Some central effects of brofaromine given repeatedly are phase-dependent

Effects of the MAO-A-inhibitor brofaromine (BRO), 10 mg/kg po after repeated (twice daily for 14 days) administration on the spontaneous behavior (exploratory and basal locomotor activities) and the exploratory activity modified by methoxamine, clonidine and d-amphetamine in male Wistar rats were studied in both light and dark phases of a diurnal cycle (L: 0700-1900 h). After single administration BRO in the light phase had no effects. In the dark phase BRO decreased the exploration (62% of control, p less than 0.01), increased the clonidine-evoked hypoactivity and amphetamine-evoked hyperactivity. The L-D differences occurred also after repeated administration. BRO in the light phase did not influence the exploration, decreased basal locomotor activity, did not change methoxamine and clonidine action and potentiated the action of amphetamine. In the dark phase, however, it did not influence the exploration and basal locomotor activity, intensified the methoxamine effect, and did not change the clonidine and amphetamine actions. The results demonstrate that the effects of BRO on behavior in rats: 1) differ from the effects caused by other antidepressants which are not MAO inhibitors; 2) are phase-dependent after both single and repeated administration.     

Interaction between ethanol and diazepam in mice: chronobiological aspects

The mechanism of action of benzodiazepines and ethanol demonstrates that these agents can synergistically affect the central nervous system (CNS). The effects of both ethanol and diazepam are likely to depend on the time of the day when they were administered. Diazepam influence on ethanol-induced sleeping and hypothermic activity in mice as well as the influence of combined administration of these agents on spontaneous locomotor activity and coordination in mice (rota-rod) were investigated. Experiments were carried out in the light phase (10:00-12:00 h) and the dark phase (22:00-24:00 h). It was shown that ethanol-induced sleeping time was longer in the dark phase than the light phase, and that ethanol increased spontaneous locomotor activity both in the light and the dark. Ethanol-induced hypothermia was lower in the dark than in the light. Diazepam decreased locomotor activity more strongly in the dark phase than by day. It impaired the hypothermic action of ethanol in the light phase, but did not have such an effect in the dark phase. Diazepam prolonged ethanol-induced sleep in the light phase, enhanced its action on locomotor coordination and decreased the stimulating effect of ethanol on spontaneous locomotor activity in mice. The chronobiological effect of the interaction between diazepam and ethanol seems to be of practical importance (sleep and motor coordination).     

Differences in the locomotor-activating effects of indirect serotonin agonists in habituated and non-habituated rats

The indirect serotonin (5-HT) agonist 3,4-methylenedioxymethamphetamine (MDMA) produces a distinct behavioral profile in rats consisting of locomotor hyperactivity, thigmotaxis, and decreased exploration. The indirect 5-HT agonist α-ethyltryptamine (AET) produces a similar behavioral profile. Using the Behavioral Pattern Monitor (BPM), the present investigation examined whether the effects of MDMA and AET are dependent on the novelty of the testing environment. These experiments were conducted in Sprague-Dawley rats housed on a reversed light cycle and tested during the dark phase of the light/dark cycle. We found that racemic MDMA (RS-MDMA; 3 mg/kg, SC) increased locomotor activity in rats tested in novel BPM chambers, but had no effect on locomotor activity in rats habituated to the BPM chambers immediately prior to testing. Likewise, AET (5 mg/kg, SC) increased locomotor activity in non-habituated animals but not in animals habituated to the test chambers. These results were unexpected because previous reports indicate that MDMA has robust locomotor-activating effects in habituated animals. To further examine the influence of habituation on MDMA-induced locomotor activity, we conducted parametric studies with S-(+)-MDMA (the more active enantiomer) in habituated and non-habituated rats housed on a standard or reversed light cycle. Light cycle was included as a variable due to reported differences in sensitivity to serotonergic ligands during the dark and light phases. In confirmation of our initial studies, rats tested during the dark phase and habituated to the BPM did not show an S-(+)-MDMA (3 mg/kg, SC)-induced increase in locomotor activity, whereas non-habituated rats did. By contrast, in rats tested during the light phase, S-(+)-MDMA increased locomotor activity in both non-habituated and habituated rats, although the response in habituated animals was attenuated. The finding that habituation and light cycle interact to influence MDMA- and AET-induced hyperactivity demonstrates that there are previously unrecognized complexities associated with the behavioral effects of these drugs.     

