Early experience alters limbic forebrain Fos responses to a stressful interoceptive stimulus in young adult rats.

The present study examined whether manipulation of the early life experience of rat pups might alter the later ability of an interoceptive challenge to recruit central neural circuits that receive visceral sensory signals and generate stress responses. For this purpose, litters were exposed to daily maternal separation for either 15min (MS-15) or 180min (MS-180) from postnatal days (P)1 to P10. Pups in control litters were raised under standard conditions (i.e., no separations). Similar to previous reports in adult rats, adolescent rats (P35-45) with a developmental history of MS-15 displayed less anxiety-like behavior on the elevated plus maze compared to control and MS-180 rats. As young adults (P50-60), rats were anesthetized and perfused with fixative 90min after viscerosensory stimulation via lithium chloride (LiCl, 0.15M, 1% BW, i.p.) or saline control. In all three rearing groups, Fos activation within brainstem and forebrain regions of interest was significantly enhanced after LiCl vs. saline. MS-15 rats tended to display fewer LiCl-activated neurons in most brain regions compared with rats in the other two rearing groups. This trend reached significance within the dorsal bed nucleus of the stria terminalis. The ability of MS-15 to alter limbic forebrain activation in rats after an interoceptive challenge may contribute to the effect of early life experience to modulate physiological and behavioral stress responses more generally.