An intracellular HRP study of the rat globus pallidus. I. Responses and light microscopic analysis

A study of the intracellularly recorded responses of rat globus pallidus neurons to activation of striopallidal fibers was combined with light microscopic examination of the morphology of these same neurons using intracellular horseradish peroxidase. The response to stimulation of caudate-putamen is an inhibitory postsynaptic potential with observed latencies ranging from 5.1 to 9.8 msec. These values correspond to conduction velocities of 0.4 to 0.8 m/second for striopallidal fibers. Comparison with extracellular controls shows no excitatory component to the response. All recovered and analyzed neurons (n = 11) were of the large type of pallidal neuron known from Golgi studies but the addition that two subtypes could be recognized. Large neurons located medially in the nucleus had dendritic fields with large dorsoventral extent (ca. 1 mm) when compared to their mediolateral and rostrocaudal dimensions (ca. 0.4 mm) and these neurons emitted no axon collaterals. Large neurons located laterally in the nucleus had disklike dendritic fields with both dorsoventral and rostrocaudal dimensions being on the order of 1 mm but with a minor axis of approximately 100 micrometers. The axons of these neurons possessed collaterals. As a consequence of their disk-shaped dendritic field, neurons belonging to the laterally placed subgroup and occupying the narrow (ca. 100 micrometers thick) striopallidal border zone known to receive a distinct input from neostriatum have dendrites restricted to that zone.     

Intracellular study of rat globus pallidus neurons: membrane properties and responses to neostriatal, subthalamic and nigral stimulation.

Physiological properties of globus pallidus (GP) neurons were studied intracellularly in anesthetized rats. More than 70% of the neurons exhibited continuous repetitive firing of 2-40 Hz, while others exhibited periodic burst firing or no firing. The repetitively firing neurons exhibited the following properties: spike accommodation; spike frequency adaptation; continuous firing with a frequency of about 100 Hz generated by intracellular current injections; fast anomalous rectification; ramp-shaped depolarization upon injection of depolarizing current; and post-active hyperpolarization. The burst firing neurons evoked a large depolarization with multiple spikes in response to depolarizing current, and a similar response was observed after the termination of hyperpolarizing current. The few neurons which did not fire spontaneous spikes exhibited strong spike accommodation when they were stimulated by current injections. The continuously firing neurons were antidromically activated by stimulation of the neostriatum (Str) (23 of 68), the subthalamic nucleus (STh) (55 of 75), and the substantia nigra (SN) (25 of 46). The antidromic latencies of the 3 stimulus sites were very similar (about 1 ms). None of the burst firing neurons were antidromically activated. Three non-firing neurons evoked antidromic responses only after Str stimulation. Only repetitively firing neurons evoked postsynaptic responses following stimulation of the Str and the STh. Stimulation of the Str evoked initial small EPSPs with latencies of 2-4 ms and strong, short duration IPSPs with latencies of 2-12 ms. Stimulation of the STh evoked short latency EPSPs overlapped with IPSPs. Frequently, these responses induced by Str and STh stimulation were followed by other EPSPs lasting 50-100 ms. These results indicated: (1) that the GP contains at least 3 electrophysiologically different types of neurons; (2) that GP projections to the Str, the STh, and the SN are of short latency pathways; (3) that Str stimulation evokes short latency EPSPs followed by IPSPs and late EPSPs in GP neurons; and (4) that STh stimulation evokes short latency EPSPs overlapped with short latency IPSPs and late EPSPs in GP neurons.     

Apomorphine increases the activity of rat globus pallidus neurons

Systemic administration of apomorphine, 0.08–1.0 mg/kg, caused a haloperidol-reversible increase in the unit activity of spontaneously firing neurons in the rat globus pallidus. Low doses of apomorphine (50, 20 μg/kg), which are thought to produce a net decrease in the stimulation of postsynaptic dopamine receptors, did not cause effects opposite to those observed with larger doses in 96% of the cells monitored. Blockade of dopamine receptors by administration of haloperidol did cause a moderate reduction in neuronal activity but only after administration of fairly high doses.     

