Reduced brain serotonergic activity after repeated treatment with beta-adrenoceptor antagonists

Chronic Polypharmacy with Increasing Drug Burden Index Exacerbates Frailty and Impairs Physical Function, with Effects Attenuated by Deprescribing, in Aged Mice

Polypharmacy (use of ≥5 medications) and increasing Drug Burden Index (DBI) score (measure of person's total exposure to anticholinergic/sedative medications) are associated with impaired physical function in observational studies of older adults. Deprescribing, the supervised withdrawal of medications for which harms outweigh benefits for an individual, may be a useful intervention. Current knowledge is limited to clinical observational studies that are unable to determine causality. Here, we establish a preclinical model that investigates the effects of chronic polypharmacy, increasing DBI, and deprescribing on global health outcomes in aging. In a longitudinal study, middle-aged (12 months) male C57BL/6J (B6) mice were administered control feed or feed and/or water containing polypharmacy or monotherapy with different DBI scores. At 21 months, each treatment group was subdivided (stratified by frailty at 21 months) to either continue on treatment for life or to have treatment withdrawn (deprescribed). Frailty and physical function were evaluated at 12, 15, 18, and 24 months, and were analyzed using a mixed modeling approach. Polypharmacy with increasing DBI and monotherapy with citalopram caused mice to become frailer, less mobile, and impaired their strength and functional activities. Critically, deprescribing in old age reversed a number of these outcomes. This is the first preclinical study to demonstrate that chronic polypharmacy with increasing DBI augments frailty and impairs function in old age, and that drug withdrawal in old age reversed these outcomes. It was not the number of drugs (polypharmacy) but the type and dose of drugs (DBI) that caused adverse geriatric outcomes.

Changes in physical symptoms, blood pressure and quality of life over 30 days

The existence of subjective symptoms arising from high blood pressure (BP) remains controversial. Few studies have been performed which compare symptoms of hypertensives and normotensives. The results of these studies are inconsistent. The present study investigates the intensities and prevalences of symptoms of hypertensives and normotensives and the relationship between symptoms and BP for both groups. During a 30-day period, 45 patients with primary hypertension and 45 normotensive controls documented BPs and intensities of 13 symptoms daily as well as mood and life satisfaction weekly. Starting on day 3 hypertensives received beta-blocker therapy (bopindolol, 1 mg/day). The BP values of the hypertensives normalized during the study, while the BPs of the normotensives did not change. At the beginning, hypertensives showed higher prevalences and intensities of the symptoms and poorer mood and life satisfaction. After normalization of BP, hypertensives attained scores similar to those of normotensives in all measured categories. Calculating within-S correlations between symptom intensities and systolic BPs, 70% of the hypertensives, but only 27% of the normotensives, showed at least one significant correlation. The differences observed between untreated hypertensives and the normotensive control group with respect to the prevalence and intensity of symptoms provide convincing evidence that untreated hypertensives are by no means symptom-free. The within-S correlations of the present study documented well the close relationship between symptoms and actual BP for a percentage of hypertensives.

Enhancement of GABAergic system activity by metoprolol in spontaneously hypertensive rats

The relevance of the GABAergic system for the antihypertensive action of metoprolol in spontaneously hypertensive rats was studied by comparing the effect of metoprolol with the effect of dihydralazine. Chronic oral treatment with metoprolol produced the maximum effect after 49 days (-delta 34 mm Hg). This effect persisted on the same level for up to 55 days. The measurements of gamma-aminobutyric acid (GABA) synthesis and specific [3H]GABA binding were performed in the hypothalamus, the pons-medulla, the hippocampus and the striatum. Significant stimulation of GABA synthesis and turnover appeared in the hypothalamus and the pons medulla. In contrast, chronic administration of dihydralazine had no influence on GABA synthesis rate. It was also shown that metoprolol elevated significantly (P < 0.01) specific [3H]GABA binding in the hypothalamus and the pons-medulla. In the striatum this effect of metoprolol was less pronounced. Binding constant analysis revealed changes in both the receptor density and affinity. Our results suggest that the hypotensive response to chronic treatment with metoprolol might be attributed to an enhancement of GABAergic system activity.

