A novel in vitro analog expressing learning-induced cellular correlates in distinct neural circuits

Abstract

When presented with noxious stimuli, exhibits concurrent sensitization of defensive responses, such as the tail-induced siphon withdrawal reflex (TSWR) and suppression of feeding. At the cellular level, sensitization of the TSWR is accompanied by an increase in the excitability of the tail sensory neurons (TSNs) that elicit the reflex, whereas feeding suppression is accompanied by decreased excitability of B51, a decision-making neuron in the feeding neural circuit. The goal of this study was to develop an in vitro analog coexpressing the above cellular correlates. We used a reduced preparation consisting of buccal, cerebral, and pleural-pedal ganglia, which contain the neural circuits controlling feeding and the TSWR, respectively. Sensitizing stimuli were delivered in vitro by electrical stimulation of afferent nerves. When trained with sensitizing stimuli, the in vitro analog expressed concomitant increased excitability in TSNs and decreased excitability in B51, which are consistent with the occurrence of sensitization and feeding suppression induced by in vivo training. This in vitro analog expressed both short-term (15 min) and long-term (24 h) excitability changes in TSNs and B51, depending on the amount of training administered. Finally, in vitro application of serotonin increased TSN excitability without altering B51 excitability, mirroring the in vivo application of the monoamine that induces sensitization, but not feeding suppression.

cGMP mediates short- and long-term modulation of excitability in a decision-making neuron in Aplysia

“…Animals were fed one strip of dried seaweed (3 ×19 cm; 0.5 g; Emerald Cove ® Organic Pacific Nori; Great Eastern Sun, Asheville, NC) three times a week [26]. Animals were food deprived for 2–3 days before the beginning of an experiment [27]. Prior to each experiment, the general health and motivational state of an animal were tested by presenting it with a food stimulus.…”

“…Prior to each experiment, the general health and motivational state of an animal were tested by presenting it with a food stimulus. An animal was included in the study only if it generated bites in response to the food stimulus [27].…”

“…Aplysia were anesthetized by injecting a volume of isotonic MgCl 2 (equivalent to 50% of the weight of the animal) through the foot [27,28]. The buccal ganglion was removed and pinned rostral-side up on the Sylgard-coated bottom of a Plexiglas recording chamber containing artificial seawater with a high concentration of divalent cations (high-divalent ASW), composed of 210 mM NaCl, 10 mM KCl, 145 mM MgCl2, 20 mM MgSO4, 33 mM CaCl2, and 10 mM HEPES, with the pH adjusted to 7.5 using NaOH [28].…”

“…In cases in which B51 elicited a plateau potential at 5 nA, the neuron’s response to 2 nA, 3 nA and 4 nA was also assessed to ensure that the burst threshold was not overestimated. Cells that did not exhibit a plateau potential by 25 nA were excluded from the study [27]. Post-tests were conducted identically to the pre-tests at different time points after injection/treatment protocols [19,27].…”

“…Cells that did not exhibit a plateau potential by 25 nA were excluded from the study [27]. Post-tests were conducted identically to the pre-tests at different time points after injection/treatment protocols [19,27]. An increase of burst threshold would correspond to a decrease of excitability, whereas a decrease of burst threshold would correspond to an increase of excitability.…”