Enhanced Retention in the Passive-Avoidance Task By 5-HT 1A Receptor Blockade Is Not Associated With Increased Activity of the Central Nucleus of the Amygdala

The effect of blockade of 5-HT 1A receptors was investigated on (1) retention in a mildly aversive passive-avoidance task, and (2) spontaneous single-unit activity of central nucleus of the amygdala (CeA) neurons, a brain site implicated in modulation of retention. Systemic administration of the selective 5-HT 1A antagonist NAN-190 immediately after training markedly—and dose-dependently—facilitated retention in the passive-avoidance task; enhanced retention was time-dependent and was not attributable to variations in wattages of shock received by animals. Systemic administration of NAN-190 had mixed effects on spontaneous single-unit activity of CeA neurons recorded extracellularly in vivo; microiontophoretic application of 5-HT, in contrast, consistently and potently suppressed CeA activity. The present findings—that 5-HT 1A receptor blockade by NAN-190 (1) enhances retention in the passive-avoidance task, and (2) does not consistently increase spontaneous neuronal activity of the CeA—provide evidence that a serotonergic system tonically inhibits modulation of retention in the passive-avoidance task through activation of the 5-HT 1A receptor subtype at brain sites located outside the CeA.