Beta-amyloid-induced cholinergic denervation correlates with enhanced nitric oxide synthase activity in rat cerebral cortex: reversal by NMDA receptor blockade

Ample experimental evidence indicates that acute beta-amyloid infusion into the nucleus basalis of rats elicits abrupt degeneration of the magnocellular cholinergic neurons projecting to the cerebral cortex. In fact, involvement of a permanent Ca2+ overload, partially via N-methyl-D-aspartate (NMDA) receptors, was proposed as a pivotal mechanism in beta-amyloid-induced neurodegeneration. A definite measure of NMDA receptor-mediated processes and subsequent Ca2+ entry is the induction of Ca2+/calmodulin-activated neuronal nitric oxide synthase (nNOS) in nerve cells. In the present account we therefore assessed activation of nNOS in correlation with cholinergic decline after beta-amyloid(1-42) or beta-amyloid(25-35) infusion into the rat nucleus basalis. The results demonstrate the beta-amyloid conformation-dependent enhancement of cortical nitric oxide synthase (NOS) activity. Furthermore, chronic application of the polyamine site NMDA receptor blocker ifenprodil effectively attenuated beta-amyloid neurotoxicity. We propose that nNOS activation reflects the degree of beta-amyloid-induced excitotoxic injury in a proportional manner. Moreover, Ca2+-mediated processes via NMDA receptors, or direct binding of beta-amyloid to this receptor may be a critical step in the neurotoxic mechanisms in vivo.

The functional sensitisation of sigma receptors following chronic selective serotonin reuptake inhibitor treatment

The purpose of the present study was to investigate the potential impairment of normal motor function following chronic selective serotonin reuptake inhibitor treatment that may result from sensitisation of sigma receptors. Rats were chronically treated with either sertraline, citalopram, paroxetine or fluvoxamine and a selective sigma receptor ligand, di-o-tolylguanidine (DTG), for 28 days. All animals then received an acute intra-rubral injection of either DTG or saline. Following the direct injection of DTG into the red nucleus, rats chronically treated with DTG exhibit a maximal behavioural response characterised as a pronounced dystonia. Animals chronically treated with sertraline and citalopram elicited a response similar to that of control animals following the acute DTG challenge, whereas chronic treatment with paroxetine and fluvoxamine significantly decreased and increased the dystonic response, respectively. Facial spasticity and vacuous chewing movements were associated with, and reflected the extent of, the DTG-induced dystonia. Changes in regional biogenic amine concentrations were also determined. The concentrations of serotonin and noradrenaline were determined in the brain stem and cerebellum following the intra-rubral injection of either saline or DTG in animals that had been chronically treated with a selective serotonin reuptake inhibitor or DTG. There was a significant increase in serotonin concentration in the brain stem as a result of chronic DTG and fluvoxamine treatments. The increase in serotonin correlated with the reported potentiation of dystonia in animals that received 28 days treatment with these drugs. The potentiation of dystonia following chronic DTG and fluvoxamine treatments suggests that these drugs sensitise the sigma2 receptors, an effect that does not appear to be shared by citalopram, sertraline or paroxetine.

Comparison between the effects of sigma receptor ligand JO 1784 and neuropeptide Y on immune functions

Recent evidence suggests that sigma receptor ligands and neuropeptide Y may act through the same pathways to modulate centrally mediated immune function. The present study demonstrated that both the sigma receptor ligand igmesine: (+)-N-cyclopropylmethy-N-methyl-1, 4-diphenyl-1-yl-but-3-en-1-ylamine, hydrochloride (JO 1784) (10(-7) and 10(-5) M) and neuropeptide Y (10(-9) and 10(-7) M) in vitro significantly reduced neutrophil phagocytosis and decreased mitogen stimulated lymphocyte proliferation. By contrast, central administration of JO 1784 (0.5 and 5 microg/5 microl) significantly reduced the activity of neutrophil phagocytosis, but enhanced lymphocyte proliferation without changing the serum concentration of corticosterone. Neuropeptide Y (10(-9) and 10(-7) M), following intracerebroventricular infusion, also decreased the neutrophil response, but significantly raised the corticosterone concentration. These results indicate that different mechanisms (involving various neurotransmitters and their receptors, changes in the activity of the hypothalamic-pituitary-adrenal axis, or sigma receptor subtypes) may be involved in the central effects of JO 1784 and neuropeptide Y.

Depression, stress and immunological activation: the role of cytokines in depressive disorders

Traditionally, both stress and depression have been associated with impaired immune function and increased susceptibility to infectious and neoplastic disease. However over the last number of years a large body of evidence suggests that major depression is associated with signs of immunological activation. Moreover it has been suggested that cytokine hypersecretion may be involved in the aetiology of depressive disorders. The present article reviews the evidence from both clinical and experimental studies which implicates immunological activation and particularly hypersecretion of cytokines in the onset and maintenance of depressive illness. Both clinical and experimental studies indicate that stress and depression are associated with increased circulating concentrations of cytokines such as IL-1beta, IL-6 and gamma-IFN and positive acute phase proteins, and hyperactivity of the HPA-axis. In addition, it has been reported that immunological activation induces "stress-like" behavioural and neurochemical changes in laboratory animals. Although for many years it has been suggested that stress acts a predisposing factor to depressive illness, the precise mechanisms by which stress-induced depressive symptoms occur are not fully understood. Nevertheless, behavioural changes due to stress have often been explained in terms of changes in neurotransmitter function in the brain. In the present article increased cytokine secretion is implicated as a mechanism whereby stress can induce depression.

Beta-amyloid(Phe(SO3H)24)25-35 in rat nucleus basalis induces behavioral dysfunctions, impairs learning and memory and disrupts cortical cholinergic innervation

Long-term behavioral effects, changes in learning and memory functions and aberrations of cholinergic fibers projecting to the parietal cortex were investigated after bilateral injections of beta-amyloid(Phe(SO3H)24)25-35 peptide in rat nucleus basalis magnocellularis (nbm). The beta-amyloid peptide used in these experiments contained the original beta-amyloid 25-35 sequence which was coupled to a phenylalanine-sulphonate group at position 24. This additional residue serves as a protective cap on the molecule without influencing its neurotoxic properties and results in water-solubility, stability and low rates of peptide metabolism. In this paper, home cage, locomotor and open-field activities, passive shock-avoidance and 'Morris' water maze learning abilities were assessed throughout a 35-day survival period. Subsequently, acetylcholinesterase (AChE) histochemistry was used to visualize alterations of parietal cortical cholinergic innervation. In response to the neurotoxic action of beta-amyloid(Phe(SO3H)24)25-35, a progressive hyperactivity developed in the rats in their home cages which were maintained throughout the 5-week post-injection period. This was accompanied by a significant hypoactivity in the novel environment of a locomotor arena. Beta-amyloid(Phe(SO3H)24)25-35-treated animals showed greatly impaired cortical memory functions in the step-through passive shock-avoidance paradigm, while spatial learning processes remained unaffected. Moreover, beta-amyloid(Phe(SO3H)24)25-35 injections in the nucleus basalis suppressed explorative behavior in rats and inhibited conditioned stress responses 28 days after surgery. Reductions of cortical cholinergic (AChE-positive) projections provided anatomical substrate for the behavioral changes. This indicated extensive, long-lasting neurodegenerative processes as a result of beta-amyloid(Phe(SO3H)24)25-35 infusion.

