Influence of electrical stimulation and lesion in limbic structure upon biosynthesis of adrenocorticoid in the rabbit

Sex differences in the vulnerability of the hippocampus to prenatal stress

Distressing events during pregnancy that engage activity of the body's endocrine stress response have been linked with later life cognitive deficits in offspring and associated with developmental changes in cognitive-controlling neural regions. Interestingly, prenatal stress (PS)-induced alterations have shown some sex specificity. Here, we review the literature of animal studies examining sex-specific effect of physical PS on the function and structure of the hippocampus as hippocampal impairments likely underlie PS-associated deficits in learning and memory. Furthermore, the connectivity between the hypothalamic-pituitary-adrenal (HPA) axis and the hippocampus as well as the heavy presence of glucocorticoid receptors (GRs) in the hippocampus suggests this structure plays an important role in modulation of activity within stress circuitry in a sex-specific pattern. We hope that better understanding of sex-specific, PS-related hippocampal impairment will assist in uncovering the molecular mechanisms behind sex-based risk factors in PS populations across development, and perhaps contribute to greater precision in management of cognitive disturbances in this vulnerable population.

UV-Induced Neuronal Degeneration in the Rat Cerebral Cortex

Irradiation with ultraviolet (UV) light on the cortical surface can induce a focal brain lesion (UV lesion) in rodents. In the present study, we investigated the process of establishing a UV lesion. Rats underwent UV irradiation (365-nm wavelength, 2.0 mWh) over the dura, and time-dependent changes in the cortical tissue were analyzed histologically. We found that the majority of neurons in the lesion started to degenerate within 24 h and the rest disappeared within 5 days after irradiation. UV-induced neuronal degeneration progressed in a layer-dependent manner. Moreover, UV-induced terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) positivity and heme oxygenase-1 (HO-1) immunoreactivity were also detected. These findings suggest that UV irradiation in the brain can induce gradual neural degeneration and oxidative stress. Importantly, UV vulnerability may vary among cortical layers. UV-induced cell death may be due to apoptosis; however, there remains a possibility that UV-irradiated cells were degenerated via processes other than apoptosis. The UV lesion technique will not only assist in investigating brain function at a targeted site but may also serve as a pathophysiological model of focal brain injury and/or neurodegenerative disorders.

A Comprehensive Overview on Stress Neurobiology: Basic Concepts and Clinical Implications

Stress is recognized as an important issue in basic and clinical neuroscience research, based upon the founding historical studies by Walter Canon and Hans Selye in the past century, when the concept of stress emerged in a biological and adaptive perspective. A lot of research after that period has expanded the knowledge in the stress field. Since then, it was discovered that the response to stressful stimuli is elaborated and triggered by the, now known, stress system, which integrates a wide diversity of brain structures that, collectively, are able to detect events and interpret them as real or potential threats. However, different types of stressors engage different brain networks, requiring a fine-tuned functional neuroanatomical processing. This integration of information from the stressor itself may result in a rapid activation of the Sympathetic-Adreno-Medullar (SAM) axis and the Hypothalamus-Pituitary-Adrenal (HPA) axis, the two major components involved in the stress response. The complexity of the stress response is not restricted to neuroanatomy or to SAM and HPA axes mediators, but also diverge according to timing and duration of stressor exposure, as well as its short- and/or long-term consequences. The identification of neuronal circuits of stress, as well as their interaction with mediator molecules over time is critical, not only for understanding the physiological stress responses, but also to understand their implications on mental health.

Focal brain lesions induced with ultraviolet irradiation

Lesion and inactivation methods have played important roles in neuroscience studies. However, traditional techniques for creating a brain lesion are highly invasive, and control of lesion size and shape using these techniques is not easy. Here, we developed a novel method for creating a lesion on the cortical surface via 365 nm ultraviolet (UV) irradiation without breaking the dura mater. We demonstrated that 2.0 mWh UV irradiation, but not the same amount of non-UV light irradiation, induced an inverted bell-shaped lesion with neuronal loss and accumulation of glial cells. Moreover, the volume of the UV irradiation-induced lesion depended on the UV light exposure amount. We further succeeded in visualizing the lesioned site in a living animal using magnetic resonance imaging (MRI). Importantly, we also observed using an optical imaging technique that the spread of neural activation evoked by adjacent cortical stimulation disappeared only at the UV-irradiated site. In summary, UV irradiation can induce a focal brain lesion with a stable shape and size in a less invasive manner than traditional lesioning methods. This method is applicable to not only neuroscientific lesion experiments but also studies of the focal brain injury recovery process.

