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Background The emerging line of research suggests that neuro-inflammation and oxidative stress are linked to the development of depression-like behavior. The tryptophan metabolizing enzyme, indolamine 2,3-dioxygenase (IDO), serves as an important interface between chronic inflammation and depression. IDO is induced by pro-inflammatory cytokines and diverts tryptophan towards the kynurenine pathway, decreasing serotonin synthesis. Further, the metabolites of kynurenine pathway increase brain oxidative stress and also cause N-methyl-D-aspartate (NMDA) receptor-mediated exitotoxicity. The resulting oxidative damage and dysfunction in glutamatergic neurotransmission alters the network connectivity of the brain, which may be the further mechanism for emergence of depression-like symptoms. Methods A depression-like illness was induced in mice by injecting Bacillus Calmette-Guerin (BCG) suspended in isotonic saline at a dose of 107 CFU I.P. The mice were then divided into different groups and were administered MK-801 or normal saline for the next 21 days, after which a battery of behavior and biochemical tests were conducted to assess them. Results The BCG group had significantly reduced sucrose preference index and an increase in immobility time in forced swim test (FST) and Tail Suspension Test (TST) as compared to the saline group. There was also a significant increase in the brain MDA levels and a decline in the brain GSH levels. The hippocampal tissue from the BCG group had significantly more comet cells than the saline group. The NMDA receptor antagonist, MK-801, was able to reverse the BCG-induced depression-like behaviour. MK-801 also showed significant decrease in brain oxidative stress but failed to show significant protection against BCG-induced neurotoxicity observed in comet assay. Conclusions The NMDA receptor antagonist, MK-801, mitigated BCG-induced, depressive-like behavior in mice by improving the sucrose preference and decreasing the duration of immobility time in TST and FST. The overall improvement in depression-like behavior was accompanied by a reduction in brain oxidative stress and comet cells, thus suggesting the antioxidant and neuroprotective action of MK-801.

The high affinity binding sites for serotonin and benzodiazepine in the frontal cortex, for dopamine in the striatum and muscarinic cholinergic receptors in the hippocampus were investigated in the brains of Charles Foster rats treated for 3 days. Transfer latency on elevated plus maze (TL), passive and active avoidance behaviour (PA and AA) and electroconvulsive shock (ECS) induced amnesia were also studied. Pilot studies indicated that single dose administration of Indian Hypericum perforatum (IHp) had little or no acute behavioural effects and hence the extract of IHp was administered orally at two dose levels (100 and 200 mg/kg, p.o.) once daily for 3 consecutive days, while piracetam (500 mg/kg, i.p.), a clinically used nootropic agent, was administered acutely to rats as the standard nootropic agent. Control rats were treated with an equal volume of vehicle (0.3% carboxymethyl cellulose). The results indicate that IHp treatment caused a significant decrease in the binding of [3H] spiroperone (DA-D2 receptor) to the striatum and an increase in the binding of [3H] ketanserin (5-HT2A receptor) and [3H] flunitrazepam (BDZ receptor) to the frontal cortex in rats. Preliminary pharmacological studies with IHp extract indicate the presence of two major behavioural actions, namely, antidepressant and anxiolytic. The present findings tend to elucidate the mechanism of earlier observations, the downregulation of the dopamine D2 receptor being consonant with anxiolytic and the upregulation of 5-HT2A and BDZ receptors being consonant with antidepressant activity. Piracetam when given alone, shortened the TL on days 1, 2 and 9 day and also antagonized the amnesic effects of ECS on the TL significantly, whereas IHp antagonized the amnesia produced by ECS. IHp had no significant effect per se on the retention of the PA in rats but produced a significant reversal of ECS induced PA retention deficit. Piracetam showed a significant facilitatory effect per se on PA retention and also reversed the ECS induced impaired PA retention. In the AA test, piracetam facilitated the acquisition and retention of AA in rats but IHp had no effect per se. Both the doses of IHp and piracetam significantly attenuated the ECS induced impaired retention of AA. These results indicate a possible nootropic action of IHp in amnesic animals, which was comparable qualitatively to piracetam.

