Progressive pathology of the caudate nucleus, the substantia nigra pars reticulata and the deeper layers of the colliculus superior: acute behavioural and metabolic effects of intrastriatal kainic acid

Impact of Prolonged Temporal Discrimination Threshold on Finger Movements of Parkinson's Disease

INTRODUCTION

Sensory information is essential for the precise control of movement. Patients with Parkinson's disease (PD) have higher-order sensory dysfunctions including prolonged temporal discrimination threshold (TDT). However, the impact of prolonged TDT on parkinsonian motor deficits is uncertain.

METHODS

This study includes 33 PD patients and 24 healthy controls. TDT values were measured in the index finger. Using coin rotation task (CRT), dexterous finger movement was assessed. Using an inertial sensor, the speed, amplitude, and frequency of finger tapping were measured. The impact of prolonged index finger TDT on two different finger movements was analyzed using the general estimating equation.

RESULTS

Compared to healthy controls, TDT was prolonged in the PD patients. There was no impact of TDT on mean values or decrement for amplitude and speed, as well as mean values, decrement and variability of tapping frequency. However, prolonged TDT had a significant impact on the variability in amplitude (B = 436.905 × 10-4, Wald χ2 = 9.140, p = 0.014) and speed (B = 425.655 × 10-4, Wald χ2 = 9.876, p = 0.014) of finger tapping. There was a marginal correlation between TDT and CRT. In addition, CRT correlated with variability in amplitude and speed of finger tapping.

CONCLUSION

In PD, cutaneous temporal discriminative sensory dysfunction appears to be related to increased variabilities in the speed and amplitude of fast repetitive finger movements and disturbed finger dexterity.

Behavioral pharmacology of orofacial movement disorders

Dysfunction in orofacial movement is evident in patients with schizophrenia, Parkinson's disease and Huntington's disease. In animal studies on orofacial dyskinesia, these neurological disorders have been considered as a starting point to examine the pathophysiology and mechanisms underlying the symptoms. There is circumstantial evidence that orofacial dyskinesia in humans might be the consequence of hyperfunctioning mesolimbic-pallidal circuitry, in which the mesolimbic region occupies a central role, in contrast to typical Parkinson-like symptoms which involve hypofunction in the nigrostriato-nigral circuity. Studies in animals suffer from technical difficulties concerning the assessment of orofacial behaviors. There are some experimental designs that provide detailed information on the amplitude and the frequency of the jaw movements. By using such methods, the involvement of neurotransmitter systems and functional neural connections within the basal ganglia has been studied in rat rhythmical jaw movements. Regarding neurotransmitter systems, dopaminergic, cholinergic, γ-aminobutyric acid (GABA)ergic and glutamaterigic systems have been shown to be involved in rat rhythmical jaw movements. The involved neural connections have also been investigated, focusing on the differential role between the dorsal and ventral part of the striatum, the shell and core of the nucleus accumbens and the output pathways from the striatum and the nucleus accumbens. Taking available clinical and experimental evidence, the orofacial dyskinesias are thought to arise when hierarchically lower order output stations of the mesolimbic region start to dysfunction as a consequence of the arrival of distorted information sent by the mesolimbic region. This review seeks to provide an overview of prior and recent findings across several orofacial movement disorders and interpret new insights in the context of the limitations of behavioral pharmacology and prior knowledge of the regulation of behavior by dopamine receptors and other related neuronal systems.

Cortical lesion-induced visual hemineglect is prevented by NMDA antagonist pretreatment

Large unilateral visual cortex lesions produce enduring contralesional visual orientation deficits. To examine whether glutamate excitotoxicity is involved in establishing these deficits, cats were pretreated with the NMDA receptor antagonist dizocilpine (MK-801) 30 min before unilateral visual cortex ablation. Pretreated MK-801 animals were trained first in an orientation task in which they were required to fixate directly ahead and then orient to stimuli introduced at various eccentricities throughout the visual field. They did not display the characteristic ipsilesional head and neck asymmetries and/or spontaneous ipsiversive rotational behaviors or show the profound contralesional visual neglect seen postoperatively in nonpretreated control animals. Rather, pretreated animals were able to orient to visual stimuli in the contralesional hemifield immediately following surgical recovery. Postmortem histology revealed severe retrograde degeneration of the ipsilesional lateral geniculate nucleus in both experimental groups, suggesting that postlesion visuomotor behavioral competencies in pretreated animals are attributable to preserved function in nongeniculocortical visual pathways. These observations are consistent with the hypothesis that visual cortex lesions normally induce secondary alterations via NMDA-mediated excitotoxicity in these other pathways that prevents them from supporting visuomotor behaviors. The similar behavioral competencies of MK-801-pretreated animals and those whose lesion-induced deficits are ameliorated by removing basal ganglia afferents to the ipsilesional superior colliculus are consistent with this hypothesis and highlight the normal functional capabilities of this circuit. It is likely that MK-801 pretreatment acts, at least in part, by preserving the normal interhemispheric control dynamics with which the basal ganglia influence superior colliculus-mediated orientation behaviors.

