Diazepam affects both level and amplitude of rat locomotor activity rhythm but has no effect on core body temperature

The present study investigates the effects of a chronic administration of diazepam, a benzodiazepine widely used as an anxiolytic, on locomotor activity and body core temperature rhythms in male Wistar rats housed under 12:12 light:dark (LD) cycle conditions. Diazepam was administered subcutaneously for 3 wks in a dosage of 3 mg/kg body weight/day, 1 h before the onset of darkness. Diazepam increased the level of locomotor activity from the first day until the end of treatment, and also increased the amplitude of the activity circadian rhythm, but only on the third wk of treatment. Diazepam exerted no effects on the length of the period and did not affect the phase of the locomotor activity rhythm. The body temperature rhythm of rats was affected neither by short-term (a single injection) nor by long-term (every day for 3 wks) diazepam treatment. Diazepam lacked effect on body core temperature even on the first day of administration, thereby ruling out the possibility of drug tolerance development. The fact that diazepam affects locomotor activity, but not core body temperature, suggests that different mechanisms mediate the actions of diazepam on locomotor activity and on core body temperature.     

Pharmacological actions of the peptide hormone amylin in the long-term regulation of food intake, food preference, and body weight

The ability of amylin to reduce acute food intake in rodents is well established. Longer-term administration in rats (up to 24 days) shows a concomitant reduction in body weight, suggesting energy intake plays a significant role in mediating amylin-induced weight loss. The current set of experiments further explores the long-term effects of amylin (4-11 wk) on food preference, energy expenditure, and body weight and composition. Furthermore, we describe the acute effect of amylin on locomotor activity and kaolin consumption to test for possible nonhomeostatic mechanisms that could affect food intake. Four-week subcutaneous amylin infusion of high-fat fed rats (3-300 microg.kg(-1).day(-1)) dose dependently reduced food intake and body weight gain (ED(50) for body weight gain = 16.5 microg.kg(-1).day(-1)). The effect of amylin on body weight gain was durable for up to 11 wks and was associated with a specific loss of fat mass and increased metabolic rate. The body weight of rats withdrawn from amylin (100 microg.kg(-1).day(-1)) after 4 wks of infusion returned to control levels 2 wks after treatment cessation, but did not rebound above control levels. When self-selecting calories from a low- or high-fat diet during 11 wks of infusion, amylin-treated rats (300 microg.kg(-1).day(-1)) consistently chose a larger percentage of calories from the low-fat diet vs. controls. Amylin acutely had no effect on locomotor activity or kaolin consumption at doses that decreased food intake. These results demonstrate pharmacological actions of amylin in long-term body weight regulation in part through appetitive-related mechanisms and possibly via changes in food preference and energy expenditure.     

Influence of diazepam on regenerating adrenal cortex in Wistar rats

The influence of diazepam on the mitotic activity of regenerating adrenal cortex in male Wistar rats was investigated. Diazepam administration (5 mg/kg/day) was shown to inhibit the mitotic index of adrenocortical cells on the 4th and 8th day after adrenal enucleation combined with contralateral adrenalectomy. The possible mechanism of diazepam action is discussed.     

Effect of Ethanol and Theophylline on Circadian Rhythm of Rat Locomotion

The effect of ethanol and theophylline on the circadian rhythm of rat locomotion was investigated. Male Wistar rats synchronized to 12: 12 h light-dark cycles were divided into four groups for treatment with saline, ethanol, theophylline, and ethanol plus theophylline. Animals in each group were orally administered saline, ethanol (2.0 g/kg body wt), theophylline (10 mg/kg body wt), and ethanol plus theophylline, respectively, six times every 2 h during the 12-h light span. Spontaneous loco-motor activity was continuously monitored by an animal activity recorder at 15-min intervals. Total activity count, circadian rhythm characteristics of activity (amplitude, acrophase, and mesor), power spectral patterns, and slope of fluctuation (a measurement of ultradian periodicity) were calculated. Ethanol administration decreased the total activity count by 60% and phase-delayed the onset of activity rhythm by 9.5 h on the day after treatment. The absolute value of the slope of fluctuation was increased by ethanol administration. The mean recovery time evaluated by rhythm detection was 3.8 days. Theophylline administration increased the light phase activity, but caused no phase delay of the onset time of the locomotor activity rhythm. The decrease in total activity count and phase delay of onset of the activity rhythm caused by ethanol were partially antagonized by theophylline. However, the prolonged effects of ethanol, represented by a late recovery time and an increase in the slope of fluctuation, were not influenced by theophylline.     

