We investigated the excitatory and inhibitory input to cardioaccelerator (CA) and cardioinhibitor (CI) neurons located in the thoracic ganglia of the isopod crustacean Bathynomus doederleini by extracellular and intracellular recording. Electrical stimuli applied to the anterior and posterior connectives of single-ganglion preparations, containing either the 2nd or 3rd thoracic ganglion alone, and each of three paired ganglionic nerve roots produced excitatory postsynaptic potentials (EPSPs) in the cell body of a CA neuron. Artificial movements of appendages, such as the thoracic limbs and the swimmerets, also evoked EPSPs in the CA neuron. Electrical stimuli applied to the peripheral nerves running to appendages induced inhibitory postsynaptic potentials (IPSPs) in a CI neuron. Since artificial movements of the appendages caused decrease of CI impulse rate, these IPSPs in the CI neuron may be caused by mechanoproprioceptors in the appendages. Since tachycardia was accompanied by excitation of CA neurons and inhibition of CI neurons, activation of the mechanoproprioceptors may be responsible for tachycardia. EPSPs in CA neurons produced by stimulation of peripheral nerves were augumented by eserinization and blocked by curarization. The activation of CA neurons by ganglionic roots may be mediated by cholinergic processes ascending from mechanoproprioceptors.
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