The Effect of Centrally Administered D-Alanine-Methionine-Enkephalinamide (Dala) on the Copulatory Behavior of Male Hamsters
Male rats exhibit inhibited copulatory behavior following central injections of D-alanine-methionine- enkephalinamide (DALA) with increased mounting latencies and decreased mounting frequencies (Gessa, 1979). To determine DALA's effect on a related but more seasonally breeding species and to examine the effect of repeated exposures to increased central enkephalins, sexually experienced male hamsters received intracerebroventricular (ICV) injections in the lateral ventricle. On postoperative days 7 and 11, 2ug of DALA was administered ICV. One day 15, 4mg/kg of Naloxone, a competitive opiate antagonist was given intraperitoneal (IP) 10 minutes before DALA ICV. Ten minutes after each administration of DALA, males were exposed to estrus females for 50 minutes and their copulatory behavior observed. Investigative latencies, first mounting latencies, and ejaculatory latencies were increased on the first DALA injection. The second exposure to DALA had greater inhibitory effects. Some animals completely failed to mount after the second exposure. The frequency of mounts during the 50 minutes decreased on the first exposure and this decrease was greater on the second exposure. Naloxone pretreatment suppressed the DALA inhibitory effect on these reproductive behaviors.
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