Light-dark phase differences in behavioral effects of moclobemide in rats

Effects of single and repeated administration of the MAO-A-inhibitor moclobemide (MOC) on the spontaneous locomotor activity and the locomotor hyper- and hypoactivity induced by d-amphetamine and clonidine, resp., in male Wistar rats were studied in both the light (L) and the dark (D) phase of the diurnal cycle (L:0700-1900 h). In the light phase, two hours after single administration, MOC (10 and 50 mg/kg po) increased the basal activity and a dose of 50 mg/kg decreased the exploratory and gross activities and enhanced the effects of amphetamine and clonidine. On the other hand, in the dark phase MOC (50 mg/kg) increased the gross activity and potentiated amphetamine hyperactivity. Only exploration was diminished to the same extent as in the light phase. After repeated administration MOC increased only the gross activity in the light phase. In the dark phase, however, MOC diminished exploration and potentiated the d-amphetamine hyperactivity. MOC, in both doses used, diminished food and water consumption and the body weight gain during the treatment period. These results demonstrate that MOC influences the behavior of rats in a phase-dependent manner after both single and repeated administration.     

Effects of diurnal phase and pimozide on cholecystokinin-elicited hypoactivity in the hamster.

Locomotor activity in golden Syrian hamsters was measured following IP injections of cholecystokinin (CCK; 25 micrograms/kg) and pimozide (0.5 mg/kg), the dopamine receptor antagonist. In addition, animals were tested during either the dark or light phase of the diurnal cycle in either dark or light running wheel environments. Results indicated that CCK-elicited hypoactivity was blocked by pimozide and that the effect of CCK was evident only among animals tested during the light phase of the daily cycle. Ambient lighting conditions in the test environment did not modify the drug effects. Independently of any drug effect, locomotor activity was affected by diurnal phase and ambient lighting in the test environment. Animals were more active when tested during the dark phase than during the light phase and locomotor activity was higher under dark than under light ambient conditions. It is concluded that diurnal phase modulates CCK's effect on hamster locomotion and that CCK's effect on locomotion is mediated, in part, by dopaminergic mechanisms.     

Characteristics of the psychotropic action of melatonin in relation to the dosage and time of day

When administered in a low dose (0.1 mg/kg) the main pineal hormone melatonin decreased the locomotor activity and exploratory behavior of rats in the open field both during the light and dark phases of the day. High doses (1.0 and 10.0 mg/kg) were effective only at night hours (01.00-03.00). After administration of 0.1 mg/kg of melatonin no changes in the main parameters and rhythmicity of forced swimming occurred irrespective of the time of use. However the effect of 1.0 mg/kg of the hormone in the daytime manifested itself in an increase of the immobility and a decrease of the depression index.     

Effects of repeated DSIP and DSIP-P administration on the circadian locomotor activity of rats

Daily intravenous evening injections of 30 nmol/kg DSIP (Delta Sleep-Inducing Peptide) in rats adapted to a constant 24 hr light:dark cycle produced changes in the circadian locomotor behavior. After 3 days the normally high locomotor activity during the dark phase was reduced while during the light (sleeping) phase the animals became relatively more active. Similar, but more rapid and more marked changes were observed (with the same schedule of injections) after 0.1 nmol/kg DSIP-P (the analogue of DSIP phosphorylated at the serine in position 7). In fact the peptide and its analogue induced a relative reversal or shift of the circadian locomotor activity phases opposite to the persisting light:dark conditions (=Zeitgeber). This suggests that DSIP exerts rather complex “programming” effects on the circadian activities and has more than just a sleep-inducing activity.     

