Fos expression in forebrain afferents to the hypothalamic paraventricular nucleus following swim stress

Abstract

The paraventricular nucleus of the hypothalamus (PVN) serves as the origin of the final common pathway in the secretion of glucocorticoid hormones in response to stress. Various stress-related inputs converge upon the cells of the medial parvocellular division of the PVN. These neurons, which synthesize and release corticotropin-releasing hormone, arginine vasopressin, and other secretagogues, are responsible for a cascade of events which culminates in the adrenocorticotropin-induced release of corticosteroids from the adrenal cortex. Previous data have suggested complex afferent regulation of PVN neurons, although the neuronal pathways by which the effects of stress are mediated remain to be fully disclosed. The present experiment sought to identify forebrain areas potentially involved in afferent regulation of the PVN in response to an acute stressor. Discrete injections of the retrograde tracer Fluoro-gold were delivered to the PVN, and rats were subsequently subjected to an acute swim stress. Brains were processed immunocytochemically for the simultaneous detection of the tracer and Fos, the protein product of the immediate early gene c-fos, utilized as a marker for neuronal activation. The majority of Fluoro-gold/Fos labeled neurons were detected in the parastrial nucleus, the medial preoptic area, the anterior hypothalamic area, the dorsomedial hypothalamic nucleus and adjacent posterior hypothalamic area, and, to a lesser extent, the supramammillary nucleus. These findings are discussed in relation to neural pathways mediating activation and inhibition of the hypothalamic-pituitary-adrenocortical axis.

Circuitry Underlying Regulation of the Serotonergic System by Swim Stress

“…The distribution of c-fos immunolabeling in rats subjected to swim stress was similar to that reported previously (Duncan et al, 1993;Cullinan et al, 1996). For example, c-fos-immunoreactive profiles were numerous in the LC, dorsolateral parabrachial nucleus, lateral habenula, paraventricular nucleus of the hypothalamus, and lateral septum of swim-stressed rats.…”

Stress-Induced c-Fos Expression is Differentially Modulated by Dexamethasone, Diazepam and Imipramine

“…Similar to what was discussed for dexamethasone, irrespective to the mechanisms, diazepam can change the stress responses by modulation of inhibitory and excitatory inputs to the HPA axis. Based on this view, although diazepam did not have any effect on the c-Fos expression on the PVH, it has reduced the activation of the MPO that sends direct excitatory projections to PVH (Cullinan et al, 1996). On the other hand, diazepam reduced the c-Fos expression in areas that can inhibit as well as activate the HPA axis.…”

Acute and chronic effects of ferret odor exposure in Sprague–Dawley rats

“…Regions of the brain that are routinely associated with HPA axis activity express ferret odor-induced c-fos induction; among these, the bed nucleus of stria terminalis, cingulate cortex, lateral septum, and paraventricular nucleus of the hypothalamus were most prominent. As with a number of other stressors, ferret odor induces c-fos mRNA in a number of additional areas, including the orbitofrontal cortex, piriform cortex, anterodorsal preoptic, dorsomedial and ventromedial nuclei of the hypothalamus, the dorsal premammillary nucleus, supramammillary nucleus, basolateral and posterodorsal medial amygdala, and periaqueductal gray Chen and Herbert, 1995;Cullinan et al, 1996Cullinan et al, ,1995Dielenberg et al, 2001b;Imaki et al, 1993;Melia et al, 1994;Pace et al, 2005). In addition, the similarities between c-fos IEG induction between cat and ferret odors is striking; regions such as the lateral septum, dorsomedial hypothalamus, ventromedial hypothalamus, premammillary nucleus, posteroventral medial nucleus of the amygdala, and periaqueductal gray (dorsolateral, dorsomedial, and ventrolateral parts) all displayed high levels of cat and ferret odor induced c-fos (Dielenberg et al, 2001b).…”

“…Thus, in addition to being relatively similar to cat odor, ferret odor elicits a pattern of c-fos mRNA induction that includes many of the same brain regions activated by forced swim, restraint, and loud noise, especially in limbic areas and the hypothalamus (Burow et al, 2005;Watson, 1997, 2000;Chowdhury et al, 2000;Cullinan et al, 1996Cullinan et al, , 1995Melia et al, 1994). Although many of the same regions appear to be influenced by a variety of stress conditions, the extent to which the same cell populations are activated within any one region by different stressors is unknown, which could best be determined by detecting brain activity patterns from at least two different stressors in the same rats simultaneously.…”