Gm. Sizemore et al., Ventral pallidal extracellular fluid levels of dopamine, serotonin, gamma amino butyric acid, and glutamate during cocaine self-administration in rats, PSYCHOPHAR, 150(4), 2000, pp. 391-398
Rationale: Dopamine innervation of the nucleus accumbens is thought to have
a major role in the biological processes underlying cocaine self-administr
ation. Recent data suggest that dopamine innervation of the ventral pallidu
m (VP) may also play an important role. Objectives: This experiment was ini
tiated 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 guid
e cannula into the VP and trained to self-administer (SA) three different d
oses of cocaine during each daily session. Other rats (yoked rats) were sur
gically prepared in identical fashion and received vehicle infusions during
microdialysis sessions when the SA rat to whom they were yoked produced co
caine infusions. When stable baselines of self-administration were obtained
, microdialysates were collected during two consecutive daily self-administ
ration sessions. Neurotransmitter levels were measured using HPLC with elec
trochemical (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) w
ere 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 [5-HT](e) were dose-dependent. Extracellular fluid levels of
GABA [GABA](e) were unchanged, as were levels of all four neurotransmitter
s in the yoked rats. Conclusions: These data support a potential role for D
A and 5-HT innervations of the VP in intravenous cocaine self-administratio
n.