[NFLUENCE OF SPONTANEOUS PARTIAL SENSORY DEPRIVATION ON MALE C57BL/6N MICE BEHAVIOR].

Vibrissae loss associated with the peculiarities of the intragroup social interaction may be an important factor affecting the animals' performance in various behavioral tests. To evaluate the influence of spontaneous partial sensory deprivation as a consequence of the barbering activity of a cage mate, the battery of tests was conducted in male C57Bl/6N mice. The results indicate that the behavior of mice without vibrissae significantly differs from control animals in the tube, open field, social interaction and forced swim tests. Thus, the present findings suggest that vibrissae conditions have to be assessed before the inclusion of animals into experimental groups and/or further considered in data analysis.

[Morphine-induced Straub tail reaction as a model of spasticity in mice: effects of serotonergic compounds]. / Vyzvannaia morfinom reaktsiia Shtrauba kak model' spastichnosti u myshei: éffekty serotoninergicheskikh soedinenii.

AIM: To adopt and validate the Straub tail reaction (SR) for comparative assessment of spastic effects of serotonergic compounds. MATERIAL AND METHODS: To measure the muscle relaxant activity, the morphine-induced Straub-tail assay was used. SR was graded according to modified intensity-score basis in a scale decribed by Kameyama et al. (1978). Subcutaneous injections of different doses of morphine (10-60 mg/kg) induced a dose-dependent SR with maximum response obtained 15-30 min after the morphine administration. RESULTS AND CONCLUSION: The centrally acting muscle relaxant baclofen (3-10 mg/kg) reduced SR induced by morphine (40 mg/kg) at all used doses; tizanidine decreased the intensity of SR at highest doses tested (0.6 and 1 mg/kg). Dantrolene (20-100 mg/kg), a peripherally acting muscle relaxant, did not affect SR. Effects of serotonergic agents depended on the specific mechanism of action. SR appears to be available for rapid evaluation of the effect of antispasticity drugs.

Antidepressant-like effects of mGluR1 and mGluR5 antagonists in the rat forced swim and the mouse tail suspension tests.

Drugs that act to reduce glutamatergic neurotransmission such as NMDA receptor antagonists exert antidepressant-like effects in a variety of experimental paradigms, but their therapeutic application is limited by undesired side effects. In contrast, agents that reduce glutamatergic tone by blocking type I metabotropic glutamate receptors have been suggested to have more a favorable side-effect profile. The present study aimed to compare the effects of mGluR1 antagonist (EMQMCM; JNJ16567083, 3-ethyl-2-methyl-quinolin-6-yl)-(4-methoxy-cyclohexyl)-methanone methanesulfonate, 0.156-10 mg/kg) and mGluR5 antagonist (MTEP, [(2-methyl-1,3-thiazol-4-yl)ethynyl]pyridine, 1.25-10 mg/kg) in two behavioral screening assays commonly used to assess antidepressant-like activity. In the modified forced swim test in rats, imipramine (used as a positive control) decreased immobility (MED 40 mg/kg) and increased the duration of escape-oriented (climbing and diving; MED 20 mg/kg) behaviors. Both EMQMCM and MTEP decreased the floating duration (MED 1.25 and 2.5 mg/kg) and increased the duration of mobile behaviors (paddling and swimming; MED 2.5 and 5 mg/kg). EMQMCM but not MTEP increased the duration of escape behaviors (climbing and diving; MED 1.25 mg/kg). In the mouse tail suspension test, EMQMCM (5 but not 2.5, 10 and 25 mg/kg), 2-methyl-6-(phenylethynyl)-pyridine (MPEP, 10 but not 1 mg/kg) and MTEP (MED 25 mg/kg) decreased immobility scores. For EMQMCM, the dose-effect relationship was biphasic. With the exception of EMQMCM (10 mg/kg), locomotor activity in mice was not affected by treatments. The present study therefore suggests that acute blockade of mGluR5 and also of mGluR1 exerts antidepressant-like effects in behavioral despair tests in rats and mice.

[Study of pharmacological activation of the male sexual behavior]. / K metodam izucheniia farmakologicheskoi aktivatsii polovogo povedeniia samtsov.

The model of sexual exhaustion of male rats was used in the study. The specific aim was to compare the effects of cocaine on the mount latency, number of mounts, intromissions and ejaculations during the entire copulatory cycle with the same indices during the first 30 min of observation (the latter is most frequently used in laboratory settings). Experiments consisted of four 3-day test periods. On days 1 and 2, male rats were allowed to interact with receptive females until the satiation criterion was reached (30 min without mounts). On day 3, male rats were injected with cocaine (5, 10, or 30 mg/kg, i.p.) or its vehicle 15 min prior to testing. Cocaine administration in a dose-dependent way increased the total number of mounts and ejaculations during the entire observation session but not during the initial 30-min period. The mount latency was unaffected by cocaine treatment. The results suggest that the expression of the stimulating effects of cocaine on sexual behavior depends on the duration of the observation period.

