Peptide injections into the amygdala of conscious rats: effects on blood pressure, heart rate and plasma catecholamines

Advances of radiolabeled GRPR ligands for PET/CT imaging of cancers

GRPR is a type of seven-transmembrane G-protein coupled receptor that belongs to the bombesin protein receptor family. It is highly expressed in various cancers, including prostate cancer, breast cancer, lung cancer, gastrointestinal cancer, and so on. As a result, molecular imaging studies have been conducted using radiolabeled GRPR ligands for tumor diagnosis, as well as monitoring of recurrence and metastasis. In this paper, we provided a comprehensive overview of relevant literature from the past two decades, with a specific focus on the advancements made in radiolabeled GRPR ligands for imaging prostate cancer and breast cancer.

Cannabidiol tempers alcohol intake and neuroendocrine and behavioural correlates in alcohol binge drinking adolescent rats. Focus on calcitonin gene-related peptide's brain levels

Alcohol binge drinking is common among adolescents and may challenge the signalling systems that process affective stimuli, including calcitonin gene-related peptide (CGRP) signalling. Here, we employed a rat model of adolescent binge drinking to evaluate reward-, social- and aversion-related behaviour, glucocorticoid output and CGRP levels in affect-related brain regions. As a potential rescue, the effect of the phytocannabinoid cannabidiol was explored. Adolescent male rats underwent the intermittent 20% alcohol two-bottle choice paradigm; at the binge day (BD) and the 24 h withdrawal day (WD), we assessed CGRP expression in medial prefrontal cortex (mPFC), nucleus accumbens (NAc), amygdala, hypothalamus and brainstem; in addition, we evaluated sucrose preference, social motivation and drive, nociceptive response, and serum corticosterone levels. Cannabidiol (40 mg/kg, i.p.) was administered before each drinking session, and its effect was measured on the above-mentioned readouts. At BD and WD, rats displayed decreased CGRP expression in mPFC, NAc and amygdala; increased CGRP levels in the brainstem; increased response to rewarding- and nociceptive stimuli and decreased social drive; reduced serum corticosterone levels. Cannabidiol reduced alcohol consumption and preference; normalised the abnormal corticolimbic CGRP expression, and the reward and aversion-related hyper-responsivity, as well as glucocorticoid levels in alcohol binge-like drinking rats. Overall, CGRP can represent both a mediator and a target of alcohol binge-like drinking and provides a further piece in the intricate puzzle of alcohol-induced behavioural and neuroendocrine sequelae. CBD shows promising effects in limiting adolescent alcohol binge drinking and rebalancing the bio-behavioural abnormalities.

Neuromedin B excites central lateral amygdala neurons and reduces cardiovascular output and fear-potentiated startle

Neuromedin B (NMB) and gastrin-releasing peptide (GRP) are the two mammalian analogs in the bombesin peptide family that exert a variety of actions including emotional processing, appetitive behaviors, cognition, and tumor growth. The bombesin-like peptides interact with three receptors: the NMB-preferring bombesin 1 (BB1) receptors, the GRP-preferring bombesin 2 (BB2) receptors and the orphan bombesin 3 (BB3) receptors. Whereas, injection of bombesin into the central amygdala reduces satiety and modulates blood pressure, the underlying cellular and molecular mechanisms have not been determined. As administration of bombesin induces the expression of Fos in the lateral nucleus of the central amygdala (CeL) which expresses BB1 receptors, we probed the effects of NMB on CeL neurons using in vitro and in vivo approaches. We showed that activation of the BB1 receptors increased action potential firing frequency recorded from CeL neurons via inhibition of the inwardly rectifying K+ (Kir) channels. Activities of phospholipase Cβ and protein kinase C were required, whereas intracellular Ca2+ release was unnecessary for BB1 receptor-elicited potentiation of neuronal excitability. Application of NMB directly into the CeA reduced blood pressure and heart rate and significantly reduced fear-potentiated startle. We may provide a cellular and molecular mechanism whereby bombesin-like peptides modulate anxiety and fear responses in the amygdala.

Adolescent binge-like alcohol exposure dysregulates NPY and CGRP in rats: Behavioural and immunochemical evidence

Alcohol binge drinking during adolescence impacts affective behaviour, possibly impinging on developing neural substrates processing affective states, including calcitonin gene-related peptide (CGRP) and neuropeptide Y (NPY). Here, we modelled binge-like alcohol exposure in adolescence, by administering 3.5 g/kg alcohol per os, within 1 h, to male adolescent rats every other day, from postnatal day 35 to 54. The effects on positive and negative affective behaviour during abstinence were explored including: consummatory behaviour and weight gain; social behaviour in the modified social interaction test; thermal nociception in the tail-flick test; psychosocial stress coping in the resident-intruder paradigm. Moreover, CGRP and NPY levels were evaluated in functionally relevant brain regions. Our data shows that binge-like intermittent alcohol administration during adolescence decreased weight gain, social preference and motivation, nociception, and active psychosocial stress coping during abstinence. In addition, intermittent alcohol-exposed rats displayed increased expression of CGRP and NPY in the prefrontal cortex and nucleus accumbens; decreased NPY levels in the amygdala; opposite changes in CGRP levels in the hypothalamus and brainstem. Overall, our data shows that adolescent binge-like alcohol exposure, through the allostatic load of alternate intoxication and withdrawal, produces long-term consequences in sensory and affective processes and dysregulated complementary neuropeptidergic systems. Thus, neuropeptide-targeted interventions hold promising potential for addressing negative affect during prolonged withdrawal in young subjects.

Behavioural and cardiovascular effects of orexin-A infused into the central amygdala under basal and fear conditions in rats

The neuropeptide orexin-A (OX-A) has diverse functions, including maintaining arousal, autonomic control, motor activity and stress responses. These functions are regulated at different terminal regions where OX-A is released. The current study examined the physiological and behavioural effects of OX-A microinjections into the central amygdala (CeA) under basal and stressed conditions in rats. When OX-A was microinjected into the CeA and the animals returned to the home-cage, heart rate and mean arterial pressure were increased compared to vehicle-injected controls. General activity of the animal was also increased, indicating that OX-A activity in CeA contributes to increased arousal. This outcome is similar to the effects of central intracerebroventricular infusions of OX-A, as well as the cardiovascular effects previously demonstrated at many of OX's efferent hypothalamic and brainstem structures. In a second study, animals were fear-conditioned to a context by delivery of electric footshocks and then animals were re-exposed to the conditioned context at test. When OX-A was microinjected at test, freezing behaviour was reduced and there was a corresponding increase in the animal's activity but no impact on the pressor and cardiac responses (i.e, blood pressure and heart rate were unchanged). This reduction in freezing suggests that OX-A activates amygdala neurons that inhibit freezing, which is similar to the actions of other neuropeptides in the CeA that modulate the appropriate defence response to fearful stimuli. Overall, these data indicate that the CeA is an important site of OX-A modulation of cardiovascular and motor activity, as well as conditioned freezing responses.

