An evaluation of the selectivity of fenmetozole (DH-524) reversal of ethanol-induced changes in central nervous system function

Pharmacology of flibanserin

Flibanserin has preferential affinity for serotonin 5-HT(1A), dopamine D(4k), and serotonin 5-HT(2A) receptors. In vitro and in microiontophoresis, flibanserin behaves as a 5-HT(1A) agonist, a very weak partial agonist on dopamine D(4) receptors, and a 5-HT(2A) antagonist. In vivo flibanserin binds equally to 5-HT(1A) and 5-HT(2A) receptors. However, under higher levels of brain 5-HT (i.e., under stress), flibanserin may occupy 5-HT(2A) receptors in higher proportion than 5-HT(1A) receptors. The effects of flibanserin on adenylyl cyclase are different from those of buspirone and 8-OH-DPAT, two other purported 5-HT(1A) receptor agonists. Flibanserin reduces neuronal firing rate in cells of the dorsal raphe, hippocampus, and cortex with the CA1 region being the most sensitive in the brain. Flibanserin-induced reduction in firing rate in the cortex seems to be mediated through stimulation of postsynaptic 5-HT(1A) receptors, whereas the reduction of the number of active cells seems to be mediated through dopamine D(4) receptor stimulation. Flibanserin quickly desensitizes somatic 5-HT autoreceptors in the dorsal raphe and enhances tonic activation of postsynaptic 5-HT(1A) receptors in the CA3 region. Flibanserin preferentially reduces synthesis and extracellular levels of 5-HT in the cortex, where it enhances extracellular levels of NE and DA. Flibanserin displays antidepressant-like activity in most animal models sensitive to antidepressants. Such activity, however, seems qualitatively different from that exerted by other antidepressants. Flibanserin seems to act via direct or indirect stimulation of 5-HT(1A), DA, and opioid receptors in those animal models. Flibanserin does not display consistent effects in animal models of anxiety and seems to exert potential antipsychotic effects. Flibanserin may induce some sedation but does not induce observable toxic effects at pharmacologically relevant doses.

Air righting: role of the NMDA receptor channel and hippocampal LTP

Air righting results in an animal turning over when it is dropped from a height in an inverted position. In the rat, air righting is a complex set of movements that depends only on an intact labyrinth and the normal vestibular input. Visual modulation of air righting does not develop until adulthood; and the ability to estimate the time to impact requires bilateral visual cues and indicates that air righting is a complex set of perceptually controlled movements and learning. The general purpose of this study was to determine the role of the NMDA receptor-ion channel on air righting and hippocampal LTP. Specifically: to measure the effects of various doses of CPP, an NMDA receptor antagonist, and MK-801, an ion channel blocker, on (a) air righting and (b) hippocampal LTP induction in medial perforant path-granule cell synapses. The following doses were used: CPP-0, 1, 5, and 10 mg/kg i.p.; MK-801-0. 0, 0.05, 0.1, 0.2, 0.3, 0.4, and 0.5 mg/kg i.p. Data were analyzed by appropriate ANOVAs and post hoc tests. Results were significant and demonstrate dose-dependent impairment of air righting and inhibition of LTP for both CPP and MK-801, implicating the role of the NMDA receptor and Na(+)/K(+)/Ca(2)+ channel in these effects. Air righting is a complex behavior and appears to be dependent upon NMDA mediated hippocampal LTP.

Differentiating analgesic and non-analgesic drug activities on rat hot plate: effect of behavioral endpoint