Effects of short-acting NMDA receptor antagonist MRZ 2/576 on morphine tolerance development in mice.

The present study sought to evaluate the ability of a short-acting glycineB site NMDA receptor antagonist, MRZ 2/576, to affect morphine tolerance development in mice. It was found that MRZ 2/576 (10 mg/kg, i.p.) significantly retarded development of morphine analgesic tolerance (20 mg/kg, s.c., 8 days, once a day; tail-flick test) when administered 120 min or 150 min after each daily morphine injection. MRZ 2/576 did not affect the development of morphine tolerance when administered immediately, 15, 30, 60, 90, 180, 240, 300 or 360 min after the daily morphine injections. Thus, short-acting NMDA receptor antagonists may be useful in exploring the temporal characteristics of opioid tolerance (i.e., periods after morphine injection that are critical for tolerance induction) and the present study suggests that after morphine administration there is a period of NMDA receptors activation crucial for the development of tolerance.

Antinociceptive activity of combination of morphine and NMDA receptor antagonists depends on the inter-injection interval.

The actual time-course of morphine antinociception is shorter than what would be predicted from its elimination kinetics, suggesting the presence of an acute tolerance phenomenon. Since antagonists acting at NMDA subtype of glutamate receptors were repeatedly shown to prolong acute morphine antinociception, acute tolerance may be attributed to hyperactivity of NMDA receptors. The ability of various site-selective NMDA receptor antagonists to affect morphine antinociception (tail-flick test) was assessed in mice 30 and 120 min after acute morphine challenge. Competitive NMDA receptor antagonist 3-(2-carboxypiperazin-4-yl)-1-propenyl-1-phosphonic acid (D-CPPene) (SDZ EAA 494; 0.1-1 mg/kg), low-affinity channel blockers 1-amino-3,5-dimethyl adamantane (memantine) (1-10 mg/kg) and 1-amino-1,3,3,5,5-pentamethyl-cyclohexan hydrochloride (MRZ 2/579) (1-10 mg/kg), glycine site antagonists 5-nitro-6,7-dichloro-1, 4-dihydro-2,3-quinoxalinedione (ACEA-1021) (5 or 10 mg/kg) and 8-chloro-4-hydroxy-1-oxo-1,2-dihydropyridaliono(4, 5-b)quinoline-5-oxide choline salt (MRZ 2/576) (1-10 mg/kg) were administered intraperitoneally (i.p.) 15 or 30 min prior to the tail-flick test (i.e., interval between injections of morphine and NMDA receptor antagonist was either 0-15 or 90-105 min). ACEA-1021, MRZ 2/576 and to the lesser extent, memantine and MRZ 2/579 enhanced morphine antinociception when tests were conducted 120 but not 30 min post-morphine. D-CPPene potentiated morphine antinociception irrespective of the interval between morphine administration and the tail-flick test. The results suggest that NMDA receptor antagonists may restore analgesic activity of morphine in acutely tolerant mice.

[The effect of GABA-positive agents on the formation of morphine dependence and on the manifestations of a withdrawal syndrome]. / Vliianie GAMK-pozitivnykh sredstv na formirovanie zavisimosti ot morfina i proiavleniia sindroma otmeny.

Experiments on mice showed that the GABA-positive preparations (THIP, baclofen, fenibut, valproate sodium) intraperitoneally injected in the course of the morphine addiction development (double daily subcutaneous injections at a dose increasing from 10 to 100 mg/kg over a period of 8 days) and, to a greater extent, upon cessation of the morphine injections, partly reduce manifestations of the naloxone-enhanced (0.1 mg/kg, s.c.) daily abstinence, as evaluated by the hopping activity and pair interaction tests.

Short-acting NMDA receptor antagonist MRZ 2/576 produces prolonged suppression of morphine withdrawal in mice.

The present study sought to evaluate the time-course of the effects of a short-acting glycine site NMDA receptor antagonist, MRZ 2/576 (half-life of about 20 min), on the expression of morphine withdrawal syndrome in mice. Morphine-naive and morphine-dependent mice (10-100 mg/kg, b.i.d., s.c., 9 days) were injected with a combination of naltrexone (vehicle or 1 mg/kg, s.c.) and MRZ 2/576 (vehicle, 0.3-10 mg/kg, i.p.) 24 h after the last morphine injection. MRZ 2/576 suppressed expression of several signs of morphine withdrawal (jumping, shaking, forelimb tremor). Effects of MRZ 2/576 were equally expressed throughout 1-h observation test of both spontaneous and naltrexone-facilitated withdrawal. These results suggest that despite its short half-life, MRZ 2/576 produces prolonged suppression of morphine withdrawal syndrome and this effect cannot be attributed to repeated morphine-induced increase in sensitivity to naltrexone.

[Regulation of the mouse aggressive behavior (pharmacologic analysis of the GABAergic mechanism)]. / Reguliatsiia agressivnogo povedeniia myshei (farmakologicheskii analiz GAMKergicheskikh mekhanizmov).

