Effect of TRH and DN-1417 on the vestibulo-ocular reflex in squirrel monkeys

Thyrotropin-releasing hormone (TRH) and DN-1417, a synthetic derivative of TRH, have been reported to have various effects on the central nervous system. We examined the vestibulo-ocular reflex (VOR) by systemic administration of TRH and DN-1417 in squirrel monkeys. Our results showed that a lower dose of TRH (0.2 mg/kg) had an inhibitory effect on VOR gain, 15-30 min after injection. DN-1417 (0.02-2.0 mg/kg) also had an inhibitory effect on the gain of VOR for 60 min. However, a higher dose of TRH (2 mg/kg) showed a facilitatory effect on VOR gain 60 min after injection. It must be pointed out that TRH had a dual action on VOR.