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Biomedical subjects

M Leyton

Publications and source records attributed to M Leyton.

33 records · Page 2Linked to original sources
PubMed1997

Differences between males and females in rates of serotonin synthesis in human brain.

Rates of serotonin synthesis were measured in the human brain using positron emission tomography. The sensitivity of the method is indicated by the fact that measurements are possible even after a substantial lowering of synthesis induced by acute tryptophan depletion. Unlike serotonin levels in human brain, which vary greatly in different brain areas, rates of synthesis of the indolamine are rather uniform throughout the brain. The mean rate of synthesis in normal males was found to be 52% higher than in normal females; this marked difference may be a factor relevant to the lower incidence of major unipolar depression in males.

Adult↗
PubMed1997

The effect of tryptophan depletion on mood in medication-free, former patients with major affective disorder.

Acute tryptophan depletion (ATD) induces transient clinical relapse in medicated patients with major affective disorder. Our objective was to determine whether this effect persists once patients are euthymic and off antidepressants. Thus, we examined the effects of ATD in fully remitted, medication-free, former patients with major depression (n = 14). ATD had no significant effect on mood. These results suggest that the previous report that ATD substantially lowers mood in pharmacologically treated patients reflects a reversal of mechanisms involved in the therapeutic effects of antidepressants. Alternatively, ATD might induce clinical relapse only in subgroups that have yet to be identified.

Adult↗
PubMed1997

Stress and depressed mood in medical students, law students, and graduate students at McGill University.

PURPOSE: To investigate stress in medical students, law students, and graduate students at McGill University using a well-validated measure, the Derogatis Stress Profile (DSP). METHOD: The DSP was administered to the medical students in November and December 1994. For comparison, the DSP was also administered to the undergraduate law students and the graduate students. In November 1995 the DSP was administered to the first- and second-year medical students. Results were analyzed with a number of statistical methods. RESULTS: The response rates for the medical students, the law students, and the graduate students in 1994-95 were 70%, 96%, and 43%, respectively. The response rate for the first- and second-year medical students in 1995-96 was 57%. The medical students had subjective feelings of stress that are marginally above population norms, but their total-stress scores (related to environmental factors, personality mediators, and emotional responses) were below those of the general population, the law students, and the graduate students. Elevated depression scores in a minority of the students did not seem to be related directly to the stresses associated with medical school. The transition from basic science training to clinical training was associated with an increase in stress and depressed mood. CONCLUSION: Medical students are not greatly stressed relative to other groups, hence other explanations must be sought for the elevated levels of depression in some students. One situation in which stress appears to be particularly important is in the transition from basic science training to clinical training. Targeted interventions may be an effective way of dealing with this problem.

Adult↗
PubMed1996

Cardiovascular, neuroendocrine, and monoaminergic responses to psychological stressors: possible differences between remitted panic disorder patients and healthy controls.

Both clinical symptomatology and stress research suggest that panic attacks might be partially attributable to exaggerated psychophysiological responses to environmental stressors. In the present study, we aimed to explicitly test this idea by measuring the physiological responses to a mild psychological stressor in both healthy controls (n = 8) and fully remitted, medication-free panic disorder patients (n = 8). One hour before the stressor, former patients, compared to healthy controls, exhibited higher diastolic blood pressure. From a blood sample taken 30 min before the stressor, patients, compared to controls, had lower paroxetine platelet binding site densities. During the stressor, patients, compared to controls, had greater increases in plasma levels of cortisol. These preliminary findings suggest that remitted panic disorder patients might have disturbed physiological responses to mild psychological stressors. These disturbances might be related to the development of future episodes.

Adult↗
PubMed1996

Acute and repeated activation of male sexual behavior by tail pinch: opioid and dopaminergic mechanisms.

