LACK OF EVIDENCE FOR DOPAMINE AUTORECEPTORS IN THE MEDIOBASAL HYPOTHALAMUS - A MICRODIALYSIS STUDY IN AWAKE RATS

To determine the functional presence of dopamine (DA) autoreceptors on tuberoinfundibular dopamine (TIDA)-ergic neurons in awake rats, a mic rodialysis probe was implanted into the mediobasal hypothalamus (MBH). In the presence of the re-uptake inhibitor nomifensine, which increas ed DA levels to 350% of basal values, systemic administration of the n on-selective D1/D2 antagonist haloperiol induced an immediate increase in DA and DOPAC levels to 145% of pretreatment values. However, neith er local infusion of the selective D2 antagonist sulpiride nor of the D1 antagonist SCH 23390 affected the nomifensine-elevated extracellula r DA or DOPAC levels in the MBH. Systemic administration of the D2 ant agonist raclopride equally did not affect the nomifensine-elevated DA release in the MBH. Upon basal extracellular DA levels (without nomife nsine), local infusion of the D2 agonist (-)N-0437 equally did not aff ect the DA or DOPAC levels in the MBH. Furthermore, the increase in DA levels induced by haloperidol could not be antagonized by the D1 agon ist CY 208-243. Therefore, the present study does not provide support for the concept of functional autoreceptors located on TIDA neurons re gulating the release of DA. Possibly, the effect of haloperidol was no n-DA-ergic in character.