Mesbah Alam

The rotenone-induced rat model of Parkinson's disease: behavioral and electrophysiological findings.

Exposure to rotenone leads to parkinsonian features, such as loss of dopaminergic neurons in the substantia nigra and motor impairment, however, the validity of this model has recently been questioned. In rodent and monkey models of Parkinsons disease (PD) abnormal neuronal activity in the basal ganglia motor loop has been described, with hyperactivity of the subthalamic nucleus (STN) similar to that found in PD. The present study aims at providing new and more specific evidence for the validity of the rotenone rat model of PD by examining whether neuronal activity in the STN is altered. Male Sprague Dawley rats were treated with rotenone injections (2.5mg/kg bodyweight intraperitoneally) for 60 days. Behavioral analysis showed an impairment in the rotarod and hanging wire test in the rotenone group (p<0.05), accompanied by a decline in tyrosine hydroxylase immunoreactive neurons in the nigro-striatal region (p<0.001). Thereafter, single unit (SU) activities and local field potentials were recorded in the STN in urethane anesthetized rats. The SU analysis revealed a higher neuronal discharge rate (p<0.001), more bursts per minute (p=0.006) and a higher oscillatory activity (p=0.008) in the STN of rotenone treated rats. Spectral analysis showed an increase of relative beta power in the STN as well as in the motor cortex. We found electrophysiological key features of PD pathology and pathophysiology in the STN of rotenone treated rats. Therefore, the rotenone-induced rat model of PD deserves further attention since it covers more aspects than dopamine depletion and implies the reproducibility of PD specific features.

Pedunculopontine nucleus region deep brain stimulation in Parkinson disease: surgical techniques, side effects, and postoperative imaging

The pedunculopontine nucleus (PPN) region has received considerable attention in clinical studies as a target for deep brain stimulation (DBS) in Parkinson disease. These studies have yielded variable results with an overall impression of improvement in falls and freezing in many but not all patients treated. We evaluated the available data on the surgical anatomy and terminology of the PPN region in a companion paper. Here we focus on issues concerning surgical technique, imaging, and early side effects of surgery. The aim of this paper was to gain more insight into the reasoning for choosing specific techniques and to discuss shortcomings of available studies. Our data demonstrate the wide range in almost all fields which were investigated. There are a number of important challenges to be resolved, such as identification of the optimal target, the choice of the surgical approach to optimize electrode placement, the impact on the outcome of specific surgical techniques, the reliability of intraoperative confirmation of the target, and methodological differences in postoperative validation of the electrode position. There is considerable variability both within and across groups, the overall experience with PPN DBS is still limited, and there is a lack of controlled trials. Despite these challenges, the procedure seems to provide benefit to selected patients and appears to be relatively safe. One important limitation in comparing studies from different centers and analyzing outcomes is the great variability in targeting and surgical techniques, as shown in our paper. The challenges we identified will be of relevance when designing future studies to better address several controversial issues. We hope that the data we accumulated may facilitate the development of surgical protocols for PPN DBS.

Deep brain stimulation of the pedunculopontine tegmental nucleus modulates neuronal hyperactivity and enhanced beta oscillatory activity of the subthalamic nucleus in the rat 6-hydroxydopamine model.

Deep brain stimulation (DBS) of the pedunculopontine nucleus (PPN) area has been introduced as a novel surgical therapy for dopamine refractory gait problems, freezing and postural instability in the late stage of Parkinsons disease (PD). Lesions of the pedunculopontine tegmental (PPTg) nucleus, the equivalent of the PPN in rodents, were shown to reduce the elevated discharge rate of the subthalamic nucleus (STN) in the 6-hydroxydopamine (6-OHDA) rat model of PD. In order to further elucidate the modulatory effect of the PPTg on the STN we examined the effect of 25 Hz low frequency PPTg stimulation on neuronal single unit activity and oscillatory local field potentials (LFPs) of the STN, and on the electrocorticogram (ECoG) of the primary motor cortex region in rats with unilateral 6-OHDA induced nigrostriatal lesions. Stimulation of the PPTg reduced the enhanced firing rate in the STN, without affecting the firing pattern or approximate entropy (ApEn). It also reduced the activity in the beta band (15-30 Hz) of the STN, which is elevated in 6-OHDA lesioned rats, without affecting beta activity in the motor cortex. We showed a modulatory effect of PPTg stimulation on altered neuronal STN activity in the PD 6-OHDA rat model, indicating that PPTg DBS may alter activity of the basal ganglia circuitry at least partially. It remains unclear, however, how these changes are exactly mediated and whether they are relevant with regard to the descending PPTg projections in the lower brainstem.

