Biomedical subjects

J E Lachowicz

Publications and source records attributed to J E Lachowicz.

21 records · Page 2Linked to original sources

PubMed1994

Altered striatal function in a mutant mouse lacking D1A dopamine receptors.

Of the five known dopamine receptors, D1A and D2 represent the major subtypes expressed in the striatum of the adult brain. Within the striatum, these two subtypes are differentially distributed in the two main neuronal populations that provide direct and indirect pathways between the striatum and the output nuclei of the basal ganglia. Movement disorders, including Parkinson disease and various dystonias, are thought to result from imbalanced activity in these pathways. Dopamine regulates movement through its differential effects on D1A receptors expressed by direct output neurons and D2 receptors expressed by indirect output neurons. To further examine the interaction of D1A and D2 neuronal pathways in the striatum, we used homologous recombination to generate mutant mice lacking functional D1A receptors (D1A-/-). D1A-/- mutants are growth retarded and die shortly after weaning age unless their diet is supplemented with hydrated food. With such treatment the mice gain weight and survive to adulthood. Neurologically, D1A-/- mice exhibit normal coordination and locomotion, although they display a significant decrease in rearing behavior. Examination of the striatum revealed changes associated with the altered phenotype of these mutants. D1A receptor binding was absent in striatal sections from D1A-/- mice. Striatal neurons normally expressing functional D1A receptors are formed and persist in adult homozygous mutants. Moreover, substance P mRNA, which is colocalized specifically in striatal neurons with D1A receptors, is expressed at a reduced level. In contrast, levels of enkephalin mRNA, which is expressed in striatal neurons with D2 receptors, are unaffected. These findings show that D1A-/- mice exhibit selective functional alterations in the striatal neurons giving rise to the direct striatal output pathway.

Animals↗

PubMed1994

The D2S and D2L dopamine receptor isoforms are differentially regulated in Chinese hamster ovary cells.

To investigate and compare the regulatory properties of the two isoforms of the D2 dopamine receptor, we have stably expressed their cDNAs in Chinese hamster ovary (CHO) cells. Cell lines were selected that express similar levels of [3H]methylspiperone-binding activity. Both isoforms mediate a dose-dependent and pharmacologically specific inhibition of adenylyl cyclase activity in both intact cell and membrane preparations. Pretreatment of both D2L and D2S receptor-expressing cells with 100 microM dopamine produces a approximately 5-fold shift (to lower affinity) in the EC50 for dopamine inhibition of cAMP accumulation, with a 25-30% decrease in the maximum response. Dopamine treatment also results in a approximately 25% decrease in the maximum receptor binding activity of the D2S receptor-expressing cells. In contrast, the D2L receptors are up-regulated by about 2-fold in response to dopamine exposure. This difference in response between the D2S and D2L receptors is not cell line specific, inasmuch as other CHO clones expressing these isoforms show identical responses. The dopamine-induced up-regulation of D2L receptor binding is time dependent, reaching maximal levels after 10 hr (t1/2 = 2 hr). Upon removal of dopamine, the receptor binding activity returns to control levels within 20 hr. The adenylyl cyclase desensitization response is also time dependent but exhibits a slower time course (t1/2 = 5 hr) than the receptor up-regulation. Both regulatory responses are induced in a dose-dependent fashion by dopamine, albeit with different potencies (up-regulation EC50 = 100 nM, desensitization EC50 = 2 microM). These regulatory effects are pharmacologically specific, being mimicked by D2-selective agonists but not agonists of other receptor subtypes. The dopamine-induced receptor up-regulation is blocked by prior treatment of the cells with pertussis toxin and is not mimicked by cAMP analogs. Conversely, elevation of intracellular cAMP levels results in down-regulation of the D2L receptor activity. To test whether protein synthesis is required for the D2L receptor up-regulation, cycloheximide was used to block mRNA translation. This was found to completely inhibit the up-regulation of D2L binding activity; however, there was no effect on the desensitization of the adenylyl cyclase response. RNA dot-blot analyses indicate that dopamine treatment is associated with a sustained 2-fold increase in the steady state levels of D2L mRNA, whereas D2S mRNA is transiently increased by only 50%.(ABSTRACT TRUNCATED AT 400 WORDS)

Adenylyl Cyclase Inhibitors↗

PubMed1992

Topographic nonoverlapping distribution of D1 and D2 dopamine receptors in the amygdaloid nuclear complex of the rat brain.

The distribution of D1 and D2 dopamine (DA) receptors in the nuclei and subnuclear zones of the rat amygdaloid complex was mapped using quantitative light microscopic autoradiography. [125I]iodosulpiride and [125I]SCH 23982 (in the presence of 50 nM ketanserin) were used to label D2 and D1 DA receptors, respectively. The DA receptor subtypes exhibited a topographic, nonoverlapping distribution which generally conformed to the cytoarchitectonic boundaries of the component nuclei and subnuclear zones of the amygdaloid complex. The highest density of [125I]iodosulpiride binding sites was observed in the main intercalated cell group and the central amygdaloid nucleus where a medial to lateral gradient of binding sites was localized to its subnuclear zones. [125I]SCH 23982 binding sites were localized in the main intercalated cell group and the basolateral amygdaloid nucleus with a uniform low density in the central nucleus. The functional topography of mesoamygdaloid DA neurons may therefore be mediated, in part, at the level of DA receptor subtypes. The pattern of distribution of [125I]iodosulpiride binding sites in subdivisions of the central amygdaloid nucleus and bed nucleus of the stria terminalis suggests that the functions of the "extended amygdala," a major system of the functional organization of the basal forebrain, may be regulated by DA afferents at multiple key sites of D2 receptor action.

Amygdala↗