On the mechanism of potentiation of apomorphine-induced stereotypy due to electroconvulsive shock.

Electroconvulsive shock-induced changes in the intensity of stereotype induced by apomorphine, the binding of [3H]spiroperidol in the corpus striatum, the accumulation of [3H]dopamine in brain and the permeability of the blood-brain barrier, were monitored in rats 30 min after single, or 24 hr after chronic (once daily for 7 days) electroconvulsive shock. There was significant potentiation in stereotypy induced by apomorphine after chronic electroconvulsive shock. The binding of [3H]spiroperidol did not show any change in the affinity (Kd) or density (Bmax) of receptors in the striatum after acute or chronic electroconvulsive shock. The accumulation of dopamine increased significantly in the hypothalamus after acute electroconvulsive shock and in the corpus striatum and hypothalamus after chronic electroconvulsive shock. A significant increase in the entry of sodium fluorescein into the hypothalamus occurred after acute electroconvulsive shock; it increased in all the regions of the brain after chronic electroconvulsive shock. Alteration in the blood-brain barrier (BBB) by electroconvulsive shock leading to increased accumulation of dopamine in the corpus striatum may be responsible for the potentiation of stereotypy.

The mechanism of opening of the blood-brain barrier by hypertonic saline.

The permeability of the blood-brain barrier was assessed in the cat, using Evan's blue as circulant. Regional blood flow and vascular resistance in various areas of brain were measured using radioactive microspheres. Cardiac output (CO), blood pressure (BP), heart rate (HR), pH, pO2 and pCO2 were also measured. Hypertonic saline (5 M, 0.5 ml/kg), administered intravenously, increased the staining of the brain substance. It also produced a marked increase in cerebral blood flow after 5 min and a marked decrease in blood flow to all the regions of the brain after 20 min. The flow returned to normal after 40 min. The vascular resistance decreased at 5 min, increased at 20 min and returned to normal at 40 min. Cardiac output increased significantly at 5 min and decreased at 20 min, while at 40 min it returned to normal. Blood pressure decreased at 5 min, increased at 20 min, while heart rate steadily decreased. A complete recovery of cardiac output, blood pressure and heart rate occurred in 1 hr. No change was observed in pH, pCO2 and pO2. It is concluded that intravenous administration of hypertonic saline causes marked haemodynamic changes and increases the permeability of the blood-brain barrier due to transient impairment of autoregulation.

Effects of interferon in malaria infection.

Earlier, we reported that prophylactic treatment with human interferon gamma (rHuIFN-gamma) protected monkeys against Plasmodium cynomolgi B malaria infection. We have tested the efficacy of rHuIFN-gamma on relapsing stage of experimental P. cynomolgi B malaria infection in rhesus monkeys. No effect of rHuIFN-gamma was seen against experimental relapsing stage compared with controls; however, it appears that chloroquine (CHL) may have interfered with the antimalarial effect of IFN, since treatment with CHL inhibits the antiviral activity of mouse alpha/beta IFN and polyinosinic-polycytidylic acid (poly I:C) against Semliki forest virus (SFV) in mice. These results may have clinical implications especially with the use of IFN against virus infection, cancer and in parasitic infections in malaria endemic areas where CHL is one of the most widely used antimalarial drugs. Our result also shows that CHL treatment enhances the virus replication in mice and suggest a possible connection between AIDS and malaria infection, since the spread of AIDS has been rapid in parts of tropical Africa that have a high incidence of malaria, and chloroquine has been frequently used in the chemotherapy of malaria.

Facilitation of the flexor reflex in the cat by intrathecal injection of catecholamines.

1. Effects of some alpha- and beta-adrenoceptor stimulants and antagonists were investigated on flexor reflex (FR) in chloralosed cats.2. Noradrenaline (NA) produced facilitation of FR which was dose-dependent and reproducible and was blocked by alpha-adrenoceptor blocking agents.3. Strychnine also produced facilitation of FR but the response was unaffected by alpha-adrenoceptor blocking agents.4. Metaraminol and alpha-methyl-noradrenaline had little effect on FR but blocked the NA response.5. beta-adrenoceptor stimulants and antagonists had neither any effect on FR nor modified the NA response.6. Vasopressin and histamine also failed to modify FR.7. Possibility of alpha-adrenoceptors in the neurones integrating FR is suggested.

