Ontogeny of neurohormonal regulation of the cardiovascular system in the crayfish Procambarus clarkii

Adult crayfish have a neurogenic heart which is modulated via inputs from the central nervous system and neurohormones, which act on the cardiac ganglion or directly on the myocardium. This study investigates the ontogeny of cardiac regulation by exploring the temporal sequence of cardiac sensitivity to injections of cardioactive neurohormones (proctolin, serotonin and octopamine) and the neurotransmitter γ-aminobutyric acid. The cardiac response (Δ in heart rate, stroke volume, or in cardiac output) to each neurohormone at each developmental stage was assessed. The observed response elicited by each cardioactive drug was stage dependent and changed as the animals progressed from embryonic through larval and juvenile periods. During early developmental stages, octopamine, serotonin, and proctolin (10^-9-10^-3 M) did not result in a modulation of stroke volume, yet in later developmental stages they caused significant increases in stroke volume, at comparable concentrations. Early developmental stages are capable of regulating cardiac function, however, the mechanisms appear to be quite different from those used by adults. Evidence is also provided to support the hypothesis that cardiac function is initiated prior to the establishment of an adult-like regulatory system.