Neurotransmitters and depression Too much, too little, or too unstable?

Le sommeil de sujets dépressifs endogenes avant, pendant et apres un décalage des horaires de sommeil

Cette étude décrit la structure et l'organisation temporelle du sommeil de 5 sujets dépressifs endogènes qui participèrent à un processus de décalage en avance de 5 heures des horaires de sommeil maintenu pendant deux semaines.

Comparée à ces témoins du même âage, I'architecture du sommeil est, chez les dépressifs avant décalage, très perturbée avec, notamment, fragmentation et inefficacité du sommeil, réduction du taux de sommeil lent et raccourcissement de la latence du sommeil paradoxal. L'organisation temporelle semble traduire, elle, une lutte entre tendance au sommeil lent et tendance au sommeil paradoxal.

Le sommeil des mêmes sujets s'est pratiquement normalisé pendant et surtout après le decalage des horaires de sommeil, exceptée la persistance de la réduction importante de la latence du sommeil paradoxal.

Il serait ainsi possible d'associer la dépression à une désynchronisation entre rythmicités contrôlant sommeil lent, sommeil paradoxal et d'autres rythmes circadiens. Une resynchronisation forcée par décalage des horaires de sommeil pourrait alors rendre compte des améliorations cliniques et biologiques qui ont été observées.

Aquatic blues: modeling depression and antidepressant action in zebrafish

Depression is a serious psychiatric condition affecting millions of patients worldwide. Unipolar depression is characterized by low mood, anhedonia, social withdrawal and other severely debilitating psychiatric symptoms. Bipolar disorder manifests in alternating depressed mood and 'hyperactive' manic/hypomanic states. Animal experimental models are an invaluable tool for research into the pathogenesis of bipolar/unipolar depression, and for the development of potential treatments. Due to their high throughput value, genetic tractability, low cost and quick reproductive cycle, zebrafish (Danio rerio) have emerged as a promising new model species for studying brain disorders. Here, we discuss the developing utility of zebrafish for studying depression disorders, and outline future areas of research in this field. We argue that zebrafish represent a useful model organism for studying depression and its behavioral, genetic and physiological mechanisms, as well as for anti-depressant drug discovery.

Performance on a Visual Sustained Attention and Discrimination Task is Associated with Urinary Excretion of Norepineprhine Metabolite in Children with Attention-Deficit/Hyperactivity Disorder (AD/HD)

The degree of association between performance on a sustained attention task requiring visual discrimination and urinary excretion of catecholamine metabolites was examined in a cohort of 6- to 12-year-old children (n = 31) strictly selected and diagnosed with attention-deficit/hyperactivity disorder (AD/HD) according to DSM-IV and other strict criteria. Sustained visual attention and discrimination were measured using the Test of Variables of Attention (T.O.V.A.). Urinary excretion of dopamine (DA) and norepinephrine (NE) metabolites was measured by reversed high-pressure liquid chromatography (HPLC). Pearson product-moment correlations were used to investigate the relationship between T.O.V.A. errors of omission (OMM), errors of commission (COM), response time (RT), and response time variability (RTV) and catecholamine metabolites of DA and NE. All T.O.V.A. indexes under investigation were significantly correlated with urinary excretion of NE metabolites, but correlations were low-to-moderate in magnitude (.37-.50). In contrast, there were no statistically significant correlations between T.O.V.A. indices and DA metabolites. These findings and their concordance with past research in human adults and animals, as well as theoretical issues associated with the present results, are discussed.

