Enhanced 5-hydroxytryptamine and dopamine-mediated behavioural responses following convulsions--I. The effects of single and repeated bicuculline-induced seizures

Chronic electroconvulsive shock enhances 5-HT2 receptor-mediated head shakes but not brain C-fos induction

Chronic electroconvulsive shock (ECS), a widely used treatment for intractable depression, increases the density of 5-HT2A receptor binding sites and mRNA in rat frontal cortex. In contrast, this treatment appears to have no significant effect on 5-HT-stimulated phosphatidyl inositol turnover in rat brain. To investigate the effect of chronic ECS on the 5-HT2 receptor family further, we determined its effects on head shakes and c-fos expression in the rat in response to the 5-HT2A/2C receptor agonist DOI [1-(2,5-dimethoxy-4-iodophenyl)-2-amino-propane]. Chronic ECS (5 electroconvulsive shocks over 10 days, via earclips under halothane anaesthesia) caused a significant enhancement in the number of head shakes counted in a 30 min period after administration of 2 or 8 mg/kg DOI. In contrast, this treatment had no effect on Fos expression, induced by either dose of DOI, in any region of rat forebrain examined. Fos expression was low-to-undetectable in the brains of animals treated with chronic ECS followed by saline and sham ECS animals that had been treated identically, but with no administration of electrocurrent. Thus the lack of any change in PI turnover, following chronic ECS administration, appears to be mirrored by the failure of this treatment to alter 5-HT2 receptor-mediated Fos expression.

Effect of barbitone sodium and thiopental sodium on brain dopamine, noradrenaline, serotonin and 5-hydroxyindoleacetic acid content in Arvicanthis niloticus

The quantitative estimation of total dopamine (DA), noradrenaline (NE), serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) content in the whole brain tissue of normal Nile grass rat, Arvicanthis niloticus, gives and average of 631 +/- 12 ng DA/g, 366 +/- 12 ng NE/g, 617 +/- 15 ng 5-HT/g and 431 +/- 10 ng 5-HIAA/g fresh brain tissue. The effect of barbitone sodium and thiopental sodium on the total DA, NE, 5-HT and 5-HIAA content in the brain tissue of the Nile grass rat, Arvicanthis niloticus, was studied. The total DA, NE, 5-HT and 5-HIAA contents were determined 5 hr after i.p. injection of different doses of barbitone sodium (20, 40 and 80 mg/ml/100 g body wt) and thiopental sodium (5, 10 and 20 mg/ml/100 g body wt). The effect of different time intervals (1, 10, 30 min, 1, 2.5, 5, 8, 16, 24 and 48 hr) on the total brain DA, NE, 5-HT and 5-HIAA content was investigated after i.p. injection of 40 mg of barbitone sodium and 10 mg of thiopental sodium/ml/100 g body wt. Both barbitone sodium and thiopental sodium caused an increase in DA, NE and 5-HT content and a decrease in 5-HIAA content in the brain tissue of Arvicanthis niloticus. The increase in the whole brain contents of DA, NE and 5-HT after the administration of barbitone sodium and thiopental sodium may be due either to inhibition of transmitter release by an action at the monoamine nerve terminal or to effects causing a decrease in nerve impulse flow. On the other hand, the decrease in 5-HIAA may be due to the decrease in the turnover of 5-HT.

Antidepressants and serotonergic neurotransmission: an integrative review

The effects of acute and chronic antidepressant treatment on various aspects of 5-HT neurotransmission are reviewed, in order to assess the net effect of antidepressants on transmission across 5-HT synapses. Events considered include presynaptic effects of antidepressants (on autoreceptor function, uptake and turnover) and effects on postsynaptic receptor function (assessed by electrophysiological, neuroendocrine, behavioural, and receptor binding methods). Acute antidepressant treatment has variable effects: transmission may be enhanced, unchanged or reduced, depending mainly upon the relative contributions of 5-HT uptake blockade and 5-HT receptor antagonism. However, on chronic administration, most antidepressants appear to enhance 5-HT transmission. This effect is clearest in the case of ECS, which has little effect on 5-HT turnover, but reduces uptake and increases postsynaptic receptor function. MAOIs may be an exception: there is little evidence that MAOIs enhance 5-HT transmission following chronic treatment. Most other antidepressant drugs, including some which are powerful receptor antagonists on acute administration, reduce 5-HT receptor function briefly, but enhance receptor function if several hours elapse between the final injection and testing. Zimelidine has little effect on postsynaptic receptor function, but enhances 5-HT transmission by its powerful blockade of 5-HT uptake. Chronic treatment with antidepressant drugs has usually been found to reduce binding to 5-HT2 receptors; it is difficult to reconcile these observations with the functional studies. In general, with the possible exception of MAOIs, chronic administration of antidepressants may enhance 5-HT transmission by both pre- and post-synaptic effects, and the relative contributions vary. This conclusion supports the classical "indoleamine hypothesis of depression" rather than the more recent "hypersensitive serotonin receptor" theory.

Repeated administration of subconvulsant doses of GABA antagonist drugs. II. Effect on monoamine-mediated behaviour

The effect on monoamine-medical behaviour of repeated daily subconvulsive doses of the GABA antagonist drugs pentylenetetrazol (PTZ) (30 mg/kg for 8 days), picrotoxin (5 mg/kg for 4 days) and bicuculline (3.5 mg/kg for 16 days) was investigated. None of the drugs, administered chronically, increased behavioural responses to the 5-hydroxytryptamine agonist quipazine (25 mg/kg), and neither picrotoxin nor bicuculline altered the locomotor response to the dopamine agonist apomorphine (AP) (0.1 mg/kg). By contrast, repeated doses of PTZ increased the locomotor response to AP, and also increased circling responses to both AP (0.5 mg/kg) and methamphetamine (2.0 mg/kg) in unilateral nigrostriatal-lesioned rats.