Transmitter amines in depression

Diurnal patterns of serotonin, 5-hydroxyindoleacetic acid, tryptophan and fibrinolytic activity in blood of depressive patients and healthy volunteers

Diurnal changes of serotonin-related factors in whole blood and fibrinolytic activity were determined in depressed patients and healthy controls. Whole blood serotonin concentration of depressed patients showed marked changes throughout daytime, with maximum values in the evening and lowest values in the morning, whereas its metabolite 5-HIAA followed a contrary pattern. The circadian rhythm of 5-HT and 5-HIAA in the control group was quite different from depressed patients. Plasma levels of tPA decreased from 12:30 to 16:30. Concentrations of free plasminogen activator inhibitor (PAI-1) and complex of tPA-PAI-1 decreased from 8:30 to 16:30. Plasma levels of total PAI-1 decreased from 8:30 to 16:30. Plasma levels of the fibrinolytic parameters may be lower in depressive patients than in normal controls. These results support the changes in the circadian rhythm of serotonin and its related substances in the blood of depressive patients.

Serotonin function in affective disorders

The evidence indicating a specific abnormality of brain 5-HT function in depressed patients is reviewed. Biochemical studies have indicated that low plasma levels of tryptophan are unlikely to be the primary 'cause' of depression or of abnormal brain 5-HT function in depression. However, there may be a reduction of 5-HT synthesis or function in the brains of depressed patients and the uptake of 5-HT into platelets from depressed patients is consistently reduced. Neuroendocrine studies have suggested that various groups of depressed patients may exhibit different types of abnormal 5-HT-mediated responses. It is important to distinguish between the acute and chronic pharmacological effects of antidepressant treatment, which may account for the latency seen between onset of therapy and full clinical effect. Clinical studies have provided further evidence that 5-HT is implicated in the causation and treatment of depression, as both 5-HT precursors and selective inhibitors of 5-HT uptake are effective in the treatment of depression. Furthermore, inhibition of 5-HT synthesis can block the effect of antidepressant compounds. It is concluded that 5-HT function is decreased during depression, and that this carries important implications for the pharmacology of antidepressant drugs.

A test of possible cognitive and environmental influences on the mood lowering effect of tryptophan depletion in normal males

In a previous study we found that a tryptophan-deficient amino acid mixture, designed to lower tissue tryptophan and thus brain 5-hydroxytryptamine (5HT) levels, caused a rapid (5 h) lowering of mood in normal males. Because of the importance of this evidence indicating a direct causal connection between low 5HT and low mood, we have now investigated other possible explanations for the mood lowering effect. Research strongly supports the involvement of environmental setting and cognition in the production and experience of emotions. Therefore we investigated how these factors might influence the mood-lowering effects of tryptophan depletion. In an instructional manipulation subjects were either supplied or not supplied with information designed to account for any possible peripheral sensations that might be related to depressive affect. In an environmental manipulation subjects were exposed either to a supportive and comfortable atmosphere (positive environment), or an unrewarding and unstimulating environment (negative environment). In the control group, which received a balanced amino acid mixture, the positive and negative environments had the expected effects on the scores of the Multiple Affect Adjective Checklist, thus indicating the effectiveness of these procedures. In the tryptophan depletion group neither the instructional nor the environmental manipulation had any influence on the mood lowering effect. It may be that tryptophan depletion lowers mood in normal males because low 5HT influences mood directly rather than via cognitive processes. Our data strongly support the idea that 5HT exerts an effect on mood and that low 5HT may, in some patients, be an important factor contributing to the etiology of clinical depression.