The contribution of behavioral endpoint to results obtained in the 55 degrees C rat hot plate procedure was assessed. Specifically, the use of a hind paw lick-only endpoint was compared to that of a hind paw lick-or-jump endpoint. Effects of prototypical analgesic and non-analgesic compounds on response latency increases were determined under each condition. Whereas the effects of morphine, oxycodone and codeine were similar under each condition, effects of a number of non-analgesic agents differed markedly depending upon the endpoint used. Clozapine, chlorpromazine, thioridazine, atropine, scopolamine, benactyzine, yohimbine, idazoxan and cyproheptadine produced dose-dependent increases in response latency under the hind paw lick-only condition but did not increase latencies when the hind paw lick-or-jump endpoint was used. Haloperidol, sulpiride, benztropine, methyl atropine, phentolamine, prazosin, methiothepin, methysergide, diphenhydramine, pargyline and diazepam failed to increase response latencies under the hind paw lick-only condition. Moreover, whereas diazepam, chlorpromazine, pentobarbital, dantrolene and ethanol produced dose-dependent increases in the height required for successful aerial righting, increases in hind paw lick-or-jump latencies occurred only following near-anesthetic doses of pentobarbital and ethanol. These data indicate that the hind paw lick endpoint is susceptible to perturbation by extraneous pharmacologic activities. Drugs exerting muscarinic cholinergic and alpha 2-adrenergic antagonist effects are particularly able to disrupt this behavior. Disruption is not associated specifically with any other pharmacologic action, although other activities may interfere with the response. In contrast, the hind paw lick-or-jump endpoint fails to detect skeletal muscle relaxant activity and only detects gross motor impairment when near-anesthetic doses of drugs are used. The present data suggest that detection of non-analgesic drug activities by rat hot plate can be minimized by use of a hind paw lick-or-jump endpoint.

Genetic analyses of the biphasic nature of the alcohol dose-response curve

Ethanol (ETOH)-induced locomotor activation and depression were studied in 23 genotypes of mice. This included a diallel cross of four inbred strains tested with a range of ETOH doses from 0 to 2.75 g/kg. The diversity in shapes of the biphasic ETOH dose-response curves was both qualitative and quantitative, and additive gene action characterized the genetic control of the dose-response curve. Small dominance effects were typically directional in the direction of more activation, or resistance to sedation. No evidence was found for maternal effects, sex linkage, or epistasis. Sex differences were seen in the increased susceptibility of male mice to locomotor sedation at higher ETOH doses. In the diallel cross, there was no correlation between the degree of activation produced by low ETOH doses and sedation produced by higher doses. This indicates that while considerable genetic influences exist for both activational and sedative domains of ETOH effects, these genetic influences are relatively independent.

Locomotor activity responses to ethanol in selectively bred long- and short-sleep mice, two inbred mouse strains, and their F1 hybrids

Locomotor activity responses to sub-hypnotic doses of ethanol (ETOH) were assessed in selected lines of mice (LS and SS), inbred strains, and their F1 hybrids. Data were obtained as photocell beam interruptions in a 15-min test for a dose range of 0 to 2.75 or 3.5 g/kg for LS and SS mice, respectively. Biphasic dose-response curves were obtained for LS and SS mice with the SS mice showing a sedative limb of the dose-response curve shifted to the right. The effects of 2.0 g/kg ETOH were also assessed in a diallel cross of the selected LS/SS lines and C57BL/6Abg and MOLD/RkAbg inbred strains. The 2.0 g/kg dose produced a wide range of responses, from sedation in C57BL/6Abg mice to extreme activation in SS and MOLD/RkAbg mice, and no effect in LS mice. The responses of F1 hybrids reflected a typical pattern of partial dominance, with heterosis in some crosses. When present, dominance was in the direction of greater locomotor activation. These patterns were confirmed by biometrical genetic analysis of the 4 x 4 diallel cross of the two lines and the two inbred strains. The data indicate that loci in addition to those responsible for selection for sedative sensitivity in LS and SS mice can influence locomotor activation produced by sub-hypnotic ETOH doses, and that SS and MOLD mice show locomotor activation for different genetic reasons.

