Abstract
1. The age-dependence of the modulatory actions of octopamine on the dorsal longitudinal flight muscle of the locust,Schistocerca gregaria, is described. 2. The maximal levels of octopaminergic potentiation of the amplitude and of the rates of contraction and relaxation of twitch tension occurred in the late 5th instar hopper and in the adult at the day of moulting. After 1 day of adult life the effects on twitch amplitude and contraction rate had declined to basal levels which were maintained for up to 28 days. The effect on the relaxation rate declined progressively up to day 7 of adult life before reaching a maintained level. Parallel effects were observed for the changes mediated by stimulation of the dorsal unpaired median modulatory octopaminergic neurone (DUMDL) to this muscle. 3. The octopamine-induced changes in the physiological parameters of twitch tension exhibited motor unit specificity as did changes in the octopamine-mediated increases in cyclic AMP levels. 4. Studies on the age-dependence of the modulatory effects of exogenously applied cyclic nucleotides suggest that age-dependent changes occur at multiple sites in the response cascade between the activation of octopamine receptors and the observed physiological responses.
Published Version
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