Adrenalectomy alters the response of neurons in the bed nucleus of the stria terminalis to electrical stimulation of the medial amygdala

Behavioral and hormonal regulation of expression of the clock protein, PER2, in the central extended amygdala

PER2, a key molecular component of the mammalian circadian clock, is expressed rhythmically in many brain areas and peripheral tissues in mammals. Here we review findings from our work on the nature and regulation of rhythms of expression of PER2 in two anatomically and neurochemically defined subregions of the central extended amygdala, the oval nucleus of the bed nucleus of the stria terminalis (BNSTov) and the central nucleus of the amygdala (CEA). Daily rhythms in the expression of PER2 in these regions are coupled to those of the master circadian pacemaker, the suprachiasmatic nucleus (SCN) but, importantly, they are sensitive to homeostatic perturbations and to hormonal states that directly influence motivated behavior.

Hepatic vagotomy alters limbic and hypothalamic neuropeptide responses to insulin-dependent diabetes and voluntary lard ingestion

Hypothalamic anorexigenic [corticotropin-releasing factor (CRF) and proopiomelanocortin] peptides decrease and the orexigen, neuropeptide Y, increases with diabetic hyperphagia. However, when diabetic rats are allowed to eat lard (saturated fat) as well as chow, both caloric intake and hypothalamic peptides normalize. These neuropeptide responses to lard require an intact hepatic vagus [la Fleur et al. (2003) Diabetes, 52, 2321-2330]. Here, we delineate temporal interactions after lard consumption +/- hepatic vagotomy (HV) between feeding and brain neuropeptide expression in insulin-dependent diabetic rats. CRF-mRNA was reduced in the paraventricular nuclei (PVN) by 6 h after presentation of lard, before caloric intake increased in HV-diabetic rats, and did not increase at 30 or 36 h, as it did in shamHV-diabetic rats eating lard. CRF-mRNA was increased in the bed nuclei of the stria terminalis of HV-diabetic rats compared with shamHV-diabetic rats only when caloric intake was high at 30 or 36 h. At 36 h, shamHV-diabetic rats eating chow had increased CRF-mRNA in the central amygdala but diabetic rats eating lard had decreased CRF-mRNA, whereas HV-diabetic rats eating chow or lard had normal CRF-mRNA in the central amygdala. We conclude that eating lard restores peptide expression to normal in the hypothalamus of diabetic rats, and because decreased CRF-mRNA in the PVN precedes the increase in caloric intake in HV-diabetic rats eating lard, that the loss of a hepatic vagal signal to PVN may be responsible for increased intake; moreover, CRF-mRNA in limbic structures is also sensitive to both HV and lard ingestion in diabetic rats.

Androgens alter corticotropin releasing hormone and arginine vasopressin mRNA within forebrain sites known to regulate activity in the hypothalamic-pituitary-adrenal axis

To reveal direct effects of androgens, independent of glucocorticoids, we studied the effects of gonadectomy (GDX) in adrenalectomized (ADX) rats with or without androgen replacement on corticotropin releasing hormone (CRH) and arginine vasopressin (AVP) mRNA expression within various forebrain sites known to regulate the hypothalamic-pituitary-adrenal axis. These included the medial parvocellular portion of the paraventricular nucleus of the hypothalamus (mp PVN), the central and medial nuclei of the amygdala and bed nuclei of the stria terminalis (BNST). In the mp PVN, ADX stimulated both CRH and AVP mRNA expression. Combined ADX + GDX inhibited only AVP, and testosterone and dihydrotestosterone (DHT) restored AVP mRNA. In the central nucleus of the amygdala, ADX decreased CRH mRNA expression, and this response was unaffected by GDX +/- testosterone or DHT replacement. In the medial amygdala, AVP mRNA expression was decreased by ADX, abolished by ADX + GDX, and restored by androgen replacement. ADX had no effect on CRH and AVP mRNA expression in the BNST. GDX + ADX, however, reduced CRH mRNA expression only within the fusiform nuclei of the BNST and reduced the number of AVP-expressing neurones in the posterior BNST. Androgen replacement reversed both responses. In summary, in ADX rats, AVP, but not CRH mRNA expression in the amygdala and mp PVN, is sensitive to GDX +/- androgen replacement. Both CRH- and AVP-expressing neurones in the BNST respond to GDX and androgen replacement, but not to ADX alone. Because androgen receptors are not expressed by hypophysiotropic PVN neurones, we conclude that glucocorticoid-independent, androgenic influences on medial parvocellular AVP mRNA expression are mediated upstream from the PVN, and may involve AVP-related pathways in the medial amygdala, relayed to and through CRH- and AVP-expressing neurones of the BNST.

The effects of the medial and cortical amygdala lesions on post-stress analgesia in rats

The role of the medial, and cortical nuclei of amygdala was studied in 54 Möll-Wistar rats under two modes of foot-shock analgesia. In all but control animals bilateral electrolytic lesions were performed. Pre- and post-stress pain reactivity were measured in the hot-plate and the tail-flick tests. The damage of the medial nucleus decreases animals' primordial pain reactivity. Four minutes of continuous foot-shock produced post-stress analgesia in all control and lesioned rats, but 20 min of regularly intermittent foot-shock failed to evoke analgesia in the lesioned rats, especially in subjects with the dorsal part of the medial nucleus injuries. The results indicate that the medial and cortical nuclei are important in regulation of the post-stress antinociceptive processes evoked only by prolonged intermittent shock action. It has been previously shown that the behaviour evoked by this stressor is related to opioid mechanisms, and modulated by the hypothalamic-pituitary-adrenocortical system. Present finding is in agreement with our concept of the dorsomedial amygdala involvement in painful and stressful stimuli processing.