The influence of drug ,reatment on norepinephrine levels and ultrastructure of the rat hypothalamus and caudate nucleus during a programmed light-dark cycle

Chronopharmacology and Chronotoxicology of CNS Drugs: Interrelationships with Neuromodulators

It has been demonstrated that the effect of a drug, chemical, or poison is diurnal phase dependent. The circadian variation in drug response could be attributed to the diurnal fluctuations of several factors, including absorption, distribution, metabolism, and excretion. Another important factor in determining the response to CNS drugs is the circadian rhythm of brain sensitivity to drugs. The diurnal variability in the concentration of brain neuromodulators could in part explain the circadian rhythm of brain sensitivity. The present paper focuses on the interrelationships between the levels of neuromodulators and the chronopharmacology and chronotoxicology of CNS drugs. Evidence is presented to show that the circadian rhythm of specific brain neuromodulators plays an important role in the pharmacologic or toxicologic action of amphetamine, barbiturates, morphine, and ethanol.

Hypothalamic alpha 2- and beta-adrenoceptor rhythms are correlated with circadian feeding: evidence from chronic methamphetamine treatment and withdrawal

The circadian regulation of food intake in rats is correlated with a bimodal rhythm of beta-adrenoceptor binding in the lateral hypothalamus and a unimodal rhythm of alpha 2-adrenoceptor binding in the medial hypothalamus. Chronic methamphetamine treatment provides evidence for a functional correlation: beta-adrenoceptor binding in the lateral hypothalamus is reduced at dusk, together with reduction of food intake; alpha 2-adrenoceptor binding in the medial hypothalamus is increased at dawn, together with persistent food intake. Long-term changes in these two adrenergic systems are also correlated with homeostasis of food intake: 24-h mean beta-adrenoceptor binding is reduced and alpha 2-adrenoceptor binding is increased upon methamphetamine withdrawal, when rebound feeding occurs. Corticosterone, although normally coupled to adrenergic mechanisms that regulate feeding, is phase delayed after chronic methamphetamine treatment.

Twenty-four hour rhythm in monoamine oxidase activity in specific areas of the rat brain stem

Diurnal variations in activities of both type A and type B monoamine oxidase (MAO) in specific areas of the brain stem were investigated in male rats maintained on a 12 h light-12 h dark schedule (06.00 to 18.00 h light). A significant diurnal variation in the activity of both type A and type B MAO was observed in the areas A1, A2 and in the locus coeruleus, but not in the cerebellar cortex. For both type A and type B MAO lowest activities were found during the morning, while highest activities occurred in the late afternoon and the beginning of the night. These results may reflect a role of MAO in the circadian variation of the concentrations of catecholamines in the brain stem.

Antagonism by chlorisondamine and propranolol, but not by atenolol, of the circadian phase-dependent phentolamine-induced changes in the cardiac noradrenaline turnover in the rat

The effects of phentolamine alone or in combination with propranolol, atenolol and chlorisondamine were studied on the concentration and turnover of noradrenaline in the heart of light-dark (L:D = 12:12 h) synchronized rats. In order to detect possible circadian phase-dependent variations in the drug effects, the same experiments were performed in the light-period and dark-period, respectively. The parameters of the turnover were calculated from the exponential decline of i.v. injected 3H-(-)-noradrenaline. Phentolamine significantly decreased the noradrenaline concentration during L, but not during D. Reduction in 3H-noradrenaline accumulation by phentolamine was 42.3% during L and 22.2% during D. Phentolamine increased the turnover rate of cardiac noradrenaline more than 3-fold in either photoperiod. Chlorisondamine reversed all the effects of phentolamine studied. Propranolol, but not atenolol, antagonized the effects of phentolamine in a dose-dependent and stereospecific way, being more effective when applied during D. Thus, the chronopharmacological studies in unrestrained rats show a circadian phase-dependency of the effects of adrenoceptor blocking drugs. It is concluded that a central site of action is responsible for the antagonism by propranolol of the phentolamine-induced increase in the turnover of the cardiac noradrenaline in vivo.

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.

Chlorpromazine causes vesicle population changes in the monoaminergic synapse of the rat caudate nucleus

The population of monoaminergic synaptic vesicles in the rat caudate nucleus remained unchanged or slightly decreased 3 h after chlorpromazine (CP) administration, and clearly increased after 24 h. The diameter of synaptic vesicles became smaller when the vesicles increased. These findings suggest that CP causes presynaptic blocking in part of its actions and leads to a condition in which neural transmission is inactive. In the control animals, population of the vesicles tended to fluctuate following the circadian rhythm.

Light-dark patterns in running-wheel activity in rats during chronic administration of theophylline

Running-wheel activity for 24 hr and activity patterns were studied during chronic theophylline administration. Theophylline altered the normal relations between activity level and illumination. Dark-time activity was decreased to approximately 50% and 24 hr activity was unaffected. These observations were consistent with previous results showing that theophylline suppressed dark-time feeding but had no effect on 24 hr food intake. A possible mechanism to account for these results may be dependent on levels and turnover of brain norepinephrine.