Effects of septal and hippocampal stimuli on paraventricular nucleus neurons

Prenatal stress modulates HPA axis homeostasis of offspring through dentate TERT independently of glucocorticoids receptor

In response to stressful events, the hypothalamic-pituitary-adrenal (HPA) axis is activated, and consequently glucocorticoids are released by the adrenal gland into the blood circulation. A large body of research has illustrated that excessive glucocorticoids in the hippocampus exerts negative feedback regulation of the HPA axis through glucocorticoid receptor (GR), which is critical for the homeostasis of the HPA axis. Maternal prenatal stress causes dysfunction of the HPA axis feedback mechanism in their offspring in adulthood. Here we report that telomerase reverse transcriptase (TERT) gene knockout causes hyperactivity of the HPA axis without hippocampal GR deficiency. We found that the level of TERT in the dentate gyrus (DG) of the hippocampus during the developmental stage determines the responses of the HPA axis to stressful events in adulthood through modulating the excitability of the dentate granular cells (DGCs) rather than the expression of GR. Our study also suggests that the prenatal high level of glucocorticoids exposure-induced hypomethylation at Chr13:73764526 in the first exon of mouse Tert gene accounted for TERT deficiency in the DG and HPA axis abnormality in the adult offspring. This study reveals a novel GR-independent mechanism underlying prenatal stress-associated HPA axis impairment, providing a new angle for understanding the mechanisms for maintaining HPA axis homeostasis.

A metabolic function of the hippocampal sharp wave-ripple

The hippocampus has previously been implicated in both cognitive and endocrine functions1-15. We simultaneously measured electrophysiological activity from the hippocampus and interstitial glucose concentrations in the body of freely behaving rats to identify an activity pattern that may link these disparate functions of the hippocampus. Here we report that clusters of sharp wave-ripples recorded from the hippocampus reliably predicted a decrease in peripheral glucose concentrations within about 10 min. This correlation was not dependent on circadian, ultradian or meal-triggered fluctuations, could be mimicked with optogenetically induced ripples in the hippocampus (but not in the parietal cortex) and was attenuated to chance levels by pharmacogenetically suppressing activity of the lateral septum, which is the major conduit between the hippocampus and the hypothalamus. Our findings demonstrate that a function of the sharp wave-ripple is to modulate peripheral glucose homeostasis, and offer a mechanism for the link between sleep disruption and blood glucose dysregulation in type 2 diabetes16-18.

Independent effects of early-life experience and trait aggression on cardiovascular function

Early-life experience (ELE) can significantly affect life-long health and disease, including cardiovascular function. Specific dimensions of emotionality also modify risk of disease, and aggressive traits along with social inhibition have been established as independent vulnerability factors for the progression of cardiovascular disease. Yet, the biological mechanisms mediating these associations remain poorly understood. The present study utilized the inherently stress-susceptible and socially inhibited Wistar-Kyoto rats to determine the potential influences of ELE and trait aggression (TA) on cardiovascular parameters throughout the lifespan. Pups were exposed to maternal separation (MS), consisting of daily 3-h separations of the entire litter from postnatal day (P)1 to P14. The rats were weaned at P21, and as adults were instrumented for chronic radiotelemetry recordings of blood pressure and heart rate (HR). Adult aggressive behavior was assessed using the resident-intruder test, which demonstrated that TA was independent of MS exposure. MS-exposed animals (irrespective of TA) had significantly lower resting HR accompanied by increases in HR variability. No effects of MS on resting blood pressure were detected. In contrast, TA correlated with increased resting mean, systolic, and diastolic arterial pressures but had no effect on HR. TA rats (relative to nonaggressive animals) also manifested increased wall-to-lumen ratio in the thoracic aorta, increased sensitivity to phenylephrine-induced vascular contractility, and increased norepinephrine content in the heart. Together these data suggest that ELE and TA are independent factors that impact baseline cardiovascular function.

Androgenic influence on serotonergic activation of the HPA stress axis

The higher incidence of stress-mediated affective disorders in women may be a function of gonadal hormone influence on complex interactions between serotonin and neural circuits that mediate the hypothalamic-pituitary-adrenal (HPA) stress axis. The paraventricular nucleus of the hypothalamus (PVN) receives serotonergic innervation, and selective serotonin reuptake inhibitors such as citalopram activate the HPA axis independent of stress. We have previously demonstrated that the magnitude of this serotonergic activation was greater in females and was attenuated by testosterone administration; however, the potential central sites of action where androgens reduce these serotonergic effects have not been determined. Therefore, we examined a time course of corticosterone production and used central c-Fos protein levels to assay neuronal activation in stress-related brain regions in female, male, and gonadectomized male mice after an acute citalopram injection (15 mg/kg). In the hippocampus, c-Fos-immunoreactivity was greater in males than in females or gonadectomized males. This same pattern emerged in the lateral septum after vehicle and gonadectomy reversed the effect of citalopram. These regions are important for inhibitory influences on the PVN, and accordingly, hippocampal c-Fos levels were negatively correlated with corticosterone production. No sex differences in c-Fos were detected in the PVN, cingulate cortex, or paraventricular thalamus in response to vehicle or citalopram. These data support brain region-specific regulation of the HPA axis where sex differences may be mediated partly through androgen enhancement of signaling in inhibitory regions.

Cannabinoid CB1 receptors in the paraventricular nucleus and central control of penile erection: Immunocytochemistry, autoradiography and behavioral studies

[N-(piperidin-1-yl)-5-(4-chlorophenyl)-4-methyl-1H-pyrazole-3-carboxyamide] (SR 141716A), a selective cannabinoid CB1 receptor antagonist, injected into the paraventricular nucleus of the hypothalamus (PVN) of male rats, induces penile erection. This effect is mediated by the release of glutamic acid, which in turn activates central oxytocinergic neurons mediating penile erection. Double immunofluorescence studies with selective antibodies against CB1 receptors, glutamic acid transporters (vesicular glutamate transporters 1 and 2 (VGlut1 and VGlut2), glutamic acid decarboxylase-67 (GAD67) and oxytocin itself, have shown that CB1 receptors in the PVN are located mainly in GABAergic terminals and fibers surrounding oxytocinergic cell bodies. As GABAergic synapses in the PVN impinge directly on oxytocinergic neurons or on excitatory glutamatergic synapses, which also impinge on oxytocinergic neurons, these results suggest that the blockade of CB1 receptors decreases GABA release in the PVN, increasing in turn glutamatergic neurotransmission to activate oxytocinergic neurons mediating penile erection. Autoradiography studies with [(3)H](-)-CP 55,940 show that chronic treatment with SR 141716A for 15 days twice daily (1 mg/kg i.p.) significantly increases the density of CB1 receptors in the PVN. This increase occurs concomitantly with an almost twofold increase in the pro-erectile effect of SR 141716A injected into the PVN as compared with control rats. The present findings confirm that PVN CB1 receptors, localized mainly in GABAergic synapses that control in an inhibitory fashion excitatory synapses, exert an inhibitory control on penile erection, demonstrating for the first time that chronic blockade of CB1 receptors by SR 141716A increases the density of these receptors in the PVN. This increase is related to an enhanced pro-erectile effect of SR 141716A, which is still present 3 days after the end of the chronic treatment.

