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Query: UMLS:C0011570 (depression)
 172,036 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The cortical depression induced by the stimulation of some afferent fibers affects strychnine spikes elicited in two different ways: by direct electrical stimulation, and through the evoked potentials induced at the somatosensory area by single shocks to the radial nerve. The effects on these two types of responses were found to be very similar, which was taken to indicate that the site of action of the mechanism involved is the same, that is, the non-synaptic membranes of the dendrites of pyramidal neurons. It is suggested that the depressant action is mediated through the serotonergic neurons, since the previous administration of 5,6-Dihydroxytryptamine (5,6-DHT) blocked the changes. The 5-Hydroxytryptamine (5-HT) liberated would act as a neurohumoral agent, since the synaptic mechanisms do not seem to be involved and the effects are manifested in a diffuse manner.
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PMID:On the mechanism of the cortical depression induced by afferent stimulation. 61 62

In animal models of depression, the 5-HT1A agonists, 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT), buspirone, gepirone and ipsapirone administered i.p. have been shown to mimic the behavioural effects of antidepressants. For instance, in the present study, using the learned helplessness paradigm, 8-OH-DPAT dose-dependently reversed helpless behaviour. To assess the possible role of pre- or postsynaptic 5-HT1A receptors in this effect, the ability of 8-OH-DPAT to reduce helpless behaviour was investigated following (1) i.p. administration (0.125 or 0.25 mg/kg/day) in rats whose ascending 5-HT neurons were partially destroyed by previous 5,7-dihydroxytryptamine (5,7-DHT) injection (5 micrograms free base in 0.6 microliter) into the raphe nuclei or (2) after local microinjection (0.1 or 1.0 microgram in 0.5 microliter) into the raphe nuclei or into the septum. The reversal of helpless behaviour by 8-OH-DPAT (i.p.) was still observed in 5,7-DHT-treated rats with telencephalic 5-HT uptake reduced by 50-75% depending on the region. 8-OH-DPAT microinjected into the raphe nuclei did not reverse helpless behaviour; in contrast, 8-OH-DPAT microinjected into the septum reversed helpless behaviour. These results suggest that the ability of 8-OH-DPAT to reverse helpless behaviour probably involved the stimulation of postsynaptic rather than presynaptic 5-HT1A receptors.
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PMID:Antidepressant-like action of 8-OH-DPAT, a 5-HT1A agonist, in the learned helplessness paradigm: evidence for a postsynaptic mechanism. 214 88

The role of serotonin in the anorexic response of rats to an amino acid-imbalanced diet was investigated. After chronic depletion of serotonin with parachlorophenylalanine (PCPA, 300 mg/kg) or 5,7-dihydroxytryptamine (DHT, 200 micrograms/rat, intracisternally), initial intake of a mild isoleucine-imbalanced diet was reduced by 60% vs. a 17% reduction after saline injection. After acute treatment with the agonist, quipazine (quip, 5 mg/kg ip) or the precursor, tryptophan (TRP, 1% added to the diet), imbalanced diet intake was also exacerbated. PCPA and DHT may have caused receptor supersensitivity, such that the food intake depression after serotonin depletion was similar to that seen with the quip and TRP treatments. Injection of the autoreceptor agonist, 8-hydroxy-2(di-n-propylamino)tetralin (8-OH-DPAT, 500 micrograms/kg sc), to reduce transmission in the serotonergic systems resulted in an attenuation of the usual food intake depression of the amino acid-imbalanced diet (only a 7%, nonsignificant reduction). Also measurements made in the absence of pharmacological treatment showed that the ratio 5-hydroxyindole acetic acid-to-serotonin, a putative index of serotonin turnover, was increased 155% in the raphe nuclei and 140% in the hippocampus 3.5 h after ingestion of the mild isoleucine-imbalanced diet. Therefore increased serotonergic activity in some brain areas may be associated with the initial depression of food intake in rats fed an imbalanced amino acid diet.
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PMID:Serotonin and feeding responses of rats to amino acid imbalance: initial phase. 244 14