Depression as a spreading adjustment disorder of monoaminergic neurons: a case for primary implication of the locus coeruleus

A model for the pathophysiology of depression is discussed in the context of other existing theories. The classic monoamine theory of depression suggests that a deficit in monoamine neurotransmitters in the synaptic cleft is the primary cause of depression. More recent elaborations of the classic theory also implicitly include this postulate, other theories of depression frequently prefer to depart from the monoamine-based model altogether. We suggest that the primary defect emerges in the regulation of firing rates in brainstem monoaminergic neurons, which brings about a decrease in the tonic release of neurotransmitters in their projection areas, an increase in postsynaptic sensitivity, and concomitantly, exaggerated responses to acute increases in the presynaptic firing rate and transmitter release. It is proposed that the initial defect involves, in particular, the noradrenergic innervation from the locus coeruleus (LC). Dysregulation of the LC projection activities may lead in turn to dysregulation of serotonergic and dopaminergic neurotransmission. Failure of the LC function could explain the basic impairments in the processing of novel information, intensive processing of irrational beliefs, and anxiety. Concomitant impairments in the serotonergic neurotransmission may contribute to the mood changes and reduction in the mesotelencephalic dopaminergic activity to loss of motivation, and anhedonia. Dysregulation of CRF and other neuropeptides such as neuropeptide Y, galanin and substance P may reinforce the LC dysfunction and thus further weaken the adaptivity to stressful stimuli.

Depression as a spreading neuronal adjustment disorder

The outlines of a theory of the pathophysiology of depression are presented. The classic monoamine theory of depression as well as its more recent elaborations suggests that a deficit in monoamine neurotransmitters in the synaptic cleft is the primary cause of depression. We suggest that the primary defect emerges in the regulation of firing rates in brainstem monoaminergic neurons, which brings about a decrease in the tonic release of neurotransmitters in their projection areas, an increase in postsynaptic sensitivity and, concomitantly, exaggerated responses to acute increases in presynaptic firing rate and transmitter release. We propose that the initial defect involves, in particular, the noradrenergic innervation from the locus coeruleus, which in turn leads to dysregulation of 5-HT-ergic and dopaminergic neurotransmission.

The depolarization block hypothesis of neuroleptic action: implications for the etiology and treatment of schizophrenia

Antipsychotic drugs are known to block dopamine receptors soon after their administration, resulting in an increase in dopamine neuron firing and dopamine turnover. Nonetheless, antipsychotic drugs must be administered repeatedly to schizophrenics before therapeutic benefits are produced. Recordings from dopamine neurons in rats have revealed that chronic antipsychotic drug treatment results in the time-dependent inactivation of dopamine neuron firing via over-excitation, or depolarization block. Furthermore, the clinical profile of the response to antipsychotic drugs appears to correspond to the dopamine system affected: antipsychotic drugs that exert therapeutic actions in schizophrenics inactivate dopamine neuron firing in the limbic-related ventral tegmental area, whereas drugs that precipitate extrapyramidal side effects cause depolarization block of the motor-related substantia nigra dopamine cells. One factor that remains unresolved with regard to the actions of antipsychotic drugs is the relationship between dopamine turnover and depolarization block--i.e., why does a significant level of dopamine release or turnover remain after antipsychotic drug treatment if dopamine cells are no longer firing? We addressed this question using an acute model of neuroleptic-induced depolarization block. In this model, dopamine cells recorded in rats one month after partial dopamine lesions could be driven into depolarization block by the acute administration of moderate doses of haloperidol. However, similar doses of haloperidol, which were effective at increasing dopamine levels in the striatum of intact rats, failed to change dopamine levels in lesioned rats. This is consistent with a model in which neuroleptic drugs exert their therapeutic effects in schizophrenics by causing depolarization block in DA cells, thereby preventing further activation of dopamine neuron firing in response to external stimuli. Thus, attenuating the responsivity of the dopamine system to stimuli may be more relevant to the therapeutic actions of antipsychotic drugs than receptor blockade or decreases in absolute levels of dopamine, which could presumably be circumvented by homeostatic adaptations in this highly plastic system.

