Because dihydroergocryptine (DHE) (13,14) have found that DHE acts as a pure dopamine-like agonist on pituitary cells in culture. It is also known that 2-bromocryptine, which is chemically similar to DHE, has dopamine-like agonist activity on rat behavior (15), mimicks the effect of L-3,4-dihydroxyphenylalanine on patients with Parkinson disease (16), and reduces prolactin secretion in patients in a fashion similar to other dopamine-mimetic drugs (17).These previous studies on the ergot compounds (13)(14)(15)(16)(17) METHODS AND MATERIALS Preparation of Calf Caudate Homogenates. The experiments were done on crude homogenates of calf caudate, prepared as described (6). In order to retain all the dopamine receptors, the homogenates were not purified or subfractionated. Calf brains were obtained fresh from the Canada Packers Hunnisett plant (Toronto, Canada). The caudates were removed within 2 hr after death, pooled, sliced into small cubes, and suspended in buffer at an approximate concentration of 50 mg of wet weight per ml of buffer. The buffer contained 15 mM Tris-HCI (pH 7.4), 5 mM Na2EDTA, 1.1 mM ascorbate, and 12.5 ,uM nialamide. A preliminary crude homogenate of the suspension was made with a glass homogenizer with a Teflon piston (0.13-0.18 mm clearance). This piston, rotating at 500 rpm, was passed up and down 20 times in the homogenizer. The crude homogenate was first incubated at 370 for 60 min and then stored in 3-ml aliquots at -20°for future use. Before using, the samples were thawed, resuspended in the glass-Teflon homogenizer and homogenized by hand (10 upand-down passes), and centrifuged at 39,000 X g for 15 min at 40; the supernatant was discarded and the pellet was resuspended in 10 ml of buffer. The suspension was finally homogenized by a Polytron homogenizer (Brinkman Instrument Co.) at a setting of 7 (full range = 10) for 20 sec, by using a PT-10 homogenizer probe and a 50-ml polycarbonate tube to contain the suspension. Homogenization at settings higher than 7 led to a loss of protein through the glass fiber GF/B filters used in the radioreceptor assays. Except were indicated, the homogenates were always kept chilled on ice.[