Neuronal firing activity and gene expression changes in the subthalamic nucleus after transplantation of dopamine neurons in hemiparkinsonian rats

Dopamine (DA) depletion in the nigrostriatal system leads to basal ganglia dysfunction both in Parkinsons disease (PD) and in 6-hydroxy dopamine (6-OHDA)-lesioned rats with neuronal hyperactivity in the subthalamic nucleus (STN), i.e. increased firing rate and burst activity, together with enhanced beta oscillatory activity. Moreover, intrastriatal transplantation of DA neurons has been shown to functionally re-innervate the host striatum and restore DA input. However, the effects of those transplanted cells on the STN are not well characterized. Therefore, we transplanted cells, derived from the ventral mesencephalon of E12 rat embryos, intrastriatally in the unilateral 6-OHDA-lesioned rat model of PD. We combined behavioral and histological findings with electrophysiological extracellular recordings in the STN, as well as qRT-PCR analyses of dopaminergic, GABAergic, and glutamatergic transporter and receptor genes in the striatum and the STN. Transplanted animals displayed improved rotational behavior after amphetamine injection by 50% in rats with small grafts (586±109 SEM dopamine cells), or even overcompensation by 116% in rats with large grafts (3486±548 SEM dopamine cells). Electrophysiological measurements revealed, that in rats with large grafts burst activity was not affected, while STN neuronal firing rate, as well as beta oscillatory activity was alleviated, whereas small grafts had less impact. Interestingly, both behavioral and electrophysiological measures were dependent on the number of surviving tyrosine hydroxylase positive cells. Although grafted rats displayed restored expression of the GABA synthesizing enzymes Gad65 and Gad67 in the striatum compared to naive rats, the grafts induced a decreased mRNA expression of dopamine receptor Drd2, glutamate receptors AMPA3, NMDA2A, and NMDA2B, and glutamate transporter Eaat3. Interestingly, the NMDA receptor subunit 2B and glutamate transporter Eaat3 were also less expressed in the STN of grafted animals compared to naive rats. In summary, DA grafts restore functional deficits and cause partial improvement of subthalamic neuronal activity. Incomplete recovery, however, may be due to decreased receptor gene expression induced by DA grafts in the striatum and in the STN.

Pedunculopontine Nucleus Region Deep Brain Stimulation in Parkinson Disease: Surgical Anatomy and Terminology

Several lines of evidence over the last few years have been important in ascertaining that the pedunculopontine nucleus (PPN) region could be considered as a potential target for deep brain stimulation (DBS) to treat freezing and other problems as part of a spectrum of gait disorders in Parkinson disease and other akinetic movement disorders. Since the introduction of PPN DBS, a variety of clinical studies have been published. Most indicate improvements in freezing and falls in patients who are severely affected by these problems. The results across patients, however, have been variable, perhaps reflecting patient selection, heterogeneity in target selection and differences in surgical methodology and stimulation settings. Here we outline both the accumulated knowledge and the domains of uncertainty in surgical anatomy and terminology. Specific topics were assigned to groups of experts, and this work was accumulated and reviewed by the executive committee of the working group. Areas of disagreement were discussed and modified accordingly until a consensus could be reached. We demonstrate that both the anatomy and the functional role of the PPN region need further study. The borders of the PPN and of adjacent nuclei differ when different brainstem atlases and atlas slices are compared. It is difficult to delineate precisely the PPN pars dissipata from the nucleus cuneiformis, as these structures partially overlap. This lack of clarity contributes to the difficulty in targeting and determining the exact localization of the electrodes implanted in patients with akinetic gait disorders. Future clinical studies need to consider these issues.