The role of noradrenaline in depression: a review

This review summarizes some of the evidence implicating a dysfunction in the noradrenergic system in depression. Whereas the results of studies reporting changes in the concentration of the main noradrenaline metabolite, 3-methoxy-4-hydroxyphenylglycol, are equivocal, changes in adrenoceptor density and function and changes in adrenoceptors associated with the pituitary-adrenal axis function strongly implicate a disorder in central noradrenergic transmission in depression. This dysfunction may be caused by changes in the activity of tyrosine hydroxylase, the rate-limiting enzyme in the synthesis of catecholamines. The effect of corticotrophin releasing factor in modulating the activity of noradrenergic neurons in the locus coeruleus may provide the link between environmental trigger factors and central noradrenergic dysfunction. At the cellular level, evidence is presented of a link between noradrenaline and glutamate (via the N-methyl-aspartate receptor) and receptors. Such a link may provide a basis for the future development of novel antidepressants.

Forced swim test-induced endocrine and immune changes in the rat: effect of subacute desipramine treatment

Previously it has been reported that forced swim test (FST) exposure activates the HPA-axis and produces alterations in both cellular and noncellular immunity in rats. Furthermore, there is evidence to suggest that pretreatment with antidepressants has a protective effect against FST-induced immune changes. The purpose of the present study was to examine the effect of subacute treatment with the tricyclic antidepressant desipramine (DMI, 5 and 10 mg/kg; I.P.) on immobility in the FST, and on FST-induced changes in endocrine and immune parameters in the rat. DMI treatment at a dose of 10 mg/kg produced a significant reduction in immobility time in the FST, while the 5 mg/kg dose was ineffective. FST exposure produced a significant increase in serum corticosterone and a decrease in adrenal ascorbic acid concentrations, neither of which were significantly attenuated by DMI pretreatment. There was a slight but nonsignificant suppression of PHA-induced lymphocyte proliferation 15 min post-FST exposure. However, DMI treatment produced a significant increase in lymphocyte proliferation at this time point. FST exposure caused a reduction in the percentage of lymphocytes and an increase in the percentage of neutrophils in the peripheral blood; DMI treatment failed to significantly alter these stress-induced changes. There was a profound reduction in relative spleen weight observed in DMI-treated animals 120 min post-FST exposure and this was accompanied by an increase in circulating RBC concentrations. In conclusion, although the FST-induced behavioral changes were normalized by DMI treatment the peripheral aberrations induced by FST exposure (with the exception of lymphocyte proliferation) were not. In addition, DMI pretreatment induced stress-like changes in corticosterone, adrenal ascorbic acid and leucocyte subpopulations in the control animals.

Acute 3,4-methylenedioxymethamphetamine(MDMA) administration produces a rapid and sustained suppression of immune function in the rat

(+)-3,4-Methylenedioxymethamphetamine (MDMA;'Ecstasy') is a ring substituted phenylisopropylamine that is structurally related to both amphetamines and hallucinogens. The unique behavioural activating properties of MDMA have led to its widespread abuse. MDMA induces many neurochemical, behavioural and endocrine alterations which closely resemble those elicited by exposure to acute stress, suggesting that MDMA could be regarded as a 'chemical stressor'. In addition to the neurochemical, behavioural and endocrine effects of stressor exposure, it has been reported that stress produces alterations in immune function. However, to date the effects of MDMA on immune function have been restricted to in vitro investigations. In this study we report, for the first time, that acute in vivo administration of MDMA (20 mg/kg, i.p.) produced a rapid (within 30 min) suppression of Con A-induced lymphocyte proliferation and a profound reduction in the total leucocyte count in rats that persisted for at least 6 h following injection. These alterations in immune function were accompanied by a significant increase in plasma corticosterone concentrations 30 min post MDMA administration which had returned to baseline values within 6 h of drug administration. In addition, there was a significant depletion in cortical 5-HT concentrations both 30 min and 6 h after MDMA administration. The results of this study provide evidence that in addition to the well established toxic effects of MDMA on the central serotonergic system, a single administration of this widely abused drug induces a rapid and sustained suppression of immune function.

BIMT 17: a putative antidepressant with a fast onset of action?

BIMT 17, the only compound reported to be a full 5-HT1A agonist and a 5-HT2A antagonist at the frontal cortex, was assessed in three animal paradigms sensitive to antidepressants in rats: olfactory bulbectomy (OB), differential-reinforcement-of-low rate 72-s (DRL 72-s) and learned helplessness (LH). In the OB rats, BIMT 17, given once daily for 14 consecutive days at an i.p. dose of 10 mg/kg, but not of 20 mg/kg, reduced the increase in ambulation of OB rats, 24 h after the last administration. In the DRL 72-s test, BIMT 17 had a different profile than imipramine. A single i.p. injection of 5, 10, 15 or 20 mg/kg BIMT 17, in contrast to the same doses of imipramine, did not affect response and reinforcement rate in DRL 72-s 1 h after the administration. On the other hand, BIMT 17 slightly shifted the peak of the interresponse time (IRT) distribution towards shorter IRT duration, while imipramine shifted the peak of the IRT distribution towards longer IRT duration. In the LH test, acute oral doses (36, 48 or 60 mg/kg) of BIMT 17, given 30 min before testing, reduced the number of escape failures in LH without altering the intertrial crossings. This effect was also induced by a repeated, but not single, administration with 8 or 16 mg/kg imipramine. The plasma levels following i.p. 10 or oral 48 mg/kg BIMT 17 were in the same range. These results indicate that BIMT 17 does not behave like imipramine in all the tests, and suggest that BIMT 17 acts through different mechanisms of action than imipramine. Only clinical trials will tell whether these mechanisms will be relevant, but if so, BIMT 17 might induce a faster onset of therapeutic activity.

Forced swim test-induced neurochemical endocrine, and immune changes in the rat

The forced swim test (FST) is a behavioral paradigm that is widely used as a screening test for antidepressant activity in rodents. The objectives of the present study were to characterize the corticosterone and immune responses and in addition to examine neurotransmitter levels, in five brain regions at intervals (15, 30, 60, 90, and 120 min) following the second exposure to the FST. There was a significant but transient reduction in noradrenaline and 5-HT concentrations, in the hypothalamus 15 min post-FST exposure. 5-HT turnover in the frontal cortex and amygdala was significantly increased between 20-120 min post-FST exposure. The FST elicited a robust corticosterone response that peaked significantly at 30 min and had almost returned to baseline 120 min after exposure. There was a significant reduction in total white blood cell count 120 min after the FST, which was accompanied by a significantly reduced percentage of lymphocytes 90 and 120 min post-FST exposure. In addition, there was a significant but transient suppression of both PHA and Con A-induced lymphocyte proliferation 15 min following FST exposure. This study demonstrates that there are neurochemical changes that are coincident with the endocrine and immune changes associated with FST exposure in rats. Furthermore, this model could be used to examine the effects of manipulation of this stress response by antidepressant drugs. Such an investigation could add to our understanding of the interactions between antidepressants, stress and the neuroendocrine and immune systems.

