Specificity of Repetition Priming: The Role of Chemical Coding

Abstract

We investigate stimulus specificity of repetition priming in a tractable model system; the feeding network of Aplysia. Previous studies primarily focused on an aspect of behavior that is altered during ingestive priming, radula opening. Priming of radula opening occurs when two modulatory peptides [feeding circuit activating peptide (FCAP) and cerebral peptide-2 (CP-2)] are released from the cholinergic command-like neuron cerebral buccal interneuron 2. Effects of FCAP/CP-2 on radula opening motor neurons are cAMP mediated. The present experiments sought to determine whether FCAP/CP-2 and cAMP are also involved in the priming of radula opening during an incompatible activity, i.e., during egestive motor programs. Egestive priming is induced when motor programs are triggered by afferents with processes in the esophageal nerve. We demonstrate that egestive priming is not FCAP/CP-2 mediated. Instead, it is induced by an unrelated peptide (small cardioactive peptide), which exerts PKC-mediated effects. Our data, therefore, suggest that different feeding motor programs are primed via actions of different sets of intercellular and intracellular substances. We suggest that this accounts for the stimulus specificity that can be characteristic of repetition priming. Different stimuli activate different central pattern generator inputs. These inputs release different modulators, which induce functionally distinct motor programs.

Consequences of degeneracy in network function

“…The egestive input to the feeding CPG, the esophageal nerve (EN) can be stimulated so that more than one cycle of motor activity is triggered [42,43,45]**. In this situation there are progressive changes in the firing patterns of motor neurons, and after a few cycles, activity becomes egestive.…”

“…This has been referred to as ‘egestive repetition priming’. It is presumably mediated by cumulative effects of modulatory neuropeptides that are released by repeated EN stimulation [43,47]**.…”

Activity-dependent increases in [Ca2+]i contribute to digital-analog plasticity at a molluscan synapse

“…One possibility is that the two types of currents are differentially modulated. The feeding circuitry is subjected to a great deal of modulation because of the release of neuropeptides and monoamines (Due et al 2004;Friedman and Weiss 2010;Friedman et al 2015;Jing et al 2007;Jing et al 2010;Koh et al 2003;Koh and Weiss 2007;Morgan et al 2000;Morgan et al 2002;Siniscalchi et al 2016). For example, neuropeptides play an important role in determining whether motor programs are ingestive or egestive.…”

Agent-causal libertarianism, statistical neural laws and wild coincidences

“…Also, it has, for instance, been observed that, as a behavior is repeated, certain motor--related neural activities become more probable under certain conditions (e.g., Costa 2007;Wickens et al 2007;Graybiel 2008;Verstynen & Sabes 2011;Hikosaka et al 2013;Kim et al 2015;Anderson 2016). together are subsequently more likely to be active together under certain conditions, and vice versa (e.g., Hebb 1949;Klaes et al 2012). These changes can happen rapidly (within milliseconds), and involve intracellular biochemical changes which influence synaptic transmission among other things (e.g., Friedman et al 2015;Cichon and Gan 2015;Svensson et al 2016). They can also involve rapid morphological changes (within minutes to hours) to neurons and their synaptic connections (e.g., Kandel 2001;Dash et al 2004;Fu et al 2012;Bailey et al 2015;Chen et al 2015;Hayashi--Takagi et al 2015).…”