Changes in the expression of corticotrophin-releasing hormone, mineralocorticoid receptor and glucocorticoid receptor mRNAs in the hypothalamic paraventricular nucleus induced by fornix transection and adrenalectomy

The paraventricular nucleus (PVN) in the hypothalamus receives inputs from the hippocampus The present study explored the influence of the hippocampus on genes mediating glucocorticoid feedback in the PVN. Accordingly, the expression of mRNAs for corticotrophin-releasing hormone (CRH), the mineralocorticoid receptor (MR) and the glucocorticoid receptor (GR) in the PVN was examined by in situ hybridisation in rats subjected to transection of the fornix. Significant increases in CRH, MR and GR mRNAs were observed in the parvocellular PVN after fornix transection (FT). FT-animals subjected to adrenalectomy also showed an increase in the number of cells positive for CRH and GR mRNAs. CRH, MR and GR mRNA expression was also increased by bilateral adrenalectomy, and GR mRNA expression was further enhanced in the parvocellular PVN of the FT transected animals. However, no such changes were evident in the magnocellular PVN. These results suggest that the input from the hippocampus to the PVN, particularly to its parvocellular region, has distinct and differential inhibitory effects on the expression of MR,GR and CRH mRNAs that may operate independently from the feedback actions of corticosterone.

The role of the hypothalamic-pituitary-adrenal axis in neuroendocrine responses to stress

Animals respond to stress by activating a wide array of behavioral and physiological responses that are collectively referred to as the stress response. Corticotropin-releasing factor (CRF) plays a central role in the stress response by regulating the hypothalamic-pituitary-adrenal (HPA) axis. In response to stress, CRF initiates a cascade of events that culminate in the release of glucocorticoids from the adrenal cortex. As a result of the great number of physiological and behavioral effects exerted by glucocorticoids, several mechanisms have evolved to control HPA axis activation and integrate the stress response. Glucocorticoid feedback inhibition plays a prominent role in regulating the magnitude and duration of glucocorticoid release. In addition to glucocorticoid feedback, the HPA axis is regulated at the level of the hypothalamus by a diverse group of afferent projections from limbic, mid-brain, and brain stem nuclei. The stress response is also mediated in part by brain stem noradrenergic neurons, sympathetic andrenornedullary circuits, and parasympathetic systems. In summary, the aim of this review is to discuss the role of the HPA axis in the integration of adaptive responses to stress. We also identify and briefly describe the major neuronal and endocrine systems that contribute to the regulation of the HPA axis and the maintenance of homeostasis in the face of aversive stimuli.

The cannabinoid CB1 receptor antagonist SR 141716A induces penile erection by increasing extra-cellular glutamic acid in the paraventricular nucleus of male rats

The cannabinoid CB1 receptor antagonist SR 141716A (0.1, 0.5 and 1 microg) induces penile erection when injected into the paraventricular nucleus of the hypothalamus of male rats. The pro-erectile effect of SR 141716A occurs concomitantly with an increase in the concentration of glutamic acid in the paraventricular dialysate obtained by means of intra-cerebral microdialysis. Glutamic acid increase and penile erection did not occur when SR 141716A was given after tetrodotoxin, a voltage-dependent Na(+) channel blocker. Both penile erection and glutamic acid increases were also reduced by the cannabinoid CB1 receptor agonists WIN 55,212-2 or HU 210 given into the paraventricular nucleus before SR 141716A at doses unable to induce penile erection or to modify glutamic acid. In contrast, dizocilpine ((+)MK-801), an antagonist of excitatory amino acid receptors of the N-methyl-d-aspartic acid (NMDA) subtype, given into the paraventricular nucleus reduced penile erection, but was ineffective on the glutamic acid increase induced by the CB1 receptor antagonist. 6-Cyano-7-nitro-quinoxaline-2,3-dione (CNQX) and (+/-)-2-amino-4-phosphono-butanoic acid (AP(4)), antagonists of the excitatory amino acid receptors of the AMPA subtype and of the metabotropic subtype, respectively, were ineffective on both penile erection and glutamic acid increase. SR 141716A responses were also reduced by muscimol, a GABA(A) receptor agonist, but not by baclofen, a GABA(B) receptor agonist, given into the paraventricular nucleus before SR 141716A. The present results show that SR 141716A induces penile erection by activating glutamic acid neurotransmission, which causes in turn the activation of paraventricular oxytocinergic neurons mediating penile erection.

Central control of penile erection: Role of the paraventricular nucleus of the hypothalamus

The paraventricular nucleus of the hypothalamus is an integration centre between the central and peripheral autonomic nervous systems. It is involved in numerous functions from feeding, metabolic balance, blood pressure and heart rate, to erectile function and sexual behaviour. In particular, a group of oxytocinergic neurons originating in this nucleus and projecting to extra-hypothalamic brain areas (e.g., hippocampus, medulla oblongata and spinal cord) control penile erection in male rats. Activation of these neurons by dopamine and its agonists, excitatory amino acids (N-methyl-D-aspartic acid) or oxytocin itself, or by electrical stimulation leads to penile erection, while their inhibition by gamma-amino-butyric acid (GABA) and its agonists or by opioid peptides and opiate-like drugs inhibits this sexual response. The activation of these neurons is secondary to the activation of nitric oxide synthase, which produces nitric oxide. Nitric oxide in turn causes, by a mechanism that is as yet unidentified, the release of oxytocin in extra-hypothalamic brain areas. Other compounds recently identified that facilitate penile erection by activating central oxytocinergic neurons are peptide analogues of hexarelin, a growth hormone releasing peptide, pro-VGF-derived peptides, endogenous peptides that may be released by neuronal nerve endings impinging on oxytocinergic cell bodies, SR 141716A, a cannabinoid CB1 receptor antagonist, and, less convincingly, adrenocorticotropin-melanocyte-stimulating hormone (ACTH-MSH)-related peptides. Paraventricular oxytocinergic neurons and similar mechanisms are also involved in penile erection occurring in physiological contexts, namely noncontact erections that occur in male rats in the presence of an inaccessible receptive female, and during copulation. These findings show that the paraventricular nucleus of the hypothalamus plays an important role in the control of erectile function and sexual activity. As the male rat is a model of sexual behaviour and penile physiology, which has largely increased in the last years our knowledge of peripheral and central mechanisms controlling erectile function (drugs that induce penile erection in male rats usually do so also in man), the above results may have great significance in terms of a human perspective for the treatment of erectile dysfunction.

Variations of maternal care differentially influence 'fear' reactivity and regional patterns of cFos immunoreactivity in response to the shock-probe burying test

Natural variations in maternal care in the rat influence the development of neuronal systems that regulate endocrine and behavioral responses to stress. Thus, as adults, rats that received higher levels of maternal licking/grooming (LG) in infancy are less 'fearful' in response to novelty, compared with adult offspring of Low LG mothers. The present study examined the influence of maternal care on behavioral and neuronal responses to a more specific, localizable form of threat using an electrified probe in the shock-probe burying test. Even under these conditions, adult offspring of High LG mothers displayed lower levels of fear reactivity (i.e. less shock-induced freezing and probe burying) throughout the test than did offspring of Low LG mothers. These differences in fearfulness were associated with differential patterns of cFos immunoreactivity (cFos-IR), 120 min following test exposure. Relative to control rats exposed to a non-electrified probe, cFos-IR was increased in the offspring of High LG mothers exposed to an electrified probe in the dentate gyrus, ventral subiculum, lateral and medial septum, nucleus accumbens and the dorsal periaqueductal gray. Shock-exposed offspring of Low LG dams displayed a very different pattern of neuronal activation characterized by both increases (area CA1 of the ventral hippocampus and the inferior colliculus) and decreases (paraventricular nucleus of the hypothalamus and the ventrolateral periaqueductal gray) in cFos-IR compared with the no-shock controls. Together these results suggest that maternal care serves to 'program' neuronal circuits that modulate fear-related responding in the rat resulting in qualitatively different neuronal responses to stress.

