Electroconvulsive shock increases dopamine D1 and D2 receptor mRNA in the nucleus accumbens of the rat

Electroconvulsive therapy in treatment resistant depression

Electroconvulsive therapy (ECT) is a treatment modality for patients with treatment resistant depression (TRD), defined as failure of two adequate antidepressant medication trials. We provide a qualitative review of ECT's effectiveness for TRD, methods to optimize ECT parameters to improve remission rates and side effect profiles, and ECT's proposed neurobiological mechanisms. Right unilateral (RUL) electrode placement has been shown to be as effective for major depression as bilateral ECT, and RUL is associated with fewer cognitive side effects. There is mixed evidence on how to utilize ECT to sustain remission (i.e., continuation ECT, psychotropic medications alone, or a combination of ECT and psychotropic medications). Related to neurobiological mechanisms, an increase in gray matter volume in the hippocampus-amygdala complex is reported post-ECT. High connectivity between the subgenual anterior cingulate and the middle temporal gyrus before ECT is associated with better treatment response. Rodent models have implicated changes in neurotransmitters including glutamate, GABA, serotonin, and dopamine in ECT's efficacy; however, findings in humans are limited. Altogether, while ECT remains a highly effective therapy, the neurobiological underpinnings associated with improvement of depression remain uncertain.

A longitudinal study of the association between basal ganglia volumes and psychomotor symptoms in subjects with late life depression undergoing ECT

Psychomotor dysfunction (PMD) is a core element and key contributor to disability in late life depression (LLD), which responds well to electroconvulsive therapy (ECT). The neurobiology of PMD and its response to ECT are not well understood. We hypothesized that PMD in LLD is associated with lower striatal volume, and that striatal volume increase following ECT explains PMD improvement. We analyzed data from a two-center prospective cohort study of 110 LLD subjects (>55 years) receiving ECT. Brain MRI and assessment of mood, cognition, and PMD was performed 1 week before, 1 week after, and 6 months after ECT. Volumetry of the caudate nucleus, putamen, globus pallidus, and nucleus accumbens was derived from automatically segmented brain MRIs using Freesurfer®. Linear multiple regression analyses were used to study associations between basal ganglia volume and PMD. Brain MRI was available for 66 patients 1 week post ECT and in 22 patients also six months post ECT. Baseline PMD was associated with a smaller left caudate nucleus. One week after ECT, PMD improved and volume increases were detected bilaterally in the caudate nucleus and putamen, and in the right nucleus accumbens. Improved PMD after ECT did not relate to the significant volume increases in these structures, but was predicted by a nonsignificant volume change in the right globus pallidus. No volume differences were detected 6 months after ECT, compared to baseline. Although PMD is related to lower striatal volume in LLD, ECT-induced increase of striatal volume does not explain PMD improvement.

Effects of repeated electroconvulsive shocks on dopamine supersensitivity psychosis model rats

While the long-term administration of antipsychotics is known to cause dopamine supersensitivity psychosis (DSP), recent studies revealed that DSP helps form the foundation of treatment resistance. Electroconvulsive shock (ES) is one of the more effective treatments for treatment-resistant schizophrenia. The objective of this study was to examine whether repeated ES can release rats from dopamine supersensitivity states such as striatal dopamine D2 receptor (DRD2) up-regulation and voluntary hyperlocomotion following chronic administration of haloperidol (HAL). HAL (0.75 mg/kg/day) was administered for 14 days via mini-pumps implanted in rats, and DRD2 density and voluntary locomotion were measured one day after drug cessation to confirm the development of dopamine supersensitivity. The rats with or without dopamine supersensitivity received repeated ES or sham treatments, and then DRD2 density was assessed and a voluntary locomotion test was performed. Chronic treatment with HAL led to the up-regulation of striatal DRD2 and hyperlocomotion in the rats one day after drug cessation. We thus confirmed that these rats experienced a dopamine supersensitivity state. Moreover, after repeated ES, locomotor activity and DRD2 density in the DSP model rats fell to the control level, while an ES sham operation had no effect on the dopamine supersensitivity state. The present study suggests that repeated ES could release DSP model rats from dopamine supersensitivity states. ES may be helpful for patients with DSP.

Electroconvulsive stimulation differentially affects [11C]MDL100,907 binding to cortical and subcortical 5HT2A receptors in porcine brain

BACKGROUND

Electroconvulsive therapy is an effective therapy of depression. We hypothesized that the beneficial effects are mediated partly by decreased serotonin receptor availability in the cortex.

