Diurnal thermal response to pinealectomy and photoperiod in the pigeon

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Abstract
An increase in body temperature (Tb) observed in pinealectomized (Px) early winter pigeons as opposed to sham‐operated (SPx) ones, at two as well as three weeks post‐surgery, was found to have disappeared when examined one year later during corresponding season. Following this one‐year post‐surgery period under 12‐h daily photoperiod and 25°C ambient temperature (Ta), neither a 3‐week exposure to continuous light nor a 1‐week exposure to continuous darkness was found to produce any difference in Tb between Px and SPx pigeons. In pigeons (Px, SPx/Normal) maintained on a 12‐h daily photocycle, and 25°CTa, the diurnal Tb rhythm of being high during photophase and low during scotophase was observed in all the seasons studied. Under continuous light as well as continuous darkness, however, the diurnal Tb rhythm was found to be effaced. Seasonal variations in Tb were observed in response to pinealectomy. Summer Px pigeons showed no significant hyperthermia whereas early winter, mid‐winter and fall pigeons showed varying degrees of hyperthermia in response to pinealectomy. The obliteration of hyperthermia in Px pigeons following long‐term post‐surgery period, as well as the lack of any hyperthermic effect in Px summer pigeons is attributed to possible increased melatonin synthesis at non‐pineal sites. An apparent decrease in foot temperature (Tl) following pinealectomy observed in mid‐winter and fall pigeons tends to suggest that the Tb hyperthermia in Px winter and fall pigeons, was due to reduced heat dissipation in those pigeons.