Development of the medial hypothalamus: forming a functional hypothalamic-neurohypophyseal interface.

The medial hypothalamus is composed of nuclei of the tuberal hypothalamus, the paraventricular nucleus of the anterior hypothalamus, and the neurohypophysis. Its arrangement, around the third ventricle of the brain, above the adenohypophysis, and in direct contact with the vasculature, means that it serves as an interface with circulating systems, providing a key conduit through which the brain can sample, and control, peripheral body systems. Through these interfaces, and interactions with other parts of the brain, the medial hypothalamus centrally governs diverse homeostatic processes, including energy and fluid balance, stress responses, growth, and reproductive behaviors. Here, we summarize recent studies that reveal how the diverse cell types within the medial hypothalamus are assembled in an integrated manner to enable its later function. In particular, we discuss how the temporally protracted operation of signaling pathways and transcription factors governs the appearance and regionalization of the hypothalamic primordium from the prosencephalic territory, the specification and differentiation of progenitors into neurons in organized nuclei, and the establishment of interfaces. Through analyses of mouse, chick, and zebrafish, a picture emerges of an evolutionarily conserved and highly coordinated developmental program. Early indications suggest that deregulation of this program may underlie complex human pathological conditions and dysfunctional behaviors, including stress and eating disorders.

A deficit of brain dystrophin 71 impairs hypothalamic osmostat.

Patients with Duchenne muscular dystrophy (DMD) and mdx mice, devoid of dystrophin proteins, show altered ionic homeostasis. To clarify dystrophin's involvement in the central control of osmotic stimuli, we investigated the effect of the disruption of Dp71, the major form of dystrophin in the brain, on the hypothalamoneurohypophysis system (HNHS) osmoregulatory response. Dp71 and Dp140 are the principal DMD gene products in the supraoptic nucleus (SON) and neurohypophysis (NH). They are present in astrocyte and pituicyte end-feet, suggesting involvement in both intrinsic osmosensitivity of the SON and vasopressin (AVP) release from the NH. In Dp71-null mice, the cellular distribution of Dp140 was modified, this protein being detected on the membrane of magnocellular soma. The plasma osmolality of Dp71-null mice was lower than that of wild-type mice under normal conditions, and this difference was maintained after salt loading, indicating a change in the set point for osmoregulation in the absence of Dp71. The increase in AVP levels detected in the SON and NH of the wild-type was not observed in Dp71-null mice following salt loading, and the increase in AVP mRNA levels in the SON was smaller in Dp71-null than in wild-type mice. This suggests that Dp71 may be involved in the functional activity of the HNHS. Its astrocyte end-feet localization emphasizes the importance of neuronal-vascular-glial interactions for the central detection of osmolality. In the SON, Dp71 may be involved in osmosensitivity and definition of the "osmostat," whereas, in the neurohypophysis, it may be involved in fine-tuning AVP release.

The circumventricular organs: an atlas of comparative anatomy and vascularization.

The circumventricular organs are small sized structures lining the cavity of the third ventricle (neurohypophysis, vascular organ of the lamina terminalis, subfornical organ, pineal gland and subcommissural organ) and of the fourth ventricle (area postrema). Their particular location in relation to the ventricular cavities is to be noted: the subfornical organ, the subcommissural organ and the area postrema are situated at the confluence between ventricles while the neurohypophysis, the vascular organ of the lamina terminalis and the pineal gland line ventricular recesses. The main object of this work is to study the specific characteristics of the vascular architecture of these organs: their capillaries have a wall devoid of blood-brain barrier, as opposed to central capillaries. This particular arrangement allows direct exchange between the blood and the nervous tissue of these organs. This work is based on a unique set of histological preparations from 12 species of mammals and 5 species of birds, and is taking the form of an atlas.

Long form leptin receptor mRNA expression in the hypothalamus and pituitary during early pregnancy in the pig.

OBJECTIVE: The aim of this study was the detection and location of long form leptin receptor (OB-Rb) in different area of hypothalamus and pituitary in the pig during early pregnancy. SETTINGS AND DESIGN: Expression of OB-Rb was examined by RT-PCR in the different area of hypothalamus: medial basal hypothalamus (MBH), preoptic area (POA), stalk median eminence (SME), as well as pituitary: the anterior (AP) and posterior (NP) lobe collected from gilts at days 14-16 (n=4) and 30-32 (n=4) of pregnancy. RESULTS: The results showed that OB-Rb mRNA was expressed in the hypothalamus (MBH, POA and SME), pituitary (AP, NP) and adipose tissue in the pig during early pregnancy (at days 14-16 and 30-32). CONCLUSION: These findings support the idea that leptin might play a role in the regulation of the hypothalamic-pituitary axis activity, and consequently in the control of pregnancy during critical period of embryo implantation in the pig.