Cardiovascular functions of central corticotropin-releasing factor related peptides system

The corticotropin-releasing factor (CRF) related peptides system has widespread distributions in central nervous system, to perform many physiological and pathophysiological functions, including cardiovascular functions. A complex connection exists between the central CRF related peptides system and cardiovascular system. There are multiple pathways and mechanisms through which the central CRF related peptides system influences cardiovascular functions. A dysfunction in the central CRF related peptides system may lead to a wide range of alterations in cardiovascular functions. Though there are difficulties or limitations in establishing exact modulatory roles of the central CRF related peptides system in cardiovascular functions. The central CRF related peptides system as target to prevent cardiovascular diseases is being pursued with increasing interest. In this review, we summarize recent understanding on cardiovascular functions of the CRF related peptides system in limbic forebrain, hypothalamus and brain stem structures, discuss mechanisms of the central CRF related peptides system in control of cardiovascular functions, and suggest that the central CRF related peptides system may be a potent candidate for prevention of cardiovascular diseases.

Essential Role of Ovarian Hormones in Susceptibility to the Consequences of Witnessing Social Defeat in Female Rats

BACKGROUND

Women are at greater risk than men of developing depression and comorbid disorders such as cardiovascular disease. This enhanced risk begins at puberty and ends following menopause, suggesting a role for ovarian hormones in this sensitivity. Here we used a model of psychosocial witness stress in female rats to determine the stress-induced neurobiological adaptations that underlie stress susceptibility in an ovarian hormone-dependent manner.

METHODS

Intact or ovariectomized (OVX) female rats were exposed to five daily 15-minute witness-stress exposures. Witness-stress-evoked burying, behavioral despair, and anhedonia were measured. Cardiovascular telemetry was combined with plasma measurements of inflammation, epinephrine, and corticosterone as indices of cardiovascular dysfunction. Finally, levels of interleukin-1β and corticotropin-releasing factor were assessed in the central amygdala.

RESULTS

Witness stress produced anxiety-like burying, depressive-like anhedonia, and behavioral despair selectively in intact female rats, which was associated with enhanced sympathetic responses during stress, including increased blood pressure, heart rate, and arrhythmias. Moreover, intact female rats exhibited increases in 12-hour resting systolic pressure and heart rate and reductions in heart rate variability. Notably, OVX female rats remained resilient. Moreover, intact, but not OVX, female rats exposed to witness stress exhibited a sensitized cytokine and epinephrine response to stress and distinct increases in levels of corticotropin-releasing factor and interleukin-1β in the central amygdala.

CONCLUSIONS

Together these data suggest that ovarian hormones play a critical role in the behavioral, inflammatory, and cardiovascular susceptibility to social stress in female rats and reveal putative systems that are sensitized to stress in an ovarian hormone-dependent manner.

Contribution of amygdala to the pressor response elicited by microinjection of angiotensin II into the bed nucleus of the stria terminalis

The bed nucleus of the stria terminalis (BST) is part of the limbic system located in the rostral forebrain. BST is involved in behavioral, neuroendocrine and autonomic functions, including cardiovascular regulation. The amygdala, plays an important role in mediating the behavioral and physiological responses associated with fear and anxiety, including cardiovascular responses. In a previous study, we showed that microinjection of AngII into the BST produced a pressor and two types of single-unit responses in the BST, short excitatory and long inhibitory. This study was performed to find possible involvement of amygdala in cardiovascular responses elicited by microinjection of AngII into the BST, using blockade of the central nucleus of amygdala (CeA) and single unit recording from the CeA, while injecting AngII into the BST in anesthetized rat. Blockade of CeA attenuated the pressor response to microinjection of AngII into the BST. Eighty-six AngII microinjections were given into the BST and 198 single unit responses were recorded from CeA simultaneously, from which 89 showed a short duration excitatory response and 109 showed no responses. In conclusion, microinjection of AngII into the BST produces a short excitatory single unit response in the CeA, resulting in contribution of amygdala to the resulted pressor response. Taken together, our study and previous studies suggest a plausible hypothesis that these two nuclei perform their cardiovascular functions in cooperation with each other.

Acute and long term effects of chronic intermittent noise stress on hypothalamic-pituitary-adrenocortical and sympatho-adrenomedullary axis in pigs

Noise is a potential environmental stressor and has also been identified as an aversive stimulus during animal housing. The impact of a 4-week chronic intermittent noise exposure on plasma adrenaline, noradrenaline, ACTH, cortisol and behaviour was studied in 24 male castrated German Landrace pigs. Three treatment groups were formed: N1 animals were subjected to a daily stimulation with broad-band noise (2 h, 90 dB(Lin)), N2 animals were subjected to the same stimulus three times a week and control animals were equally handled but experienced no noise exposure. Blood was serially sampled once a week via jugular vein catheters before, during and after a noise session. Behavioural observations of focal animals were performed by video technique. The first noise exposure of the animals caused no significant changes of stress hormone levels compared with the controls despite indices for more locomotion and less lying at the beginning of the noise stimulation, indicating that this noise stimulus is a rather mild stressor compared with other stimuli. The chronic intermittent noise stimulation, however, caused an increase of plasma ACTH and cortisol concentrations in the N1 animals after 4 days. The cortisol response of the N2 animals was unchanged compared to the controls at day 4, increased thereafter and at day 11 and 18 these animals tended to have higher cortisol levels compared with the controls. The noradrenaline/adrenaline ratio was significantly increased in N1 animals after 11 days and thereafter, whereas this ratio was unchanged in N2 animals until day 18, but also increased at day 25. In tendency, chronic intermittent noise exposure tended to reduce social behaviour and increase lying behaviour in both noise groups. In addition, the growth performance of pigs was negatively affected by the daily noise stimulation. In a second experiment with 16 male castrated German Landrace pigs, the impact of the daily intermittent noise exposure (N1) on the endocrine response to an acute stressor (restraint) and on the adrenocortical sensitivity to an ACTH challenge was studied. The time course of cortisol levels during the ACTH test indicated alterations in the time dynamics of the adrenocortical response with a more rapid response in the N1 animals. The results show that chronic intermittent noise exposure causes time-dependent alterations of the adrenocortical and sympathetic neural systems and may lead to behavioural suppression and growth retardation in pigs. Thus, repeated exposure of animals to noise levels over 90 dB should be avoided in pig husbandry to sustain productivity and animal welfare.

Vasopressin and sympathetic system mediate the cardiovascular effects of the angiotensin II in the bed nucleus of the stria terminalis in rat

The bed nucleus of the stria terminalis (BST) is involved in cardiovascular regulation. The angiotensin II (Ang II) receptor (AT1), and angiotensinogen were found in the BST. In our previous study we found that microinjection of Ang II into the BST produced a pressor response. This study was performed to find the mechanisms mediating this response in anesthetized rats. Ang II was microinjected into the BST and the cardiovascular responses were re-tested after systemic injection of a blocker of autonomic or vasopressin V1 receptor. The ganglionic nicotinic receptor blocker, hexamethonium dichloride, attenuated the pressor response to Ang II, indicating that the cardiovascular sympathetic system is involved in the pressor effect of Ang II. A selective vasopressin V1 receptor antagonist greatly attenuated the pressor effect of Ang II, indicating that the Ang II increases the arterial pressure via stimulation of vasopressin release as well. In conclusion, in the BST, Ang II as a neurotransmitter increases blood pressure by exciting cardiovascular sympathetic system and directly or indirectly causing vasopressin to release into bloodstream by VPN. This is an interesting new finding that not only circulating Ang II but also brain Ang II makes vasopressin release.

