The theta-related firing activity of parvalbumin-positive neurons in the medial septum-diagonal band of Broca complex and their response to 5-HT1A receptor stimulation in a rat model of Parkinson's disease

Lateral habenula 5-HT1B receptors are involved in regulation of anxiety-like behaviors in parkinsonian rats

Although the output of the lateral habenula (LHb) controls the activity of midbrain dopaminergic and serotonergic systems, which are implicated in the pathophysiology of anxiety, it is not clear the role of LHb 5-HT1B receptors in regulation of anxiety-like behaviors, particularly in Parkinson's disease-related anxiety. In this study, unilateral 6-hydroxydopamine lesions of the substantia nigra pars compacta in rats induced anxiety-like behaviors, led to decreased normalized δ power and increased normalized θ power in the LHb, and decreased dopamine (DA) level in the prelimbic cortex (PrL) compared with sham rats. Down-regulation of LHb 5-HT1B receptors by RNA interference produced anxiety-like effects, decreased normalized δ power and increased normalized θ power in the LHb in both sham and lesioned rats. Further, intra-LHb injection of 5-HT1B receptor agonist CP93129 induced anxiolytic-like responses, increased normalized δ power and decreased normalized θ power in the LHb, and increased DA and serotonin (5-HT) release in the PrL; conversely, 5-HT1B receptor antagonist SB216641 produced anxiety-like effects, decreased normalized δ power and increased normalized θ power in the LHb, and decreased DA and 5-HT release in the PrL in sham and lesioned rats. Additionally, effects of CP93129 and SB216641 on the behaviors, normalized δ and θ power in the LHb, and DA and 5-HT release in the PrL were decreased in lesioned rats, which were consistent with down-regulation of LHb 5-HT1B receptors after DA depletion. Collectively, these findings suggest that 5-HT1B receptors in the LHb are involved in the regulation of anxiety-like behaviors.

Long-term intermittent theta burst stimulation enhanced hippocampus-dependent memory by regulating hippocampal theta oscillation and neurotransmitter levels in healthy rats

Intermittent theta burst stimulation (iTBS), an updated pattern of high-frequency repetitive transcranial magnetic stimulation, is a potential candidate for improving memory. The hippocampus has been shown to be involved in the memory-enhancing effect induced by iTBS. However, it remains largely unknown whether this effect is achieved by regulating hippocampal theta oscillation and neurotransmitters gamma-aminobutyric acid (GABA) and glutamate, which are strongly related to memory. Thus, we investigated the effect of 14 days of iTBS on hippocampus-dependent memory and further explored the roles of hippocampal theta oscillation and neurotransmitters GABA and glutamate in this effect. We found that compared to sham iTBS, real iTBS enhanced hippocampus-dependent memory measured by hole-board test and object place recognition test. Further, real iTBS increased the density of c-Fos positive neurons and normalized power of theta oscillation in the dorsal hippocampus (dHip) compared to sham iTBS. Interestingly, we observed a decrease in the level of extracellular GABA and an increase in the level of extracellular glutamate in the dHip after real iTBS. Our results suggest that long-term iTBS improved hippocampus-dependent memory, which may be attributed to the enhancement of theta oscillation and altered levels of extracellular GABA and glutamate in the dHip.

Dose and time-dependence of acute intermittent theta-burst stimulation on hippocampus-dependent memory in parkinsonian rats

Background

The treatment options for cognitive impairments in Parkinson's disease (PD) are limited. Repetitive transcranial magnetic stimulation has been applied in various neurological diseases. However, the effect of intermittent theta-burst stimulation (iTBS) as a more developed repetitive transcranial magnetic stimulation paradigm on cognitive dysfunction in PD remains largely unclear.

Objective

Our aim was to explore the effect of acute iTBS on hippocampus-dependent memory in PD and the mechanism underlying it.

Methods

Different blocks of iTBS protocols were applied to unilateral 6-hydroxidopamine-induced parkinsonian rats followed by the behavioral, electrophysiological and immunohistochemical analyses. The object-place recognition and hole-board test were used to assess hippocampus-dependent memory.

Results

Sham-iTBS and 1 block-iTBS (300 stimuli) didn't alter hippocampus-dependent memory, hippocampal theta rhythm and the density of c-Fos- and parvalbumin-positive neurons in the hippocampus and medial septum. 3 block-iTBS (900 stimuli) alleviated 6-hydroxidopamine-induced memory impairments, and increased the density of hippocampal c-Fos-positive neurons at 80 min post-stimulation but not 30 min compared to sham-iTBS. Interestingly, 3 block-iTBS first decreased and then increased normalized theta power during a period of 2 h following stimulation. Moreover, 3 block-iTBS decreased the density of parvalbumin-positive neurons in the medial septum at 30 min post-stimulation compared to sham-iTBS.