Clinical investigation of monoamine neurotransmitter interactions

Monoamine neurotransmitter systems are widely thought to be involved in the pathophysiology of affective disorders and schizophrenia and the mechanism of action of antidepressant and antipsychotic drugs. Previous clinical studies have focused on individual monoamine function in isolation, even though a large number of preclinical studies have demonstrated that monoamine neurotransmitter systems interact with one another. In the present paper, preclinical data on monoamine neurotransmitter interactions are reviewed, and two methods for examining monoamine neurotransmitter system interactions in clinical data are presented. One of the best replicated findings in biological psychiatry is that monoamine metabolites in CSF correlate with one another. The degree of correlation may be in part a measure of the degree of interaction between the parent monoamine neurotransmitter systems. Another approach to studying interactions is the use of HVA/5HIAA and HVA/MHPG ratios as an index of interactions between 5HT-DA and NE-DA. When these methods are applied in schizophrenia, patients are found to have decreased monoamine metabolite correlations compared to normal controls. Metabolite correlations increase significantly after antipsychotic treatment, and the HVA/5HIAA and HVA/MPHG ratios also increase, suggesting that neuroleptics may act in part by strengthening interactions between monoamines. BPRS ratings are negatively correlated with HVA/5HIAA and HVA/MHPG so that patients with higher ratios have fewer symptoms, particularly after treatment. These results provide direct experimental support for hypotheses suggesting that interactions between monoamine neurotransmitters are important in schizophrenia. Some of the effects of the atypical neuroleptic, clozapine, on metabolite correlations and ratios are also discussed.

The effect of adrenergic drugs on serotonin metabolism in the nucleus raphe dorsalis of the rat, studied by in vivo voltammetry

The serotonin (5-HT) and norepinephrine (NE) system participate in the control of behavioural functions. The experiments were aimed at the question whether the NE system of the locus coeruleus interferes with the 5-HT activity of the nucleus raphe dorsalis and of which receptors are possibly involved. The alpha 1- and beta-adrenoceptor agonists methoxamine and isoproterenol, as well as a high dose (600 micrograms/kg i.p.) of the alpha 2-adrenoceptor agonist clonidine, increased extraneuronal 5-hydroxyindoleacetic acid (5-HIAA) levels in the nucleus raphe dorsalis as measured by in vivo voltammetry. In contrast, a low dose (60 micrograms/kg i.p.) of clonidine and the alpha 1-, alpha 2- and beta-adrenoceptor antagonists, prazosin, piperoxane, and atenolol, reduced the 5-HIAA concentration. In the locus coeruleus, the origin of NE projections to the nucleus raphe dorsalis, clonidine decreased whereas piperoxane enhanced extracellular 3,4-dihydroxyphenylacetic acid (DOPAC), an index of NE metabolism in the locus coeruleus. The results suggest that 5-HT neurotransmission in the nucleus raphe dorsalis is stimulated by the NE system of the locus coeruleus and that adrenoceptor drugs may affect 5-HT neuronal activity in addition to NE neurotransmission.

Flerobuterol, a beta-adrenoceptor agonist, enhances serotonergic neurotransmission: an electrophysiological study in the rat brain

The two beta-adrenoceptor agonists salbutamol and clenbuterol have been shown to be effective antidepressant drugs. Flerobuterol, a new beta-adrenoceptor agonist, exhibits antidepressant activity in animal models. Given the long-standing notion that the serotonergic (5-HT) system might be involved in the etiology and/or the therapeutics of affective disorders and that this class of adrenergic agents can alter factors regulating 5-HT transmission, the effects of acute and repeated administrations of flerobuterol on the 5-HT system were studied. Acute administration of flerobuterol (up to 2 mg/kg, IV) did not modify the firing rate of dorsal raphe 5-HT neurons. However, the sustained administration of flerobuterol for two days (0.5 mg/kg/day, SC. delivered by an osmotic minipump) produced a marked decrease of the firing rate of 5-HT neurons. The reversal of this effect of flerobuterol by the somatodendritic 5-HT autoreceptor antagonist spiperone suggests that this decrease in the firing activity of 5-HT neurons in rats treated for 2 days with flerobuterol resulted from an enhanced synaptic availability of 5-HT. This initial decrease in firing activity of 5-HT neurons was followed by a progressive recovery to normal after 14 days of treatment with flerobuterol. At this point in time, the effect of intravenous lysergic acid diethylamide on the firing of 5-HT neurons was attenuated, indicating that the somatodendritic 5-HT autoreceptors had desensitized. The effectiveness of the electrical stimulation of the ascending 5-HT pathway in suppressing the firing activity of dorsal hippocampus pyramidal neurons was markedly enhanced in rats treated with flerobuterol for 14 days.(ABSTRACT TRUNCATED AT 250 WORDS)