Cardiovascular and single-unit responses to microinjection of angiotensin II into the bed nucleus of the stria terminalis in rat

The bed nucleus of the stria terminalis (BST) is part of the limbic system located in the rostral forebrain. BST is involved in behavioral, neuroendocrine and autonomic functions, including cardiovascular regulation. The angiotensin II (Ang II) receptor, AT1, was found in the BST, however its effects on the cardiovascular system and on single-unit responses have not been studied yet. In the present study, Ang II was microinjected into the BST of anesthetized rats and cardiovascular and single-unit responses were recorded simultaneously. Furthermore the responses were re-tested after the microinjection of a blocker of the AT1 receptor, losartan, into the BST. We found that microinjection of Ang II into the BST produced a pressor response of 11±1mmHg for a duration of 2-8min. Ang II had no consistent effect on heart rate. It also produced two types of single-unit responses in the BST, short excitatory and long inhibitory. Blockade of AT1 receptors abolished both the cardiovascular and single-unit responses, indicating that the responses were mediated through AT1 receptors. These findings imply that Ang II may be utilized as a neurotransmitter and may play a role in returning blood pressure toward normal during hypotension.

CGRP as a neuropeptide in migraine: lessons from mice

Migraine is a neurological disorder that is far more than just a bad headache. A hallmark of migraine is altered sensory perception. A likely contributor to this altered perception is the neuropeptide calcitonin gene-related peptide (CGRP). Over the past decade, CGRP has become firmly established as a key player in migraine. Although the mechanisms and sites of action by which CGRP might trigger migraine remain speculative, recent advances with mouse models provide some hints. This brief review focuses on how CGRP might act as both a central and peripheral neuromodulator to contribute to the migraine-like symptom of light aversive behaviour in mice.

Corticotropin-releasing factor in the mouse central nucleus of the amygdala: ultrastructural distribution in NMDA-NR1 receptor subunit expressing neurons as well as projection neurons to the bed nucleus of the stria terminalis

Corticotropin-releasing factor (CRF) and glutamate are critical signaling molecules in the central nucleus of the amygdala (CeA). Central amygdala CRF, acting via the CRF type 1 receptor (CRF-R1), plays an integral role in stress responses and emotional learning, processes that are generally known to involve functional NMDA-type glutamate receptors. There is also evidence that CRF expressing CeA projection neurons to the bed nucleus of the stria terminalis (BNST) play an important role in stress related behaviors. Despite the potentially significant interactions between CRF and NMDA receptors in the CeA, the synaptic organization of these systems is largely unknown. Using dual labeling high resolution immunocytochemical electron microscopy, it was found that individual somata and dendrites displayed immunoreactivity for CRF and the NMDA-NR1 (NR1) subunit in the mouse CeA. In addition, CRF-containing axon terminals contacted postsynaptic targets in the CeA, some of which also expressed NR1. Neuronal profiles expressing the CRF type 1 receptor (CRF-R1), identified by the expression of green fluorescent protein (GFP) in bacterial artificial chromosome (BAC) transgenic mice, also contained NR1, and GFP immunoreactive terminals formed synapses with NR1 containing dendrites. Although CRF and GFP were only occasionally co-expressed in individual somata and dendritic profiles, contacts between labeled axon terminals and dendrites were frequently observed. A combination of tract tracing and immunocytochemistry revealed that a population of CeA CRF neurons projected to the BNST. It was also found that CRF, or GFP expressing terminals directly contacted CeA-BNST projection neurons. These results indicate that the NMDA receptor is positioned for the postsynaptic regulation of CRF expressing CeA neurons and the modulation of signals conveyed by CRF inputs. Interactions between CRF and NMDA receptor mediated signaling in CeA neurons, including those projecting to the BNST, may provide the synaptic basis for integrating the experience of stress and relevant environmental stimuli with behaviors that may be of particular relevance to stress-related learning and the emergence of psychiatric disorders, including drug addiction.

Calcitonin gene-related peptide in the bed nucleus of the stria terminalis produces an anxiety-like pattern of behavior and increases neural activation in anxiety-related structures

Calcitonin gene-related peptide (CGRP) evokes anxiety-like responses when infused into the lateral ventricle of rats. Because the bed nucleus of the stria terminalis (BNST) lies immediately adjacent to the lateral ventricle, is rich in CGRP receptors, and has itself been implicated in anxiety, we evaluated the hypothesis that these effects are attributable to stimulation of CGRP receptors within the BNST itself. Bilateral intra-BNST, but not dorsal, CGRP infusions (0, 200, 400, 800 ng/side) enhanced startle amplitude in a dose-dependent manner, and produced an anxiety-like response on the elevated plus maze. Intra-BNST infusion of the CGRP antagonist, αCGRP(8-37), blocked the effect of CGRP on startle, and also blocked startle potentiation produced by exposure to trimethylthiazoline (a component of fox feces that induces anxiety-like behavior in rats). Intra-BNST, but not dorsal, CGRP infusions also increased c-Fos immunoreactivity in a number of anxiety-related brain areas (central nucleus of the amygdala, locus ceruleus, ventrolateral septal nucleus, paraventricular hypothalamic nucleus, lateral hypothalamus, lateral parabrachial nucleus, dorsal raphe nucleus, and nucleus accumbens shell), all of which receive direct projections from the BNST. Together, the results indicate that the activation of BNST CGRP receptors is both necessary and sufficient for some anxiety responses and that these effects may be mediated by activation of a wider network of BNST efferent structures. If so, inhibition of CGRP receptors may be a clinically useful strategy for anxiety reduction.

Somatostatin and nociceptin inhibit neurons in the central nucleus of amygdala that project to the periaqueductal grey

The central nucleus of amygdala (CeA) plays an important role in modulation of the descending antinociceptive pathways. Using whole-cell patch clamp recordings from brain slices, we found that CeA neurons responded to the endogenous ligands somatostatin (SST) and nociceptin/orphanin FQ (OFQ) via an increased K-conductance. Co-application with selective antagonists suggested that SST and OFQ act on SSTR2 and ORL1 receptors, respectively. Taking account of anatomical localisation of recorded neurons, the present study showed that many responsive neurons were located within the medial subdivision of CeA and all CeA projection neurons to the midbrain periaqueductal grey invariably responded to these peptides. Randomly selected agonist-responsive neurons in CeA predominantly classified physiologically as low-threshold spiking neurons. The similarity of SST, OFQ and, as previously reported, opioid responsiveness in a sub-population of CeA neurons suggests converging roles of these peptides to inhibit the activity of projections from CeA to vlPAG, and potentially similar antinociceptive actions in this pathway.

Phasic vs sustained fear in rats and humans: role of the extended amygdala in fear vs anxiety

Data will be reviewed using the acoustic startle reflex in rats and humans based on our attempts to operationally define fear vs anxiety. Although the symptoms of fear and anxiety are very similar, they also differ. Fear is a generally adaptive state of apprehension that begins rapidly and dissipates quickly once the threat is removed (phasic fear). Anxiety is elicited by less specific and less predictable threats, or by those that are physically or psychologically more distant. Thus, anxiety is a more long-lasting state of apprehension (sustained fear). Rodent studies suggest that phasic fear is mediated by the amygdala, which sends outputs to the hypothalamus and brainstem to produce symptoms of fear. Sustained fear is also mediated by the amygdala, which releases corticotropin-releasing factor, a stress hormone that acts on receptors in the bed nucleus of the stria terminalis (BNST), a part of the so-called 'extended amygdala.' The amygdala and BNST send outputs to the same hypothalamic and brainstem targets to produce phasic and sustained fear, respectively. In rats, sustained fear is more sensitive to anxiolytic drugs. In humans, symptoms of clinical anxiety are better detected in sustained rather than phasic fear paradigms.