Conclusion

The results indicate that multiple blocks of iTBS elicit dose and time-dependent effects on hippocampus-dependent memory in PD, which may be attributed to changes in c-Fos expression and the power of theta rhythm in the hippocampus.

Low intensity repetitive transcranial magnetic stimulation modulates brain-wide functional connectivity to promote anti-correlated c-Fos expression

Repetitive transcranial magnetic stimulation (rTMS) induces action potentials to induce plastic changes in the brain with increasing evidence for the therapeutic importance of brain-wide functional network effects of rTMS; however, the influence of sub-action potential threshold (low-intensity; LI-) rTMS on neuronal activity is largely unknown. We investigated whether LI-rTMS modulates neuronal activity and functional connectivity and also specifically assessed modulation of parvalbumin interneuron activity. We conducted a brain-wide analysis of c-Fos, a marker for neuronal activity, in mice that received LI-rTMS to visual cortex. Mice received single or multiple sessions of excitatory 10 Hz LI-rTMS with custom rodent coils or were sham controls. We assessed changes to c-Fos positive cell densities and c-Fos/parvalbumin co-expression. Peak c-Fos expression corresponded with activity during rTMS. We also assessed functional connectivity changes using brain-wide c-Fos-based network analysis. LI-rTMS modulated c-Fos expression in cortical and subcortical regions. c-Fos density changes were most prevalent with acute stimulation, however chronic stimulation decreased parvalbumin interneuron activity, most prominently in the amygdala and striatum. LI-rTMS also increased anti-correlated functional connectivity, with the most prominent effects also in the amygdala and striatum following chronic stimulation. LI-rTMS induces changes in c-Fos expression that suggest modulation of neuronal activity and functional connectivity throughout the brain. Our results suggest that LI-rTMS promotes anticorrelated functional connectivity, possibly due to decreased parvalbumin interneuron activation induced by chronic stimulation. These changes may underpin therapeutic rTMS effects, therefore modulation of subcortical activity supports rTMS for treatment of disorders involving subcortical dysregulation.

Blockade of pre-synaptic and post-synaptic GABAB receptors in the lateral habenula produces different effects on anxiety-like behaviors in 6-hydroxydopamine hemiparkinsonian rats

Although the output of the lateral habenula (LHb) controls the activity of midbrain dopaminergic and serotonergic systems, which are implicated in the pathophysiology of anxiety, it is not known how blockade of GABA_B receptors in the region affects anxiety-like behaviors, particularly in Parkinson's disease-related anxiety. In this study, unilateral 6-hydroxydopamine lesions of the substantia nigra pars compacta in rats induced anxiety-like behaviors, led to hyperactivity of LHb neurons and decreased the level of extracellular dopamine (DA) in the basolateral amygdala (BLA) compared to sham-lesioned rats. Intra-LHb injection of pre-synaptic GABA_B receptor antagonist CGP36216 produced anxiolytic-like effects, while the injection of post-synaptic GABA_B receptor antagonist CGP35348 induced anxiety-like responses in both groups. Further, intra-LHb injection of CGP36216 decreased the firing rate of the neurons, and increased the GABA/glutamate ratio in the LHb and release of DA and serotonin (5-HT) in the BLA; conversely, CGP35348 increased the firing rate of the neurons and decreased the GABA/glutamate ratio and release of DA and 5-HT in sham-lesioned and the lesioned rats. However, the doses of the antagonists producing these behavioral effects in the lesioned rats were lower than those in sham-lesioned rats, and the duration of action of the antagonists on the firing rate of the neurons and release of the neurotransmitters was prolonged in the lesioned rats. Collectively, these findings suggest that pre-synaptic and post-synaptic GABA_B receptors in the LHb are involved in the regulation of anxiety-like behaviors, and degeneration of the nigrostriatal pathway up-regulates function and/or expression of these receptors.

Involvement of lateral habenula α1 subunit-containing GABAA receptor-mediated inhibitory transmission in the regulation of depression-related behaviors in experimental Parkinson's disease

The lateral habenula (LHb) plays an important role in the regulation of depression. At present, it is not clear whether GABA_A receptor-mediated inhibitory transmission in the LHb is involved in Parkinson's disease (PD)-associated depression. In this study, unilateral 6-hydroxydopamine lesions of the substantia nigra in rats induced depressive-like behaviors and led to hyperactivity of LHb neurons compared to sham-operated rats, which attribute to depletion of dopamine, and decreased synthesis and release of GABA and increased release of glutamate in the LHb. Intra-LHb injection of GABA_A receptor agonist muscimol produced antidepressant-like effects, while the injection of GABA_A receptor antagonist picrotoxin induced or increased the expression of depressive-like behaviors in sham-operated and the lesioned rats. However, the doses producing these behavioral effects in the lesioned rats were lower than those in sham-operated rats. Intra-LHb injection of muscimol decreased the firing rate of LHb neurons and increased the medial prefrontal cortex serotonin (5-HT) release; conversely, picrotoxin increased the firing rate of the neurons and decreased 5-HT release in two groups of rats. Compared to sham-operated rats, the duration of muscimol and picrotoxin action on the firing rate of the neurons and 5-HT release was prolonged in the lesioned rats. These changes in the lesioned rats were associated with up-regulation of the expression of α1 subunit-containing GABA_A receptors and reduction of GABA release in the LHb. Collectively, our findings suggest that degeneration of the nigrostriatal pathway impairs GABA_A receptor-mediated inhibitory transmission in the LHb, and the transmission is important for regulating PD-associated depression.