Catecholamines and diagnoses in children

Theoretically, noradrenergic (NA) function may be lower in subjects with undersocialized conduct disorder (CDU) and higher in subjects with anxiety/depressive disorder. To test this hypothesis, diagnostic and 24-hour urine catecholamine measures were compared between subjects with plasma dopamine-beta-hydroxylase (D beta H) activities less than 6 mumoles/min/L (low D beta H group) and greater than 15 mumoles/min/L (high D beta H group). Several measures relating to norepinephrine metabolism were lower in the low D beta H group, and the low D beta H group had more diagnoses of CDU and fewer anxiety and depressive disorder diagnoses. Comparisons between clinical and biological measures within each of the D beta H groups were also consistent with the hypothesized relationship between NA function, CDU, and anxiety/depressive disorder.

Norepinephrine and (Na+, K+)-ATPase: evidence for stabilization by lithium or imipramine

These experiments examined the effects of lithium and imipramine on the regulation by norepinephrine in vivo of (Na+, K+)-ATPase in brain and heart. The binding of ouabain and the activity of K+-phosphatase were used as indices of (Na+, K+)-ATPase. In the cerebral cortex, imipramine prevented, and lithium reduced, the increase in (Na+, K+)-ATPase associated with repeated injections of yohimbine. Imipramine and yohimbine had synergistic effects on the increased release of norepinephrine and on decreased binding to beta-receptors. Effects on the binding of beta-noradrenergic receptors suggested that imipramine partially reduced stimulation of ATPase by reducing the maximum effect of beta-receptors, while the effect of lithium may have involved a reduction in the exposure of receptors to norepinephrine. Imipramine also increased (Na+, K+)-ATPase in the cerebral cortex of reserpine-treated rats. These results suggest that lithium and imipramine, by different mechanisms, can stabilize fluctuations in the physiological consequences of binding to noradrenergic receptors.

[Correlation of "latent hyperthyroidism" with psychological and somatic changes]

The study reported here was undertaken to establish the degree to which a person in a preclinical state of hyperthyroidism, with (by definition) euthyroid T3 and T4 levels but suppressed TRH on testing, already exhibits psychological changes and clinical symptoms. Two groups of 20 patients each, with clear clinical and preclinical hyperthyroidism (as defined by laboratory parameters), were studied, as well as a group of 20 controls. The subjects' psychological state of mind was investigated using self-rating scales, including the state-trait-anxiety inventory (STAI), "Befindlichkeits"-Skala (Bf-S'), depression scale (D-S'), and a list of adjectives (EWL-K) with 14 different aspects of affective moods. Cognitive achievements were evaluated using the d2 test. Subjects were examined for somatic symptoms in accordance with Crooks' index of hyperthyroidism. The results clearly showed that typical psychological and somatic changes are already present in preclinical hyperthyroidism, these changes being partly identical with those of definite hyperthyroidism. In both patient groups, a significant increase in anxiety, a sense of not feeling well, and emotional irritability were found, as well as a tendency towards depressiveness, and an increased lack of vitality and activity. Attentiveness and concentration in both patient groups were lower than in the control group. Both patient groups showed the same prevalence of symptoms, such as palpitations, preference of cold over heat, excessive sweating, nervousness, fine digital tremor, and increased heart rate. With regard to the results, the diagnosis "preclinical hyperthyroidism" thus gains importance. Further prospective studies are required to answer the question whether antithyroidal treatment will influence the described psychological and somatic state of patients with preclinical hyperthyroidism.

Indices of noradrenergic output in depression

Concentrations of plasma norepinephrine (NE) and plasma-3-methoxy-4-hydroxyphenylglycol (MHPG), blood pressure, and heart rate were measured on 2 days in 25 depressed patients and 25 controls. Comparisons were made between patients and controls, and also between days for both groups, to determine the short-term stability of these measures. The means of the plasma and urinary noradrenergic metabolite measures were not significantly different between groups. The variance of plasma MHPG, plasma NE, and mean blood pressure was greater in the depressed patients than in controls. Blood pressure, plasma MHPG, and plasma NE were relatively stable as suggested by the significant correlations between the 2 days for each of these variables. Plasma NE, plasma MHPG, and the sum of the deaminated urinary metabolites (MHPG and vanillylmandelic acid) were significantly intercorrelated. These results support other data in suggesting that plasma concentrations of NE and MHPG may be useful measures of noradrenergic activity, but may not consistently distinguish depressed patients from controls.

