The effects of thyrotropin releasing hormone on a visual discrimination task in rats

The effects of intracerebroventricular (ICV) administration of thyrotropin releasing hormone (TRH, 1 and 50 micrograms) were assessed on a two-choice visual discrimination task. The data were analysed using signal detection theory techniques in order to test for changes in cognitive and response factors. No significant changes in performance were observed. In a second experiment, the effects of TRH (100 micrograms ICV) on performance were compared with amphetamine (AMP, 1 mg/kg, intra-peritoneally, IP) and a metabolite of TRH, histidyl-proline diketopiperazine (DKP, 100 micrograms ICV). No significant effects on performance as measured by standard indices were observed. However, both TRH and AMP, but not DKP, significantly increased perseverative responding on one lever with respect to saline. In keeping with recent evidence, it is concluded that the traditional non-parametric signal detection parameters of sensitivity and bias are insensitive to certain strategies. Possible mechanisms for the perseveration of responding, and its relationship to stereotypic behaviour, are discussed in the light of the known effects of each compound on dopaminergic systems.