Plasticity of nonapeptidergic neurosecretory cells in fish hypothalamus and neurohypophysis.

The structure and function of nonapeptidergic neurosecretory cells (NP-NSC) are considered in terms of comparative morphology. Among NSC of different ergicity for NP-NSC the most characteristic involve massive accumulation and storage of neurohormonal products. Only in NP-NSC are the secretory cycles of functioning clearly expressed. Their highest reactivity is established during experimental and physiological stresses. In contrast, liberinergic, statinergic, and monoaminergic NSC, unlike NP-NSC, are characterized even in the "norm" by a constantly high level of extrusion processes. As signs of maximum NP-NSC plasticity, we consider the largest size of elementary neurosecretory granules, the diversity of secretion forms, and the maximum development of Herring bodies-clear manifestations of secretory cycles of functioning. In particular, phases of massive storage of neurosecretory granules in the extrusion cycle of NP-NSC neurosecretory terminals express accumulation of neurosecretory products. It is concluded that a particularly high degree of plasticity of NP-NSC is provided by their capability for functional reversion. This reversion is manifested first in the form of the restoration of the initial moderate level of functioning and especially in the accumulation of neurosecretory products. The reversion is considered an important mechanism providing a high degree of NSC plasticity. This degree turns out to be sufficient for participation of NP-NSC in the integration of fish reproduction. It is shown that NP-NSC are organized by the principle of a triad of the balanced system. This system consists of two alternative states: accumulation and release of neurosecretory products and the center of control of dynamics of their interrelations, the self-regulating center. In the latter, the key role is probably played by the Golgi complex.

Regulation of oxytocin secretion.

A baby sucks at a mother's breast for comfort and, of course, for milk. Milk is made in specialized cells of the mammary gland, and for a baby to feed, the milk must be released into a collecting chamber from where it can be extracted by sucking. Milk "let-down" is a reflex response to the suckling and kneading of the nipple--and sometimes in response to the sight, smell, and sound of the baby--and is ultimately affected by the secretion of oxytocin. Oxytocin has many physiological roles, but its only irreplaceable role is to mediate milk let-down: oxytocin-deficient mice cannot feed their young; the pups suckle but no milk is let down, and they will die unless cross-fostered. Most other physiological roles of oxytocin, including its role in parturition, are redundant in the sense that the roles can be assumed by other mechanisms in the absence of oxytocin throughout development and adult life. Nevertheless, physiological function in these roles can be altered or impaired by acute interventions that alter oxytocin secretion or change the actions of oxytocin. Here we focus on the diverse stimuli that regulate oxytocin secretion and on the apparent diversity of the roles for oxytocin.

Corticotropin-releasing hormone-synthesizing neurons of the human hypothalamus receive neuropeptide Y-immunoreactive innervation from neurons residing primarily outside the infundibular nucleus.

Immunohistochemical single- and double-labeling studies were performed on the hypothalami of postmortem human brains to elucidate the distribution of corticotropin-releasing hormone (CRH)-immunoreactive (IR) neuronal elements and their interaction with the neuropeptide Y (NPY)-ergic neuronal system. The great majority of CRH-IR perikarya were found in the paraventricular nucleus (PVN), whereas a considerable number of CRH-IR neurons were also observed in the periventricular and infundibular nuclei. The dorsomedial nucleus and the perifornical region contained only scattered CRH-IR neurons. Dense CRH-IR fiber networks were found throughout the hypothalamus. However, the medial preoptic, the dorsolateral part of the supraoptic, the suprachiasmatic, the ventromedial, and the different mammillary nuclei showed a relative paucity of fibers. The terminal fields of NPY-IR axons overlapped the distribution of CRH-IR neurons in the hypothalamus. NPY-IR axon varicosities were juxtaposed to both dendrites and perikarya of the majority of CRH-IR neurons residing in the paraventricular, periventricular, and infundibular nuclei. These neurons were frequently contacted by multiple NPY axons that either formed baskets around their perikarya or completely ensheathed the emanating CRH dendrites. Because NPY and agouti-related protein (AGRP) are co-contained in neurons of the human infundibular nucleus, we used AGRP as a marker of NPY fibers originating exclusively from the infundibular nucleus. Only a small proportion of CRH neurons in the PVN was contacted by AGRP-IR axon varicosities, suggesting that NPY-IR innervation of CRH neurons in the PVN derive mainly from regions outside the infundibular nucleus. The present morphological findings support the view that NPY regulates the CRH system of the human hypothalamus and therefore at least some of the effects of NPY on metabolic, autonomic, and endocrine functions may be mediated through CRH.