Influences of a light-dark profile and the pineal gland on the hypnotic activity of melatonin in mice and rats

We have investigated the influences of the light-dark cycle and the pineal gland on the hypnotic activity of melatonin in rats and mice. The results showed that melatonin significantly shortened time to sleep onset and wakefulness time, increased slow wave sleep, paradoxical sleep, and total sleep time in rats during the light phase of a 12-h light:12-h dark cycle, by electroencephalogram recording. However, during the dark phase it had almost no significant sleep-promoting effect except shortened time to sleep onset. Melatonin exhibited more potent sleep-promoting effect in rats exposed to constant light compared with rats exposed to 12:12-h light:dark at 2000 h. Melatonin markedly prolonged sleeping time in the mice exposed to constant illumination. It was found that pinealectomy was an important factor that influenced the hypnotic activity of melatonin. When melatonin was administered to pinealectomized mice, the hypnotic activity of melatonin was more intense compared with sham-operated mice. These results demonstrated that the hypnotic activity of melatonin displayed a light-dependence manner. These results suggested that light exposure and the functional state of the pineal gland could substantially impact the hypnotic activity of melatonin at pharmacological dosage.     

Effect of agomelatine in the chronic mild stress model of depression in the rat.

Chronic mild stress (CMS), a well-validated model of depression, was used to study the effects of the melatonin agonist and selective 5-HT(2C) antagonist agomelatine (S 20098) in comparison with melatonin, imipramine, and fluoxetine. All drugs were administered either 2 h before (evening treatment) or 2 h after (morning treatment) the dark phase of the 12-h light/dark cycle. Chronic (5 weeks) evening treatment with agomelatine or melatonin (both at 10 and 50 mg/kg i.p.) dose-dependently reversed the CMS-induced reduction in sucrose consumption. The magnitude and time course of the action of both drugs was comparable to that of imipramine and fluoxetine (both at 10 mg/kg i.p.); however, melatonin was less active than agomelatine at this dose. The effect of evening administration of agomelatine and melatonin was completely inhibited by an acute injection of the MT(1)/MT(2) antagonist, S 22153 (20 mg/kg i.p.), while the antagonist had no effect in animals receiving fluoxetine or imipramine. When the drugs were administered in the morning, agomelatine caused effects similar to those observed after evening treatment (with onset of action faster than imipramine) but melatonin was ineffective. Moreover, melatonin antagonist, S 22153, did not modify the intakes in stressed animals receiving morning administration of agomelatine and in any other control and stressed groups tested in this study. These data demonstrate antidepressant-like activity of agomelatine in the rat CMS model of depression, which was independent of the time of drug administration. The efficacy of agomelatine is comparable to that of imipramine and fluoxetine, but greater than that of melatonin, which had no antidepressant-like activity after morning administration. While the evening efficacy of agomelatine can be related to its melatonin receptors agonistic properties, its morning activity, which was not inhibited by a melatonin antagonist, indicates that these receptors are certainly required, but not sufficient to sustain the agomelatine efficacy. It is therefore suggested that the antidepressant-like activity of agomelatine depends on some combination of its melatonin agonist and 5-HT(2C) antagonist properties.     

Effect of clonidine,amphetamine, and their combinations on the locomotor activity of CD-1 and C57BL/6 mice

Clonidine inhibited the exploratory motor activity of C57BL/6 mice non-habituated to the testing conditions. In CD-1 mice clonidine did not depress exploratory activity but did elevate the basal locomotor activity of animals both non-habituated and habituated to testing conditions. Amphetamine increased the locomotor activity of many C57BL/6 mice and conversely inhibited the locomotion of many CD-1 mice. In both strains, amphetamine in doses up to 2 mg/kg was unable to alter effects produced by clonidine. Results suggest that the locomotor activity of C57BL/6 mice is more sensitive than that of CD-1 mice to drugs affecting the central noradrenergic system.     

Lipopolysaccharide-induced hypoactivity and behavioral tolerance development are modulated by the light-dark cycle in male and female rats