The olfactory bulbectomized rat as a model of depression: an update

The olfactory bulbectomized (OB) rat has been proposed as an animal model of depression. The following behavioural changes have been observed following bilateral olfactory bulbectomy: hyperactivity in an enclosed arena, such as the open-field; enhanced nocturnal hyperactivity in a 24-hr home cage activity monitor; deficits in memory, as shown by passive avoidance behaviour and in the Morris maze and the 8-arm radial maze; increased open arm entries in the elevated plus-maze; and changes in food motivated and conditioned taste aversion behaviour. Alterations in the noradrenergic, serotonergic, cholinergic, gamma-aminobutyric acid (GABA)ergic and glutamatergic neurotransmitter systems are also associated with olfactory bulbectomy. The variety of immune changes following olfactory bulbectomy includes reduced neutrophil phagocytosis, lymphocyte mitogenesis, lymphocyte number and negative acute phase proteins, increased leucocyte adhesiveness/aggregation, monocyte phagocytosis, neutrophil number and positive acute phase proteins. An enhanced nocturnal secretion of corticosterone is observed in OB rats, which is normally suppressed by dexamethasone. The most commonly employed behavioural indicator of antidepressant activity is attenuation of the OB-related hyperactivity in the open-field. However, many of the other behavioural, neurotransmitter and immune changes have been shown to be attenuated by chronic (but not acute) antidepressant treatment. Tricyclic antidepressants (amitriptyline, desipramine), atypical agents (mianserin), selective serotonin reuptake inhibitors (paroxetine, sertraline, fluvoxamine), reversible inhibitors of monoamine oxidase A (moclobemide), as well as putative antidepressants such as 5-hydroxytryptamine1A agonists (zalospirone, ipsapirone), noncompetitive N-methyl-D-aspartate antagonists (MK-801) and triazolobenzodiazepines (alprazolam, adinazolam), have demonstrated antidepressant-like activity in this model. As many of the changes exhibited by the OB rat are qualitatively similar to those observed in depressed patients, it may be concluded that the OB rat is a model of depression and not just a means whereby putative antidepressants may be tested.

Lisuride prevents learning and memory impairment and attenuates the increase in extracellular dopamine induced by transient global cerebral ischemia in rats

In this experiment, we tested the efficacy of neuroprotection with lisuride, a dopamine agonist, using the 4-vessel occlusion rat model. Functional improvement was evaluated with two behavior tests exploring learning and memorization capacity in the rat, the Morris water maze and the 14-unit T-maze, 18 days after ischemia. Extracellular dopamine levels during ischemia were determined in search of a possible neuroprotection mechanism. Dopamine and its metabolites, DOPAC and HVA, as well as the serotonin metabolite, 5-HIAA, were assayed with HPLC-EC, in striatal extracellular fluid obtained by in vivo microdialysis in the awake rat. Lisuride was administered at a total dose of 10 ng by continuous intrastriatal infusion or at the dose of 0.5 mg/kg by i.p. infusion, 160 minutes before onset of ischemia for the neurochemical study and at the dose of 0.5 mg/kg via i.p. infusion, 1 hour before occlusion of the carotid arteries, for the behavior tests. Behavioral testing showed significantly better recovery in both sets of behavioral tests, with more pronounced positive results with the 14-unit T-maze, in comparison with the saline-treated animals. Microdialysis confirmed a significant attenuation of the ischemia-induced dopamine surge, whatever the mode of administration, compared with saline-treated animals. These results show that lisuride offers significant neuroprotection from the effect of experimental transient global forebrain cerebral ischemia in the rat; the mechanism would imply, at least in part, reduced levels of extracellular dopamine.

Behavioural and neurochemical effects of dizocilpine in the olfactory bulbectomized rat model of depression

The activity of dizocilpine (MK-801; 0.1 and 0.3 mg/kg) administered once daily intraperitoneally (I.P.) was assessed in the olfactory bulbectomized rat model of depression. Olfactory bulbectomy (OB) is associated with a variety of behavioural abnormalities, such as hyperactivity in the "open field" test. Previous studies have shown that chronic administration of antidepressants can reverse this behavioural deficit. In the present study, chronic treatment with 0.1 and 0.3 mg/kg of dizocilpine (I.P.) antagonized the lesion-induced hyperactivity in the "open field" test. Acute treatment with dizocilpine was associated with an increase in locomotor activity in both sham-operated and OB rats, with a greater response in the sham-operated group. Following chronic treatment, this hyperactivity was found to be greater in the OB-treated animals compared with the sham-treated animals. Olfactory bulbectomy reduced serotonin (5-HT), noradrenaline (NA), and dopamine (DA) concentrations in the frontal cortex. Chronic dizocilpine administration did not alter the 5-HT or NA response. In contrast, chronic administration of dizocilpine to OB animals did attenuate the OB-related deficit in DA. In the OB-operated control animals, there was an increase in DOPAC levels. In conclusion, chronic dizocilpine administration displays antidepressant-like activity in the OB rat model of depression. However, unlike conventional antidepressants, dizocilpine does not correct the 5-HT and NA neurotransmitter deficits that occur in this model.

An appraisal of the pharmacological and toxicological effects of a single oral administration of 3,4-methylenedioxymethamphetamine (MDMA) in the rat

This study examined some acute pharmacological and toxicological effects of 3,4 methylenedioxymethamphetamine (MDMA, "Ecstasy") over a range of doses (20, 40, 80, 160 and 320 mg/kg orally) in adult female rats. Deaths were observed from the 40 mg/kg MDMA group onwards. Reductions in body weight change, food and water intake were found in the 80 mg/kg group, whilst food intake alone was reduced in the 20 and 40 mg/kg groups. Significant hyperthermic responses were found over the first 8 hr following MDMA administration which were dose-related. A significant hyperactivity of approximately 9 hr duration was observed in the 20 mg/kg and 40 mg/kg groups, whereas there was evidence of a serotonin syndrome in the higher dosage groups. Thus, acute oral administration of MDMA results in a variety of measurable responses. The cause of death in this study is probably a combination of serotonin syndrome and hyperthermia.

The effects of the 5-HT1A agonist flesinoxan, in three paradigms for assessing antidepressant potential in the rat

5-HT1A receptor agonists have been shown to be effective clinically in the treatment of depression and anxiety. Flesinoxan is an example which is highly selective for the 5-HT1A receptor subtype. The objective of this study was to appraise the antidepressant potential of flesinoxan (1 and 3 mg/kg s.c.) in three tests which are indicative of antidepressant activity. These are (1) the forced swim test, following sub-acute administration, (2) 'open field' activity in the olfactory bulbectomised (OB) rat, following chronic administration, and (3) 8-OH-DPAT-induced hypothemia following chronic treatment. Both doses of flesinoxan significantly reduced the immobility time in the sham and OB groups when compared to their respective controls. In the 'open field', there was a significant increase in the ambulation of the OB control group. The higher dose of flesinoxan significantly reduced this deficit. In addition both doses of flesinoxan significantly attenuated the 8-OH-DPAT-induced hypothermic response. These effects of flesinoxan are quantitatively similar to those seen following the chronic administration of antidepressants. These studies illustrate the potential antidepressant properties of flesinoxan, and hence further emphasise the role of the 5-HT1A receptor in the pathogenesis of depression.