Changes in amphetamine-induced anorexia and stereotypy during chronic treatment with antidepressant drugs

Amphetamine-induced anorexia and stereotyped behaviour were studied in rats, following pretreatment with the antidepressants DMI, inprindole and mianserin. A complex drug-dependent and dose-dependent pattern of results was obtained. Acute pretreatment with DMI and iprindole enhanced amphetamine anorexia and stereotypy; at high doses only, the enhancement of anorexia disappeared during chronic treatment. Mianserin had no effects acutely, but chronic treatment with high doses attenuated anorexia and enhanced stereotypy. High doses of all three drugs attenuated anorexia and enhanced stereotypy during withdrawal. The most parsimonious account of these results is that the acute affects of DMI and iprindole are artefactual, and that chronic administration of all three antidepressants increased dopaminergic function and decreased beta-adrenergic function.

Melanin: the organizing molecule

The hypothesis is advanced that (neuro)melanin (in conjunction with other pigment molecules such as the isopentenoids) functions as the major organizational molecule in living systems. Melanin is depicted as an organizational "trigger" capable of using established properties such as photon-(electron)-phonon conversions, free radical-redox mechanisms, ion exchange mechanisms, and semiconductive switching capabilities to direct energy to strategic molecular systems and sensitive hierarchies of protein enzyme cascades. Melanin is held capable of regulating a wide range of molecular interactions and metabolic processes primarily through its effective control of diverse covalent modifications. To support the hypothesis, established and proposed properties of melanin are reviewed (including the possibility that (neuro)melanin is capable of self-synthesis). Two "melanocentric systems"--key molecular systems in which melanin plays a central if not controlling role--are examined: 1) the melanin-purine-pteridine (covalent modification) system and 2) the APUD (or diffuse neuroendocrine) system. Melanin's role in embryological organization and tissue repair/regeneration via sustained or direct current is considered in addition to its possible control of the major homeostatic regulatory systems--autonomic, neuroendocrine, and immunological.

Chronic in vivo treatment with desmethylimipramine and mianserin does not alter adenosine A-1 radioligand binding in rat cortex

Antidepressants and electroconvulsive shock therapy (ECS) have been reported to alter adenosine-sensitive adenylate cyclase responses in rat brain, suggesting an involvement of the purine in the mechanisms by which antidepressants and antidepressant therapy produce their clinical effects. Chronic (14-21 days, 10 mg/kg/day by Alzet minipump) treatment with desmethylimipramine (DMI) and mianserin, while producing changes in beta-adrenoceptor (DMI) and serotonin-2 (DMI and mianserin) radioligand binding similar to those reported in the literature, has no effect on adenosine A-1 radioligand binding.

Evidence suggesting that DMI-induced resistance to extinction is not mediated by the dorsal noradrenergic bundle

Rats were trained to press a lever for food rewards, then given a 5 week break, followed by a single extinction session. Animals which received 14 daily desmethylimipramine (DMI) injections, ending 4 days before the extinction session, showed resistance to extinction; no effect was seen in animals which received DMI during acquisition. The opposite pattern of results would be predicted if the effect were mediated by changes in the efficacy of the dorsal noradrenergic bundle.

Hyperactivity induced in rats by long-term isolation: further studies on a new animal model for the detection of antidepressants

Male rats isolated at the time of calcification of the incisors show after 10 months of social deprivation a marked and sustained increase in locomotor activity together with other behavioural changes. The ages of separation as well as the prolonged isolation period appear to be critical with regard to the stability of the behavioural syndrome and to the sensitivity of the rats to different pharmacological treatments. The locomotor activity of solitary housed rats is selectively blocked after acute treatment with several antidepressants which are inactive according to the traditional laboratory procedures for detecting the activity of this class of drugs. Handling of the isolated animals for 30 consecutive days produces, on the other hand, a permanent attenuation of the hyperactivity syndrome. It is suggested that the present animal model may be of value for the detection of antidepressants and for elucidating the role of an important social variable in the production of neurochemical changes associated to depressive disorders.

