The Journal of Neuroscience, January 15, 2003, 23(2):693-699
Effects of Sex and Estrogen on Behavioral Sensitization to
Cocaine in Rats
Ming
Hu and
Jill B.
Becker
Psychology Department, Neuroscience Program and Reproductive
Sciences Program, University of Michigan, Ann Arbor, Michigan 48109
Estrogen rapidly enhances dopamine (DA) activity in the striatum
and nucleus accumbens as well as behavioral responses to psychomotor
stimulants in female rats but not males. This experiment was conducted
to investigate the role of pulsatile estrogen treatment on and sex
differences in the development and expression of sensitization of
cocaine-induced rotational behavior in rats with unilateral striatal DA
denervation. Four groups were tested: ovariectomized (OVX) females
treated with 5 µg of estradiol benzoate (OVX+E), OVX females,
castrated (CAST) males, and intact males. Animals received
estrogen or vehicle 30 min before cocaine (0, 5, 10, or 20 mg/kg, i.p.)
on 4 consecutive days, followed by 3 d without treatment for 3 weeks. At the conclusion of the experiment, animals were withdrawn from
hormone and/or cocaine for 10 d, and all groups underwent a
challenge test with 10 mg/kg cocaine. We report here that OVX+E females
exhibit significantly greater sensitization of rotational behavior with
a faster rate of sensitization than the three other groups. There is
also a sex difference independent of gonadal hormones: OVX females
exhibit a greater magnitude of sensitization of rotational behavior
than do CAST males at 20 mg/kg cocaine. Furthermore, on the challenge
test, OVX+E animals tested without estrogen treatment continue to
exhibit greater rotational behavior than do all other groups. Thus,
estrogen enhances sensitization to cocaine, there are sex differences
in behavioral sensitization, and sensitization that develops under
conditions with estrogen persists even when estrogen levels are low.
Key words:
cocaine; behavioral sensitization; rotational
behavior; estrogen; sex differences; drug abuse
Copyright © 2003 Society for Neuroscience 0270-6474/03/232693-07$05.00/0