Mrinal K. Poddar

Caffeine-induced locomotor activity: Possible involvement of GABAergic-dopaminergic-adenosinergic interaction

Caffeine (10–40 mg/kg, p.o.) enhanced locomotor activity (LA). Administration of GABA antagonist, bicuculline (0.5–1.0 mg/kg, i.p.), potentiated this caffeine-induced increase of LA, as well as LA of control rats. Treatment with the GABA agonist, muscimol (0.25–1 mg/kg, i.p.) or dopaminergic antagonist, haloperidol (0.25–1 mg/kg, i.p.) or muscarinic receptor blocker, atropine (3.75–5 mg/kg, i.p.), or inhibitor of acetylcholine esterase physostigmine (0.05–0.30 mg/kg, i.p.) or nicotine (0.5–1.5 mg/kg, i.p.) an nicotinic receptor agonist all decreased the LA of both caffeinetreated and control rats. Haloperidol-induced reduction in caffeine-induced increase in LA was found to be withdrawn with higher dose of caffeine. The dopamine agonist L-Dopa (75–150 mg/kg, p.o.) along with carbidopa (10 mg/kg, p.o.) increased the LA in control rats and potentiated the LA of caffeine treated rats. The haloperidol attenuated the bicuculline-induced increase in LA and atropine or physostigmine attenuated the bicuculline or L-Dopa+carbidopa-induced increase in LA in both caffeine treated and control rats when those drugs were administered concomitantly with bicuculline or L-Dopa+carbidopa. These results suggest that (a) the GABAergic system has direct role in the regulation of LA, and (b) caffeine potentiates LA by antagonism of the adenosine receptor and activation of the dopaminergic system which, in turn, reduces GABAergic activity through the reduction of cholinergic system.

In vivo and in vitro effects of Δ9-tetrahydrocannabinol on rat liver microsomal drug-metabolizing enzymes☆

Abstract The in vivo and in vitro effects of Δ9-tetrahydrocannabinol (Δ9-THC) on rat liver microsomal dimethylaniline-N-demethylase, p-nitroanisole-O-demethylase and aniline hydroxylase activities were studied. In vivo acute administration of Δ9-THC produced a marked inhibitory effect of these drug-metabolizing enzyme activities at the higher dose (50 mg/kg) after 6 hr of ip injection. The inhibition was of mixed type for the two demethylases and noncompetitive in case of aniline hydroxylase, whereas comparatively fewer inhibitory effects on these enzyme activities were observed at the lower dose (10 mg/kg). Chronic treatment with Δ9-THC for 21 days (10 mg/kg/day) competitively inhibited the N- and O-demethylase activities but had no inhibitory effect on aniline hydroxylase. Under in vitro conditions of drug treatment at doses of 2, 4, and 8 μg/mg of protein, two demethylase activities were found to be inhibited in a competitive manner whereas comparatively less and mixed type of inhibition was observed with aniline hydroxylase only at higher doses of the drug. These results suggest that Δ9-THC changes the conformation of the hepatic microsomal membrane in a characteristic way, and there exists a qualitative difference between the two substrate-binding sites of the microsomal membrane regarding their interaction with a highly lipophilic drug like Δ9-THC.

Effect of pentylenetetrazol on carbaryl-induced changes in striatal catecholamines

Administration of pentylenetetrazol (PTZ) (60 mg/kg, s.c.) to normal or carbaryl (200 mg/kg, p.o.) treated adult male albino rats produced characteristic changes in the steady-state levels of striatal dopamine (DA), noradrenaline (NA) and homovanillic acid (HVA) at different time intervals (0.5, 1.0 and 2.0 hr). The elevation of striatal NA level was found to be more pronounced with PTZ than that produced by carbaryl. Treatment of rats with PTZ alone caused a significant elevation of DA levels only at 2.0 hr without any significant change in the level of HVA at any time interval. Carbaryl which did not have any significant effect on striatal DA level produced an elevation of HVA at 0.5 hr and 1.0 hr in striatum. The simultaneous administration of PTZ and carbaryl, under similar conditions, caused a marked reduction in the level of NA at 0.5 hr and DA at 1.0 hr without any significant effect on (i) both the amine levels at 2.0 hr and (ii) HVA level at any of the time intervals. Measurement of (a) alpha-methyl-p-tyrosine (alpha-MpT) (250 mg/kg, i.p.) induced depletion of striatal DA and NA, (b) FLA-63 (25 mg/kg, i.p.) induced disappearance of NA, (c) pargyline (75 mg/kg, i.p.) induced reduction and probenecid (200 mg/kg, i.p.) induced accumulation of striatal HVA in the presence or absence of PTZ and/or carbaryl revealed that: (1) PTZ or carbaryl alone caused a significant increase in the turnover of striatal DA; (2) the turnover of striatal NA was significantly increased after PTZ treatment but not after carbaryl administration; (3) the simultaneous administration of carbaryl and PTZ, on the other hand, attenuated (a) PTZ- or carbaryl-induced increase in metabolic activity of the striatal dopaminergic system, and (b) the enhanced anabolic activity of striatal noradrenergic system caused by PTZ, but failed to affect the enhanced utilization of striatal NA induced by PTZ alone.