Protective effects of vanoxeamine (GBR 12909) against ischaemia-induced hyperactivity and neurodegeneration in the gerbil model of cerebral ischaemia

In Mongolian gerbils, bilateral carotid occlusion (BCO) followed by reperfusion causes uniform destruction of the CA1 pyramidal neurons in the hippocampus, and this damage correlates with an increase in locomotor activity. Various drugs, such as NMDA antagonists, calcium channel blockers, and free radical scavengers, have provided neuroprotection against ischaemia-induced damage. More recently, the neuroprotective effects of dopamine have been investigated. A large release of dopamine has been shown to occur at the onset of ischaemia, and dopamine levels return to basal values following reperfusion. In the present study, we investigated the effects of vanoxeamine (GBR 12909) (5 or 10 mg/kg i.p., administered 1 h prior to occlusion) on behavioural and histological changes following global ischaemia in the Mongolian gerbil. Ischaemia was induced by bilateral carotid occlusion for 5 min. Both doses of GBR 12909 significantly potientiated the hyperactivity of the BCO animals measured in the home cage during the first 24 h following surgery and in the locomotor activity arena after 24 h and 48 h. Significant neuroprotection of cells in the CA1 region of the bippocampus was observed in drug-treated animals 96 h postsurgery. The neuroprotective effect of GBR 12909 may be ascribed to sensitisation of the dopamine D, autoreceptor, consequently reducing the release of dopamine that occurs following ischaemia. Alternatively, GBR 12909 may have a direct interaction with the Na+ ion channel-glutamate complex, resulting in reduced release of glutamate and thereby reducing NMDA receptor activation and neuronal damage.

Effect of chronic treatment with piracetam and tacrine on some changes caused by thymectomy in the rat brain

Thymectomized rats, 5 weeks after surgery, showed a significant impairment in learning and memory as shown by deficits in passive avoidance and in the Morris water maze test. The behaviour of the thymectomized rats in the "open field" apparatus was largely unchanged. Following treatment for 20 days with either piracetam (500 mg/kg) or tacrine (3.0 mg/kg), the deficit in passive avoidance learning was largely reversed. Chronic treatment with tacrine also reversed the deficit in the behaviour of the thymectomized rats in the Morris water maze. The effects of thymectomy on the biogenic amines and some of their metabolites in the amygdaloid cortex, hypothalamus, striatum and olfactory bulbs were also determined. Relative to the sham-operated controls, thymectomy resulted in a reduction in the noradrenaline concentration in the amygdala, hypothalamus, and olfactory bulbs. This effect was reversed by chronic piracetam and tacrine treatments. The concentration of dopamine was also reduced in the olfactory bulbs after thymectomy whereas in the striatum the concentration of 5-hydroxytryptamine (5-HT; serotonin) was increased. The concentration of gamma amino butyric acid (GABA) was determined in amygdaloid cortex and hippocampus only. The only significant change occurred following chronic treatment of thymectomized rats with tacrine, when a significant elevation of GABA was found. Neither piracetam nor tacrine produced any change in the amines of their metabolites in the sham-operated controls. Tacrine, however, elevated the dopamine and reduced the 5-HT content of the hypothalamus and increased the 3,4-dihydroxylphenylacetic acid concentration of the striatum of thymectomized rats. Examination of the differential white blood cell count of the thymectomized rats showed that the percentage of lymphocytes was decreased, and the percentage of neutrophils increased, relative to the sham-operated controls. Chronic lacrine, but not piracetam, treatment reversed the lesion-induced changes.

Noradrenaline in basic models of depression

This review reports anatomical studies evaluating central and peripheral alpha 2- and beta-adrenoceptors. The results suggest abnormalities exist in the noradrenergic system in depressed patients. Most animal models involve the use of stress to simulate depression in man. All models that have been developed lead to differential changes in noradrenergic function. We have assessed the effects of reboxetine, a novel, selective noradrenaline-reuptake inhibitor (NARI) in olfactory bulbectomised rats, a procedure that induces significant changes in amygdala function. Reboxetine is an effective antidepressant in the forced swim test and open field test in bulbectomised rats. Unlike the tricyclic antidepressants (TCAs) and selective serotonin reuptake inhibitors (SSRIs), reboxetine is ineffective in the 8-OH-DPAT hypothermia test, indicating that reboxetine is selective for the noradrenergic system. Owing to the abnormalities that occur in depression, it would seem sensible to target the noradrenergic system for treatment of this condition.

Altered expression of amyloid protein precursor mRNA in the rat hippocampus following trimethyltin intoxication: an in situ hybridization study

Previous studies have reported increased levels of amyloid protein precursor (APP) and APP mRNA in the hippocampus and basal forebrain of patients with Alzheimer's disease. Similar changes have been found in the brains of aged rodents and transgenic mice. It now appears that alterations in the expression of individual isoforms of APP mRNA may have a role to play in amyloid-pathogenesis. Here we examined the effect of acute administration of the limbic system neurotoxin trimethyltin (TMT) (8 mg/kg i.p.) on APP-751 and APP-695 mRNA expression in the rat hippocampus (CA1, CA2, CA3 and CA4) using in situ hybridization techniques. We found that following TMT treatment the expression of APP-751 mRNA was increased in CA1 pyramidal cells while that of APP-695 mRNA remained unchanged. TMT also increased the numbers of APP-751 and APP-695 mRNA positively hybridized cells in the CA1 pyramidal layer. These findings suggest that an alteration in APP mRNA expression is involved in the response of the rodent brain to TMT intoxication.

Behavioural effects of selective serotonin reuptake inhibitors following direct micro injection into the left red nucleus of the rat

The behavioural effects of selective serotonin reuptake inhibitors (paroxetine, sertraline, citalopram, fluvoxamine, fluoxetine) and reference compounds (N,N'-di(o-tolyl)guanidine, haloperidol, 3-(3-hydroxyphenyl)-N-(l-propyl)piperidine and chlorpromazine) were studied for their ability to produce dystonia and torticollis following direct micro injection into the left red nucleus of the rat, an area of the brain containing a high density of sigma2 receptors but relatively devoid of biogenic amine receptors. Each animal was monitored for abnormalities in posture and movement for a period of 30 min and then sacrificed 40 min following drug administation. Only fluvoxamine (100 nmol) and fluoxetine (100 nmol) elicited acute dystonic behaviour (1-5 min). The onset of dystonia was accompanied by facial spasticity, vacuous chewing movements and grooming behaviour which reflected the extent of dystonia. The dystonic behaviour following the direct intrarubal injection of fluvoxamine and fluoxetine suggest the possible activation of sigma2 receptors while citalopram, sertraline and paroxetine were without effect. The results of this study support the role of sigma2 receptors in the regulation and control of movement and coordination and provides preliminary evidence to suggest the in vivo activity of sigma receptors by fluoxetine and fluvoxamine.

