The insect neuropeptide proctolin can affect the CNS and the smooth=muscle of mammals

The insect neurotransmitter proctolin can affect different behavioural parameters in rats after intracerebroventricular administration. Proctolin decreased the horizontal exploratory activity and induced a long-lasting analgesia in a hot-plate test. Proctolin lenghthened the passive avoidance latency of rats after post-trial treatment and also in the pre-retention test situation. The self-stimulation rate of rats was significantly diminished after i.c.v. proctolin administration. Proctolin also induced in rat and mouse ileum in vitro a dose-dependent contraction of the gut smooth-muscle that can be blocked by atropine. The results show that an invertebrate neuropeptide (or its fragments) can also be active in mammals. The physiological relevance of the effects observed recently is unknown.