Evidence for the presence of -adrenoceptors in the central thermoregulatory mechanism of rabbits.

1. The effects of intracerebroventricular administration of some alpha- and beta-adrenoceptor stimulants and antagonists on the body temperature of rabbits were investigated.2. Noradrenaline produced a dose dependent rise in body temperature. Other catecholamines were less active.3. The noradrenaline response was blocked by alpha-adrenoceptor blocking agents while beta-adrenoceptor antagonists had no effect.4. alpha-Methyl-noradrenaline and metaraminol had some hyperthermic effect, but significantly reduced the response of noradrenaline.5. The possible presence of alpha-adrenoceptors in the central thermoregulatory mechanisms is suggested.

Anti-inflammatory and some other pharmacological effects of 3,4-trans-2,2-dimethyl-3-phenyl-4-(p-(beta-pyrrolidinoethoxy)-phenyl)-7-methoxy-chroman (Centchroman).

1. Anti-inflammatory, analgesic, antipyretic and other pharmacological activities of a new chroman derivative, Centchroman, have been described.2. Centchroman was found to possess significant anti-inflammatory action in the carrageenin-induced oedema test in mice and rats. It inhibited granuloma formation in the cotton pellet test. The anti-arthritic activity was also evident in formaldehyde-induced arthritis and adjuvant-induced arthritis in rats.3. Centchroman had a lower ulcerogenic index than phenylbutazone.4. The mechanism of the anti-inflammatory action of Centchroman seemed to be independent of endogenous adrenocortical hormones or of its weak oestrogenic activity.5. Centchroman antagonized phenylquinone writhing and bradykinin-induced bronchospasm but was devoid of any antipyretic activity.

Analysis of histamine receptors in the central thermoregulatory mechanism of Mastomys natalensis.

1 The effect of intracerebroventricular (i.c.v.) injection of histamine on the rectal temperature of Mastomys natalensis at ambient temperatures of 10, 24 and 33 degrees C has been studied. 2 Low doses (0.1-1.0 microgram) of histamine produced hypothermia while larger doses (5-20 micrograms) produced dose-dependent hyperthermia. The hypothermic effect was significantly antagonized by mepyramine while the hyperthermia was blocked by cimetidine. 3 Histamine H1-receptor agonists, 2-methyl-histamine and 2-pyridyl-ethylamine, also produced hypothermia which could be blocked by mepyramine. 4 Histamine H2-receptor agonists, impromidine and dimaprit, produced hyperthermia which was antagonized by cimetidine. 5 Pretreatment of the animals with a beta-adrenoceptor antagonist, MJ1999, did not affect the response to histamine. 6 The hyperthermic effect of histamine (10 micrograms) was most marked at 10 degrees C and was attenuated at 33 degrees C. 7 It is concluded that both H1 and H2-histamine receptors are present in the brain of Mastomys. The H1-receptors mediate hypothermia and H2-receptors hyperthermia.

Selective inhibition by glycine of some somatic reflexes in the cat.

1. The effects of intracerebroventricular or intrathecal administration of glycine on some somatic reflexes in chloralosed cats were investigated.2. Glycine produced marked inhibition of the flexor reflex (FR) and crossed extensor reflex (CER) at low doses (2.5-5.0 mg) but even large doses (up to 40.0 mg) had no effect on the facilitation or inhibition of the patellar reflex produced by stimulation of either the reticular formation or the sciatic nerve. The linguomandibular reflex (LMR) could be blocked by 10-20 mg glycine.3. Glycine antagonized strychnine-induced facilitation of FR, CER and LMR and was 5-6 times as active as gamma-aminobutyric acid in this respect.4. The possibility of glycine being a transmitter in spinal pathways is discussed.

Effect of clonidine on the excitability of vasomotor loci in the cat.

