Antidepressant biochemical profile of the novel bicyclic compound Wy-45,030, an ethyl cyclohexanol derivative.

The novel bicyclic compound Wy-45,030 [1-2-(dimethylamino)-1-(4-methoxyphenyl)ethyl cyclohexanol, hydrochloride] exhibited a neurochemical profile predictive of antidepressant activity. Like the tricyclic antidepressants, it inhibited rat brain imipramine receptor binding and synaptosomal monoamine uptake (dopamine as well as norepinephrine and serotonin). It did not inhibit monoamine oxidase. Unlike the tricyclic antidepressants, it was not antimuscarinic in the guinea pig ileum, nor did it have any appreciable affinity for brain alpha-1 adrenergic or histamine-1 binding sites. Wy-45,030 was also without affinity for alpha-2 or beta adrenergic, benzodiazepine, serotonin-1, serotonin-2, dopamine-2, and opiate receptors. Such a profile is predictive of antidepressant activity devoid of the side-effects common to tricyclic therapy.

Antidepressants and protein kinases: desipramine treatment affects pineal gland cAMP-dependent protein kinase activity.

To further describe the molecular mechanisms involved in reductions in noradrenergic responsiveness induced by antidepressants, the effects of antidepressant treatment on the rat pineal gland cAMP-dependent protein kinase system were examined. The concentration of cyclic AMP-dependent protein kinase activity was reduced 24 h after acute treatment with desipramine, as well as in animals treated repeatedly with desipramine. Assays performed in the presence of cAMP protein kinase inhibitor showed no significant effects of either acute or repeated desipramine treatment on the concentration of cAMP-independent protein kinase activity. Neither acute nor repeated treatment with other antidepressants (zimelidine, iprindole or fluoxetine) significantly altered the concentration of cAMP-dependent or cAMP-independent protein kinase activity. Using activity ratios to judge the extent of activation of cAMP-dependent protein kinase in vivo, it was found that isoproterenol-induced increases in cAMP protein kinase activity were similar in control and acutely-treated animals, but were reduced with repeated desipramine treatment. The extent of protein kinase activation was also elevated by both acute and repeated treatment in the absence of isoproterenol. In further studies, desipramine (10 microM) did not directly affect activation of the kinase by cAMP or maximum kinase catalytic activity. These results show that the concentration and extent of activation of cAMP protein kinase is altered following desipramine treatment in the rat pineal gland and that modulation of cAMP protein kinase may be a locus of regulation for desipramine-mediated reduction in noradrenergic responsiveness.

Antidepressants and protein kinases: inhibition of Ca2+-regulated myosin phosphorylation by fluoxetine and iprindole.

The effects of several antidepressant and antipsychotic agents on Ca2+-calmodulin-regulated myosin light chain phosphorylation were evaluated. At a concentration of 100 microM, the antidepressant agents buproprion, mianserin and maprotiline were ineffective; zimelidine, desipramine and imipramine produced 40-50% inhibition; and iprindole and fluoxetine produced 75-90% inhibition. The efficacies of iprindole and fluoxetine were similar to the phenothiazine antipsychotics chlorpromazine and trifluoperazine. Clozapine, an atypical antipsychotic and the butyrophenone haloperidol were relatively ineffective as myosin light chain phosphorylation inhibitors. IC50 values of the most effective agents were: trifluoperazine 16 microM, fluoxetine 28 microM, chlorpromazine and iprindole 56 microM. As with trifluoperazine, inhibition of myosin phosphorylation by iprindole was completely attenuated in the presence of exogenous calmodulin. However, a significant component (30%) of the inhibitory effect of fluoxetine was not reversible with calmodulin. These results show that some antidepressant agents, most notably iprindole and fluoxetine, are capable of antagonizing a calmodulin-regulated protein kinase through calmodulin inhibition; and in the case of fluoxetine, through an additional calmodulin-independent mechanism.

DMI, Wy-45,030, Wy-45,881 and ciramadol inhibit locus coeruleus neuronal activity.

Wy-45,030 and Wy-45,881 block the uptake of norepinephrine and serotonin in rat brain synaptosomal preparations and share several in vivo and in vitro effects with known tricyclic antidepressants. To further characterize their activity, these compounds were compared to desipramine and ciramadol in electrophysiological studies of their acute effects on noradrenergic neuronal activity. All four compounds inhibited locus coeruleus neuronal activity with a rank order of potency of desipramine greater than Wy-45,881 greater than Wy-45,030 greater than ciramadol. Administration of the alpha-adrenergic blocking drug, piperoxane, increased locus coeruleus firing rate after desipramine, Wy-45,030 and Wy-45-881. Pretreatment with naloxone prevented the reduction in locus coeruleus impulse flow observed after ciramadol administration but had no effect on the inhibition produced by Wy-45,030. Wy-45,030 and Wy-45,881, like classical antidepressants, appear to inhibit locus coeruleus neuronal firing by potentiating neuroinhibitory transmission of locus coeruleus neurons by blocking the uptake of norepinephrine into presynaptic terminals.

