The Journal of Neuroscience, October 1, 2001, 21(19):7781-7787
Differential Regulation of the Mesoaccumbens Circuit by Serotonin
5-Hydroxytryptamine (5-HT)2A and 5-HT2C
Receptors
Lance R.
McMahon1,
Malgorzata
Filip2, and
Kathryn A.
Cunningham1
1 Department of Pharmacology and Toxicology, The
University of Texas Medical Branch, Galveston, Texas 77555-1031, and
2 Department of Pharmacology, Institute of Pharmacology,
Polish Academy of Sciences, Krakow 31-343, Poland
Serotonin [5-hydroxytryptamine (5-HT)] 5-HT2A and
5-HT2C receptors (5-HT2ARs and
5-HT2CRs), which innervate the dopamine
mesoaccumbens pathway, may play an important role in the
behavioral effects of cocaine. To test this hypothesis, the present
study measured cocaine-evoked locomotor activity after bilateral
microinjection of selective 5-HT2AR and 5-HT2CR
antagonists into the ventral tegmental area (VTA) or the nucleus
accumbens (NAc) shell. Locomotor activity was measured after
intracranial microinjection of saline (0.2 µl/side), the selective
5-HT2AR antagonist
R-(+)-
-(2,3-dimethoxyphenyl)-1-[2-(4-fluorophenylethyl)]-4-piperidine methanol (M100907) (0.1 or 0.3 µg · 0.2
µl
1 · side
1), or the
selective 5-HT2CR antagonist
8-[5-(2,4-dimethoxy-5-(4-trifluoromethylphenylsulfon-amido)phenyl-5-oxopentyl)]-1,3,8-triazaspiro[4.5]decane-2,4-dione hydrochloride (RS 102221) (0.05-0.5 µg · 0.2
µl
1 · side
1) followed
by an injection of saline (1 ml/kg, i.p.) or cocaine (10 mg/kg, i.p.).
Microinjection of M100907 (0.1-0.3 µg/side) into the VTA or RS
102221 (0.15-0.5 µg/side) into the NAc shell attenuated
cocaine-induced hyperactivity in a dose-related manner. However, hyperactivity evoked by cocaine was not altered by
microinjection of RS 102221 into the VTA or M100907 into the NAc shell.
No changes in basal activity were observed after microinjection of
M100907 or RS 102221 into either brain region. These findings are the first to demonstrate that the behavioral effects of cocaine are generated in part by activation of 5-HT2ARs in the VTA and
by activation of 5-HT2CRs in the NAc shell. The selective
regulation of the mesoaccumbens circuit by 5-HT2ARs and
5-HT2CRs implicates these 5-HT receptors as important in
the behavioral outcomes of systemic cocaine administration.
Key words:
behavior; cocaine; nucleus accumbens; serotonin; 5-HT2A receptor; 5-HT2C receptor; ventral
tegmental area
Copyright © 2001 Society for Neuroscience 0270-6474/01/21197781-07$05.00/0