The neurotransmitter, dopamine, binds to dopamine receptor (DR), and is involved in several functions of the brain. such as initiation and execution of movement. emotion, prolactin secretion, etc. Of all the five DRs, D2 dopamine receptor has maximal affinity for dopamine. D2 has a short isoform. D2S, and a long isoform D2L. D2L is longer than D2S by 29 aminoacid residues. We studied the expression of the gene and protein of D2 receptor in the cerebral and cerebellar cortices of the brain of new born, developing, adult, and old male mice to find out: (i) at what stage of development, expression of the gene peaks and (ii) if it undergoes any changes as the animal ages. which may account for the neurodegenerative changes and symptoms of Parkinson's and other diseases seen in old age. RT-PCR and Western blot studies show that peak expression of D2 gene occurs in the cerebral and cerebellar cortices around 15-day after birth. We speculate that the majority of dopaminergic synapses are established and possibly become functional in the brain around 15-day after birth. The expression of D2 receptor is upregulated in the cerebral cortex in old mice. However, it is down-regulated in the cerebellar cortex. (c) 2006 Elsevier Inc. All rights reserved.