1. The effect of clonidine on the direct excitability of hypothalamic, medullary and spinal vasomotor loci has been investigated in cats anaesthetized with chloralose. 2. Clonidine inhibited the excitability of these loci when it was localized to the central sites by intracerebroventricular, intravertebral arterial or intrathecal injection in very low doses (1-2 mug). 3. Topical application of clonidine (0.01 percent and 1.0 percent) to the floor of the fourth ventricle inhibited pressor responses evoked either by stimulation of medullary or hypothalamic vasomotor areas. Inhibition of the pressor responses was accompanied by hypotension and bradycardia in many experiments. 4. It appears that effects of clonidine on the vasomotor loci of the medulla oblongata and the spinal cord contribute to its hypotensive action.

Picroliv, picroside-I and kutkoside from Picrorhiza kurrooa are scavengers of superoxide anions.

Picroliv, the active principle of Picrorhiza kurrooa, and its main components which are a mixture of the iridoid glycosides, picroside-I and kutkoside, were studied in vitro as potential scavengers of oxygen free radicals. The superoxide (O2-) anions generated in a xanthine-xanthine oxidase system, as measured in terms of uric acid formed and the reduction of nitroblue tetrazolium were shown to be suppressed by picroliv, picroside-I and kutkoside. Picroliv as well as both glycosides inhibited the non-enzymic generation of O2- anions in a phenazine methosulphate NADH system. Malonaldehyde (MDA) generation in rat liver microsomes as stimulated by both the ascorbate-Fe2+ and NADPH-ADP-Fe2+ systems was shown to be inhibited by the Picroliv glycosides. Known antioxidants tocopherol (vitamin E) and butylated hydroxyanisole (BHA) were also compared with regard to their antioxidant actions in the above system. It was found that BHA afforded protection against ascorbate-Fe(2+)-induced MDA formation in microsomes but did not interfere with enzymic or non-enzymic O2- anion generation; and tocopherol inhibited lipid peroxidation in microsomes by both prooxidant systems and the generation of O2- anions in the non-enzymic system but did not interfere with xanthine oxidase activity. The present study shows that picroliv, picroside-I and kutkoside possess the properties of antioxidants which appear to be mediated through activity like that of superoxide dismutase, metal ion chelators and xanthine oxidase inhibitors.

Analgesic effect of morphine, clonidine and serotonin microinjected into the PTN of rats.

The study was aimed to delineate the neurotransmitter receptors involved in pretectal analgesic mechanisms by direct microinjection of neurotransmitter agonists and antagonists through chronically implanted cannulae in the pretectal nucleus of rats. Morphine, clonidine and serotonin, at doses of 2.5 and 5.0 micrograms microinjected into the pretectal nucleus, produced a significant and prolonged analgesia as measured by the tail-flick test. The analgesia produced by morphine, clonidine and serotonin is significantly attenuated by pretreatment of the animals with naloxone (1 micrograms), yohimbine (5 micrograms) and methysergide (5-10 micrograms) respectively. The results indicate the possible involvement of opioid, adrenergic and serotonergic mechanisms in pretectal analgesia.

Atropine and naloxone sensitive stimulation produced analgesia from pretectal nucleus in rat.

Mild and brief electrical stimulation of sites in the pretectal nucleus (PTN) of rats evoked potent analgesia of long duration, without significant aversions and was unassociated with motor deficit. The present study has analysed effects of opioidergic and cholinergic neurotransmitter antagonists administered intracerebroventricularly (i.c.v.) on this analgesia. Pretreatment either with naloxone or atropine sulphate both in doses of 30 and 50 micrograms each, respectively i.c.v., 10 min prior to subsequent pretectal stimulation, significantly attenuated the increase in tailflick latency. The antagonism of pretectal stimulation produced analgesia (PSPA) by naloxone and atropine, raises the possibility of involvement of both endogenous opioids and cholinergic mechanisms in pretectal analgesia.

Evidence for involvement of nitric oxide in pretectal analgesia in rat.

The study was undertaken to evaluate the role of nitric oxide (NO) in pretectal (PTN)-induced analgesia in rats. Microinjection of varying concentrations of L-arginine (1 nM to 1 microM) produced a quick, long-lasting and concentration-dependent analgesic response, whereas similar concentrations of D-arginine failed to produce analgesia. Moreover pretreatment with N-nitro-L-arginine methyl ester (L-NAME, 1 microM) significantly prevented L-arginine induced analgesia. Further, pretreatment of animals with methylene blue, a known guanylate cyclase inhibitor also prevented the development of analgesia. Our study suggests that L-arginine caused production of NO, which in turn activates pretectal analgesic system involving cyclic GMP.

