Corticotropin-releasing factor-overexpressing mice exhibit reduced neuronal activation in the arcuate nucleus and food intake in response to fasting

Abstract

Corticotropin-releasing factor (CRF) overexpressing (OE) mice are a genetic model that exhibits features of chronic stress. We investigated whether the adaptive feeding response to a hypocaloric challenge induced by food deprivation is impaired under conditions of chronic CRF overproduction. Food intake response to a 16-h overnight fast and ip injection of gut hormones regulating food intake were compared in CRF-OE and wild type (WT) littermate mice along with brain Fos expression, circulating ghrelin levels, and gastric emptying of a nonnutrient meal. CRF-OE mice injected ip with saline showed a 47 and 44% reduction of 30-min and 4-h cumulative food intake response to an overnight fast, respectively, compared with WT. However, the 30-min food intake decrease induced by ip cholecystokinin (3 microg/kg) and increase by ghrelin (300 microg/kg) were similar in CRF-OE and WT mice. Overnight fasting increased the plasma total ghrelin to similar levels in CRF-OE and WT mice, although CRF-OE mice had a 2-fold reduction of nonfasting ghrelin levels. The number of Fos-immunoreactive cells induced by fasting in the arcuate nucleus was reduced by 5.9-fold in CRF-OE compared with WT mice whereas no significant changes were observed in other hypothalamic nuclei. In contrast, fasted CRF-OE mice displayed a 5.6-fold increase in Fos-immunoreactive cell number in the dorsal motor nucleus of the vagus nerve and a 34% increase in 20-min gastric emptying. These findings indicate that sustained overproduction of hypothalamic CRF in mice interferes with fasting-induced activation of arcuate nucleus neurons and the related hyperphagic response.

Figure 1

CRF-OE mice had a reduced food intake response to an overnight fast compared with WT mice, whereas the CCK satiation effect was not altered. After an overnight fast, CRF-OE and WT littermate mice were injected ip with saline or CCK-8S (3 μg/kg BW) and cumulative food intake (expressed as grams per 25 g BW) was measured at 30 min and 1, 2, and 4 h. Data are expressed as mean ± sem; the numbers of mice per group are indicated in parentheses. *, P < 0.05.

Figure 2

Freely fed CRF-OE mice had a similar food intake response to ip ghrelin as WT mice. Freely fed CRF-OE and WT littermate mice were injected ip with saline or ghrelin (300 μg/kg BW) and cumulative food intake (expressed as grams per 25 g BW) was measured at 30 min and 1, 2, and 4 h. Data are expressed as mean ± sem; the numbers of mice per group are indicated in parentheses. *, P < 0.05.

Figure 3

Plasma levels of total ghrelin in nonfasted and overnight fasted CRF-OE and WT littermate mice. Data are expressed as mean ± sem of n = 4 and 6 (nonfasted) or n = 3 and 4 (fasted) CRF-OE and WT mice. *, P < 0.05 vs. WT nonfasted; #, P < 0.05 vs. the nonfasted same genotype.

Figure 4

The number of Fos-ir neurons in hypothalamic and brain stem nuclei in overnight-fasted CRF-OE and WT mice (n = 3 and 4). Each bar represents the mean ± sem of the number of Fos-ir cells/section counted unilaterally in the Arc, PVN, DMV, and NTS. *, P < 0.05 vs. WT mice.

Figure 5

Microphotographs of Fos immunoreactivity in the Arc, PVN, and dorsal-vagal complex (DMV and NTS) of overnight fasted CRF-OE (right panels) and WT (left panels) mice. Overnight fasted CRF-OE mice showed much less Fos-ir neurons in the Arc (B) compared with WT mice (A). No difference was detectable in the PVN (C and D) and NTS (E and F). Overnight fasting resulted in a significantly increased number of Fos-ir neurons in the DMV of CRF-OE mice (F) compared with WT mice (E). The scale bar in photo A represents the magnification for photos A–D and the one in E for E and F. 3V, Third cerebral ventricle; AP, area postrema.