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