Hypothalamic and limbic expression of CRF and vasopressin during lactation: implications for the control of ACTH secretion and stress hyporesponsiveness.

Lactation is associated with physiological and behavioral changes that optimize conditions for development of the offspring. Although neuroendocrine and emotional stress responses are blunted, the central mechanisms involved are unclear. In addition to a reduction in stimulatory noradrenergic inputs to paraventricular nucleus (PVN) neurons, we demonstrate that lactation induces: (1) unique phenotypic changes in neuropeptide expression by hypothalamic PVN neurons (reduced expression of corticotropin-releasing factor (CRF) mRNA and increased expression of vasopressin mRNA in parvocellular PVN neurons); and (2) changes in pituitary sensitivity to CRF (reduced) and vasopressin (increased) as a consequence of differential CRF/vasopressin secretion into the hypophysial portal blood. Neurons in the bed nucleus of the stria terminalis (BNST) and the central amygdala (CeA) that are implicated in the control of the hypothalamopituitary-adrenal axis also display changes in lactation: expression of CRF mRNA in the CeA is reduced, consistent with the diminished responsiveness to acoustic startle observed in nursing mothers. In contrast, expression of CRF mRNA is increased in the dorsolateral portion of the BNST, probably because of the tonic increases in endogenous glucocorticoid production during this period. Using immuno-targeted lesions of CRF or vasopressin in the PVN of virgin females, we have shown that CRF neurons of the PVN send inhibitory projections to the dorsolateral portion of the BNST and stimulatory inputs to CRF neurons in the CeA. Thus, it is possible that lactation-induced changes in the activity of parvocellular PVN neurons might also modulate the expression of neuropeptides and neurotransmitters in the BNST and the amygdala.

The hypothalamo-neurohypophysial response to melatonin.

The present paper reviews the findings accumulated on the role of pineal gland and its hormone - melatonin - in regulation of the hypothalamo-neurohypophysial system activity. Effects of modified photoperiod, pinealectomy or treatment with melatonin on the vasopressin and oxytocin biosynthesis and/or secretion have been described. Taken together, the in vivo and in vitro data suggest that the effect of melatonin on the vasopressin and oxytocin secretion depends on this pineal hormone concentration and experimental conditions.

Galanin-like peptide mRNA in neural lobe of rat pituitary. Increased expression after osmotic stimulation suggests a role for galanin-like peptide in neuron-glial interactions and/or neurosecretion.

Galanin-like peptide (GALP) was recently identified in the porcine hypothalamus, pituitary gland and gut, and has reported selectivity for the GalR2, c.f. the GalR1 receptor. GALP cDNAs have been cloned from pig, rat and human, and GALP mRNA expression is restricted to the arcuate nucleus in normal rat brain. This study examined the regional and cellular distribution of GALP mRNA in the rat pituitary gland, and subsequently determined the effect of osmotic stimulation on GALP transcript levels. GALP mRNA was not detected in the anterior or intermediate lobes, but moderate levels of GALP mRNA were present in the neural (posterior) lobe, in presumed pituicytes, of normal male and female rats. Osmotic stimulation by dehydration or salt loading produced a time-dependent increase in GALP mRNA levels in the neural lobe. Thus, dehydration for 4 days increased GALP mRNA 40-fold, while salt loading for 4, 7 or 10 days increased GALP levels 14-, 21- and 25-fold, respectively (p < or = 0.001). Levels of vasopressin (VP) mRNA in the neural lobe were also increased by these treatments, consistent with previous reports. Galanin (GAL) and GalR2 receptor mRNAs were not detected in the neural lobe, under normal or osmotic stimulation conditions. In addition, GALP mRNA levels in the arcuate nucleus were not altered in dehydrated or salt-loaded rats; and GALP mRNA was not detected in magnocellular neurons of the supraoptic or paraventricular nucleus, despite the characteristic up-regulation of VP and GAL mRNA in these cells. In view of the established anatomy and function of VP/oxytocin neurons in the hypothalamo-neurohypophysial system and the role played by pituicytes in their regulation, the likely synthesis/release of GALP by these specialized astrocytes strongly suggests a role for this novel peptide in regulation of pituicyte morphology/function and/or neurohormone release.