The effect of selective 5-hydroxytryptamine uptake inhibitors on 5-methoxy-N,N-dimethyltryptamine-induced ejaculation in the rat

The ejaculatory response and the 5-hydroxytryptamine (5-HT) behavioural syndrome induced by 5-methoxy-N,N-dimethyltryptamine (5-MeODMT) (3 mg kg-1 i.p.) were studied following acute and repeated treatment of rats with the selective uptake inhibitors of 5-HT, fluoxetine, zimeldine, alaproclate, and citalopram. The oral doses used were based on the respective ED50 values for uptake inhibition. Acute doses of fluoxetine and zimeldine significantly reduced the ejaculatory response when given 48 h before 5-MeODMT. This blockade was prevented by treatment of the rats with the postsynaptic 5-HT receptor antagonist methergoline. An acute dose of fluoxetine given 7 and 14 days before 5-MeODMT significantly enhanced the ejaculatory response. On day 24, the response returned to the control level. Repeated treatment every second day (5 times over 9 days and 10 times over 19 days) with fluoxetine caused a longer blockade of the ejaculatory response and the sensitization of the response came later than after an acute dose. Parallel with the ejaculatory response three other components of the 5-HT behavioural syndrome also decreased significantly. Acute doses of alaproclate and citalopram significantly blocked the ejaculatory response at 1 h, but they failed to affect the response at any other time point after either acute or repeated treatment. Neither did these drugs attentuate the 5-HT syndrome. It is concluded that acute and repeated treatment of rats with different selective 5-HT uptake inhibitors does not produce a common alteration in 5-HT2-receptor functions.

Central serotonergic responses and behavioural adaptation to repeated immobilisation: the effect of the corticosterone synthesis inhibitor metyrapone

Rats were immobilised for 2 h/day. Twenty-four hours after the 1, 3 or 7 immobilisation periods they were injected with the 5HT agonist 5-methoxy-N,N-dimethyltryptamine (5MeODMT; 5 mg/kg i.p.) and behavioural responses (i.e. hind limb abduction, forepaw treading, head weaving, tremor, Straub tail) compared with those of a control group. As we have previously observed after 7 (but not after 1 or 3 immobilisations) forepaw treading and tremor were enhanced and the other responses unaffected. Pretreatment with metyrapone (a corticosterone synthesis inhibitor 150 mg/kg i.p., 3 h before each immobilisation) did not affect the above responses to 1 immobilisation, increased tremor after 3 immobilisations and also increased forepaw treading, hind limb abduction and Straub tail after 7 immobilisations but decreased head weaving under the latter conditions. Metyrapone without immobilisation had no effect on responses to 5MeODMT. Twenty four hours after 1 or 3 (but not 7) immobilisation periods, rats placed for the first time in an open field showed less locomotion and rearing and more defaecation than control animals. Rats also given metyrapone exhibited normal open field behaviour after only 3 immobilisations. The drug also accelerated the return to normal on repeated immobilisation of the impairment of food intake and growth rate which occurred after a single immobilisation. The results as a whole suggest that metyrapone promotes behavioural adaptation to repeated immobilisation and that this is associated with enhanced postsynaptic responses to 5HT. These findings suggest that immobilisation stress-induced changes might be relevant as an animal model for depression which incorporates reported biochemical abnormalities in the illness and is of relevance to proposals concerning its precipitation by stress.

Mood and the menstrual cycle

A majority of women are aware of menstrual cycle-related changes in mood and behaviour. Psychiatric disorders may also be influenced by the menstrual cycle. A premenstrual tension syndrome has been described. Research into the prevalence, aetiology and management of this condition has been hampered by additions and alterations to the original description and methodological difficulties involved in menstrual cycle research. Biological, psychological and sociological theories have been proposed to explain menstrual cycle-related mood changes. Our own studies have found evidence of ovarian steroid disturbances, and impaired psychological functioning in women with the premenstrual syndrome. Therapeutic approaches must consider both aspects. Medication often makes the patient more accessible and receptive to regimens aimed at increasing coping skills. More vigorous research into this disorder is needed.

The effect of amitriptyline treatment on the growth hormone response to apomorphine

The growth hormone response to subcutaneous administration of the dopamine agonist apomorphine (0.005 mg/kg) was assessed in six normal male subjects before and at the end of a course of amitriptyline. Amitriptyline treatment significantly reduced the growth hormone response to apomorphine, confirming the findings of an earlier study in depressed patients. The way in which amitriptyline attenuates the effect of apomorphine is not clear. Direct blockade of dopamine receptors in the hypothalamus is a possibility, but long-term amitriptyline treatment could result in adaptive changes in the monoamine pathways which control GH release.