Effect of Ethanol and Theophylline on Circadian Rhythm of Rat Locomotion

The effect of ethanol and theophylline on the circadian rhythm of rat locomotion was investigated. Male Wistar rats synchronized to 12: 12 h light-dark cycles were divided into four groups for treatment with saline, ethanol, theophylline, and ethanol plus theophylline. Animals in each group were orally administered saline, ethanol (2.0 g/kg body wt), theophylline (10 mg/kg body wt), and ethanol plus theophylline, respectively, six times every 2 h during the 12-h light span. Spontaneous loco-motor activity was continuously monitored by an animal activity recorder at 15-min intervals. Total activity count, circadian rhythm characteristics of activity (amplitude, acrophase, and mesor), power spectral patterns, and slope of fluctuation (a measurement of ultradian periodicity) were calculated. Ethanol administration decreased the total activity count by 60% and phase-delayed the onset of activity rhythm by 9.5 h on the day after treatment. The absolute value of the slope of fluctuation was increased by ethanol administration. The mean recovery time evaluated by rhythm detection was 3.8 days. Theophylline administration increased the light phase activity, but caused no phase delay of the onset time of the locomotor activity rhythm. The decrease in total activity count and phase delay of onset of the activity rhythm caused by ethanol were partially antagonized by theophylline. However, the prolonged effects of ethanol, represented by a late recovery time and an increase in the slope of fluctuation, were not influenced by theophylline.     

Diazepam phase shifts the circadian clock of the field mouseMus booduga

Single 2h administration of diazepam (benzodiazepine) in 3.5% ethanol solution was found to evoke advance and delay phase shifts in the locomotor activity rhythm in the field mouseMus booduga. Through such pulsed administration of diazepam at various phases of circadian rhythm a phase response curve could be constructed. Phase advance occurred during early subjective day (CT 2) and phase delays were observed in the remaining phases. The shape of the diazepam phase response curve is similar to the general shape of the phase response curves generated by intraperitoneal injections of other benzodiazepines in hamsters. The phase shifting action of diazepam may be explained by its agonistic action on the neurotransmitter gamma-aminobutyric acid.     

Circadian dysfunction in a rotenone-induced parkinsonian rodent model

Parkinson's disease (PD) is a neurodegenerative disorder that also involves circadian rhythm alterations. Modifications of circadian rhythm parameters have been shown to occur in both PD patients and toxin-induced PD animal models. In the latter case, rotenone, a potent inhibitor of mitochondrial complex I (nicotinamide adenine dinucleotide [NADH]-quinone reductase), has been used to elicit degeneration of dopaminergic neurons and development of parkinsonian syndrome. The present work addresses alterations induced by rotenone on both locomotor and body temperature circadian rhythms in rats. Rotenone-treated rats exhibited abnormalities in equilibrium, postural instability, and involuntary movements. Long-term subcutaneous administration of rotenone significantly reduced mean daily locomotor activity in most animals. During rotenone administration, mean body temperatures (BTs) and BT rhythm amplitudes were significantly lower than those observed in the control group. After long-term rotenone administration, the circadian rhythms of both locomotor activity (LA) and BT displayed decreased amplitudes, lower interdaily phase stability, and higher rhythm fragmentation, as compared to the control rats. The magnitude of the LA and BT circadian rhythm alterations induced by rotenone positively correlated with degree of motor impairment. These results indicate that rotenone induces circadian dysfunction in rats through some of the same mechanisms as those responsible for the development of motor disturbances.     