Effect of deep brain stimulation on levodopa-induced dyskinesias and striatal oscillatory local field potentials in a rat model of Parkinson's disease.

BACKGROUND In Parkinsons disease (PD) dyskinesias appear after long-term dopaminergic treatment. Deep brain stimulation (DBS) of the subthalamic nucleus (STN) or the globus pallidus internus (GPi) is a well-established treatment option for both PD symptoms and complications of medication. OBJECTIVE To elucidate physiological mechanisms of the effect of DBS on levodopa-induced dyskinesias (LID) we investigated both DBS in the GPi and the centromedian-parafascicular complex (CM-Pf), which are part of an internal basal ganglia loop connecting with the dorsolateral striatum. In particular, we focused on changes of oscillatory activity in the dorsolateral striatum, which also presents the entrance region of the basal ganglia (BG). METHODS 6-Hydroxydopamine (6-OHDA) hemiparkinsonian (HP) rats and 6-OHDA lesioned HP rats with LID (HP-LID) were used to compare the effect of DBS in the entopeduncular nucleus (EPN, the equivalent to the human GPi) and the thalamic parafascicular nucleus (Pf, the equivalent of the human CM-Pf) on dyskinesias and neuronal oscillatory activity of selected frequency bands in the dorsolateral striatum on and off levodopa. RESULTS In HP-LID rats the relative beta and gamma power was lower, while relative theta power was higher as compared to HP rats. Chronic DBS of either the EPN or the Pf improved dyskinesia scores in HP-LID rats, and no differences in oscillatory activity were observed between groups. CONCLUSIONS Stimulation of the Pf has a specific impact on dyskinesias, which is similar to that found after EPN stimulation, and which is accompanied by changes of oscillatory activity.

Neuronal Entropy-Rate Feature of Entopeduncular Nucleus in Rat Model of Parkinson’s Disease

The function of the nigro-striatal pathway on neuronal entropy in the basal ganglia (BG) output nucleus, i.e. the entopeduncular nucleus (EPN) was investigated in the unilaterally 6-hyroxydopamine (6-OHDA)-lesioned rat model of Parkinsons disease (PD). In both control subjects and subjects with 6-OHDA lesion of dopamine (DA) the nigro-striatal pathway, a histological hallmark for parkinsonism, neuronal entropy in EPN was maximal in neurons with firing rates ranging between 15 and 25 Hz. In 6-OHDA lesioned rats, neuronal entropy in the EPN was specifically higher in neurons with firing rates above 25 Hz. Our data establishes that the nigro-striatal pathway controls neuronal entropy in motor circuitry and that the parkinsonian condition is associated with abnormal relationship between firing rate and neuronal entropy in BG output nuclei. The neuronal firing rates and entropy relationship provide putative relevant electrophysiological information to investigate the sensory-motor processing in normal condition and conditions such as movement disorders.

Neuronal activity of the prefrontal cortex is reduced in rats selectively bred for deficient sensorimotor gating

Rats selectively bred for deficient prepulse inhibition (PPI), an operant measure of sensorimotor gating in which a weak prepulse stimulus attenuates the response to a subsequent startling stimulus, may be used to study certain pathophysiological mechanisms and therapeutic strategies for neuropsychiatric disorders with abnormalities in information processing, such as schizophrenia and Tourettes syndrome (TS). Little is known about neuronal activity in the medial prefrontal cortex (mPFC) and the nucleus accumbens (NAC), which are involved in the modulation of PPI. Here, we examined neuronal activity in these structures, and also in the entopeduncular nucleus (EPN), since lesions of this region alleviate the PPI deficit. Male rats with breeding-induced high and low expression of PPI (n=7, each) were anesthetized with urethane (1.4 mg/kg). Single-unit activity and local field potentials were recorded in the mPFC, the NAC and in the EPN. In the mPFC discharge rate, measures of irregularity and burst activity were significantly reduced in PPI low compared to PPI high rats (P<0.05), while analysis in the NAC showed approximately inverse behavior. In the EPN no difference between groups was found. Additionally, the oscillatory theta band activity (4-8 Hz) was enhanced and the beta band (13-30 Hz) and gamma band (30-100 Hz) activity was reduced in the NAC in PPI low rats. Reduced neuronal activity in the mPFC and enhanced activity in the NAC of PPI low rats, together with altered oscillatory behavior are clearly associated with reduced PPI. PPI low rats may thus be used to study the pathophysiology and therapeutic strategies for neuropsychiatric disorders accompanied by deficient sensorimotor gating.