Subchronic treatment with the tricyclic antidepressant DMI increases isolation-induced fighting in rats

Male rats treated with desmethylimipramine (DMI) (20 mg/kg for 7 days) were more likely than controls to attack an intruder rat placed in their home cage; they were also more likely to submit when attacked by the intruder. These behavioural changes were not seen at lower doses of DMI. Similar results were obtained in experiments in which is drugged animal and a control were placed together in a "neutral" cage; in this paradigm it was also found that lower doses of DMI were effective, provided that either the period of drug treatment was increased, or a delay of 3-4 days after withdrawal of DMI preceded behavioural testing. A dose dependent resistance to handling developed during drug treatment; drugged animals also showed weight loss and decreased open-field activity. In previous studies, acute treatment with tricyclic antidepressants has not been found to increase fighting; the present results underline the importance of chronic drug studies.

Symptom patterns in unipolar and bipolar depression correlating with monoamine metabolites in the cerebrospinal fluid: I. General patterns

The symptom scores on the Schedule for Affective Disorders and Schizophrenia (SADS) of 21 unipolar and 12 bipolar depressive patients diagnosed with Research Diagnostic Criteria (RDC) were correlated with the monoamine metabolites homovanillic acid (HVA), 3-methoxy-4-hydroxyphenylglycol (MHPG), and 5-hydroxyindoleacetic acid (5HIAA) in the cerebrospinal fluid (CSF). For the unipolar group, multiple regression analyses revealed strong multiple correlations (from r = 0.92 to 0.97) to the effect that high- and low-HVA, high- and low-MHPG, and high- and low-5HIAA syndromes, respectively, could be isolated. The bipolars were too few for the same analyses to work well, but there is evidence for the high- and low-monoamine syndromes to be characterized by differential symptomatology in bipolar and unipolar patients. Through the comparison of monoamine metabolite values predicted from a total of 18 SADS symptom items with the true CSF values, a computer program was able to classify 20 of the 21 unipolar and all the 12 bipolars correctly. The results are consistent with a hypothesis of the pathoplastic role of individually set (genetically determined?) brain monoamine homeostases in shaping the profile of an affective episode.

Glucocorticoid effects on serotonergic and noradrenergic facilitation of spinal monosynaptic transmission

The ability of an intensive glucocorticoid regimen (i.e., triamcinolone diacetate, 8 mg/kg i.m./7 days) to modify the lumbar spinal monosynaptic reflex response to serotonergic and noradrenergic agents has been examined in unanesthetized acute spinal (C-1 sectioned) cats. Triamcinolone pretreatment enhances the 2N facilitatory actions of amitriptyline (AMIT), 5 mg/kg i.v., when given after D,L-5-hydroxytryptophan (5--HTP), 50 mg/kg i.v., as compared to untreated control preparations. Subsequent administration of methysergide, a serotonin receptor blocking drug, in a dose of 1 mg/kgh i.v. promptly and completely reverses the monosynaptic response increase by AMIT in untreated animals, but not in the glucocorticoid treated ones. In contrast, the monosynaptic facilitation normally produced in untreated preparations by methoxmine (MX), 1 mg/kg i.v., a centrally active noradrenergic agonist, is prevented as a result of triamcinolone dosing. These results demonstrate a glucocorticoid effect on spinal biogenic amine function such that serotonergic monosynaptic reflex activation is enhanced while noradrenergic reflex stimulation is depressed. Furthermore, they suggest that the elevations in plasma cortisol in certain cases of psychiatraic depression may; contribute to alterations in central biogenic amine synaptic activity.