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Neurochemical characterization of individual vulnerability to addictive drugs in rats
Author(s) -
Lucas Louis R.,
Angulo Jesus A.,
Moal Michel Le,
McEwen Bruce S.,
Piazza Pier V.
Publication year - 1998
Publication title -
european journal of neuroscience
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.346
H-Index - 206
eISSN - 1460-9568
pISSN - 0953-816X
DOI - 10.1046/j.1460-9568.1998.00321.x
Subject(s) - dopaminergic , ventral tegmental area , substantia nigra , nucleus accumbens , striatum , dopamine , neurochemical , neuroscience , tyrosine hydroxylase , chemistry , midbrain , psychology , tegmentum , medicine , endocrinology , biology , central nervous system
Rats exposed to a low‐light, low‐noise, novel environment exhibit differences in individual locomotor response to the novelty stressor. The categorization of rats in a locomotor screening procedure as low‐ (LR) or high‐responders (HR), where LRs are in the low locomotor range while HRs belong to the high locomotor range, is significant in that HRs show higher activity in mesencephalic dopaminergic projection neurons, and also show a higher propensity to self‐administer psychostimulants and other drugs of abuse compared with LRs. In this study, we examined the neurobiological basis of dopaminergic hyperactivity by comparing in HRs and LRs the steady‐state differences in regulatory inputs to mesencephalic (substantia nigra and ventral tegmental area: VTA) dopaminergic neurons. In particular, using in situ hybridization, we studied levels of mRNA for tyrosine hydroxylase (TH) and cholecystokinin (CCK) in the mesencephalon, and for preprodynorphin (DYN), preproenkephalin (PPE), and preprotachykinin (PPT) in the striatum and nucleus accumbens (Acb). We also evaluated TH levels by radioimmunocytochemistry (TH‐RIC) in striatal, accumbal and mesencephalic regions. HRs versus LRs had lower levels of neurochemicals belonging to the intrinsic inhibitory input to dopaminergic neurons in the VTA, e.g. lower TH‐RIC (–25%) and CCK‐mRNA (–48%). In contrast, HRs showed higher levels of parameters belonging to extrinsic facilitating inputs, e.g. higher PPE‐mRNA (+ 37%). In addition, HRs had higher DYN‐mRNA in Acb (+ 61%), which has been shown to be positively correlated with higher dopaminergic activity. These results enhance our knowledge of the neurobiological correlates of individual rats' propensities to develop drug‐intake and provide some putative mechanisms for the dopaminergic hyperactivity that characterizes drug‐prone animals.