Neuronal activity in the medial associative‐limbic and lateral motor part of the rat subthalamic nucleus and the effect of 6‐hydroxydopamine‐induced lesions of the dorsolateral striatum

Lesions of the rat nigrostriatal dopamine system by injection of 6‐hydroxydopamine (6‐OHDA) lead to abnormal neuronal activity in the basal ganglia (BG) motor loop similar to that found in Parkinsons disease (PD). In the BG motor loop the subthalamic nucleus (STN) represents an important structure, which, however, also comprises areas of the BG associative and limbic loops. We were interested whether neuronal activity would differ between the STN medial associative‐limbic and lateral motor part, and whether selective 6‐OHDA‐induced lesions of the dorsolateral striatum, the entrance region of the BG motor loop, would differently affect these subregions. In male Sprague–Dawley rats 6‐OHDA (n = 12) or vehicle (n = 10) was bilaterally injected in the dorsolateral striatum. Four weeks later extracellular single‐unit activity and local field potentials were recorded in medial and lateral STN neurons of urethane‐anesthetized rats. In sham‐lesioned rats the discharge rate and burst activity were higher in the lateral compared to the medial STN. Similar differences were found for other neuronal activity measures (coefficient of variation of interspike interval, skewness, kurtosis, approximate entropy). After 6‐OHDA injection neuronal burst activity was enhanced, while the discharge rate was not affected. In addition, in 6‐OHDA‐lesioned rats β‐band oscillatory activity was enhanced, with no difference between STN subregions. We found important differences of neuronal activity between STN subregions, indicating functional segregation. However, selective 6‐OHDA lesions of the dorsolateral striatum also had a pronounced effect on the medial STN subregion, indicating interaction between BG loops. J. Comp. Neurol. 521:3226–3240, 2013.

The anterior and posterior pedunculopontine tegmental nucleus are involved in behavior and neuronal activity of the cuneiform and entopeduncular nuclei.

Loss of cholinergic neurons in the mesencephalic locomotor region, comprising the pedunculopontine nucleus (PPN) and the cuneiform nucleus (CnF), is related to gait disturbances in late stage Parkinsons disease (PD). We investigate the effect of anterior or posterior cholinergic lesions of the PPN on gait-related motor behavior, and on neuronal network activity of the PPN area and basal ganglia (BG) motor loop in rats. Anterior PPN lesions, posterior PPN lesions or sham lesions were induced by stereotaxic microinjection of the cholinergic toxin AF64-A or vehicle in male Sprague-Dawley rats. First, locomotor activity (open field), postural disturbances (Rotarod) and gait asymmetry (treadmill test) were assessed. Thereafter, single-unit and oscillatory activities were measured in the non-lesioned area of the PPN, the CnF and the entopeduncular nucleus (EPN), the BG output region, with microelectrodes under urethane anesthesia. Additionally, ECoG was recorded in the motor cortex. Injection of AF64-A into the anterior and posterior PPN decreased cholinergic cell counts as compared to naive controls (P<0.001) but also destroyed non-cholinergic cells. Only anterior PPN lesions decreased the front limb swing time of gait in the treadmill test, while not affecting other gait-related parameters tested. Main electrophysiological findings were that anterior PPN lesions increased the firing activity in the CnF (P<0.001). Further, lesions of either PPN region decreased the coherence of alpha (8-12 Hz) band between CnF and motor cortex (MCx), and increased the beta (12-30 Hz) oscillatory synchronization between EPN and the MCx. Lesions of the PPN in rats had complex effects on oscillatory neuronal activity of the CnF and the BG network, which may contribute to the understanding of the pathophysiology of gait disturbance in PD.