Biomedical subjects
S M Stahl
Publications and source records attributed to S M Stahl.
Neuroendocrine markers of serotonin responsivity in depression.
1. Studies of the biochemical mechanism of action of antidepressant drugs show that virtually all drugs, regardless of acute biochemical effects, result in the down regulation of CNS beta-1 adrenergic, serotonin-2 (5HT2), and perhaps 5HT1A receptors in rats in a time course which parallels the onset of antidepressant action in patients with major depressive disorder. 2. Recently, neuroendocrine techniques have been described which allow the study of 5HT receptor subtypes in man. These include fenfluramine-induced changes in ACTH, cortisol and prolactin secretion (perhaps for 5HT2 receptors) and ipsapirone-induced changes in ACTH and cortisol (for 5HT1A receptors). 3. Depressed subjects treated with antidepressants down regulate these markers of both 5HT2 and 5HT1A receptors in a time course consistent with their recovery from depression. 4. Studies in progress are attempting to demonstrate links between these receptor changes and clinical antidepressant responses.
Serotonin receptor down regulation by antidepressants: platelet and neuroendocrine markers in humans.
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Pharmacology: policy implications of new psychiatric drugs.
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Serotonin neuroscience discoveries usher in a new era of novel drug therapies for psychiatry.
Serotonin basic neuroscience discoveries are evolving at a very fast pace and are leading to innovations in clinical psychiatry and in drug development. Numerous novel pharmacological tools, each selective for a given serotonin receptor subtype, are being applied to several psychiatric disorders. The strategy employed is theory driven and hypothesis oriented, aiming for new drug development that selectively targets receptors that are rational sites for therapeutic actions. Thus, serotonin uptake inhibitors are targeting not only depression, but also obsessive-compulsive disorder (OCD). Serotonin1A agonists are targeting not only depression and anxiety, but also mixed anxiety depression. These and other agents selective for additional receptors are being tested in impulse control disorders; eating disorders; addictive disorders; and aggressive, violent, self-destructive, and suicidal behaviors. Serotonin research is an excellent example of how basic science discoveries in the 1990's "Decade of the Brain" are resulting in important advances in therapeutics for psychiatry.
5-Hydroxytryptamine (5-HT)-induced shape change in human platelets determined by computerized data acquisition: correlation with [125I]-iodoLSD binding at 5-HT2 receptors.
The 5-HT-induced shape change and subsequent aggregation of platelets provides a functional assay for 5-HT2 receptors. In the present study we describe a method to increase aggregometer sensitivity by digital conversion of the voltage produced by changes in light transmittance through a platelet suspension, thereby allowing accurate analyses of the primary shape-change response. The pharmacology of 5-HT-induced shape change was then compared with that of [125I]-iodoLSD binding in human platelets. 5-HT caused a dose-dependent change in platelet shape (maximum response 5 x 10(-6) M, EC50 10(-6) M). Furthermore, there was a significant correlation across a selection of drugs between IC50 values for inhibition of 5-HT-induced shape change and for inhibition of platelet binding of the 5-HT2 receptor ligand [125I]-iodoLSD. These results support the hypothesis that 5-HT-induced shape change and [125I]-iodoLSD binding in human platelets are mediated through the same receptor, and validate the methods of data acquisition described.
Cortisol and growth hormone responses to the 5-HT1A agonist gepirone in depressed patients.
The 5-HT1A agonist properties of gepirone were used to test for effects on serum cortisol levels in humans, 90 min after a 10 mg oral dose. Fourteen patients with major depression were tested in a single-blind, within-subjects, placebo design. Serum cortisol levels were significantly higher 90 min after gepirone compared to placebo (p less than 0.05). Baseline Hamilton depression ratings were correlated with the serum cortisol levels after acute administration of gepirone (r = 0.54, p less than 0.05), but not placebo. Cortisol levels after a 10 mg gepirone challenge were significantly (p less than 0.02) attenuated after 3-6 weeks chronic administration of gepirone. These preliminary findings suggest that relatively low doses of gepirone may stimulate human cortisol secretion in depressed patients, and cortisol levels after gepirone challenge may correlate with depression severity. Furthermore, a desensitization to gepirone's effects on cortisol may occur after chronic gepirone administration.
