Serotonergic neurons and axons were mapped in the central ganglia of Aplysia californica using antiserotonin antibody on intact ganglia and on serial sections. Immunoreactive axons and processes were present in all ganglia and nerves, and distinct somata were detected in all ganglia except the buccal and pleural ganglia. The cells stained included known serotonergic neurons: the giant cerebral neurons and the RB cells of the abdominal ganglion. The area of the abdominal ganglion where interneurons are located which produce facilitation during the gill withdrawal reflex was carefully examined for antiserotonin immunoreactive neurons. None were found, but two bilaterally symmetric pairs of immunoreactive axons were identified which descend from the contralateral cerebral or pedal ganglion to abdominal ganglion. Because of the continuous proximity of this pair of axons, they could be recognized and traced into the abdominal ganglion neuropil in each preparation. If serotonin is a facilitating transmitter in the abdominal ganglion, these and other antiserotonin immunoreactive axons in the pleuroabdominal connectives may be implicated in this facilitation.

Fischer 344 (F-344) rats fail to prefer NaCl solutions to water at any concentration and avoid NaCl solutions preferred by other strains, including Wistar rats. Behavioral and electrophysiological responses of the mammalian gustatory system to NaCl have been shown to depend on a sodium transport system that is specifically blocked by lingual application of the sodium-transport blocker amiloride. The present study examined whether strain differences exist between F-344 and Wistar rats in the amiloride sensitivity of the chorda tympani (CT) electrophysiological response to NaCl. Whole nerve CT recordings were obtained from adult F-344 and Wistar rats during chemical stimulation of the anterior tongue. Responses to NaCl solutions ranging from 0.01 to 1.0 M were examined both before and after pretreatment with amiloride hydrochloride. Integrated whole nerve responses to NaCl solutions were expressed relative to the response to 0.5 M NH4Cl. Strain differences in the response to NaCl solutions emerged, with F-344 animals showing a significantly larger amplitude of the tonic response to NaCl, relative to NH4Cl, than Wistars. F-344 rats were also more sensitive to the sodium-channel blocker amiloride. These results suggest that strain differences in amiloride sensitive signals mediated by the CT nerve may contribute to the NaCl aversion displayed by F-344 rats.

Serotonin-like immunoreactivity was mapped using an antiserotonin antibody in wholemounts of the ventral nerve cord from dragonfly nymphs (Epitheca sp. and Pachydiplax longipennis). In both species, an immunoreactive cell ventral to each connective tract and an immunoreactive median cell cluster on the ganglion ventral surface were found in the unfused abdominal ganglia. Axon(s) from the median cell cluster branch in the anterior unpaired median nerve. Posterolaterally, in all of the ganglia examined, two or more intensely immunoreactive, bilaterally symmetric pairs of neurons were seen. Comparison of these posterolateral neurons, which appear to be serially homologous, with similar antiserotonin immunoreactive neurons described in other insects suggests that these neuron pairs may have cross-species homology as well.

Patterns of tracheation in the abdominal central nervous system and the cerci of Acheta domesticus are described from whole mounts, and light and electron microscopy. The tracheal supply of the ganglia is derived from ventral longitudinal tracheal trunks which have segmental connections to the spiracels. Each abdominal ganglion is served by a single pair of tracheal trunks, except the terminal ganglion, which has two pairs. Within the ganglia, tracheoles occur principally in association with glia-rich areas of the neuropile. We suggest that the respiratory exchange may be concentrated in the cell bodies of neurons and glia. Each cercus has a tracheal supply in paralle with a large air sac which, it is suggested, serves to lighten the cercus, functions as a resonator for sound reception, or facilitates tidal flow of hemolymph and postecdysial expansion of the cercus. No tracheae run continuously between ganglia or between the terminal ganglion and the cerci, and they do not appear to have a potential role as a contact guidance pathway for cercal nerve growth.

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