AIMS

We used positron emission tomography with the serotonin 5HT_2A receptor radioligand [¹¹C]MDL100,907 to determine serotonin receptor availability in response to electroconvulsive stimulation (ECS).

METHODS

Seven Göttingen minipigs were deeply anaesthetized and imaged at baseline before the onset of ECS, and at 1-2 and 8-10 days after the end of a clinical course of ECS, consisting of 10 sessions over 3.5 weeks, and post-ECS values were compared to baseline. One additional minipig was anaesthetized over 10 sessions without ECS, as a control. We analysed images with the Ichise model for binding in cortex and hippocampus, followed by whole-brain analysis by statistical non-parametric mapping.

RESULTS

We found significantly increased binding potential of [¹¹C]MDL100,907 in the cortex and hippocampus 1-2 days after ECS, consistent with increased serotonin receptor availability compared to baseline. By 8-10 days after the final ECS, the average tracer binding had returned towards baseline. However, we also found significantly decreased tracer binding in the subcortical regions of olfactory bulb, pons, thalamus and striatum.

CONCLUSIONS

With ECS, minipigs, unlike primates but like rodents, have higher availability at cortical and hippocampal 5HT_2A receptors. Decreased tracer binding is consistent with reduced serotonin receptor availability as a differential effect of ECS on 5HT_2A receptors in subcortical regions of minipig brain.

Elevated dopamine D1 receptor availability in striatum of Göttingen minipigs after electroconvulsive therapy

Electroconvulsive therapy (ECT), a direct form of brain stimulation, is an effective antidepressant. We hypothesized that the beneficial effects of ECT are mediated by increased dopaminergic neurotransmission, in which the baseline activity of D1 receptors may predict the response to ECT. We established a novel model of brain stimulation in Göttingen minipigs based on the protocol of ECT applied in humans. With positron emission tomography (PET), we determined a measure of dopaminergic neurotransmission with the dopamine D1 receptor antagonist [¹¹C]SCH23390. Seven minipigs were anesthetized and completed PET at baseline, prior to the onset of ECT treatment, and at 24-48 h and 8-10 days after the end of a clinical course of ECT, consisting of 10 ECT sessions over a 3.5-week period. In all pigs, the binding of [¹¹C]SCH23390 to striatal D1 receptors had increased by 24-48 h after ECT, and in most, binding returned towards baseline at 8-10 days. Increased binding was observed in inverse proportion to baseline binding rates. Increased binding to dopamine D1 receptors suggests facilitation of dopaminergic neurotransmission, which may contribute to the therapeutic effects of ECT. Importantly, the baseline binding capacity of D1 receptors predicts the magnitude of increased binding, up to a maximum binding capacity.

Rapid and lasting enhancement of dopaminergic modulation at the hippocampal mossy fiber synapse by electroconvulsive treatment

Electroconvulsive therapy (ECT) is an established effective treatment for medication-resistant depression with the rapid onset of action. However, its cellular mechanism of action has not been revealed. We have previously shown that chronic antidepressant drug treatments enhance dopamine D₁-like receptor-dependent synaptic potentiation at the hippocampal mossy fiber (MF)-CA3 excitatory synapse. In this study we show that ECT-like treatments in mice also have marked effects on the dopaminergic synaptic modulation. Repeated electroconvulsive stimulation (ECS), an animal model of ECT, strongly enhanced the dopamine-induced synaptic potentiation at the MF synapse in hippocampal slices. Significant enhancement was detectable after the second ECS, and further repetition of ECS up to 11 times monotonously increased the magnitude of enhancement. After repeated ECS, the dopamine-induced synaptic potentiation remained enhanced for more than 4 wk. These synaptic effects of ECS were accompanied by increased expression of the dopamine D₁ receptor gene. Our results demonstrate that robust neuronal activation by ECS induces rapid and long-lasting enhancement of dopamine-induced synaptic potentiation at the MF synapse, likely via increased expression of the D₁ receptor, at least in part. This rapid enhancement of dopamine-induced potentiation at the excitatory synapse may be relevant to the fast-acting antidepressant effect of ECT.