Rationale Although the behavioral effects of systemic injection of lipopolysaccharide (LPS) have been extensively investigated, the modulation of these effects by natural environmental factors has received little attention.Objectives The present study investigated whether or not locomotor activity reductions and the development of behavioral tolerance in response to LPS treatment would occur to the same degree if male and female rats were treated with LPS at four distinct time points across the light-dark (LD) cycle.Methods On day 1, male and female rats were injected with either LPS (200 g/kg IP) or saline at light onset (0400 hours), 2 h into light period (0600 hours), at dark onset (1600 hours) or 2 h into the dark period (1800 hours). Two hours after injection, rats were placed in non-novel, automated open-fields and locomotor activity was assessed. The development of behavioral tolerance to LPS was evaluated three days later (day 4) using the same procedure.Results On day 1, LPS-treated animals displayed robust activity decrements during the light period with males displaying greater reductions than females. During the dark period, LPS-treated animals showed a similar hypoactivity response. After LPS treatment on day 4, all rats exhibited some behavioral tolerance to LPS. Rats given LPS treatment at light onset and during the dark period showed complete tolerance development while LPS-treated rats during the light phase at dark onset showed incomplete tolerance, still displaying significant reductions in some activity variables.Conclusions It appears that the magnitude of hypoactivity and the development of behavioral tolerance in response to LPS depend on the phase of the LD cycle during which it is administered.     

Characteristics of home cage locomotion in cynomolgus monkeys

The profiles of home cage locomotor activity and its rhythmicity were investigated using a camera system for 4 consecutive days in cynomolgus monkeys. Nine male and nine female cynomolgus monkeys were used in this study, and were found to have the same profile in nocturnal behavior in that they were mostly inactive during the night. The locomotor activity of both sexes showed a normal activity and inactivity rhythm, which had an inverse relationship between normal activity and inactivity, showing a fluctuation profile of being higher in the light cycle and lower in the dark cycle. The four-day locomotion time of the females was higher than that of the males in the dark period. The females also showed a higher locomotion count and D/L ratio in the dark period than the males during the 4 consecutive days. These findings indicate that the females have greater locomotor activity in the dark period than that of the males. The present findings may serve as useful basic data for the behavioral assessment of overall animal movements in toxicological studies using monkeys.     

ORL1 receptor-mediated down-regulation of mPER2 in the suprachiasmatic nucleus accelerates re-entrainment of the circadian clock following a shift in the environmental light/dark cycle

The circadian pacemaker in the suprachiasmatic nucleus (SCN) generates the near 24-h period of the circadian rhythm and is entrained to the 24-h daily cycle by periodic environmental signals, such as the light/dark cycle (photic signal), and can be modulated by various drugs (non-photic signals). The mechanisms by which non-photic signals modulate the circadian clock are not well understood in mice. In mice, many reportedly non-photic stimuli have little effect on the circadian rhythm in vivo. Herein, we investigated the molecular mechanism in W-212393-induced phase advance using mice. W-212393 caused a significant phase advance of locomotor activity rhythm in mice at subjective day. Injection of W-212393 during subjective day elicited down-regulation of mPER2 protein in the SCN shell region, but not mPer2 mRNA. Administration of W-212393 during subjective day failed to produce phase advance in mPer2-mutant mice as well as in ORL1 receptor deficient mice. Furthermore, we show that such inhibition of mPER2 accelerates re-entrainment of the circadian clock following an abrupt shift in the environmental light/dark cycle, such as occurs with transmeridian flight. The present results suggest that post-translational down-regulation of mPER2 protein in the shell region of mouse SCN may be involved in W-212393-induced non-photic phase advance.     

Central effects of corticotropin releasing factor (CRF): evidence for similar interactions with environmental novelty and with caffeine

Centrally administered rat/human corticotropin-releasing factor (rCRF) increases low levels of locomotor activity by rats tested in a familiar environment but suppresses the higher levels of activity associated with exposure of the animals to a novel environment. These opposing responses do not appear to be manifestations of a simple rate-dependent effect, since ICV-administered rCRF did not lower the higher levels of locomotor activity associated with the dark (active) phase of the animal's activity cycle. Caffeine, which has anxiogenic effects in man, produces effects in rats which are similar to those of rCRF. That is, both compounds elevate activity in a familiar environment but lower activity in a novel environment. Furthermore, caffeine appears to substitute for novelty in determining the direction of the locomotor effect of rCRF. Animals made hyperactive by caffeine show decreased activity when co-administered rCRF. These findings are consistent with the view that CRF acts through pathways which also subserve the responsiveness to novelty and to the anxiogenic compound caffeine.     