Novel effects of MPTP: MAO-B unrelated opioidergic activity in mice.

The presence of opioidergic activity after i.p. injection of N-methyl-4-phenyl tetrahydropyridine (MPTP) has been investigated in albino mice by studying analgesia and the Straub reaction. MPTP (6.25-25 mg kg-1) produced a dose-related analgesic response and Straub reaction. These effects of MPTP were effectively antagonized by prior naloxone treatment but remained unaffected after the MAO-B inhibitor deprenyl. MPTP thus possesses significant opioidergic activity and this, unlike its neurotoxic actions, does not appear to be dependent on oxidative conversion to MPP+ (1-methyl-4-phenyl pyridinium).

Reversal of chloroquine resistance in murine malaria parasites by prostaglandin derivatives.

An oligomeric ester of prostaglandin B2 (OC-5186) was found to reverse chloroquine resistance in the murine malarial parasite Plasmodium berghei. When mice were infected with either chloroquine-sensitive or -resistant P. berghei on day 0 (by intraperitoneal injection of 1 x 10(6) parasitized erythrocytes), they died before day 23. When treated with 15 mg/kg/day of chloroquine for the first four days of infection, all mice infected with the sensitive-strain survived, while all those infected with the resistant strain died before day 23. When OC-5186 (3-12 mg/kg/day) was administered in combination with chloroquine for the first four days, 60% of the animals infected with the resistant strain survived. The differences in the survival rate between the group treated with chloroquine only and the group treated with a combination of drugs (chloroquine plus 3-12 mg/kg/day of OC-5186) were significant. There was also a significant inhibition of parasitemia in the group treated with the combination of drugs. The combinations of chloroquine and a monomer ester of prostaglandin B2 (OC-5181) had some antimalarial activity, but the differences between the chloroquine-treated group and the combination treatment group were not significant in terms of both the parasitemia and the survival rate. Another oligomeric ester of prostaglandin E1 (MR-356) as well as unesterified monomer prostaglandins (PGA2 and PGB2) were ineffective by themselves and in combination with chloroquine.

Possible involvement of nitric oxide in red nucleus stimulation-induced analgesia in the rat.

There is considerable evidence that nitric oxide (NO) plays a role in synaptic transmission in both central and peripheral nervous systems. Recent studies have suggested the involvement of the L-arginine-NO pathway in nociceptive transmission/modulation. Electrical stimulation of the red nucleus in the rat evokes potent analgesia. Microinjection of different concentrations of L-arginine (1 nmol-1 mumol), but not of D-arginine, produced quick and long-lasting analgesia. Pretreatment with N-nitro-L-arginine methyl ester (1 mumol), a nitric oxide synthase inhibitor, significantly prevented L-arginine-induced analgesia. Further, pretreatment of animals with methylene blue, a known guanylate cyclase inhibitor, also attenuated the development of analgesia. Our results suggest that L-arginine caused production of NO, which in turn activated the red nucleus analgesic system.

A primate model of anxiety.

Pentylenetetrazol (PTZ; 30 mg/kg, i.m.) produced an acute anxiogenic effect on the behaviour of a social colony of rhesus monkeys acclimatized to laboratory conditions. The animals exhibited hypervigilance, aggressiveness, tachypnea, piloerection and frequent change of posture and also had raised plasma cortisol levels. These effects of PTZ were antagonized by benzodiazepines (diazepam; 1 mg/kg, i.v. and alprazolam; 0.05 mg/kg, p.o.). Non-benzodiazepine anxiolytic drug (buspirone; 10 mg/kg, p.o.) blocked the behavioural effects but not the rise in plasma cortisol concentration. On the other hand, pretreatment with hypnosedative (promethazine; 5 mg/kg, i.m.) or anticonvulsant (sodium valproate; 40 mg/kg, p.o.) agents did not attenuate the effects of PTZ indicating the specificity of its anxiogenic response. The model, thus, seems suitable for evaluation of potential anxiolytic agents.