NEW & NOTEWORTHY

We show that electroconvulsive therapy (ECT)-like stimulation greatly enhances synaptic potentiation induced by dopamine at the excitatory synapse formed by the hippocampal mossy fiber in mice. The effect of ECT-like stimulation on the dopaminergic modulation was rapidly induced, maintained for more than 4 wk after repeated treatments, and most likely mediated by increased expression of the dopamine D1 receptor. These effects may be relevant to fast-acting strong antidepressant action of ECT.

Electroconvulsive therapy alters dopamine signaling in the striatum of non-human primates

Electroconvulsive therapy (ECT) is one of the most effective therapies for depression and has beneficial motor effects in parkinsonian patients. However, little is known about the mechanisms of therapeutic action of ECT for either condition. The aim of this work was to explore the impact of ECT on dopaminergic function in the striatum of non-human primates. Rhesus monkeys underwent a course of six ECT treatments under a human clinical protocol. Longitudinal effects on the dopaminergic nigrostriatal system were studied over 6 weeks using the in vivo capabilities of positron emission tomography (PET). PET scans were performed prior to the onset of ECT treatments and at 24-48 h, 8-10 days, and 6 weeks after the final ECT treatment. Early increases in dopamine transporter and vesicular monoamine transporter 2 binding returned to baseline levels by 6 weeks post-ECT. Transient increases in D1 receptor binding were also observed, whereas the binding potential to D2 receptors was unaltered. The increase in dopaminergic neurotransmission suggested by our results may account in part for the therapeutic effect of ECT in mood disorders and Parkinson's disease.

Repeated electroconvulsive shock induces changes in high-affinity [3H]-ouabain binding to rat striatal membranes

Repeated electroconvulsive shock is an effective treatment for affective disorders. Striatum, hippocampus and brainstem are involved in affective disorders. Sodium-potassium/ATPase is of paramount importance for the proper functioning of the brain and its involvement in the affective disorders has been claimed for a long time. Sodium-potassium/ATPase has an extracellular regulatory binding site to which cardiotonic glycosides, such as ouabain, bind to, thus regulating the activity of the enzyme. Endogenous "ouabain-like" substances exist in the brain and their actions on the sodium-potassium/ATPase resemble ouabain biological properties. The aim of this work was to determine if electroconvulsive shock (ECS) would induce changes in the high-affinity binding of ouabain to the sodium-potassium/ATPase from rat brain regions. Adult, male Wistar rats received one (ECSx1 group) or seven electroshocks (ECSx7 group) delivered daily through ear-clips electrodes. Control rats received the same manipulations; however, no current was delivered through the electrodes (SHAMx1 and SHAMx7 groups). All groups were sacrificed 24 h after the last ECS session. The B (max) and K (D) of high-affinity [(3)H]-ouabain binding were determined in crude membrane preparations from the striatum, hippocampus and brainstem. The results obtained showed a statistically significant increase in the affinity of [(3)H]-ouabain (lower K (D)) to striatal membranes in those rats receiving seven ECS. In the striatum there was no change in the K (D) after one ECS; as well as there was no change in the B (max) after a single or seven ECS. High-affinity [(3)H]-ouabain binding to hippocampus and brainstem did not reveal any significant differences either in K (D) or B (max) after one or seven ECS. The increased affinity of ouabain to the striatal sodium-potassium/ATPase induced by repeated ECS suggests an increased interaction in vivo of the endogenous "ouabain-like" substances with the enzyme and the involvement of the extracellular regulatory allosteric ouabain binding site in the striatal sodium-potassium/ATPase in the effects of electroconvulsive shock.

Multi-target strategies for the improved treatment of depressive states: Conceptual foundations and neuronal substrates, drug discovery and therapeutic application

Major depression is a debilitating and recurrent disorder with a substantial lifetime risk and a high social cost. Depressed patients generally display co-morbid symptoms, and depression frequently accompanies other serious disorders. Currently available drugs display limited efficacy and a pronounced delay to onset of action, and all provoke distressing side effects. Cloning of the human genome has fuelled expectations that symptomatic treatment may soon become more rapid and effective, and that depressive states may ultimately be "prevented" or "cured". In pursuing these objectives, in particular for genome-derived, non-monoaminergic targets, "specificity" of drug actions is often emphasized. That is, priority is afforded to agents that interact exclusively with a single site hypothesized as critically involved in the pathogenesis and/or control of depression. Certain highly selective drugs may prove effective, and they remain indispensable in the experimental (and clinical) evaluation of the significance of novel mechanisms. However, by analogy to other multifactorial disorders, "multi-target" agents may be better adapted to the improved treatment of depressive states. Support for this contention is garnered from a broad palette of observations, ranging from mechanisms of action of adjunctive drug combinations and electroconvulsive therapy to "network theory" analysis of the etiology and management of depressive states. The review also outlines opportunities to be exploited, and challenges to be addressed, in the discovery and characterization of drugs recognizing multiple targets. Finally, a diversity of multi-target strategies is proposed for the more efficacious and rapid control of core and co-morbid symptoms of depression, together with improved tolerance relative to currently available agents.

