Neuronal electrical high frequency stimulation modulates presynaptic GABAergic physiology

The electrical stimulation of the central nucleus of the amygdala in combination with dopamine receptor antagonist reduces the acquisition phase of morphine-induced conditioned place preference in male rat

Background and purpose

The central nucleus of the amygdala (CeA) is one of the nuclei involved in the reward system. The aim of the current study was to investigate the electrical stimulation (e-stim) effect of the CeA in combination with dopamine D1 receptor antagonist on morphine-induced conditioned place preference (CPP) in male rats.

Experimental approach

A 5-day procedure of CPP was used in this study. Morphine was administered at an effective dose of 5 mg/kg, and SCH23390 as a selective D1 receptor antagonist was administrated into the CeA. In addition, the CeA was stimulated with an intensity of the current of 150 μA. Finally, the dependence on morphine was evaluated in all experimental groups.

Findings/Results

Morphine significantly increased CPP. While the blockade of the D1 receptor of the CeA reduced the acquisition phase of morphine-induced CPP. Moreover, the combination of D1 receptor antagonist and e-stim suppressed morphine-induced CPP, even it induced an aversion.

Conclusion and implication

The current study suggests that the administration of dopamine D1 receptor antagonist into the CeA in combination with e-stim could play a prominent role in morphine dependence.

Inhibition Within the Lateral Habenula-Implications for Affective Disorders

The lateral habenula (LHb) is a key brain region implicated in the pathology of major depressive disorder (MDD). Specifically, excitatory LHb neurons are known to be hyperactive in MDD, thus resulting in a greater excitatory output mainly to downstream inhibitory neurons in the rostromedial tegmental nucleus. This likely results in suppression of downstream dopaminergic ventral tegmental area neurons, therefore, resulting in an overall reduction in reward signalling. In line with this, increasing evidence implicates aberrant inhibitory signalling onto LHb neurons as a co-causative factor in MDD, likely as a result of disinhibition of excitatory neurons. Consistently, growing evidence now suggests that normalising inhibitory signalling within the LHb may be a potential therapeutic strategy for MDD. Despite these recent advances, however, the exact pharmacological and neural circuit mechanisms which control inhibitory signalling within the LHb are still incompletely understood. Thus, in this review article, we aim to provide an up-to-date summary of the current state of knowledge of the mechanisms by which inhibitory signalling is processed within the LHb, with a view of exploring how this may be targeted as a future therapy for MDD.

Electrical cortical stimulations modulate spike and post-spike slow-related high-frequency activities in human epileptic foci

OBJECTIVE

Using interictal epileptiform discharges (IEDs), consisting of spikes and post-spike slow waves (PSSs), and IED-related high-frequency activities (HFAs), we elucidated inhibitory effects of electrical cortical stimulation (ECS) on human epileptic foci.

METHODS

We recruited 8 patients with intractable focal epilepsy, and 50-Hz ECS was applied to the seizure-onset zone (SOZ) and non-SOZ. Before (5-min) and after (20-min) ECS, we evaluated the number of IED, the amplitudes of spikes and PSSs, spike-related HFA power, and PSS-related low gamma (30-50 Hz) activities.

RESULTS

SOZ stimulation significantly decreased the number of IEDs and amplitude of spikes. Spike-related HFA power values in fast ripple (200-300 Hz) and ripple (80-150 Hz) bands were significantly suppressed only by SOZ stimulation in 4 and 3 patients, respectively. Among 4 patients with discrete PSSs, the amplitude ratio of spike/PSS decreased and the PSS-related low gamma activity power increased significantly in 2 patients and marginally in 1 patient.

CONCLUSIONS

ECS potentially modulates cortical excitability by reducing excitation and increasing inhibition, and monitoring IED-related HFAs may help achieve the optimal effects of ECS.

SIGNIFICANCE

IED and IED-related HFAs are dynamic, potential surrogate markers for epileptic excitability during the interictal period.

