IN-SITU HYBRIDIZATION ANALYSIS OF PREPROTACHYKININ-A AND PREPROTACHYKININ-B MESSENGER-RNA LEVELS IN SHORT-TERM SODIUM DEPLETION

Tachykinins inhibit salt appetite when applied intracranially in a num ber of brain legions and may function as endogenous inhibitors of sodi um intake. To test the hypothesis that induced increases in salt appet ite might involve disinhibition via a reduction in endogenous tachykin in expression, we used a semi-quantitative in situ hybridization analy sis to investigate changes in brain areas expressing preprotachykinin- A (PPT-A) and preprotachykinin-B (PPT-B) mRNAs of rats after 1 day of sodium depletion (Id Na dep). PPT-A mRNA levels were detected in neuro ns of the olfactory tubercle (Tu), the nucleus of the olfactory tuberc le (LOT), the dorsal and ventral caudate-putamen (d-CPu and v-CPu), th e bed nucleus of the stria terminalis (BNST), the medial preoptic area (mPOA), the habenula (Hb) and the postero-dorsal part of the amygdala (MePD). PPT-B mRNA levels were measured in fundus striati (FStr), d-C Pu, v-CPu, BNST, mPOA, dorsomedial hypothalamic nucleus (DMD), arcuate nucleus (Are), central amygdaloid nucleus (CeL), basolateral amygdalo id nucleus (BLV), LOT, Hb and basal nucleus of Meynert (B). Id Na dep reduced by 33-61% the mean number of PPT-A grains/cell in Tu, LOT, d-C Pu, BNST, mPOA, Hb and MePD compared to control animals. Levels of PPT -B mRNA were not reduced as much by Id Na dep, although statistically significant reductions of 26, 34 and 17% were found in v-CPu, BNST and B, respectively. These findings, therefore, support the hypothesis th at endogenous tachykinins exert an inhibitory influence over sodium ap petite. (C) 1997 Elsevier Science B.V.