Placebo-controlled study of rTMS for the treatment of Parkinson's disease

The objective of this study is to assess the safety and efficacy of repetitive transcranial magnetic stimulation (rTMS) for gait and bradykinesia in patients with Parkinson's disease (PD). In a double-blind placebo-controlled study, we evaluated the effects of 25 Hz rTMS in 18 PD patients. Eight rTMS sessions were performed over a 4-week period. Four cortical targets (left and right motor and dorsolateral prefrontal cortex) were stimulated in each session, with 300 pulses each, 100% of motor threshold intensity. Left motor cortex (MC) excitability was assessed using motor evoked potentials (MEPs) from the abductor pollicis brevis. During the 4 weeks, times for executing walking and complex hand movements tests gradually decreased. The therapeutic rTMS effect lasted for at least 1 month after treatment ended. Right-hand bradykinesia improvement correlated with increased MEP amplitude evoked by left MC rTMS after individual sessions, but improvement overall did not correlate with MC excitability. rTMS sessions appear to have a cumulative benefit for improving gait, as well as reducing upper limb bradykinesia in PD patients. Although short-term benefit may be due to MC excitability enhancement, the mechanism of cumulative benefit must have another explanation.

The effect of electroconvulsive shock seizures on behaviour induced by dopaminergic agonists and on immobility in the Porsolt test

Male, Wistar rats were given a course of eight electroconvulsive shock seizures (ECS group) or matched handling (control group). They were then tested for locomotion and rearing (7 days post-ECS), for grooming and yawning (9 days post-ECS), and for immobility in the Porsolt test (7, 14 and 21 days post-ECS). Seven days post-seizure, the ECS group showed significantly more locomotion following intraperitoneal administration of apomorphine (0.2 mg/kg), but not following injections of amphetamine (1 mg/kg). Drug-induced rearing was not different in the ECS and control animals. Nine days post-seizure, the ECS group showed significantly more grooming induced by the D-1 dopamine receptor agonist, SKF 38393 (1 mg/kg), but no difference in the yawning induced by the D-2 dopamine receptor agonist, quinpirole (0.05 mg/kg). In the Porsolt test, immobility was decreased in the ECS animals at 7 and 14, but not at 21 days post-ECS. It is concluded that ECS increases activity in the dopaminergic systems of the rat brain for at least 1-2 weeks post-seizure. The beneficial effects of electroconvulsive therapy (ECT) may relate to these dopaminergic alterations.

Electroconvulsive stimuli alter the regional concentrations of nerve growth factor, brain-derived neurotrophic factor, and glial cell line-derived neurotrophic factor in adult rat brain

In this study we investigated whether electroconvulsive stimuli (ECS) altered the regional brain protein concentrations of nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and glial cell line-derived neurotrophic factor (GDNF) in Sprague Dawley rats. Electroconvulsive stimuli were administered once daily for 8 days. At the end of the experiment, rats were killed, the brains were dissected into five regions, and the neurotrophic factors were extracted and measured by enzyme-linked immunosorbent assay. Electroconvulsive stimuli increased the concentrations of NGF in the frontal cortex and concentrations of BDNF in the hippocampus, the striatum, and the occipital cortex. In contrast, ECS decreased GDNF concentrations in the hippocampus and the striatum. Our data indicate that neurotrophic factors play a role in the mechanism of action of ECS and, by extrapolation, may play a role in the mechanism of action of electroconvulsive treatment.