Transmitter self-regulation by extracellular glutamate in fresh human cortical slices

Glutamate is thought to be the most important excitatory neurotransmitter in the CNS, while glutamine predominantly serves as a precursor and metabolite in the glutamate-glutamine cycle. To verify the interaction between intrinsic extracellular glutamate, y-aminobutyric acid (GABA) levels and glial glutamine outflow in human tissue, fresh brain slices from human frontal cortex were incubated in superfusion chambers in vitro. Human neocortical tissue was obtained during surgical treatment of subcortical brain tumors. For superfusion experiments, the white matter was separated and discarded from the gray matter, which finally contained all six neocortical layers. Outflows of endogenous glutamate, GABA and glutamine were established after a 40-min washout period and amounts were simultaneously quantified after two-phase derivatization by high-performance liquid chromatography with electrochemical detection. Under basal conditions, amounts of glutamate could be found 20-fold in comparison to the inhibitory neurotransmitter GABA, whereas this excitatory predominance markedly declined after veratridine-induced activation. The basal glutamate:glutamine ratio of extracellular levels was approximately 1:2. Blockade or activation of the voltage-gated sodium channel by tetrodotoxin or veratridine significantly modulated glutamate levels, but the glutamate:glutamine ratio was nearly constant with 1:2. When the EAAT blocker TBOA was employed, glutamine remained nearly unchanged whereas glutamate significantly enhanced. These results led us to suggest that glutamine release through glial SN1 is related to EAAT activity that can be modulated by intrinsic extracellular glutamate in human cortical slices.

High-frequency stimulation of nucleus accumbens changes in dopaminergic reward circuit

Deep brain stimulation (DBS) of the nucleus accumbens (NAc) is a potential remedial therapy for drug craving and relapse, but the mechanism is poorly understood. We investigated changes in neurotransmitter levels during high frequency stimulation (HFS) of the unilateral NAc on morphine-induced rats. Sixty adult Wistar rats were randomized into five groups: the control group (administration of saline), the morphine-only group (systematic administration of morphine without electrode implantation), the morphine-sham-stimulation group (systematic administration of morphine with electrode implantation but not given stimulation), the morphine-stimulation group (systematic administration of morphine with electrode implantation and stimulation) and the saline-stimulation group (administration of saline with electrode implantation and stimulation). The stimulation electrode was stereotaxically implanted into the core of unilateral NAc and microdialysis probes were unilaterally lowered into the ipsilateral ventral tegmental area (VTA), NAc, and ventral pallidum (VP). Samples from microdialysis probes in the ipsilateral VTA, NAc, and VP were analyzed for glutamate (Glu) and γ-aminobutyric acid (GABA) by high-performance liquid chromatography (HPLC). The levels of Glu were increased in the ipsilateral NAc and VP of morphine-only group versus control group, whereas Glu levels were not significantly changed in the ipsilateral VTA. Furthermore, the levels of GABA decreased significantly in the ipsilateral NAc, VP, and VTA of morphine-only group when compared with control group. The profiles of increased Glu and reduced GABA in morphine-induced rats suggest that the presence of increased excitatory neurotransmission in these brain regions. The concentrations of the Glu significantly decreased while the levels of GABA increased in ipsilateral VTA, NAc, and VP in the morphine-stimulation group compared with the morphine-only group. No significant changes were seen in the morphine-sham stimulation group compared with the morphine-only group. These findings indicated that unilateral NAc stimulation inhibits the morphine-induced rats associated hyperactivation of excitatory neurotransmission in the mesocorticolimbic reward circuit.

Chronic deep brain stimulation of the lateral habenula nucleus in a rat model of depression

In the present study, we aim to determine the antidepressant effects of chronic deep brain stimulation (DBS) of the lateral habenula nucleus (LHb) in a rat model of depression and to explore the potential mechanism of DBS induced improvement of depressive symptoms. To establish the rat depression model, animals were repeatedly exposed to a set of chronic mild stressors for four consecutive weeks. The open-field and sucrose consumption tests were used as measures of depression. For DBS treatment, rats were stereotaxically implanted with electrodes into the LHb and stimulated over a course of 28 d. A separate positive control group was given pharmacotherapy with clomipramine hydrochloride. Open-field testing was used to determine behavioral changes following DBS treatment. Monoamine concentrations in blood and brain tissues were determined by fluorescence spectrophotometry. This study demonstrates that DBS of the LHb region significantly improved depressive-like symptoms in the rat model. These improvements manifested as elevated numbers of crossings and rearings during the open-field test in DBS-treated depressed rats compared to controls. In addition, concentrations of monoamines including norepinephrine (NE), dopamine (DA), and serotonin (5-HT) in blood serum and brain tissues were also increased by DBS of the LHb. Therefore, significant improvements in all outcomes were detected following chronic DBS treatment. These results indicate that long-term DBS treatment of the LHb region effectively improved depressive symptoms in rats, likely as a result of elevated monoamine levels. LHb DBS may therefore provide a valuable therapeutic strategy for the clinical treatment of depression.