Inducible expression of tryptophan hydroxylase without serotonin synthesis in hypothalamic dopaminergic neurons.

In the present study we have further studied the previous findings that rat hypothalamic dopaminergic neuronal cell groups may express tryptophan hydroxylase (TpH), the serotonin synthesizing enzyme, without a detectable serotonin synthesis. Chemical and mechanical neuronal injuries, namely colchicine treatment and axonal transection, respectively, were performed, and distributions of neurons exhibiting immunoreactivity for TpH and/or tyrosine hydroxylase (TH), the dopamine synthesizing enzyme, were analyzed throughout the hypothalamic periventricular and arcuate nuclei. After colchicine treatment there was a statistically significant 87% (P = 0,01) increase in the number of TpH expressing neurons, while TH expression remained essentially similar. Axonal transection resulted also in a statistically significant 131% (P < 0,01) increase in the number of TpH expressing neurons, while TH expression was not significantly altered. All TpH expression coexisted with TH expression, and the induction of TpH expression by neuronal injuries occurred evenly throughout the rostrocaudal length of the territory studied. A possible serotonin synthesis by TpH was examined by giving drugs that increase brain serotonin synthesis, but no immunohistochemically detectable serotonin synthesis could be found in any of the TpH expressing neurons. Finally the possibility was studied that the relative shortage of the cofactor tetrahydrobiopterin would limit serotonin synthesis. However, an administration of tetrahydrobiopterin did not result in detectable serotonin synthesis in these neurons. Taken together these results suggest that dopaminergic neurons in the hypothalamic periventricular and arcuate nuclei are able to express TpH, this expression is induced after neuronal injury, and this induction occurs similarly throughout the territories studied. TpH expression occurs independently of TH expression, and the newly expressed TpH appears not to synthesize serotonin, regardless of pharmacological pretreatments. Thus, our findings (i) support the idea that neurons may possess inducible expression of nonfunctional transmitter-synthesizing enzymes, in this case TpH, and (ii) suggest that expression of an enzyme synthesizing a certain transmitter may not necessarily imply the corresponding transmitter phenotype.

Molecular and functional remodeling of electrogenic membrane of hypothalamic neurons in response to changes in their input.

Neurons respond to stimuli by integrating generator and synaptic potentials and generating action potentials. However, whether the underlying electrogenic machinery within neurons itself changes, in response to alterations in input, is not known. To determine whether there are changes in Na+ channel expression and function within neurons in response to altered input, we exposed magnocellular neurosecretory cells (MNCs) in the rat supraoptic nucleus to different osmotic milieus by salt-loading and studied Na+ channel mRNA and protein, and Na+ currents, in these cells. In situ hybridization demonstrated significantly increased mRNA levels for alpha-II, Na6, beta1 and beta2 Na+ channel subunits, and immunohistochemistry/immunoblotting showed increased Na+ channel protein after salt-loading. Using patch-clamp recordings to examine the deployment of functional Na+ channels in the membranes of MNCs, we observed an increase in the amplitude of the transient Na+ current after salt-loading and an even greater increase in amplitude and density of the persistent Na+ current evoked at subthreshold potentials by slow ramp depolarizations. These results demonstrate that MNCs respond to salt-loading by selectively synthesizing additional, functional Na+ channel subtypes whose deployment in the membrane changes its electrogenic properties. Thus, neurons may respond to changes in their input not only by producing different patterns of electrical activity, but also by remodeling the electrogenic machinery that underlies this activity.

Neurohypophyseal and fluid homeostasis in transgenic rats expressing a tagged rat vasopressin prepropeptide in hypothalamic neurons.