Up-regulation of D3 dopaminergic receptor mRNA in the core of the nucleus accumbens accompanies the development of seizures in a genetic model of absence-epilepsy in the rat

The basal ganglia system is thought to play a key role in the control of absence-seizures and there is ample evidence that epileptic seizures modify brain dopamine function. We recently reported that local injections of dopamine D1 or D2 agonists in the core of the nucleus accumbens suppressed absence-seizures in a spontaneous, genetic rodent model of absence-epilepsy whereas injections of D1 or D2 antagonists had aggravating effects. These findings raised the possibility that the dopaminergic system may be altered in absence-epilepsy prone rats. Therefore, we studied by in situ hybridization histochemistry the expression of pre- and postsynaptic components of the dopaminergic system in this strain of rats. When compared to non-epileptic control rats, epileptic rats displayed no change in the expression of mRNAs coding for the neuronal dopaminergic markers (tyrosine hydroxylase, membraneous and vesicular dopamine transporters). In addition, there was no difference between the two strains concerning the expression of the dopamine receptor transcripts D1, D2 and D5. In adult absence-epilepsy prone rat with an overt epileptic phenotype, however, an elevated level of D3 mRNA expression was observed in neurons of the core of the nucleus accumbens (+23% increase in silver grain density compared to non-epileptic control rats). D3 transcripts were not increased in juvenile epileptic rats without seizures. These findings suggests that up-regulation of D3 receptor mRNA is part of the epileptic phenotype in absence-epilepsy prone rats. Its localization in the core of the nucleus accumbens bears close resemblance to the dopamine-sensitive antiepileptic sites in ventral striatum and further support the involvement of ventral structures of the basal ganglia system in the control of absence-seizures.

Regulation of expression and enzymatic activities of tyrosine and tryptophan hydroxylases in rat brain after acute electroconvulsive shock

Acute electroconvulsive shock (ECS) causes a significant increase of protein synthesis in depressive patients and such an increase raises the possibility that the regulation of specific proteins and enzymatic activities in the brain might be one of the mechanisms required for the induction of long-term adaptive neurochemical changes after electroconvulsive therapy. In current studies, we investigated and compared simultaneously the short- and long-term effects of an acute ECS on the expression and enzymatic activities of both tyrosine and tryptophan hydroxylases (TH and TpOH, respectively) in different rat brain areas. Our results demonstrated that an acute ECS produced: (1) a long-lasting decrease in TH and TpOH protein levels in locus ceruleus (LC), ventral tegmental area (VTA) and in TpOH protein level in the raphe centralis (RC), maximal at 72 h, with concomitant changes in mRNA levels and enzymatic activities in the LC only; (2) large increase of TpOH protein levels in the frontal cortex (Cxf) (+145%) and increase of TH protein levels in the hippocampus (Hip) (+207%), maximal at 72 h and 7 days which was not accompanied by corresponding increase of in vivo enzymatic activities. Furthermore, a second ECS increased in vivo TpOH activity in the Cxf (+19%) while decreasing K(m) value (-50%) for tetrahydrobiopterin cofactor. A stability of the observed findings on TpOH activity in the Cxf after repeated ECS might be one of the mechanisms for the antidepressant effects of electroconvulsive therapy.

Electroconvulsive shock increases tachykinin NK(1) receptors, but not the encoding mRNA, in rat cortex

Recent studies have suggested that the substance P (tachykinin NK(1)) receptor may be a pharmacological target for the treatment of mood disorders. Here, the effects of electroconvulsive shock on tachykinin NK(1) receptor gene expression in the rat brain was investigated. Rats received either a single electroconvulsive shock or five shocks on alternate days. Quantitative autoradiography with [(125)I]Bolton Hunter-substance P, and in situ hybridisation histochemistry, were used to measure tachykinin NK(1) receptor-binding site densities and mRNA abundance, respectively. Densities of tachykinin NK(1) receptor-binding sites were significantly increased in the cerebral cortex following repeated electroconvulsive shock compared to sham treated animals. Densities remained unchanged in the hippocampus, striatum and amygdala. Neither single nor repeated electroconvulsive shock altered tachykinin NK(1) receptor mRNA in the brain regions examined. Hence, repeated electroconvulsive shock increases tachykinin NK(1) receptors in the rat brain in a regionally specific way. Upregulation of receptor-binding sites without a change in mRNA indicates that translational or post-translational mechanisms underlie this process.