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.

Inhibitory effects of electroacupuncture on stress responses evoked by tooth-pulp stimulation in rats

The mechanism of electroacupuncture (EA) on the stress responses induced by tooth-pulp stimulation was investigated in anesthetized adult female Sprague-Dawley rats. The Hoku point in the Chinese meridian was used for acupuncture stimulation. Constant rectangular current (1 mA) pulses of 5-ms duration were delivered at 3 Hz through a pair of needles for 15 min. As for stress response indexes, we have monitored changes in arterial blood pressure and the levels of blood catecholamines, corticosterone, and ACTH. Arterial blood pressure was increased by high frequency stimulation (0.1 mA, 0.5 ms, 100 Hz for 15 s) of tooth-pulp in the control condition. After EA, we did not observe the same responses of the arterial blood pressure changes with the same stimuli. The tooth-pulp stimulation increased the concentrations of plasma norepinephrine (NE), epinephrine (E), dopamine (DA), corticosterone, and ACTH significantly from the levels of those before stress. After treatment with EA, the stress-induced increase in NE, DA, corticosterone, and ACTH but not the rise in E, were inhibited. When naloxone, an opioid antagonist, was administered intraperitoneally before EA, the effects of EA on stress responses were reduced. In this study, it can be suggested that EA has not only an analgesic effect but also suppressive effects on the stress responses primarily through the mediation of an endogenous opioid.

Aging in the hippocampus: interrelated actions of neurotrophins and glucocorticoids

Over the past two decades, evidence has been accumulating that diffusible molecules, such as growth factors and steroids hormones, play an important part in neural senescence, particularly in the hippocampus. There is also evidence that these molecules do not act as independent signals, but show interrelated regulation and cooperative control over the aging process. Here, we review some of the changes that occur in the hippocampus with age, and the influence of two classes of signaling substances: glucocorticoids and neurotrophins. We also examine the interactions between these substances and how this could influence the aging process.

Role of interleukin-1 in stress responses. A putative neurotransmitter

Recently, the central roles of interleukin-1 (IL-1) in physical stress responses have been attracting attention. Stress responses have been characterized as central neurohormonal changes, as well as behavioral and physiological changes. Administration of IL-1 has been shown to induce effects comparable to stress-induced changes. IL-1 acts on the brain, especially the hypothalamus, to enhance release of monoamines, such as norepinephrine, dopamine, and serotonin, as well as secretion of corticotropin-releasing hormone (CRH). IL-1-induced activation of the hypothalamo-pituitary-adrenal (HPA) axis in vivo depends on secretion of CRH, an intact pituitary, and the ventral noradrenergic bundle that innervates the CRH-containing neurons in the paraventricular nucleus of the hypothalamus. Recent studies have shown that IL-1 is present within neurons in the brain, suggesting that IL-1 functions in neuronal transmission. We showed that IL-1 in the brain is involved in the stress response, and that stress-induced activation of monoamine release and the HPA axis were inhibited by IL-1 receptor antagonist (IL-1Ra) administration directly into the rat hypothalamus. IL-1Ra has been known to exert a blocking effect on IL-1 by competitively inhibiting the binding of IL-1 to IL-1 receptors. In the latter part of this review, we will attempt to describe the relationship between central nervous system diseases, including psychological disorders, and the functions of IL-1 as a putative neurotransmitter.