Effect of ethanol on gamma-vinyl GABA-induced GABA accumulation in the substantia nigra and on synaptosomal GABA content in six rat brain regions

Two recently developed methods for estimating changes in presynaptic gamma-aminobutyric acid (GABA) homeostasis were used for the first time to evaluate the effects of acute and chronic ethanol treatments on GABA utilization. GABA accumulation in the left substantia nigra zona reticulata (SNR) following unilateral microinjection of gamma-vinyl GABA (GVG; 5 micrograms) was linear for at least 180 min while GABA concentrations in the uninjected right SNR did not change over this period. Net GABA accumulation (left minus right SNR) also increased linearly over this interval. Intraperitoneal (i.p.) administration of ethanol (0.3, 1 or 3 g/kg) 15 min after GVG microinjection did not significantly change either the rate of GABA accumulation in left SNR, the net GABA accumulated or the concentration of GABA in the uninjected right SNR relative to saline injected controls over the 45-min test interval. Likewise, GABA accumulation in the left SNR or steady-state GABA concentrations in the right SNR of chronically intoxicated rats or physically dependent animals withdrawn from ethanol for 12 h did not change significantly from that dextrose-fed controls. In a separate study, the effects of acute and chronic ethanol treatments on the concentration of GABA in synaptosomes isolated from the frontal cortex, hippocampus, tectum, striatum, cerebellum or brainstem were determined. Thirty min after acute treatment with ethanol (0.5, 1, 2 or 4 g/kg, i.p.) the concentration of GABA in synaptosomes from any of these brain regions was not significantly altered. Furthermore, chronic ethanol treatment sufficient to induce physical dependence and a severe ethanol withdrawal syndrome also did not significantly modify synaptosomal GABA concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Environmental variables differentially affect ethanol-stimulated activity in selectively bred mouse lines

Low doses of ethanol (EtOH) stimulate activity in an open field in many strains of laboratory mice. We are selectively breeding two lines of mice to exhibit a large (FAST) response on this test, and two other lines to exhibit a small (SLOW) response (Crabbe et al. 1987). The lines initially diverged in response to EtOH, but despite continued selection pressure, the difference between each pair of FAST and SLOW lines has not increased over generations as much as expected. Our practice has been to test animals on the 1st day after saline injection, and repeat the test after EtOH injection 24 h later. Lister (1987) recently demonstrated that the order in which an animal was exposed to EtOH and saline influenced the magnitude of the response to EtOH, with animals tested initially after EtOH having greater stimulation. Middaugh et al. (1987) recently demonstrated that the magnitude of EtOH stimulation was greater under conditions of relatively bright light than under dim light. Using non-selected Swiss mice, the current experiments essentially confirmed Lister's findings. Using FAST and SLOW mice, the predictions of both groups were tested. Both hypotheses were confirmed. Additionally, these experiments demonstrated that the magnitude of the difference between FAST and SLOW mice was greater under bright light than under dim light. The line difference was also greater when tested in the EtOH-Saline order. In experiments with Swiss mice, the possible role of peritoneal irritation in the EtOH effect was eliminated, and the optimal dose and time for demonstrating the effect was determined.(ABSTRACT TRUNCATED AT 250 WORDS)

Mice genetically selected for differences in open-field activity after ethanol

Starting from a population of genetically heterogeneous mice, selective breeding is being used to develop lines differing in sensitivity to ethanol-induced open-field activity. Mice are tested twice for 4 min in an open field. The first test is between min 2-6 after injection of saline. Twenty-four hr later, a similar test is performed after injection of ethanol (1.5 g/kg). Two independent FAST lines are being selected for ethanol-induced increases in activity, and two independent SLOW lines are being selected for ethanol-induced decreases. After four generations of selection, the lines have diverged significantly. These lines should be useful for exploring the neuropharmacological basis for the activating and rewarding properties of ethanol.

An inhalation procedure to produce tolerance to the behavioral effects of ethanol

In male Sprague-Dawley rats the acute effect of ethanol administration (1.0, 2.0, or 3.0 g/kg, IP) on motor coordination was measured by the aerial righting reflex. Ethanol in doses of 2.0 and 3.0 g/kg produced significant impairment of motor coordination with corresponding elevated blood ethanol levels. The rate of ethanol dissappearance from the blood was 0.32 +/- 0.03 mg/ml/hr. Functional tolerance to the effect of ethanol on motor coordination and hypnosis (sleep time) was produced in rats by a 24 hr period of exposure to ethanol vapor (28 mg/liter of air) in a chamber. Animals tested 48 hr after the ethanol inhalation period showed less motor impairment from acute ethanol (3.0 g/kg, IP) and other animals exhibited a reduced sleep time from ethanol (4.0 g/kg, IP) when they were compared with controls. The rate of ethanol elimination from the blood was unchanged in ethanol vapor treated animals (0.30 +/- 0.01 mg/ml/hr) and air-treated animals (0.33 +/- 0.02 mg/ml/hr).

