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C A Hubbard

Publications and source records attributed to C A Hubbard.

6 recordsLinked to original sources
PubMed2001

Early changes in neuropeptide mRNA expression in the striatum following reserpine treatment.

Chronic dopamine depletion produces neurochemical changes within the striatum as well as enhanced behavioral and metabolic responses to dopamine agonists. Changes in striatal neuropeptides have been consistently described, including increased expression of preproenkephalin mRNA and decreased expression of preprotachykinin and prodynorphin mRNA. Acute dopamine depletion following treatment with reserpine also produces enhanced behavioral and metabolic responses to agonist treatment which develop rapidly. In the present study, we used in situ hybridization histochemistry to investigate whether acute neurochemical changes occur following reserpine treatment. We evaluated neuropeptide mRNA expression in the striatum and nucleus accumbens at several time points from 6 to 120 h following single doses of reserpine and AMPT. The aim of these studies was to determine if changes in neuropeptide mRNA expression occur following acute dopamine depletion and whether such changes are specific to the striatum. Changes in striatal neuropeptide mRNA expression developed rapidly. Preproenkephalin mRNA expression by striatopallidal neurons was unchanged at 48 h, but increased by 44% at 120 h. Preprotachykinin mRNA expression in striatonigral neurons was increased at 6 h and then fell, with a maximal decrease of 45% at 48 h and partial recovery by 120 h. Prodynorphin mRNA expression was unchanged. Expression of preproenkephalin and preprotachykinin mRNA was also examined in subregions of the striatum and the nucleus accumbens. Expression of preproenkephalin mRNA was uniform in the striatum and higher in the core than the shell of the nucleus accumbens. Preprotachykinin mRNA expression in the striatum was higher in the lateral quadrants and was higher in the shell than in the core of the nucleus accumbens. The changes in neuropeptide mRNA following treatment with reserpine were only found in the striatum. These data provide further evidence for early alterations in neuronal function in the striatum following acute dopamine depletion and suggest that neuropeptide expression by striatonigral neurons may be more rapidly regulated in response to changes in dopamine levels.

Adrenergic Uptake Inhibitors↗
PubMed1996

Dose-related effects of continuous levodopa infusion in rats with unilateral lesions of the substantia nigra.

Preclinical studies in rats have demonstrated markedly different effects of intermittent and continuous levodopa administration on many biochemical and functional parameters yet the dose regimens employed have not been fully evaluated. In this study, rats with unilateral 6-hydroxydopamine nigral lesions were administered levodopa (0-1200 mg/kg/day) and benserazide (25 mg/kg/day) subcutaneously via osmotic minipump and studied 20-22 h later for rotational behavior, striatal dopamine concentration, and regional cerebral glucose utilization (RCGU). Levodopa infusion at 100 mg/kg/day resulted in minimal rotation and minimal striatal dopamine replacement but did increase RCGU in the subthalamic nucleus and decrease RCGU in the lateral habenula, consistent with a selective inhibition of the striatopallidal GABAergic (indirect striatal output) pathway. Levodopa infusion at 100 mg/kg/day did not significantly increase RCGU in the entopeduncular nucleus (EP) and substantia nigra pars reticulata (SNr), as does the acute injection of levodopa (25-50 mg/kg), indicating that this levodopa dose elicits only part of the spectrum of metabolic effects elicited by acute levodopa injection. Higher doses of levodopa (400-1200 mg/kg/day) resulted in moderate rates of rotation, dose-dependent increases in striatal dopamine, and increased RCGU in the EP and SNr, consistent with activation of the striatonigral GABAergic (direct striatal output) pathway. In the EP and SNr, the two major output nuclei of the basal ganglia, levodopa infusion at 800 and 1200 mg/kg/day reproduced the metabolic effects elicited by acute injection of levodopa. These results demonstrate, for the first time, dose-dependent effects of levodopa on distinct populations of striatal output neurons which may be relevant to the pathogenesis of levodopa-induced dyskinesias in Parkinson's disease. The minimal dopamine replacement and partial functional effects elicited by levodopa infusion at 100 mg/kg/day indicate the need for caution in the interpretation of prior studies of continuous levodopa infusion which employed this dose.

Animals↗
PubMed1993

Reversal of reserpine-induced catalepsy by selective D1 and D2 dopamine agonists.

To gain insight into the antiparkinsonian effects of selective D1 and D2 dopamine receptor stimulation, we examined the ability of D1 (SKF 38393) and D2 (quinpirole) agonists to reverse catalepsy induced by the combined administration of reserpine and alpha-methyl-p-tyrosine (AMPT) in rats. Catalepsy, the failure to correct an externally imposed posture, is a measure of akinesia and was assessed using the bar test. Rats injected with reserpine alone (2.5 mg/kg i.p.) developed akinesia and ptosis within 60-90 min. The D1 agonist SKF 38393 (30 mg/kg i.v.) rapidly reversed ptosis and restored near-normal mobility when administered 24 h after reserpine and AMPT; catalepsy was reversed for 90 min, after which the drug effect wore off. Quinpirole (1 mg/kg i.v.) reversed catalepsy for the duration of the test period (4 h) but did not consistently reverse ptosis or promote normal mobility; the rats continued to exhibit kyphotic postures with little spontaneous locomotion. These results indicate that selective D1 stimulation is sufficient to reverse reserpine-induced akinesia and highlight the need for the development of potent selective D1 agonists for clinical trial in Parkinson's disease. In severe dopamine depletion, D2 stimulation alone appears to be insufficient to restore normal movement. Quinpirole, but not SKF 38393, elicited paroxysmal limb/body jerking in reserpine-AMPT-treated rats, providing further evidence that atypical jerking can be elicited by D2 stimulation in the complete absence of D1 stimulation. This laboratory observation suggests that some jerking dyskinesias seen in treated parkinsonian patients may be mediated by an imbalance in D1-D2 receptor stimulation.

Animals↗