Responses of cat cerebellar cortex neurons to stimulation of the caudate nucleus, globus pallidus and substantia nigra

Impulsive responses (IR) of the Purkinje cells (PC) and other units of the cerebellar cortex in the paramedian lobules, lobulus simplex and tuber vermis were evoked by stimulation of nucleus caudatus (NC) in cats under chloraloze-nembutal narcosis. The phasic IR as simple discharges (due to mossy fibre activation) were exhibited mainly with a latency of 5-12 and 14-20 ms; a latency of the compound responses ) due to climbing fibre PC activation) was equal to 5-6, 9-22 ms and more. There were differences in rhythmic reproduction of the responses depending on their latency. The recruitment responses were found during a 4-6/s NC stimulation. There was an inhibitory pause as an obligatory component of the tonic neuronal responses. Reactions of the same types (phasic and tonic) as in the case of the NC stimulation, but differing in unit's quantitative distribution according to the latency appeared in the globus pallidus (GP) stimulation. The minimal latency was 4 ms. Recruitment was observed as well. The substantia nigra (SN) stimulation evoked PC responses, activated by the climbing fibres with a stable latency (8.5 +/- 0.3 ms). SN, GP, n. inferior olive as well as thalamic nuclei are considered to play a definite role in realizing caudate-cerebellar connections, both oligosynaptic and polysynaptic.     

Slow oscillatory activity of rat globus pallidus neurons in vitro

The neurons in the external segment of the pallidum in the primate develop a characteristic firing pattern consisting of alternately occurring long, 2-20 s, strongly active phases and long completely silent phases when the subthalamo-pallidal excitatory inputs are blocked. The induction of the activity might be a factor in the development of dyskinesias after the loss of subthalamic output. In this study, we used globus pallidus (GPe) slice preparations obtained from juvenile rats to examined the conditions that support the alternatively occurring long depolarized and hyperpolarized phases which we refer to as the slow oscillation (SO). SO was not induced by the blockade of glutamatergic inputs but was induced by treatments that depolarized dendrites and, at the same time, hyperpolarized the somata with current injections. The treatments included elevation of extracellular K(+), application of K-current blockers and the lowering of extracellular Ca(2+). Application of TTX or intracellular BAPTA injection blocked the SO, while the SO could be maintained in hyperpolarization-activated inward current blockers, organic Ca-current blockers and up to 200 microm CdCl(2). These results suggest that Na currents play a major role in the generation of SO in vitro. It can be speculated that Na currents are involved in the development of active phases observed in the GPe after blockade of the glutamatergic inputs in vivo and that the unique property of GPe neurons in maintaining strong activity after the elimination of the glutamatergic driving force contributes to the development of motor disorders such as dyskinesia.     

Subthalamic projections to the globus pallidus: An electrophysiological study in the rat

The connections between the subthalamic nucleus (STN) and the globus pallidus (GP) were investigated electrophysiologically. By the use of stimulating electrode arrays it was determined that the predominant response of globus pallidus neurons to stimulation of the subthalamic nucleus was inhibition. A smaller proportion of short-latency orthodromic activation was also observed. Antidromic activation from the subthalamic nucleus was seen occasionally, although more laterally located in the pallidum. The results demonstrate the existence of reciprocal connections between these two regions and show that the predominant effect of subthalamic activation is inhibition of pallidal cells.     

Subcellular distribution of high-voltage-activated calcium channel subtypes in rat globus pallidus neurons.

Globus pallidus (GP) neurons receive dense inhibitory synaptic inputs interspersed with sparse excitatory inputs distributed across the entire extent of their somata and dendrites. Yet, despite this predominance of inhibitory influence, GP neurons fire at a high tonic rate, suggesting that intrinsic properties play an important role in determining the physiological characteristics of these neurons. High-voltage-activated (HVA) calcium channels represent an important class of conductances that plays roles in controlling neurotransmitter release, postsynaptic excitability, and intracellular calcium signaling. To better understand the intrinsic properties of GP neurons, we examined the subcellular localization of HVA calcium channels by using immunocytochemistry at the electron microscopic level. Peroxidase labeling with antibodies against P/Q-, N-, and R-type HVA calcium channels demonstrated the presence of these channels in both proximal and distal dendrites of GP neurons. P/Q-, N-, and R-type channels were also found in presynaptic terminals, whereas L-type channels were found exclusively postsynaptically in neuronal elements. Immunogold labeling demonstrated that, although the density of intracellular L-type calcium channel labeling remains constant throughout the proximal-distal extent of the dendritic tree of GP neurons, the density of plasma membrane-bound channels is greater in distal dendrites. The finding of HVA calcium channels distributed throughout the whole dendritic tree of GP neurons indicates that these channels may interact with synaptic inputs to allow rich processing possibilities for GP neuron dendrites. Furthermore, the finding of a greater density of plasma membrane-bound L-type channels in distal dendrites expands the view that L-type channels are important only in somatic and proximal locations.     