Psychological and physiological responses to stress: the right hemisphere and the hypothalamo-pituitary-adrenal axis, an inquiry into problems of human bonding

In addition to repeated reexperiencing of the event, the delayed effects of severe psychological trauma, i.e., post traumatic stress disorder (PTSD), present a paradoxical mix of symptoms. There is enhancement of the self-preservative catecholamine states; anger and fear with a contrasting sense of meaninglessness and a blunting of the emotional responses of the attachment behavior so critical for species preservation. Hormonally, there is a striking separation of the catecholamine response, which stays elevated and that of the hypothalamo-pituitary-adrenal (HPA) axis, which may remain at normal levels. Pathophysiologically, the reexperiencing of the trauma and the arousal may be associated with dysfunction of the locus coeruleus, amygdala and hippocampal systems. This article explores the consequences of an additional dysfunction: a dissociation of the hemispheres that appears to be responsible for the alexithymic avoidance and failure of the cortisol response that so often follow severe psychological trauma. There is neurophysiological evidence that the left and right hemispheres subserve different emotional sets that correspond to "control" and "appraisal," i.e., very approximately to the self and species preservative behavioral complexes, respectively. Several studies point to physiological dissociation of hemispheric functions during alexithymia. This raises the question: What has been lost if in this condition the right side no longer fully contributes to integrated cerebral function? Right hemispheric damaged children lose critical social skills and in adults the related sense of familiarity critical for bonding is lost. Such losses of social sensibilities may account for the lack of empathy and difficulties with bonding found in sociopathy and borderline personality: conditions now believed to result from repeated psychological trauma during development. On the other hand, systems that promote right hemispheric contributions provide solacing access to a "Higher Power." They also appear to protect against socially disordered behavior, substance abuse, the failure of the HPA axis and some aspects of the pathophysiology of chronic disease.

Interaction of some limbic structures which exert inhibitory effect on corticosterone secretion

The interaction between limbic structures which exert inhibitory influence on corticosterone secretion was investigated in the rat. The following experiments were performed: 1) electrical stimulation at mammillary medial nucleus (MMN) in rats with lesioned anterodrosal thalami nucleus (ADTN) or intermediate tegmental area; 2) electrical stimulation at ADTN in rats with lesioned retrosplenial cortex (RC). Bilateral stimulation at MMN in ADTN or RC-lesioned rats produces an increase in plasma corticosterone concentration. In animals with lesioned RC, values of plasma corticosterone after stimulation at ADTN were higher than before stimulation. Taking into consideration that electrical stimulation of MMN or ADTN in intact rats produces a decrease in plasma corticosterone concentration, these studies demonstrate that MMN and ADTN exert inhibitory influence on corticoadrenal activity only when their projection areas remain intact.

Dexamethasone and corticosterone receptor sites. Differential topographic distribution in rat hippocampus revealed by high resolution autoradiography

High resolution light microscopic autoradiography was used, together with regional surveys and combined acridine orange staining, to define in rat hippocampus cellular and subcellular sites of concentration and retention of 3H dexamethasone and to compare the topographic pattern of labeling with that of 3H corticosterone. Nuclear uptake of 3H dexamethasone in the hippocampus is demonstrated for the first time in vivo. With 3H dexamethasone, strongest nuclear radioactive labeling was observed in certain glial cells throughout the hippocampus, followed by strong nuclear labeling in most neurons in area CA1 and in the adjacent dorsolateral subiculum and weak nuclear labeling in granule cells of the dentate gyrus. Neurons in areas CA2, CA3, CA4, and in the dorsomedial subiculum and indusium griseum showed little or no nuclear labeling after 3H dexamethasone. With 3H corticosterone, strongest nuclear labeling was observed in neurons in area CA2 and in the dorsomedial subiculum and indusium griseum, followed by area CA1, then CA3 and CA4; the dentate gyrus contained scattered strongly labeled cells among cells with intermediate nuclear labeling. At the subcellular level, evidence for both nuclear and cytoplasmic accumulation of label was found. The results indicate that dexamethasone and corticosterone have both nuclear and cytoplasmic binding sites and that particular patterns of target cell distribution exist, characteristic for each agent. This suggests a differential regulation of cellular functions for the two compounds. Corticosterone nuclear binding appears to be more extensive and encompasses regions with dexamethasone binding. Whether in certain of these common regions corticosterone binds to the same receptor as dexamethasone, which seems possible, or to different receptors, remains to be clarified.