Effect of excitatory amino acid receptor agonists on penile erection after administration into the CA3 hippocampal region in the rat

OBJECTIVES

To examine whether hippocampal injection of specific agonists for glutamate ionotropic (NMDA, AMPA) and metabotropic (ACPD) receptors modulates erectile response in adult male rats. The paraventricular nuclei of the hypothalamus and hippocampus are believed to play a role in the central regulation of erectile function.

METHODS

Four groups of 5 male Sprague-Dawley rats each were anesthetized and placed in a stereotaxic apparatus after carotid artery catheterization for measurement of arterial pressure and insertion of a 25-gauge needle in the corpus cavernosum for measurement of intracavernous pressure (ICP). The rats underwent hippocampal injections of saline (1 muL), NMDA (10 nmol/L), AMPA (10 nmol/L), or ACPD (10 nmol/L) followed by perfusion with saline and 10% formalin solutions. Brain slices 24 mum thick were mounted and stained with cresyl violet to identify the drug injection sites.

RESULTS

Hippocampal injection of glutamate receptor subtype agonists produced multiple episodes of ICP elevation. NMDA injection was associated with a greater maximal ICP increase, duration of action, and mean onset of action latency than AMPA injection. ACPD injection had no statistically significant impact on ICP or arterial pressure changes. Histologic evaluation confirmed the injected sites were the CA3 fields of the hippocampus.

CONCLUSIONS

Our results suggest hippocampal glutamate receptors may be involved in initiation of penile erection. Ionotropic receptors appear to play a significant role in these regulatory mechanisms. NMDA receptors appear to be more potent than AMPA receptors, which appear to mediate fast excitatory synaptic transmission.

The role of oxytocin and the paraventricular nucleus in the sexual behaviour of male mammals

The paraventricular nucleus of the hypothalamus contains the cell bodies of a group of oxytocinergic neurons projecting to extrahypothalamic brain areas and to the spinal cord, which are involved in the control of erectile function and copulation. In male rats, these neurons can be activated by dopamine, excitatory amino acids, nitric oxide (NO), hexarelin analogue peptides and oxytocin itself to induce penile erection and facilitate copulation, while their inhibition by gamma-aminobutyric acid (GABA) and GABA agonists and by opioid peptides and opiate-like drugs inhibits sexual responses. The activation of paraventricular oxytocinergic neurons by dopamine, oxytocin, excitatory amino acids and hexarelin analogue peptides is apparently mediated by the activation of nitric oxide (NO) synthase. NO in turn activates, by a mechanism that is as yet unidentified, the release of oxytocin from oxytocinergic neurons in extrahypothalamic brain areas. Paraventricular oxytocinergic neurons and mechanisms similar to those reported above are also involved in the expression of penile erection in physiological contexts, namely, when penile erection is induced in the male by the presence of an inaccessible receptive female, which is considered a model for psychogenic impotence in man, as well as during copulation. These findings show that paraventricular oxytocinergic neurons projecting to extrahypothalamic brain areas and to the spinal cord and the paraventricular nucleus play an important role in the control of erectile function and male sexual behaviour in mammals.

Expression of c-Fos-like immunoreactivity in the brain of mice with learned helplessness

The learned helplessness (LH) developed after repeat inescapable stress is a well validated animal model of human major depression and is not species specific. c-Fos, the protein product of the protooncogene c-fos, is expressed in neurons under a variety of stressors and could reflect the regional neuronal activation. Using the LH paradigm in mice, we examined c-Fos expression in several brain regions related to stress response or major depression. The LH mice showed significantly lower c-Fos-like immunoreactivity (FLI) in the hippocampus dentate gyrus and the lateral septal nucleus, and higher FLI in the hypothalamic paraventricular nucleus compared with the naive mice. Our finding in the mice LH model supported previous studies in rats showing that the lateral septal nucleus and the hypothalamic paraventricular nucleus are important in LH behaviors. We further demonstrated that hippocampus dentate gyrus, a region important for learning and major depression, may also be involved in the LH behaviors. These related brain regions could provide a basis for further exploration of the molecular mechanisms underlying LH behaviors.

Extracellular excitatory amino acids increase in the paraventricular nucleus of male rats during sexual activity: main role of N-methyl-d-aspartic acid receptors in erectile function

The concentrations of glutamic and aspartic acids were measured in the dialysate obtained with vertical microdialysis probes implanted into the paraventricular nucleus of the hypothalamus of sexually potent male rats during sexual activity. Animals showed noncontact erections when put in the presence of, and copulated with, a receptive (ovarietomized oestrogen- and progesterone-primed) female rat. The concentrations of glutamic and aspartic acids in the paraventricular dialysate increased by 37 and 80%, respectively, above baseline values during exposure to the receptive female rat and by 55 and 127%, respectively, during copulation. No changes in the concentrations of glutamic and aspartic acids were detected in the paraventricular dialysate when sexually potent male rats were exposed to nonreceptive (ovariectomized not oestrogen- and progesterone-primed) female rats or when impotent male rats were used. The injection into the paraventricular nucleus of the excitatory amino acid receptor antagonist dizocilpine (5 micro g), a noncompetitive N-methyl-d-aspartic acid receptor antagonist, reduced noncontact erections and significantly impaired copulatory activity. The alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptor antagonist 6-cyano-7-nitro-quinoxaline-2,3-dione (5 micro g) was also able to impair copulatory activity, but to a much lower extent than dizocilpine. In contrast, (+/-)-2-amino-4-phosphono-butanoic acid, a metabotropic receptor antagonist (5 micro g), was found to be ineffective. These results confirm the involvement of the paraventricular nucleus in the control of erectile function and copulatory behaviour and show that excitatory amino acid concentration increases in the paraventricular nucleus when penile erection occurs in physiological contexts.

A neural network underlying individual differences in emotion and aggression in male golden hamsters

In rodents, aggressive behavior can be altered by experimental manipulations of emotional responsiveness. The goal of this study was to identify characteristics of emotional reactivity associated with individual differences in aggressive behavior and their integration within a common neural network. Male golden hamsters were first screened for offensive aggression. Then, the animals were trained through immediate reinforcement and tested for their adaptation to a delayed reward. Similar protocols have been used to test behaviors associated with frustration. At first, all hamsters showed increased frequency of bar pressing per reward during delayed reinforcement. However, Low-Aggression animals were able to adapt to the delay and showed a decreased rate of bar pressing per reward within 5 days. In contrast, High-Aggression animals maintained a high rate of bar pressing per reward. In addition, brains were collected after immediate reward training or delayed reward testing, and labeled for pCREB-immunoreactivity as a marker of trans-synaptic activity. In High-Aggression individuals, elevated density of cyclic AMP response element binding protein, phosphorylated (pCREB) immunostaining was found within the anterior hypothalamus, an area critical to the control of aggression. Delayed reinforcement was associated with enhanced pCREB immunostaining within the central amygdala, medial amygdala and preoptic area/hypothalamus continuum. Further analysis of the data also showed a positive correlation in labeling density between the lateral septum and the anterior hypothalamus, specifically in Low-Aggression animals exposed to delayed reward. Therefore, as High-Aggression individuals lack control of their emotional reactivity, they are also characterized by a de-synchronization between the inhibitory output of the septum and the aggression areas of the hypothalamus. Finally, our data also show that frustration is associated with an extensive activation of the preoptic area/hypothalamus continuum and amygdala.