The effect of acute administration of 50% standardised ethanolic extract of Indian Hypericum perforatum (IHp) was studied on the rat brain concentrations of monoamines and their metabolites in five different brain regions, viz. hypothalamus, hippocampus, striatum, pons-medulla and frontal cortex by a HPLC technique. IHp extract was administered at the doses of 50 and 200 mg/kg, p.o. and the brain monoamines were assayed after 30 min of the treatment. IHp treatment significantly decreased the levels of serotonin (5-HT) and its metabolite 5-hydroxy indole acetic acid (5-HIAA) and 5-HT turnover in all the brain regions assayed. On the other hand, IHp treatment significantly augmented the levels of norepinephrine (NE) and its metabolite methylhydroxy phenyl glycol (MHPG) and NE turnover in all the brain regions studied. Similarly, the levels of dopamine (DA) were also significantly augmented in the hypothalamus, striatum and frontal cortex. Likewise, the levels of dihydroxyphenyl acetic acid (DOPAC), the major metabolite of DA, were also increased in these brain areas. Pharmacological studies with IHp extract have shown two major behavioural actions, namely, anxiolytic and antidepressant effects. The present findings tend to rationalise these observations, reduced 5-HT activity being consonant with anxiolytic and increased NA and DA activity being consonant with antidepressant action.

The antioxidant activity of Withania somnifera (WS) glycowithanolides was assessed in chronic footshock stress induced changes in rat brain frontal cortex and striatum. The stress procedure, given once daily for 21 days, induced an increase in superoxide dismutase (SOD) and lipid peroxidation (LPO) activity, with concomitant decrease in catalase (CAT) and glutathione peroxidase (GPX) activities in both the brain regions. WS glycowithanolides (WSG), administered orally 1 h prior to the stress procedure for 21 days, in the doses of 10, 20 and 50 mg/kg, induced a dose-related reversal of the stress effects. Thus, WSG tended to normalise the augmented SOD and LPO activities and enhanced the activities of CAT and GPX. The results indicate that, at least part of chronic stress-induced pathology may be due to oxidative stress, which is mitigated by WSG, lending support to the clinical use of the plant as an antistress adaptogen.

Effect of tannoid principles emblicanin A, emblicanin B, punigluconin, and pedunculagin of E. officinalis was assessed on chronic unpredictable footshock-induced stress-induced perturbations in oxidative free radical scavanging enzymes in rat brain frontal cortex and striatum. Chronic stress, administered over a period of 21 days, induced significant increase in rat brain frontal cortical and striatal superoxide dismutase (SOD) activity, concomitant with significant reduction in catalase (CAT) and glutathione peroxidase (GPX) activity. The changes in the enzyme activities was accompanied by an increase in lipid peroxidation, in terms of augmented thiobarbituric acid-reactive products. Administration of Emblica tannoids (10 and 20 mg, po) for 21 days, concomitant with the stress procedure, induced a dose-related alteration in the stress effects. Thus, a tendency towards normalization of the activities of SOD, CAT and GPX was noted in both the brain areas, together, with reduction in lipid peroxidation. The results indicate that the reported antistress rasayana activity of E. officinalis may be, at least partly due to its tendency to normalize stress-induced perturbations in oxidative free radical scavenging activity, in view of the postulate that several stress-induced diseases, including the process of aging, may be related to accumulation of oxidative free radicals in different tissues.

Brain antioxidant enzymes, superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPX) levels were studied in the brains of early diabetic (72 hr) and long term diabetic (one month) rats. Diabetes was induced by injecting streptozotocin (50 mg/kg, i.p.) in citrate buffer. One group of diabetic rats was treated with insulin (1U/day/animal). The results indicate that early diabetic rats exhibit increased SOD and CAT activities with no alteration in the GPX activity. On the contrary, increased CAT decreased GPX activities with no alteration in the SOD activity, was noted in the long-term Diabetic rats. Insulin treatment reversed these alterations in both the groups. It can be concluded that, in diabetic condition antioxidant enzyme levels are elevated and insulin treatment attenuated these changes. Hence, diabetes mellitus, if left untreated, may initiate degenerative processes and other CNS complications due to accumulation of oxidative free radicals.