The effect of intracerebroventricular administration of catecholamines and their antagonists on rectal temperature of Mastomys natalensis.

Noradrenaline (NA), adrenaline (ADR), isoprenaline (ISO) and dopamine (DA) were given through a chronically implanted cannula in the lateral cerebral ventricle of Mastomys natalensis. Low doses of NA (0.05-0.25 microgram) reduced rectal temperature while larger doses (0.35 microgram upwards) produced dose-dependent hyperthermia. The hypothermic effect was antagonised by alpha-adrenoceptor and the hyperthermia by beta-adrenoceptor antagonists. alpha-Methyl noradrenaline produced less hyperthermia but it antagonised the hyperthermic effect of NA. Adrenaline (0.1-10 microgram) was ineffective per se but when given after tolazoline it produced hyperthermia and after propranolol it produced hypothermia. The dose-dependent hyperthermia with isoprenaline (0.1-10 microgram) was blocked by propranolol and MJ-1999. Dopamine (0.5-20 microgram) and its agonists apomorphine, amantadine and BS 9641 produced hyperthermia which was antagonised by haloperidol and pimozide but not by alpha- or beta adrenoceptor antagonists. Noradrenaline (1.0 microgram) produced hypothermia at ambient temperature of 10 degrees C and 16 degrees C. It had no effect at 20 degrees C which seems to be the thermoneutral zone for mastomys. The hyperthermic effect at 33 degrees C was less than at 24 degrees C. Dopamine (10 micrograms) response was attenuated at 33 degrees C and unaffected at other ambient temperatures. It is concluded that alpha- and beta-adrenoceptors and DA-receptors exist in the central thermoregulatory mechanism in mastomys. The alpha-receptors are concerned with lowering the body temperature whereas the beta-receptors and DA-receptors are involved in raising it.

An analysis of stereotyped behaviour in Mastomys natalensis.

The stereotyped behaviour was analysed in Mastomys natalensis, a species of desert rat recently introduced in laboratory practice. The components of stereotyped behaviour were similar to rat characterised by repetitive sniffing, rearing, licking, head movements and biting. Apomorphine (0.5-2.0 mg/kg), amphetamine (2.5-10 mg/kg), methylphenidate (10-30 mg/kg) and adamantanamine (10-50 mg/kg) administered intraperitoneally, induced stereotyped behaviour in dose-dependent manner. Positive response was also obtained by other drugs acting on dopamine receptors like l-dopa, GBR 12909, piribedil, tyramine, BS 9648, BS 9641 and BS 8824. Yohimbine (2 mg/kg) failed to produce any response. Apomorphine (2 mg/kg), amphetamine (10 mg/kg), methylphenidate (30 mg/kg) and piribedil (12 mg/kg) induced stereotypy which could be blocked by dopamine receptor blockers haloperidol (1 mg/kg) or pimozide (1 mg/kg) but yohimbine (2 mg/kg) an alpha adrenoceptor blocker was ineffective. Adamantanamine, piribedil and GBR 12909 enhanced the stereotypy induced by low doses of apomorphine, amphetamine and methylphenidate. The data shows that the stereotyped behaviour in Mastomys natalensis is mediated through dopaminergic mechanisms. It appears that both excitatory and inhibitory types of dopamine receptors are involved.

Curative effect of picroliv on primary cultured rat hepatocytes against different hepatotoxins: an in vitro study.

Picroliv, the standardized active principle from the plant Picrorhiza kurrooa showed significant curative activity in vitro in primary cultured rat hepatocytes against toxicity induced by thioacetamide (200 microg/mL), galactosamine (400 microg/mL), and carbon tetrachloride (3 microl/mL). Activity was assessed by determining the change in hepatocyte viability and rate of oxygen uptake and other biochemical parameters (GOT, GPT, and AP). The toxic agents alone produced a 40-62% inhibition of cell viability and a reduction of biochemical parameters after 24 h of incubation at 37 degrees C which (on removal of the toxic agents) was reversed after further incubation for 48 h. Incubation of damaged hepatocytes with picroliv exhibited a concentration- (1-100 microg/mL) dependent curative effect in restoring altered viability parameters. The results warrant the use of this in vitro system as an alternative for in vivo assessment of hepatoprotective activity of new agents.