Ventral pallidal extracellular fluid levels of dopamine, serotonin, gamma amino butyric acid, and glutamate during cocaine self-administration in rats.
BACKGROUND
Dopamine innervation of the nucleus accumbens is thought to have a major role in the biological processes underlying cocaine self-administration. Recent data suggest that dopamine innervation of the ventral pallidum (VP) may also play an important role.


OBJECTIVE
This experiment was initiated to assess extracellular fluid levels of dopamine (DA), serotonin (5-HT), gamma-aminobutyric acid (GABA), and glutamate (Glu) in the VP of rats self-administering cocaine using in vivo microdialysis.


METHODS
Rats were implanted with intravenous jugular catheters and a microdialysis probe guide cannula into the VP and trained to self-administer (SA) three different doses of cocaine during each daily session. Other rats (yoked rats) were surgically prepared in identical fashion and received vehicle infusions during microdialysis sessions when the SA rat to whom they were yoked produced cocaine infusions. When stable baselines of self-administration were obtained, microdialysates were collected during two consecutive daily self-administration sessions. Neurotransmitter levels were measured using HPLC with electrochemical (DA and 5-HT) or fluorescence detection (GABA and Glu).


RESULTS
In SA rats, extracellular fluid levels of DA [DA]e and 5-HT [5-HT]e were elevated throughout the session and levels of Glu [Glu]e showed small increases at a few isolated time points during the session. The increases in [DA]e and 15-HT]e were dose-dependent. Extracellular fluid levels of GABA [GABA]e were unchanged, as were levels of all four neurotransmitters in the yoked rats.


CONCLUSIONS
These data support a potential role for DA and 5-HT innervations of the VP in intravenous cocaine self-administration.
Sizemore
G M
GM
Department of Physiology and Pharmacology, Wake Forest School of Medicine, Winston-Salem, NC 27157-1083, USA. sizemore@wfubmc.edu
Co
C
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Smith
J E
JE
D000818:Animals; D003042:Cocaine / Q000008:administration & dosage* / Q000032:analysis; D004298:Dopamine / Q000032:analysis* / Q000502:physiology; D005110:Extracellular Space / Q000737:chemistry*; D005917:Globus Pallidus / Q000502:physiology*; D018698:Glutamic Acid / Q000032:analysis*; D008297:Male; D017551:Microdialysis; D009714:Nucleus Accumbens / Q000502:physiology; D051381:Rats; D011916:Rats, Inbred F344; D012646:Self Administration; D012701:Serotonin / Q000032:analysis* / Q000502:physiology; D005680:gamma-Aminobutyric Acid / Q000032:analysis*
D012701:Serotonin; D018698:Glutamic Acid; D005680:gamma-Aminobutyric Acid; D003042:Cocaine; D004298:Dopamine