The effect of ethanol and haloperidol on dopamine receptor (D2) density.

The study was performed to investigate the influence of ethanol on haloperidol-induced changes of the dopamine (D2) receptors in rat striatal membrane preparations. Subchronic administration of the neuroleptic in the drinking water resulted in an increase of the number of binding sites in a dose-dependent manner. Simultaneous treatment with both haloperidol and ethanol prevented the rise of D2 receptors.

Muscle stiffness and continuous electromyographic activity in old rats; an animal model for spasticity?

A mechanomyographic response of the hind foot to passive straightening and bending, as well as an electromyographic activity of the gastrocnemius and tibialis anterior muscles were recorded in old (35-44-month-old) and young female rats. In old rats, spontaneous, tonic electromyographic activity patterns were concurrently observed in both antagonistic muscles; they were low-amplitude, dense tonic activity and continuous, high-amplitude, sparse electromyographic activity. The tonic electromyographic activity was correlated with a decline in the strength and mass of muscles, as well as with motor disturbances, including paresis of the rigidly straightened backward hind legs, dragged behind by an animal. In muscles of old rats, morphological features of a chronic denervation atrophy were found. Baclofen (10 and 15 mg/kg, i.p.) diminished the spontaneous tonic electromyographic activity and potently decreased the whole body muscle tone, whereas Madopar (50 mg/kg of L-DOPA+12.5 mg/kg of benerazide) was ineffective. It is suggested that old rats in which the above-described pathologic alterations are observed might be a useful animal model in the search for basic etiopathological mechanisms of spasticity and similar disturbances found in humans.

Age-related muscle stiffness: predominance of non-reflex factors.

This study was aimed at assessing the contribution of reflex and non-reflex factors to the muscle tone of old female Wistar rats. The hind foot of a rat was flexed or extended at the ankle joint by 25 degrees over 250 ms. The resistance of the foot to passive movements (torque, mechanomyogram), as well as the reflex electromyographic activity in the gastrocnemius and tibialis anterior muscles, were recorded simultaneously. Moreover, the impact of the blockade of the reflex activity caused by the local anesthetic lignocaine (1-2 ml of a 2% solution, injected in the vicinity of the sciatic nerve) on the muscle tone was investigated. Additionally, old rats' hind leg muscle samples were analysed using fluorescent microscopy for the expression of fibronectin, which is an early marker of connective tissue formation. It has been shown that old rats are characterized by (i) a substantially increased resistance of flexor muscle stiffness (measured during extension) and unchanged resistance of extensors (measured during flexion), (ii) the loss of a major part of the reflex electromyographic activity and (iii) the increased content of fibronectin in muscles. Moreover, it has been shown that lignocaine, which completely blocked the electromyographic reflex activity in the gastrocnemius and tibialis anterior muscles in young animals, was unable to counteract the resistance of these muscles to passive movements in old rats. The present results suggest that the muscle stiffness seen in old rats is not due to a reflex response, but depends mainly on non-reflex factors--chiefly on a large overgrowth of non-elastic connective tissue replacing degenerated active muscle fibers.

Motor performance achievements in rats of different ages.

Motor performance of rats of different ages was determined in a cross sectional study. The design includes a test battery of seven motor tasks of graduated complexity. The results show a hierarchical order of impairments of motor functions in aging rats; that is, the more complex the task requirement, the earlier and more pronounced is the susceptibility to deterioration of motor coordination. In spontaneous activity and swimming no difference could be observed between young and old rats. With increasing requirements for the tilting-plane, horizontal wire, climbing and chimney tests as well as the rotarod test, the older rats show a differentiated decrease in performance. The findings are discussed in respect to the theory that aging is a reverse process of early development.

Modification of different morphine actions by 6-hydroxydopamine and 6-hydroxydopamine plus desmethylimipramine.

