Thyroid testis inter-relationship in Indian palm squirrel, Funambulus pennanti Wroughton.

The present work attempts to find out a relationship between testicular functions and thyroid activity in a seasonal breeder, Indian palm squirrel, Funambulus pennanti Wroughton. In addition to radioiodine studies used for assessing thyroid status during different months in the year, biochemical estimations and histological studies have also been undertaken with a view to determine thyroid and testicular functions. Testicular recrudescence in Indian palm squirrel starts in January and peak activity is reached during April and May. June marks the beginning of testicular regression and the maximal regression is reached in October. Fluctuations in thyroid function are clearly manifested by variations observed in radioiodine uptake during different phases of reproductive cycle. Cytoarchitecture of thyroid also changes somewhat during different periods of the year and these changes are in accordance with the results obtained from radioiodine uptake studies. The present investigation suggests that the thyroid has a definite and significant role to play during the period of testicular recrudescence and regression in seasonal breeder Funambulus pennanti and it seems to help in tapering off sexual arousal and regression rather than sudden switching on and off of the reproductive cycle. In addition, it seems to facilitate peak testicular activity. However, mechanisms whereby thyroid influences various testicular functions seem to involve a complex series of interactions.