Effects of diazepam and stress on lung inflammatory response in OVA-sensitized rats

The influence of stress and diazepam treatment on airway inflammation was investigated in ovalbumin (OVA)-sensitized rats. Animals were injected with OVA plus aluminum hydroxide intraperitoneally (day 0) and boosted with OVA subcutaneously (day 7). From the first to 13th day after sensitization, rats were treated with diazepam, and 1 h later they were placed in a shuttle box where they received 50 mild escapable foot shocks/day preceded by a sound signal (S). Response during the warning (S) canceled shock delivery and terminated the S. On day 14, rats were submitted to a single session of 50 inescapable foot shocks preceded by S and then were challenged with OVA. High levels of stress were detected in shocked animals, manifested as ultrasonic vocalizations. Morphometric analysis of stressed animals revealed a significant increase in both edema and lymphomononucleated cells in airways compared with controls. Diazepam treatment reduced edema in stressed and nonstressed rats. No differences were found in polymorphonucleated cell infiltration. Diazepam treatment reduced lymphomononucleated cell infiltration in stressed animals. These data suggest that stress and diazepam treatment play relevant roles in edema and lymphomononucleated airway inflammation in OVA-sensitized rats.     

Different behavior of body temperature and total locomotor activity daily rhythms during light/dark cycle in stabled Oryctolagus cuniculus

In order to investigate the potential causal link between the rhythm of activity and body temperature, we simultaneously recorded rectal temperature and total locomotor activity in five clinically healthy female rabbits (blue Vienna breed), 12 week old and mean body weight 2.7 ± 0.3. Animals were housed in individual cages (90?×?50?×?35 cm) under natural 12/12 light/dark cycle. Total locomotor activity was monitored for 15 days by an activity data logger. On day 1, 5, 10, and 15 rectal temperature was recorded every 2 h for a 24-h period. Application of single cosinor method showed a nocturnal daily rhythm of rectal temperature with a range of oscillation of about 1 °C, acrophase after dusk and low robustness value. The daily rhythm of locomotor activity showed its acrophase in the middle of the scotophase and a high robustness value. This information improves the knowledge available on the circadian biology of rabbits useful in the evaluation of physiology of this species.     

Effect of diazepam on the electroencephalographic pattern and vigilance of unanaesthetized and curarized rats with a chronic cobalt-gelatin focus.

The author studied the effect of diazepam in doses of 1 and 3 mg/kg on rats with a chronic cortical cobalt-gelatin focus and implanted cortical and subcortical electrodes. Focal spike activity localized at the site of the focus and hypersynchronous generalized episodes of spikes (and waves) of 8--9/sec frequency were studied in the electroencephalogram and the main phases of vigilance (waking, telencephalic slow waves/SWS/and REM sleep) after diazepam were evaluated. The effect of diazepam on rats temporarily immobilized with tubocurarine was also evaluated. 1. Focal spike activity during sleep was mildly inhibited by diazepam. If present in the waking state, it was markedly inhibited. 2. The number of episodes diminished significantly after diazepam. The maximum decrease occurred 30--45 minutes after administering diazepam and after that they slowly recovered. 3. Diazepam did not inhibit alteration of the phases of vigilance, but there was an increase in the proportion of telencephalic sleep with large numbers of spidles of 12--14/sec frequency and the incidence of REM phases rose by 250--300%. 4. Diazepam brought no renewal of the episodes which disappeared from the waking EEG recording of rats with a chronic focus temporarily immobilized with tubocurarine. Its administration was followed mostly by sleep activity with spindles. 5. Despite certain effects in common (disappearance of episodes), the action of diazepam differs from that of barbiturates in many respects and is effected by different mechanisms.     