The present study sought to determine whether rats, treated neonatally with 5,7-dihydroxytryptamine (5,7-DHT), have an increased sensitivity to the respiratory and cough-depressant effects induced by dihydrocodeine. The serotonin (5-HT) levels in the whole brain of 5,7-DHT-treated rats were reduced to 19% of the corresponding control values. The 5,7-DHT-treated rats were supersensitive to the depression in frequency of respiration and cough reflex produced by i.p. administration of dihydrocodeine. The increased sensitivity to dihydrocodeine in terms of the depression of frequency of respiration and the cough reflex in 5,7-DHT-treated rats could possibly have been due to changes in the sensitivity of serotonergic receptors.
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PMID:Supersensitivity of 5,7-dihydroxytryptamine-treated rats to the respiratory depressant and antitussive effects of dihydrocodeine. 318 Dec 91

Central serotonergic fiber systems of the rat were selectively lesioned by intraventricular injection of the neurotoxin 5,7-dihydroxytryptamine (5,7-DHT). At various times thereafter, the sensitivity of rostral cortical neurons to microiontophoretically administered serotonin (5-HT) was compared in groups of lesioned and sham-operated animals pretreated with the 5-HT uptake inhibitor CGP 6085. Twenty-four hours after the injection of 5,7-DHT, at which time the cortical 5-HT and 5-hydroxyindoleacetic acid (5-HIAA) levels were both reduced by 40%, there was no significant difference in the sensitivity of cortical neurons to 5-HT. However, 3 days after such treatment, when the cortical 5-HT and 5-HIAA levels were reduced by 52% and 53% respectively, pronounced supersensitivity to 5-HT was noted. The depressant action of 5-HT on neuronal firing was potentiated with regard to both maximal firing depression and duration of the firing inhibition. A similar potentiation of the 5-HT responses was observed 7 days after lesioning. Supersensitivity thus appears to develop between 1 and 3 days after the injection of 5,7-DHT. Seven days after lesioning, the sensitivity of rostral cortical neurons to gamma-aminobutyric acid was unchanged compared to that observed in sham-operated animals.
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PMID:Experimentally induced supersensitivity of neocortical neurons to microiontophoretically administered serotonin. 616 11

(3H)Imipramine binding sites in the brain are localized mainly on serotonergic nerve terminals. In the hippocampus of rats with a lesion of serotonergic nerve terminals produced by neonatal administration of 5,7-DHT, the depletion of serotonin was paralleled by a decrease in (3H)imipramine recognition sites. (3H)Imipramine recognition sites in brain tissue or platelets are associated with serotonin uptake sites. A significant correlation exists between the potency of a series of antidepressants and other compounds to displace high affinity (3H)imipramine binding and to inhibit the neuronal uptake of serotonin but not of norepinephrine. There is a significant correlation between the ability of drugs to displace (3H)desipramine binding and to inhibit norepinephrine but not serotonin reuptake. (3H)Desipramine recognition sites are located, at least in part, at noradrenergic nerve terminals since destruction of these terminals by 6-OH-DA results in parallel decrease in (3H)desipramine, but not in (3H)imipramine binding. The high affinity recognition sites of (3H)imipramine and (3H)desipramine in the brain could be physiologically and pharmacologically relevant regulatory sites associated with neuronal uptake of serotonin and norepinephrine, respectively. Treatments which clinically lead to improvement of depression (eg. antidepressants, ECT, REM sleep deprivation) were shown to "down-regulate" (3H)imipramine binding sites in brain of experimental animals. The density of (3H)imipramine binding sites was shown to be lower in platelets from depressive patients and in brains of suicide victims. It appears that decreased binding of (3H)imipramine to platelets of depressed patients is a promising biological marker of depression, although there is no conclusive evidence to indicate whether it is a state- or trait-dependent phenomenon.
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PMID:Antidepressant binding: implications for the mode of action and the biology of depression. 632 Feb 97

