Effects of neurotropic substances—apomorphine, piribedil, bromocriptine and metergoline—on the excitability of identifiable molluscan giant neurons sensitive to dopamine and 5-hydroxytryptamine

Abstract

1. It was examined whether four neurotropic substances—apomorphine, piribedil, bromocriptine and metergoline—have either an agonistic or antagonistic effect to dopamine (DA) and 5-hydroxytryptamine (5-HT), by using the two giant neurons (PON, periodically oscillating neuron and TAN, tonically autoactive neuron), which are sensitive to the two putative neurotransmitters and identified in the suboesophageal ganglia of an African giant snail ( Achatina fulica Férussac). 2. The four neurotropic substances examined at 10 −4 kg/1 had neither an agonistic nor antagonistic effect to both 5-HT and DA on the two giant neurons. 3. Both apomorphine and metergoline at 10 −4 kg/1 sometimes produced abnormal spike discharges of TAN, such as the doublet spikes or the slow oscillations of membrane potential. 4. Bromocriptine at 10 −4 kg/1 occasionally caused a transient hyperpolarization of the TAN membrane potential, which was probably due to the synaptic influences.