5HT2 receptor changes in rat cortex and platelets following chronic ritanserin and clorgyline administration.
Chronic administration of clorgyline or ritanserin to adult rats for 28 days followed by a 3 day drug-free period results in a significant decrease in 5HT2 receptor number (Bmax) in rat frontal cortex from 315.23 +/- 10.72 fmol/mg protein to 249.63 +/- 13.99 fmol/mg protein and 222.55 +/- 17.17 fmol/mg protein, respectively. On rat blood platelets, ritanserin significantly increases recept number from 26.18 +/- 3.83 fmol/mg protein to 50.94 +/- 7.96 fmol bound/mg protein, whereas clorgyline has no significant effect (21.32 +/- 4.78 fmol/mg protein). Following both drug regimens, the affinity (Kd) of the respective ligands for the receptor is not significantly different from controls: the mean Kd value of the three groups for [3H]ketanserin is 1.57 +/- 0.05 nM in cortex and 0.83 +/- 0.25 nM for [125I]iodolysergic acid diethylamide (LSD) on platelets. Clorgyline increases serotonin (5HT) and noradrenaline (NA) levels in cerebellum, and decreases 5-hydroxyindole acetic acid (5HIAA) and homovanillic acid (HVA): ritanserin does not change the levels of the amines or their metabolites. The data shows that platelet and brain changes are not comparable after ritanserin administration. The receptor binding data demonstrates that curve fitting to two data points provides information which is comparable to and as statistically robust as that obtained from eight point saturation curves. Thus, if pilot studies show that the data follows a rectangular hyperbola, two point assays (optimal at 0.1 Kd and 3 Kd) can be used to obtain estimates of Bmax and Kd.
The antiparkinsonian actions and pharmacokinetics of transdermal (+)-4-propyl-9-hydroxynaphthoxazine (+PHNO): preliminary results.
(+)-4-Propyl-9-hydroxynaphthoxazine (+PHNO) is a potent dopamine agonist that has been administered transdermally to four patients with Parkinson's disease and "on-off" fluctuations. Skin patches of increasing size were used to treat these patients, who also received infrequent doses of oral levodopa if required. The effect of +PHNO was measured as an increased duration of action of individual levodopa doses. The clinical effect measured in this way was directly proportional to the plasma concentrations of +PHNO achieved. The plasma concentrations of +PHNO began to rise 4-6 h after patch application and reached a steady state by 24 h. The final plasma concentration of +PHNO was proportional to the area of skin covered.
Effects of lorazepam on memory, attention and sedation in man: antagonism by Ro 15-1788.
In this study we examined the effects of lorazepam (2.0 mg PO) plus either placebo or one of three doses of the benzodiazepine antagonist Ro 15-1788 (0.3 mg, 1.0 mg or 3.0 mg IV) on measures of memory, attention and sedation. We found that lorazepam impaired verbal secondary memory performance, but also produced subjective and objective sedation; it increased reaction time, reduced critical flicker fusion thresholds and caused subjects to make more errors on a sustained attention task and rate themselves as drowsy. Ro 15-1788 dose dependently blocked the deficit in secondary memory produced by lorazepam, but also showed monotonic dose-related antagonism of its effects on indices of sedation (with the exception of the critical flicker fusion deficit, which was unaffected). These results demonstrate that lorazepam-induced cognitive deficits can be blocked by a benzodiazepine receptor antagonist. They also suggest that the memory deficits produced in this pharmacological model of organic amnesia are not readily dissociated from deficits in attention.
Hallucinogenic drugs are partial agonists of the human platelet shape change response: a physiological model of the 5-HT2 receptor.
