Interstrain comparison of avoidance behavior and neurochemical parameters of brain cholinergic function

Five rat strains (Long-Evans Hooded, Zivic Miller, Lewis, Buffalo and Fischer-344) were tested in a shuttlebox conditioned avoidance task and the differences in the performance levels among the strains were noted. In parallel experiments using naive rats, the acetylcholine concentrations in eight brain regions and the acetylcholine turnover rate in five brain regions were determined for these strains. Interstrain differences in these parameters were found but no correlation between avoidance performance and either of these measures was apparent in any brain region studied. In separate experiments, no differences were found in the hippocampal acetylcholine concentration or the turnover rate among good performing Hooded, poor performing Hooded or untested Hooded rats. Similarly, no differences in regional acetylcholine turnover rates were found between naive rats of the Iowa Reactive and Nonreactive strains. [³H]-QNB (quinuclidinyl benzilate) binding was studied in three brain regions in the five strains, but no large interstrain differences in binding characteristics were found. In contrast to interpretations of other workers based on less direct assay methods involving fewer strains, we conclude that no strong correlation exists between avoidance performance ability and basal levels of brain cholinergic activity.     

Diurnal rhythms in noradrenaline turnover and motility after reserpine and 6-hydroxydopamine

Experiments were performed in male Wistar rats synchronized by controlled conditions of light (0700--1900 hr) and of darkness (1900--0700 hr). Separately in each photo-period the effects of reserpine or 6-OHDA on the cardiac noradrenaline turnover. Whereas peripheral chemical sympathectomy did not greatly affect the diurnal rhythm in the motor activity were investigated. Initial depletion of the cardiac noradrenaline after acute application of either drug was significantly greater when injected at 2000 hr compared to 0800 hr. In both photo-periods the cardiac turnover of noradrenaline was increased after peripheral chemical sympathectomy with 6-OHDA as well as after amine depletion with reserpine. Inhibition of the protein synthesis had no effect, ganglionic blockade by chlorisondamine on the other hand abolished the rhythm in the motor activity, subacute treatment with reserpine differently affected motor activity in both photo-periods, depending on the time of drug application within 24 hr of a day. The results show that diurnal variations in the levels of neuronal and of motor activity are able to influence drug effects and have thus to be taken into account in animal studies.     

Effects of Intermittent and Continuous Subchronic Administration of Raclopride on Motor Activity,Dopamine Turnover and Receptor Occupancy in the Rat

Abstract: With the purpose of finding means to circumvent the marked pharmacokinetic differences of raclopride between rats and man, the effects of intermittent and continuous administration of raclopride were compared in rats. Intermittent administration of raclopride via subcutaneous injections resulted in a prompt increase of dopamine (DA) turnover and decrease of motor activity but these effects were of short duration, probably due to rapidly decreasing raclopride DA D₂ receptor occupancy. In contrast, but similar to schizophrenic patients on raclopride treatment, stable plasma raclopride levels and a steady DA D₂ receptor occupancy above 70% were produced in the caudate-putamen and nucleus accumbens/olfactory tubercle, when raclopride was administered continuously via minipumps at daily doses above 2 mg/kg. Tolerance to the acute effects of raclopride on DA turnover and locomotion was found with both routes of administration but it was more marked with continuous administration. At continuous raclopride administration, tolerance to the effects of raclopride on DA turnover and spontaneous motor activity as well as supersensitivity to amphetamine-induced motor activity occurred when 70% or more of DA D₂ receptor sites were occupied, i.e. the same degree of receptor occupancy as found in patients given therapeutic doses of raclopride.     