Chronic administration of sertraline, a selective serotonin uptake inhibitor, decreased the density of beta-adrenergic receptors in rat frontoparietal cortex

Sertraline, a potent and selective inhibitor of serotonin uptake, was chronically administered to laboratory rats. Using in vitro receptor autoradiographic techniques, we found that the binding of [3H]dihydroalprenolol ([3H]DHA) was reduced in cortex layers IV-VI. Results of a saturation experiment indicated that the reduction in cortex layer IV was due to a change in number but not affinity of beta-adrenergic receptors.

Modulation of oxotremorine-induced tremor by central beta-adrenoceptors

The muscarinic agonist oxotremorine was used to induce tremor in rats pretreated with methylatropine. An objective assessment of tremor intensity was accomplished by means of an accelerometer-based recording system. The non-selective, lipophilic beta-adrenoceptor antagonist propranolol dose-dependently suppressed tremor intensity, whereas the R-isomer of propranolol was without effect, verifying beta-adrenoceptor involvement. Since the hydrophilic, non-selective beta-antagonist nadolol was ineffective, the effect appears to be located inside the blood-brain barrier. The beta 2-selective antagonist ICI 118, 551 dose-dependently reduced tremor intensity, whereas selective blockade of beta 1-adrenoceptors with metoprolol had no effect, indicating the participation of a beta 2-adrenoceptor. On the other hand, the lipophilic beta 2-agonist clenbuterol dose-dependently enhanced tremor induced by oxotremorine. Determination of circulating plasma catecholamine concentrations revealed that the effect of beta-antagonists on tremor was not secondary to an effect on the oxotremorine-induced rise in catecholamine levels. Thus, the results suggest that beta 2-adrenoceptors located inside the blood-brain barrier are able to modulate oxotremorine-induced tremor in rats.

Blockade of central beta-adrenoceptors attenuates tremor induced by 5-hydroxytryptamine (5-HT)-receptor activation in rats

The effect of beta-adrenoceptor antagonists, varying in lipophilicity and receptor selectivity, were studied on tremor elicited by L-5-hydroxytryptophan (L-5-HTP) in rats pretreated with a peripherally acting decarboxylase inhibitor and a monoamine oxidase inhibitor, or by the directly acting 5-HT agonist 5-methoxy-N,N-dimethyltryptamine (5-MeODMT). Plasma levels of the beta-adrenoceptor antagonists were determined simultaneously. The non-selective lipophilic adrenoceptor antagonist propranolol was found to dose-dependently reduce tremor intensity, whereas the non-selective hydrophilic adrenoceptor antagonist sotalol had no effect, indicating a central site of action. Furthermore, beta 1-selective blockade with the adrenoceptor antagonist metoprolol had no effect on tremor intensity, whereas the beta 2-selective antagonist ICI 118,551 dose-dependently suppressed tremor intensity, suggesting that the beta-adrenoceptor subtype involved is of the beta 2-type. These results suggest that blockade of centrally located beta 2-adrenoceptors are able to attenuate the tremor response following 5-hydroxytryptamine receptor activation.

Circadian covariation of norepinephrine and serotonin in the locus coeruleus and dorsal raphe nucleus in the rat

We report robust correlations between concentrations of the neurotransmitters norepinephrine and serotonin in the locus coeruleus and the dorsal raphe nucleus of the brainstem in rats analyzed at 7 different time points over 24 h. We found similar circadian rhythmicities for both monoamines with acrophases just before the onset of the dark period. The monoamine concentrations diminished and the significant intercorrelation between norepinephrine and serotonin in the locus coeruleus disappeared during the night suggestive of a noradrenergic stimulation of dorsal raphe serotonin during the day. Timing of experiments is crucially important in studies on brain monoaminergic indices and their interrelationships.