After intracisternal 6-hydroxydopamine (6-OHDA) in mice, brain noradrenaline (NA) and dopamine (DA) are diminished, although the reduction of NA is more pronounced. Intracisternal injection of 6-OHDA in desmethylimipramine (DMI)-pretreated animals strengthens the depletion of DA while NA is partly protected. The concentration of 5-hydroxytryptamine (5-HT) is not influenced by 6-OHDA or 6-OHDA + DMI. Chronic morphine treatment to some extent enhances reduced NA and DA levels after 6-OHDA, but the decreased central catecholamine (CA) content after 6-OHDA + DMI is not raised. Morphine analgesia is highly attenuated in 6-OHDA and 6-OHDA + DMI mice. The reduction occurs in non-tolerant as well as in tolerant animals. The acute effect of morphine on body temperature is abolished with 6-OHDA, but not with 6-OHDA + DMI, whereas the interaction of central CA in morphine-induced running shows distinctly marked reduction with 6-OHDA + DMI, but not with 6-OHDA. Acute toxicity is enhanced by 6-OHDA + DMI whereas the development of tolerance against the toxicity of morphine is diminished by 6-OHDA. Lack of CA in the brain decreases sensitivity against naloxone withdrawal in acute as well as in chronic experiments.

The development of tolerance to morphine in the rat.

Tolerance to various effects of morphine in the rat can be quantified by means of a shift of semi-logarithmic dose-response curves. Tolerance to analgesia (hot plate, acetic acid writhing), catalepsy, and the tilted plane develops in a closely similar manner. Also, the stimulating effects of about 1 mg/kg morphine-HC1 tested in an open-field procedure are somewhat less pronounced in chronically treated rats than in naive ones. There is no correlation between tolerance development and the acute ED50 of different tests.

Is tolerance to delta-9-THC cellular or metabolic? The subcellular distribution of delta-9-tetrahydrocannabinol and its metabolites in brains of tolerant and non-tolerant rats.

Rats were injected intraperitoneally once every 12 h with 10 mg/kg delta-9-THC and the time course of the depressant effect was determined after one and nine injections. The motor activity of naive rats was maximally depressed between 1 and 4 h and returned to control levels 8 h after treatment. After nine injections, the maximum intensity of the depressant effect was not different from that after one injection but had completely disappeared at an earlier time point (4 h p.i.) indicating the development of tolerance to the duration of effect on motor activity. The subcellular distribution studies in brains of tolerant and non-tolerant rats indicated that an accelerated shift in the concentrations of delta-9-THC and 11-OH-delta-9-THC towards highly polar metabolites in the brains, rather than an increased elimination of these cannabinoids or decreased sensitivity of the brain may be responsible for the development of tolerance to delta-9-THC.

Interaction between d-amphetamine and ethanol with respect to locomotion, stereotypies, ethanol sleeping time, and the kinetics of drug elimination.

The interaction between d-amphetamine and ethanol with respect to locomotor activity, stereotyped behavior, and sleeping time was investigated in rats. Ethanol 0.8 g/kg i.p. enhanced and prolonged locomotor activity produced by d-amphetamine 1 mg/kg s.c. The increased motility after 5 mg/kg d-amphetamine was not influenced by alcohol 0.8 g/kg i.p. or 3.2 g/kg orally, but slightly protracted. Stereotyped head and paw movements, as well as stereotyped licking, were distinctly strengthened and protracted by 3.2 g/kg ethanol orally. The modified d-amphetamine motility and stereotypies can be explained by alcohol-induced proloneation of the life of d-amphetomine. The effect is produced by alcohol's inhibition d-amphetamine p-hydroxylation in rat liver. After 3.2 g/kg ethanol i.p., the sleeping time of male rats amounted to 153 min. Simultaneous administration of 5 mg/kg d-amphetamine s.c. reduced the sleeping time to 84 min. This is obviously based on a central antagonism.

Development and loss of tolerance to morphine in the rat.

The development of a differential tolerance to morphine was investigated with respect to the mean effective dose, the threshold dose of tolerance, the degree of tolerance after a fixed dose, and the speed of tolerance loss. The mean effective doses, the threshold doses of tolerance, and the degree of tolerance differed considerably from effect to effect, whereas in all tests tolerance loss remained the same. The mean effective doses were not correlated to threshold doses of tolerance, degree of tolerance, or to the loss of tolerance, but a strong correlation exists between threshold doses of tolerance and degree of tolerance to all effects measured. Consequences of these results upon current theories of tolerance are discussed.