We studied the effect of tail pinch on male sexual behavior and its neurochemical basis. Male rats were gonadectomized and maintained on low doses of testosterone propionate (20.0 micrograms/day). Tail pinch significantly increased the percentage of males that mounted, intromitted, and ejaculated within a 30-min test, and these increases were attenuated by both pimozide (1.0 mg/kg, i.p.) and by naloxone (0.5, 1.0, and 2.0 mg/kg, s.c.). Moreover, tail pinch in the presence of an estrous female led to significantly increased female-directed behavior 48 h later during a test without tail pinch. Repeated tail pinch tests led to progressively more sexual activity, and the development of this behavioral sensitization was prevented by naloxone. These findings suggest that tail pinch increases the salience of the incentive characteristics of the female. Furthermore, during subsequent tests, with or without tail pinch, the increased salience of the female remains, as measured by the continued increases in sexual activity. These acute and sensitized behavioral increases might result from tail pinch-induced activation of the midbrain dopamine system via an opioid mechanism; either preventing tail pinch-induced dopamine activation (by an opioid antagonist) or blocking the effects of dopamine activation (by a dopamine antagonist) attenuated the long-term facilitation of sexual behavior seen after pairing the female with tail pinch.

Animals↗
PubMed1995

Psychotic symptoms and vulnerability to recurrent major depression.

The demographic characteristics and psychiatric course of primary unipolar depressed patients, either with or without psychotic features, were compared in a retrospective study. 15% (25/165) of the patients had had at least one episode of psychotic depression. Compared with the 140 non-psychotic patients, the psychotic patients were more likely to be female, had been ill for significantly longer and endured significantly more episodes of depression. The greater number of episodes was not attributable to the greater length of illness. Various reasons for the group differences are examined. Particular consideration is given to the possibility that a propensity for recurrent psychotic major depression might be related to sensitized dopamine neurons.

Adult↗
PubMed1992

The stimulation of central kappa opioid receptors decreases male sexual behavior and locomotor activity.

Systemic injections of the kappa (kappa) opioid receptor agonist U-50,488H decreased male sexual behavior, locomotor activity, body temperature and bodily grooming, and induced body flattening. The U-50,488H-induced inhibitions of male sexual behavior were prevented by systemic injections of naloxone and by intra-cranial injections of the kappa opioid antagonist nor-binaltorphimine (NBNI). Injections of NBNI to either the ventral tegmental area (VTA) or the nucleus accumbens septi (NAS) increased female-directed behavior, and prevented the U-50,488H-induced decreases in female-directed behavior. Intra-VTA NBNI prevented U-50,488H-induced decreases in the mean number of ejaculations, intra-NAS NBNI prevented U-50,488H-induced increases in copulation latencies. Intra-medial preoptic area (mPOA) injections of NBNI increased female-directed behavior, and attenuated U-50,488H-induced decreases in female-directed behavior as well as U-50,488H-induced increases in both copulation and ejaculation latencies. Injections of NBNI dorsal to the mPOA were ineffective. Two of 26 days following the central injection of NBNI, systemic injections of U-50,488H remained behaviorally ineffective, leaving both sexual behavior and locomotor activity undiminished. These results suggest that the stimulation of central kappa opioid receptors inhibits sexual behavior in the male rat; perhaps endogenous kappa opioid agonists induce sexual refractory periods.

3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cycloh↗
PubMed1992

U-50,488H into A10 reduces haloperidol-induced elevations of accumbens dopamine.

Injections of kappa (k) opioid agonists into the A10 ventral tegmental area (VTA) induce behavioral inhibitions and decreased interest in incentive stimuli, behavioral changes indicative of decreased mesolimbic dopamine (DA) transmission. In seeming contrast, three separate laboratories have recently reported that intra-VTA injections of k agonists do not affect nucleus accumbens septi (NAS) basal levels of extracellular DA. In the present experiment, we investigated whether intra-VTA injections of a k agonist would decrease pharmacologically-stimulated increased levels of extracellular NAS DA. It was found that intra-VTA injections of the k agonist U-50,488H significantly attenuated haloperidol-induced elevations of DA, as measured by in vivo microdialysis.

3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cycloh↗
PubMed1992

[The evaluation of transabdominal pelvic fluid collections. Clinical cases].