Further studies on the ethanol antagonism exhibited by 2(2-chloro-5-trifluoromethyl phenylimino) imidazolidine (St 587)

A lipid soluble alpha 1-adrenoceptor agonist 2-(2-chloro-5-trifluoromethyl phenylimino) imidazolidine (St 587) dose-dependently antagonized the hypnotic, hypothermic and respiratory depressant effects of ethanol in C57B1/6 mice. This effect was present whether St 587 was given before or after ethanol. St 587 did not block the pentobarbitone-induced hypnosis. It also did not influence the elimination of ethanol. Combined treatment with a subhypnotic dose of ethanol and St 587 resulted in marked hyperactivity in mice. This effect was completely abolished by pimozide pretreatment. It was inferred that the dopamine released from brain areas by this dose of ethanol together with the norepinephrine receptor activation offered by St 587 resulted in this hyperactivity. Cirazoline, a more potent alpha 1-adrenoceptor agonist than St 587 was relatively more effective than the latter in blocking the ethanol-induced hypnosis in mice. It seems that alpha 1-adrenoceptor stimulation is a major contributing factor to the ethanol antagonism exerted by St 587. This drug might prove to be useful in the treatment of acute ethanol intoxication and in understanding the mode of action of ethanol.

Sampling of orbital sinus blood closely reflects brain ethanol content in rats

It was demonstrated that the aerial righting reflex can be used as an index of acute ethanol-induced impairment of motor coordination in rats, and was found to directly correlate with blood ethanol content from the infraorbital plexus. A study of ethanol within the blood and its distribution in brain regions showed that the ethanol content of orbital sinus blood closely reflected that in the cerebral cortex, midbrain, and cerebellum. Ethanol administration by intraperitoneal (IP) injection (2, 3 or 4 g/kg) produced the same distribution as 24 hr ethanol vapor inhalation (28 mg/l). Blood ethanol concentrations were slightly higher than brain ethanol concentrations when measured at 10, 30, and 60 min after IP injection and immediately following ethanol vapor administration. Also, in rats 48 hr following ethanol vapor inhalation when tolerance to ethanol is exhibited, the distribution and concentrations of ethanol in blood and brain from acute ethanol (2 g/kg, IP) were unaltered when compared with controls. These data suggest that ethanol distribution within the brain does not play a role in the phenomenon of tolerance to ethanol.

The relationship between ethanol-induced locomotor activation and narcosis in long-sleep and short-sleep mice

Mice selectively bred for marked response to hypnotic doses of ethanol (long-sleep, LS) respond to subhypnotic doses of ethanol (ETOH) with less stimulation of locomotor activity than their short-sleep (SS) counterparts. This assessment was made by comparing ETOH-induced alterations in locomotor activity to an untreated baseline within individual subjects, and to a saline-treated control group. A correlational study, using the same method in F2 generation hybrids of the LS and SS lines, produced a negative correlation (-.36) between locomotor stimulant effects of a subhypnotic dose of ETOH and length of loss of the righting reflex following a hypnotic dose. This relationship also appeared in a factor analysis of baseline locomotor activity, ETOH-stimulated activity, and depressant response variables. The genetic selection for LS and SS mice appears to have differentiated loci that influence more than one type of behavioral response to ETOH, an example of pleiotropism.