Interaction between delta(9)-tetrahydrocannabinol and d-amphetamine.

d-Amphetamine increases the motor activity at a dose range of 0.5-4 mg/kg. delta(9)-Tetrahydrocannabinol (THC) diminishes this effect dose-dependently. Also, the hyperthermia caused by 5 mg/kg d-amphetamine is antagonized by THC, whereas the d-amphetamine induced stereotype movements (above 4 mg/kg) are prolonged by the cannabinoid. THC and d-amphetamine both reduce the food and water intake and the normal development body weight of rats. In combination the two substances have an additive effect. Rats treated with 5 mg/kg d-amphetamine show a significant enhancement of the dopamine (DA) concentration (26%) in the brain stem 2 h p.i. Pretreatment with 10 mg/kg THC, which also causes an increase of DA by 15%, raises the DA content by 50%. Norepinephrine (NE) in the brain stem and hypothalamus is reduced by d-amphetamine but THC has no effect on the concentration of this monoamine. After subchronical treatment with THC tolerance is demonstrable to all THC effects tested. But there is no cross tolerance between delta(9)-THC and d-amphetamine since the pharmacological as well as the biochemical effects of d-amphetamine occur despite the subchronical treatment with THC.

L-701,324, a selective antagonist at the glycine site of the NMDA receptor, counteracts haloperidol-induced muscle rigidity in rats.

RATIONALE: It has recently been suggested that the overactivity of glutamatergic neurotransmission may contribute to the pathophysiology of Parkinson's disease. Therefore, a search for new compounds which block glutamatergic receptors and show antiparkinsonian properties in animal models of this disease seems to be justified. OBJECTIVE: The aim of this study was to determine whether L-701,324 [7-chloro-4-hydroxy-3(3-phenoxy) phenylquinoline-2-(H)-one], a selective and full antagonist at the glycine site of the NMDA receptor, counteracts parkinsonian-like muscle rigidity and catalepsy induced by haloperidol in rats. METHODS: The muscle tone was measured as the resistance developed to passive flexion and extension of the hind limb. Electromyographic (EMG) activity was additionally recorded in the gastrocnemius and tibialis anterior muscles. RESULTS: L-701,324 (2.5-40 mg/kg IP) dose-dependently decreased the muscle tone enhanced by haloperidol (1-5 mg/kg IP). Likewise, the haloperidol-enhanced resting EMG activity and the EMG reflex response to passive movements were diminished by lower and almost abolished by higher doses of L-701,324. However, up to a dose of 20 mg/kg IP, L-701,324 did not influence haloperidol (0.5 mg/kg IP)-induced catalepsy. Moreover, L-701,324 (1.25-5 mg/kg IP) given alone or together with haloperidol (0.5-1 mg/kg IP) disturbed rotarod performance. Gross observation of behaviour indicated that rats injected with L-701,324 in doses equal to or higher than 5 mg/kg, alone or in combination with haloperidol, were markedly ataxic, i.e. rats showed signs of disturbed balance and loss of control over their hind limbs. CONCLUSIONS: The present study suggests that L-701,324 exhibits a beneficial action in the animal model of parkinsonian rigidity, but not that of parkinsonian akinesia. Nonetheless, this compound is not devoid of motor side-effects.

Adaptation capacity of biogenic amines turnover to hypoxia in different brain areas of old rats.