Effects of acute and chronic electroconvulsive stimuli on cAMP and cGMP efflux in the rat striatum and hippocampus

The effects of acute and chronic electroconvulsive stimuli (ECS) on extracellular concentrations of the cyclic nucleotides, cAMP and cGMP, from the striatum and hippocampus of awake rats were studied with in vivo microdialysis in conjunction with radioimmunoassay. Acute ECS, but not acute sham-ECS, significantly increased cAMP and cGMP efflux from the striatum by about 75 and 50%, respectively. Chronic ECS did not influence significantly basal efflux of cAMP or cGMP from the striatum or the hippocampus in comparison to control animals receiving chronically sham-ECS. Administration of a challenge ECS in animals treated chronically with sham-ECS resulted in an increase in cAMP and cGMP concentrations in the striatum by 20%, but it failed to affect significantly efflux of these nucleotides in animals treated chronically with ECS. Similarly, in the hippocampus, administration of a challenge ECS in animals treated chronically with sham-ECS resulted in an increase in cAMP and cGMP concentrations by about 40 and 65%, respectively, whereas it failed to affect significantly efflux of these nucleotides in animals treated chronically with ECS. Thus, acutely administered ECS increases cAMP and cGMP efflux in the striatum and hippocampus of rats, an effect that is greatly diminished in animals chronically receiving ECS. These findings suggest changes in the cAMP and cGMP signal transduction mechanisms in response to acute and chronic ECS that may be related to the therapeutic effects of this antidepressant and antipsychotic treatment.

Repeated administration of fluoxetine, desipramine and tranylcypromine increases dopamine D2-like but not D1-like receptor function in the rat

We tested the effect of repeated treatment (twice daily for 14 days) of rats with the antidepressant drugs fluoxetine, desipramine and tranylcypromine, on the behavioural response to the non-selective dopamine (DA) receptor agonist, apomorphine, the D1-like receptor agonists, SKF 38393 and SKF 81297 and the D2-like receptor agonists, RU 24213 and quinpirole. Agonist-induced behaviour was monitored by automated activity meters and direct observation using a checklist scoring method. Fluoxetine, desipramine and tranylcypromine enhanced (albeit to a varying degree) the behavioural responses to apomorphine (0.75 mg/kg, s.c.), quinpirole (0.25 mg/kg, s.c.) and RU 24213 (0.75 mg/kg, s.c.). In contrast, fluoxetine, desipramine and tranylcypromine did not increase the behavioural responses to SKF 38393 (7.5 mg/kg, s.c.) and SKF 81297 (0.5 mg/kg, s.c.). Finally, fluoxetine, despiramine and tranylcypromine did not modify the behavioural responses to the concomitant administration of SKF 38393 (7.5 mg/kg, s.c.) and quinpirole (0.25 mg/kg, s.c.). Our data suggest that repeated administration of fluoxetine, desipramine and tranylcypromine increases central DA D2-like but not D1-like receptor function.

Repeated electroconvulsive shock promotes the sprouting of serotonergic axons in the lesioned rat hippocampus

This study reports the effect of repeated electroconvulsive shock on the sprouting of 5-hydroxytryptamine neurons in the partly lesioned rat dorsal hippocampus. We have adopted a 5-hydroxytryptamine homotypic collateral sprouting model to examine whether electroconvulsive shock administration altered the rate of 5-hydroxytryptamine axonal reinnervation of the dorsal hippocampus. The 5-hydroxytryptamine innervation of hippocampus originates from the median raphe via the cingulum bundle and the fimbria-fornix. Lesioning of the cingulum bundle has previously been shown to cause sprouting of intact 5-hydroxytryptamine afferents originating from the unharmed fimbria-fornix. Rats were unilaterally injected with the 5-hydroxytryptamine neurotoxin, 5,7-dihydroxytryptamine, into the right cingulum bundle and 5-hydroxytryptamine immunoreactivity in the dorsal hippocampus was investigated 1, 3, 6 and 12weeks after the injection. The lowest level of 5-hydroxytryptamine-immunoreactivity in the hippocampus was detected at three weeks after the lesion. At six weeks, 5-hydroxytryptamine immunoreactive fibres started to reappear, and at 12weeks the level of 5-hydroxytryptamine immunoreactivity was similar to that observed on the unlesioned side. Based on this time-course, six weeks was chosen as the time-point to investigate the action of a course of repeated electroconvulsive shock administrations. Repeated electroconvulsive shock (five shocks over 10days) doubled the number of sprouting 5-hydroxytryptamine-immunoreactive fibres and significantly increased levels of the 5-hydroxytryptamine metabolite, 5-hydroxyindoleacetic acid. The present data provide the first direct evidence that electroconvulsive shock enhances 5-hydroxytryptamine axon sprouting in the partly lesioned hippocampus. This is an effect which may contribute to the therapeutic effect of electroconvulsive therapy in major depression.

