Localization of molecular correlates of memory consolidation to buccal ganglia mechanoafferent neurons after learning that food is inedible in Aplysia

Abstract

Training paradigms affecting Aplysia withdrawal reflexes cause changes in gene expression leading to long-term memory formation in primary mechanoafferents that initiate withdrawal. Similar mechanoafferents are also found in the buccal ganglia that control feeding behavior, raising the possibility that these mechanoafferents are a locus of memory formation after a training paradigm affecting feeding. Buccal ganglia mechanoafferent neurons expressed increases in mRNA expression for the transcription factor ApC/EBP, and for the growth factor sensorin-A, within the first 2 h after training with an inedible food. No increases in expression were detected in the rest of the buccal ganglia. Increased ApC/EBP expression was not elicited by food and feeding responses not causing long-term memory. Increased ApC/EBP expression was directly related to a measure of the efficacy of training in causing long-term memory, suggesting that ApC/EBP expression is necessary for the expression of aspects of long-term memory. In behaving animals, memory is expressed as a decrease in the likelihood to respond to food, and a decrease in the amplitude of protraction, the first phase of consummatory feeding behaviors.To determine how changes in the properties of mechanoafferents could cause learned changes in feeding behavior, synaptic contacts were mapped from the mechanoafferents to the B31/B32 neurons, which have a key role in initiating consummatory behaviors and also control protractions. Many mechanoafferents monosynaptically and polysynaptically connect with B31/B32. Monosynaptic connections were complex combinations of fast and slow excitation and/or inhibition. Changes in the response of B31/B32 to stimuli sensed by the mechanoafferent could underlie aspects of long-term memory expression.[Supplemental material is available for this article.]In a number of learning paradigms affecting Aplysia withdrawal reflexes, the connection from mechanoafferent neurons to effectors has been a major focus of research on how neural plasticity is translated into behavioral change (Byrne and

New learning while consolidating memory during sleep is actively blocked by a protein synthesis dependent process

“…As in numerous previous studies examining learning that food is inedible in Aplysia (Botzer et al, 1998; Katzoff et al, 2002, 2006; Levitan et al, 2012), 24 hr before being trained animals were transferred to 10 L experimental aquaria that were maintained at room temperature (23°C). They were kept two to an aquarium, with the two animals separated by a partition allowing the flow of water.…”

“…In some experiments, training proceeded until the animals stopped responding to food, which was defined as a lack of entry of food into the mouth for 3 min. In experiments in which the initial training was continued until the animals stopped responding (full training), data were included only from animals in which food was in the mouth eliciting failed attempts to swallow for at least 100 s, since previous experience (Levitan et al, 2012) showed that such animals almost always show long-term memory. Animals in which food was not in the mouth for 100 s during a full training were discarded.…”

“…Training produces a gradual decrease in responsiveness to food, and animals stop responding after 10–25 min of training. Training during the active phase of the day produces short, intermediate, long-term (Botzer et al, 1998; Michel et al, 2013), and persistent (Levitan et al, 2012; Schwarz et al, 1991) memories, with the long-term memory dependent on protein synthesis adjacent to the training and persistent memory dependent on a somewhat later round of protein synthesis (Levitan et al, 2010). Training during the inactive, sleep phase of the day is ineffective in producing long-term memory (Lyons et al, 2005).…”

Molecular correlates of separate components of training that contribute to long-term memory formation after learning that food is inedible in Aplysia

“…Learning that food is inedible in Aplysia is a complex associative learning task in which animals attempt to eat a tough food, but fail to swallow it (Susswein et al 1986;Botzer et al 1998;Katzoff et al 2002;Levitan et al 2008Levitan et al , 2010Levitan et al , 2012Michel et al 2010Michel et al , 2011Michel et al , 2012Levy et al 2016;Lyons et al 2017). The task is nonetheless relatively easily studied, and some of the physiological and molecular correlates of the learning have been identified (Levitan et al 2008(Levitan et al , 2012Michel et al 2010Michel et al , 2011Levy et al 2016). In this task, animals progressively decrease their responses to a particular food, and eventually stop responding to it, while maintaining their response to other foods (Schwarz et al 1988).…”

Sleep supports inhibitory operant conditioning memory in Aplysia

“…Performance was measured by the accumulated time the food was kept in the mouth cavity (total mouth time) and the total time the animal engaged in biting and spitting the food (total response time). Animals with ,200 sec of accumulated mouth time or a total response time ,600 sec during Training were excluded from analysis (n ¼ 4), as previous studies indicated that these animals show unreliable learning outcome, and to homogenize the groups with regard to training performance (Levitan et al 2012). Results were analyzed using analysis of variance including a group factor representing the Sleep and Wake groups and a repeated-measures factor representing the different test occasions (Training, Retrieval 1, and Retrieval 2).…”