Catecholamines and indoleamines serve in the CNS as neurotransmitters in a great number of functional pathways. In order to contribute findings which might help to understand differences in functioning and behavioral performances with aging, the concentrations of dopa, dopamine, noradrenaline, 5-hydroxytryptophane (5-HTP), 5-hydroxytryptamine (5-HT), 5-hydroxyindoleacetic acid (5-HIAA) in four brain regions (hypothalamus, c. striatum, hippocampus, cortex) of young and old rats were determined 30 min after i.p. injection of NSD1015 (3-hydroxybenzylhydrazine hydrochloride). The influence of 12 h hypoxia of 10 and 8% O(2) as well as 36 h hypoxia of 10% was investigated. Accumulation of dopa and 5-HTP under normoxic conditions is reduced in old rats compared to young rats; the concentration of dopamine, noradrenaline and 5-HT is not significantly different between the age groups. After 12 h of 10% O(2) in young rats a drop of dopa accumulation occurs, only at 8% O(2) in both groups can a significant reduction be observed; dopamine and noradrenaline do not show a uniform tendency. Under the same conditions 5-HTP accumulation is reduced in both groups, 5-HT and 5-HIAA decrease at 10% O(2) but are in the range of controls at 8% O(2). After 36 h 10% O(2) hypoxia dopa accumulation in young rats returns to normal whereas in the striatum of old rats the decrease continues, but in the hypothalamus an increase above normal occurs. Dopamine and noradrenaline return to normal. Besides, in the hypothalamus of young rats 5-HTP accumulation is compensated. 5-HT and 5-HIAA rise even above control values.

Impaired plasticity of neurons in aging. Biochemical, biophysical, and behavioral studies.

Age-related correlation of impaired plasticity of neurons (biochemical and biophysical aspects) and behavioral alterations were investigated in young (3.5 months) and extremely aged (approximately 40 months) female Wistar rats. Age-dependent significant differences in second messenger (cAMP and Ins (1,4,5)P3) concentration and signal transduction via muscarinic and dopaminergic receptors were found. The results point to the specifically impaired coupling between dopamine D1 receptor and GS protein, which underlies normal brain aging. However, cholinergic neurotransmission may be modulated at another level in extremely aged rats. Thus, it appears that the site of affection in coupling of receptor and G protein and/or G protein-dependent signal transduction in aging cannot be generalized. This indicates that alterations in the coupling of signal transduction depend on diverse neurotransmitter receptors with advanced age. The age-dependent alterations in the cAMP and PI signal pathways could be due to changes in the physical properties of the membranes. To support this hypothesis, age-dependent changes in the physical state and the biochemical composition of synaptosomal membranes from the cortex, cerebellum, and striatum were examined by measuring the steady-state fluorescence amisotropy of the membrane probes 1,6-diphenyl-1,3,5-hexatriene (DPH), trimethylammonium-DPH (TMA-DPH), and trimethylammoniumpropyl-DPH (TMAP-DPH). Significant differences in the physical properties of the synaptosomal membranes existed between young and very aged rats, expressed by a higher anisotropy in the 40-month-old rat brain tissue. The changes in the physical properties of the membranes were in line with the determined age-dependent alterations in the chemical composition, e.g., the increase in cholesterol content of the aged membranes.

Decline in motor functions in aging is related to the loss of NMDA receptors.

The aim of the study was to assess the contribution of central dopaminergic and glutamatergic systems to the age-dependent loss of motor functions in rats. Rats of three age groups were compared: young (3-5-month-old), middle-aged (20-21-month-old) and old (29-31-month-old). The obtained results showed an age-dependent decline in the electromyographic (EMG) resting and reflex activities in the gastrocnemius and tibialis anterior muscles, as well as in the T-maze performance. Although these disturbances were accompanied with significant age-dependent decreases in the binding to NMDA, AMPA and dopamine D2 receptors, and a decline in the number of nigral dopamine neurons, they were significantly correlated with the loss of the binding to NMDA receptors only. The reduction in T-maze performance with aging was additionally correlated with a decrease in motor functions (EMG activity). The study suggests a crucial role of the loss of NMDA receptors in age-dependent motor disabilities, as well as in disturbances measured in the T-maze.

The influence of antihistamine compounds on the oral intake of different addictive drugs.

The influence of two antihistamines on the oral intake of various drugs with addictive potency was investigated in rats. Under the chosen conditions neither tripelennamine nor diphenhydramine have reinforcing properties. The reinforcing potency of addictive drugs is not augmented by the both substances. On the contrary, in some cases they led to a decrease in oral intake of the drug solutions offered.

