Nitric oxide is necessary for labilization of a consolidated context memory during reconsolidation in terrestrial snails

Abstract

Nitric oxide (NO) is known to be involved in associative memory formation. We investigated the influence of blocking NO function on the reconsolidation of context memory in terrestrial snails (Helix lucorum L.). After a 10 day session of electric shocks in one context only, context memory in snails was observed in test sessions as the significant difference of amplitudes of withdrawal responses to tactile stimuli in two different contexts. After a 1 day rest, a session of 'reminding' was performed, preceded by injection in different groups of the snails with either vehicle or combination of the protein synthesis blocker anisomycin (ANI) with one of the following drugs: the NO scavenger carboxy-PTIO, the NO-synthase inhibitors N-omega-nitro-L-arginin, nitroindazole and NG-nitro-L-arginine methyl ester hydrochloride, or the NO donor S-nitroso-N-acetyl-DL-penicillamine. Testing the context memory at different time intervals after the reminder under ANI injection showed that the context memory was impaired at 24 h and later, whereas the reminder under combined injection of ANI and each of the NO-synthase inhibitors used or the NO scavenger showed no impairment of long-term context memory. Injection of the NO donor S-nitroso-N-acetyl-DL-penicillamine with or without reminder had no effect on context memory. The results obtained demonstrated that NO is necessary for labilization of a consolidated context memory.

Effects of Thryptophan Hydroxylase Blockade by P-Chlorophenylalanine on Contextual Memory Reconsolidation after Training of Different Intensity

“…Thus, the procedure of reminding the situation and the subsequent injection of a protein synthesis blocker led to almost complete amnesia in animals of this group. These results indicated the presence of reconsolidation of contextual memory, which required the protein synthesis [47,60,78] and correlated with other data [44,45,48,49,[52][53][54][55]61].…”

“…However, the defensive reactions of animals in the context of "on a ball" increased up to 20 times after training. Comparison of the levels of defensive responses of animals in the context of "on a ball" and on a flat surface gave evidence of contextual memory, as in the case of previous studies [47,60,78]. After that we investigated the possibility of reconsolidation of contextual memory on the situation in all 4 groups of animals of this series ( Figure 1).…”

“…The training procedure lasted 5 days, during training the snails did not receive food. The deprivation of food in invertebrate animals during the developing of conditioned reflexes is a standard technique, it is not associated with the metabolism of certain substances, but is determined by the need for an active state of the animal [28,60,61,78]. The procedure for "reminding" the training environment was to place the animals for 20 min in a training context of "on a ball".…”

“…The process of repeated consolidation of a memory with reminding was called reconsolidation, which also needs protein synthesis [52][53][54][55]. Reconsolidation of a contextual memory has been shown in invertebrate animals [49,[56][57][58][59][60][61]. The investigation of the memory formation process and memory reconsolidation in mollusks is also attractive due to the possibility of investigate the correlations between memory mechanisms and changes occurs at the cellular and receptor level [40,[62][63][64][65][66][67][68][69][70][71][72][73][74][75].…”

An Update on Memory Reconsolidation Updating

“…While there is relatively little understanding of the neurochemical mechanisms of memory destabilization, several processes have been identified [101]. At the intracellular level, there appears to be a requirement for protein degradation at the proteasome [102, 103], protein phosphatase activity [104], CamKII [105] and nitric oxide [106, 107]. At the cell surface, there is a functional involvement of cholinergic [108] and dopaminergic receptors [109], at least for non-fear memory destabilization.…”