Morphology, innervation, and peripheral sensory cells of the siphon of aplysia californica.
The siphon of Aplysia californica has several functions, including involvement in respiration, excretion, and defensive inking. It also provides sensory input for defensive withdrawals that have been studied extensively to examine mechanisms that underlie learning. To better understand the neuronal bases of these functions, we used immunohistochemistry to catalogue peripheral cell types and innervation of the siphon in stage 12 juveniles (chosen to allow observation of tissues in whole-mounts). We found that the siphon nerve splits into three major branches, leading ultimately to a two-part FMRFamide-immunoreactive plexus and an apparently separate tyrosine hydroxylase-immunoreactive plexus. Putative sensory neurons included four distinct types of tubulin-immunoreactive bipolar cells (one likely also tyrosine hydroxylase immunoreactive) that bore ciliated dendrites penetrating the epithelium. A fifth bipolar neuron type (tubulin- and FMRFamide-immunoreactive) occurred deeper in the tissue, associated with part of the FMRFamide-immunoreactive plexus. Our observations emphasize the structural complexity of the peripheral nervous system of the siphon, and the importance of direct tests of the various components to better understand the functioning of the entire organ, including its role in defensive withdrawal responses.
Department of Biology, St. Francis Xavier University, Antigonish, Nova Scotia, B2G 2W5, Canada.
Ian D
ID
Carrigan
Department of Physiology and Biophysics, Dalhousie University, Halifax, NS, B3H 4R2, Canada.
Roger P
RP
Croll
Department of Biology, St. Francis Xavier University, Antigonish, Nova Scotia, B2G 2W5, Canada.
Russell C
RC
Wyeth
D000818:Animals; D001048:Aplysia / Q000033:anatomy & histology* / Q000378:metabolism; D019835:FMRFamide / Q000378:metabolism; D007150:Immunohistochemistry; D018613:Microscopy, Confocal; D011984:Sensory Receptor Cells / Q000166:cytology* / Q000378:metabolism; D014404:Tubulin / Q000378:metabolism; D014446:Tyrosine 3-Monooxygenase / Q000378:metabolism
D014404:Tubulin; D019835:FMRFamide; D014446:Tyrosine 3-Monooxygenase
RRID: AB_261811; RRID: AB_477585; RRID: AB_477593; RRID: AB_572263; RRID: AB_572268; gill withdrawal; mantle cavity; peripheral nervous system; sensory cells; plexus