Differential progression of proprioceptive and visual information processing deficits in Parkinson's disease

Indirect evidence suggests that patients with Parkinson's disease (PD) have deficits not only in motor performance, but also in the processing of sensory information. We investigated the role of sensory information processing in PD patients with a broad range of disease severities and in a group of age-matched controls. Subjects were tested in two conditions: pointing to a remembered visual target in complete darkness (DARK) and in the presence of an illuminated frame with a light attached to the index finger (FRAME). Differences in pointing errors in these two conditions reflect the effect of visual feedback on pointing. PD patients showed significantly larger constant and variable errors than controls in the DARK and FRAME condition. The difference of the variable error in the FRAME and DARK condition decreased as a function of the severity of PD. This indicates that any deficits in the processing of proprioceptive information occur already at very mild symptoms of PD, and that deficits in the use of visual feedback develop progressively in later stages of the disease. These results provide a tool for early diagnosis of PD and shed new light on the functional role of the brain structures that are affected in PD.

Discharge rate of substantia nigra pars reticulata neurons is reduced in non-parkinsonian monkeys with apomorphine-induced orofacial dyskinesia

Involuntary movements (dyskinesia) are a common symptom of dopamine-replacement therapy in parkinsonian patients, neuroleptic drug treatment of mental patients, and tic disorders. Levodopa-induced dyskinesia has been shown to be associated with substantial reduction of firing rate in the internal part of the globus pallidus. This study characterizes the changes that occur in the activity of the substantia nigra pars reticulata (SNr) of non-parkinsonian (normal) monkeys with apomorphine (APO)-induced orofacial dyskinesia. We conducted extracellular recordings of SNr neurons of two monkeys before and after induction of orofacial dyskinesia by systemic administration of APO. Involuntary orofacial movements appeared a few minutes after the injections and lasted 20-40 min. Almost all recorded neurons changed their firing rate after APO injection (96%), and most declined (70%). The mean amplitude of decreases was also larger than that of increases (40 vs. 21% of the control rate). Changes in firing pattern were not significant on average. Pairs of SNr neurons were uncorrelated before APO injection, similar to the normal pallidum. However, unlike the increased correlations in the pallidum that accompany parkinsonism, orofacilal dyskinesia in non-parkinsonian monkeys was not associated with changes in correlation between SNr neurons. We conclude that normal monkeys treated with APO can model orofacial dyskinesia and tic disorders that are a consequence of dopaminergic over-activity. These symptoms appear to be more related to reduced firing rate of SNr neurons and thus to disinhibition of their targets, than to changes in pattern and synchronization.

The superior colliculus contains a discrete region involved in the control of jaw movements: role of GABAA receptors

The role of GABA(A) receptors in the superior colliculus in the production of rat repetitive jaw movements was examined, as this nucleus receives tonic GABAergic inhibitory inputs from the dorsolateral part of the substantia nigra pars reticulata and the entopeduncular nucleus. Both regions are also connected with the ventrolateral striatum where stimulation of either dopamine or acetylcholine receptors has been found to elicit distinct types of jaw movements in rats. The GABA(A) receptor antagonist bicuculline (50 and 150 ng/0.2 microl per side) dose-dependently produced repetitive jaw movements only when injected bilaterally into a circumscribed region (A 3.0) of the lateral deeper layers of the superior colliculus; this region is known to receive input predominantly from the dorsolateral part of the substantia nigra pars reticulata. The effects of bicuculline were GABA(A) receptor specific because the effects were abolished by muscimol, a GABA(A) receptor agonist, given into the same site. The bicuculline-induced jaw movements differed qualitatively from those elicited by injection of a mixture of (+/-)-6-chloro-7,8-dihydroxy-3-allyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine-7,8-diol (SKF 82958; 5 microg) and quinpirole (10 microg), agonist at dopamine D1 and D2 receptors, respectively, or carbachol (2.5 microg), an acetylcholine receptor agonist, into the ventrolateral striatum. Nevertheless, injection of muscimol into the lateral deeper layers of the superior colliculus (A 3.0) inhibited jaw movements evoked by the dopamine D1/D2 receptor stimulation. Conversely, the jaw movements evoked by acetylcholine receptor stimulation were enhanced by injection of muscimol into the superior colliculus. In conclusion, GABA(A) receptor blockade in a circumscribed region (A 3.0) of the lateral deeper layers of the superior colliculus elicits characteristic repetitive jaw movements, and the GABA(A) receptors in that region modulate the dopamine D1/D2 receptor-mediated and acetylcholine receptor-mediated jaw movements in an opposite manner.

