Elsevier

Neuroscience

Volume 112, Issue 1, 12 June 2002, Pages 39-49
Neuroscience

Dopamine autoreceptor regulation of release and uptake in mouse brain slices in the absence of D3 receptors

https://doi.org/10.1016/S0306-4522(02)00067-2Get rights and content

Abstract

The effects of the dopamine D3 receptor, a putative autoreceptor, have been investigated by comparing behavioral and neurochemical properties of wild-type mice and mice with a genetic deletion of the D3 receptor. The D3 knock-out mice were modestly hyper-responsive to a novel environment relative to wild-type mice, and, consistent with this, quantitative in vivo microdialysis revealed elevated striatal dopamine extracellular levels. The dynamic actions of autoreceptors on electrically evoked dopamine release were examined in striatal brain slices from these animals and monitored with fast scan cyclic voltammetry at carbon-fiber microelectrodes. Quinpirole, a dopamine receptor agonist with potency at both D2 and D3 receptors, inhibited evoked dopamine in a dose-dependent manner with a slightly higher dose required in the knock-out animals (EC50 of 60±10 nM in wild-type animals and 130±40 in D3 knock-out animals; both curves had a Hill slope near 2). Dopamine synthesis inhibition with α-methyl-p-tyrosine caused released dopamine levels to decrease in each genotype. However, regulation of secretion by autoreceptors was still operant. Dose–response curves to quinpirole were unchanged in D3 knock-out tissue, but secretion-regulated release exhibited a Hill slope decreased to 1 in the wild-type animals. In both genotypes, similar quinpirole-evoked increases in uptake rate were evident following synthesis inhibition.

These data are consistent with the D3 receptor having a small but significant role as a dopamine autoreceptor that partially regulates secretion, but not synthesis, in the caudate–putamen.

Section snippets

Animals

The mice used in this study were of the mixed strain C57B6/129SvJ (F2 generation) and were 4–8-month-old males. Both the DAT-KO (DAT−/−) (Giros et al., 1996) and D3-KO mice were generated by homologous recombination. Food and water was provided ad libitum. Animal care was in accordance with institutional guidelines.

Locomotion measurements

Locomotor activity measurements were measured with an Omnitech monitor, a device equipped with infrared photobeam detectors. Horizontal activity was measured as total distance

Generation of D3-KO mice

A genomic clone containing exon 1 of the murine D3 receptor gene was isolated from a 129/SvJ genomic library (Stratagene) with a PCR-generated probe derived from exon 1 sequences of the rat D3 receptor gene (Giros et al., 1991). In the targeting construct D (Fig. 1A), exon 1 is replaced by the neomycin gene cassette under the control of the PGK promoter (PGK-neo) (Adra et al., 1987). A MC1-TK gene was positioned upstream for negative selection with gancyclovir. The total length of homology is

Discussion

These investigations confirm previous reports (Accili et al., 1996, Xu et al., 1997) that mice with a genetic deletion of the D3 receptor are hyper-responsive to a novel environment. While measurable, the hyperactivity is modest, and in fact has gone unnoticed by some investigators (Jung et al., 1999). Consistent with the role of DA in behavioral activation (Carlsson, 1993), the hyperactivity in D3-KO mice is accompanied by elevated concentrations of striatal extracellular DA, in agreement with

Acknowledgements

We gratefully acknowledge Dr. Peter Fuchs and Dr. Adolf Himmler (Bender Wien, Vienna, Austria) for contributing the inactivation construct used to generate D3-KO mice. This research was supported by NIH (NS 15841 to R.M.W. and NS 19576 to M.G.C.). M.G.C. is an investigator of the Howard Hughes Medical Institute.

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