Alterations in the hepatic glucocorticoid response to mirex treatment

Corticosterone has been shown to be involved in the regulation of mirex-induced adaptive liver growth. To further investigate the role of corticosterone in this response, plasma corticosterone, hepatic tyrosine aminotransferase (TAT) activity, and hepatic cytosolic binding of glucocorticoids were determined in male Sprague-Dawley rats following a single oral dose of mirex (100 mg/kg body wt). Mirex stimulated a significant elevation in plasma corticosterone levels 12 and 24 hr after dosing; however, hepatic tyrosine aminotransferase activity was not induced above control levels 6, 12, or 24 hr after mirex dosing. Mirex does not appear to directly inhibit the enzyme because tyrosine aminotransferase activity was increased in a dose-dependent manner in both intact and adrenalectomized rats when corticosterone supplements (1-50 mg/kg body wt) were given after mirex dosing. In an effort to explain the lack of hepatic TAT induction, the concentration of cytosolic binding sites for [3H]dexamethasone in intact, adrenalectomized, and adrenalectomized corticosterone-supplemented rats was measured 12, 24, and 48 hr after mirex dosing. There was a significant decrease in the total concentration of cytosolic binding sites for [3H]dexamethasone 12 and 48 hr after mirex dosing in intact rats, 12 and 48 hr after mirex dosing in adrenalectomized rats, and 12 and 24 hr after mirex dosing in adrenalectomized corticosterone-supplemented rats. There was a significant increase in the apparent dissociation constant (Kd) in intact rats dosed with mirex as compared to the oil controls, but there was no difference in Kd after mirex dosing in the adrenalectomized (ADX) rats when compared to the Kd for the oil-dosed control rats. The maximal binding capacity (Bmax) was not significantly different from oil controls after mirex dosing in either intact or ADX rats. The lack of hepatic TAT induction in the presence of increased plasma levels of corticosterone appears to be related to glucocorticoid receptor alterations in the liver of intact rats.     

Effect of clonidine on the turnover rate of noradrenaline in peripheral tissues of the rat

The turnover of noradrenaline (NA) was studied from the decline in specific activity of ³H-NA in heart, spleen, kidneys and sub-maxillary glands of rats maintained at room temperature (22°C) or exposed to 4°C. Cold-exposure enhanced NA turnover in heart, spleen and kidneys but not in submaxillary glands.Clonidine (2 × 50 μg/kg, i.p., 12 and 6 hr before sacrifice) did not change significantly the endogenous levels of NA in the various organs of animals placed at 22°C. In cold-exposed rats, a significant 15% decrease in the cardiac NA level was observed after clonidine treatment.In the submaxillary glands, clonidine significantly reduced NA turnover, the biological half-lives of ³H-NA increasing from 4.8 to 7.9 hr in the case of rats exposed to 22°C and from 4.8 to 7.6 hr in rats exposed to 4°C. NA turnover in the heart was not significantly altered by clonidine in animals at 22°C whereas it was markedly reduced in animals exposed to cold, the ³H-NA half-lives rising from 4.2 to 6.8 hr. In spleen and kidneys, reductions in NA turnover were also observed after clonidine treatment but the variations were never significant.The mechanisms by which clonidine reduces the peripheral NA turnover are discussed.     

Correlation of lithium effects on motor activity with its brain concentrations in rats

Effects of lithium (Li) on motor activity have been investigated at different post-drug intervals (0.5–72 hr) after adminstration of 1, 2 and 3 mequiv/kg of lithium cholride (LiCl) to rats. The activity gradually decreased until the maximum effects of these doses were observed at 8 hr, after which the activity returned to control levels (48–72 hr). Lithium concentrations were estimated in various brain areas (cortex, caudate nucleus, hypothalmus, rest of the diencephalon, midbrain, ponsmedulla and cerebellum) following administration of a 3 mequiv/kg dose of LiCl to rats at different post-drug intervals (0.5–48 hr). Lithium concentrations increased gradually reaching their peak at 8 hr in almost all brain areas except for the caudate nucleus where the peak level was achieved at 12 hr. The time-course of the depressant effect of Li on motor activity correlated with the changes in Li concentrations in the brain areas related to emotion and psychomotor activity.     

Genetically determined differences in the effects of morphine on mice.

We have compared a variety of well known behavioral actions of morphine across four strains of laboratroy mice. Thes measures included locomotor activation, analgesia, tolerance, dependence and drug-seeking. We found that analgesia and drug-seeking did not vary greatly among strains, although some statistically significant differences were found. The interstrain rank ordering for locomotor activity, tolerance and dependence was different for each of these measures. This suggests that each of these effects of morphine may depend upon separate mechanisms, perhaps with each under independent genetic control. Other experiments were carried out to determine whether or not there were differences in the in vivo brain uptake of an opiate or the in vitro binding of naloxone to 'stereospecific receptors'. No significant interstrain differences could be found.     