We have assayed several phenylalkylamine and indolealkylamine hallucinogens, as well as structurally similar nonhallucinogens, for their effect on human platelet shape change, a physiological model for the central serotonergic 5-HT2 receptor. The hallucinogenic drugs lysergic acid diethylamide (LSD-25), N,N-dimethyltryptamine (N,N-DMT), 5-methoxy-N,N-dimethyltryptamine (5-MeODMT), 4-iodo-2,5-dimethoxyphenylisopropylamine (DOI), bufotenine, and mescaline all showed a characteristic 5-HT2 partial agonist effect on platelet shape change. Nonhallucinogens with structural similarity to hallucinogens did not share this profile. Lisuride, methysergide, and lysergic acid showed antagonism of 5-HT-induced shape change, but none were shape change agonists. Other "psychoactive" or mood-altering drugs (cocaine, amphetamine, phencyclidine) showed poor antagonism of 5-HT-induced platelet shape change. This work refines recent ideas that some of the behavioral effects of LSD-type hallucinogens in humans are due to their actions at 5-HT2 receptors and suggests that these hallucinogens are partial 5-HT2 agonists.
A strategy for measuring the therapeutic properties of new antiparkinsonian drugs, such as +PHNO, in patients with on-off fluctuations.
We describe a simple quantitative bedside method for assessing the dopaminergic properties of new therapeutic agents, namely, by documenting their duration of action in patients with Parkinson's disease who exhibit "on-off" fluctuations. This model represents a form of human dopaminergic "bioassay".
Therapeutic efficacy of a novel transdermal delivery system for (+)-PHNO in parkinsonian squirrel monkeys.
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Antiparkinsonian efficacy of a novel transdermal delivery system for (+)-PHNO in MPTP-treated squirrel monkeys.
We examined the ability of the antiparkinsonian agent (+)-4-propyl-9-hydroxynaphthoxazine (PHNO) to enter the systemic circulation in therapeutic concentrations after continuous transdermal absorption in squirrel monkeys rendered parkinsonian by MPTP. Direct subcutaneous administration of (+)-PHNO in the dose range of 2.5 to 20 micrograms/kg restored locomotor activity to levels seen in normal monkeys for approximately 1 hour. Application of transdermal patches capable of delivering, into an infinite sink, an estimated 2.6 micrograms/cm2/h of (+)-PHNO over a skin surface area of 4.78 to 19.12 cm2 also restored locomotor activity to the normal range during a 24-hour period. We suggest the use of transdermal application of PHNO as a novel drug delivery system for the improved management of Parkinson's disease.
Retraction: CSF monoamine metabolites in movement disorders and normal aging.
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Long-term motor stimulant effects of (+)-4-propyl-9-hydroxynaphthoxazine (PHNO), a dopamine D-2 receptor agonist: interactions with a dopamine D-1 receptor antagonist and agonist.
Rats were given continuous infusions of (+)-4-propyl-9-hydroxynaphthoxazine (PHNO, 5 micrograms/h), a dopamine D-2 receptor agonist, using subcutaneous implants of ALZET osmotic minipumps. It was observed that tolerance occurred to the motor stimulant effects of PHNO during the light cycle of each day, but not during the dark cycle. Rather, the motor stimulant actions of PHNO were gradually augmented during successive nights. Daytime tolerance to the stimulant actions of PHNO was reversed by a mild environmental stress or by administration of the D-1 receptor agonist, SKF 38393 (6 mg/kg i.p.). Co-administration of the dopamine D-1 receptor antagonist, (SCH 23390, 20 micrograms/h s.c. by ALZET osmotic minipumps), initially blocked the motor stimulant actions of PHNO and also attenuated the reversal of tolerance to PHNO produced by stress, without blocking the actions of stress on activity in vehicle-infused animals. These results indicate that tolerance to the behavioural effects of PHNO may result from a loss of activation of D-1 receptors by endogenous DA.
In vitro selectivity of agonists and antagonists for beta 1- and beta 2-adrenoceptor subtypes in rat brain.
A radioreceptor binding assay was developed to determine the selectivity of beta-adrenoceptor agents in rat brain. This was achieved by using the highly selective unlabelled antagonists CGP 20712A and ICI 118-551 to block beta 1- or beta 2-sub-populations respectively in rat cerebral cortex membranes. This permitted the selective labelling of beta-adrenoceptors with the antagonist (-)-[125I]pindolol. Using this method, compounds could be routinely screened and selectivity profiles for binding in the CNS determined with a high degree of sensitivity and resolution.