Effects of enkephalin and morphine on rat globus pallidus neurons

This study was conducted in order to compare the effects of microiontophoretically-applied morphine and met-enkephalin (met-ENK) on spontaneous and/or glutamate-evoked activity of single globus pallidus (GP) neurons in locally anesthetized, paralyzed rats. The predominant effect of both morphine and met-ENK was a depression of pallidal neuronal activity. While very few GP neurons were excited by morphine (2/89), a small population of neurons was excited by met-ENK (16/89). Both the inhibitory and excitatory responses produced by morphine and met-ENK could be attenuated by the microiontophoretic application of naloxone. It was also found that morphine and met-ENK did not affect all GP neurons in a similar manner. When applied to the same neurons, morphine elicited depression in 11 of 16 GP neurons which were excited by the application of met-ENK. In contrast, neither of two GP neurons excited by morphine in this study displayed inhibition upon application of met-ENK. Thus the microiontophoresis of morphine and met-ENK to single GP neurons has demonstrated that these two substances can produce opposite effects when applied to the same neurons and suggests that two functionally distinct types of opiate receptor may exist within rat GP, one which mediates the inhibitory effects of morphine and met-ENK, possibly the classical mu (mu) receptor, and one that is preferentially selective to met-ENK and which mediates the excitatory effects of opiates within this region, possibly the classical delta (delta) receptor.     

Monkey globus pallidus external segment neurons projecting to the neostriatum.

Experiments were performed to assess the number and parvalbumin (PV) immunoreactivity of neurons participating in the pallidostriatal projection in macaque monkeys. Injection of WGA-HRP into the right caudate nucleus and the left putamen of a Macaca mulatta and a M. fuscata labeled a large number of the globus pallidus external segment (GPe) neurons. Counting neurons labeled with WGA-HRP and those stained with neuronal markers indicated that approximately 30% of GPe neurons project to neostriatum. Approximately 2/3 of the pallidostriatal neurons are PV-immunoreactive. This study revealed that a significant number of primate GPe PV immunoreactive neurons project to the neostriatum, and suggest that the pallidostriatal projection should be taken into account in the analysis of functional roles of the basal ganglia circuitry.     

Glucose-sensitive neurons of the globus pallidus: I. Neurochemical characteristics

The lateral hypothalamic area (LHA) and globes pallidtaz (GP) are basically involved in the regulation of feeding and metabolic processes. In the LHA, glucose-sensitive (GS) neurons were described: their activity was found to be specifically suppressed by electrophoretic application of glucose, and these neurons appeared to be also influenced by various feeding-associated neurochemical signals. The main goal of the present experiments was to examine whether similar GS neurons exist in the GP. In addition, neurochemical attributes of the cells were also tested. In anesthetized rats and anesthetized or awake monkeys, single-neuron activity of the GP was recorded by means of carbon fiber multibarreled microelectrodes and the effects of glucose, glutamate (Gt), GABA, dopamine (DA), noradrenaline (NA) and acetylcholine (Ach) were studied. In both the rat and monkey GP, approximately 12% of the neurons examined responded, with inhibition, to glucose. GP neurons, in a high proportion, were also inhibited by GABA and NA. After application of Gt, DA, or Ach, activity increase or decrease occurred. GS neurons exhibited remarkable sensitivity to these neurochemicals previously identified as neurotransmitters of the complex pallidal, extrapyramidel-limbic neuron loops. The results, along with previous data, indicate that GS cells of the GP, while possessing complex neurochemical characteristics, may belong to a hierarchically organized central glucose-monitoring system essential in the regulation of feeding.     

Motor effects of globus pallidus stimulation in the rat: lesions to corticofugal fibers block the motor effects.

Unilateral electrical stimulation of the globus pallidus (GP) in anesthetized male rats was used to determine the nature of the activity driven in muscles of the neck and shoulder by GP output. In 6 groups of animals stimulation was coupled with lesions to sites that interrupted corticofugal fibers or GP output. Interruption of corticofugal fibers blocked the driven activity while lesions that compromised GP output left the activity unaffected.     

Glucose-sensitive neurons of the globus pallidus: II. Complex functional attributes