Although some promising results have been achieved by acetylcholinesterase inhibitors, an effective therapeutic intervention in Alzheimer's disease still remains an important goal. Sitoindosides VII-X, and withaferin-A, isolated from aqueous methanol extract from the roots of cultivated varieties of Withania somnifera (known as Indian Ginseng), as well as Shilajit, a pale-brown to blackish brown exudation from steep rocks of the Himalaya mountain, are used in Indian medicine to attenuate cerebral functional deficits, including amnesia, in geriatric patients. The present investigation was conducted to assess whether the memory-enhancing effects of plant extracts from Withania somnifera and Shilajit are owing to neurochemical alterations of specific transmitter systems. Therefore, histochemistry to analyse acetylcholinesterase activity as well as receptor autoradiography to detect cholinergic, glutamatergic and GABAergic receptor subtypes were performed in brain slices from adult male Wistar rats, injected intraperitoneally daily with an equimolar mixture of sitoindosides VII-X and withaferin-A (prepared from Withania somnifera) or with Shilajit, at doses of 40 mg/kg of body weight for 7 days. Administration of Shilajit led to reduced acetylcholinesterase staining, restricted to the basal forebrain nuclei including medial septum and the vertical limb of the diagonal band. Systemic application of the defined extract from Withania somnifera, however, led to differential effects on AChE activity in basal forebrain nuclei: slightly enhanced AChE activity was found in the lateral septum and globus pallidus, whereas in the vertical diagonal band AChE activity was reduced following treatment with sitoindosides VII-X and withaferin-A. These changes were accompanied by enhanced M1-muscarinic cholinergic receptor binding in lateral and medial septum as well as in frontal cortices, whereas the M2-muscarinic receptor binding sites were increased in a number of cortical regions including cingulate, frontal, piriform, parietal and retrosplenial cortex. Treatment with Shilajit or the defined extract from Withania somnifera affected neither GABAA and benzodiazepine receptor binding nor NMDA and AMPA glutamate receptor subtypes in any of the cortical or subcortical regions studied. The data suggest that Shilajit and the defined extract from Withania somnifera affect preferentially events in the cortical and basal forebrain cholinergic signal transduction cascade. The drug-induced increase in cortical muscarinic acetylcholine receptor capacity might partly explain the cognition-enhancing and memory-improving effects of extracts from Withania somnifera observed in animals and humans.

Morphine (10 mg/kg), ethanol (8% w/v, 2 ml/kg), nicotine (0.1 mg/kg), cannabis extract (200 mg/kg), lorazepam (10 mg/kg) and ondansetron (0.1 mg/kg) were each administered to rats twice daily i.p. for 14 days and the anxiogenic response following their withdrawal was monitored by the elevated plus-maze test 24 h later. Brains were removed and endogenous monoamine oxidase (MAO) A and B inhibitory activity (tribulin) levels measured on day 14 and 24 h after drug withdrawal in different groups of animals. Morphine, ethanol, lorazepam and nicotine withdrawal was associated with significant anxiety and corresponding increase in brain tribulin activity, particularly its MAO A inhibitory component. Cannabis and ondansetron withdrawal were neither associated with anxiety or change in tribulin levels. The investigation supports the postulated role of tribulin as an endogenous correlate of anxiety, its MAO A inhibitory component accounting for a major part of this effect.

Intracerebroventricularly (icv) administered met-enkephalin, leu-enkephalin, and morphine induced dose-related attenuation of carrageenin-induced acute paw oedema in rats. Naloxone (10 micrograms, icv) antagonized the anti-inflammatory effects of the enkephalins (20 micrograms) and morphine (20 micrograms), but itself induced an anti-inflammatory effect at a higher dose (50 micrograms, icv). The anti-inflammatory effects of the enkephalins, morphine, and the higher dose of naloxone were significantly inhibited by metyrapone, an inhibitor of endogenous corticoid synthesis. The icv-administered doses of the enkephalins and morphine induced insignificant inflammation-attenuating effects when administered i.p. Results suggest that the anti-inflammatory effects of the enkephalins and morphine are exerted through central opiate receptors. Furthermore, the inflammation-attenuating effects of these drugs and the higher dose of naloxone appear to be dependent upon endogenous corticoids, suggesting that activation of the hypothalamo-pituitary-adrenocortical axis may be involved.