Effects of some atypical antidepressants on beta-adrenoceptor binding and adenylate cyclase activity in the rat forebrain

The effects of daily administration to rats of desipramine, talsupram, tomoxetine, maprotiline, nomifensine, mianserin and citalopram (each 10 mg kg-1 day-1) for 4 weeks on [3H]dihydroalprenolol ([3H]DHA) binding in the cerebral cortex and on the noradrenaline-sensitive adenylate cyclase in the limbic forebrain were determined. Of these compounds, desipramine was alone in reducing [3H]DHA binding and in attenuating the cAMP response. Two selective noradrenaline uptake inhibitors, talsupram and tomoxetine each reduced the cAMP response but without affecting [3H]DHA binding. The other drugs lacked effect on both measures indicating (except for citalopram) that reduction in sensitivity of beta-adrenoceptors and of the noradrenaline-sensitive cAMP response might not be a simple consequence of noradrenaline uptake inhibition. The lack of effect of citalopram on the sensitivity of the beta-adrenoceptor system suggests that antidepressants with selective 5-HT uptake inhibitory properties owe their antidepressant activity to other mechanisms.

Central nervous system side-effects with hydrophilic and lipophilic beta-blockers

Previous investigations have suggested that hydrophilic beta-blockers, which appear at low concentrations in brain tissue, are less likely to produce CNS-related side-effects than are lipophilic beta-blockers, which occur at higher concentrations in the brain. The validity of this hypothesis was tested in a double-blind crossover study in which the hydrophilic beta-blocker atenolol was compared with the lipophilic agents metoprolol and propranolol, in 14 patients with a previous history of nightmares or hallucinations when treated with lipophilic beta-blockers. Nightmares or hallucinations were reported by all patients receiving lipophilic beta-blockers but by only three patients receiving atenolol. The total number of episodes was significantly lower (p less than 0.01) for patients receiving atenolol (8) than for those receiving lipophilic beta-blockers (54). It is concluded that atenolol is significantly less likely to provoke nightmares and hallucinations than are the lipophilic beta-blockers, metoprolol and propranolol. It seems likely that this finding is due to the differences in hydrophilicity amongst these drugs.

Decreased brain serotonergic activity after acute propranolol

Acute propranolol reduced the synthesis rate of serotonin in several rat brain structures (hypothalamus, midbrain, pons, frontal cortex and medulla oblongata). Both optical isomers of propranolol were tested. From our results it may be concluded that both the beta-blocking property and the local anaesthetic action of the drug could be involved in its inhibitory effect, except in hypothalamus where only the levorotating isomer was effective. Our results suggest the possibility of a noradrenergic influence on brain serotonergic neurons.

Effect of S-adenosyl-L-homocysteine upon sleep in p-chlorophenylalanine pretreated rats

S-Adenosyl-L-homocysteine (7 mg/kg), administered to PCPA-pretreated rats, was able to restore normal SWS and PS quantities, as well as circadian rhythms. This effect was at its maximum when SAH was injected 48 h after PCPA (400 mg/kg). These results are discussed in terms of post-synaptic synergetic control by SAH of serotonergic and noradrenergic nerve terminals via the periventricular system and caudal medulla in relation to environmental input.

Brain part monoamines in the neuroendocrine mechanisms activated by immobilization stress in the rat

The long suspected and recently demonstrated abnormality in neuroendocrine control in patients with severe depression indicates that the neurochemical and neuroanatomical analysis of the neuroendocrine response to stress may provide valuable information in understanding the etiology of severe endogenous depression. Rats were immobilized for 1, 2, 3 or 5 hours consecutively or 2 hours per day for 5 days, sacrificed and plasma corticosterone (as an index of the release of adrenocorticotropic hormone from the pituitary) and brain part noradrenaline, dopamine, and serotonin concentrations were determined fluorometrically. Plasma corticosterone and brain part monoamines were also measured in other rats given 2 hour immobilization stress one week after the intraventricular injection of the neurotoxins 6-hydroxydopamine and/or 5,6-dihydroxytryptamine. Plasma corticosterone increased by 30% to 50% after all periods of stress and serotonin was increased in all brain parts after 1, 2 or 3 hours of stress but not after 5 hours or chronic stress. Forebrain dopamine was decreased by 30% after 1 hour stress, slowly increased with increasing duration of stress becoming a marked increase of 85% over controls after prolonged or chronic stress. The destruction of catecholamine nerve terminals with 6-hydroxydopamine prevented the stress induced rise in brain part serotonin but had no effect on the plasma corticosterone response to immobilization stress. Destruction of serotonin nerve terminals with 5,6-dihydroxytryptamine potentiated by 50% the stress induced rise in plasma corticosterone. Plasma corticosterone after 2 hours immobilization stress was the same as controls in rats given both neurotoxins. These data support the hypothesis that ACTH release is stimulated by serotonergic neural activity.