Sex-related difference in hepatic glutathione conjugation of hexachlorobenzene in the rat.

Hexachlorobenzene (HCB) induces hepatic porphyria and liver cancer in female rats, whereas toxicity is minimal in male rats. HCB is biotransformed to sulfur-containing metabolites originating from conjugation to glutathione (GSH). This study aimed to assess differences in GSH conjugation of HCB between male and female rats. Sprague-Dawley rats of both sexes were given (po, 10 ml/kg in corn oil) five consecutive doses of 100 mg/kg HCB [2 bid (7:30, 15:30) + 1 sid (7:30)]. This cumulative dose produced porphyria in female but not male rats after a delay period of 6 weeks. Animals were killed 0, 6, 12, 18, or 24 hr after the last dose. Hepatic GSH level showed a diurnal cycle in rats of both sexes, but it was more pronounced in males; the minimum level was observed at 12 hr after dosing. The GSH level in HCB-treated male rats was significantly lower than control at 6, 18, and 24 hr, whereas no significant differences were observed for HCB-treated female rats. Biliary excretion of pentachlorothiophenol, a metabolite originating from GSH conjugation of HCB, was higher in male than female rats. Liver cytosolic GSH transferase activity toward 3,4-dichloronitrobenzene was significantly higher than control level in male but not female rats given HCB. GSH transferase activity toward 1,2-epoxy-3-(p-nitrophenoxy)propane in male and female rats was not increased by HCB treatment. The liver HCB concentration at 24 hr after dosing was higher in male rats than in female rats but decreased faster thereafter. These results suggest that hepatic GSH conjugation of HCB is more important in male than in female rats. This may be related to the reduced liver porphyria observed in HCB-treated male rats compared to female rats.     

Dopamine in the basal ganglia and benzodiazepine-induced sedation

The effects of the anxiolytic benzodiazepine flurazepam on motor activity and the turnover of dopamine were measured in rats. Changes in motor activity were measured using a doppler-shift device; changes in extracellular homovanillic acid (HVA), monitored by linear sweep voltammetry with carbon paste electrodes implanted in the striatum and nucleus accumbens and ex vivo measurements of changes in 3,4-dihydroxyphenylacetic acid/dopamine (DOPAC/DA) ratios in the striatum and nucleus accumbens were used as indices of changes in the turnover of dopamine. Injection of vehicle increased the nocturnal rise in the concentration of HVA and the ex vivo DOPAC/DA ratio in the nucleus accumbens. Injection of flurazepam decreased the nocturnal rise in HVA and DOPAC/DA ratio in the nucleus accumbens below control levels. There was also a decrease in the nocturnal rise in motor activity. Neither injection of vehicle nor injection of flurazepam caused changes in either the concentration of HVA or the DOPAC/DA ratio in the striatum. The correlation coefficient for motor activity compared to concentration of HVA remained high for the nucleus accumbens but was reduced for the striatum after administration of flurazepam. The results suggest that the sedative effect of flurazepam may be due to an action on the mesolimbic but not the nigrostriatal dopaminergic pathway.     

Biochemical and Behavioural Effects of Thiothixene: Relation to Tissue Levels of the Drug

Abstract Male Sprague-Dawley rats were given a single intraperitoneal dose of a thioxanthene neuroleptic, thiothixene. The effect on the spontaneous motor activity and the level of homovanillic acid in the striatum and the olfactory tubercle were studied at various times after the injection of the drug. The concentration of thiothixene in the blood and brain was also followed. The rats showed a significant decrease in motor activity from 15 min. to 12 hours after the injection. The HVA-levels in the striatum and olfactory tubercle were significantly elevated from 0.5 to 18 hours, the effect on the striatum being relatively more pronounced. No clear relation between drug levels and changes in motor activity of HVA-levels was found.     