Central mechanisms of stress integration: hierarchical circuitry controlling hypothalamo-pituitary-adrenocortical responsiveness

Appropriate regulatory control of the hypothalamo-pituitary-adrenocortical stress axis is essential to health and survival. The following review documents the principle extrinsic and intrinsic mechanisms responsible for regulating stress-responsive CRH neurons of the hypothalamic paraventricular nucleus, which summate excitatory and inhibitory inputs into a net secretory signal at the pituitary gland. Regions that directly innervate these neurons are primed to relay sensory information, including visceral afferents, nociceptors and circumventricular organs, thereby promoting 'reactive' corticosteroid responses to emergent homeostatic challenges. Indirect inputs from the limbic-associated structures are capable of activating these same cells in the absence of frank physiological challenges; such 'anticipatory' signals regulate glucocorticoid release under conditions in which physical challenges may be predicted, either by innate programs or conditioned stimuli. Importantly, 'anticipatory' circuits are integrated with neural pathways subserving 'reactive' responses at multiple levels. The resultant hierarchical organization of stress-responsive neurocircuitries is capable of comparing information from multiple limbic sources with internally generated and peripherally sensed information, thereby tuning the relative activity of the adrenal cortex. Imbalances among these limbic pathways and homeostatic sensors are likely to underlie hypothalamo-pituitary-adrenocortical dysfunction associated with numerous disease processes.

Electrical stimulation of the dorsal hippocampus caused a long lasting inhibition of ACTH and adrenocortical responses to photic stimuli in freely moving rats

The effect of a single train of electrical hippocampal stimulation on ACTH and corticosterone (CS) responses to subsequent photic stimulation was studied in freely moving male rats. The hippocampal stimulation inhibited the stress-induced rise [corrected] in serum CS levels up to 150 h when compared to sham stimulated animals. This effect did not exist at 300 h following stimulation. This sustained hippocampal inhibitory effect on the adrenocortical response, which was not reported previously, was partially abolished by section of the dorsal fornix. The present data demonstrate that dorsal hippocampal stimulation has a long lasting inhibitory effect on pituitary adrenocortical secretion following neural stimuli and this is partially mediated by the dorsal fornix.

Axon terminals containing CGRP-immunoreactivity form synapses with CRF- and Met-enkephalin-immunopositive neurons in the laterodorsal division of the bed nucleus of the stria terminalis in the rat

The lateral division of the bed nucleus of the stria terminalis (BSTL) is an important forebrain structure that relays information between limbic structures and the hypothalamus. The BSTL displays a very dense calcitonin gene-related peptide-immunoreactive (-ir) fiber terminal network, and contains a substantial number of the corticotropin releasing factor (CRF)-ir neurons. Several Met-enkephalin-ir perikarya have also been observed in the BSTL. The distributions of CRF- and Met-enkephalin-ir neurons and that of the calcitonin gene-related peptide (CGRP)-ir axon terminals overlap within the BSTL, suggesting synaptic connections between CRF- and Met-enkephalin-ir neurons and axon terminals immunoreactive for CGRP. Double staining immunohistochemistry revealed that CGRP-ir axon terminals were within close proximity to dendrites or perikarya of corticotropin releasing factor and Met-enkephalin-ir neurons. When viewed at the electron microscopic level, axodendritic or axosomatic synapses between CGRP-ir fiber terminals and neurons immunoreactive for CRF and Met-enkephalin were detected. Most of the CRF-ir neurons project to brainstem centers, which modulate the physiological changes accompanying stress, whereas the Met-enkephalin-ir perikarya are most likely interneurons that often colocalize with GABA. The parabrachial nucleus, a vital autonomic center, is the primary source of CGRP-ir fiber terminals to the BSTL. The synaptic contacts between the CGRP axon terminals and CRF- and Met-enkephalin-ir neurons underlie the importance of connections between autonomic brainstem centers and BSTL, which can be fundamental in the modulatory control of endocrine, physiological and behavioral responses during stress.

Induction and adaptation of Fos expression in the rat brain by two types of acute restraint stress

The present study was designed to examine whether both induction and adaptation of brain Fos expression during acute stress depend on the intensity and duration of stressors. For this purpose, different durations of two types of acute stress, mild (restraint) and severe (immobilization) stress, were employed. Stress-induced Fos expression was analyzed quantitatively by immunohistochemistry. Adaptation of Fos expression to the acute stressors was not apparent in the hypothalamic paraventricular nucleus (PVN) or locus coeruleus (LC) but was observed in the amygdala, hippocampus, and cerebral cortex. A higher level of Fos expression was seen in the PVN, LC, and amygdala, following severe stress than was seen following mild stress. In the hippocampus, the dentate gyrus showed reduced Fos expression in response to stressors, although both mild and severe acute stress increased Fos expression in other regions of the hippocampus. The cingulate cortex showed increased Fos expression during mild stress, whereas long-duration severe stress reduced Fos expression. In the somatosensory cortex, both stressors increased Fos expression. These results indicate that the PVN and LC are relatively resistant to adaptation to acute stress compared to other brain regions. In addition, the PVN, LC, and amygdala may play important roles in the perception of the severity of stress.

Topographical organization of projections from the subiculum to the hypothalamus in the rat

The projections from the subiculum to the hypothalamus were comprehensively examined in the rat by using the anterograde Phaseolus vulgaris leucoagglutinin (PHA-L) and retrograde cholera toxin B subunit (CTb) methods. Tracing of efferents with PHA-L indicated that the medial preoptic region received projection fibers from the temporal two-thirds of the subiculum, whereas the anterior, tuberal, and mammillary regions received those from the full longitudinal extent of the subiculum. The subicular projections to the anterior and tuberal hypothalamic regions were also found to be organized in a topographical manner such that the temporal-to-septal axis of origin in the subiculum determined a ventromedial-to-dorsolateral axis of termination in the medial zone of the hypothalamus: Massive labeled fibers from the temporalmost part of the subiculum terminated in the subparaventricular zone and its caudal continuum around the dorsal and medial aspects of the ventromedial nucleus, and those from progressively more septal parts terminated in progressively more dorsolateral parts of the medial zone. In addition, the temporal-to-septal axis of origin in the subiculum tended to determine a medial-to-lateral axis of termination in the preoptic region as well as a ventral-to-dorsal axis of termination in the mammillary region. Furthermore, the temporal-to-septal axis of origin in the septal two-thirds of the subiculum corresponded to a ventrolateral-to-dorsomedial axis of termination in the medial mammillary nucleus. The topographical projections from the subiculum to the medial zone of the hypothalamus were confirmed by CTb experiments, representatively in the subicular projections to the anterior hypothalamic region. These results suggest that different populations of neurons existing along the longitudinal axis of the subiculum may exert their influences on the execution of different hypothalamic functions.

Medullo adrenal response to lesion of anterodorsal thalamic nuclei in rats

Anterodorsal thalamic nuclei (ADTN) exert an inhibitory influence on hypophyso-adrenal system (HAS) in rats. With the purpose of evaluating if ADTN are also involved in the control of medullo adrenal activity, experiments were conducted on female rats with bilateral lesion of these nuclei. Thirty days after lesion, plasma epinephrine (E) concentration in lesioned rats was higher than that in sham-lesioned control group (P < 0.02). Meanwhile, adrenal E content was significantly lower in lesioned animals than that found in the control group (P < 0.005). Plasma norepinephrine (NE) values in lesioned rats were not significantly different from those in the control ones, however, there was a significant decrease in adrenal NE when compared to the control one (P < 0.02). Basal values of plasma ACTH and plasma and adrenal corticosterone (C) were signicantly higher than those in sham lesioned rats (P < 0.05; P < 0. 001; P < 0.001 respectively). These findings demonstrate that the ADTN in rats are involved in the regulation of both cortico and medullo adrenal activity.