The role of functional postsynaptic NMDA receptors in the central nucleus of the amygdala in opioid dependence

Activation of ionotropic N-methyl-D-aspartate (NMDA)-type glutamate receptors in limbic system nuclei, such as the central nucleus of the amygdala (CeA), plays an essential role in autonomic, behavioral, and affective processes that are profoundly impacted by exposure to opioids. However, the heterogeneous ultrastructural distribution of the NMDA receptor, its complex pharmacology, and the paucity of genetic models have hampered the development of linkages between functional amygdala NMDA receptors and opioid dependence. To overcome these shortcomings, high-resolution imaging and molecular pharmacology were used to (1) Identify the ultrastructural localization of the essential NMDA-NR1 receptor (NR1) subunit and its relationship to the mu-opioid receptor (microOR), the major cellular target of abused opioids like morphine, in the CeA and (2) Determine the effect of CeA NR1 deletion on the physical, and particularly, psychological aspects of opioid dependence. Combined immunogold and immuoperoxidase electron microscopic analysis showed that NR1 was prominently expressed in postsynaptic (i.e., somata, dendrites) locations of CeA neurons, where they were also frequently colocalized with the microOR. A spatial-temporal deletion of NR1 in postsynaptic sites of CeA neurons was produced by local microinjection of a neurotropic recombinant adeno-associated virus (rAAV), expressing the green fluorescent protein (GFP) reporter and Cre recombinase (rAAV-GFP-Cre), in adult "floxed" NR1 (fNR1) mice. Mice with deletion of NR1 in the CeA showed no obvious impairments in sensory, motor, or nociceptive function. In addition, when administered chronic morphine, these mice also displayed an acute physical withdrawal syndrome precipitated by naloxone. However, opioid-dependent CeA NR1 knockout mice failed to exhibit a conditioned place aversion induced by naloxone-precipitated withdrawal. These results indicate that postsynaptic NMDA receptor activity in central amygdala neurons is required for the expression of a learned affective behavior associated with opioid withdrawal. The neurogenetic dissociation of physical and psychological properties of opioid dependence demonstrates the value of combined ultrastructural analysis and molecular pharmacology in clarifying the neurobiological mechanisms subserving opioid-mediated plasticity.

Angiotensin II and CRF receptors in the central nucleus of the amygdala mediate hemodynamic response variability to cocaine in conscious rats

Stress or cocaine evokes either a large increase in systemic vascular resistance (SVR) or a smaller increase in SVR accompanied by an increase in cardiac output (designated vascular and mixed responders, respectively) in Sprague-Dawley rats. We hypothesized that the central nucleus of the amygdala (CeA) mediates this variability. Conscious, freely-moving rats, instrumented for measurement of arterial pressure and cardiac output and for drug delivery into the CeA, were given cocaine (5 mg/kg, iv, 4-6 times) and characterized as vascular (n=15) or mixed responders (n=10). Subsequently, we administered cocaine after bilateral microinjections (100 nl) of saline or selective agents in the CeA. Muscimol (80 pmol), a GABA(A) agonist, or losartan (43.4 pmol), an AT(1) receptor antagonist, attenuated the cocaine-induced increase in SVR in vascular responders, selectively, such that vascular responders were no longer different from mixed responders. The corticotropin releasing factor (CRF) antagonist, alpha-helical CRF(9-41) (15.7 pmol), abolished the difference between cardiac output and SVR in mixed and vascular responders. We conclude that greater increases in SVR observed in vascular responders are dependent on AT(1) receptor activation and, to a lesser extent on CRF receptors. Therefore, AT(1) and CRF receptors in the CeA contribute to hemodynamic response variability to intravenous cocaine.

Role of central calcitonin gene-related peptide (CGRP) in locomotor and anxiety- and depression-like behaviors in two mouse strains exhibiting a CGRP-dependent difference in thermal pain sensitivity

We have previously shown that, in AKR and C57BL/6 mice, a genetic polymorphism results in differential expression of the peptide, calcitonin gene-related polypeptide (CGRP), explaining a strain difference in thermal pain sensitivity. Although CGRP is widely distributed in the brain, little is known about the effects of supraspinal CGRP. We used AKR and C57BL/6 mice as a model to explore the effects of centrally (intracerebroventricular) injected CGRP and the CGRP receptor antagonists, CGRP(8-37) and BIBN4096BS, in a series of behavioral assays. Locomotor activity was significantly increased in C57BL/6 mice following the injection of BIBN4096BS and in both strains after the administration of CGRP(8-37) into the third ventricle. CGRP increased paw-withdrawal latencies in C57BL/6 mice only, while decreasing depression-like behaviors in both strains in the forced-swimming test. CGRP and CGRP receptor antagonists failed to modulate activity in the elevated plus maze, a model of anxiety. Taken together, these results suggest a complex role for supraspinal CGRP systems in the regulation of locomotion, nociception, and depression-like behaviors.

The role of corticotrophin-releasing hormone receptors in the calcitonin gene-related peptide-induced suppression of pulsatile luteinising hormone secretion in the female rat

Corticotrophin-releasing hormone (CRH) plays a pivotal role in the suppression of the gonadotrophin-releasing hormone (GRH) pulse generator in response to stress and intracerebroventricular (i.c.v.) administration of calcitonin gene-related peptide (CGRP). We have previously shown both CRH receptor subtypes, CRH-R1 and CRH-R2, are involved in the stress-induced suppression of LH pulses. The aims of the present study were to examine the role of CRH-R1 and CRH-R2 in CGRP-induced suppression of LH pulses, and to investigate the effects of CGRP on CRH expression in the paraventricular nucleus (PVN) and central nucleus of the amygdala (CeA), which have prominent CRH neurone populations that receive dense CGRP innervations. The suppression of LH pulses by CGRP (1.5 microg i.c.v.) was completely prevented by intravenous administration of the CRH-R1 antagonist SSR125543Q (7.5 mg/rat i.v., 30 min before CGRP), but was not affected by the CRH-R2 antagonist, astressin(2)-B (100 microg i.c.v., 10 min before CGRP). CGRP increased the CRH mRNA expression in PVN and CeA. These results provide evidence of a role for CRH-R1 in mediating the suppressive effects of CGRP on pulsatile LH secretion in the female rat, and additionally raise the possibility of an involvement of PVN and CeA CRH neuronal populations in this suppression.

