Morphology, innervation, and peripheral sensory cells of the siphon of XXXX .

@entity11066 @entity12927 @entity4149
UNASSIGNED: The siphon of @entity11066 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 @entity12927 -immunoreactive plexus and an apparently separate @entity4149 hydroxylase-immunoreactive plexus. Putative sensory neurons included four distinct types of tubulin-immunoreactive bipolar cells (one likely also @entity4149 hydroxylase immunoreactive) that bore ciliated dendrites penetrating the epithelium. A fifth bipolar neuron type (tubulin- and @entity12927 -immunoreactive) occurred deeper in the tissue, associated with part of the @entity12927 -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. J. Comp. Neurol. 523:2409-2425, 2015.    2015 Wiley Periodicals, Inc.