Involvement of the anterodorsal thalami nuclei on the hypophysoadrenal response to chronic stress in rats

Anterodorsal thalami nuclei (ADTN) exert an inhibitory influence on the hypophysoadrenal system (HAS) under basal and acute stress conditions; however, after chronic stress, the effect is different. The response to chronic immobilization stress (IMO) (forced immobilization for 15 min/day for 12 days) and variable chronic stress (V) (24-day exposure to different stressors per day) of plasma ACTH and corticosterone (C) in rats with anterodorsal thalami nuclei lesions was studied. In sham-lesioned rats, chronic immobilization stress and variable chronic stress induced a significant increase in plasma ACTH and C and a reduction of adrenal C content. After exposure of lesioned rats to chronic immobilization stress, there was a decrease of plasma ACTH compared to that in unstressed lesioned rats. In contrast, there was significant increase in ACTH levels after variable chronic stress, this increase being smaller than the variable increase elicited in sham-lesioned rats. In all stressed lesioned animals, plasma C remained unchanged. However, adrenal C content decreased significantly compared to that in unstressed lesioned rats. These findings demonstrate that anterodorsal thalami nuclei lesions attenuated the hypophysoadrenal system response to chronic stress. These data are in contrast to those obtained in previous studies under basal and acute stress conditions. The reason for this discrepancy is at present unknown, and its elucidation will require further studies.

Axon terminals containing PACAP- and VIP-immunoreactivity form synapses with CRF-immunoreactive neurons in the dorsolateral division of the bed nucleus of the stria terminalis in the rat

The bed nucleus of the stria terminalis (BST) is a highly heterogeneous forebrain structure, within which the median and lateral BST play distinct functional roles. The medial BST (BSTM) is thought to be related to sexual behavior, while the lateral BST (BSTL) may have a stress-related function. In the human brain, the BST shows marked sexual dimorphism in the distribution of vasoactive intestinal polypeptide (VIP) immunoreactive fibers and also contains a very high concentration of pituitary adenylate cyclase activating polypeptide (PACAP) immunoreactivity (ir). Using immunohistochemistry (IHC) to examine the rat brain, the present study found that both VIP and PACAP containing afferent fibers are abundant in the BSTLd (dorsolateral division of BST), but not in the BSTM. IHC did not reveal any apparent difference between the sexes in the size of distribution of either immunoreactivity. Double staining IHC showed that axonal terminals of both VIP and PACAP neurons were in close proximity to dendrites or perikarya of corticotropin releasing factor (CRF) neurons. At the electron microscopic level IHC revealed the presence of axodendritic or axosomatic synapses between VIP-ir and PACAP-ir axon terminals and CRF-ir neurons. Although the origin of PACAP-ir fibers in the BSTLd remains to be determined, these morphological findings suggest that PACAP and VIP regulate the activity of CRF neurons in the BSTLd as neurotransmitters or neuromodulators.

Participation of paraventricular nucleus of hypothalamus in central regulation of penile erection in the rat

PURPOSE

To investigate the possible participation of the paraventricular nucleus of hypothalamus in central regulation of penile erection.

MATERIALS AND METHODS

Male adult Sprague-Dawley rats were anesthetized and maintained with pentobarbital sodium. The intracavernous pressure (ICP) was used as an experimental index for penile erection, and was recorded alongside systemic arterial pressure and heart rate. The effect on ICP of electrical (30-s train of 30-120 microA, 40-160 Hz, 1-ms rectangular pulses) or chemical (L-glutamate, 0.5 nmol/50 nl.) activation of the paraventricular nucleus of hypothalamus (PVN) or hippocampal formation was evaluated.

RESULTS

Electrical activation of the PVN elicited both multiple and single episodes of elevation in ICP, along with visible erection and ejaculation. The former pattern exhibited an increase in ICP that was more sustained, with higher peak amplitude and longer latency. Chemical stimulation of neuronal perikarya in the PVN also resulted in similar patterns of rise in ICP and visible erection. These effects were, nonetheless, not accompanied by significant alterations in systemic arterial pressure and heart rate. Activation of the hippocampal formation, as we reported previously, similarly elicited multiple and single episodes of increase in ICP. These erectile responses, however, were substantially reduced or eliminated upon electrolytic lesion of the ipsilateral PVN.

CONCLUSION

These observations suggest that the PVN may be an important nucleus that participates in central neural regulation of penile erection in the rat. Furthermore, an efferent pathway(s) from the hippocampal formation to PVN may constitute part of the neural circuitry in the forebrain in the regulation of erectile functions.

Physiological mapping of local inhibitory inputs to the hypothalamic paraventricular nucleus

Local inhibitory synaptic inputs to neurons of the rat hypothalamic paraventricular nucleus (PVN) were studied by using glutamate microstimulation and conventional intracellular and whole-cell patch-clamp recording in coronal, horizontal, and parasagittal slices of rat hypothalamus. PVN cells were classified as magnocellular or parvocellular neurons on the basis of electrophysiological and post hoc immunohistochemical analyses; GABA-producing neurons were localized with in situ hybridization. Glutamate microstimulation of different sites around the PVN evoked volleys of postsynaptic potentials in 43% of the PVN neurons tested. Some responses to stimulation at each site were blocked by bicuculline, suggesting that they were mediated by the activation of presynaptic GABA neurons. In the coronal plane, presynaptic inhibitory sites were located lateral to the PVN and ventral to the fornix, corresponding to the lateral hypothalamic area and the posterior bed nucleus of the stria terminalis (BNST). In the horizontal plane, presynaptic inhibitory sites were found rostral, lateral, and caudal to the nucleus, corresponding to parts of the anterior hypothalamic area, the posterior BNST, the medial preoptic area, and the dorsomedial hypothalamus. In the parasagittal plane, presynaptic inhibitory neurons were revealed at sites rostral and caudal to the nucleus, corresponding to the medial preoptic area and the dorsomedial hypothalamus, and in a site dorsal to the optic chiasm that included the suprachiasmatic nucleus. These presynaptic sites each contained GABA-producing neurons based on in situ hybridization with a glutamic acid decarboxylase riboprobe and together formed a three-dimensional ring around the PVN. Unexpectedly, both magnocellular and parvocellular neurons received inhibitory synaptic inputs from common sites.

Limbic pathways and hypothalamic neurotransmitters mediating adrenocortical responses to neural stimuli

One of the major phenomena related to the stress response is the activation of the hypothalamo-pituitary-adrenocortical (HPA) axis. This axis consists of corticotropin releasing factor-41 in the paraventricular nucleus of the hypothalamus (PVN), which in response to a variety of stimuli is released into the portal circulation and stimulates pituitary ACTH secretion and subsequently adrenocortical discharge. The mechanisms involved in the activation are not uniform and the responses to various stimuli are mediated by different neural pathways. Since extrahypothalamic limbic structures play a significant role in the HPA function, it is the purpose of this review to describe the neural pathways between the hippocampus, septum and amygdala and the hypothalamus in relation to adrenocortical activity and the differential role of the medial forebrain bundle as well as the effects of various hypothalamic deafferentation on the transmission of the neural impulses to the hypothalamus. Also, the importance of norepinephrine and serotonin in the activation of the HPA axis will be delineated.

