Lesions of the lateral hypothalamus impair pilocarpine-induced salivation in rats

Abstract

In the present study we investigated the effects of electrolytic lesions of the lateral hypothalamus (LH) in the salivation induced by intracerebroventricular (i.c.v.) or intraperitoneal (i.p.) injection of the cholinergic agonist pilocarpine. Rats with sham or LH lesions and stainless steel cannulas implanted into the lateral ventricle (LV) were used. In rats anesthetized with urethane (1.25 mg/kg of body weight) saliva was collected using pre-weighed cotton balls inserted in the animal mouth during a period of 7 min following i.c.v. or i.p. injection of pilocarpine. Injection of pilocarpine (1 mg/kg of body weight) i.p. in sham-operated rats (6 h, 2, 7, and 15 days after the surgery) induced salivation (497±24, 452±26, 476±30, and 560±75 mg/7 min, respectively). The effects of i.p. pilocarpine was reduced 6 h, 2 and 7 days after LH lesions (162±37, 190±32, and 229±27 mg/7 min, respectively), not 15 days after LH lesions (416±89 mg/7 min). Injection of pilocarpine (120 μg/ μl) i.c.v., in sham-operated rats (6 h, 2, 7, and 15 days after the surgery) also produced salivation (473±20, 382±16, 396±14, and 427±47 mg/7 min, respectively). The salivation induced by i.c.v. pilocarpine was also reduced 6 h, 2 and 7 days after LH lesions (243±19, 278±24, and 295±27 mg/7 min, respectively), not 15 days after LH lesions (385±48 mg/7 min). The present results show the participation of the LH in the salivation induced by central or peripheral injection of pilocarpine in rats, reinforcing the involvement of central mechanisms on pilocarpine-induced salivation.