GABA turnover in the brain of rat lines developed for differential ethanol-induced motor impairment

The role of GABAergic neurons in the differential sensitivity to ethanol between the AT (Alcohol Tolerant) and ANT (Alcohol Nontolerant) rat lines developed for low and high degree of motor impairment from ethanol, was studied by comparing the effect of ethanol (2 or 4 g/kg, IP) on GABA turnover in different regions of the brain in these rat lines. GABA turnover was estimated from the accumulation of GABA after inhibition of GABA aminotransferase with aminooxyacetic acid (AOAA, 50 mg/kg, IP) given 10 min after administration of ethanol. The rats were killed two hours after the AOAA treatment with focused microwaves. The concentrations of GABA, aspartate, glutamate, glutamine and taurine were analyzed with HPLC. The saline-treated ANT rats were found to have a higher concentration of GABA in the striatum and a higher rate of GABA accumulation in the cerebellum than the AT rats. Ethanol suppressed the accumulation of GABA in both lines, but the suppression was significantly greater in the AT rats than in the ANT rats. In specific regions, this line difference was significant in the cerebral cortex and cerebellum with the higher ethanol dose. No line differences were found in the brain or tail blood ethanol concentration. AOAA increased the concentration of glutamine, decreased that of aspartate and glutamate, and did not modify that of taurine. The AOAA-induced changes in the concentrations of these amino acids were, however, minor relative to those found in the concentrations of GABA. The results that GABAergic mechanisms are involved in the differential sensitivity to the motor-impairing effects of ethanol between the AT and ANT rats.     

Reactivity to amphetamine in perinatally undernourished rats: behavioral and neurochemical correlates

Adult rats deprived at perinatal age and then rehabilitated on balanced chow were treated with a multiple amphetamine (AMPH) schedule (2 mg/kg/48 hr) and submitted, on days of injections, to an open-field test. Throughout 11 sessions, deprived rats showed a progressive increase of locomotor activity as compared with controls. Stereotyped activity evaluated during the AMPH treatment did not differ between control and deprived animals. No differences were detected in basal values of the dopaminergic function measured in naive control and deprived animals. By the end of the multiple AMPH treatment, a reduction of striatal DA and DOPAC levels together with a lower apparent DA turnover rate was detected in deprived animals. Besides, DA receptor binding was significantly increased in striatum from deprived rats as compared with controls. These results demonstrate that a repeated AMPH treatment, that was unable to alter the normal behavior of control rats, produced in early undernourished animals a progressive sensitization to AMPH effects, in addition to significant changes in the striatal dopaminergic function.     

Nasal cavity deposition,histopathology, and cell proliferation after single or repeated formaldehyde exposures in B6C3F1 mice and F-344 rats

Inhalation exposure for 2 years to 14.3 ppm formaldehyde (HCHO) induced a 50% incidence of squamous cell carcinoma in the nasal cavity of F-344 rats but only a 3.3% incidence in B6C3F1 mice. Since the response was concentration and species dependent, species differences in nasal cavity “dose” were examined as a possible mechanism for the differences in tumor incidence. Naive (nonpretreated) and HCHO-pretreated (6 or 15 ppm, 6 hr/day, 4 days) mice and rats were exposed to HCHO for 6 hr during which respiratory rate and tidal volume were recorded to calculate the theoretical deposition (μg/min/cm²) of HCHO on the nasal epithelium. Species differences in delivered “dose” were further assessed by comparative autoradiography, histopathology, and cell turnover studies. Because mice were better able to reduce minute ventilation upon repeated exposures, they had less HCHO available for deposition than rats, resulting in less tissue damage and a lower rate of cell turnover in the nasal epithelium. The correlation between calculated “dose” and observed nasal toxicity, including nasal tumor incidence, demonstrates that by normalizing the dosimetry to nasal surface area, species differences in nasal toxicity may be better understood.     