Effects of high frequency electrical stimulation and R-verapamil on seizure susceptibility and glutamate and GABA release in a model of phenytoin-resistant seizures

The present study was focused to characterize the effects of intrahippocampal application of R-verapamil, a P-glycoprotein blocker, and High Frequency Electrical Stimulation (HFS) at 130 Hz, on seizure susceptibility and extracellular concentrations of glutamate and γ-aminobutyric acid (GABA) in hippocampus of kindled rats with drug-resistant seizures. Fully kindled rats classified in responsive and non-responsive to phenytoin were used for this purpose. In contrast with responsive animals, non-responsive rats showed lower afterdischarge threshold (ADT) values in pre-kindling conditions and required less number of kindling trials to achieve the kindled state. Once the animals attained the kindled state, both epileptic groups presented high glutamate and low GABA interictal release, effect more evident in non-responsive rats. In hippocampus of responsive animals, GABA levels demonstrated two increases at 120 and 240 min after the ictal event, a situation no detected for non-responsive rats. Kindled animals receiving hippocampal HFS showed augmented ADT, an effect associated with enhanced GABA release in responsive rats. Intrahippocampal perfusion of R-verapamil (5 mM) decreased the seizure susceptibility (high ADT values), enhanced the interictal GABA release and the postictal levels of glutamate and GABA in responsive and non-responsive rats. It is conclude that alterations of glutamate and GABA release in the epileptic hippocampus of non-responsive animals resemble those found in hippocampus of patients with refractory TLE. In addition, intrahippocampal application of HFS and R-verapamil modifies the amino acid release and reduces the seizure susceptibility of both, responsive and non-responsive rats.

Selective GABA release as a mechanistic basis of high-frequency stimulation used for the treatment of neuropsychiatric diseases

Electrical high-frequency stimulation (HFS) is applied in many brain areas to treat various clinical syndromes. The nearly identical constellation of stimulation parameters raises the question of a unique mechanism of action of this therapeutic option. The identification of a single HFS mechanism may help to optimize the HFS technology by targeting this single mechanism. Experimentally, only axonal membranes are targets of HFS, but not other membranes of neurons or glial cells. Within all HFS target regions, axons of excitatory glutamatergic and inhibitory GABAergic neurons are present and play roles in all clinical syndromes treated successfully with HFS. Therefore, glutamatergic or GABAergic fibres are likely candidates as mediators of a unique HFS mode of action. The selective involvement of another neuronal fibre type (e.g. monoaminergic, cholinergic, etc.) in the HFS mode of action is highly unlikely since the regional and syndromal dissimilarity of the clinical HFS applications precludes the assumption of such a fibre type as primary HFS site of action. Our recent experimental finding that HFS of human neocortical slices induces the action potential-mediated release of GABA, but not of glutamate, simplifies the possibilities to explain the HFS mode of action, as the explanation now may concentrate on GABAergic axons only. Thus, we are analysing, on the basis of the pathophysiological grounds of the various syndromes treated with deep brain stimulation, whether a selective GABA release is a collective explanation of the mode of action of HFS. We suggest that selective GABA release indeed may needfully and sufficiently explain efficacy and side effects of HFS.

