydroxylase immunohistochemistry as a marker for dopaminergic neurons. The retrograde labelling studies of cholera toxin alone and the double-immunostaining of cholera toxin and wheat germ agglutinin on the same sections revealed that the cat median eminence receives major afferent projections originating in midline hypothalamic nuclear groups such as the anterior periventricular nucleus, the periventricular part of the paraventricular nucleus and the arcuate nucleus; minor afferent projections arise from the anterior hypothalamic area, the rostral part of the medial preoptic area around the organum vasculosum of the lamina terminalis and to a lesser extent from the posterior hypothalamic region. We further determine that the rostral part of the parvocellular arcuate neurons constitutes the main source of dopaminergic afferents to the median eminence in the cat brain.

Tuberal supraoptic neurons--I. Morphological and electrophysiological characteristics observed with intracellular recording and biocytin filling in vitro

Previous studies of the tuberal, or retrochiasmatic, portion of the supraoptic nucleus suggest its functional similarity to the more densely populated anterior supraoptic nucleus, but the basic electrophysiological and morphological features of tuberal supraoptic nucleus neurons have not been described. Using the hypothalamo-neurohypophysial explant preparation in the rat, intracellular recordings and biocytin injections were made in tuberal supraoptic nucleus neurons and the results indicate that the two parts of the nucleus are similar. The generally oval-shaped somata of tuberal supraoptic nucleus neurons exhibited short, irregularly shaped appendages, and possessed 2-5 varicose, sparsely branching dendrites oriented in the horizontal plane. Many tuberal supraoptic nucleus neurons could be antidromically stimulated (mean latency = 6.4 ms). Filled neurons had varicose axons which were traced to the median eminence and even as far as the neural stalk, but which did not bifurcate. Both axons and dendrites were sparsely invested with short, hair-like appendages. The input resistance of the recorded neurons (mean = 177.7 M omega) was positively correlated with the membrane time constant (mean = 13.1 ms; r = 0.83). Tuberal supraoptic nucleus neurons displayed a prominent afterhyperpolarization following individual spikes or bursts of spikes, as well as firing frequency adaptation in response to positive current pulses. Although numbering far fewer than those of the anterior supraoptic nucleus, tuberal supraoptic nucleus neurons have axons which are more often intact in this preparation, and a dendritic tree which radiates within the plane of the explant. Thus these neurons should provide a useful model for further study of the electrophysiological and morphological characteristics of mammalian neurosecretory neurons.

Cells of origin of histaminergic afferents to the cat median eminence

The exact origin of histaminergic neuronal perikarya sending axons to the median eminence and posterior pituitary was investigated in the cat by using two colour double-immunostaining methods: unconjugated wheat germ agglutinin or cholera toxin as retrograde tracers combined with histamine (HA) immunohistochemistry. HA immunohistochemistry revealed the presence of HA-immunoreactive terminal-like fibers both in the external layer of the median eminence and neural lobe of the pituitary. The double-labeling studies further demonstrated the histaminergic innervation of the median eminence and neural lobe by a few HA-immunoreactive neuronal perikarya located in the posterior hypothalamus.

Paraventricular nucleus injections of noradrenaline: cardiovascular effects in conscious Long-Evans and Brattleboro rats

The cardiovascular effects of noradrenaline injected into the hypothalamic paraventricular nucleus (PVN) were investigated in conscious Long-Evans (control) rats and homozygous vasopressin (AVP)-deficient Brattleboro rats. Unilateral microinjection of noradrenaline (3-30 nmol) into the PVN produced dose-dependent increases in systolic and diastolic blood pressure of Long-Evans rats, and a concomitant decrease in heart rate. Only the highest dose of noradrenaline tested (30 nmol) caused a significant pressor response in Brattleboro rats (9 +/- 4/9 +/- 4 mm Hg, systolic/diastolic, n = 7) which was significantly smaller than the response produced by the same dose of noradrenaline in Long-Evans rats (32 +/- 8/27 +/- 6 mm Hg, n = 7). Intravenous pretreatment of Long-Evans rats with the V1-receptor antagonist, d(CH2)5Tyr[Et]DAVP, almost completely abolished the pressor effect of noradrenaline (10 nmol) without significantly attenuating the bradycardia. The alpha 2-adrenoceptor antagonist, idazoxan (4 nmol), injected into the PVN abolished the pressor response produced by noradrenaline (10 nmol) in Long-Evans rats but had no significant effect on the bradycardia. Pretreatment with the alpha 1-adrenoceptor antagonist, prazosin (0.7 nmol), significantly attenuated both the pressor and bradycardic effects of noradrenaline in Long-Evans rats. These results suggest that the pressor response produced by microinjection of noradrenaline into the hypothalamic PVN of conscious Long-Evans rats is mediated largely through stimulation of alpha 2-adrenoceptors and is dependent, in part, on release of AVP into the circulation. A component of the bradycardia seen with this intervention may be mediated through stimulation of alpha 1-adrenoceptors in the PVN.