Differential effects of TRH, amphetamine, naloxone, and fenmetozole on ethanol actions: attenuation of the effects of punishment and impairment of aerial righting reflex

The effects of four putative ethanol antagonists [thyrotropin releasing hormone (TRH), naloxone, d-amphetamine, and fenmetozole] on two distinct behavioral actions of ethanol were compared. TRH (20-40 mg/kg) reduced ethanol-induced impairment of the aerial righting reflex (ARR) but enhanced the ethanol-induced increase in punished drinking (anticonflict effect). Naloxone antagonized both actions of ethanol but only at high doses (20-60 mg/kg). Amphetamine (1-4 mg/kg) abolished the ethanol effect on punished drinking but did not alter its impairment of the ARR (1-8 mg/kg). Conversely, fenmetozole antagonized the ethanol impairment of the ARR (15-30 mg/kg) but not ethanol's anticonflict action. The inconsistent pattern of "antagonist" interactions of these drugs with the behavioral actions of ethanol suggests that ethanol alters several neurochemical systems to produce its behavioral effects.

Modification of the actions of ethanol by centrally active peptides

Ethanol (2.0-5.0 g/kg, IP) caused a dose-related impairment of the aerial righting reflex of mice 60 min after injection. Ethanol (3.5 g/kg, IP) given simultaneously with neurotensin (30 micrograms, IC), bombesin (30 micrograms, IC) or beta-endorphin (20 micrograms, IC) caused a greater impairment of the reflex than ethanol alone. Simultaneous treatment with ethanol (4.0 g/kg, IP) and thyrotropin-releasing hormone (TRH, 3.0-30 micrograms, IC) caused less impairment of this measure than ethanol alone. None of the peptides altered the height of aerial righting when administered alone, or when administered with ethanol no peptide altered blood or brain ethanol content. Unexpectedly, TRH (20 and 40 mg/kg, IP) potentiated the action of ethanol by increasing punished licking in water-deprived rats, rather than antagonizing this acute action of ethanol. Like ethanol (1.0 and 2.0 g/kg, IP), beta-endorphin (100 micrograms, IC) suppressed ethanol-withdrawal tremor and audiogenic-seizure susceptibility in ethanol-dependent rats. beta-Endorphin (1 microgram) and bombesin (10 and 30 micrograms, IC) reduced only audiogenic-seizure susceptibility. TRH (10-100 micrograms, IC, or 1-40 mg/kg, IV) and neurotensin (10-100 micrograms, IC) had no effect on these ethanol-withdrawal signs. These findings suggest that centrally active peptides may play a role in certain acute and chronic actions of ethanol. Because TRH, neurotensin, bombesin and beta-endorphin do not alter all actions of ethanol in the same way, an interaction of ethanol with many functionally independent neuronal circuits is suggested.

An evaluation of the locomotor stimulating action of ethanol in rats and mice

The locomotor activity of groups of three CD-1 female mice was increased by 1.0 and 2.0 g/kg ethanol, IP, was decreased during the first hour and increased during the second hour by 3.0 and 4.0 g/kg, and was decreased by 5.0 g/kg. The dose (2.0 g/kg) that caused the greatest increase in locomotor activity did not impair motor coordination, measured by the height of aerial righting in mice. Tests after oral administration of ethanol showed that the increase in locomotor activity of mice was not due to peritoneal irritation. The same dose (2.0 g/kg) did not increase the locomotor activity of C57BL/6J mice. Ethanol (0.1 to 3.0 g/kg) had no effect or decreased the locomotor activity of individual male Sprague-Dawley rats. These findings suggest that biological differences in strains and species of laboratory rodents contribute to the apparent variability of locomotor stimulation caused by ethanol. The presence or absence of an ethanol-induced increase in locomotor activity was not dependent on the sex or number of mice or rats tested. Intertrial-interval crossing by rats acquiring or performing an active avoidance task in a shuttle box was increased by ethanol. This action was dependent on the presentation of electric foot shock. Apomorphine (0.25 and 2.5 mg/kg) and fenmetozole (7.5 and 15.0 mg/kg) failed to inhibit the ethanol-induced increase in intertrial-interval crossing by rats, although these drugs have been shown previously to antagonize the ethanol-induced increase in the activity of mice ethanol treatment. The ethanol-induced increases in the spontaneous locomotor activity of CD-1 mice in photocell activity monitors and in intertrial-interval crosses in rats in a shuttle box task thus do not appear to share a common mechanism.