Maternal diazepam exposure on brain ornithine decarboxylase and growth of offspring

The prenatal treatment of diazepam on the developmental pattern of brain ornithine decarboxylase and the general growth of offspring were studied. Diazepam (120 mg/kg/day) was administered orally to pregnant Sprague-Dawley rats from day 14 to day 20 of gestation. The activity of brain ornithine decarboxylase and body weight of the offspring were measured from the late fetal stage to the early postnatal stage. It was found that diazepam inhibited both the prenatal and 4-hour postnatal ornithine decarboxylase activities, though the general maturation pattern of the enzyme in the brain was not much altered. It may indicate that diazepam inhibits early brain development. The enzyme activity fell off as it reached maturation. Prenatal treated neonates of 6-hour or older age group had the normal activities of brain ornithine decarboxylase. The general growth of the treated offspring was substantially retarded. Their body weights were very much lower than the control offspring. The results of the present study is an additional evidence that diazepam and other benzodiazepines should be used with great care in pregnant women.     

Influence of diazepam on the mitotic activity of adrenocortical cells in rats after unilateral adrenalectomy

The effect of diazepam on adrenocortical cell proliferation was investigated in unilaterally adrenalectomized Wistar rats by evaluation of the mitotic ratio. Diazepam administration (5 mg/kg/day) was shown to decrease the mitotic index of the adrenal cortex on the 5th day after monoadrenalectomy, while on the 10th day after the operation the inhibitory effect became insignificant. The possible mechanism of diazepam action is discussed.     

Chronopharmacological Study of Cephalexin in Dogs

Recent studies have identified a 24 h rhythm in the expression and function of PEPT1 in rats, with significantly higher levels during the nighttime than daytime. Similarly, temporal variations have been described in glomerular filtration rate and renal blood flow, both being maximal during the activity phase and minimal during the rest phase in laboratory rodents. The aim of this study was to assess the hypothesis that the absorption of the first‐generation cephalosporin antibiotic cephalexin by dogs would be less and the elimination would be slower after evening (rest span) compared to morning (activity span) administration, and whether such administration‐time changes could impair the medication's predicted clinical efficacy. Six (3 male, 3 female; age 4.83±3.12 years) healthy beagle dogs were studied. Each dog received a single dose of 25 mg/kg of cephalexin monohydrate per os at 10∶00 and 22∶00 h, with a two‐week interval of time between the two clock‐time experiments. Plasma cephalexin concentrations were determined by microbiological assay. Cephalexin peak plasma concentration was significantly reduced to almost 77% of its value after the evening compared to morning (14.52±2.7 vs. 18.77±2.8 µg/mL) administration. The elimination half‐life was prolonged 1.5‐fold after the 22∶00 h compared to the 10∶00 h administration (2.69±0.9 vs. 1.79±0.2 h). The area under the curve and time to reach peak plasma concentration did not show significant administration‐time differences. The duration of time that cephalexin concentrations remained above the minimal inhibitory concentrations (MIC) for staphylococci susceptiblity (MIC=0.5 µg/mL) was>70% of each of the 12 h dosing intervals (i.e., 10∶00 and 22∶00 h). It can be concluded that cephalexin pharmacokinetics vary with time of day administration. The findings of this acute single‐dose study require confirmation by future steady‐state, multiple‐dose studies. If such studies are confirmatory, no administration‐time dose adjustment is required to ensure drug efficacy in dogs receiving an oral suspension of cephalexin in a dosage of 25 mg/kg at 12 h intervals.     

Locomotor Activity and Temperature Rhythms in Cirrhotic and Portal Hypertensive Rats

This study was performed to examine the circadian variations in body temperature and locomotor activity in two rat models of liver damage and portal-systemic collateralization, it is, cirrhosis by common bile duct ligature and portal vein ligation. Locomotor activity and temperature were measured telemetrically, and the degree of portal-systemic shunting was evaluated by the radioactive microsphere technique. In cirrhotic rats a significant increase in portal pressure and portal-systemic shunting occurred, with extensive liver damage and ascitis. These changes were accompanied by a derangement of the activity rhythm (decrease in total activity, night/day ratio and Qp) and an increase in the amplitude of the temperature rhythm. In portal vein-ligated rats, portal vein pressure and portal-systemic shunting increased significantly, with no changes in any of the rhythm parameters analyzed (total, diurnal and nocturnal activity pulses, night/day activity ratio and Qp for activity; mesor, amplitude and free-running period for temperature). The results indicate that liver dysfunction, and not merely portal hypertension or portal-systemic shunting, is the main factor affecting daily rhythms in cirrhotic rats.     