Corticotropin-releasing factor receptor-1: a therapeutic target for cardiac autonomic disturbances

Corticotropin-releasing factor (CRF), a neuropeptide involved in triggering a myriad of responses to fear and stress, is favourably positioned in the CNS to modulate the sympathetic and parasympathetic branches of the cardiac autonomic nervous system. In vivo studies suggest that central CRF inhibits vagal output and stimulates sympathetic activity. Therefore, CRF may function to inhibit exaggerated vagal activation that results in severe bradycardia or even vasovagal syncope. On the other hand, CRF receptor-1 (CRF(1)) antagonists increase cardiac vagal and decrease sympathetic activity, thereby also implicating CRF(1) as a therapeutic target for autonomic disturbances resulting in elevated sympathetic activity, such as hypertension and coronary heart disease. The central distribution of CRF(1) and the cardiovascular effects of CRF(1) agonists and antagonists, suggest it mediates CRF-induced autonomic changes. However, there is insufficient information regarding the autonomic effects of CRF(2)-selective compounds to rule out CRF(2) contribution. This review provides an update on the autonomic effects of CRF and the neuronal projections thought to mediate these cardiovascular responses.

Topography of thalamic and parabrachial calcitonin gene-related peptide (CGRP) immunoreactive neurons projecting to subnuclei of the amygdala and extended amygdala

Injections of calcitonin gene-related peptide (CGRP) into the amygdala evoke fear-related behaviors and antinociceptive effects. In the present study we therefore characterized CGRP-containing amygdaloid afferents by injecting the retrograde tracer FluoroGold (FG) into subnuclei of the amygdala and adjacent divisions of the extended amygdala, namely, the lateral (LA) and central (CE) amygdaloid nuclei, interstitial nucleus of the posterior limb of the anterior commissure (IPAC), and the amygdalostriatal area (AStr). The distribution of retrogradely FG-labeled neurons and colocalization of CGRP-immunoreactivity with FG-labeling were mapped in the posterior paralaminar thalamic complex and parabrachial nuclei. The analysis of the posterior thalamus revealed that about 50% of CGRP-containing neurons projected to the AStr, the projections originating in the medial part of the medial geniculate body, posterior intralaminar nucleus, parvicellular subparafascicular nucleus, and peripeduncular nucleus. However, the percentage of CGRP-containing thalamic neurons projecting to the adjacent LA, medial part of the CE, and ventrocaudal part of the caudatoputamen rapidly dropped to 3-9%. There were no double-labeled cells after injections into the lateral and capsular parts of the CE and the IPAC. Thus, the AStr received the heaviest CGRP-containing projection from the posterior thalamus. CGRP-containing parabrachial neurons projected to the AStr and lateral, capsular, and medial parts of the CE, the projections originating in the external, crescent, and central parts of the lateral parabrachial nucleus and external part of the medial parabrachial nucleus. The results demonstrate a distinct projection pattern of CGRP-containing thalamic and parabrachial neurons to subnuclei of the amygdala and extended amygdala.

Cardiovascular response to renin substrate microinjection into the central nucleus of the amygdala of rats

Central nucleus of the amygdala is involved in cardiovascular regulation. Although most components of the renin-angiotensin system have been found to be distributed in amygdala, renin expression in brain has remained controversial. This work was undertaken to elucidate the extent of renin presence in this nucleus. A cannula was implanted bilaterally into the central nucleus of the amygdala. Mean arterial pressure and heart rate were directly measured via indwelling femoral artery cannula post bilateral intra central nucleus of the amygdala microinjection of renin substrate. Renin substrate microinjection dose-dependently increased mean arterial pressure and heart rate, whereas captopril, saralasin and losartan pretreatment inhibited these effects. The results suggest the presence of local renin or similar proteases in this nucleus.

Doxapram increases corticotropin-releasing factor immunoreactivity and mRNA expression in the rat central nucleus of the amygdala

Doxapram causes panic anxiety in humans. To determine whether doxapram alters corticotropin-releasing factor (CRF) expression in the central nucleus of the amygdala (CeA), paraventricular nucleus of hypothalamus (PVN), or bed nucleus of the stria terminalis (BNST), we used immunohistochemistry to measure CRF peptide in these brain areas after doxapram injection. Doxapram injection significantly increased CRF-like immunoreactivity (CRF-IR) within the CeA, but not in the BNST or PVN, and this increase was significant 2h after injection. In addition, doxapram significantly increased CRF mRNA expression within the CeA, and this was most prominent 30min after injection. These results suggest that doxapram selectively increases CRF expression within the CeA, and that this is mediated by increased CRF gene transcription. This increase in CRF-IR within the CeA might explain the doxapram-induced anxiety reaction.

ROLE OF THE CENTRAL NUCLEUS OF THE AMYGDALA IN THE CONTROL OF BLOOD PRESSURE: DESCENDING PATHWAYS TO MEDULLARY CARDIOVASCULAR NUCLEI

1. One of the key areas that links psychologically induced stress with the blood pressure-regulatory system is the central nucleus of the amygdala (CeA). This is an integratory forebrain nucleus that receives input from higher centres in the forebrain and has extensive connections with the hypothalamus and the medulla oblongata, areas involved in the regulation of the cardiovascular reflexes. 2. Based on studies using electrical or chemical stimulation or electrolytic lesions of the CeA, it has become clear that the CeA plays an important role in the regulation of blood pressure in response to stressful or fearful stimuli. 3. Two important medullary areas known to receive projections from the CeA are the nucleus tractus solitarius (NTS) and the rostral ventrolateral medulla (RVLM). The NTS is the site of the first synapse for afferent fibres originating from baroreceptors, chemoreceptors and the heart, whereas the RVLM contains neurons that maintain resting blood pressure and sympathetic nerve activity via projections to sympathetic preganglionic neurons in the intermediolateral cell column of the thoracolumbar spinal cord. 4. Electron microscopic studies using combined anterograde tracing and pre- and post-embedding immunogold labelling have shown that the pathways originating from the CeA to the NTS are inhibitory and may use GABA as a neurotransmitter. The results of these studies suggest that blood pressure changes produced by activation of the CeA may be mediated by attenuation of baroreceptor reflexes through a GABAergic mechanism at the level of the NTS. 5. Neuronal tract tracing combined with neurofunctional studies using the Fos protein as a marker of activated neurons indicate that the CeA projects directly to baroreceptive neurons in the NTS and RVLM that are activated by changes in blood pressure. 6. In conclusion, studies that have examined the efferent pathways of the CeA suggest that CeA neurons with projections to medullary baroreceptive neurons may play a vital role in the reflex changes in sympathetic nerve activity that are involved in blood pressure regulation in response to stress or anxiety.

Stress-induced suppression of the gonadotropin-releasing hormone pulse generator in the female rat: a novel neural action for calcitonin gene-related peptide

In addition to its role as a potent vasodilator, calcitonin gene-related peptide (CGRP) is centrally involved in a variety of stress responses, including activation of the hypothalamo-pituitary-adrenocortical axis. It is well known that stress suppresses the activity of the hypothalamic GnRH pulse generator, the central regulator of LH and FSH pulses, resulting in reproductive dysfunction. The aim of this study was to test the hypothesis that CGRP has a critical role in mediating stress-induced suppression of pulsatile LH secretion in the rat. Ovariectomized rats were implanted with intracerebroventricular and iv cannulae. Central administration of CGRP (75 pmol-1.2 nmol) into the lateral cerebral ventricle resulted in a profound, dose-dependent suppression of LH pulses, which was reversed by a CGRP receptor antagonist (CGRP(8-37),1 nmol). Although the site of action of CGRP remains to be established, the induction of c-Fos expression in the preoptic area and hypothalamic paraventricular nucleus might suggest an involvement of these brain regions. Intravenous administration of CGRP did not affect LH pulses. Coadministration (intracerebroventricular) of CGRP (400 pmol) with a CRH antagonist (alpha-helical CRF(9-41), 26 nmol) partly blocked the CGRP-induced suppression of LH pulses. Furthermore, CGRP(8-37) (1 nmol) completely blocked hypoglycemic stress-induced suppression of LH pulses. These results suggest that the suppression of pulsatile LH secretion by central administration of CGRP may be mediated in part by CRH, and that CGRP may play a pivotal role in the normal physiological response of stress-induced suppression of the hypothalamic GnRH pulse generator, and hence the reproductive system.

