DIPSOGENIC EFFECT OF PITUITARY ADENYLATE-CYCLASE ACTIVATING POLYPEPTIDE (PACAP38) INJECTED INTO THE LATERAL HYPOTHALAMUS

PACAP38 bilaterally injected in the vicinity of the perifornical lateral hypothalamus (pfLH) induced drinking behavior in rats. The animals (n = 12) drank 19.7 +/- 4.1 ml of water during the hour following PACAP38 microinjections (1 nmol/0.5 mu l). In the same rat sulpiride microinjections (45 nmol/0.5 mu l) had relatively mild effects (7.8 +/- 1.4 ml/h). The dipsogenic effects of sulpiride and PACAP38 were well correlated suggesting that both substances trigger drinking behavior activating the same hypothalamic mechanisms. Neither sulpride nor PACAP38 promoted drinking when injected just 1.3 mm behind the effective zone. This negative result is an evidence of the neuroanatomical specificity of the dipsogenic effects of both substances. These preliminary results suggest that PACAP38 in the pfLH could be a neuropeptide regulating drinking behavior and perhaps body fluid volume and osmolarity and arterial blood pressure.