The effects of i.p. injection of 3 aromatic amino acids and two anxiogenic agents on rat brain isatin concentration and tribulin (endogenous monoamine oxidase inhibitor) activity were investigated. Isatin levels were significantly increased by pentylenetetrazole, confirming the link with 'anxiety', but were unaffected by the other compounds. In contrast, tribulin activity was significantly increased by phenylalanine and tryptophan as well as by both pentylenetetrazole and yohimbine. Whilst these findings shed no light on the mode of synthesis of isatin, they clearly demonstrate the existence of rat brain monoamine oxidase inhibitory activity that is different from it.

The effects of acute and subacute supramaximal and submaximal electroshock-induced convulsions on rat brain tribulin activity were investigated. Both supramaximal and submaximal shocks induced a marked increase, as measured 30 min after the onset of convulsions, with a significantly greater effect from the former. The effects were no longer present 24 h after stimulus. Repeated electroshock for 5 and 10 days showed that submaximal stimuli produced little change, whereas supramaximal shock brought about a significant increase in tribulin activity, the effect being greater with 10-day exposure. The results are not inconsistent with the clinical observation that a single electroconvulsive therapy (ECT) shock has little clinical usefulness but that repeated shocks, spread over several days, result in therapeutic benefit due, perhaps, to an increase in brain concentrations of tribulin, an endogenous monoamine oxidase inhibitor.

Earlier studies from this laboratory have indicated that CNS exerts a modulatory influence over acute inflammation in rats. The present study examines the existence of a similar modulatory effect of CNS on a subacute inflammatory paradigm, the croton oil-induced granuloma pouch in rats. The inflammatory exudate, collected on 6th day after croton oil administration, was found to be substantially less in intracerebroventricular (icv) cannulated and artificial cerebrospinal fluid administered rats as compared to their uncannulated saline (ip) administered counterparts. This effect may be due to stress induced by cannulation. Centrally administered pharmacological agents which attenuate central monoaminergic, cholinergic or prostaglandin systems had insignificant effects on the inflammatory exudate. However, induced increase in central noradrenergic activity was found to attenuate the inflammation when the treatment was done before, but not 48 hr after, the induction of the inflammation. In contrast, induced increase in central serotonergic activity had no effect on the volume of the inflammatory exudate at either time period. Steady state levels of rat brain noradrenaline and serotonin, but not dopamine, were enhanced by the inflammatory procedure. However, these effects may be attributed to the stress induced by croton oil inflammation. The investigation indicates that the modulatory influence of CNS remains limited to the acute phase of inflammation, being exerted mainly by the central noradrenergic system. Once the inflammation has progressed, this modulatory influence of CNS is no longer apparent.

Cannabis resin (CI) produced a dose-related increase in rat brain serotonin concentrations, whereas restraint stress produced maximal rise of the neurotransmitter concentrations at 1 h, followed by a tendency to normalise by 4 h. The prostaglandin (PG) synthesis inhibitors, diclofenac and paracetamol, antagonized CI and restraint stress induced rise in serotonin concentrations. The findings lend credence to earlier reports that PG synthesis inhibitors antagonize serotonin-mediated neuropharmacological actions of CI and restraint stress in rats.

Intracerebroventricular (i.c.v.) administered bradykinin (2.5 and 5.0 micrograms/rat) was found to augment carrageenan-induced acute paw oedema throughout the 4 h post-carrageenan observation period. The effect was statistically significant with the higher dose. The pro-inflammatory effect of i.c.v. bradykinin was antagonized following pretreatment with hemicholinium and atropine ethoiodide administered i.c.v., drugs that reduce central cholinergic activity. Similarly, central administration of drugs that inhibit the synthesis of eicosanoids, hydrocortisone, diclofenac and paracetamol, also attenuated the pro-inflammatory effect of bradykinin. The findings indicate that the inflammation-promoting effect of centrally administered bradykinin involves the central prostaglandin and cholinergic neurotransmitter systems.

