Morphological changes in gland cells and axons resulting from stimulation of the salivary nerves of the cockroach, Nauphoeta cinerea.

The salivary glands of the cockroach, Nauphoeta cinerea (Oliver, 1789), are innervated and there is considerable evidence to suggest that dopamine is the neurotransmitter at the neuroglandular junction. As the gland is a bilaterally symmetrical structure it was possible to electrically stimulate the salivary nerve supplying the ipsilateral side of the gland whilst the contralateral side of the gland served as a convenient control. Saliva elicited from the glands by electrical stimulation of these nerves was collected and used to monitor the physiological state of the tissue. Glands were fixed for light and electron microscopy during secretion and it was observed that the ductules in peripheral acinar cells were distended in stimulated sides of the glands but not in contralateral unstimulated sides. This evidence implies that peripheral cells are responsible for the initiation of salivary fluid secretion. Changes were also observed in the catecholamine containing axons that innervate the glands. In stimulated axons a statistically significant reduction in numbers of small agranular vesicles was observed when compared with contralateral unstimulated controls and freshly fixed tissue. This was not the case with the larger granular vesicles of the same axons which showed no reduction in number as a result of stimulation. In addition it was also noted that the small agranular vesicles tended to aggregate and change their shapes in response to nerve stimulation. These results imply that the small agranular vesicles play a role in transmitter release.