1. In adult rats under urethane anesthesia, a vast majority of spontaneously active neurons in the frontoparietal cortex undergo a prolonged depression of their firing rate upon microiontophoretic application of 5-HT. 2. In 5,7-DHT-deafferented cortex, this effect is of a longer duration (mean 14 min) than in controls (mean 5 min). Moreover, small ejection currents of 5-HT are sufficient to induce a prolonged depression of the firing rate. 3. In PCPA-pretreated rats, there are no changes in the responsiveness to 5-HT. 4. In control and PCPA-pretreated rats, blocking of the 5-HT reuptake with fluoxetine increases the duration of responses to 5-HT (mean 15 min), whereas small ejection currents remain without effect. 5. These data indicate that, in the cerebral cortex, denervation supersensitivity to 5-HT results primarily from the removal of 5-HT afferents, and not from depletion of their 5-HT content. The enhanced responsiveness to microiontophoresed 5-HT appears to be due to a suppression of reuptake mechanisms, mainly responsible for the prolongation of 5-HT effects, and to a modification of receptors on target cells, which accounts for their greater sensitivity to 5-HT.
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PMID:Responsiveness of cortical neurons to serotonin after 5,7-DHT denervation or PCPA depletion. 645 41

Aryl hydrocarbon hydroxylase (AHH) activity was determined in castrate and intact male Syrian hamster kidney and liver microsomes following in vivo treatment with either diethylstilbestrol (DES) or 17 beta-estradiol as well as other steroid hormones. After 1 month of estrogen treatment, there was a 5-fold decline in AHH activity in castrated hamster kidneys compared with untreated castrate levels. The amount of AHH activity in the kidney was depressed more than 75% of untreated castrate levels even after the estrogen had been withdrawn for 6 days. Consistent with a nearly 2.5-fold higher renal AHH activity observed in intact male hamsters compared to castrates was the finding of a 1.7-fold elevation in the activity of this enzyme after treatment of castrated animals with androgen[5 alpha-dihydrotestosterone (5 alpha-DHT)] for 1 month. Moreover, following withdrawal of estrogen from intact hamsters, the increase in AHH activity in the kidney essentially paralleled the rise in serum testosterone levels. In castrated animals, the depression of AHH activity by estrogen was partially reversed by concomitant 5 alpha-DHT treatment. However, no appreciable changes were seen in liver AHH activity with androgen treatment in the presence or absence of estrogen. Similarly, the level of AHH activity, which was nearly 7- and 14-fold higher than intact and castrate kidney levels, respectively, was not altered by estrogen treatment. Neither progesterone nor cortisone had any effect on the levels of AHH activity in either the kidney or liver. Therefore, AHH activity in the male hamster kidney, but not the liver, is responsive to both estrogens and androgenic hormone.
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PMID:Effect of steroid hormone treatment on aryl hydrocarbon hydroxylase activity in the Syrian hamster kidney. 662 58

Brain 5-hydroxytryptamine (5-HT) was depleted in rats by intraventricular injection with 5,7-dihyroxytryptamine (5,7-DHT) prior to feeding rats a liquid diet containing ethanol. After withdrawal of ethanol, withdrawal reactions were significantly less severe in 5-HT-depleted rats than control rats. Sleeping times after a standard dose of ethanol or pentobarbitone were significantly prolonged in 5-HT-depleted rats. However, metabolic and pharmacodynamic tolerance developed to a similar extent in 5-HT-depleted rats as in control rats. It was concluded that 5-hydroxytryptaminergic neurons are not directly involved in the development of physical dependence on or tolerance to ethanol. Depletion of brain 5-HT by 5,7-DHT appears to result in a non-specific central nervous system depression that potentiates the depressant actions of ethanol and pentobarbitone and antagonises the hyperexcitability of ethanol withdrawal.
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PMID:Effect of depletion of brain 5-hydroxytryptamine by 5,7-dihydroxytryptamine on ethanol tolerance and dependence in the rat. 676 80

Calciphylactic blockade of Reticulo endothelial system (REB) was used to study the role of reticulo-endothelial system (RES) in hepatic regeneration. REB was induced by i.v. egg yolk administration in DHT sensitized animals, which were subsequently partially hepatectomized. Mitotic index and percentage regeneration were studied in these animals 48 hr after partial hepatectomy. REB produced a significant depression of the mitotic index and percentage regeneration in regenerating livers. This suggests that functional integrity of the RES in essential hepatic parenchymal proliferation after partial hepatectomy.
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PMID:The possible role of reticulo endothelial system in hepatic regeneration. 714 15


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