The role of brain monoamines in the anticonvulsant action of Cannabis indica resin (CI), against maximal electroshock-induced seizures in albino rats, was investigated by using pharmacologic agents that influence brain monoamine activity. Delta-9-tetrahydrocannabinol content of cannabis resin was estimated to be 17%. The anticonvulsant action of CI (200 mg/kg, i.p.) was significantly inhibited after pretreatment with drugs that reduce brain serotonin activity but not by drugs that reduce brain catecholamine activity. Similarly, the anticonvulsant action of a subanticonvulsant dose (50 mg/kg, i.p.) of CI was potentiated by serotonin precursors but not by catecholamine precursors. Potentiation of the anticonvulsant action of CI by nialamide or by imipramine was inhibited after pretreatment with 5,6-dihydroxytryptamine. The results suggest that the anticonvulsant action of CI in the rat is serotonin- and not catecholamine-mediated.

Carrageenin-induced pedal inflammation in rats, was found to significantly enhance brain levels of prostaglandin (PG) E2 and PGF2 alpha. PG levels increased after 30 min of induction of the inflammation, peaked at 1 h, and attained normal levels by 4 h. Bilateral adrenalectomy had little effect on carrageenin-induced increase in rat brain PGs. The pattern of elevation of central PGs and the time course of carrageenin inflammation were at variance, the latter peaking between 3 and 4 h. The findings lend credence to the postulate that inflammatory hyperalgesia involves participation of central pain circuits, and that fever accompanying inflammation is caused by the central release of PGs. The central nociceptive and hyperthermic actions of PGs are well documented. However, the increase in central PG levels may well be caused by stress induced by the peripheral inflammation, since the pattern of elevation in either case is qualitatively similar.

Two hours of cold restraint stress in rats resulted in significantly increased brain concentrations of endogenous monoamine oxidase inhibitor (tribulin). Young and old rats showed the same order of response. Tribulin levels were also increased by immobilisation stress alone but to a lesser extent.

Paw inflammation was induced in rats by sub-plantar administration of carrageenan. Significant inflammatory oedema was observed 1 h later and the peak effect was noted between 3-4 h. The oedema was markedly reduced after 12-24 h. Steady state levels of whole brain and hypothalamic monoamines were estimated spectrofluorometrically during the course of the carrageenan-induced paw inflammation. In addition, the rate of accumulation of the brain 5-hydroxytryptamine (5-HT) and noradrenaline (NA) was assessed in clorgyline-pretreated rats during the inflammation. The whole brain and hypothalamic concentrations of 5-HT and NA were augmented during the early phase of the inflammation, but fell below control values when peak inflammation was achieved. Thereafter, the monoamine levels tended to normalize by 24 h when the inflammation had virtually subsided. On the contrary, whole brain and hypothalamic dopamine levels remained largely unaffected. The rate of accumulation of brain 5-HT and NA were enhanced during carrageenan inflammation, indicating that the turnover of these monoamines is augmented during the inflammatory process. The results suggest that acute peripheral inflammation may significantly affect central 5-HT and noradrenergic activity in rats.

Intracerebroventricular administration of prostaglandin D2 (PGD2), the major PG in the rat brain, produced a dose-related anti-nociceptive effect in rats as assessed by the rat tail-hot wire, hot plate and phenylquinone-induced writhing techniques. The antinociceptive action of centrally-administered PGD2 was markedly attenuated after pretreatment of the rats with 5,6-dihydroxytryptamine, a selective neurotoxin for central serotonergic neurones, and p-chlorophenylalanine, a specific inhibitor of serotonin synthesis, indicating that the PGD2 action is serotonin-mediated. Naloxone, an antagonist of endogenous opioid receptors, also antagonised the antinociceptive action of PGD2. Earlier reports from this laboratory have shown that the antinociceptive action of centrally-administered PGE1 in rats is a serotonin-mediated effect and is also antagonised by naloxone. It was further shown that PGD2, like PGE1, augments serotonin turnover in the rat brain. The present findings support the view that PGD2 shares some of the central actions of PGEs and, like the latter, may function as a neuromodulator in the central nervous system.

Loading of L-tryptophan for 7 and 21 days increased brain 5-hydroxytryptamine (5-HT) level which was associated with decreased plasma testosterone level. Human chorionic gonadotropin (HCG) administration in L-tryptophan treated rats for 21 days increased the plasma testosterone level in spite of increased brain 5-HT level. These results suggest that brain 5-HT exerts an inhibitory influence on testicular steroidogenesis by modulating the gonadotropin-releasing-factor (GnRH) release and thence pituitary gonadotropins.