TAIL PINCH INDUCES FOS IMMUNOREACTIVITY WITHIN SEVERAL REGIONS OF THEMALE-RAT BRAIN - EFFECTS OF AGE

Brief, intermittent stressors, such as low-level foot shock or tail pi nch, induce a general excitement and autonomic arousal in rats that in creases their sensitivity to external incentives. Such stimulation can facilitate a variety of behaviors, including feeding, aggression, sex ual activity, parental behavior, and drug taking if the appropriate st imuli exist in the environment. However, the ability of tail pinch to induce general arousal and incentive motivation appears to diminish wi th age. Here we report on the ability of tail pinch to induce Fos immu noreactivity within several brain regions as a function of age. Young (2-3 months) and middle-aged (12-13 months) male rats were administere d either five tail pinches (one every 2 min), one tail pinch, or zero (sham) tail pinches (n = 4 per stimulation condition). Rats were sacri ficed 75 min following the onset of stimulation, and their brains were prepared for immunocytochemical detection of Fos protein. Fos immunor eactivity was induced by one and five tail pinches in several brain re gions, including the anterior medial preoptic area (mPOA), paraventric ular nucleus of the hypothalamus (PVN), paraventricular nucleus of the thalamus (PV-Thal), medial amygdala (MEA), basolateral amygdala (BLA) , lateral habenula (LHab), and ventral tegmental area (VTA), of young rats compared with those that received zero tail pinches. In contrast to young rats, middle-aged rats had significantly less Fos induced by one and five tail pinches in the mPOA, PVN MEA, BLA, and VTA, but an e quivalent amount induced in the LHab. Fos immunoreactivity was not fou nd within the medial prefrontal cortex, nucleus accumbens, striatum, l ateral septum, or locus coeruleus in either young or old rats. Tail pi nch appears to activate regions of the brain known to be involved in b ehavioral responses to both incentive cues and stressors. The lower le vel of cellular reactivity to tail pinch in middle-aged rats suggests a diminished neural responsiveness to incentives and stressors. (C) 19 97 Elsevier Science Inc.