Suppression of histamine-induced adrenocorticotropic hormone release by antihistamines and antidepressants.

The antihistaminic activity of many antidepressant drugs is well documented in vitro but has not been investigated as thoroughly in vivo. In the course of an investigation of the roles of H1 and H2 receptors in histamine-induced adrenocorticotropic hormone (ACTH) release in rats, it was observed that several antidepressants were potent inhibitors of this response. Male Sprague-Dawley rats were injected with test drugs and then with histamine or histamine agonists. Serum ACTH concentrations were determined by radioimmunoassay. ACTH secretion was induced by both H1 and H2 receptor stimulation. Histamine-induced ACTH release was markedly attenuated by several H1 antihistamines, whereas the H2 antagonists were not as effective. The antidepressants imipramine, doxepin, mianserin, desipramine and amitriptyline suppressed histamine-induced ACTH release. However, iprindole and the antianxiety agent diazepam were without effect. ACTH release induced by histamine agonists was also diminished by pretreatment with some of these blocking agents.

On the mechanism of renin release by restraint stress in rats.

Restraint causes an increase in plasma renin activity (PRA) which is not affected by pretreatment with dl-propranolo (1 mg/kg IP) or sotalol (15 mg/kg IP). These doses of beta-adrenergic blocking agents are effective in suppressing the stimulation of PRA by isoproterenol. Large doses of dl-propranolol (10 mg/kg IP) and d-propranolol (5 mg/kg IP) attenuate the restraint-induced PRA increase. Adrenal demedullectomy does not affect the PRA response to restraint. Renal denervation blunts the PRA rise due to restraint, but not to direct stimulation by the beta-adrenergic agonist, isoproterenol. It is concluded that the increase in PRA during restraint stress in rats is not solely dependent on an intact renal sympathetic innervation. A significant portion of this stress-induced PRA increase appears to involve a non-adrenergic mechanism.

Plasma corticosterone and brain catecholamines in stress: effect of psychotropic drugs.

In nonstressed rats, subcutaneous administration of haloperidol (HAL) and large doses of diazepam (DZ) increased plasma corticosterone (CS). Hypothalamic norepinephrine (NE) was lowered significantly by desmethylimipramine (DMI), HAL and, to a lesser extent, by DZ and phenobarbital (PHB). In rats pretreated with either DZ, DMI, HAL or PHB the restraint-induced rise of CS was diminished, DZ being most potent. CPZ had a variable effect, slightly increasing or decreasing the CS response. Pretreatment (16 hr) with pargyline (PA) did not affect the CS rise to stress. The reduction of hypothalamic NE evoked by restraint was attenuated by DZ, and to a lesser extent, by PHB and HAL. Restraint of PA-treated rats did not lower the PA-elevated hypothalamic NE. The stress-induced increase in hypothalamic dopamine was prevented by CPZ and, partially, by PHB. It is emphasized that the net plasma CS and brain catecholamine changes in response to stress are dependent on the drug-induced neuroendocrine feedback state prevalent immediately before commencement of the stress procedure.

Physiological and biochemical concomitants of restraint stress in rats.

Restraint stress of 30 min increases plasma CS and lowers hypothalamic NE. Restraints of longer durations are associated with an attenuation of these changes. Daily repetitive restraint enhances the CS response on the second day and progressively diminishes it on subsequent days. Whole brain NE increases on the first day and decreases on Day 2 to 5. The CS response to acute restraint is similar in 5 different normotensive rat strains, but is enhanced in the genetically hypertensive SH rat, its normotensive backbreed WKY, and the DOCA hypertensive Sprague-Dawley rat. Comparison with other stressors (electric foot shock and novel environment) indicate that the responses to restraint are different at least in time course, if not qualitatively.

Plasma corticosterone following alterations of hypothalamic catecholamines in rats.

The role of central catecholamines in the regulation of resting ACTH secretion has been investigated by relating plasma corticosterone to changes in hypothalamic catecholamines after treating rats with various amine depleting agents. The hypothesis of a noradrenergic inhibitory control is not supported by the data since a correlation between hypothalamic catecholamine content and plasma corticosterone levels could not be established.