Effect of chronic pretreatment with the sigma ligand JO 1784 on CRF-induced changes in behaviour, neurotransmitter and immunological function in the rat

The effects of the chronic administration of the sigma ligand JO 1784 (igmesine) CRF-induced changes in some behavioural, immune, endocrine and neurotransmitter parameters were studied. In the elevated plus maze, CRF (1.0 microgram i.c.v. daily x 5 days) induced a reduction in the number of entries and time spent on the open arms was significantly attenuated by the sigma ligand JO 1784 (3 mg/kg x 21 days) treatment. In the open field apparatus, the CRF-induced increase in the locomotor activity was also reduced by JO 1784 administration. JO 1784 treatment did not alter the concentration of the biogenic amine transmitters in the hypothalamus, nor reverse the increase in the turnover of serotonin and dopamine caused by CRF. JO 1784 treatment also failed to reverse a CRF-induced increase in the serum corticosterone, but it did reverse the reduction in phytohaemagglutinin and concanavalin A-induced lymphocyte proliferation caused by CRF but not the changes in the lymphocyte and neutrophil numbers caused by the peptide. These results demonstrate that JO 1784 has some antistress properties in CRF-treated rats.

The characterization of oxotremorine-induced hypothermic response in the rat

Oxotremorine is a muscarinic receptor agonist that induces a variety of physiological and behavioural effects including hypothermia in mice. These effects are antagonized dose-dependently by classical anticholinergic compounds such as atropine. Although the oxotremorine-induced hypothermic response has been demonstrated in mice, few studies of the effects of this muscarinic agonist have been made in the rat. The following studies were made in male Sprague Dawley rats: 1. an investigation of the dose-response relationship between oxotremorine and hypothermia; 2. an examination of the effect of housing on the oxotremorine-induced hypothermic response, and 3, an investigation of the acute administration of various doses of atropine sulphate on the hypothermia caused by oxotremorine. The results indicate that the dose-response relationship between oxotremorine and the antagonism of hypothermia is similar in rat as it is in mice. The results also showed that this effect did not occur in group-housed animals.

Pharmacokinetics of milnacipran in comparison with other antidepressants

Despite the large number of antidepressants currently available, it is still necessary to develop new drugs that combine the efficacy of the older antidepressant with improved safety, tolerability and therapeutic profile that will allow them to be used in depressed patients who are elderly or with cardiac, renal or hepatic disease. This article reviews the pharmacokinetic characteristics of the tricyclic antidepressants, the selective serotonin reuptake inhibitors (SSRIs) and more recently introduced antidepressants such as venlafaxine and nefazodone. Milnacipran (Ixel), a novel drug, combines antidepressant efficacy with some unique pharmacokinetic features. A summary of its pharmacokinetic profile shows that milnacipran has a high bioavailability, low plasma protein binding and that it is largely eliminated in the urine as parent drug or as a glucuronide. These features suggest that the likelihood of interactions with other drugs given concurrently is lower than would occur with most second generation antidepressants and the tricyclic antidepressants. Furthermore, studies in patients with liver dysfunction, and in the elderly, suggest that dose adjustment is not necessary when milnacipran is administered to these patients. The decrease in milnacipran elimination is correlated to the degree of renal impairment, allowing adjustment of schedules. In comparison to earlier antidepressants, milnacipran combines efficacy and a relatively low side-effect profile with the added advantage of fewer interactions with drugs that may be given concurrently.

Behavioural and immunological effects of the antihistamine terfenadine in olfactory bulbectomized rats

The effects of chronic treatment with the non-sedative histamine H1 receptor antagonist terfenadine (5 mg/kg, i.p.) for 16 days on some behavioural and immunological parameters were studied in the olfactory bulbectomized (OB) rat model of depression. In the open field apparatus, OB rats showed a significant increase in ambulation and rearing scores. Following terfenadine treatment, this hyperactivity was significantly attenuated. In untreated OB rats, neutrophils phagocytosis and lymphocyte proliferation were significantly suppressed. Terfenadine administration markedly reversed the suppression of these immunological parameters in the treated OB animals, but did not reverse the abnormalities in the differential white blood cell count caused by bulbectomy. These results suggest that the histamine H1 receptor antagonist terfenadine may have antidepressant properties and that terfenadine is effective in reversing some of behavioural and immune changes in the olfactory bulbectomized rat model of depression.

Stress and the immune system in the etiology of anxiety and depression

There is clinical and experimental evidence that various aspects of the immune and endocrine systems are severely compromised in chronic stress and depression. For example, it has been shown that a reduced lymphocyte response occurs to mitogens in depressed patients, effects that are not reversed by chronic antidepressant treatment. By contrast, monocyte phagocytosis is increased, while neutrophil phagocytosis is decreased in depressed patients. Such changes are normalized by effective antidepressant treatment. The results of such studies and others that demonstrate alterations in noncellular immune processed in depression indicate that the changes in immune function correlate with the severity and duration of the external and/or internal stressful stimuli. There is evidence that some of the immune changes are a reflection of increased plasma glucocorticoids that characterize both stress and depression. However, it is also apparent that the cytokines, prostaglandins, and corticotrophic releasing factor (CRF) also play an important role in initiating the behavioral and pathophysiological changes that are characteristic of both depression and chronic stress. This review attempts to critically assess the interplay between CRF, the immune and neurotransmitter systems, and behavior in chronic stress and depression.

The sigma ligand JO 1784 prevents trimethyltin-induced behavioural and sigma-receptor dysfunction in the rat

Recently much research interest has focused on the possible therapeutic uses of sigma-receptor ligands in psychiatric and neurodegenerative disorders. In the present study, the potential neuroprotective effects of chronic (52 days) administration of (+) cinnamyl-l-phenyl-l-N-methyl-N-cyclo propylene (JO 1784) (1 and 3 mg/kg subcutaneously), a potent and selective sigma receptor ligand, were assessed in the trimethyltin (8 mg/kg intraperitoneally) model of memory dysfunction. JO 1784 (3 mg/kg subcutaneously) prevented the trimethyltin-induced deficits in locomotor activity, passive avoidance and radial maze performance, while the lower dose of JO 1784 had little or no effect. Trimethyltin was also shown to produce a marked reduction in the binding of [3H] (+)-pentazocine to sigma-receptor sites in limbic brain structures, as detected by quantitative autoradiography, which was particularly evident in the hippocampal pyramidal cells. JO 1784 (3 mg/kg subcutaneously) successfully attenuated this loss of [3H] (+)-pentazocine binding sites in the hippocampus (CA1, CA3 and CA4 regions) and in the substantia innominata. This neuroprotective effect of JO 1784 in the trimethyltin model would seem to be related to the modulatory effects of this sigma ligand on trimethyltin-induced glutamate neurotoxicity.

The effects of MK-801, ifenprodil, JO 1784, JO 1994 and JO 1997 on PK 11195 receptor binding, nitric oxide synthase (NO synthase) activity and infarct volume in a mouse model of focal cerebral ischaemia

Middle cerebral artery occlusion (MCAO) is a widely used surgical procedure for inducing focal cortical ischaemia in mice. In the present study, all experiments were performed on 4-week-old, male Swiss mice (OF-1 Iffa Credo, France), 20-25 g at the time of surgery. Sham-operated mice were subjected to simple exposure of the middle cerebral artery. Mice were injected with either MK-801, ifenprodil, JO 1784, JO 1994 or JO 1997 at the following time points after surgery; 5, 15, 45 min and 3, 6, 24, 30, 48 and 54 h. Mice were sacrificed 72 h after surgery and both ipsilateral and contralateral cortices were dissected in their entirety, weighed, and assayed for [3H]PK 11195 binding while the brain-stem and cerebellum were assayed for nitric oxide synthase (NO synthase) activity. In a separate experiment the area of ischaemic damage was determined planimetrically by means of an image analysis system. Coagulation of the middle cerebral artery induced a marked enhancement of the ipsilateral cortical omega 3 peripheral-type benzodiazepine binding site (PTBB'S) densities, an increase in NO synthase activity in the brain-stem and cerebellum, and an increase in the cortical infarct area. MK-801, ifenprodil, JO 1784, JO 1994 and JO 1997 demonstrated comparable neuroprotective effects on all three indices of cortical damage. A down-regulation of cortical omega 3 peripheral-type benzodiazepine binding site (PTBB'S) densities and a decrease in NOS activity occurred following pharmacological intervention. In contrast to JO 1784, JO 1994 and JO 1997 have a bimodal effect on omega 3 PTBB'S densities.

