Abstract
Excitotoxic lesion of the ventral hippocampus in neonatal rats is a putative animal model of schizophrenia with characteristic developmental abnormalities in dopaminergic neurotransmission and prefrontal cortical functions. Converging evidence also points to the involvement of the central cholinergic system in neuropsychiatric disorders. These two neurotransmitter systems are interlinked in the prefrontal cortex (PFC) where dopamine stimulates acetylcholine (ACh) release. In the present study, we investigated the role of dopamine in the developmental regulation of prefrontal cortical ACh release and the expression of nicotinic and muscarinic receptors in pre- and post-pubertal rats with neonatal ibotenic acid-induced lesions of the ventral hippocampus (NVH). In vivo microdialysis in the PFC revealed that systemic injections of the D(1)-like receptor agonist (+/-)-6-chloro-7,8-dihydroxy-1-phenyl2,3,4,5-tetrahydro-1H-3-benzazepine hydrobromide (SKF 81297) (2.5 and 5.0 mg/kg i.p.) caused significantly higher ACh release in post-pubertal NVH-lesioned animals (250 and 300% baseline for 2.5 and 5.0 mg/kg, respectively) compared with post-pubertal shams (150 and 220% baseline for 2.5 and 5.0 mg/kg, respectively). Most interestingly, while prefrontal cortical perfusion of SKF 81297 (100 and 250 microM) had no significant effect on ACh release in post-pubertal sham-operated animals, it significantly stimulated ACh release to approximately 250% baseline at both doses in post-pubertal NVH-lesioned animals. Receptor autoradiography demonstrated a significant and selective increase in M(1)-like receptor binding sites in the infralimbic area of the PFC in the post-pubertal NVH-lesioned animals. For all experiments, significant differences between sham and NVH-lesioned animals were observed only in post-pubertal rats. These results suggest a developmentally specific reorganization of the prefrontal cortical cholinergic system involving D(1)-like receptors in the NVH model.
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