Inhibitory effect of norepinephrine on the single-unit activity of caudally projecting paraventricular neurons

The role of norepinephrine (NE) in controlling the single-unit activity of paraventricular (PVN) neurons projecting to or passing through the caudal ventrolateral medulla (CVLM) was investigated in adult male rats anesthetized with urethane. Of 72 PVN neurons studied, 19 were antidromically activated by CVLM stimulation (Group I) and 48 were antidromically activated by posterior pituitary (PP) stimulation (Group II). The remaining 5 neurons were antidromically driven by both CVLM and PP stimulation (Group III). In 14 of the 19 Group I neurons and in all the 5 Group III neurons, iontophoretically applied NE was demonstrated to be inhibitory to the single-unit activity. No excitatory effect of NE was observed. In contrast, both excitatory and inhibitory actions of NE were observed in the Group II neurons. Of 37 Group II neurons tested, 28 were excited and 7 were inhibited by NE. The inhibitory effect of NE in Group I and Group III neurons was selectively blocked by the alpha antagonist, phentolamine, that was coiontophoresed with NE, but not by the beta antagonist, timolol (n = 9). The unit activity of Group I neurons that were inhibited by NE was not altered by an increase in arterial blood pressure (n = 3), whereas the unit activity of one NE-insensitive Group I neuron was decreased by an increase in blood pressure. Taken together, the results suggest that NE plays an alpha-adrenoreceptor-mediated inhibitory role in controlling the single-unit activity of caudally projecting PVN neurons. These neurons include a subpopulation of PVN neurons that project caudally as well as to the PP. The possible function associated with the NE-sensitive, caudally projecting PVN neurons may be other than the regulation of blood pressure.

Modulation of hypothalamic cholecystokinin receptor density with changes in magnocellular activity: a quantitative autoradiographic study

A combination of autoradiographical techniques and computerized image analysis has been used to study the distribution and density of cholecystokinin receptors in the paraventricular and supraoptic nuclei of animals in which the magnocellular-posterior pituitary axis is activated, namely, in salt-loaded (2% sodium chloride) and homozygous Brattleboro rats. [125I]cholecystokinin octapeptide binding was greatly elevated in the paraventricular, supraoptic and accessory nuclei of salt-loaded and homozygous Brattleboro rats, compared to the respective control animals. Furthermore, under these conditions [125I]cholecystokinin octapeptide binding in the paraventricular nucleus was localized almost exclusively to magnocellular subdivisions, and especially to those containing predominantly oxytocin neurons. Autoradiographical competition studies revealed that the increase in [125I]cholecystokinin octapeptide binding in magnocellular nuclei reflected an increase in receptor number (Bmax) rather than affinity (Kd). These results suggest that cholecystokinin receptor density in the paraventricular, supraoptic and accessory magnocellular nuclei is closely linked to magnocellular neurosecretory activity and raises the possibility that cholecystokinin receptors may be involved in oxytocin and vasopressin release processes.

Co-localization of tyrosine hydroxylase (TH)- and serotonin (5-HT)-immunoreactive innervation in the rat pituitary gland

Adult male Sprague-Dawley rats were examined for possible co-localization of tyrosine hydroxylase (TH) and serotonin (5-HT) within innervation of the pituitary neurointermediate lobe. Use of sheep antiserum to TH and a secondary antibody coupled to fluorescein isothiocyanate (FITC), followed by rabbit anti-5-HT, then rhodamine-coupled second antibody, produced co-existent staining in some, but not all fibers of both the neural and intermediate lobes, using paraffin embedded tissues. Application of a combination of the two primary antibodies followed by sequential application of secondary antibody also resulted in co-localized antigens in selected fibers. Multiple 'classic' neurotransmitters within the same nerve terminals may modulate selected areas of endocrine tissue to control hormone release.