The effects of central administration of neuropeptide Y on behavior, neurotransmitter, and immune functions in the olfactory bulbectomized rat model of depression

The effects of subchronicly administered neuropeptide Y (NPY) intracerebroventricularly on behavioral, neurochemical, and immunological parameters were examined in sham operated and olfactory bulbectomized (OB) rats. In the untreated OB rats, an increase in ambulation, rearing, grooming, and defecation scores was found in the novel stressful environment of an "open field." Following 7 days of NPY administration, these behaviors were largely attenuated. In the elevated plus-maze apparatus, OB rats showed an increase in the number of entries into the open arms and time spent on the open arms compared with sham operated animals; NPY had no significant effect on the behavior of either sham operated or OB animals in this test. A decrease in the NA concentration was found in the amygdloid cortex of OB rats. NPY infusion significantly increased the NA concentration in amygdala, reduced 5-HIAA but increased 5-HT concentrations in the hypothalamus, and increased the dopamine level in the hippocampus. NPY administration also reversed the suppression of lymphocyte proliferation in the OB rat. However, the changes in the differential white blood cell count and the elevated phytohemagglutinin-induced chemiluminescence of mononuclear cells in the OB were not altered by NPY. These results suggest that NPY may have a modulatory effect on some behavioral, neurotransmitter, and immune aspects of the OB rat model of depression.

High 222Rn levels, enhanced surface deposition, increased diffusion coefficient, humidity, and air change effects

Measurements have been made of surface deposition rates for 218Po radon decay products in a small (0.283m3) aluminum test chamber for 222Rn levels from 1 to 1,600 kBq m-3. an increase in macroscopic surface deposition rate has been found to be induced by the high 222Rn concentrations. A distinct 222Rn level threshold has been found below which plateout is constant at the normal rate for ambient residential conditions. Above the threshold, an increase in plateout is observed and the transition quickly reaches a constant, higher plateout. With all environmental conditions remaining constant and varying humidity, the threshold 222Rn level decreases with increasing relative humidity. The rate of rise to the new plateau is found to increase with increasing humidity. For the constant air change rate of ACH = 0.2 h-1, the fraction of airborne 218Po lost by the enhanced plateout was consistently 0.4 +or- 0.25 for seven values of humidity from 8 to 54% RH. For a fixed RH = 40 +or- 2%, it was found that the threshold increases from 5 to 58 kBq m-3 for a change in ACH from 0 1.06 h-1. In converting the deposition data to values of diffusion coefficient D, using Crump and Seinfeld's theory, a very high D of 0.18 cm2s-1 is assumed for ambient air conditions. Results indicate an ambient D = 0.027 cm2s-1. The results may impact on research utilizing high levels in test chambers and diffusion coefficients and attached and unattached fractions, and also for cancer studies using animals with 222Rn levels as much as 10(4) times greater than ambient residential levels.

Serotonin receptors and their function in sleep, anxiety disorders and depression

Thirty-three years ago, Gaddum and Picarelli classified the serotonin receptors in the guinea pig ileum into D and M types based on the activity of dibenzyline (D) and morphine (M) to block contractions of intestinal smooth muscle caused by serotonin. The subsequent location of specific ligand binding sites for serotonin in the brain has led to the identification of 14 serotonin receptor sub-types in rat brain. The cloning of these receptor sub-types has been of importance in enabling them to be classified as specific-protein molecules encoded by specific genes. The problem now arises with regard to the linking of the changes in the cellular activity of the various receptor sub-types with the plethora of behavioural changes that arise as a consequence of the actions of serotonin in the brain. The present review summarizes the evidence implicating the role of specific serotonin receptor sub-types in sleep, anxiety states, schizophrenia and depression. A summary of the relationship between these receptor sub-types and their possible involvement in the aetiology of schizophrenia, depression, anxiety and sleep disorders.

The novel sigma ligand JO 1994 protects against ischaemia-induced behavioural changes, cell death and receptor dysfunction in the gerbil

To assess the effects of the novel sigma ligand JO 1994 on behavioural, histological and autoradiographical changes following global ischaemia, the Mongolian gerbil was used. Three experiments were carried out and in each case ischaemia was induced by bilateral carotid occlusion (BCO) for 5 min. In the first experiment we examined the effects of JO 1994 administered at doses of 0.25, 0.5 and 1 mg/kg i.p. 1 h before 5 min BCO on histological parameters 96 h after surgery. In the second experiment the effects of JO 1994 administered at doses of 2.5, 5, 10 and 20 mg/kg i.p. 1 h before 5 min BCO on locomotor activity 24, 48 and 72 h after surgery and on histological parameters 96 h after surgery was examined. In the third experiment the effects of JO 1994 (2.5 and 5 mg/kg i.p.), BMY 14802 (1 and 10 mg/kg i.p.) and MK-801 (2.5 mg/kg i.p.) administered 30 min, 6, 24, 48, 72, 96 and 120 h post-surgery on the densities of M1 and M2 muscarinic receptors in 35 brain regions, 7 days after surgery was examined. Results indicated that 5 min bilateral carotid occluded animals were hyperactive 24, 48 and 72 h after surgery. JO 1994 attenuated this hyperactivity. Extensive neuronal death was observed in the CA1 layer of the hippocampus in 5 min BCO animals 96 h after surgery. The low doses of JO 1994 (0.25, 0.5 and 1 mg/kg) had no effect on the ischaemia-induced cell death. However JO 1994 (2.5, 5, 10 and 20 mg/kg i.p.) protected against the neuronal death of cells in the CA1 layer (P < 0.01-0.03). There was a large loss of M1 and M2 receptors in the CA1 regions of the hippocampus. MK-801, BMY 14802 and JO 1994 provided significant (P < 0.01) protection against this ischaemia-induced receptor loss.

Effects of chronic desipramine on waiting behaviour for a food reward in olfactory bulbectomized rats

The effects of olfactory bulbectomy (OB) on the 'waiting behaviour' of rats for a food reward in a T-maze, as well as the effect of chronic treatment with desipramine (7.5 mg/kg, i.p. x 14 days) prior to and throughout testing was assessed. In the T-maze, the time spent in locating a reward was longer in OB rats during the first phase of the food reward test. However, all groups chose the larger reward in at least 80% of trials by day 5 of test. Upon imposition of a delay in acquisition of the larger reward (phase 2), sham-operated rats chose the larger reward in correspondingly fewer trials until, by day 5, only 13% (control sham group) and 29% (desipramine-treated sham group) of trials were for the larger but delayed reward. By contrast, both OB rat groups continued to choose the larger but delayed reward throughout phase 2 in the majority of trials. The typical behavioural hyperactivity of OB rats in the 'open field' apparatus was attenuated by chronic administration of DMI. The results suggest that the OB rat has a deficit in food-motivated behaviour and appears to have reduced adaptation of this learned response when the conditions of the test are altered. Chronic desipramine treatment did not attenuate this effect.