Effects of trimethyltin on the mouse hippocampus and adrenal cortex

The effects of trimethyltin (TMT) on the mouse adrenal histology and its relationship with neuropathology occurrence was studied. Young, male CD-1 mice were divided into three groups: group I, injected on 3 consecutive days with 1.0 mg TMT/kg body weight (b.w.); group II, injected on 2 consecutive days with 1.5 mg TMT/kg b.w.; and group III, injected with a single acute dose of 3.0 mg TMT/kg b.w. Control animals were injected with saline solution. The brain and adrenal glands were sampled for light-microscopic examination. Although all animals received the same total amount of TMT, pathological changes in the granule cells of the fascia dentate appeared to be group III greater than group II greater than group I, suggesting that acute exposures produced a more severe damage to the fascia dentate neurons. Likewise, the adrenal weights of the animals were group III greater than group II greater than group I greater than or equal to control. Significant proliferation and enlargement of the eosinophilic or the "X zone" were observed in the TMT-treated, particularly groups II and III, animals. The expansion of the eosinophilic cell layer (X zone) was accomplished at the expense of the cortical fasciculata cells. Transformation of fasciculata cells into eosinophilic cells could also be demonstrated. As the eosinophilic cells are known to be active in corticosterone production as seen in stress situations, the proliferation of these cells may reflect a feedback response to the hippocampal hyperexcitation.

Influence of cadmium chloride, mercuric chloride, and sodium vanadate on the glutathione-conjugating enzyme system in liver, kidney, and brain of mice

Sublethal doses of CdCl2 (3 mg/kg iv), HgCl2 (2 mg/kg iv), or NaVO3 (6 mg/kg iv) did not alter the content of reduced glutathione (GSH) in the livers of mice during the 24-h observation period. In the kidneys, a tendency to increased GSH content was seen, especially after HgCl2 treatment; in lung and brain the GSH levels were significantly lowered upon the treatment with all three metals. The activities of GSH S-transferase toward an aryl substrate (CDNB; 1-chloro-2,4-dinitrobenzene) was enhanced in all tissues by the administration of HgCl2 greater than NaVO3 greater than CdCl2. The activity of GSH S-transferase toward an epoxide substrate [1,2-epoxy-3-(p-nitrophenoxy)propane was only measurable in the livers and was inhibited 1 and 2 h after the administration of HgCl2 and NaVO3. It is concluded that sublethal doses of CdCl2, HgCl2, or NaVO3 do not impair the GSH concentration and GSH-conjugating enzyme activities toward the aryl substrate in different target organs of their toxicity, which is in contrast to results obtained in vitro.

Neuroendocrine effects of limbic activation by electrical, spontaneous, and pharmacological modes: relevance to the pathophysiology of affective dysregulation in psychiatric disorders

1. Literature is reviewed that implicates various limbic structures (particularly amygdala and hippocampus) in the modulation of stress-associated neuroendocrine systems. 2. Procaine and related local anesthetics may show a selective proclivity for activating limbic structures. 3. Procaine stimulates ACTH-cortisol and prolactin, but not growth hormone secretion. This pattern is most comparable to that elicited by stimuli which act bilaterally on temporal lobe and limbic areas. 4. Procaine may be a useful agent for helping to elucidate the anatomic and physiologic basis for mood, endocrine, and cognitive dysregulation associated with stress and affective disorders. 5. The endocrine concomitants of limbic activation may have relevance to the course and symptom complex of affective disorders and related psychiatric conditions.

Differential effects of medial forebrain bundle lesions on adrenocortical responses following limbic stimulation

Adult male rats had electrolytic lesions placed bilaterally in the medial forebrain bundle and were subsequently implanted with stimulating electrodes in one of the following limbic regions: (1) dorsal hippocampus; (2) ventral hippocampus; (3) medial septal nucleus; (4) basolateral amygdala; (5) mesencephalic reticular formation. Following electrical stimulation, blood was drawn by acute venesection, under either, for plasma corticosterone determinations. In non-lesioned animals, electrical stimulation in all of the limbic regions led to elevated plasma corticosterone levels. In rats with lesions in the medial forebrain bundles, the adrenocortical response to stimulation in the dorsal hippocampus, the basolateral amygdala or the reticular formation was markedly attenuated. On the contrary, the same lesions were without effect upon the corticosterone secretory response to medial septal stimulation, and had only a slight inhibitory effect upon the response to electrical stimulation in the ventral hippocampus. The results demonstrate that the medial forebrain bundle plays a major role in the transmission of impulses to the mediobasal hypothalamus, originating in the dorsal hippocampus, basolateral amygdala or mesencephalic reticular formation, which activate adrenocortical secretion; its role in the transmission of cues arising in the ventral hippocampus or medial septum is, however, minor.