Prenatal stress and risk for psychopathology: specific effects or induction of general susceptibility?

This review focuses on prenatal stress as a risk factor for psychopathology. Evidence from animal studies is summarized, and the relevance of prenatal stress models in animals for human studies is discussed. In the offspring of prenatally stressed animals, overactivity and impaired negative feedback regulation of the hypothalamic-pituitary-adrenal axis are consistent findings and may reflect a pathophysiological mechanism involved in the development of psychopathology. Reduced activity of the opioid GABA/benzodiazepine, serotonin, and dopamine systems and increased activity of the sympathico-adrenal system have been found as well. These alterations have been linked to a diverse spectrum of psychopathology. Therefore, the evidence supports the view that exposure to prenatal stress may result in a general susceptibility to psychopathology, rather than exerting a direct effect on a specific form of psychopathology.

Prenatal stress and cognitive development and temperament in infants

Studies in rodents and nonhuman primates indicate that maternal stress during pregnancy can influence the developing fetus, resulting in delay of motor and cognitive development and impaired adaptation to stressful situations. These effects may be mediated by the hypothalamic-pituitary-adrenal (HPA) axis. We examined whether stress during pregnancy predicted developmental outcome of human infants in a prospective design. Self-report data about daily hassles and pregnancy-specific anxiety and salivary cortisol levels were collected in nulliparous pregnant women. Dependent measures were scores on the Bayley Scales of Infant Development and on temperamental questionnaires at 3 and 8 months. Pregnancy-specific anxiety in mid pregnancy predicted lower mental and motor developmental scores at 8 months. Early morning values of cortisol in late pregnancy were negatively related to both mental and motor development at 3 months and motor development at 8 months. Pregnancy-specific anxiety explained 7% of the variance of test-affectivity and goal-directedness at 8 months. Increased maternal stress during pregnancy seems to be one of the determinants of temperamental variation and delay of development of infants and may be a risk factor for developing psychopathology later in life.

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.

Central corticotropin releasing factor (CRF) and adrenergic receptors mediate hemodynamic responses to cocaine

Cocaine administration evokes cardiovascular responses that are variable in rats such that the pressor response is attributable to either a large increase in systemic vascular resistance and a decrease in cardiac output (vascular responders) or a smaller increase in systemic vascular resistance and no change or an increase in cardiac output (mixed responders). This study was designed to determine the role of central corticotropin releasing factor (CRF) and adrenergic receptors in mediating specific hemodynamic response patterns. Rats were instrumented for ascending aortic blood flow determination (cardiac output) using a pulsed Doppler system, arterial pressure measurement and for intravenous and intracerebroventricular (icv) administration of drugs. After characterizing the hemodynamic response pattern in individual rats to cocaine (5 mg/kg, i.v., 4-6 trials), selective receptor antagonists were administered icv 10 min before cocaine (5 mg/kg, i.v.). Pretreatment with the CRF antagonist alpha-helical CRF(9-41) (10 microg/5 microl, icv) prevented the decrease in cardiac output in vascular responders without altering hemodynamic responses to cocaine in mixed responders. Astressin (5 microg/5 microl, icv) exerted a similar effect in vascular responders. The alpha(2) receptor antagonist, yohimbine (3 microg/microl, icv) also prevented the decrease in cardiac output in vascular responders. Lower doses of alpha-helical CRF(9-41) (1 and 3 microg) were ineffective whereas higher doses of either CRF antagonist were lethal within 24 h. In contrast, propranolol (3 or 30 microg, icv) pretreatment enhanced the cocaine-induced decrease in cardiac output and increase in systemic vascular resistance noted in vascular responders and resulted in a decrease in cardiac output in mixed responders. We conclude that CRF and adrenoceptors in the CNS play an important role in determining the hemodynamic response pattern to cocaine. Furthermore, central beta-adrenoceptors may be responsible for the reported effects of intravenous propranolol on cocaine-induced responses.

Calcitonin gene-related peptide released within the amygdala is involved in Pavlovian auditory fear conditioning

The effects of CGRP and the CGRP receptor antagonist hCGRP(8-37) injected into the amygdala on both the acquisition and expression of fear behavior to a discrete auditory conditional stimulus (CS) and the training context were assessed. In Experiment 1, pretraining injections of CGRP but not hCGRP(8-37) produced fear-like behavior before any aversive stimuli were presented. While both compounds attenuated freezing to the contextual CS on the test day, neither affected learning about the auditory CS. In Experiment 2, pretesting injections of hCGRP(8-37) (0.63 mM) selectively attenuated freezing to the auditory CS but left freezing to the contextual CS intact. These data suggest that CGRP in the amygdala may selectively contribute to the expression of learning about auditory stimuli during fear conditioning.

The amygdala: vigilance and emotion

Here we provide a review of the animal and human literature concerning the role of the amygdala in fear conditioning, considering its potential influence over autonomic and hormonal changes, motor behavior and attentional processes. A stimulus that predicts an aversive outcome will change neural transmission in the amygdala to produce the somatic, autonomic and endocrine signs of fear, as well as increased attention to that stimulus. It is now clear that the amygdala is also involved in learning about positively valenced stimuli as well as spatial and motor learning and this review strives to integrate this additional information. A review of available studies examining the human amygdala covers both lesion and electrical stimulation studies as well as the most recent functional neuroimaging studies. Where appropriate, we attempt to integrate basic information on normal amygdala function with our current understanding of psychiatric disorders, including pathological anxiety.

Importance of endogenous nitric oxide synthase in the rat hypothalamus and amygdala in mediating the response to capsaicin

Although capsaicin has been shown to activate certain neuronal groups in the hypothalamus and amygdala, the neurotransmitters involved and the exact mechanism of action are not clearly understood at present. The aim of this study was to examine the hypothesis that the effect of capsaicin in the rat hypothalamus and amygdala primarily involves direct activation of the endogenous nitric oxide synthase (NOS) neurons responsible for the synthesis of nitric oxide (NO). Subcutaneous capsaicin injection in male rats, compared with vehicle, caused a significant increase in Fos expression in the paraventricular nucleus (PVN), supraoptic nucleus (SON), and medial and cortical amygdala. The expression of nicotinamide adenine dinucleotide phosphate diaphorase, a histochemical marker for NOS, was also increased in these brain areas in addition to the periventricular and lateral hypothalamic area and central amygdaloid nucleus. Also, capsaicin significantly increased the expression of neuronal NOS messenger RNA and protein in the PVN, SON, and medial amygdala as demonstrated by in situ hybridization and immunohistochemistry, respectively. A higher proportion of the NOS neurons in the PVN, periventricular region, SON and amygdala showed Fos expression in response to capsaicin than vehicle injection. There was little, if any, Fos activation in the NOS-positive neurons in the lateral hypothalamic area. The capsaicin-induced activation of the hypothalamic PVN and SON neurons and the medial amygdaloid nucleus was attenuated in the NOS inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME) -pretreated animals in comparison with the inactive enantiomer D-NAME. These observations indicate that activation of the endogenous NOS system and production of NO constitute a major pathway through which capsaicin exerts its effect within the hypothalamus and amygdala.