Ethological procedures were used to study the effects of GABA-positive drugs on aggression in male albino mice kept in isolation (opponent test). The results revealed several variants of antiaggressive effects of the tested GAB Aergic drugs: 1) antiaggressive, re-socializing of GABAA agonists muscimol (0.125 and 0.5 mg/kg) and THIP (2.0 mg/kg), and GABAB agonist baclofen (2.5-10 mg/kg); 2) antiaggressive, sedative of GABAB agonists baclofen (12.5 mg/kg), phenibut (50-100 mg/kg), and inhibitor of GABA transamininase sodium valproate (100 mg/kg); 3) antiaggressive, anxiogenic for muscimol (1 mg/kg), THIP (5 mg/kg), and sodium valproate (25-50 mg/kg).

Morphine tolerance and dependence in mice with history of repeated exposures to NMDA receptor channel blockers.

Mice were subjected to two successive treatment protocols: first with NMDA receptor channel blockers (14 days, once a day) and second with morphine (5 mg/kg, 8 days, once a day). Treatment with the higher doses of dizocilpine (1 mg/kg), memantine (30 mg/kg), and MRZ 2/576 (30 mg/kg) upon discontinuation revealed only minor behavioral abnormalities attributable to the state of withdrawal. Following repeated administration of low-dose morphine, tolerance to morphine analgesia developed in mice preexposed to dizocilpine (1 mg/kg but not 0.3 mg/kg) but not memantine (10 and 30 mg/kg), MRZ 2/579 (10 and 30 mg/kg), or saline. There were no signs of morphine dependence in any treatment group. Overall, the present study found only minor effects of the subchronic administration of high doses of NMDA receptor channel blockers, suggesting that clinical use of NMDA receptor channel blockers such as memantine will not be accompanied by increased propensity to induction of morphine tolerance and dependence.

Effects of NMDA receptor channel blockers, dizocilpine and memantine, on the development of opiate analgesic tolerance induced by repeated morphine exposures or social defeats in mice.

Development of tolerance to opiates involves various neurochemically and pharmacologically distinct processes. For instance, the diversity of opiate tolerance has been suggested by experiments comparing the establishment of diminished response to different effects of opiate agonists. Antagonists acting at N-methyl-D-aspartate (NMDA) receptors has become a very useful tool for studying opiate tolerance mechanisms since these drugs have been shown to retard the development of tolerance to analgesic properties of opiates. The present study compared the ability of two NMDA receptor channel blockers, dizocilpine and memantine, to affect the development of tolerance to morphine analgesia induced by repeated social defeat or by repeated morphine administrations. Male BALB/c mice were assessed for the tail-flick response before and after the defeat in five social confrontations, or before and after repeated morphine injections (20 mg/kg, s.c., once daily for 8 days). Repeated morphine injections were explicitly paired with environmental cues. Socially-defeated as well as morphine-treated mice developed significant tolerance to morphine analgesia. Separate groups of mice were exposed to repeated social confrontations or injections of morphine with each defeat or morphine injection followed by administration of either dizocilpine (0.03-0.3 mg/kg, i.p.) or low-affinity channel blocker memantine (3-30 mg/kg, i.p.). Both dizocilpine and memantine were effective in preventing the development of repeated morphine-induced tolerance to acute morphine analgesia. Treatments with NMDA receptor antagonists that retarded development of non-associative tolerance also suppressed the establishment of associative tolerance significantly. Social defeat-induced tolerance was prevented by dizocilpine but not by memantine. Our results suggest some degree of similarity in the mechanisms of morphine analgesic tolerance induced by pharmacological, contextual and social stimuli.

[A pharmaco-ethological study of the GABA-ergic mechanisms regulating the depression-like behavior of mice]. / Farmako-étologicheskoe izuchenie GAMKergicheskikh mekhanizmov reguliatsii depressivnopodobnogo povedeniia myshei.

It is known that repeated stress may result in depression-like alterations of behavior. This behavior is characterized by decreased social exploratory activity and increase in occurrence of defensive postures in a social interaction test in mice. The passive defensive behavior is effectively antagonized by antidepressant drugs thus providing a useful animal model of depression. Effects of several GABAergic drugs were studied in opponent test in individually housed male mice. For two weeks preceding the test, mice were repeatedly exposed to foot shock stimulation and/or social confrontation with an aggressive mouse. Muscimol, a selective agonist of GABA(A) receptors, decreased the frequency and duration of defensive postures and increased the duration of some forms of individual activity (grooming and eating), like the agonist of GABA(B) receptors baclofen. Muscimol was the only compound that facilitated exploratory activity towards an unfamiliar partner and did not suppress the locomotion. Effects of another agonist of GABA(B) receptors phenibut and inhibitor of GABA transaminase valproate Na were less specific and consisted in general suppression of behavior (prevalence of static forms of behavior). It can be thought that GABA(A) receptors are essential for regulation of depression-like behavior of mice.