High Level of Footshock during Inhibitory Avoidance Training Prevents Amnesia Induced by Intranigral Injection of GABA Antagonists

Disruption of synaptic activity of a number of cerebral structures (e.g., neostriatum, amygdala, and thalamus) produces marked deficits in retention of instrumentally conditioned behaviors. When animals are given a relatively high number of training trials or high intensities of footshock during learning, however, such disruption is considerably less effective. Since there is a close anatomical and functional relationship between the neostriatum and the substantia nigra, it was of interest to determine whether enhanced training with a high level of footshock would prevent the reported amnesic state induced by injections of GABA antagonists into the latter structure. Rats were trained in a one-trial inhibitory task, using 0.2 or 0.4 mA, and then injected with microgram quantities of picrotoxin or bicuculline into the substantia nigra and posterior region of the zona incerta; retention was measured 24 h later. Only those groups that had been injected into the nigra and trained with 0.2 mA showed amnesia. These results support the hypotheses that (a) the normal activity of a set of structures is essential for the development of memory consolidation and (b) after an enhanced learning experience these structures may participate in memory consolidation, but are not necessary for the occurrence of this process.