New approaches to the treatment of depression

This review considers the various modes of action and possible advantages of the different types of second generation antidepressants. The biochemical changes that may be causally related to depression and the mechanisms whereby these changes may be attenuated by antidepressant treatment are briefly considered. Whereas the monoamine theory of depression and the receptor adaptation hypothesis of antidepressant action have been influential in helping to unify the mechanisms of action of antidepressants with the possible pathologic basis of depression, the introduction of novel antidepressants and the development of treatment strategies suggestive of a rapid onset of antidepressant response may initiate a revision of these concepts. The review ends with a consideration of the nonaminergic changes that may be of fundamental importance not only in the pathologic basis of depression but also to the means whereby antidepressants bring about their clinical effects.

The dopamine agonists lisuride and piribedil protect against behavioural and histological changes following 4-vessel occlusion in the rat

The 4-vessel occlusion model of ischaemia in the rat was used to assess the effects of two dopaminergic agonists, lisuride and piribedil, on some behavioural and histological changes. Animals were either sham-operated, subjected to 20 min 4-vessel occlusion, or administered lisuride (0.5 mg/kg i.p.) or piribedil (10 mg/kg i.p.) 1 h before 20 min 4-vessel occlusion. Both drugs attenuated deficits in neurological testing, Morris water maze and 14-unit T-maze (p < 0.05). Extensive neuronal death was observed in the CA1, CA3 and CA4 regions of the hippocampus of 4-vessel-occluded animals. Pretreatment with both lisuride and piribedil provided protection against cell death in the hippocampal regions. These findings suggest dopamine may play a role in cerebral ischaemia and dopaminergic agonists may be beneficial in preventing ischaemia-induced neurodegeneration.

Some behavioural and neurochemical effects of ipsapirone in two rodent models of depression

The effect of ipsapirone (3 and 10 mg/kg once daily, i.p. for 21 days), was assessed in two animal models of depression, namely the forced swim test and on the hyperactive response of the olfactory bulbectomized (OB) rat in the 'open field' test. The response to 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT; 0.15 mg/ kg, s.c.)-induced hypothermia in rats was examined on day 16 of ipsapirone treatment. In the forced swim test, subacute treatment with ipsapirone (3 and 10 mg/kg) significantly reduced the immobility time in both sham and OB groups. In the OB rat model, chronic treatment with 10 mg/kg ipsapirone antagonized the lesion- induced hyperactivity in the 'open field' apparatus. The hypothermic response to 8-OH-DPAT was attenuated after chronic treatment with 3 mg/kg ipsapirone in both sham and OB groups, while 10 mg/kg ipsapirone attenuated this temperature reduction only in the sham group (p<0.05). Ipsapirone (10 mg/kg) significantly increased home cage locomotor activity counts on days 15 and 21 of drug treatment in the OB dose group, but only on day 21 in the sham dose group (p < 0.05). Ipsapirone (10 mg/kg) caused a significant reduction in rectal temperature 30 min following drug administration in the sham group on day 1 (p < 0.05) but in the OB group on days 1, 7, 15 and 22 (p < 0.05) of drug treatment. No significant differences in basal serum corticosterone concentrations were found either associated with olfactory bulbectomy or drug treatment. Chronic ipsapirone treatment did not attenuate the reductions in noradrenaline and serotonin in the frontal cortex of OB animals. It can be concluded that ipsapirone shows antidepressant-like activity in the forced swim test and the OB rat model of depression.

Behavioral, neurochemical, and immunological responses to CRF administration. Is CRF a mediator of stress?

The effect of subacute intracerebroventricular (icv 0.1, 0.5, and 1.0 microgram) administration of corticotropin-releasing factor (CRF) for 5 days on behavior, neurotransmitter concentrations, and immune functions was studied in rats. The results showed that CRF administration produced a dose-dependent increase in locomotor activity in the "open field" test compared with controls; rearing scores were also significantly increased. In the elevated plus maze apparatus, rats given 1.0 microgram CRF spent considerably less time on the open arms when compared with controls. Following 0.5 and 1.0 microgram of CRF infusion, the concentrations of noradrenaline (NA), dopamine (DA) and 5-hydroxy indole acetic acid (5-HIAA) were significantly increased in the hypothalamus. There was no significant change in the concentrations of neurotransmitters in the other brain regions. CRF administration also produced a dose-dependent increase in the levels of corticosterone in the serum. The immunological results clearly showed that subacute icv CRF administration caused a reduction of lymphocyte proliferation, a decrease in the percentage of lymphocytes, and an increase in neutrophil percentage in the differential white blood cell (WBC) count, a decrease in neutrophil phagocytosis, and elevated leucocyte adhesiveness/aggregation (LAA) compared with control animals. These results suggest that icv subacute administration of CRF has anxiogenic effects, increases biogenic amine concentrations in the hypothalamus, and changes in some aspects of immune functions that may reflect the stress-inducing properties of the peptide. These effects are time and dose dependent.

Influence of an n-6 polyunsaturated fatty acid-enriched diet on the development of tolerance during chronic ethanol administration in rats

This study investigates the effects of n-6 polyunsaturated fatty acids (PUFAs), in the form of dietary Evening Primrose Oil (EPO) and safflower oil, on the development of tolerance to ethanol. The degree of fluorescence polarization of the fluoroprobes DPH, PROP-DPH, and TMA-DPH in isolated cortical synaptosomal membranes was measured. In addition, the development of tolerance, as shown by changes in synaptosomal membrane fluidity after an acute in vitro ethanol challenge, was also determined after 20 weeks of ethanol administration, either alone or together with a PUFA-enriched diet. Although the administration of EPO-enriched diet did not significantly render the inner core of the cortical synaptosomal membrane tolerant to the acute ethanol challenge, concomitant administration of ethanol and EPO was found to increase further the rigidity and tolerance to the acute ethanol challenge in the inner core. Chronic administration of safflower oil, which lacks gamma-linolenic acid (18:3, n-6) but like EPO contains linoleic acid, either alone or together with chronic ethanol had no effect on synaptosomal membrane fluidity after an acute ethanol challenge. The results suggest that gamma-linolenic acid or its metabolites may have an important role to play in the development of tolerance to chronic ethanol.

Some behavioural and neurochemical aspects of subacute (+/-)3,4-methylenedioxymethamphetamine administration in rats

(+/-)3,4-methylenedioxymethamphetamine (MDMA; "Ecstasy"), an increasingly popular recreational drug, is known to damage brain serotonin (5-hydroxytryptamine [5-HT]) neurons, whilst also having a less pronounced effect on the dopaminergic system. Treatment with MDMA results in an increased locomotor activity, elevated basal serum corticosterone concentrations, decreased exploratory activity, and changes in body temperature. The aim of this study was to examine the dose related effects of subacute administration of MDMA (5, 10, and 20 mg/kg IP twice daily for 4 days) on home cage locomotor activity, "open field" and "step-down passive avoidance" behaviours, changes due to an 8-hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT) challenge, and on plasma corticosterone and brain neurotransmitter concentrations. Total locomotor activity counts were significantly increased by both 10 and 20 mg/kg MDMA for the 4 days of drug administration. There were no significant differences seen in the "open field" or "step down passive avoidance" behaviour, in the 8-OH-DPAT induced hypothermia, or in basal serum corticosterone concentrations. MDMA caused a significant depletion of both 5-HT and 5-hydroxyindoleacetic acid (5-HIAA) in the frontal cortex and amygdala and a significant elevation of dopamine and noradrenaline in the hippocampus. Apart from the increase in locomotor activity following subacute administration, the observed behaviour of the MDMA treated rats would not appear to reflect the substantial changes in brain biogenic amine neurotransmitters.