The afferent connections of the suprachiasmatic nucleus of the golden hamster with emphasis on the retinohypothalamic projection

The afferent connections of the hypothalamic suprachiasmatic nucleus (SCN) of the golden hamster were examined using horseradish peroxidase (HRP) as the retrograde tracer molecule. Unilateral iontophoretic deposition of HRP into the SCN labeled ganglion cells bilaterally in the retinae. The labeled ganglion cells all had large somata and were randomly distributed across the retina. A similar number were labeled in each retina, which contrasted with the findings from injections into the optic chiasm and lateral geniculate body. Chiasm and geniculate injections both labeled three classes of ganglion cell (small, large, and giant) predominantly in the contralateral retinae. Telencephalic afferent projections to the SCN included the ventral subicular cortex and the septum. Notable diencephalic afferents included the dorsal lamina of the internal division of the ventral lateral geniculate nucleus (vLGN); the ipsilateral input was twice that of the contralateral projection. The same region of the vLGN was also noted to be reciprocally connected to the contralateral vLGN. The thalamic paraventricular nucleus was also heavily labeled but only ipsilaterally. Of functional significance, the SCN was discovered to innervate its contralateral homologue. Other less numerous afferents in the midbrain included the dorsal and median raphe nuclei and the dorsal nucleus of the lateral lemniscus. The afferent projections to the SCN determined in this study are discussed in regard to the known physiological role of the SCN as part of the circadian clock system.

The descending afferent connections of the paraventricular nucleus of the hypothalamus (PVN)

The distribution of afferents to the paraventricular nucleus of the hypothalamus (PVN) was studied following iontophoresis of horseradish peroxidase (HRP) into the nucleus. This report describes the descending connections to this structure. The PVN receives a substantial input from limbic system structures, especially from the lateral septal nucleus and the ventral portion of the subicular cortex. A small number of labeled cells were found in the amygdala, primarily the medial nucleus. Of the circumventricular organs, the subfornical organ and OVLT both project to the PVN, the former very strongly. In both the preoptic area and hypothalamus, medial cell groups have more input than do the lateral areas. Labeled cells were found in the medial and hypothalamus, medial cell groups have more input than do the lateral areas. Labeled cells were found in the medial and lateral preoptic areas, suprachiasmatic nucleus, ventromedial nucleus, arcuate nucleus, retrochiasmatic and lateral hypothalamic areas. Of particular interest is the finding that the PVN receives input from the contralateral PVN and ipsilateral SON. Of the other diencephalic structures only the zone incerta showed a consistent number of labeled cells. The results are discussed in relationship to the possible neural structures that might mediate the response of the PVN neurons to adrenalectomy.

5HT blockade and the stimulant effects of D- and L-amphetamine: no interaction in self-stimulation of prefrontal cortex, hypothalamus, or dorsal tegmentum. unexpected lethality in hippocampal sites

We investigated the role of serotonin in the differential stimulatory effects of D- and L-amphetamine (1.0 mg/kg) on locomotor activity and on self-stimulation (SS) in rats. The serotonin antagonist methysergide (12.5 mg/kg) had no effects alone on activity or on SS. Methysergide enhanced the strong locomotor stimulatory effects of D-amphetamine and the weaker effects of L-amphetamine. D-amphetamine facilitated SS more strongly than L- in hypothalamic, dorsal tegmental, hippocampal and medial prefrontal cortical sites, but the effect of D-amphetamine was much weaker in prefrontal cortex than in other sites. Methysergide did not alter the effects of D- or L-amphetamine in any site except the hippocampus. Here, methysergide plus L-amphetamine suppressed SS; methysergide plus D-amphetamine suppressed SS in some rats and greatly increased it in others. When SS was facilitated by D-amphetamine plus methysergide, the combination was lethal. The possibility that lethality was due to adrenal crisis is discussed.

