Use of theAplysiafeeding network to study repetition priming of an episodic behavior

Abstract

Many central pattern generator (CPG)-mediated behaviors are episodic, meaning that they are not continuously ongoing; instead, there are pauses between bouts of activity. This raises an interesting possibility, that the neural networks that mediate these behaviors are not operating under "steady-state" conditions; i.e., there could be dynamic changes in motor activity as it stops and starts. Research in the feeding system of the mollusk has demonstrated that this can be the case. After a pause, initial food grasping responses are relatively weak. With repetition, however, responses strengthen. In this review we describe experiments that have characterized cellular/molecular mechanisms that produce these changes in motor activity. In particular, we focus on cumulative effects of modulatory neuropeptides. Furthermore, we relate research to work in other systems and species, and develop a hypothesis that postulates that changes in response magnitude are a reflection of an efficient feeding strategy.

Cellular Effects of Repetition Priming in the Aplysia Feeding Network Are Suppressed during a Task-Switch But Persist and Facilitate a Return to the Primed State

“…In vitro, ingestive programs were induced using established procedures (e.g., Proekt et al, 2004;Friedman et al, 2009;Friedman and Weiss, 2010;Dacks et al, 2012;Dacks and Weiss, 2013;) (see Fig. 1A).…”

“…Established procedures were also used to trigger egestive motor programs (Proekt et al, 2004(Proekt et al, , 2007Friedman et al, 2009Friedman et al, , 2015. Namely, programs were triggered by stimulating the posterior branch of the esophageal nerve (EN) at 2 Hz, with 3 ms constant voltage pulses.…”

“…This network generates two incompatible types of outputs: egestive and ingestive motor programs (e.g., Elliott and Susswein, 2002;Cropper et al, 2004). These programs are triggered by egestive and ingestive inputs to the feeding central pattern generator Church and Lloyd, 1994;Sánchez and Kirk, 2001;Morgan et al, 2002;Cropper et al, 2004;Proekt et al, 2005;Friedman et al, 2009Friedman et al, , 2015. Central pattern generator inputs release modulatory neurotransmitters that configure network activity.…”

“…Central pattern generator inputs release modulatory neurotransmitters that configure network activity. Thus, stimulation of an egestive input releases one set of modulators, which creates an egestive bias to motor programs (Proekt et al, 2004(Proekt et al, , 2007Friedman et al, 2009Friedman et al, , 2015Wu et al, 2010;Dacks et al, 2012). Stimulation of an ingestive input releases a second set of modulators, which creates an ingestive bias (Koh et al, 2003;Proekt et al, 2004Proekt et al, , 2007Friedman et al, 2009;Friedman and Weiss, 2010;Dacks et al, 2012).…”

Successful and unsuccessful attempts to swallow in a reduced Aplysia preparation regulate feeding responses and produce memory at different neural sites

“…Another possibility is that swallowing responses elicited during the first exposure to CCh + edible food prime the feeding system, so that the system is biased to elicit swallowing when activated again. Repetition priming is present in the Aplysia feeding motor system (Friedman and Weiss 2010;Dacks et al 2012;Cropper et al 2017;Perkins et al 2018). However, the priming should also be evident during the third exposure to CCh, which was not paired with edible food.…”