Role of pharmacokinetics and metabolism in the enhanced susceptibility of middle-aged male Sprague-Dawley rats to acetaminophen nephrotoxicity

Middle-aged male Sprague-Dawley (SD) rats (9-12 months) are more susceptible to acetaminophen (APAP)-induced nephrotoxicity than are young (2-3 months) adult males. The present studies were designed to evaluate the role of pharmacokinetics and renal and hepatic metabolism of APAP in age-dependent nephrotoxicity. Following 750 mg/kg APAP, ip, a nephrotoxic dosage in 12-month-old but not 3-month-old rats, renal cortical APAP concentrations were significantly greater in 12-month-old compared with 3-month-old SD rats at 3, 4, and 6 hr after treatment. Renal medullary APAP concentrations in 12 month-old rats were significantly greater than in 3-month-old rats at 2, 3, and 5 hr after treatment. Serum APAP concentrations were significantly elevated in 12-month-old compared with 3-month-old rats from 2 through 5 hr after APAP (750 mg/kg ip). However, APAP tissue/serum concentration ratios were similar in 3- and 12-month-old rats, indicating that differences in tissue concentration were secondary to increased serum concentrations in older rats. Conjugated APAP metabolites in blood were similar in 3- and 12-month-olds during the initial 2-3 hr after 750 mg/kg APAP, ip, but began to accumulate in 12-month-old but not 3-month-old rats within 6-8 hr after APAP administration, perhaps secondary to declining renal function. After 500 mg/kg APAP, iv, blood APAP concentrations were markedly elevated in 12-month-old compared with 3-month-old rats during the entire course of the experiment.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of chronic treatment with ethanol and withdrawal of ethanol on levels of dopamine, 3,4-dihydroxyphenylacetic acid and homovanillic acid in the striatum of the rat. Influence of benzodiazepines, barbiturate and somatostatin.

Administration of ethanol for 40 days, at 10.53 +/- 0.25 g/kg/day did not modify levels of dopamine (DA) or 3,4-dihydroxyphenylacetic acid (DOPAC) in the striatum of the rat; however, the concentration of homovanillic acid (HVA) and the ratio of turnover were increased in a statistically significant way (P < 0.05). Twenty-four hours after withdrawal of ethanol appears as the central time of the ethanol-induced abstinence syndrome, showing noticeable decreases in levels of DA (P < 0.05) and DOPAC (P < 0.05), with respect to control and chronically ethanol-treated groups. The concentrations of DA, DOPAC and HVA and ratio of turnover values showed a tendency to return to control normal levels of 48 hr after ethanol withdrawal, although the differences still showed statistical significance (P < 0.05). The intraperitoneal injection of saline, the water soluble benzodiazepine midazolam, the barbiturate thiopental and somatostatin, in single doses, resulted in a noticeable increase in levels of DA, DOPAC and HVA and ratio of turnover values. The intraperitoneal injection of midazolam produced statistically significant decreases in levels of DOPAC and ratio of turnover values (P < 0.01) in rats 48 hr after withdrawal of ethanol, with respect to control and chronically ethanol-treated animals, in contrast to the absence of changes produced when injecting thiopental or somatostatin.     

Behavioral responses of high and low active male rats to the chronic ingestion of desipramine

Male rats arbitrarily selected for high and low motor activity (HA and LA-rats) were submitted to the chronic ingestion (30 days) of desipramine (DSP) in doses of about 1.5, 3 and 6 mg/kg/24 hr. Their motor activity was assessed in an animal activity monitor providing a measure of total horizontal movements and vertical movements and in a hole-board providing a measure of locomotion, head-dipping and grooming. There were significant differences between HA and LA-rats in their behavioral response to DSP treatment. At the doses used DSP did not affect horizontal and vertical movements and hole-board locomotion or exploration in HA-rats (Experiment 1). In LA-rats, however (Experiment 2), these motor activities were significantly stimulated by DSP. Such effect was dose dependent; 1.5 mg/kg/24 hr was ineffective while 6 mg/kg/24 hr produced a clear cut reversion of hypoactivity. It is speculated that DSP treatment increased resistance of LA-rats to the mild stress caused by testing.     