Locomotor Activity and Temperature Rhythms in Cirrhotic and Portal Hypertensive Rats

This study was performed to examine the circadian variations in body temperature and locomotor activity in two rat models of liver damage and portal-systemic collateralization, it is, cirrhosis by common bile duct ligature and portal vein ligation. Locomotor activity and temperature were measured telemetrically, and the degree of portal-systemic shunting was evaluated by the radioactive microsphere technique. In cirrhotic rats a significant increase in portal pressure and portal-systemic shunting occurred, with extensive liver damage and ascitis. These changes were accompanied by a derangement of the activity rhythm (decrease in total activity, night/day ratio and Qp) and an increase in the amplitude of the temperature rhythm. In portal vein-ligated rats, portal vein pressure and portal-systemic shunting increased significantly, with no changes in any of the rhythm parameters analyzed (total, diurnal and nocturnal activity pulses, night/day activity ratio and Qp for activity; mesor, amplitude and free-running period for temperature). The results indicate that liver dysfunction, and not merely portal hypertension or portal-systemic shunting, is the main factor affecting daily rhythms in cirrhotic rats.     

Glycogen synthase kinase 3β in the nucleus accumbens core mediates cocaine‐induced behavioral sensitization

Glycogen synthase kinase 3β (GSK‐3β) is a ubiquitous serine/threonine protein kinase involved in a number of signaling pathways. Previous studies have demonstrated a role for GSK‐3β in the synaptic plasticity underlying dopamine‐associated behaviors and diseases. Drug sensitization is produced by repeated exposure to the drug and is thought to reflect neuroadaptations that contribute to addiction. However, the role of GSK‐3β in cocaine‐induced behavior sensitization has not been examined. The present study investigated the effects of chronic cocaine exposure on GSK‐3β activity in the nucleus accumbens (NAc) and determined whether changes in GSK‐3β activity in the NAc are associated with cocaine‐induced locomotor sensitization. We also explored whether blockade of GSK‐3β activity in the NAc inhibits the initiation and expression of cocaine‐induced locomotor sensitization in rats using systemic or brain region‐specific administration of the GSK‐3β inhibitors lithium chloride (LiCl) and SB216763. GSK‐3β activity in the NAc core, but not NAc shell, increased after chronic cocaine (10 mg/kg, i.p.) administration. The initiation and expression of cocaine‐induced locomotor sensitization was attenuated by systemic administration of LiCl (100 mg/kg, i.p.) or direct infusion of SB216763 (1 ng/side) into the NAc core, but not NAc shell. Collectively, these results indicate that GSK‐3β activity in the NAc core, but not NAc shell, mediates the initiation and expression of cocaine‐induced locomotor sensitization, suggesting that GSK‐3β may be a potential target for the treatment of cocaine addiction.     

Evidence for tolerance following repeated dosing in rats with ciproxifan, but not with A-304121

Blockade of presynaptic histamine H(3) receptors with potent and selective ligands improves cognitive function in rodents and there is significant interest in developing such drugs for long-term symptomatic treatment of CNS disorders such as attention deficit hyperactivity disorder (ADHD). Unfortunately, little is known about the effects of repeated exposure to H(3) receptor antagonists/inverse agonists. We therefore investigated the effects of acute and repeated daily administration of two potent, brain penetrating H(3) receptor antagonists/inverse agonists, ciproxifan and A-304121, on rat body weight, food and water intake, core temperature and locomotor activity, as well as H(3) receptor density and gene expression levels. Methylphenidate, used clinically for the treatment of ADHD, was included as an additional comparator. Ciproxifan, an imidazole-based compound, decreased food intake over the first 10 days and locomotor activity acutely, but these effects were lost after further repeated administration. The ex vivo binding studies revealed increased H(3) receptor density in rats following repeated administration of ciproxifan for 10 or 15 days; however, H(3) receptor gene expression was not changed. In contrast, rats treated with the non-imidazole, A-304121, did not differ from controls on any measure during the observation period, while rats treated with methylphenidate exhibited hyperthermia and hyperactivity. The implications for potential long-term treatment with H(3) receptor antagonists in CNS disorders such as ADHD are discussed.     