We have developed a transgenic system that, for the first time, facilitates monitoring of the regulatory dynamics of a central peptidergic system from transcription of a neuropeptide gene to the storage and release of the mature secretory product. A rat vasopressin (VP) transgene (5-VCAT-3), the expression of which is restricted to hypothalamic vasopressinergic magnocellular neurons in rats, contains a sequence that, if translated, would place a unique hexadecapeptide (DRSAGYYGLFKDRKEK, abbreviated to DR-12-EK) at the C-terminus of the VP precursor. We have raised an antibody against this "tag" and, using immunohistochemistry, electron microscopy, RIA, and HPLC, have shown for the first time that a VP transgene RNA is translated into a protein product found, in a processed form, in secretory granules in the posterior pituitaries of transgenic rats. Disruption of the C-terminus of the VP precursor by the peptide tag is well tolerated and does not disrupt VP production or disturb salt and water balance. An osmotic stimulus increased hypothalamic DR-12-EK levels, but changes in posterior pituitary DR-12-EK levels were more complex. After 5 days of salt-loading, DR-12-EK levels fell, as would be expected if its release was coordinate with that of VP. However, after 10 days of salt-loading, posterior pituitary DR-12-EK levels increased, despite the lower level of VP. This probably reflects the greater response of the transgene to osmotic challenge at the RNA level, increasing the proportion of DR-12-EK-containing translation products transported to the posterior pituitary relative to those derived from the endogenous gene. The exaggerated response of the tagged transgene to osmotic challenge at both RNA and protein levels affords a new opportunity to study the regulatory dynamics of the VP system at the molecular level, but within the physiologically advantageous context of the intact animal.

Cholecystokinin octapeptide and the daily rhythm of vasopressin and oxytocin release.

The daily rhythm of neurohypophysial hormone release was monitored in rats given intracerebroventricularly (i.c.v.) CCK-8 (50 ng/10 microliters--once daily over five days). In animals injected i.c.v. with vehicle solution (0.9% NaCl) plasma oxytocin and vasopressin concentrations were seen to rise significantly over the hours of daylight, decreasing during the night. The changes seen in the neurohypophysial vasopressin and oxytocin content were inversely related to the plasma concentrations. Under i.c.v. treatment with CCK-8, the daily rhythm of the vasopressin and oxytocin release was similar to daily rhythm in the control group; respective figures were, however, reduced for the hypothalamus and neurohypophysis as well as increased for the blood plasma. It is suggested that CCK-8 may be involved in some circadian regulatory processes related to vasopressin and oxytocin release from the rat hypothalamo-neurohypophysial system.

Opioid tolerance and dependence in the magnocellular oxytocin system: a physiological mechanism?

At the neurosecretory terminals in the neural lobe, oxytocin secretion is restrained by co-secreted endogenous opioids, which act via kappa-receptors. The co-secreted opioids include products of pro-dynorphin (released by both vasopressin and oxytocin terminals) and proenkephalin (released by oxytocin terminals). In morphine-tolerant rats this opioid mechanism is more effective, but in late pregnancy it is less effective. Opioids also act directly on oxytocin cell bodies, via separate mu- and kappa-receptors, inhibiting excitation by all stimuli tested, and also exert presynaptic and more distal actions on afferent systems. During chronic morphine exposure, tolerance and dependence develop in oxytocin neurones; the former involves reduction in mu-opioid receptor density, while the latter may involve compensatory upregulation of mechanisms regulating Ca2+ influx. In mid-pregnancy, the effectiveness of opioid mechanisms in the neural lobe increases, assisting the accumulation of oxytocin stores in advance of parturition, but by the end of pregnancy the effectiveness of these mechanisms is reduced. At this time, a separate endogenous opioid system, acting via mu-receptors, actively restrains the electrical activity of oxytocin neurones. Release of this endogenous opioid inhibition may contribute to the increase in activity during parturition analogous to that occurring during morphine withdrawal excitation. Central opioid mechanisms retain the ability to control oxytocin neurones during parturition, and can interrupt established parturition by inhibiting oxytocin neurone firing rate in disadvantageous environmental circumstances.

The central oxytocin pulse generator: a pacemaker for luteolysis.