Involvement of central histaminergic systems in modafinil-induced but not methylphenidate-induced increases in locomotor activity in rats

Modafinil is a novel wake-promoting drug used for the treatment of narcolepsy, the mechanism of action of which remains unclear. Previous studies have shown that modafinil produces a different pattern of c-Fos activation in the brain to the classical stimulants amphetamine and methylphenidate. Modafinil, given i.p. to urethane-anesthetized rats, is associated with an increase in histamine release from the anterior hypothalamus, indicating that its behavioral actions may involve histaminergic systems. In the present study, the effects of modafinil on histamine release using in vivo microdialysis and locomotor activity in freely moving rats were examined, and compared with those of the classical psychostimulant methylphenidate. Modafinil (75 and 150 mg/kg, i.p.) increased both histamine release and locomotor activity, significantly. Methylphenidate (3 mg/kg, i.p.) also increased locomotor activity to the same extent as modafinil (150 mg/kg, i.p.) without stimulating histamine release. Depletion of neuronal histamine using alpha-fluoromethylhistidine abolished the effect of modafinil on locomotor activity in mice but had no effect on methylphenidate-induced locomotion. Examination of the effects of modafinil and methylphenidate on locomotor activity in the dark phase at doses that produced comparable effects in the light phase showed that the effect of modafinil in the dark phase was less than that of methylphenidate, a possible indication that modafinil-induced locomotor activity may be partly related to its wake-promoting actions. These findings suggest that the locomotor effects of modafinil but not of methylphenidate, involve the central histaminergic systems.     

Individual differences in the feeding effects of amphetamine: role of nucleus accumbens dopamine and circadian factors

Evidence indicates that amphetamine (AMP) affects feeding in a baseline-dependent fashion and that the nucleus accumbens (Acc) is an important site of action for AMP's effects on feeding. Experiment 1 examined the contribution of Acc-dopamine (DA) mechanisms to the baseline-dependent feeding effects of a 0.125 mg/kg dose of AMP using intra-Acc administrations of cis-flupenthixol (FLU). Results showed that there was an inverse relation beetween baseline sugar intake and the feeding response to AMP, such that AMP stimulated feeding in animals with low baseline intake and inhibited feeding in animals with high baseline intake. Intra-Acc FLU administration reversed the stimulatory but not the inhibitory effect of AMP. Further, intra-Acc FLU attenuated baseline feeding in high but not low baseline feeders. Experiment 2 sought to determine whether AMP would affect feeding in a baseline-dependent manner when administered in the dark photoperiod of the rat circadian cycle, when rats do most of their feeding. To this end, rats were administered three doses (0.05, 0.1, and 0.25 mg/kg) of AMP in the dark photoperiod and the intake of sugar monitored. Results showed that in low baseline feeders, AMP stimulated intake at lowest dose and had no effect at higher doses. In high baseline feeders, AMP inhibited intake in a dose-dependent manner. Taken together, these results further establish that AMP affects feeding in a baseline-dependent fashion. Moreover, the similar effects of AMP across the light and dark photoperiods suggest that a straightforward rate-dependency interpretation is not adequate. Finally, it is speculated that Acc-DAergic activity may play a role in the observed differences in baseline intake levels and in the response to AMP.     

Light-dark variation in response to chronic nicotine treatment and the density of hypothalamic alpha-bungarotoxin receptors

Chronic nicotine administration increased locomotor activity during the light, but not the dark, in rats maintained on a 12:12-hr light/dark cycle, but the period and peak of the circadian rhythm (CR) were not affected. In Experiment I, 24 male rats were implanted with battery-operated telemeters and locomotor activity was continuously measured for 10 days before and 10 days after the implantation of osmotic mini-pumps which delivered 0, 0.5, 3.0 or 10 mg/kg/day of (+/-)-nicotine tartrate. Nicotine increased locomotor activity during the light in a dose-dependent manner. Tolerance to the stimulant effects of nicotine during the light occurred in 5-6 days. To determine if the stimulant properties of nicotine were associated with light as opposed to disruption by the environmental stimuli normally present during the day in our animal facility, a second experiment was conducted in which rats were treated with saline or 10 mg/kg/day (+/-)-nicotine di(+)hydrate tartrate and maintained on a reversed light/dark cycle. Again nicotine increased activity during the light (21:00-09:00) but not the dark (09:00-21:00). In a third experiment, the density of alpha-bungarotoxin binding sites was found to be significantly decreased when animals were sacrificed at 06:00 in comparison with animals sacrificed at 10:00 and 14:00.     