NG-nitro-L-arginine methyl ester protects against lipid peroxidation in the gerbil following cerebral ischaemia

The aim of this study was to assess the role of nitric oxide (NO) in lipid peroxidation following 5 min of bilateral carotid occlusion in the Mongolian gerbil. The study consisted of 4 experimental groups (n = 10). Animals were either sham operated, subjected to bilateral carotid occlusion or administered the NO synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME) (10 mg/kg i.p.) 30 min, 6, 24 and 48 h following sham operation or 5 min bilateral carotid occlusion. Animals were killed 96 h post surgery and changes in the concentrations of malonaldehyde and 4 hydroxyalkenals (the main decomposition products of peroxides derived from polyunsaturated fatty acids and related esters) were measured in the hippocampus and cortex using the LPO-586 colorimetric method. The results showed a significant increase in the concentrations of both decomposition products following 5 min of bilateral carotid occlusion. L-NAME administered to sham operated controls had no effect, but in those animals subjected to 5 min of bilateral carotid occlusion L-NAME significantly decreased the levels of both decomposition products. These results suggest that inhibition of NO synthase activity decreases lipid peroxidation in the gerbil model of cerebral ischaemia.

SSRI differentiation: Pharmacology and pharmacokinetics

Although the acute pharmacology properties of antidepressants is predominantly due to their presynaptic action, their therapeutic activity is believed to derive from adaptive post-synaptic changes in monoaminergic neurones. The selective serotonin reuptake inhibitors (SSRIs) exhibit differences in potency at inhibiting serotonin reuptake, although the differences do not correlate with clinical posology. There are also differences in their effects on neurotransmitter receptors; paroxetine has a slight affinity for muscarinic cholinergic receptors whilst citalopram has a slight affinity for histamine-H1 receptors. These properties may be related to clinical adverse effects. The pharmacokinetic profiles of the SSRIs show many differences. Whilst fluvoxamine, paroxetine and citalopram are metabolized to inactive products, fluoxetine is metabolized to norfluoxetine which is pharmacologically active and, like its parent compound, has a long half-life. Fluvoxamine is less protein-bound than the other SSRIs and sertraline is only well absorbed when taken with food. Differences are also apparent in the suitability of individual SSRIs in special patient groups. There has been considerable speculation over the inhibition of cytochrome P450 isoenzymes which are responsible for the metabolism of SSRIs and other drugs. In clinical practice, the differences between the SSRIs in this respect are probably of limited importance. However, it is worthwhile that clinicians be made aware of possible interactions between drugs that act as inhibitors or substrates of the hepatic cytochrome P450 system.

The sigma receptor ligand JO 1784 (igmesine hydrochloride) is neuroprotective in the gerbil model of global cerebral ischaemia

To assess the effects of the novel sigma receptor ligand JO 1784 ((+)-N-cyclopropyl-methyl-N-methyl-1,4-diphenyl-1-yl-but-3-en-1-ylami ne, hydrochloride or igmesine hydrochloride) on behavioural and histological changes following cerebral ischaemia, the gerbil model of cerebral ischaemia was used. Two experiments were carried out. In the first animals were either sham operated, subjected to 5 min of bilateral carotid occlusion or administered JO 1784 (25, 50, 75 or 100 mg/kg p.o.) 1, 24 and 48 h after 5 min bilateral carotid occlusion and histological evaluation carried out 96 h after surgery. In the second experiment the effects of JO 1784 administered at a dose of 100 mg/kg i.p. 30 min, 6, 24 and 48 h post-surgery on home cage activity and nitric oxide (NO) synthase activity in the cortex, hippocampus, cerebellum and brain stem 4 days after surgery was examined. Extensive neuronal death was observed in the CA1 region of 5 min occluded animals. JO 1784 (50, 75 and 100 mg/kg) provided significant protection against this ischaemia-induced cell death (P < 0.03-0.005). In the second experiment a large increase in home cage activity was observed for 5 min occluded animals for 12 h after surgery (P = 0.0018-0.02). A large increase in NO synthase activity was observed in all brain regions for 5 min occluded animals. Post-administration of JO 1784 attenuated the ischaemia-induced hyperactivity and increased NO synthase activities.(ABSTRACT TRUNCATED AT 250 WORDS)

Interleukin-2-induced changes in behavioural, neurotransmitter, and immunological parameters in the olfactory bulbectomized rat

The macrophage theory of depression proposes that abnormal secretions of the macrophage cytokines, an increase in interleukin (IL) 1, and a decrease in IL-2 may cause depression. The olfactory bulbectomized (OB) rat has been developed as an animal model of depression. In the present study, the effects of intracerebroventricular administration of IL-2 (10 U) for 7 days on behaviour, neurotransmitter concentrations, corticosterone levels, and some immune functions were investigated. In the novel environment of the 'open-field' apparatus, the OB rat showed increases in ambulation, rearing, grooming, and defaecation scores as compared with sham-operated animals. Following IL-2 administration, grooming and defaecation were significantly attenuated, while the ambulation and rearing scores were unaffected. In the elevated plus-maze, the increase in the time spent on the open arms of the maze by the OB animal was normalized by IL-2 administration. In the brain of untreated OB rats, the concentrations of noradrenaline were reduced; IL-2 treatment significantly increased the concentrations of noradrenaline and serotonin. After administration of IL-2 for 7 days, the impairments in the immune functions were also largely reversed in OB rats. Thus IL-2 significantly normalized the hyperactivity of mononuclear cells, the suppression of lymphocyte proliferation, and the reduction in the monocyte percentage in the white blood cell count in the OB rat. The concentrations of corticosterone in the serum of the OB rat were significantly reduced, but returned to control values following IL-2 treatment. The results suggest that IL-2 may have modulatory functions on behavioural, neurochemical, hormonal, and immunological aspects of the OB rat model of depression.

The effect of 2-amino-3-phosphonopropionic acid (AP-3) in the gerbil model of cerebral ischaemia

The effect of 2-amino-3-phosphonopropionate (AP-3), a metabotropic glutamate receptor antagonist on behavioral and histological changes following global ischaemia was investigated on the Mongolian gerbil. Ischaemia was induced by bilateral carotid occlusion for 5 min. AP-3 was administered i.p. (25 or 250 mg/kg) 30 min before and 24 h after surgery. Significant neuroprotection was observed 96 h after surgery to cells in the CA1 region of the hippocampus in drug treated animals. AP-3 (250 mg/kg) significantly attenuated the increase in locomotor activity measured 72 h after surgery. These results suggest that metabotropic glutamate receptors play a role in the neurodegeneration seen following ischaemia.