Interaction of central serotonin and dopamine in the regulation of carbaryl-iduced tremor

Carbaryl (50-200 mg/kg, p.o.) produced dose-dependent tremors and inhibition of striatal AChE activity. A dose-dependent elevation of striatal 5-HT and 5-HIAA levels was also observed with carbaryl but at the higher doses (100-200 mg/kg p.o.). L-Trp or 5-HTP or haloperidol potentiated the carbaryl-induced tremors. Further, 5-HTP or haloperidol, when administered (i) alone, reduced the ED50 value and increased the duration of carbaryl-induced tremors without affecting the maximum tremorogenic response of rats and (ii) together, did not change any of these measures significantly. Atropine (acetylcholine antagonist) completely blocked the tremors produced by carbaryl in the absence or presence of 5-HTP or haloperidol. Methysergide (5-HT antagonist) and bromocriptine (DA agonist) antagonised the potentiating effect of 5-HTP and haloperidol, respectively, on the carbaryl-induced tremors. Furthermore, bromocriptine antagonised the potentiating effect of 5-HTP on the carbaryl-induced tremor but, methysergide failed to achieve this antagonism in presence of haloperidol. These results indicate that carbaryl-induced tremors primarily involve the activation of central cholinoceptors and that the serotonergic potentiation of carbaryl-induced tremors is possibly mediated through the dopaminergic disinhibition of cholinergic neurons.

Lignocaine: Inhibitory effect on synaptosomal and erythrocyte membrane-bound acetylcholinesterase activity

Lignocaine (5-20 mM) reversibly inhibits (in vitro) AChE activity of rat brain synaptosome (33-66%) and erythrocyte membrane (10-54%) in a concentration dependent manner. Lineweaver-Burk plots indicate that lignocaine-induced inhibition of AChE activity in synaptosome is competitive, whereas in erythrocyte membrane inhibition of AChE is non-competitive in nature. Arrhenius plots show that transition temperatures of both synaptosomal and erythrocyte membrane-bound AChE are significantly reduced in the presence of lignocaine. These results suggest that lignocaine increases the lipid fluidity of synaptosomal and erythrocyte membrane which may be a cause of inhibition of membrane-bound AChE activity.

Dietary protein-carbohydrate ratio: exogenous modulator of immune response with age.

Manipulation of dietary variables is one the most described events to retard the aging process and maintain immune function. The present study deals with the effect of variable dietary protein-carbohydrate ratios (without caloric restriction) on the alteration of immune response of male albino rats at the level of lymphocyte viability, proliferation, cytotoxicity, DNA fragmentation of blood, spleen and thymus and corticosterone levels in plasma and adrenal gland in relation to aging and duration of dietary exposure. Young (3 months) and aged rats (18 months) maintained with control diet [protein (20%)-carbohydrate (68%)] showed age-induced decrease in immune response with an increase in plasma corticosterone level. Consumption of low protein (8%)-high carbohydrate (80%) (LP-HC) diet for short-term period (15 consecutive days) decreased immune response of young rats with little immunopotentiation of aged rats but prolongation of consumption (for 60 consecutive days) of the LP-HC diet potentiated these immunopotentiation effects. High protein (50%)-low carbohydrate (38%) (HP-LC) diet under short-term exposure contrarily showed little immunopotentiation in young with an immunosuppression in aged rats. Prolongation of exposure (for 60 consecutive days) to the HP-LC diet produced similar but more amplified effects in young rats; whereas, in aged rats a pronounced decrease in peripheral immune response with an activation in thymus-dependent immune response was observed under similar conditions. These results thus suggest that diets with variable dietary protein-carbohydrate ratios act as an exogenous modulator of immune response with age and LP-HC diet may be beneficial to slow down/reduce the impairment of immune response in aged individuals.

Short-term erythrosine B-induced inhibition of the brain regional serotonergic activity suppresses motor activity (exploratory behavior) of young adult mammals.