The globus pallidus (GP) is intimately involved in regulation of various aspects of hunger- and thirst-motivated behaviors. Our parallel neurochernical studies demonstrated the existence of GP neurons whose discharge rates are suppressed by glucose applied microelectrophoretically. In the present series of experiments, we aimed to provide complex, feeding-associated functional characterization—similar to that previously accomplished in the case of lateral hypothalamic and amygdabid chemosensitive neurons—of these glucose-sensitive (GS) and the glucose-insensitive (GIS) pallidal cells. To do so, extracellular single neuron activity of the GP was recorded in anesthetized rats and anesthetized or awake rhesus monkeys by means of carbon fiber, multibarreled glass microelectrodes during: a) microelectrophoretic administration of chemicals, b) gustatory, and c) olfactory stimulations. In alert primates, activity changes were also recorded during presentation of food and nonfood objects as well as during the performance of a conditioned, high fixed-ratio bar-press feeding task. The half of pallidal cells examined showed firing rate changes during phases of the conditioned alimentary task. In both species, about 1/7 of all neurons tested proved to be GS, while the proportion of cells responding to gustatory and olfactory stimulations was 19% and 16%, respectively. Task-related and taste- and smell-responsive units were mainly found among the GS neurons of the pallidum. These data, along with previous findings, indicate that chemosensitive cells of the GP, in an apparent overlap with units of the central gustatory representation, are involved in a hierarchically organized glucose-monitoring neural network, through which pallidal neurons exert their integrative functions in the central feeding control.     

Single subthalamic nucleus neurons project to both the globus pallidus and substantia nigra in rat

The organization of the major efferents of the rat subthalamic nucleus (STN) was investigated using a fluorescent retrograde double-labeling technique. Red fluorcrescent Evans Blue was injected into the globus pallidus and blue fluorescent DAPI-Primuline was injected into the substantia nigra. After retrograde axonal transport many double-labeled neurons were seen throughout the STN. Occasional double-labeled cells were seen in the lateral hypothalamus just medial to the STN and in a thin lateral strip of neurons extending laterally from the STN. Evidence for a mediolateral topography in both the STN-pallidal and STN-nigral pathways was obtained. The STN contains few, if any, local interneurons. Cell counts revealed that at least 94% of, and possibly all, STN neurons send axon collaterals to both the globus pallidus and substantia nigra.     

Motor effects of cholinergic stimulation of the globus pallidus in rats.

Forty-seven rats were cannulated permanently in either the globus pallidus or neostriatum and subsequently injected with carbachol, scopolamine, or carbachol plus scopolamine. The injection of carbachol (1 mug) into the globus pallidus produced transient hyperkinetic phasic dyskinesias (84%) followed in some cases by ipsilateral circling (47%) associated with hypertonic contralateral hind limbs. This condition progressed in some rats to a cataleptic state (42%). The injection of scopolamine (50 mug) or scopolamine (50mug) plus carbachol (1 mug) into the pallidum produced ipsilateral circling associated with hypotonia of the contralateral hind limb in a few rats. No hyperkinetic dyskinesias nor catalepsy were produced by these injections. The injection of carbachol (1 mug) into the neostriatum produced hyperkinetic dyskinesias (86%) of long duration, minimal circling (both directions) (10%), and catalepsy (29%). These effects were blocked by the addition of 50 mug of scopolamine to the carbachol injection. Scopolamine (50-100 mug) alone produced no effects after injection into the caudate/putamen. Saline injections in the neostriatum or globus pallidus produced no motor disturbance.     

Substance P excites globus pallidus neurons in vivo

Substance P is a member of the neurokinin family. Previous studies have reported the existence of substance P and its high-affinity receptor, neurokinin-1 receptor, in globus pallidus. Employing in vivo extracellular recording combined with behavioural tests, the effects of substance P in globus pallidus of rats were studied. Micropressure ejection of the selective neurokinin-1 receptor agonist [Sar9,Met(O2)11] substance P increased the spontaneous firing rate of pallidal neurons in a concentration-dependent manner, with increases of 27.3% at 0.01, 33.4% at 0.03, 45.5% at 0.1, 38.4% at 0.3 and 36.4% at 1.0 mm. The selective neurokinin-1 receptor antagonist SR140333B prevented the excitatory effects induced by [Sar9,Met(O2)11] substance P. In behaving rats, we observed the postural effects of neurokinin-1 receptor activation in the globus pallidus. Consistent with electrophysiological results, unilateral microinjection of [Sar9,Met(O2)11] substance P (0.1 mm) led to a SR140333B-sensitive contralateral deflection in the presence of systemic haloperidol administration. Combining electrophysiological and behavioural findings, we concluded that substance P produces excitatory effects on globus pallidus neurons via neurokinin-1 receptors.     