Effects of conditioning stimulation of the central amygdaloid nucleus on tooth pulp-driven neurons in the cat somatosensory cortex (SI)

To study the limbic control of nociception, we examined the effect of conditioning stimulation of the central amygdaloid nucleus (ACE) on tooth pulp-driven (TPD) neurons in the first somatosensory cortex (SI). Cats were anesthetized with N(2)O-O(2) (2:1) and 0.5% halothane, and immobilized with tubocurarine chloride. The tooth pulp test stimulus was applied by a single rectangular pulse (0.5 ms in duration and 3-5 times the threshold intensity for the jaw-opening reflex). Conditioning stimuli to the ACE consisted of trains of 33 pulses (300 microA) delivered at 330 Hz at intervals of 8-10 s. In 35 out of 61 of the slow (S)-type TPD neurons with latencies of more than 20 ms, conditioning stimulation in the ACE, especially in the medial division, markedly reduced the firing response to the pulpal stimulation. The inhibition of the firing rate in the S-type neurons was 74% of the control. In these S-type neurons, the neurons that were inhibited had significantly longer latencies compared to the non-inhibited neurons (45.0 +/- 17.6 ms, n = 32 vs. 34.8 +/- 10.5 ms, n = 26). In contrast, the ACE conditioning stimulation affected only one out of 18 fast-type TPD neurons with latencies of less than 20 ms. In addition, ACE stimulation had no effect on the spontaneous discharges of either S-type or F-type neurons. The ACE inhibitory effect on S-type neurons was not diminished by naloxone administration (1 mg/kg, I.V. ), while the blockade of histamine H(1)-receptor by diphenhydramine hydrochloride (0.5 mg/kg, I.V.) partially reversed the inhibitory effect. These results suggest that the ACE inhibits ascending nociceptive information to the SI and that this inhibition is mediated in part by histamine (H(1)) receptors. It seems likely that the antinociceptive effect is a neurophysiological basis for stress-induced analgesia (SIA).

Spontaneous and evoked activity of intercalated amygdala neurons

The intercalated cell masses are clusters of GABAergic neurons interposed between the basolateral and centromedial nuclear groups of the amygdala. Tract-tracing studies have revealed that the main projection sites of intercalated neurons are the central amygdaloid nucleus and the basal forebrain. Through these projections, intercalated neurons could influence the activity of widespread regions of the central nervous system. However, no data are available regarding their physiological properties because of the paramount methodological difficulties raised by the small size of intercalated cell masses. Here, we have investigated the spontaneous and evoked activity of intercalated neurons in unanaesthetized, chronically implanted cats. Extracellular recording sites were identified using stringent histological criteria. The intercalated cell masses were found to contain a population of neurons firing at much higher rates than commonly observed in neighbouring amygdaloid nuclei. Individual intercalated neurons displayed state-dependent changes in firing rates, but these varied from cell to cell. Most tested intercalated neurons displayed short-latency orthodromic responses to cortical shocks and were responsive to a variety of auditory stimuli. Considering that the vast majority of intercalated neurons use gamma-aminobutyric acid (GABA) as a transmitter, the presence of neurons with high spontaneous firing rates within the intercalated cell masses suggests that these cell clusters may provide a tonic inhibitory input to their projection sites. Moreover, the fact that the firing probability of some intercalated neurons could be altered by the presentation of sensory stimuli suggests that this inhibitory input can be modulated as a function of environmental contingencies.

Effect of prenatal stress on plasma corticosterone and catecholamines in response to footshock in rats

The effect of prenatal stress was investigated on the sympathoadrenal response to novelty and footshock by measuring the time course of the changes in circulating corticosterone (COR) catecholamines and their metabolites. Pregnant rats were subjected to noise and light stress, three times weekly on an unpredictable basis throughout gestation. When the male offspring of stressed rats (PS) and those of unstressed mothers (C) were 4.5-5 months of age, they were prepared with indwelling catheters in the tail artery 24 h before the experiment. Resting levels of plasma COR, noradrenaline (NA), adrenaline (AD), dihydroxyphenylglycol (DHPG), dihydroxyphenylacetic acid (DOPAC), and dihydroxyphenylalanine (DOPA) were measured. Further blood samples were taken within 3 min of their transfer to the shock box, 1-2, 5, 15, and 45 min after footshock. Plasma COR was significantly higher in PS than in C rats at rest, but those of adrenaline, NA, and their metabolites did not differ in the two groups. Transfer of the rats to the shock box increased plasma COR, NA, adrenaline, and dihydroxyphenylglycol in both groups, and dihydroxyphenylalanine and dihydroxyphenylacetic acid only in PS rats. All the catechols increased further 2-3 min after footshock, except dihydroxyphenylalanine in PS rats. Plasma NA and dihydroxyphenylglycol levels were significantly higher in PS than in C rats immediately after footshock, indicating a greater activation of the sympathetic nervous system in PS rats. The findings demonstrate for the first time that prenatal stress can induce long term changes in the sensitivity of the sympathoadrenal system to stress.

Prenatal stress: consequences of glucocorticoids on hippocampal development and function

Prenatally stressed offspring exhibit a variety of physiological and behavioral alterations. This paper highlights those alterations associated with prenatal stress-induced elevations in glucocorticoid secretion. Three major alterations are identified that may be produced by glucocorticoid-induced actions on the developing hippocampus. Changes include reductions in steroid receptors that bind endogenous glucocorticoids, enhanced secretion of stress hormones and increased reactivity or emotionality in stressful situations. Some of these alterations may be ameliorated by early postnatal environmental manipulations such as adoption and handling procedures. These latter results suggest that prenatal stress-induced effects of glucocorticoids extend into the early postnatal period to produce long-term hippocampal and behavioral alterations. Support for this hypothesis is based on studies demonstrating that the hippocampus undergoes considerable maturational changes during the early postnatal period such as establishing the regional distribution of corticosteroid receptor densities and development of hippocampal dentate gyrus cells as well as cholinergic systems. Hippocampal corticosteroid receptors are involved in the regulation of glucocorticoid negative feedback and hippocampal dentate gyrus and cholinergic development are influenced by endogenous glucocorticoids and are implicated in the development of defensive or stress-induced behavior. The developing hippocampus appears especially vulnerable to alterations induced by prenatal stress-induced elevations in glucocorticoids that continue to produce their effects throughout the early postnatal period.

