Biomedical subjects

N K Dhingra

Publications and source records attributed to N K Dhingra.

5 recordsLinked to original sources

PubMed1998

Chronic (-) deprenyl administration increases dendritic arborization in CA3 neurons of hippocampus and AChE activity in specific regions of the primate brain.

The mechanism by which (-) deprenyl enhances cognitive function in Alzheimer's disease (AD) is not yet understood. (-) Deprenyl (0.2 mg/kg/day) was administered intramuscularly to adult male monkeys (n = 6) for 25 days. Control monkeys (n = 6) received physiological saline by the same route. The activity of acetylcholinesterase (AChE) in different brain regions and the dendritic arborization in CA3 pyramidal neurons of hippocampus were analysed. (-) Deprenyl-treated monkeys showed a significant increase in the AChE activity by 43% (p < 0.001) in the frontal cortex, by 39% (p < 0.025) in the motor cortex, by 66% (p < 0.001) in the hippocampus and by 26% (p < 0.05) in the striatum compared to controls. The branching points and the intersections of both apical and basal dendrites of CA3 hippocampal pyramidal neurons were also significantly increased in (-) deprenyl-treated monkeys. Enhanced AChE activity may increase dendritic arborization in the hippocampus and it may also play a role in improving cognitive functions observed in AD, following (-) deprenyl treatment.

Acetylcholinesterase↗

PubMed1998

Role of monoamine oxidase type A and B on the dopamine metabolism in discrete regions of the primate brain.

The role of monoamine oxidase (MAO) type A and B on the metabolism of dopamine (DA) in discrete regions of the monkey brain was studied. Monkeys were administered (-)-deprenyl (0.25 mg/kg) or clorgyline (1.0 mg/kg) or deprenyl and clorgyline together by intramuscular injections for 8 days. Levels of DA and its metabolites, dihydroxy phenylacetic acid (DOPAC) and homovanillic acid (HVA) were estimated in frontal cortex (FC), motor cortex (MC), occipital cortex (OC), entorhinal cortex (EC), hippocampus (HI), hypothalamus (HY), caudate nucleus (CN), globus pallidus (GP) and substantia nigra (SN). (-)-Deprenyl administration significantly increased DA levels in FC, HY, CN, GP and SN (39-87%). This was accompanied by a reduction in the levels of DOPAC (37-66%) and HVA (27-79%). Clorgyline administration resulted in MAO-A inhibition by more than 87% but failed to increase DA levels in any of the brain regions studied. Combined treatment of (-)-deprenyl and clorgyline inhibited both types of MAO by more than 90% and DA levels were increased (57-245%) in all brain regions studied with a corresponding decrease in the DOPAC (49-83%) and HVA (54-88%) levels. Our results suggest that DA is metabolized preferentially, if not exclusively by MAO-B in some regions of the monkey brain.

3,4-Dihydroxyphenylacetic Acid↗

PubMed1997

Developmental expression of synaptophysin, synapsin I and syntaxin in the rat retina.

Expression of synaptophysin, synapsin I and syntaxin was studied immunocytochemically in the developing rat retina using indirect immunoperoxidase technique. In the inner plexiform layer (IPL), syntaxin immunoreactivity appeared at postnatal day 1 (P1) whereas synaptophysin and synapsin I staining were first observed at P2. In the outer plexiform layer (OPL), synaptophysin appeared at P4, while synapsin I and syntaxin appeared at P8. In the case of synaptophysin, a punctate pattern of staining was observed from the time of its appearance (P4) in the OPL and from P12 onwards in the IPL. Synapsin I and syntaxin immunoreactivity in the OPL were of a low intensity throughout the development and in the adult stage. These findings are discussed in relation to synaptogenesis in the rat retina.

Animals↗

PubMed1997

Selective reduction of monoamine oxidase A and B in the frontal cortex of subordinate rats.

We have previously shown that subordination causes a reduction in the levels of 5-hydroxytryptamine and dopamine selectively in the frontal cortex [6]. These monoamines are catabolised mainly by the enzyme monoamine oxidase (MAO) which exists in two isoforms; MAO-A and MAO-B. The present study was carried out to determine whether there is any change in the activity of these two iso-enzymes induced by subordination and if any such alteration is confined to the frontal cortex. The animal model of dominance-subordination used was a worker-parasite paradigm in male Wistar rats. The enzyme activities were measured in five brain regions, the frontal cortex, entorhinal cortex, hippocampus, hypothalamus and striatum, using kynuramine as the substrate. Clorgyline and L-deprenyl were used in vitro to block the activities of MAO-A and MAO-B, respectively. There was a significant (P < 0.001) reduction in the activity of MAO-A as well as MAO-B selectively in the frontal cortex of the subordinate animals. This finding may suggest a reduced neurotransmitter turnover in the serotonergic and dopaminergic neurons terminating in the frontal cortex.

Animals↗

PubMed1996

Subordination induced decrease in 5-hydroxytryptamine and dopamine levels in the frontal cortex--a study using worker-parasite relationship in rats as a model.

Competition for a limited resource appears to be an important factor in natural selection. Such competition when elicited experimentally, leads to the establishment of dominant-subordinate (D-S) relationship between the competitors. The present study was carried out to analyse the effect of D-S relationship on the levels of monoamines, namely, dopamine (DA), 5-hydroxytryptamine (5-HT) and norepinephrine (NE) in various brain regions. The model of D-S relationship selected for this work was a modified worker-parasite paradigm in adult male Wistar rats. The levels of monoamines were estimated in the frontal cortex, the entorhinal cortex, the hippocampus and the septum of the two competitors and a non-competitor control, using high pressure liquid chromatography (HPLC). Levels of DA and 5-HT, but not NE, were found to be lower (P < 0.05) only in the frontal cortex of the subordinate as compared to that of the dominant or the control. These findings are comparable with similar neurochemical changes reported to be caused by some of the known stressors.

Animals↗