Serotonin immunoreactivity of neurons in the gastropod Aplysia californica.

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.

Serotonin immunoreactivity in the nervous system of the dragonfly nymph.

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.