Nicotine withdrawal: a behavioral assessment using schedule controlled responding,locomotor activity,and sensorimotor reactivity

Three different behavioral measures were used to assess the effects of abrupt cessation of chronic nicotine treatment. Nicotine (0, 3, or 6 mg/kg per day) was continuously administered for 12 days in rats by surgically implanting Alzet osmotic mini-pumps subcutaneously. Experiment 1 employed a light/dark discrimination task. There were no significant effects on number of responses or percent correct responding either during nicotine administration, or following cessation of nicotine. Experiment 2 examined ambulatory (locomotor) and nonambulatory activity. Chronic nicotine administration produced significant dose-dependent increases in both ambulatory and nonambulatory activity during the first 3 days of exposure. However, no significant alterations were seen in activity levels following nicotine cessation. Experiment 3 examined sensorimotor reactivity using the auditory startle response. During nicotine withdrawal, significant increases were seen in startle amplitude in both nicotine groups for 4 days. Nicotine (0.4 mg/kg, IP) administered before startle testing during the withdrawal phase attenuated the increased reactivity seen during nicotine cessation. These studies indicate that 1) rats display increased sensorimotor reactivity after cessation of chronic nicotine exposure, and 2) the expression of nicotine dependence and withdrawal is dependent on the behavioral task employed.     

Acute neuroactive drug exposures alter locomotor activity in larval zebrafish

As part of the development of a rapid in vivo screen for prioritization of toxic chemicals, we have begun to characterize the locomotor activity of zebrafish (Danio rerio) larvae by assessing the acute effects of prototypic drugs that act on the central nervous system. Initially, we chose ethanol, d-amphetamine, and cocaine, which are known, in mammals, to increase locomotion at low doses and decrease locomotion at higher doses. Wild-type larvae were individually maintained in 96-well microtiter plates at 26 °C, under a 14:10 h light:dark cycle, with lights on at 0830 h. At 6 days post-fertilization, ethanol (1–4% v/v), d-amphetamine sulfate (0.1–20.0 µM) or cocaine hydrochloride (0.2–50.0 µM) were administered to the larvae by immersion. Beginning 20 min into the exposure, locomotion was assessed for each animal for 70 min using 10-minute, alternating light (visible light) and dark (infrared light) periods. Low concentrations of ethanol and d-amphetamine increased activity, while higher concentrations of all three drugs decreased activity. Because ethanol effects occurred predominately during the light periods, whereas the d-amphetamine and cocaine effects occurred during the dark periods, alternating lighting conditions proved to be advantageous. These results indicate that zebrafish larvae are sensitive to neuroactive drugs, and their locomotor response is similar to that of mammals.     

Effects of chronic amphetamine in BALB/cBy mice, a strain that is not stimulated by acute administration of amphetamine

The effects of d-amphetamine and methylphenidate on locomotor activity of BALB/cByJ mice were evaluated. d-Amphetamine had no effect or inhibited locomotor activity at acute doses of up to 10 mg/kg while methylphenidate stimulated locomotor activity at acute doses between 10 and 32 mg/kg. The dose-response curves for methylphenidate and d-amphetamine appeared to be quantal in nature. During a 21-day chronic treatment with 10 mg/kg d-amphetamine no evidence of tolerance to the depressant effects of relatively high doses of d-amphetamine was observed. However, a 3.2 mg/kg dose of d-amphetamine, which acutely inhibited locomotor activity, was found to stimulate locomotor activity following chronic amphetamine treatment. Doses of methylphenidate which acutely stimulated activity were without effect in mice chronically receiving amphetamine. Although the mechanism underlying these behavioral effects has yet to be established, our results indicate that inherent alterations can differentially affect both acute and chronic susceptibility to the behavioral effects of amphetamine and methylphenidate. Use of such altered strains of mice can be especially revealing of subtle behavioral effects brought about by chronic drug treatment which are not readily demonstrated following acute administration of amphetamine.