Electrical high frequency stimulation of the caudate nucleus induces local GABA outflow in freely moving rats

Electrical high frequency stimulation of the globus pallidus internus or the subthalamic nucleus has beneficial motor effects in advanced Parkinson's disease. The mechanisms underlying these clinical results remain, however, unclear. From previous in vitro studies it is proposed that the gamma-aminobutyric acid (GABA) system is involved in the effectiveness of electrical high frequency stimulation (HFS). In these experiments, we developed an in vivo model that allows for simultaneous and collocated microdialysis and HFS by electrical pulses of 124 Hz in the caudate nucleus of freely moving rats. GABA and glutamate outflow were sampled by microdialysis technique and quantified after pre-column o-phthaldialdehyde sulphite derivatization using HPLC with electrochemical detection. As the most outstanding result, we could demonstrate that high frequency stimulation significantly increased basal GABA outflow without affecting glutamate levels in freely moving rats.

K(ATP)-dependent neurotransmitter release in the neuronal network of the rat caudate nucleus

K(ATP) channels can couple the bioenergetic metabolism of the cell to membrane excitability. Here, we show gamma-aminobutyric acid (GABA) mediated inhibition of dopamine outflow from slices of the rat caudate nucleus that is regulated by extracellular glucose via high- and low-affinity K(ATP) channels. During glucose reduction, a biphasic dopamine effect could be observed with first a dopamine increase followed by a decline at low glucose concentrations. Both phases were inhibited by glibenclamide. Pinacidil decreased DA outflow without an effect of glucose reduction implying an overall activation of K(ATP) channels. The first phase with dopamine increase was related to reduced GABAergic activity and could be blocked by bicuculline. Our results may be explained by different types of K(ATP) channels with low affinity of ATP and glibenclamide on inhibitory GABAergic and high-affinity on excitatory DAergic neurons. This led us to suggest a biological principle through which neuronal networks are functioning.

Neuronal electrical high frequency stimulation enhances GABA outflow from human neocortical slices

Electrical high frequency stimulation of the globus pallidus internus or the subthalamic nucleus has beneficial motor effects in advanced Parkinson's disease. The mechanisms underlying these clinical results remain, however, unclear. From previous studies it is proposed that the gamma-aminobutyric acid (GABA) system is involved in the effectiveness of electrical high frequency stimulation. In these experiments, human neocortical slices were stimulated electrically (130 Hz) in vitro, and GABA outflow was measured after o-phthaldialdehyde sulphite derivatization using HPLC with electrochemical detection. Our results could demonstrate that high frequency stimulation (HFS) significantly increased basal GABA outflow in the presence of submaximal concentrations of the voltage-gated sodium channel opener veratridine. This effect could be abolished by the GABA antagonists bicuculline or picrotoxin. These results suggest that HFS has an activating effect on GABAergic neuronal terminals in human neocortical slices, depending on sodium and chloride influx. Since GABA plays a role in CNS disorders of basal ganglia, anxiety and epilepsy, its neocortical modulation by HFS may be (patho)physiologically relevant.

Modulation of a neuronal network by electrical high frequency stimulation in striatal slices of the rat in vitro

The effects of the GABA(A) receptor antagonist bicuculline, the D2-like receptor antagonist sulpiride and the D1-like receptor antagonist SCH-23390 on the electrical high frequency stimulation (HFS)-evoked gamma-aminobutyric acid (GABA) and dopamine (DA) release were measured from slices of the rat striatum by means of HPLC method with electrochemical detection. HFS with 130Hz stimulated veratridine-activated GABAergic neurons resulting in an increased GABA outflow while DA outflow decreased. In the presence of the GABA(A) receptor antagonist bicuculline extracellular GABA and DA outflow were enhanced. When the competitive dopamine D2-like receptor antagonist S-(-)-sulpiride was added to incubation medium, the HFS-evoked stimulatory effect on GABA outflow declined to values found after veratridine (1microM) without HFS. After co-incubation of sulpiride and the competitive D1-like receptor antagonist R-(+)-SCH-23390, the effect of sulpiride on HFS plus veratridine-evoked GABA outflow was completely reversed. Neither sulpiride nor SCH-23390 had any influence on the effect of HFS on veratridine-induced DA outflow. No effect of HFS on glutamate outflow was observed in all experiments. These results led us to suggest that in our model HFS primarily affects GABAergic neurons. These neurons are embedded in a neuronal network with a GABA-dopamine circuit, and thus, HFS interacts with a neuronal network, not only with one neurotransmitter system or one neuron population.