GABA mechanisms in the pedunculopontine tegmental nucleus influence particular aspects of nicotine self-administration selectively in the rat.
RATIONALE: The pedunculopontine tegmental nucleus (PPTg) is part of the neuronal circuit activated by self-administered nicotine. The cholinergic neurons of the PPTg comprise a prominent projection to midbrain dopamine neurons. However, anatomical studies of Fos expression suggest that nicotine targets primarily non-cholinergic neurons in the PPTg, especially GABAergic and glutamatergic neurons. OBJECTIVE: The objective of these experiments was to examine the role of GABA manipulations in the PPTg on nicotine self-administration. METHODS AND RESULTS: Rats trained to self-administer nicotine or cocaine intravenously were prepared with brain microcannulae directed to the PPTg. Intra-PPTg microinfusions of the GABA agonists muscimol (10-50 ng) and baclofen (30-60 ng) reduced nicotine self-administration maintained on a fixed-ratio schedule of reinforcement (30 microg/kg per infusion); self-administration of cocaine (0.3 mg/kg per infusion) under an identical schedule was not affected. Muscimol and baclofen were also examined after intra-PPTg microinfusion in animals trained to self-administer nicotine on a progressive-ratio schedule (10 and 30 microg/kg per infusion). Progressive-ratio responding was sensitive to pharmacological manipulations such as a change in the nicotine dose available for self-administration, or intra-PPTg microinfusion of the nicotinic antagonist dihydro-beta-erythroidine (30 microg). However, nicotine self-administration on a progressive-ratio schedule was not altered by intra-PPTg microinfusions of GABA agonists. CONCLUSIONS: These data confirm that the PPTg is involved in nicotine self-administration, a conclusion that is independent of the schedule of reinforcement that is used. GABAergic mechanisms in the PPTg play a selective role in nicotine reinforcement compared to cocaine, and that role is restricted to the characteristics of reinforcement measured by fixed-ratio responding.[1]References
- GABA mechanisms in the pedunculopontine tegmental nucleus influence particular aspects of nicotine self-administration selectively in the rat. Corrigall, W.A., Coen, K.M., Zhang, J., Adamson, K.L. Psychopharmacology (Berl.) (2001) [Pubmed]
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