Lesions of the Cerebral Cortex and Caudate-Putamen Enhance GABA Function in the Rat Superior Colliculus

Unilateral lesions of the rat frontal cortex were made either alone or in combination with the caudate-putamen in order to examine (a) their morphological influence on the substantia nigra and (b) their neurochemical influence on GABA function in the superior colliculus. One to two months following the combined lesion, neuronal somata in the ipsilateral pars reticulata of the substantia nigra were clearly hypertrophied (+ 30%). Morphological changes in the substantia nigra were not evident contralaterally or in animals bearing only cortical lesions. One to two months following cortex-only lesions, no significant alterations in tectal GABA concentration were observed. However, the combined lesion induced elevations of GABA within both the medial and lateral sectors of the intermediate and deep layers of the superior colliculus. This effect was restricted to the ipsilateral side and was most pronounced in lateral sectors. The vast majority of GABA released from superfused control tectal slices by a depolarizing stimulus (35 mM KCl) was calcium-dependent. Such evoked GABA release from ipsilateral tectal slices was significantly reduced (- 25%) by unilateral lesions of the substantia nigra, a structure that is known to provide GABA-containing inputs to the tectum. In contrast, cortical lesions alone significantly enhanced the evoked tectal GABA release (+ 66%), although their influence was again confined to the ipsilateral side. Combined lesions of the cerebral cortex and caudate-putamen significantly enhanced the evoked GABA release from tectal slices in both hemispheres but the changes were most marked ipsilaterally (+ 147%). It is suggested that the hypertrophy of GABA-containing nigrotectal somata seen after removal of corticostriatal, corticotectal and in particular GABA-containing striatonigral fibres may reflect concomitant increases in GABA synthesis within and/or sprouting of nigrotectal terminals.

Differential effects of a small, unilateral, 6-hydroxydopamine-induced nigral lesion on behavior in high and low responders to novelty

The goal of this study was to develop an animal model that evaluates striatal-specific behavior after partial, unilateral destruction of nigrostriatal neurons. 6-OHDA (1 microg) was injected intranigrally (day 0) to reduce dopaminergic innervation of the dorsal striatum (DS); 6-OHDA (5 microg) was injected to reduce innervation of DS and nucleus accumbens (ACC). We analyzed changes in (a) behavior regulated by dopamine (DA) release in the DS (hindpaw preference from day 5 to day 19, every other day) and the ACC (novelty-induced locomotion on day 16) and (b) apomorphine-induced rotation (on day 21). We used two types of rat that show differences in structure and function of the dopaminergic neurons, namely high (HR) and low (LR) responders to novelty. 6-OHDA (1 microg) significantly decreased TH immunoreactivity (TH-ir) in the DS and increased preference for the hindpaw controlled by the nonlesioned side in HRs and LRs in time. Only in LRs was the significant increase of novelty-induced locomotion accompanied by a significant increase in TH-ir density in the ACC: this suggests a lesion-induced shift in nigrostriatal/mesolimbic balance toward a dominance of the mesolimbic system. The higher 6-OHDA dose significantly decreased TH-ir in the DS and the ACC and increased preference for the hindpaw controlled by the nonlesioned side in HRs and LRs in time. However, this increase occurred significantly earlier in LRs than in HRs. Apomorphine elicited contralateral rotations solely in LRs, and not in HRs, indicating development of supersensitive dopamine receptors in the DS of LRs, but not HRs. The data show that LRs are more susceptible to 6-OHDA than HRs. The relevance of the present data for Parkinson's disease is discussed.