Effects of a Seven‐Day Continuous Infusion of Ropivacaine on Circadian Rhythms in the Rat

The present study was conducted to evaluate the effect of a 7 d continuous infusion of ropivacaine on the 24 h rhythms of body temperature, heart rate, and locomotor activity. After an initial 7 d baseline, rats were randomly divided into two groups of 4 rats each to receive ropivacaine or saline via an osmotic pump for 7 consecutive days. The pumps were removed thereafter and observed during a 7 d recovery span. The studied circadian rhythms were measured by radiotelemetry throughout each of the 7 d periods. An additional group of 4 rats was studied under the same experimental conditions to assess the plasma levels of ropivacaine on days 3 and 8 following pump implantation. Our results indicate that ropivacaine does not induce loss of the circadian rhythms of body temperature, heart rate, or locomotor activity; a prominent period of 24 h was found for all variables in all animals, before, during, and after ropivacaine treatment. However, ropivacaine treatment did modify some characteristics of the rhythms; it increased the MESOR (24 h mean) of the heart rate and locomotor activity rhythms and advanced the acrophase (peak time) of the locomotor activity circadian rhythm. The present study indicates that the circadian rhythms of heart rate and locomotor activity are modified after continuous infusion of ropivacaine, which is of particular interest, given the potential cardiotoxicity of this local anesthetic agent.     

Direct modulation of activity and body temperature of owl monkeys (Aotus lemurinus griseimembra) by low light intensities

The activity pattern of Aotus lemurinus griseimembra can be predictably altered by varying the illuminance during the dark phase of a 12:12-hour light:dark rhythm. Intensities well below full-moon brightness (0.1-0.5 lx) severely inhibit activity. This modulation is not the result of a light-induced phase shift of the circadian rhythm, but it is primarily caused by masking due to direct effects of light on the motor system. Both proportional and differential effects of light are involved. Miniature transmitters were implanted intraperitoneally in two Aotus females so that the core temperature could be measured in parallel with locomotor activity. The responses to brief reductions of the dark-phase illuminance, from 10(-1) to 10(-3) lx, 10(-5) lx or physiological darkness, indicate that the direct effects of light that modulate the activity of the owl monkeys also affect their temperature time-course. The influence on the temperature rhythm, unlike that on the activity rhythm, varies greatly over the circadian period. The finding that the core temperature does not always change in parallel with locomotor activity and, to some extent, reacts differently to the light:dark alternation indicates that temperature does not simply follow activity passively, but rather is partially subject to a 'direct' masking influence of the light.     

Effects of a seven-day continuous infusion of ropivacaine on circadian rhythms in the rat

The present study was conducted to evaluate the effect of a 7 d continuous infusion of ropivacaine on the 24 h rhythms of body temperature, heart rate, and locomotor activity. After an initial 7 d baseline, rats were randomly divided into two groups of 4 rats each to receive ropivacaine or saline via an osmotic pump for 7 consecutive days. The pumps were removed thereafter and observed during a 7 d recovery span. The studied circadian rhythms were measured by radiotelemetry throughout each of the 7 d periods. An additional group of 4 rats was studied under the same experimental conditions to assess the plasma levels of ropivacaine on days 3 and 8 following pump implantation. Our results indicate that ropivacaine does not induce loss of the circadian rhythms of body temperature, heart rate, or locomotor activity; a prominent period of 24 h was found for all variables in all animals, before, during, and after ropivacaine treatment. However, ropivacaine treatment did modify some characteristics of the rhythms; it increased the MESOR (24 h mean) of the heart rate and locomotor activity rhythms and advanced the acrophase (peak time) of the locomotor activity circadian rhythm. The present study indicates that the circadian rhythms of heart rate and locomotor activity are modified after continuous infusion of ropivacaine, which is of particular interest, given the potential cardiotoxicity of this local anesthetic agent.