Dopamine/dopaminergic system types

Dopamine is a catecholamine neurotransmitter in the CNS and at some ganglia in the autonomic nervous system. To date, three main types of receptors have been found D1( D2, and D3. The main dopaminergic systems in the brain are the nigro-neostriatal... 

According to Carpenter, Conley, and Buchanan (1998), stimulants such as cocaine and amphetamines activate the dopaminergic system in the brain, which explains why the abuse of stimulants can induce a paranoid psychosis that mimics the positive symptoms representative of schizophrenia. In turn, if a person who is diagnosed with schizophrenia is given stimulants of this type, the psychosis may be exacerbated. It follows, therefore, that the typical antipsychotic medications act by blocking the dopamine receptors. 

The dopamine precursor l-DOPA (levodopa) is commonly used in TH treatment of the symptoms of PD. l-DOPA can be absorbed in the intestinal tract and transported across the blood-brain barrier by the large neutral amino acid (LNAA) transport system, where it taken up by dopaminergic neurons and converted into dopamine by the activity of TH. In PD treatment, peripheral AADC can be blocked by carbidopa or benserazide to increase the amount of l-DOPA reaching the brain. Selective MAO B inhibitors like deprenyl (selegiline) have also been effectively used with l-DOPA therapy to reduce the metabolism of dopamine. Recently, potent and selective nitrocatechol-type COMT inhibitors such as entacapone and tolcapone have been shown to be clinically effective in improving the bioavailability of l-DOPA and potentiating its effectiveness in the treatment of PD. 

Opioids have been shown to increase the release of dopamine in the nucleus accumbens but they also subserve reinforcement in animals by a non-dopaminergic mechanism (Di Chiara 8c North,1992 Koob, 1992). Physiologically the opioid system appears to be largely involved in the con-sumatory rewards of feeding, drinking, sexual and maternal behaviour (Koob, 1992 Di Chiara 8c North, 1992) and certain types of social behaviour (Panksepp, 1981 Bolles 8c Fanselow, 1982). 

Neuroleptic drugs are used in the treatment of psychosis, such as schizophrenia they are generally antagonist ligands of dopamine at the central nervous system level. " Indications and therapeutic effects of the various families of neuroleptics result from two factors. The first one is the specifity of the ligand toward the different types of dopaminergic receptors, which are unequally distributed in the... 

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