Previous studies showed that repeated ingestion of erythrosine B (artificial food color) developed behavioral hyperactivity, but nothing is known about its single administration effect as well as the neurochemical (s) involvement. The present study provides evidence that a single higher dosage (10, 100 or 200 mg/kg, p.o.) of erythrosine administration to young adult male rats reduced motor activity (MA) maximally at 2 h and brain regional (medulla-pons, hippocampus and hypothalamus) serotonergic activity (measuring steady-state levels of 5-HT and 5-HIAA, pargyline-induced 5-HT accumulation and 5-HIAA declination rate and 5-HT receptor binding) under similar experimental condition. The degree of erythrosine-induced inhibition of both MA and brain regional serotonergic activity was dosage dependent. Lower dosage (1 mg/kg, p.o.) did not affect either of the above. Erythrosine (100 or 200 mg/kg, p.o.)-induced MA suppression was also observed in the presence of specific MAO-A inhibitor, clorgyline (5 mg/kg, i.p.) or MAO-B inhibitor, deprenyl (5 mg/kg, i.p.); but their co-application (5 mg/kg, i.p., each) effectively prevented the erythrosine-induced motor suppression. Altogether these results suggest that a single higher dosage of erythrosine (10-200 mg/kg, p.o.) may reduce MA by reducing serotonergic activity with modulation of central dopaminergic activity depending on the brain regions.

Action of Δ9-tetrahydrocannabinol on membrane-bound monoamine oxidase activity

Abstract In vivo administration (ip) of Δ 9 -tetrahydrocannabinol ( Δ 9 -THC) to adult rats under acute conditions (10 and 50 mg/kg) produced a dose-dependent stimulation of monoamine oxidase (MAO; monoamine: O 2 oxidoreductase (deaminating), EC 1.4.3.4) activity in blood platelets and in mitochondrial preparations of hypothalamus and heart. Chronic treatment (10 mg/kg/day for 15 consecutive days) produced a smaller stimulating effect on MAO activity of these tissues. In vitro treatment with Δ 9 -THC produced (1) a stimulatory effect in hypothalamic MAO up to a concentration of 4 μg/mg of protein, (2) an inhibitory effect on heart MAO, and (3) a slight though not insignificant inhibitory effect on platelet MAO. Kinetic studies of in vivo and in vitro Δ 9 -THC-treated enzyme (MAO) are discussed on the basis of K m and V max values obtained from Linewwaver-Burk plots. When KSCN, KNO 3 , and urea were used, they produced a significant inhibitory effect on MAO activity in all these tissues, even in the presence of Δ 9 -THC, indicating that a characteristic interaction between membrane-bound MAO and Δ 9 -THC can be disrupted by these chaotropic agents.

Effect of cannabis extract, Δ9-tetrahydrocannabinol and lysergic acid diethylamide on rat liver enzymes

Abstract The effect of intraperitoneal administration of cannabis extract, Δ 9 -tetrahydrocannabinol (THC) and lysergic acid diethylamide (LSD), both at high (50 mg/kg, 100 mg/kg and 100 μg/kg respectively) and low (10 mg/kg, 10 mg/kg and 10 μg/kg respectively) doses, on the rat liver tyrosine α-ketoglutarate transaminase and tryptophan pyrrolase activity was studied and found that cannabis extract and Δ 9 -tetrahydrocannabinol, but not LSD, increased the above two enzyme activities after 6 hr of injection.

Higher environmental temperature-induced increase in body temperature: involvement of serotonin in GABA mediated interaction of opioidergic system.

Exposure (2 h) of adult male albino rats to higher environmental temperature (HET, 40°C) significantly increased body temperature (BT). Administration of (a) 5-HTP (5 mg/kg, i.p.) or morphine (1 mg/kg, i.p.) or physostigmine (0.2 mg/kg, i.p.) alone significantly increased and (b) methysergide (1 mg/kg, i.p.) or naloxone (1 mg/kg, i.p.) or atropine (5 mg/kg, i.p.) reduced the BT of both normal and HET exposed rats. Further, it was observed that morphine prevented the methysergide-induced hypothermia and 5-HTP potentiated the morphine-induced hyperthermia in both normal and HET exposed conditions. Biochemical study also indicates that serotonin metabolism was increased but GABA utilization was reduced following exposure to HET. 5-HTP or bicuculline-induced hyperthermia in control and HET exposed rat was potentiated with the coadministration of bicuculline and 5-HTP. The cotreatment of bicuculline with methysergide prevented the methysergide-induced attenuation of BT of heat exposed rat, rather BT was significantly enhanced indicating that inhibition of GABA system under heat exposed condition may activate the serotonergic activity. Further (a) enhancement of (i) morphine-induced hyperthermia with physostigmine (ii) physostigmine- or morphine + physostigmine-induced increase of BT with 5-HTP and (b) reduction of (i) morphine- or morphine + 5-HTP-induced hyperthermia with atropine and (ii) atropine-induced hypothermia with 5-HTP in both normal and HET exposed conditions suggest that HET exposure activates the cholinergic system through the activation of opioidergic and serotonergic system and hence increased the BT. Thus, it may be concluded that there is an involvement of serotonergic regulation in the opioidergic-cholinergic interaction via GABA system in HET-induced increase in BT.