Release and actions of neurotransmitter molecules at neuroglandular junctions in cockroach salivary glands

The innervation of the salivary gland of the cockroach Nauphoeta cinerea (Olivier) has been investigated with the use of light and scanning electron microscopy (SEM). Light microscopy revealed the presence of a dual innervation arising from the ventral nerve cord and the stomadeal nervous system; the principal innervation is that from the ventral nerve cord which passes to the gland via the reservoir ducts. Branches of these nerves form a plexus on the acinar surface, the axons of which exhibit swellings at irregular intervals. The presence of this plexus and the axonal swellings was confirmed by SEM both in normal glands and in those in which the basement membrane had been removed by means of an HCl-collagenase digestion method. Cell bodies associated with the larger axons of the duct nerves were identified in the sub-oesophageal ganglion using an axonal filling method employing cobalt chloride and horseradish peroxidase. No acinar plexus was apparently formed by branches of the stomatogastric nerve associated with the gland. Other branches of this nerve were connected with a network of multipolar neurones on the surface of both salivary reservoirs. Intracellular recordings from the gland cells revealed that a hyperpolarizing response evoked by electrical stimulation of the duct nerve was graded according to the number of stimuli. The biogenic amines, adrenaline, dopamine, noradrenaline, 5-hydroxytryptamine and octopamine, produced dose-dependent hyperpolarizing responses. A quantitative study of the inhibition by phentolamine on the response to nerve stimulation and the bath applied agonists was made. The investigation showed that phentolamine discriminates between two kinds of receptor in this gland, one binding 5-hydroxytryptaraine and the other combining with the catecholamines and the neurotransmitter. The inhibition appeared to be competitive and measures of phentolaraines affinity constant gave values of 0*015 (^M) 1 and 1 (^M) 1 for each type of receptor respectively. It was concluded that the neurotransmitter in the cockroach salivary gland was probably dopamine