The action of peptides and cyclic nucleotides on the nervous system of an insect.

Eclosion hormone (EH) is a moderate-sized peptide that acts on the insect nervous system to release the stereotyped behaviors involved in shedding the old skin (eclosion) as well as to activate new reflex pathways. The action of the peptide has been studied by using two preparations. The first preparation involves the preeclosion and eclosion motor programs that can be released from the isolated abdominal central nervous system (CNS) in response to EH. The target sites associated with the release of these programs are scattered throughout the CNS, each apparently being associated with a segmental component of one of the programs. A fully coordinated behavioral response requires that all these segmental elements be exposed to the peptide. The second preparation has allowed the cellular analysis of a simple multisegmental reflex that is turned on by EH. The data indicate that the reflex pathway is activated by the peptide through the selective action on a key synaptic junction. In the case of both of these preparations, the action of EH appears to involve an increase in cyclic GMP levels in the CNS. The manner by which these increases result in altered neuronal activity remains unknown.