The influence of p-chlorophenylalanine on different morphine effects.

p-Chlorophenylalanine (p-CPA) reduces brain 5-hydroxytryptamine (5-HT) without altering the dopamine and norepinephrine content. Morphine does not influence the 5-HT level, but partly reverses the depletion of 5-HT by p-CPA. Morphine analgesia and toxicity are not affected by p-CPA treatment. p-CPA also has no effect on acute morphine hypothermia, but after chronic treatment of 5-HT-deficient mice the dose--response curve is no longer parallel, which suggests that another mode of morphine hypothermia occurs. p-CPA diminishes morphine-induced running after acute as well as after chronic morphine administration. p-CPA treatment reduces the sensitivity to the naloxone-precipitated withdrawal reaction, but does not affect the development of physical dependence.

Development of dependence on levorphanol in rats by oral intake of the drug -- the influence of taste on drinking behaviour in rats physically dependent on levorphanol.

Oral administration of levorphanol solution induces physical dependence in rats within a few days, as demonstrated by abstinence symptoms such as loss of body weight, sensitivity to touch and inversion of locomotor activity after withdrawal from the drug. In order to examine whether the physically dependent rats show an active drug-seeking behaviour they were given successively free choice between sweetened levorphanol solution (LSa) and two alternative drinking liquids -- sweetened tap water (WSa) and unadulterated water (W). In the case of LSa and W the rats chose LSa, but they preferred WSa to LSa. Another group of rats made dependent on unsweetened levorphanol solution (L) had the choice between L and W. They rejected L immediately.

Repeated withdrawal from barbital as a drive for 'drug taking behavior' in rats.

Investigations were performed to determine whether the pharmacodynamic effect of barbital, the development of tolerance to or the physical dependence on the hypnotic are responsible for drug-taking behavior. Three groups of male rats, untreated, tolerant to and physically-dependent on barbital, were given free choice between 0.5% barbital solution and tap water. Drug-taking behavior was estimated according to specified criteria. Initially naive rats rejected an unsweetened barbital solution. Tolerant rats also refused the hypnotic, even after they had experienced abstinence symptoms only once. However, tolerant rats that repeatedly underwent withdrawal after an intake of more than 400 mg/kg/day of barbital did show drug taking behavior. Therefore, several experiences with pronounced abstinence symptoms seem to be necessary for initiating and sustaining barbital drug taking behavior in rats.

The influence of haloperidol and aminooxyacetic acid on etonitazene, alcohol, diazepam and barbital consumption.

Four groups of rats were given free choice between water and solutions of either 3 micrograms/ml etonitazene, 5% ethanol (v/v), 0.1 mg/ml diazepam or 3 mg/ml barbital for 10-14 days. With the exception of barbital, some rats spontaneously preferred the drug solutions to water. This preference was reduced by addition of 7 micrograms/ml haolperidol. In a forced drug fluid consumption procedure, the daily administration of 15 mg/kg i.p. of the gamma-aminobutyric acid (GABA)-transaminase blocker aminooxyacetic acid (AOAA) led to a reduction of ethanol and diazepam intake, but not of etonitazene and barbital. It is suggested that the diminished consumption of ethanol and diazepam as caused by GABA-T-inhibition may also be mediated by dopamine which seems to act indirectly, via benzodiazepine receptors and GABA neurons.

(+)-Amphetamine oral 'drug taking behavior' in naive and tolerant rats.

The drinking behavior of naive rats changes predictably in a free choice experiment involving water vs. 0.02%, 0.01% and 0.003% (+)-amphetamine solutions: The higher the concentration of the amphetamine solution, the sooner a number of rats quit drinking it, and the less is ingested by those still drinking it. Physically dependent rats having undergone three withdrawals immediately reject (+)-amphetamine solution in a free choice test with water available. The avoidance of withdrawal symptoms does not motivate further self-administration. Therefore, (+)-amphetamine self-administered in drinking water is neither a reinforcer for naive nor for physically dependent rats in sustaining drug taking behavior. In acute and chronic experiments, the transition from increased motor activity to stereotypical behavior could be demonstrated and evidence was produced that tolerance develops to the (+)-amphetamine-induced increase in motor activity.