A peptide hormone, the eclosion hormone, triggers two behavioural patterns--the pre-eclosion and eclosion patterns--when injected into pharate silkmoths. Injection of cyclic nucleotides caused the same behavioural responses with cGMP being 10 to 100 times more potent than cAMP. Exogenous cGMP also acted directly on the isolated nervous system to evoke the characteristic motor programmes. Protection of endogenous cyclic nucleotides by pretreatment of moths with a phosphodiesterase inhibitor, theophylline, markedly enhanced the sensitivity of the moths to the hormone. Injection of partially purified hormone preparations was followed by an increase in nervous system cGMP but not cAMP. The increase preceded the behavioural effectiveness of each dose was correlated with its ability to cause a cGMP increase. It was concluded that the behavioural effects of the eclosion hormone are mediated through an increase in cGMP in the nervous system.

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