Hypothalamic-pituitary-adrenal function in chronic intermittently cold-stressed neonatally handled and non handled rats

Neonatally handled (H) animals, as adults, exhibit lower ACTH and corticosterone (B) responses to a number of acute stressors compared to their non-handled (NH) counterparts. However, little is known about activity within the hypothalamic-pituitary-adrenal (HPA) axis of H and NH animals under conditions of chronic stress. We, therefore, examined HPA function in adult H and NH rats exposed to chronic intermittent cold stress (4 h of 4 degrees C cold a day for 21 days; H CHR and NH CHR) and in control H and NH (H CTL and NH CTL) rats. H CTL and NH CTL animals displayed comparable ACTH and B responses to a single, acute exposure to cold. We found that H CHR animals exhibited lower levels of ACTH, but not B, during the 21st exposure to cold (the homotypic stressor) compared to the first exposure to cold in H CTL; however, ACTH and B levels in NH CHR were not different from those in NH CTL. In contrast, NH CHR animals hypersecreted ACTH and B in response to restraint (the novel, heterotypic stressor) compared to NH CTL and both H groups, whereas H CHR and H CTL animals did not differ in their responses to restraint. These endocrine responses were associated with increased basal median eminence levels of both CRH and AVP in H CHR and NH CHR relative to their control groups (with NH CHR exhibiting the highest absolute levels of each secretagogue), and with decreased glucocorticoid receptor densities in septum of both H CHR and NH CHR. In addition, the expected lower glucocorticoid receptor density in hippocampus and frontal cortex of NH rats compared to H rats was observed. We believe that the difference in glucocorticoid receptor density between H and NH animals in the hippocampus and frontal cortex and the associated differences in secretagogue content in the median eminence are related to the hypersecretion of ACTH and B in the NH CHR relative to the other groups. Furthermore, we hypothesize that an active inhibitory process is involved in the adaptation of HPA responses of H CHR animals to the homotypic stressor, and present a working model of regulation of activity within the CRH/AVP neurons in the PVN.

Neuroendocrine effects of interferon-alpha in the rat

We have previously found that recombinant human interferon-alpha 2A (rHu-IFN-alpha 2A) inhibits hypothalamo-pituitary-adrenocortical (HPA) axis activity following both peripheral and central administration. This effect is antagonized by mu-opioid receptor antagonists, suggesting transduction by this subtype of opioid receptors. We have now demonstrated that this effect is also observed with hybrid rHu-IFN-alpha A/D, rat kidney fibroblast-derived IFN-alpha, and recombinant rat IFN-alpha preparations. The inhibitory effects on HPA activity were observed after intraperitoneal (i.p.) injections of rHu-IFN-alpha2A(10(03)U), rHu-IFN-alpha A/D (10(4)U), and of Rat-IFN-alpha (1-10U). Similar effects were observed with intracerebroventricular (i.c.v.) administration of all four IFN-alpha preparations. No increases in plasma corticosterone concentrations were observed with doses of rHu-IFN-alpha A/D up to 10(6)U (i.p.) or 7x10(5)U (i.c.v.), but increases were found following i.c.v. administration of high doses of Rat-IFN-alpha (10(3) and 5x10(3)U). The inhibitory effects of all of the IFN-alpha preparations tested were antagonized by naloxone, but the stimulatory effects of 5x10(3)U Rat-IFN-alpha were not. Injections of rHu-IFN-alpha 2A(10(4)U, i.p.) to urethane-anesthetized rats decreased the electrical activity of the majority of hypothalamic paraventricular nucleus (PVN) neurons tested, including putative corticotropin-releasing factor-(CRF)-secreting neurons antidromically identified as projecting to the median eminence. Similarly, iontophoretic application of rHu-IFN-alpha 2A decreased the electrical activity of such cells. These electrophysiological data suggest that the decreases in HPA activity evoked by IFN-alpha are mediated, at least in part, by a rapid inhibitory effect at the level of the corticotropin-releasing factor-secreting neurons.

Ventral subicular interaction with the hypothalamic paraventricular nucleus: evidence for a relay in the bed nucleus of the stria terminalis

The axonal projections of the ventral subiculum to the bed nucleus of the stria terminalis (BST) were examined in the rat with the anterograde neuronal tracer Phaseolus vulgaris-leucoagglutinin (PHA-L). Axons originating in the ventral subiculum coursed to the BST through either the fimbria-fornix, or a pathway involving the stria terminalis via the amygdala. Ventral subicular axons gave rise to dense terminal networks that were preferentially distributed in medial and ventral subregions of the BST. The distribution of subicular fibers and terminals was examined in relation to BST neurons that project to the hypothalamic paraventricular nucleus (PVN). In these cases, discrete iontophoretic injections of the retrograde tracer Fluoro-gold were made in the PVN, with PHA-L delivered to the ipsilateral ventral subiculum. An immunocytochemical double-labeling protocol was then employed for the simultaneous detection of PHA-L and Fluoro-gold, and provided light microscopic evidence for subicular input to PVN-projecting cells located within the BST. In a second series of experiments, the gamma-amino butyric acid (GABA)ergic nature of the BST was examined by in situ hybridization histochemistry for detection of transcripts encoding GAD67 mRNA. The studies revealed that a high proportion of BST neurons express GAD67 transcripts. Also, experiments combining Fluoro-gold tracing with GAD67 in situ hybridization suggested that a proportion of PVN-projecting neurons in the BST are GABAergic. Taken together, the results of these sets of studies suggest that the inhibitory influences of the hippocampus on the PVN might be relayed through specific portions of the BST. These findings may have important implications for our understanding of the neural regulation of the hypothalamic-pituitary-adrenal axis.

Selective forebrain fiber tract lesions implicate ventral hippocampal structures in tonic regulation of paraventricular nucleus corticotropin-releasing hormone (CRH) and arginine vasopressin (AVP) mRNA expression

The hippocampus appears to be involved in tonic regulation of the hypothalamo-pituitary-adrenocortical axis via interactions with corticotropin-releasing hormone (CRH) and arginine vasopressin (AVP)-containing neurons of the hypothalamic paraventricular nucleus (PVN). To further investigate the anatomical basis of such interactions, lesions were made to forebrain fiber tracts in position to communicate inhibitory information from the hippocampus to the PVN. Total fimbria-fornix transections (TFF) and lateral fimbria-fornix lesions (LFF) both significantly increased CRH mRNA levels in the medial parvocellular PVN, as assayed by semi-quantitative in situ hybridization histochemistry. Medial fimbria-fornix lesions or section of the medial corticohypothalamic tracts (MCHT) did not influence CRH mRNA levels. The LFF group showed increases in both AVP mRNA and ACTH secretion, whereas no other lesion was effective in this regard. The results suggest: (1) hippocampal efferents conferring tonic inhibition of the HPA axis probably originate in regions contributing to the lateral extent of the fornix, representing structures in the ventral subiculum and ventral extent of CA1; (2) projections from the hippocampus to the medial basal hypothalamus (travelling in the MCHT) are unlikely to affect HPA function; (3) hippocampus may influence the PVN CRH/AVP neuron at multiple levels, in that LFF and TFF lesions have differential effects on PVN AVP mRNA levels and ACTH secretion.

Hippocampal oxytocin mediates apomorphine-induced penile erection and yawning

Repeated episodes of penile erection and yawning can be induced in male rats either by low doses of the dopaminergic agonist apomorphine or by oxytocin given systematically or into a lateral ventricle (ICV), respectively, or after microinjection of the two substances directly in the paraventricular nucleus (PVN) of the hypothalamus. These behavioral responses are prevented in a dose-dependent manner by the ICV administration of the potent oxytocin antagonist d(CH2)5Tyr(Me)-Orn8-vasotocin. In contrast, the PVN injection of d(CH2)5Tyr(Me)-Orn8-vasotocin (1-30 ng), while effective in preventing oxytocin effect, was unable to prevent apomorphine response. On the other hand, apomorphine-, but not oxytocin-induced penile erection and yawning was prevented by electrolytic lesion of the medial septum (MS). Such a lesion decreased oxytocin content by about 45% in the hippocampus. The above results suggest that the hypothalamic-hippocampal oxytocinergic pathway mediates apomorphine-induced penile erection and yawning and that oxytocin is involved at different levels in the CNS for the control of these behavioral responses.

