The physiological properties of amine‐containing neurones in the lobster nervous system.

Abstract

Previous studies showed that octopamine and serotonin [5-hydroxytryptamine] are found associated with a system of neurons in the connective tissue sheath of the 2nd roots of lobster [Homarus americanus] thoracic ganglia. To try to understand the mechanism of activation of these neurons, an examination of their general physiological properties was undertaken. All the neurons receive excitatory synaptic input that has a cholinergic pharmacology, which suggests that it may be from sensory neurons. A very limited number of cells, possibly 1, provides the total synaptic input to all the cells in the roots of the 2nd and 3rd thoracic segments. The cells within one root are electronically coupled to each other. The extent of coupling varies widely between cells; on occasion the coupling is sufficiently tight for action potentials originating in one cell to trigger action potentials in the neighboring cell. The majority of the cells show no spontaneous activity at temperatures < 14.degree. C, but become spontaneously active above that temperature. Cells cycle reversibly from silent to continuously active to bursting and back as the temperature is increased and decreased. Octopamine and serotonin inhibit bursting activity. The octopamine response is blocked by phentolamine but not by propranolol, while the inhibitory action of serotonin is unaffected by either of these drugs. The amine-inhibition of the firing could be an autoregulatory mechanism for cell activity. The widely dispersed amine-containing neurons in lobsters seem to behave like a neurosecretory organ in terms of their mechanism of activation.