Oxytocin (OT) is released from the neurohypophysis into the jugular vein of sheep in small 1-2 min pulses (ca. 10 pg/ml) in both cyclic and ovariectomized sheep. In intact cycling sheep, additional hour long bursts of OT (up to 200 pg/ml) occur in peripheral blood during luteolysis at intervals of 6 to 9 hrs which appear to regulate large luteolytic pulses of uterine prostaglandin F2a (PGF2a). Since the ovine corpus luteum (CL) also synthesizes OT, experiments were performed to distinguish between the relative contributions of the neurohypophysis and the CL to the large bursts of OT secreted during luteolysis. Two models were used. First, ovariectomized sheep were given exogenous E and/or P by constant infusion to simulate levels during the estrous cycle. Second, in tact cycling sheep, the CL was surgically excised during the luteal phase to exclude the CL as a source of OT and, at the same time, subject the animals to the withdrawal of P. Pulses of OT in jugular vein plasma were determined by RIA or biometry of the uterus. The findings are summarized as follows: In ovariectomized sheep, maintained on low E (0.05 g/hr) to preserve the OT pulse generator, infusion of E (1 microgram, 2 micrograms or 4 micrograms/hr) for 12 to 36 hr, caused a series (4 to 6) of rapid increases in OT pulse frequency each lasting 1 to 2 hrs at intervals of 3 hrs. The time of onset of high frequency pulses was dose-dependent. Withdrawal of 10 day infusions of P (500 micrograms/hr) superimposed on low E (0.05 microgram/hr) also evoked a series of high frequency episodes of OT pulses beginning 24 hrs after P withdrawal. In intact sheep, surgical removal of the CL resulted in a series of high frequency pulses similar in duration and frequency to those following the withdrawal of P in the ovariectomized animal. We conclude that: (1) an increase in E or returning E action causes the OT pulse generator to alter its frequency intermittently thus producing a series of 4 to 6 episodes of high frequency pulses of OT. (2) Similar changes can be evoked by withdrawal of P either by terminating an infusion of P in the presence of E in the ovariectomized sheep or by surgically removing the CL from the ovary in the intact sheep. (3) At the end of the reproductive cycle, the central OT pulse generator appears to act as a pacemaker which, acting on the endometrial OT receptors, triggers a series of pulses of PGF2a from the uterus and hence causes regression of the CL. In the sheep and other ruminants, an intermittent supplemental secretion of OT from the CL, triggered via the central OT pulse generator, may also be required to amplify the luteolytic pulses of PGF2a from the uterus. (4) In addition to the well established interaction of ovarian steroid hormones, and the hypothalamic pituitary system for the initiation of the reproductive cycle via the gonadotrophins, there is now good evidence for an interaction of ovarian steroids and the posterior pituitary for terminating the reproductive cycle.

[The oxytocinergic neurosecretory system in genetically selected rats differing by their emotionality. Morphometric research]. / Oksitotsinergicheskaia neirosekretornaia sistema u geneticheski selektirovannykh krys, razlichaiushchikhsia po émotsional'nosti. Morfometricheskoe issledovanie.

The rats selectively bred for rapid (KHA) and slow (KLA) acquisition of the avoidance response were subjected to inescapable shock (IS). Synthesis and secretion of oxytocin (OT) were higher in intact KLA rats as compared to KHA ones. Preliminary exposure to IS resulted in opposite changes of the OT synthesis and secretion. The findings suggest a dependence of the stress-reactivity of the OT-ergic system on the copying of the behaviour strategy.

Hypophysiotropic role and hypothalamic gene expression of corticotropin-releasing factor and vasopressin in rats injected with interleukin-1 beta systemically or into the brain ventricles.

Intact adult male rats were injected intravenously (i.v., 400 ng/kg), intraperitoneally (i.p., 400 ng/kg) or intracerebroventricularly (i.c.v., 100 ng/kg) with interleukin-1 beta (IL-1 beta) or its vehicle. In comparison with vehicle-treated animals, IL-1 beta induced significant (P < 0.01) increases in plasma ACTH levels measured 30 min later regardless of the route of cytokine administration. These changes were markedly blunted in rats administered specific antibodies directed against corticotropin-releasing factor (CRF). In contrast, vasopressin (VP) antibodies significantly blunted ACTH released by the i.c.v. injection of IL-1 beta, but only modestly altered the effect of the systemic injection of the cytokine. We then used semi-quantitative in situ hybridization analysis to measure changes in steady-state mRNA levels, as they might occur in response to these same doses of IL-1 beta. Following administration of the vehicle, measurement of gene expression in the paraventricular (PVN) portion of the hypothalamus indicated a measurable amount of hybridization signals for both CRF and VP. No detectable changes in either CRF or VP gene expression were observed in rats injected with IL-1 beta i.v. or i.p. 5 h earlier. In contrast, the i.c.v. administration of the cytokine significantly (P < 0.01) increased both CRF and VP mRNA levels measured 5 h later. These results suggest that while endogenous CRF modulates the response of the corticotrophs to this cytokine regardless of the route of administration, the role of VP is more important in rats injected centrally than in those injected peripherally.(ABSTRACT TRUNCATED AT 250 WORDS)