The locus coeruleus involves in consolidation and memory retrieval, but not in acquisition of inhibitory avoidance learning task

The locus coeruleus (LC) located at the level of the pons, is involved in cognitive functions such as learning and memory. The bilateral lidocaine-induced reversible inactivation of this nucleus has been considered in order to study its role in the phases of memory processing (acquisition, consolidation and retention) without any interference with the function of the same structure either during earlier and/or later phases of the same process. In this study, inhibitory avoidance (IA) learning task used to find the LC function in acquisition, consolidation and retrieval. Saline or lidocaine 4% (0.5 μl/side) microinjected into the LC, for assessing the acquisition (5 min before training), consolidation (5, 90 and 360 min after training) and memory retrieval, 5 min before testing. The retention test was done 24 h after learning. Our results indicated that: (1) The bilateral functional inactivation of LC before training did not affect acquisition, but affected subsequent memory retention 24 h later in IA task. (2) The lidocaine-induced inactivation of LC only 5 min after training impaired consolidation but did not affect it after 90 or 360 min. (3) Inactivation of the LC, 5 min before pre-retrieval test, impaired memory retrieval in IA task. In conclusion, it seems that the nucleus locus coeruleus does not affect acquisition while it involves in the memory consolidation and retrieval of inhibitory avoidance learning task.