The initial heat production associated with the nerve impulse in crustacean and mammalian non‐myelinated nerve fibres

The passage of a single impulse in non-myellnated nerves of the spider crab, Maia squinado, at 00 C is associated with a positive heat production of about 9 ,ctcal/g; this is followed by a slower heat absorption of about 7 ,tcal/g (Abbott, Hill & Howarth, 1958). Although the diphasic character of the heat production cannot at the moment be accounted for satisfactorily, it may eventually provide an important clue to the physical and chemical mechanisms underlying the nerve impulse. It seemed important, therefore, to determine whether or not similar heat changes occur in nerves of species other than Maia. We have therefore examined the heat production of the nerve of two other crustaceans, namely the Pacific Spider crab, Loxorhynchus crispatus and the lobster, Panulirus interruptus. In addition, we have studied the heat production ofmammalian non-myelinated nerve fibres. The latter experiments were done on rabbit vagus nerves (Ritchie, Abbott & Howarth, 1961) which are composed mainly of non-myelinated fibres of more uniform and smaller average diameter than those of the crab. These experiments have confirmed the presence in all the nerves examined of the early phases of positive and negative heat production which occur during, or soon after, the spike. In addition, a previously unsuspected third phase of prolonged cooling was found to occur in the rabbit nerve under certain experimental conditions.