Distribution of 72-kDa heat-shock protein in rat brain after hyperthermia

The distribution of the 72-kDa heat-shock protein (hsp72) in rat brain, 24 h following in vivo transient hyperthermia (41.5 degrees C, 15 min), was studied using immunohistochemistry (n = 22). Tissue sections were also stained with hematoxylin and eosin, and with an anti-glial fibrillary acidic protein to evaluate neuronal and astrocytic response to transient hyperthermia, respectively. hsp72 was observed in glia and endothelial cells throughout brain. hsp72 was also found in neurons located in the: dentate gyrus, habenula, and hypothalamus, granular layer of the cerebellum and the olfactory area. Our data indicate, that hyperthermia causes neuronal expression of hsp72, particularly in cerebral neuronal populations which control the neuroendocrine stress response.

Lesions of the central nucleus of the amygdala block the excitatory effects of septal ablation on the acoustic startle reflex

Many studies have investigated the role of the septum and the amygdala in emotional behavior. While the literature is somewhat inconsistent, most studies suggest a role for the septal nuclei in the inhibition of fear and stress responses (at the behavioral, autonomic and hormonal levels) while the central nucleus of the amygdala is involved in the production of such responses. The present study examined the ability of lesions of the central nucleus of the amygdala to block the excitatory effects of complete septal ablation on the acoustic startle reflex. Septal ablation produced a significant increase in startle amplitude which was blocked by concomitant lesions of the central nucleus of the amygdala. These results suggest that the increase in startle amplitude resulting from septal damage might be due to a disinhibition of neuronal activity in the central nucleus of the amygdala, a structure known to mediate the increase in startle associated with conditioned and unconditioned fear, or from antagonistic interactions at other target sites which themselves modulate startle.

Cortisol exerts site-, context- and dose-dependent effects on agonistic responding in hamsters

Abstract Site-, context- and dose-dependent actions of intrahypothalamic cortisol administration on the agonistic behaviors of adult male golden hamsters (n = 128 dyads) were examined. When cortisol-treated animals were tested in paired encounters with aggressive cholesterol-treated opponents, chronic (>/= 24 h) cortisol treatment (1 mm implants) induced significant (P < 0.05) submission in three medial hypothalamic areas (anterior hypothalamic area > medial preoptic area > ventromedial hypothalamus), but aggression in the paraventricular nucleus or third ventricle. In contrast, chronic cortisol treatment in the anterior hypothalamic area resulted in high levels of aggression during paired encounters with submissive opponents, and during territorial aggression tests with juvenile male intruders. Acute (>/= 20 min) cortisol treatment in the anterior hypothalamic area (100 nl injections) induced significant submission after 10(-2) M, but significant aggression after 10(-6) M microinjections in paired encounters with aggressive vehicle-injected opponents. These findings suggest glucocorticoid-sensitive mechanisms within the anterior hypothalamus modulate aggressive responding during intrasexual social encounters.

Paraventricular nucleus magnocellular neuronal responses following electrical stimulation of the midbrain dorsal raphe

In order to determine the responses of paraventricular nucleus magnocellular neurones following activation of central serotonergic pathways, single unit activity was recorded and responses following electrical stimulation of the midbrain dorsal raphe nucleus were examined. Approximately one third (32%) of the phasically active, vasopressin-secreting neurones were inhibited by the stimulation, the remaining such cells being nonresponsive. In contrast, only two of the non-phasic cells (13%) were inhibited by the stimulation whilst 53% were excited (p less than 0.005, chi2-test). The onset latency of both inhibitory and excitatory responses were similar, whilst offset of the inhibitory responses was about twice that of the excitatory responses (p less than 0.005, t-test). Two of the non-phasic cells were antidromically identified as projecting to the dorsal raphe. The results obtained indicate a role for dorsal raphe projections to the paraventricular nucleus in the regulation of neurohypophysial hormone secretion. The observation that different sub-populations of the cells recorded showed different responses, suggests that several mechanisms may be involved in the control of neuronal activity in the region recorded, in response to activation of the central serotonergic pathway examined. The results obtained are intended to further clarify the neural mechanisms regulating the secretion of vasopressin and oxytocin from the neurohypophysis.

Further Evidence that the Septum is not part of the Main Pathway of the Milk Ejection Reflex in the Rat

Abstract The possible role of the medial septum in the control of oxytocin release and of the milk ejection reflex induced by suckling was investigated in lactating rats by using electrical stimulations and lesions. In anaesthetized animals, brief electrical stimulation of the medial septum at 5 to 50 Hz elicited a single brief milk ejection similar to natural reflex milk ejections, whereas prolonged low frequency stimulations (5 to 10 Hz) induced a prolonged inhibition of the reflex. In acute experiments under anaesthesia, lesions of the medial septum did not impair the amplitude and pattern of reflex milk ejections. In chronic experiments, lesions of the medial septum resulted first in a loss of body weight of the mothers and a parallel reduction in growth of the litters. After a few days, the litters gained weight normally, and the pattern of milk ejections was normal. Thus, the pathways which pass through or originate from the medial septum and which are excitatory for oxytocin release appear not to be involved in the regulation of the milk ejection reflex. In view of these results and those from our previous study on the lateral septum, we conclude that the whole septum is not essential to the milk ejection reflex. However, the effects of septal stimulation suggest that the medial and lateral septum may be involved in a secondary neural circuitry that can inhibit the reflex.

Selective facilitation of putative corticotropin-releasing factor-secreting neurones by interleukin-1

The activity of single hypothalamic paraventricular nucleus (PVN) neurones was recorded in order to examine the mechanism by which the endogenous pyrogen interleukin-1 (IL-1) increases activity of the hypothalamo-hypophyseal-adrenocortical axis. IL-1 injected intravenously caused a rapid increase in the electrical activity of putative corticotropin-releasing factor (CRF)-secreting neurones located within the PVN. The activity of neighboring, electrophysiologically identified, vasopressin-secreting neurones was not altered by the stimulus, indicating a lack of involvement of this secretagogue of adrenocorticotropic hormone (ACTH) in this response to IL-1. These results support the concept of a rapid and specific activating effect of IL-1 upon hypothalamic CRF secretion as a part of a bidirectional communicating link between immune and central nervous systems.

In vivo hyperthermia induces expression of HSP70 mRNA in brain regions controlling the neuroendocrine response to stress

Regional localization of HSP70 expression in brain of rats exposed to increased ambient temperatures was examined using in situ hybridization. In addition to the cerebellar granule cell layer and choroid plexus, selective hybridization was observed in the hippocampal dentate gyrus, paraventricular and dorsomedial hypothalamic nuclei, median eminence, and medial habenula. Apparently, cells in brain regions coordinating the neuroendocrine response to stress show a preferential induction of cellular stress proteins in response to heat.

