218 Neuroscience Letters, 92 (1988) 218 221 Elsevier Scientific Publishers Ireland Ltd. NSL 05574 Stress causes an increase in endogenous monoamine oxidase inhibitor (tribulin) in rat brain S.K. Bhattacharya l, Vivette Glover 2, I. McIntyre 3, G. Oxenkrug 3 and M. Sandler 2 1Department of Pharmacology, Institute of Medical Sciences, Banaras Hindu University, Varanasi (India). 2Bernhard Baron Memorial Research Laboratories, Queen Charlotte ~ Hospital, London ( U.K.) and .¢Department of Psychiatry, Wayne State University and Psychoendocrine Research Unit, Lafayette Clinic, Detroit, M148207 (U.S.A.) (Received 6 November 1987; Revised version received 2 June 1988; Accepted 3 June 1988) Key words." Stress;Brain; Monoamine oxidase; Endogenous monoamine oxidase inhibitor; Pineal; Mela- tonin Two hours of cold restraint stress in rats resulted in significantlyincreased brain concentrations of endo- genous monoamine oxidase inhibitor (tribulin). Young and old rats showed the same order of response. Tribulin levels were also increased by immobilisation stress alone but to a lesser extent. Two types of endogenous monoamine oxidase (MAO) inhibitor have been de- scribed. One is a peptide [2], the level of which may be increased by electroconvulsive shock [14]. The other is a non-peptide, low-molecular weight, neutral molecule which we have called tribulin [7, 1 1, 19]. Its distribution in rat tissues parallels that of a benzodiazepine receptor ligand with similar properties [1] and it has been suggested that both activities derive from the same molecule or family of molecules [4]. Tribulin has now been purified from human urine [7], partially characterised and its structure is currently being determined. It is stable, extracts readily into ethyl acetate at acid pH, and competes with tyramine [7]. Tribulin output in human urine is increased in a variety of conditions characterised by stress or anxiety, including lactate-induced panic attacks [6], general anxiety dis- order [5], alcohol withdrawal [3] and benzodiazepine withdrawal [18]. Rats subjected to 2 h of cold-restraint stress also excrete significantly greater amounts in their urine [9]. The study described here was designed to determine whether cold-restraint stress, or the less severe stress of immobilisation alone, also results in an increased concen- Correspondence: M. Sandier, Bernhard Baron Memorial Research Laboratories, Queen Charlotte's Hos- pital, Goldhawk Road, London W6 0XG, U.K. 0304-3940/88/$ 03.50 © 1988 Elsevier Scientific Publishers Ireland Ltd.