Octopamine promotes rhythmicity but not synchrony in a bilateral pair of bursting motor neurons in the feeding circuit of Aplysia

Abstract

) modulatory actions on the spontaneous burst activity of the bilaterally paired B67 pharyngeal motor neurons (MNs). OA increased B67's burst duration and the number of impulses per burst. These effects reflected actions of OA on the intrinsic tetrodotoxin-resistant driver potential (DP) that underlies B67 bursting. In addition to its effects on B67's burst parameters, OA also increased the rate and regularity of burst timing. Although the bilaterally paired B67 MNs both exhibited rhythmic bursting in the presence of OA, they did not become synchronized. In this respect, the response to OA differed from that of dopamine, another modulator of the feeding motor network, which produces both rhythmicity and synchrony of bursting in the paired B67 neurons. It is proposed that modulators can regulate burst synchrony of MNs by exerting a dual control over their intrinsic rhythmicity and their reciprocal capacity to generate membrane potential perturbations. In this simple system, dopaminergic and octopaminergic modulation could influence whether pharyngeal contractions occur in a bilaterally synchronous or asynchronous fashion.

Octopaminergic system in the central nervous system of the terrestrial slug Limax

“…The prominent neuronal cluster was only found near the dorsal surface of the cerebral ganglion. This observation is almost consistent with a report on the CNS of Aplysia (Martínez‐Rubio et al, ), although a single TBH‐IR neuron found in the visceral ganglion of Limax (Figs. A, A) seems to be lacking in the abdominal ganglion of Aplysia .…”

“…However, different numbers of OA‐IR neurons have been reported in studies on the buccal ganglia of other gastropod animals. Elekes et al () reported more than 10 OA‐IR neurons in Lymnaea , whereas Vehovszky et al () and Martínez‐Rubio et al () reported only 3 OA‐IR neurons in Lymnaea and Aplysia . These discrepancies may be explained partly by species differences, and partly by differences in the methods used (immunohistochemistry of OA vs. immunohistochemistry and in situ hybridization of TBH).…”

“…It has been suggested that OA is involved in the regulation of feeding rhythm generation in the buccal ganglia (Vehovszky and Elliott, 2001;Vehovszky et al, 2005;Mart ınez-Rubio et al, 2010). In the buccal ganglia, there were 6 TBH-IR neurons that were located symmetrically in the right and left hemiganglia.…”