Mechanism underlying the therapeutic effects of electroconvulsive therapy (ECT) on depression

Electroconvulsive therapy (ECT) is used to treat drug-resistant depressive disorders. The results of studies on the mechanism underlying the effectiveness of ECT on depression are still controversial. ECT stimulus is usually larger than the threshold of induction of seizures and activation of whole-brain is believed to be necessary to produce therapeutic effects. A single ECT session induces alterations of the electroencephalogram (EEG) including initial epileptic discharges, then slow waves, and finally flattened EEG. Repeated ECT results in an increasing number of slower waves in the EEG for as long as a month. ECT-induced changes in various neurotransmitter systems have also been reported. Serotonin (5-hydroxytryptamine, 5-HT) is one of the most important neurotransmitters involved in depressive illness, and ECT alters several 5-HT-receptor subtypes in the central nervous system. 5-HT1A receptors in post-synaptic neurons are sensitized by repeated ECT, but those in pre-synaptic neurons (auto-receptors) are not changed. In addition, our electrophysiological studies have shown that ECT increases sensitivity to 5-HT of 5-HT3 receptors in the hippocampus, resulting in an increase in release of neurotransmitters such as glutamate and gamma-aminobutyric acid. In contrast, ECT decreases the auto-receptor functions in noradrenergic and dopaminergic neurons in the locus coeruleus and substantia nigra, respectively, resulting in an increase in release of noradrenaline and dopamine. In conclusion, 5-HT1A-receptor sensitization may be important for explaining the effectiveness of ECT, as this change induces a decrease in the number of 5-HT2A receptors that are elevated in depressive patients. Facilitation of neurotransmitter releases due to 5-HT3-receptor sensitization by ECT may also play an important role in effective treatment of depressive patients refractory to therapeutic drugs.

Repeated electroconvulsive shock extends the duration of enhanced gene expression for BDNF in rat brain compared with a single administration

Brain-derived neurotrophic factor (BDNF) is known to modulate synaptic function as well as to promote neuronal growth in the adult brain. The aim of the present study was to compare the duration of electroconvulsive shock (ECS)-induced BDNF gene expression following a single shock (acute ECS) to the more clinically relevant situation, where repeated shocks (chronic ECS) are administered. For this purpose, we have used quantitative in situ hybridisation with a 35S-labelled oligonucleotide probe complementary to mRNAs encoding genes for all forms of BDNF. The results confirm previous studies that the administration of ECS increases BDNF mRNA abundance in parts of rat brain with particularly marked changes in the granule cell layer of the dentate gyrus. We also for the first time show the long lasting nature of the increase in BDNF mRNA abundance measured after chronic ECS, i.e., significant increases in BDNF mRNA persisted up to 48 h after the last shock. Acute ECS at 6 h after the shock produced a slightly more pronounced effect on BDNF mRNA abundance than chronic ECS 6 h after the last shock. However, this change was not detectable already 24 h after a single ECS. These results indicate that repeated ECS induces adaptive changes in BDNF mRNA expression.

Alterations in behavior and opioid gene expression induced by the novel tropane analog WF-31

The effects of the acute administration of the serotonin-selective tropane analog, [2beta-propanoyl-3beta-(4-isopropylphenyl)-tropane, WF-31, on spontaneous locomotor activity were measured and compared to those of the highly selective serotonin uptake inhibitor, fluoxetine and cocaine, a non-selective re-uptake inhibitor of dopamine and serotonin. WF-31 (1, 10 and 30 mg/kg)-elicited increases in locomotor behaviors when compared to vehicle-treated rats. This increased activity was blocked by pre-treatment with the dopaminergic antagonist, flupenthixol, suggesting that these effects may be mediated by dopaminergic mechanisms. Cocaine, but not fluoxetine, also elicited increases in behaviors. In addition, the effects of these three compounds on opioid peptide gene expression were also assessed using in situ hybridization histochemistry in the same animals. The acute administration of both WF-31 and cocaine increased the expression of preprodynorphin mRNA in the dorsal striatum whereas fluoxetine had no effect. Expression of striatal preproenkephalin mRNA was augmented by all three compounds. Within the nucleus accumbens, PPD mRNA levels were affected only by treatment with WF-31, an effect that was blocked by pre-treatment with flupenthixol. In contrast, the acute administration of both WF-31 and fluoxetine, but not cocaine, increased the expression of preproenkephalin mRNA. These increases, however, were not reversed by pre-treatment with flupenthixol. Despite its profile in vitro as a relatively selective serotonin re-uptake inhibitor, some of the in vivo actions of WF-31 appear to be mediated by dopaminergic mechanisms. These data further suggest that the mechanisms underlying expression of the opioid peptides in the nucleus accumbens may vary from those in the dorsal striatum.

