Systemically applied thyrotropin-releasing hormone (TRH) modifies spontaneous behaviour of rats.

The effect of TRH and its analogon "RGH 2022" (Gedeon Richter, Budapest) on parameters of open field (OF) behaviour, wheel running (WR) and sleep-wakefulness cycles was recorded after intraperitoneal injections of the drugs in two dosages, 1 microgram/kg and 10 micrograms/kg, and compared with the control group. The lower TRH dose enhanced exploratory activity in the OF to 130%, WR to 150%, but reduced the entrance to central fields in the OF to 50%. The higher TRH dose reduced the locomotor activity in the OF to 53% and the entrance to central fields to 15% but enhanced the exploratory index to 190%. The analogon RGH 2022 had less effects in its lower dose and mimicked the TRH effect in its higher dose. The amount of all waking states increased after TRH to 120%. Single periods of relaxed wakefulness and sleep phases (slow wave sleep and paradoxical sleep) were 15-20% prolonged after 10 micrograms/kg TRH on account of phase frequency. There was, however, a maximum of sleep phase frequency and duration between the 35th and 55th min after TRH application.