Two cases of pelvic collections of different etiology, admitted in the isolation unit of the Gynecology and Obstetrics Department of Hospital del Salvador are presented. Both were resolved by means of ultrasound transabdominal puncture, the first a tubo-ovarian abscess, in which there was placed a percutaneous drainage, and the second, a Residual Lutein Cyst, (Subsequent' to an Ectopic Pregnancy resolved by surgery) by means only of punction. In the first case (tubo-ovarian abscess) the patient became pregnant 2 months after de punction having actually a physiologic evolution. In the second case the patient is asymptomatic and has normal medical controls.

Abscess↗
PubMed1990

Preexposure to foot-shock sensitizes the locomotor response to subsequent systemic morphine and intra-nucleus accumbens amphetamine.

The effect of repeated exposure to foot-shock on locomotor activity was examined by testing rats in the shock boxes for one hour following shock exposure. Early in testing activity was elevated relative to the nonshocked control group, between 40-60 min following shock. Over days this period of elevated activity occurred sooner in time and lengthened in duration. When these animals were tested in the absence of shock, those preexposed to shock were more active following either saline or morphine (0.5 and 5.0 mg/kg IP) injections. In a second experiment, elevated spontaneous and morphine-induced activity was also found when rats had been preexposed to shock in boxes distinct from the activity test boxes. In a final experiment, animals preexposed to shock were tested after bilateral infusions of either amphetamine (5 and 10 micrograms/microliters/side) or morphine (5 micrograms/microliters/side) into the nucleus accumbens (NAS). On the amphetamine tests, previously shocked animals were significantly more active than control animals. In contrast, intra-NAS infusions of morphine failed to differentiate between the two groups. These results suggest that repeated mild foot-shock sensitizes the mesolimbic dopamine system by mechanisms similar to those mediating the sensitized behavioral and dopaminergic responses seen following repeated opioid or stimulant administration.

Amphetamine↗
PubMed1984

Perceptual organization as nested control.

It is argued here that perceptual organization is the structuring of environmental stimuli into nested structures of control. This view is derived from our proposal that the perceptual system forces any stimulus set to have the algebraic structure G of a machine, and that G is given a specific factorization sequence, G = G1 X G2 X ... X Gn, induced by dynamical systems criteria which the organism imposes on the environment. An investigation into these factorization sequences reveals that any such sequence is split into two subsequences, one structuring the way in which the stimulus set can change under external action, and the other describing the way in which the set is perceived as internally generated. An examination of the nested control structure of the latter yields a theory of grouping. The external and internal sequences are shown to be strongly related to each other in that the symmetry axes of the internal sequence are eigenspaces of the most stable subgroup factors of the external sequence. It is claimed that cartesian reference frames are subsequences of the full sequences. Using these principles, a unified theory is offered of several apparently quite separate perceptual areas; e.g. Marr-Nishihara shape perception, gestalt grouping, the orientation-and-form problem, and motion perception. The final claim is that planning hierarchies have the same dynamically-structured algebraic sequences and therefore that the study of perceptual organization should, in a very deep sense, be formally equivalent to the study of planning.

Cognition↗
PubMed1981

[Potter syndrome].

Explore the source record for details and available documents.

Abnormalities, Multiple↗
PubMed1978

Observations on the treatment of an acute attack of migraine.

In 1976, 310 patients attended the Princess Margaret Clinic for treatment of an acute headache. 90% were either symptom-free or had only slight residual headache after 4 h. The treatment given was metaclopramide and an effervescent analgesic. 69% of patients had some form of sedation and 10% ergotamine tartrate. Those patients who had treatment between 6 and 12 h following the onset of an attack had significantly fewer attacks in the next 7 days. Patients who slept during an attack, with a sedative where indicated, recovered more quickly than those who did not sleep. The depth of sleep did not affect the rate of recovery. A higher percentage of patients with migraine compared with those with tension headache were either symptom-free or had only slight residual headache on leaving.

Acute Disease↗