Dopamine autoreceptors regulating turnover

Many of these effects can still be observed after pretreatment with kainic acid in the neostriatum (113). This treatment degenerates the neostriatal efferent pathways and by consequence also the neostriatal efferent part(s) of the nigrostriatal loop. Apparently postsynaptic dopamine receptors, if located on these striatonigral neurons play only a minor role in the regulation of dopamine synthesis and turnover in dopaminergic neurons and the major role has to be attributed to dopaminergic autoreceptors. 

Histamine H3-receptors have been reported to regulate not only the release and turnover of histamine via autoreceptors on histaminerglc nerve endings [1-3], but also the releases of noradrenaline, dopamine, serotonin, and acetylcholine via heteroreceptors on non-histaminerglc axon terminals [22-26], Thioperamide increased the release of these neurotransmitters, while... 

Dopamine induces biochemical and physiological effects in the mammalian neostriatum. The occurrence of a D-l dopamine receptor (in the classification scheme of Kebabian and Caine) accounts for the ability of dopamine to enhance cyclic AMP formation. The occurrence of a D-2 dopamine receptor accounts for the ability of dopamine to inhibit cyclic AMP formation brought about by stimulation of a D-l dopamine receptor. Dopamine receptors mediate the regulation of (1) the release or turnover of acetylcholine (postsynaptic dopamine receptor) and (2) the release or turnover of dopar mine (presynaptic autoreceptor). Both receptors can be classified as D-2 dopamine receptors. Indications for the occurrence of dopamine receptors affecting the release or turnover of GABA, glutamate, serotonin and several neuropeptides are evaluated. 

The dopamine-containing nigro-neostriatal dopaminergic neurons possess receptors for dopamine. These dopamine receptors occur on both the nerve terminals within the neostriatum (pre-synaptic autoreceptors) as well as on the soma and dendrites (soma-dendritic autoreceptors). Stimulation of either category of autoreceptor can regulate the synthesis, turnover and release of dopamine in the neostriatum but by different mechanisms. 

It was thus concluded that D2R has a major role in regulating the size of the terminal arbor in dopamine neurons projecting from the SNpc to the CPu. This is consistent with the role of the D2 autoreceptor in regulating the delivery of dopamine. It suggests that this regulation is not only confined to dopamine storage, synthesis and turnover in the terminals but is also manifested in the density of dopamine terminals. 

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