Hypercortisolism and its possible neural bases

As is clear from the pages of this journal, biological psychiatrists remain fascinated by the phenomenon of dexamethasone (DEX) resistance and the hypercortisolism of various neuropsychiatric disorders. The mere existence of the endocrine abnormalities attests to the biological reality of these disorders. Furthermore, progress continues in using the occurrence of these endocrine defects as both diagnostic and prognostic markers of disease subtypes. Progress has also been made in understanding the mechanisms underlying the endocrine defects. The adrenocortical axis is vastly complex, involving multiple hypothalamic-releasing factors under CNS control, shifting pituitary and adrenal sensitivies to hormonal signals, and feedback regulation at all three levels. What defects within this system produce DEX resistance and hypercortisolism? In this paper, we review data suggesting that the endocrine problems is, at least in part, neural in nature. Drawing upon a rodent literature, we will also suggest some models by which this can occur. The hypercortisolism found in cases of affective disorders, anorexia nervosa, Alzheimer's disease, among the very aged or the chronically stressed, is not a uniform phenomenon. Basal cortisol concentrations can be elevated in all or part of the circadian cycle. Resistance to glucocorticoid (GC) feedback inhibition (as typically demonstrated by DEX resistance) can occur; the resistance can be complete, or occur as early escape from DEX suppression. Finally, elevated basal cortisol concentrations and DEX resistance can occur independently of each other. Until the end of this review, we will conveniently refer to these variants of adrenocortical hyperactivity as "hypercortisolism." In addition, rather than using the term "hypercortisolism" for the rat, we will use "hyperadrenocorticism" (as they secrete corticosterone, rather than cortisol).

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 projections to tuberoinfundibular neurones of the paraventricular nucleus: I. Effects of stimulation of A1, A2, A6 and C2 cell groups

Extracellular electrical activity was recorded from 203 paraventricular nucleus (PVN) neurones antidromically identified as projecting to the median eminence. Spontaneous activity and the effects of stimulation of the A1, A2, A6 and C2 catecholaminergic cell groups upon the PVN neurones were examined. Cells were located at a mean height 2.29 +/- 0.03 mm above the base of the brain, corresponding with the corticotropin-releasing factor (CRF) rich component of the nucleus. The mean firing rate was 3.2 +/- 0.3 Hz and antidromic invasion latency was 9.9 +/- 0.3 msec. Seventy-six % of cells tested were activated by painful somatosensory stimuli. Electrical stimulation of the A1 or A2 region evoked excitatory responses from the majority of cells tested (76% and 85%, respectively), whilst stimulation of the A6 and C2 regions evoked more inhibitory responses (43% and 59%, respectively). Most responses (56%), whether excitatory or inhibitory, were not clearly defined in terms of latency, and were only observed following delivery of 5-10 single shocks at 0.5 Hz. Excitation recorded following A1 and A2 stimulation suggests a facilitatory role for noradrenaline in the regulation of PVN activity. Inhibitory responses following C2 stimulation indicate that adrenaline may serve to inhibit such activity, whilst the more mixed responses following A6 stimulation suggest that the projections of this region differ in some way from those of the A1 and A2 cells. Response reversals were observed, after delivery of higher frequency stimulation, for a substantial proportion (20%) of the cells tested.

Neurophysiological and endocrine consequences of immune activity

The studies presented herein demonstrate the potency with which activity of the immune system is able to influence the central nervous system. Electrophysiological recordings have demonstrated significant changes in preoptic area/anterior hypothalamic (PO/AH) multiunit electrical activity (MUA) following sensitization with sheep red blood cells. The peak of activity occurred on the fifth day after immunization, the same day that serum antibodies were first detected. A significant increase in paraventricular nucleus MUA was also demonstrated, but this appeared to be delayed with respect to that in the PO/AH, occurring on the sixth day. Further changes thought to be associated with the immune response also were found: Serum corticosterone levels were elevated on the eighth day of the response, and PO/AH tissue levels of norepinephrine were reduced between the sixth and tenth days. During induction of a secondary response, PO/AH MUA showed a different profile of activity from that recorded during the first response. Chronic administration of the immunosuppressive drug, cyclophosphamide, prevented the recorded changes in PO/AH MUA. These results suggest that some secretory product(s) of the activated immune system may be able to exert effects on the central nervous system. Various immunoactive substances therefore were administered intra-cerebroventricularly in order to examine their effects upon PO/AH MUA, cortical EEG and adrenocortical hormone secretory activity. alpha-Interferon and thymic humoral factor were both found to decrease PO/AH MUA, increase EEG synchronization, and decrease basal levels of circulating corticosterone. In contrast, histamine and interleukin-1 did not alter PO/AH MUA but did cause decreased EEG synchronization and increased serum corticosterone levels. With another preparation, a specific activating effect of interleukin-1 upon putative corticotropin-releasing factor-secreting neurones has also been found, identified vasopressinergic neurones not being affected.

Corticosterone and dexamethasone act at different brain sites to inhibit adrenalectomy-induced adrenocorticotropin hypersecretion

To investigate the involvement of different brain sites in the mediation of glucocorticoid feedback action, we implanted dexamethasone or corticosterone containing glass capillaries into the paraventricular and arcuate nuclei of the hypothalamus, into the lateral septum, the dorsal and ventral hippocampus, amygdala and the cerebral cortex of adrenalectomized male rats, and compared the plasma adrenocorticotropin (ACTH) values to those of the sham implanted controls. The ACTH hypersecretion of adrenalectomized (ADX), sham implanted rats (670 fmol/ml) was reduced significantly by dexamethasone implants placed into the paraventricular nucleus (9.97 fmol/ml), arcuate nucleus (20.54 fmol/ml) or lateral septum (44.15 fmol/ml). Corticosterone was effective only when placed into the dorsal hippocampus, but normal ACTH levels were not restored (219.67 fmol/ml). All other implants at other sites had no effect on ACTH secretion. Our results suggest that corticosterone and dexamethasone possess different feedback potencies and act at different sites in the brain to normalize the ADX-induced ACTH secretion.

Coordinate hormonal and synaptic regulation of vasopressin messenger RNA

Previous studies have shown that adrenalectomy augments arginine vasopressin (AVP) messenger RNA levels in the adult paraventricular nucleus. It is now demonstrated that unilateral lesions in the lateral septal nucleus enhance the adrenalectomy-induced expression of AVP mRNA. This effect was entirely ipsilateral to the lesion and most prominent in the rostral paraventricular nucleus and related nuclei. Moreover, AVP and AVP mRNA were found to be colocalized with oxytocin in a few neurons. These results indicate that mRNA expression is modulated by synaptic influences and raise the possibility that synaptically mediated selection of neuronal phenotypes is a dynamic feature of the mature central nervous system.

Iontophoretic application of glucocorticoids inhibits identified neurones in the rat paraventricular nucleus

In an electrophysiological study designed to examine the negative feedback effects of glucocorticoid hormones, we have recorded the electrical activity of 147 neurones in the paraventricular nucleus of the rat hypothalamus. 37 (25%) of the neurones were antidromically identified as projecting to the median eminence and were located at a mean depth of 2.35 +/- 0.08 mm from the base of the brain, corresponding with the corticotropin-releasing factor-rich region of the nucleus. The mean firing rate of the identified cells was 4.7 +/- 0.6 Hz which was not significantly different from that of adjacent, unidentified cells (5.6 +/- 0.6 Hz). Most (17/18, 94%) of these cells tested responded to painful somatosensory stimuli and 26 (74%) of the identified cells were inhibited by iontophoretic application of corticosterone and/or hydrocortisone, whereas only one cell was excited and 8 unaffected. Of the identified cells, only 18 (20%) were inhibited, 36 (41%) were excited and 34 (39%) were non-responsive. The proportion of inhibitory responses was thus greater for the identified cells (P less than 0.005; chi 2-test). For the identified cells, whose spontaneous activity was unaffected by glucocorticoid application, glutamate-evoked responses could usually be depressed by the application. The time course of all responses usually showed an immediate onset, increasing in magnitude and continuing for extended periods following cessation of iontophoresis. Electrophysiologically identified magnocellular neurones were also tested and the majority (7/12, 58%) of vasopressin-secreting neurons were also found to be inhibited, whilst all (8/8, 100%) of the oxytocin-secreting neurones were excited by the glucocorticoid application. These results may represent an electrophysiological correlate of the negative feedback control of adrenocortical secretion and are discussed within this context.