Local and Distant Input Controlling Excitation in Layer II of the Medial Entorhinal Cortex

Layer II (LII) of the medial entorhinal cortex (MEC) comprises grid cells that support spatial navigation. The firing pattern of grid cells might be explained by attractor dynamics in a network, which requires either direct excitatory connectivity between phase-specific grid cells or indirect coupling via interneurons. However, knowledge regarding local networks that support in vivo activity is incomplete. Here we identified essential components of LII networks in the MEC. We distinguished four types of excitatory neurons that exhibit cell-type-specific local excitatory and inhibitory connectivity. Furthermore, we found that LII neurons contribute to the excitation of contralateral neurons in the corresponding layer. Finally, we demonstrated that the medial septum controls excitation in the MEC via two subpopulations of long-range GABAergic neurons that target distinct interneurons in LII, thereby disinhibiting local circuits. We thus identified local connections that could support attractor dynamics and external inputs that likely govern excitation in LII.

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LII MEC excitatory neurons can be classified into four cell types

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The four cell types exhibit specific local excitatory and inhibitory connectivity

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LII neurons contribute to the excitation of contralateral LII neurons

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Distinct septal GABAergic neurons exhibit cell-type-specific inhibition in LII MEC

Brainstem system of hippocampal theta induction: The role of the ventral tegmental area

This article summarizes the results of studies concerning the influence of the ventral tegmental area (VTA) on the hippocampal theta rhythm. Temporary VTA inactivation resulted in transient loss of the hippocampal theta. Permanent destruction of the VTA caused a long-lasting depression of the power of the theta and it also had some influence on the frequency of the rhythm. Activation of glutamate (GLU) receptors or decrease of GABAergic tonus in the VTA led to enhancement of dopamine release and increased hippocampal theta power. High time and frequency cross-correlation was detected for the theta band between the VTA and hippocampus during paradoxical sleep and active waking. Thus, the VTA may belong to the broad network involved in theta rhythm regulation. This article also presents a model of brainstem-VTA-hippocampal interactions in the induction of the hippocampal theta rhythm. The projections from the VTA which enhance theta rhythm are incorporated into the main theta generation pathway, in which the septum acts as the central node. The neuronal activity that may be responsible for the ability of the VTA to regulate theta probably derives from the structures associated with rapid eye movement (sleep) (REM) sleep or with sensorimotor activity (i.e., mainly from the pedunculopontine and laterodorsal tegmental nuclei and also from the raphe).

Activation of serotonin2A receptors in the medial septum-diagonal band of Broca complex enhanced working memory in the hemiparkinsonian rats

Serotonin2A (5-HT2A) receptors are highly expressed in the medial septum-diagonal band of Broca complex (MS-DB), especially in parvalbumin (PV)-positive neurons linked to hippocampal theta rhythm, which is involved in cognition. Cognitive impairments commonly occur in Parkinson's disease. Here we performed behavioral, electrophysiological, neurochemical and immunohistochemical studies in rats with complete unilateral 6-hydroxydopamine lesions of the medial forebrain bundle (MFB) to assess the importance of dopamine (DA) depletion and MS-DB 5-HT2A receptors for working memory. The MFB lesions resulted in working memory impairment and decreases in firing rate and density of MS-DB PV-positive neurons, peak frequency of hippocampal theta rhythm, and DA levels in septohippocampal system and medial prefrontal cortex (mPFC) compared to control rats. Intra-MS-DB injection of high affinity 5-HT2A receptor agonist TCB-2 enhanced working memory, increased firing rate of PV-positive neurons and peak frequency of hippocampal theta rhythm, elevated DA levels in the hippocampus and mPFC, and decreased 5-HT level in the hippocampus in control and lesioned rats. Compared to control rats, the duration of the excitatory effect produced by TCB-2 on the firing rate of PV-positive neurons was markedly shortened in lesioned rats, indicating dysfunction of 5-HT2A receptors. These findings suggest that unilateral lesions of the MFB in rats induced working memory deficit, and activation of MS-DB 5-HT2A receptors enhanced working memory, which may be due to changes in the activity of septohippocampal network and monoamine levels in the hippocampus and mPFC.