Developing rats (newborns, 1-, 2- and 4-weeks old) are significantly less resistant than adults to the toxic action of imipramine. The resistance of 6-weeks old rats does not differ from that of adults.
Imipramine and desmethylimipramine (DMI) were effective in counteracting the ptosis and/or the hypothermia produced by reserpine equally in all age groups studied. Atropine was ineffective in this regard.
DMI reversed the sedation and hypothermia and counteracted the ptosis induced by benzquinolizine Ro 4-1284 equally in 18–19-days old and adult rats. The characteristic motor hyperactivity induced by the combination of DMI and Ro 4-1284 was pronounced in both 18–19-days old and adults rats.
Imipramine lowered the brain noradrenaline level in young and adult rats and counteracted the reserpine-induced depletion of this monoamine.
Chlorpromazine slightly lowered the brain noradrenaline level in adult rats but did not influence the reserpine-induced depletion of brain noradrenaline and reserpine syndrome.
Key-Words Antidepressive Agents - Desipramine - Imipramine - Reserpine
Preliminary data are reported at the Symposia 
Role of Mediators in Regulation of Physiological Functions
(Kazan, December 1967) and Das depressive Syndrom (West Berlin, February 1968).