Temporal changes in the messenger RNA levels of cellular immediate early genes and neurotransmitter/receptor genes in the rat neostriatum and substantia nigra after acute treatment with eticlopride, a dopamine D2 receptor antagonist.

The cellular immediate early genes are involved in the transcriptional events associated with the dopaminergic regulation of neurotransmitter expression within neurons of the neostriatum. To characterize these events in detail, quantitative in situ hybridization histochemistry was used to assess the temporal effects of acute dopamine receptor blockade with eticlopride, a dopamine D2 receptor antagonist, on the messenger RNA expression of the immediate early genes and neurotransmitters/receptors in the caudate-putamen and ventral tegmental area/substantia nigra pars compacta of the rat. Groups of rats were injected with a single dose of either isotonic saline or eticlopride (0.5 mg/kg i.p.) and killed at various time intervals ranging from 5 min to 24 h and frozen brain sections processed by in situ hybridization histochemistry. Using computerized image analysis, the changes in messenger RNA expression for c-fos, c-jun, jun B, jun D, nerve growth factor I-A and nerve growth factor I-B and for neurotensin, glutamate decarboxylase, proenkephalin, the dopamine D1 receptor and the short and long isoforms of the D2 receptor were examined in the caudate-putamen. In the ventral tegmental area and substantia nigra pars compacta, the messenger RNA expression of the above early response genes and that for neurotensin, tyrosine hydroxylase, cholecystokinin and the D2 receptor isoforms were also examined. In the neostriatum, eticlopride caused a rapid increase in c-fos messenger RNA with significantly increased levels at 10 min (P < 0.01). The levels peaked at 30 min and thereafter declined to control levels. A similar profile was observed for jun B messenger RNA, although levels were still significantly (P < 0.01) elevated at 1 h and declined to basal levels thereafter. No significant changes were observed for c-jun, jun D, nerve growth factor I-A and nerve growth factor I-B messenger RNAs. In the dorsolateral neostriatum, there was an increase in proneurotensin messenger RNA 10 min after eticlopride, this increase becoming significant (P < 0.01) at 60 min. Levels were maximal at 2-6 h and decreased after 12 h to basal levels. There were small increases in proenkephalin messenger RNA, but these were not significant (P < 0.05) until 6 h after the injection. Eticlopride did not have any significant effects on the messenger RNA levels for glutamate decarboxylase, the D1 receptor and the short and long isoforms of the D2 receptor.(ABSTRACT TRUNCATED AT 400 WORDS

Apoptotic Mode of Cell Death in Substantia Nigra Following Intranigral Infusion of the Parkinsonian Neurotoxin, MPP+ in Sprague-Dawley Rats: Cellular, Molecular and Ultrastructural Evidences

The potent parkinsonian neurotoxin 1-methyl- 4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP) is known to cause dopaminergic neurodegeneration in nigrostriatal system. In the present study we investigated the nuclear morphology of cells in the substantia nigra pars compacta (SNpc) region of rats following unilateral intranigral infusion of the active metabolite, 1-methyl-4-phenyl pyridinium ion (MPP+), which resulted in a dose-dependent and prolonged dopamine depletion in the ipsilateral striatum. There appeared a substantial loss of tyrosine hydroxylase immunoreactive neurons in the SNpc that received the neurotoxin. Specific nuclear staining with Hoechst 33342 or acridine orange revealed bright pyknotic, shrunken, distorted nuclei and condensed chromatin with perinuclear nucleolus respectively following visualization with the former and latter dyes in the ipsilateral SNpc, as compared to the round, intact nuclei and centrally positioned nucleolus in the contralateral side. Ultrastructural details of the nucleus under transmission electron microscope confirmed distorted nuclear organization with shrunken or condensed nuclei and disrupted nuclear membrane. These features are typical of nucleus undergoing apoptosis, and suggest that MPP+ causes dopaminergic neuronal death through an apoptotic mode. Typical laddering pattern of genomic DNA isolated from the ipsilateral SN in agarose gel electrophoresis conclusively established apoptosis following intranigral administration of MPP+ in rats