Sex differences in cocaine-induced behavioral responses, pharmacokinetics, and monoamine levels

Female rats display a more robust behavioral response to acute cocaine administration than do male rats. However, a clear understanding of the biological mechanisms underlying these differences remains elusive. The present study investigated whether sexual dimorphisms in cocaine-induced motor behavior might be based on monoaminergic levels and/or cocaine pharmacokinetics. An acute injection of cocaine (5, 15, 20 or 30 mg/kg) or saline was administered to male and female rats, and behavioral activity was monitored for 3 h. Following acute cocaine or saline administration motor behavior varied according to dose and sex; overall, female rats displayed greater rearing counts and stereotypic scores, greater total locomotor counts at 15, 20, and 30 mg/kg of cocaine, and greater ambulatory counts at 20 and 30 mg/kg of cocaine than did male rats. Neurochemical determinations in post-mortem tissue showed that both male and female rats had increases in total dopamine (DA) in the caudate putamen (CPu) 15 min following cocaine administration. Additionally, male rats had a decrease in dihydroxyphenylacetic acid (DOPAC)/DA turnover. Female rats showed significant reductions in total levels of DA, DOPAC, HVA, serotonin (5-HT), 5-hydroxyindole acetic acid (5-HIAA), and DOPAC/DA turnover in the nucleus accumbens (NAc). Male rats displayed a reduction only in DOPAC/DA turnover and increases in 5-HT in the NAc following cocaine administration. Furthermore, sex differences in cocaine metabolism were observed where females had greater brain/blood levels of norcocaine and ecgonine methyl ester while male rats had higher blood levels of benzoylecgonine. These results suggest that sex differences in the behavioral responses to cocaine administration could be explained in part by intrinsic differences in both monoaminergic levels and metabolic processes.     

Regional catecholamine content in the rat brain: sex differences and correlation with motor activity

Rats were pretreated with α-methyl-p-tyrosine methylester, i.p., 80 $\text{mg}\text{kg}$, every 4 hr for 12hr. At 2, 4, 8 and 12hr of the recovery phase, spontaneous motor activity (SMA), as measured by photocell, and wheel running activity (WRA) were recorded and brain samples taken for assay. α-Methyltyrosine decreased both types of activity and both amines in most brain areas. Overall, SMA was positively correlated with norepinephrine (NE) in midbrain, cerebellum, and cortex and with dopamine (DA) in striatum and midbrain of both males and females. Wheel running activity was positively correlated in females with NE levels in striatum, midbrain and medullapons and with DA levels in striatum and midbrain. Significant differences were noted between male and female controls both in activity and amine levels. The data indicated that females may have a higher utilization rate for NE in the midbrain. The data supports the hypothesis that NE and DA are involved in the central regulation of motor activity.     

Acute tolerance to barbiturate in the rat

3 experimental approaches to the quantitation of acute barbiturate tolerance have been compared in the rat. There was no difference between the brain hexobarbitone or barbitone concentration found at the time of loss of righting reflex compared with the concentration found on return of the righting reflex following the period of anaesthesia produced by a single i.p. injection of the drug. However, tolerance was induced by a 7 hr infusion of pentobarbitone which kept rats anaesthetized for approximately 8 hr. Such rats awakened with a significantly higher brain pentobarbitone concentration compared with rats awakening after a single i.p. injection. Repeated i.p. injections of pentobarbitone, sufficient to keep animals anaesthetized for 12 hr, also induced a tolerance to pentobarbitone, as indicated by a reduced sleeping time and higher brain barbiturate concentration on awakening following intracerebroventricularly administered pentobarbitone injected 12 hr after the last i.p. injection. The possible relationship between acute cellular tolerance and physical dependence is discussed.     

Reduction by propranolol of raised urinary output of MHPG in hyperactive rats

Prolonged isolation of rats resulted in hyperactivity in the open field and a significant increase in 24 hr urinary excretion of MHPG (3-methoxy-4-hydroxyphenylglycol). Exploratory activity of group-housed rats in open field was not associated with raised MHPG excretion, compared with that of rats remaining in home cages. Exposure of group-housed rats to 4°C for 2 hr also increased urinary excretion of MHPG. Pretreatment of isolated rats with dl-, d-propranolol or practolol abolished hyperactivity of isolated rats and reduced MHPG output in these rats and in rats exposed to cold. dl-Propanolol did not reduce activity of grou-housed rats in open field or their urinary excretion of MHPG. It is suggested that propranolol may have a selective inhibitory effect on stress-induced increases in noradrenaline turnover.