The Role of 5-HT 1A Receptors in Learning
The 5-HT 1A receptor is the most thoroughly studied of the 5-HT 1 receptors. Due to the high density of 5-HT 1A receptors in the hippocampus, an area linked to cognitive functions, they are suspected to have a role in learning and memory processes. This study endeavored to determine whether 5-HT 1A receptors play an integral role in learning processes by administering a full 5- HT 1A agonist (8-0H-DPAT) to rats trained under a multiple schedule of reinforcement with repeated acquisition and performance components. Additionally, we tried to determine whether the effects of 8-0H-DPAT on learning are mediated through the 5-HT 1A receptor by administering it in combination with a partial5-HTIA agonist (buspirone), and a putative 5-HT 1A antagonist (NAN-190). 8-0H-DPAT (0.056-3.2 mg/kg) produced dose-dependent disruptions in response rate and accuracy in both components. When given in combination with 8-0H-DPAT (0.32 mg/kg), buspirone (0.32 mg/kg) attenuated the effects of 8-0H-DPAT on response rate but did not antagonize the effects on percent errors. Two different doses of NAN-190 failed to attenuate the disruptive effects of 8-0H-DPAT. These data indicate that 5- HT 1A receptors are involved in learning processes, but disruptions produced in the performance component suggest that 5-HT 1A receptors are involved in other behavioral processes as well. Given that NAN-190 failed to attenuate the effects of 8-0H-DPAT, whereas buspirone produced a differential antagonism, we can not definitively say whether the disruptive effects of 8-0H-DPAT are mediated by 5-HT 1A receptors. Further studies with a more potent antagonist are needed in order to determine whether 5-HT 1A receptors are responsible for the substantial disruptions in learning processes after administration of 8-0H-DPAT.