Intra-ventral tegmental area injection of rat cocaine and amphetamine-regulated transcript peptide 55-102 induces locomotor activity and promotes conditioned place preference
Hl. Kimmel et al., Intra-ventral tegmental area injection of rat cocaine and amphetamine-regulated transcript peptide 55-102 induces locomotor activity and promotes conditioned place preference, J PHARM EXP, 294(2), 2000, pp. 784-792
Citations number
43
Categorie Soggetti
Pharmacology & Toxicology
Journal title
JOURNAL OF PHARMACOLOGY AND EXPERIMENTAL THERAPEUTICS
Cocaine- and amphetamine-regulated transcript (CART) is a novel mRNA that h
as been reported to be increased by acute psychostimulant administration, a
nd that may be involved in the effects of psychostimulants. In this study,
we examined the effect of centrally administered CART peptides on locomotor
activity and conditioned place preference in the rat. CART peptide fragmen
ts were bilaterally injected into the ventral tegmental area. CART 55-102 (
0.2-5.0 mu g/side), an endogenously occurring peptide, dose dependently inc
reased locomotor activity, whereas CART 1-26 (0.1-2.5 mu g/side; not found
endogenously) did not. The locomotor effects of CART 55-102 were dose depen
dently blocked by the dopamine D-2 receptor antagonist haloperidol (0.03-1.
0 mg/kg i.p.). Four injections of 1.0 mu g/side CART 55-102 induced a signi
ficant place preference, suggesting that CART 55-102 is reinforcing. Increa
ses in locomotor activity after each of these CART 55-102 injections were s
imilar and did not show tolerance or sensitization. This treatment regimen
of CART 55-102 also did not produce sensitization to locomotor activity aft
er a subsequent challenge with cocaine or amphetamine. When CART 55-102 (0.
2-1.0 mu g/side) was injected into the substantia nigra, no significant cha
nge in motor activity was observed. However, a higher dose of CART 55-102 (
5.0 mu g/side) induced a delayed increase in motor activity, suggesting a p
ossible diffusion from the substantia nigra into the ventral tegmental area
. Our findings suggest that CART 55-102 is behaviorally active and may be i
nvolved in the actions of psychostimulants. This is the first demonstration
of the psychostimulant-like effects of CART peptides.