Repeated administration of antidepressant drugs affects the levels of mRNA coding for D1 and D2 dopamine receptors in the rat brain

The present study examined the effects of acute and repeated administration of three antidepressant drugs (imipramine, citalopram and (+)-oxaprotiline) on the levels of mRNA coding for dopamine D1 and D2 receptors in the rat brain. Quantitive in situ hybridization with 35S-labelled oligonucleotide probes has been utilised. The level of mRNA coding for dopamine D1 receptor (D1 mRNA) is decreased following repeated administration of imipramine, both in the nucleus accumbens and in the striatum. On the other hand, the repeated administration of citalopram, the selective inhibitor of serotonin reuptake, resulted in an increase in the level of D1 mRNA in the striatum and in the core region of nucleus accumbens. A similar tendency, i.e.: an increase in the level of D1 mRNA was observed after repeated administration of (+)-oxaprotiline, a selective inhibitor of noradrenaline reuptake. The level of mRNA coding for dopamine D2 receptors (D2 mRNA) was increased in all the brain regions studied, both after administration of imipramine and citalopram. (+)-Oxaprotiline did not produce any statistically significant changes in the level of D2 mRNA. The results obtained in this study indicate that the levels of mRNA coding for dopamine D1 and D2 receptors are regulated by the antidepressant drugs. The changes concerning the dopamine D2 receptors are more consistent and fit in with the previously described binding and behavioral effects and seem to be important for the mechanism of action of antidepressant drugs.

Differential effects of acute and chronic electroconvulsive shock on the abundance of messenger RNAs for voltage-dependent potassium channel subunits in the rat brain

The effect of acute and chronic electroconvulsive shock on the abundance of messenger RNAs encoding voltage-dependent potassium channel subunits in the rat brain was determined by in situ hybridization histochemistry with [35S]dATP-labelled oligonucleotides at 6 h, 24 h and three weeks following the last shock. The messenger RNA abundance of two voltage-dependent potassium channel subunits, Kv1.2 and Kv4.2, was altered by electroconvulsive shock but in different ways. In acute electroconvulsive shock experiments, Kv1.2 and Kv4.2 messenger RNA abundance in the dentate gyrus were reduced 6 h following the shock and returned to control levels after 24 h. In chronic electroconvulsive shock-treated rats, Kv1.2 messenger RNA abundance showed similar changes to those in acute electroconvulsive shock: it was reduced 6 h after the last shock and had recovered after 24 h. Kv4.2 messenger RNA abundance in chronic electroconvulsive shock-treated rats, however, showed adaptive changes: 6 h after the last shock there were no changes in its abundance while 24 h after the last shock there was a significant increase in the dentate gyrus. The changes in Kv1.2 and Kv4.2 messenger RNA abundance following electroconvulsive shock were only observed in the dentate gyrus and not in cornu ammonis 1 and cornu ammonis 3 of hippocampus or frontal-parietal cortex. Two other potassium channel subunits, Kv1.1 and Kv1.4, were not affected by either acute or chronic electroconvulsive shock. These findings indicate that acute and chronic electroconvulsive shock affect the gene expression of voltage-dependent potassium channel subunits with specificities for channel type, anatomical region and timing.

Decreased levels of preprotachykinin-A and tachykinin NK1 receptor mRNA in specific region of the rat striatum after electroconvulsive stimuli

The effects of electroconvulsive stimuli on the expression of mRNAs coding for preprotachykinin-A and the substance P-sensitive tachykinin NK1 receptor were examined in subregions of the rat striatum. In the electroconvulsive stimuli-treated animals, a 43% decrease in preprotachykinin-A mRNA was detected in the dorso-lateral caudate-putamen as compared to sham electroconvulsive stimuli treated animals. A 75% decrease in numerical density of tachykinin NK1 receptor mRNA positive neurons was found in the caudal part of the nucleus accumbens core. These findings provide new evidence for selective effects of electroconvulsive stimuli on specific populations of neurons in the rat striatum.