Neuronal responses to 5-hydroxytryptamine and dorsal raphe stimulation within the globus pallidus of the rat

The projection from the dorsal raphe nucleus (DRN) to the globus pallidus (GP) was investigated electrophysiologically, in the urethane-anesthetized rat together with the responsiveness of cells in the GP to 5-hydroxytryptamine (5-HT) and noradrenaline (NA). The majority of spontaneously active cells in the GP had high regular firing rates. They were unaffected by both DRN stimulation (69/83 cells) and iontophoretically applied 5-HT (38/63 units) or NA (30/42 units) but were inhibited by GABA. A few cells (N = 10) were recorded from, that were spontaneously active but with a much lower and less regular firing rate, which, however, seemed to be much more responsive to 5-HT. In addition, DL-homocysteic acid (DLH) was used to activate silent cells and all seven cells activated in this manner were inhibited by 5-HT. In addition 5/6 cells that had their firings maintained by DLH were inhibited by stimulation of the dorsal raphe. The results show a lack of responsiveness to both 5-HT and DRN stimulation of the typically regular spontaneously active pallidal neurons. There seems to be a small population of normally quiescent cells, however, that is sensitive to 5-HT and receives an input from the DRN.     

Bilateral deep brain stimulation of the globus pallidus to treat tardive dyskinesia

CONTEXT: Tardive dyskinesia (TD) is a common and potentially disabling disorder induced by use of antipsychotic drugs for which medical treatment often gives disappointing results. OBJECTIVE: To assess the efficacy of bilateral deep brain stimulation of the internal part of the globus pallidus to treat severe TD. DESIGN: Prospective phase 2 multicenter study. SETTING: Six French university hospitals. Patients Patients with severe TD refractory to medical treatment were studied to evaluate the severity of abnormal involuntary movements before and after 6 months of bilateral globus pallidus deep brain stimulation. A 2-step open Fleming procedure was used to avoid unnecessary accrual of patients. A successful outcome was defined as a decrease of more than 40% in the main outcome measure at 6 months. The early stopping rule was invoked if the number of successful outcomes in 10 patients was fewer than 2, or 5 or more. A double-blind evaluation in the presence and absence of stimulation was performed at 6 months after surgery. Main Outcome Measure Change in score on the Extrapyramidal Symptoms Rating Scale. RESULTS: At 6 months after surgery, the Extrapyramidal Symptoms Rating Scale score had decreased compared with baseline by more than 40% (mean improvement, 61%; range, 44%-75%) in the first 10 patients included. In accord with the 2-step open Fleming procedure, we ended the trial at the first step and concluded that pallidal stimulation is an effective treatment for TD. The efficacy of the treatment was confirmed by a double-blind evaluation, with a mean decrease of 50% (range, 30%-66%) (P = .002) in the Extrapyramidal Symptoms Rating Scale score when stimulation was applied compared with the absence of stimulation. There were no marked changes in the patients' psychiatric status. CONCLUSION: Although these results need to be confirmed in a larger group of patients with a longer follow-up, bilateral globus pallidus deep brain stimulation seems to offer a much-needed new treatment option for disabling TD.     

Single-axon tracing study of neurons of the external segment of the globus pallidus in primate

Axonal projections arising from the external segment of the globus pallidus (GPe) in cynomolgus monkeys (Macaca fascicularis) were mapped after labeling small pools (5-15 cells) of neurons with biotinylated dextran amine. Seventy-six single axons were reconstructed from serial sagittal sections with a camera lucida. The majority of labeled GPe cells displayed long, aspiny, and poorly branched dendrites that arborized mostly along the sagittal plane, whereas others showed dendrites radiating in all directions. Numerous GPe axons emitted short, intranuclear collaterals that arborized close to their parent cell body. Based on their axonal targets, four distinct types of GPe projection neurons have been identified: 1) neurons that project to the internal segment of the globus pallidus (GPi), the subthalamic nucleus (STN), and the substantia nigra, pars reticulata (SNr; 13.2%); 2) neurons that target the GPi and the STN (18.4%); 3) neurons that project to the STN and the SNr (52.6%); and 4) neurons that target the striatum (15.8%). Labeled GPe axons displayed large varicosities that often were closely apposed to the somata and proximal dendrites of STN, GPi, and SNr neurons. At striatal levels, however, GPe axons displayed small axonal varicosities that did not form perineuronal nets. These results suggest that the GPe is an important integrative locus in primate basal ganglia. This nucleus harbors several subtypes of projection neurons that are endowed with a highly patterned set of collaterals. This organization allows single GPe neurons to exert a multifarious effect not only on the STN, which is the claimed GPe target, but also on the two major output structures of the basal ganglia, the SNr and the GPi.     

Bilateral internal globus pallidus stimulation for the treatment of spasmodic torticollis.

Three patients with spasmodic torticollis (ST) obtained substantial benefit from bilateral globus pallidus internus (GPi) stimulation. Progressive improvement in ST occurred over several months but residual cervical dystonia remained. These results corroborate those obtained by Krauss et al. on three patients with ST.