Rapid stress-induced elevations in corticotropin-releasing hormone mRNA in rat central amygdala nucleus and hypothalamic paraventricular nucleus: an in situ hybridization analysis

High densities of nerve cells containing corticotropin-releasing hormone (CRH) are located in the central nucleus of the amygdala (CeA) and paraventricular nucleus (PVN) of the hypothalamus. These brain regions play an important role in activating autonomic, behavioral, and endocrine responses to stress. This study was conducted to provide needed information concerning the acute effects of stress on CeA and PVN CRH mRNA expression. Rats were exposed to restraint stress for 1 h and brains collected after a 1-h post-stress interval. CRH mRNA expression occurring in the CeA and PVN was examined using in situ hybridization techniques. Densitometric analysis revealed that acute restraint stress produced significant increases in CRH mRNA levels in the PVN and in the rostral CeA region. In addition, the area in the rostral CeA encompassing high CRH mRNA signals increased significantly after stress. Results provide clear evidence that CRH neurons in the CeA and PVN exhibit rapid increases in CRH mRNA expression after exposure to stress.

Neurotensin receptors in the human amygdaloid complex. Topographical and quantitative autoradiographic study

The distribution of high affinity 125I-neurotensin (NT) binding sites were investigated in the amygdaloid complex of adult humans by means of dry film and emulsion autoradiography. Autoradiograms were analysed quantitatively using [125I] standards and an image analyser system, and data obtained were converted to nCi of ligand bound per mg tissue. High densities of 125I-NT binding sites were found in the following amygdaloid structures the dorsal part of the accessory basal nucleus, the medial part of the cortical nucleus, the lateral subdivision of the central nucleus, the paralaminar nucleus, the amygdalohippocampal transition area and the rostral portions of the anterior amygdaloid area. The ventral part of the accessory basal nucleus, the intercalated cell groups and the remaining parts of the anterior amygdaloid area showed moderate density of NT binding sites, while the medial, basal and lateral amygdaloid nuclei, the lateral part of the cortical nucleus, the medial subdivision of the central nucleus, as well as the corticoamygdaloid transition area exhibited low densities of 125I-NT binding sites. At microscopic level, silver grains appeared more or less evenly distributed over both neuronal perikarya and the surrounding neuropil. In comparison to NT-immunoreactivity, NT receptors showed mismatching distribution throughout most parts of the amygdala, with the exception of the lateral subdivision of the central nucleus, where NT-immunoreactive perikarya and nerve fibers as well as 125I-NT binding sites were found in high density.

Input from central nucleus of the amygdala efferents to pericoerulear dendrites, some of which contain tyrosine hydroxylase immunoreactivity

Light microscopic anterograde tracing studies indicate that neurons in the central nucleus of the amygdala (CNA) project to a region of the dorsal pontine tegmentum ventral to the superior cerebellar peduncle which contains noradrenergic dendrites of the nucleus locus coeruleus (LC). However, it has not been established whether the efferent terminals from the CNA target catecholamine-containing dendrites of the LC or dendrites of neurons from neighboring nuclei which may extend into this region. To examine this question, we combined immunoperoxidase labeling of the anterograde tracer biotinylated dextran amine (BDA) from the CNA with immunogold-silver labeling of the catecholamine-synthesizing enzyme tryrosine hydroxylase (TH) in the rostrolateral LC region of adult rats. By light microscopy, BDA-labeled processes were dense in the dorsal pons within the parabrachial nuclei as well as in the pericoerulear region immediately ventral to the superior cerebellar peduncle. Higher magnification revealed that BDA-labeled varicose fibers overlapped TH-labeled processes in this pericoerulear region. By electron microscopy, anterogradely labeled axon terminals contained small, clear as well as some large dense core vesicles and were commonly apposed to astrocytic processes along some portion of their plasmalemma. BDA-labeled terminals mainly formed symmetric type synaptic contacts characteristic of inhibitory transmitters. Of 250 BDA-labeled axon terminals examined where TH immunoreactivity was present in the neuropil, 81% contacted unlabeled and 19% contacted TH-labeled dendrites. Additionally, amygdala efferents were often apposed to unlabeled axon terminals forming asymmetric (excitatory type) synapses. These results demonstrate that amygdaloid efferents may directly alter the activity of catecholaminergic and non-catecholaminergic neurons in this pericoerulear region of the rat brain. Furthermore, our study suggests that CNA efferents may indirectly affect the activity of pericoerulear neurons through modulation of excitatory afferents. Amygdaloid projections to noradrenergic neurons may help integrate behavioral and visceral responses to threatening stimuli by influencing the widespread noradrenergic projections from the LC.

Expression of Fos protein in various rat brain areas following acute nicotine and diazepam

We studied the effects of an acute dose of (-)-nicotine (1 mg/kg) on Fos-like immunostaining (IS) in rat brain areas. Nicotine increased Fos IS significantly in the medial terminal nucleus of accessory optic tract (MT), and tended to increase it in the interpeduncular nucleus (i.p.), as well as in the stress-related areas, the paraventricular hypothalamic nucleus (PVN) and the supraoptic nucleus (SON). Previously nicotine was reported to increase Fos IS also in another stress-related area, the central nucleus of amygdala (ACe). This led us to study the interaction of nicotine with diazepam (10 mg/kg). Diazepam alone increased Fos IS in PVN and in SON as well as in ACe. In diazepam- and nicotine-treated rats Fos IS was increased in PVN and SON as well as in MT and i.p.. In MT and i.p. of diazepam and nicotine-treated rats Fos IS was similar to that induced by nicotine alone, and in PVN and SON of these rats Fos IS in ACe. Taken together, diazepam induced Fos IS in all stress-related areas studied (PVN, SON, ACe), but not in central visual structures, where nicotine induces Fos IS (MT, i.p.). No significant interactions on Fos expression were found between acute effects of diazepam and nicotine suggesting that these drugs activate different sets of neurons within the stress-related brain areas.

Forebrain pathways and their behavioural interactions with neuroendocrine and cardiovascular function in the rat

1. The forebrain is a major organizer of the complex behavioural, physiological and neuroendocrine responses to environmental challenges of a stressful nature. 2. Combined physiological and neuroanatomical studies suggest that a specific forebrain-brain stem network, composed of connections between the central nucleus of the amygdala, the paraventricular nucleus of the hypothalamus, the mesencephalic cuneiform nucleus, the parabrachial nucleus and the dorsal motor nucleus of the vagus nerve, may be important for integrating behavioural and physiological responses. 3. Based on studies using bilateral electrolytic lesions of the central nucleus of the amygdala, it has become clear that the central nucleus of the amygdala is one of the key structures involved in unconditioned responses to inescapable footshock. These responses include freezing behaviour, tachycardia and the release of adrenaline, noradrenaline, prolactin and corticosterone. However, this nucleus is involved only in the freezing behaviour and bradycardiac responses to conditioned emotional stress or to social defeat. 4. Both peptidergic (corticotropin releasing hormone and vasopressin/oxytocin) and aminergic (noradrenaline and dopamine) mechanisms in the central amygdala are involved in the regulation of integrated behavioural, physiological and neuroendocrine stress responses. This is indicated by studies with an infusion of an agonist and/or antagonist of the peptides or neurotransmitters into the central amygdala of freely moving rats. Sympathetic cardiac control is intensified by corticotropin releasing hormone and oxytocin, probably by inhibiting vagal output. In contrast, vagal activity is facilitated by vasopressin, noradrenaline and dopamine.