In vitro extinction learning in Hermissenda: involvement of conditioned inhibition molecules

Abstract

Extinction of a conditioned association is typically viewed as the establishment of new learning rather than the erasure of the original memory. However, recent research in the nudibranch, Hermissenda crassicornis (H.c.) demonstrated that extinction training (using repeated light-alone presentations) given 15 min, but not 23 h, after memory acquisition reversed both the cellular correlates of learning (enhanced Type B cell excitability) and the behavioral changes (reduced phototaxis) produced by associative conditioning (pairings of light, CS, and rotation, US). Here, we investigated the putative molecular signaling pathways that underlie this extinction in H.c. by using a novel in vitro protocol combined with pharmacological manipulations. After intact H.c. received either light-rotation pairings (Paired), random presentations of light and rotation (Random), or no stimulation (Untrained), B cells from isolated CNSs were recorded from during exposure to extinction training consisting of two series of 15 consecutive light-steps (LSs). When in vitro extinction was administered shortly (2 h, but not 24 h) after paired training, B cells from Paired animals showed progressive and robust declines in spike frequency by the 30th LS, while control cells (Random and Untrained) did not. We found that several molecules implicated in H.c. conditioned inhibitory (CI) learning, protein phosphatase 1 (PP1) and arachidonic acid (AA)/12-lipoxygenase (12-LOX) metabolites, also contributed to the spike frequency decreases produced by in vitro extinction. Protein phosphatase 2B (PP2B) also appeared to play a role. Calyculin A (PP1 inhibitor), cyclosporin A (PP2B inhibitor), and baicalein (a 12-LOX inhibitor) all blocked the spike frequency declines in Paired B cells produced by 30 LSs. Conversely, injection of catalytically-active PP1 (caPP1) or PP2B (caPP2B) into Untrained B cells partially mimicked the spike frequency declines observed in Paired cells, as did bath-applied AA, and occluded additional LS-produced reductions in spiking in Paired cells.

Identification of genes related to learning and memory in the brain transcriptome of the mollusc,Hermissenda crassicornis

“…The nudibranch Hermissenda crassicornis exhibits a simple form of associative learning, which has been studied extensively: it can learn to associate light changes with vestibular stimulation (Crow and Alkon 1978). The neural correlates of Hermissenda's associative memories formed during lightmovement pairings have been uncovered (Alkon 1980;Crow and Alkon 1980;Britton and Farley 1999;Tamse et al 2003;Cavallo et al 2014). Hermissenda has also been the subject of investigations related to many other aspects of neuroscience, including sensory and motor neuron physiology (Crow and Tian 2004;Nesse and Clark 2010;Jin and Crow 2011;Crow et al 2013) and the evolution of behaviors and neurotransmitter systems Newcomb et al 2012;Lillvis and Katz 2013).…”

Modulation of defensive reflex conditioning in snails by serotonin

“…Earlier we found that the defensive reflex conditioning in snails is accompanied by a depolarization shift of the membrane potential and a decrease of the threshold potential (Gainutdinov et al, 1998 ). In recent years there have been a sufficient number of experimental results that demonstrate the membrane correlates of learning (Gillette et al, 1982 ; Alkon, 1984 ; Frysztak and Crow, 1997 ; Cleary et al, 1998 ; Gainutdinova et al, 2003 ; Disterhoft and Oh, 2006 ; Kemenes et al, 2006 ; Nikitin et al, 2006 , 2013 ; Mozzachiodi et al, 2008 ; Jing et al, 2009 ; Debanne and Poo, 2010 ; Gainutdinov et al, 2011 ; Sakharov, 2012 ; Cavallo et al, 2014a , b ). These experiments were done on preparations from trained animals as well as within the cell analogs of learning.…”

Calcineurin Participation in Hebbian and Homeostatic Plasticity Associated With Extinction

“…The effects of CaN inhibition seem to be phylogenetically conserved, as the administration of protein phosphatases inhibitors blocked the spike frequency decline observed after an in vitro extinction procedure of classical conditioning in Hermissenda crassicornis ( Cavallo et al, 2014 ).…”