Differential fornix ablations and the circadian rhythmicity of adrenal corticosteroid secretion

Suction ablations of the medial or lateral fornix were performed in order to transect selectively the medial corticohypothalamic tract (mcht) which originates in the anteroventral subiculum and travels in the lateral fornix terminating in the basal hypothalamus. The circadian rhythmicity of plasma adrenal corticosteroid levels was assessed in individual animals 1--2 weeks postoperatively. Ablation of the lateral fornix disrupted the periodicity of corticosteroid secretion which is normally synchronized with the light--dark cycle, whereas medial fornix ablation or neocortical ablation caused no such disruption. Group mean levels of plasma adrenal corticoids were higher in the lateral fornix-ablated animals than in the medial fornix-ablated, neocortically ablated, or intact control animals. These findings suggest that the anteroventral subiculum is important in the regulation of adrenal corticosteroid rhythmicity, and that it exerts an inhibitory influence upon corticosteroid release.

The hippocampus and stress induced 17-OHCS elevations

The physiologic contribution of the limbic brain to emotionally induced stress is still poorly understood. The present study is designed to more specifically evaluate the role of the hippocampus in stress induced plasma 17-OHCS elevations. The conditional reflex to a sequential presentation of tone and shock was used as the stress agent in adult mongrel dogs. Plasma 17-OHCS levels were determined by the Porter-Silber method. Control and stress levels of 17-OHCS were determined before and after unilateral (left) hippocampectomy, and subsequent contralateral (right) hippocampectomy. A unilateral posterior hippocampal lesion partially attenuated (20%) the normal 17-OHCS stress response. In contrast to unilateral lesions, equivalent bilateral posterior hippocampal lesions abolished the normal 17-OHCS stress response. These observations support the thesis that the elevated 17-OHCS levels in response to the conditioning paradigm is dependent on the hippocampus. Furthermore, it is dependent upon the continuity of the hippocampal circuit and not upon the volumetric steroid binding capacity of the hippocampus. These studies also suggest that a unilaterally functioning hippocampus may be adequate to meet the physiologic needs of stress, as reflected by the 17-OHCS response.

Uptake and binding of [3H]hydrocortisone by various pig brain regions

The cytosol fraction of septum, hypothalamus, and hippocampus of intact and adrenalectomized pigs possessed greater concentrations of radioactivity than the cytosol fraction of amygdala, pituitary, and cortex after an intraventricular injection of [1,2-3H]hydrocortisone. Nuclear extracts from the same brain regions possessed higher concentrations of radioactivity than nuclear extracts of the other brain regions of intact pigs. Nuclear extracts of amygdala, pituitary and hypothalamus from adrenalectomized pigs exhibited the greatest increase over intact pigs in labeled hormone concentration. When adrenalectomized pigs were administered dexamethasone prior to [3H]hydrocortisone, uptake of label was most depressed in hippocampal cytosol and cuclear extract. Also sensitive to the competitive effects of dexamethasone were septal and pituitary nuclear extracts. In intact pigs, pituitary, hippocampus and cortex exhibited higher ratios of bound to total hormone in the cytososl fraction than the other brain regions. Hippocampal and amygdala cytosol possessed the greater magnitude of increase in the ratio of bound to total hormone in adrenalectomized versus intact pigs. The pituitary, septum, amygdala, and cortex of intact and adrenalectomized pigs possessed a ratio of bound to total hormone in nuclear extract 5-10 times greater than that in hippocampus and hypothalamus. However, the latter two regions exhibited a greater increase in bound: total hormone after administration of labeled hormone to adrenalectomized pigs than nuclear extracts of the other brain regions.

