[Neuron-neuroglia functional relation in the squid giant nerve fiber]

The present work reviews the results of a series of physiological studies carried out in the giant nerve fiber of the tropical squid Sepioteuthis sepioidea, aimed at exploring the possible involvement of different second mediators and receptor systems, in the modulation of the long-lasting hyperpolarizing response of the Schwann cell membrane potential to axonal excitation. These studies provide experimental evidence on the existence of distinct receptors for ACh, octopamine, and a VIP-like endogenous peptide in the Schwann cell plasma membrane. They also indicate that the cyclic nucleotide adenosine 3',5' monophosphate may be playing a role as second messenger for the actions of the Schwann cell nicotinic cholinergic and the octopaminergic receptors, whereas the VIP receptor may be acting through the hydrolysis of polyphosphatidylinositols. These experimental findings are discussed as evidence for the existence of a complex multistep interaction between the giant axon and its satellite glial cells, the Schwann cell.