Objective: 

While a large body of literature is available on the effect of thyroid hormone deficiency on learning and memory functions during the developmental stage, electrophysiological and behavioral findings, particularly on propylthiouracil administration to adult normothyroid animals, are not satisfactory. Therefore we aimed to evaluate short-term spatial working memory and short-term synaptic plasticity in adult rats with hypothyroidism.

Methods: 

The experiments were carried out on adult rats after receiving approval from Ethics Committee of Erciyes University. Hypothyroidism was induced by administering 6-n-propyl-2-thiouracil in their drinking water for 21 days at a concentration of 0.05%. Spatial learning performance of hypothyroid and control rats were studied on Y-maze. The in vivo electrophysiological recordings were taken from the dentate gyrus of hippocampus. A pair of pulses of equal intensity was administered at different inter-pulse intervals (IPI) to analyze the paired-pulse index.

Results: 

The level of spontaneous alternation was different between the groups (p<0.01). The percentage of alternation was significantly lower in the experimental group than the control group (p<0.05). In the control animals paired pulse ratio of population spike amplitudes increased with IPI, became maximal at IPI of 80 ms, and then declined at longer intervals. Similar pattern was also observed in the hypothyroid group with a significantly less facilitation than the control (p<0.05).

Conclusions: 

The present study provides in vivo evidence for the action of propylthiouracil leading to impaired paired pulse facilitation which might explain deficit in spatial memory tasks in adult hypothyroid rats.