Effects of hippocampal and amygdalar stimulation on uptake and binding of 3H-hydrocortisone in the hypothalamus of the cat

Stimulation of the hippocampus or amygdala of adrenalectomized cats occurred for 10 sec followed by a 50 sec period of no stimulation, beginning 30 min prior to and ending 30 min after administration of 100 muCi of 3H-hydrocortisone into a lateral ventricle. Sixty min after administration of labeled hormone, the hypothalamus was excised and homogenized. Cytosol and nuclear extract fractions were obtained and analyzed for radioactivity and protein content. Separation of bound from free hydrocortisone was achieved by charcoal and adsorption assay. Results reveal that stimulation of the hippocampus resulted in a greater concentration of 3H-hydrocortisone taken up into hypothalamic cells. Also, a greater percentage of total hormone found in the nuclear extract was assayed as bound 3H-hydrocortisone, and the concentration of bound radioactivity in the nuclear extract was increased over control values. Amygdalar stimulation, in general, yielded results similar to those obtained from control cats. However, although a lesser percentage of total hormone in the hypothalamic cytosol was assayed as bound hormone, there was a greater concentration of nuclear bound hormone than in controls, but less than that determined in the hippocampal stimulation group. These results add to the evidence that hippocampus and amygdala have a modulating influence upon the hypothalamo-hypophyseal axis. They also suggest that one manner in which these limbic structures may influence hypothalamic function is to modulate the uptake and binding of hydrocortisone in hypothalamic cells.

Effect of cortisol on the excitability of limbic structures of the brain in freely moving rats

The effects of cortisol on the excitability of the dorsal hippocampus, septum, hypothalamus and the pontine reticular formation in unrestrained, unanesthetized rats with permanently-implanted electrodes were investigated. The hormone produced a slowing in the spontaneous activity in these regions. The stimulation of the septum, hypothalamus and reticular formation had no appreciable influence on the local or propagated electrical activity of the brain after cortisol injection; however in 14 out of 29 experiments hippocampal stimulation with the same voltages as before cortisol administration, induced generalized convulsive activity. The attacks consisted of high-voltage spikes and slow-wave activity and were followed by a post-seizure exhaustion in the hippocampus. In half of the rats behavioral convulsions also appeared. The convulsive effects of cortisol on the brain are briefly reviewed and the specificity of hippocampal involvement in the present experiments is emphasized. The possible significance of the present findings in relation to the feedback of glucocorticoids on the brain, in the regulation of ACTH secretion, is discussed. The experiments described may also contribute to our understanding of the mechanisms of the convulsive effects of cortisol on the brain.

Radioautographic study of the rat brain after injection of [1,2-3H]corticosterone

Cryostat sections of the central nervous system of adrenalectomized male rats injected with [3H]corticosterone were examined by radioautography. One hour after the injection, radioactivity was found to be selectively concentrated in specific neurons of the septum, the hippocampal complex (precommissural hippocampus, cornu Ammonis, gyrus dentatus, subiculum), the indusium griseum, the amygdala and in certain areas of the cortex. In the hippocampus, the pyramidal neurons in fields CA1 and CA2 of the cornu Ammonis and the granule neurons of the gyrus dentatus contained more radioactivity than did other regions of the brain. Most of the silver grains were localized in the nuclei of labeled cells. The topographic distribution of corticosterone-concentrating neurons shows that the hormonal target sites in the central nervous system are mainly extrahypothalamic.

Rat brain binds adrenal steroid hormone: radioautography of hippocampus with corticosterone

Tritiated corticosterone injected subcutaneously into adrenalectomized male rats 1 hour before killing produced intense labeling of the hippocampus in radioautograms prepared by a method that reduced or prevented diffusion of the radioactive material. The pyramidal neurons of the cornu ammonis and the granule neurons of the gyrus dentatus contained more radioactivity than did other regions of the brain; however, the intensity of labeling varied among adjacent neurons. The nuclei of many neurons were clearly labeled but radioactivity was relatively sparse in the cytoplasm, in the axons where they branch from cell bodies, and in adjacent neuropil.

Telemetered recording of hormone effects on hippocampal neurons

Frequency-modulated telemetry was used to record the effects of hormones on single-unit activity in the brains of freely moving rats. Corticosterone decreased unit activity in the dorsal hippocampus. Adrenocorticotrophic hormone had the opposite effect.