Social context induces two unique patterns of c-Fos expression in adolescent and adult rats

Abstract

The study assessed possible age differences in brain activation patterns to low dose ethanol (.5 g/kg intraperitoneally) and the influence of social context on this activation. Early adolescent or young adult male Sprague-Dawley rats were placed either alone or with an unfamiliar partner of the same age and sex following saline or ethanol administration. c-Fos protein immunoreactivity was used to index neuronal activation in 15 regions of interest. Ethanol had little effect on c-Fos activation. In adolescents, social context activated an "autonomic" network including the basolateral and central amygdala, bed nucleus of the stria terminalis, lateral hypothalamus, and lateral septum. In contrast, when adult rats were alone, activation was evident in a "reward" network that included the substantia nigra, nucleus accumbens, anterior cingulate and orbitofrontal cortices, lateral parabrachial nucleus, and locus coeruleus.

Keywords: adolescent; alcohol; autonomic system; immediate early genes; rat; reward system; social context.

Figure 1

Pattern I c-Fos expression in the central amygdala (CeA), basolateral amygdala (BLA), bed nucleus of the stria terminalis (BNST), lateral hypothalamus (LH), lateral septum (LS), ventral tegmental area (VTA), Edinger-Westphal nucleus (EW), and the paraventricular nucleus of hypothalamus (PVN) of adolescents and adults tested either alone or with a social partner. An asterisk (*) reflects significant age difference within the same test context, # - depicts significant difference between the two contexts within same age.

Figure 2

Pattern II c-Fos expression in the anterior cingulate cortex (ACC), ventromedial orbitofrontal cortex (VMO), nucleus accumbens shell (nAcS0), nucleus accumbens core (nAcC), lateral parabrachial nucleus (PBI), substantia nigra (SN), and locus coeruleus (LC) of adolescents and adults tested either alone or with a social partner. An asterisk (*) reflects significant age difference within the same test context, # - depicts significant difference between the two contexts within same age.

Figure 3

Immunohistochemistry of c-Fos in an adolescent during the social condition and an adult alone condition. A. The CeA and BLA are shown in a thionin-stained section adjacent to the c-Fos-labeled sections. B. & C. The adolescent animal had high expression in both nuclei, while that in the adult was low. D. A thionin-stained section shows area 32 with each layer noted and lines were struck at the layers II/III and IV/Va borders in each section. The c-Fos labeling was particularly high in layers III and IV of the adult case, while that for the adolescent was more dispersed and somewhat less dense. All calibration bars are for 500 μm.