6-hydroxydopamine lesion in the A8 cell group of cats produces a short-lasting decreased accuracy in goal-directed forepaw-movements

Recently, feline studies have shown that a lesion in the retrorubral area, which includes the dopaminergic A8 cell group, produces motor programming deficits inherent to a hypofunction of the A9 system. A hypofunction in the striatal terminal area of A9 fibers, in turn, is known to produce a hypofunction of its first-order output station, namely the substantia nigra pars reticulata (SNR). The integrity of the SNR allows animals to execute (1) 'postural adjustments that rely on proprioceptive stimuli that originate in body parts at rest' and (2) 'non-externally guided' targeting movements. In view of these considerations, the (dys)function of the SNR of cats with a bilaterally 6-hydroxydopamine lesion of A8 cells in the retrorubral area was tested in an experimental set-up that allows the assessment of changes in these functions. The A8 lesion produced: (a) a short-lasting increase in the number of accurate targeting movements as well as an increase in the time required for the collection of six pellets: these deficits disappeared 4-7 days after the lesion; (b) a long-lasting disappearance of (1) 'postural adjustments that rely on proprioceptive stimuli that originate in body parts at rest' and (2) 'non-externally guided targeting movements'; and (c) a long-lasting display of a new strategy that allowed the lesioned cat to collect its pellets despite of its other deficits. These data led to the conclusion that a lesion of A8 cells even disrupts the function of the SNR, being one of the outputstations of the A8 cell group.

GABAergic cells and signals appear together in the early post-mitotic period of telencephalic and striatal development

Single cell suspensions derived from embryonic telencephala taken from embryos of gestational day 13 (E13) as well as rat striatal tissue from E14, 15 and 17 were prepared by tissue digestion with papain. Cell suspensions were analyzed by flow cytometry or plated onto poly-D-lysine-coated culture dishes for either nuclear staining or immunocytochemistry. Experiments on functional Na+ channels and GABAA receptor expression were carried out using a fluorescence-activated cell sorter (FACS) and a negatively charged fluorescent indicator dye (oxonol). FACS analysis of embryonic cell suspensions at E13-17 consistently revealed one major subpopulation accounting for 85-90% of the events and one minor subpopulation (10-15% of the total). When sorted, the major subpopulation consisted of phase-bright cells of 5-7 microns diameter some of which had neurites. The minor population consisted of phase-dark cells and resealed membranes of 0.5-4 microns diameter as well as debris. Almost all the cells obtained in the high FALS (forward-angle light scatter) subpopulation at E17 expressed 200-kDa neurofilament and tetanus toxin antigens while the small diameter cells seldom expressed tetanus toxin and particles never did. A small number of GABA-containing neurons were detected in the telencephalon at E13 (3%) and in the developing striatum at E14 (6%). All of the GABA-containing neurons expressed neurofilament. In the embryonic rat striatum, nanomolar concentrations of muscimol (GABAA agonist) induced depolarizing responses. A small number of cells in the high FALS subpopulation were responsive to muscimol starting at embryonic day 14, and the number of responsive cells increased at E15.(ABSTRACT TRUNCATED AT 250 WORDS)

FG7142 causes opposite changes in [3H]GABA release from nigrocollicular regions

The activity of GABAergic neurons projecting from the striatum to the substantia nigra (SN) and from the SN to the superior colliculus (SC) may be involved in regulating seizure sensitivity such that striatonigral transmission is decreased and nigrocollicular transmission is increased in proconvulsant states. To test whether these changes occur in FG7142-treated rats, GABA transmission was assessed by measuring [3H]GABA release from superfused slices of the SN and SC and measuring [35S]TBPS binding to GABAA receptors throughout the brain. Nine daily injections of FG7142 (30 mg/kg IP) greatly increased myoclonic seizures in about one half of the animals. These animals exhibited a decrease in stimulated [3H]GABA release from the SN and an increase in both basal and stimulated release from the SC. Animals that were less sensitive to FG7142 treatment also had increased collicular release but not decreased nigral release. [35S]TBPS binding was unchanged by FG7142 treatment. Thus, decreased nigral GABA release may contribute to decreased striatonigral transmission after seizure occurrence whereas increased collicular GABA release may contribute to increased nigrocollicular transmission preceding multiple-seizure occurrence.

Selective changes in GABAergic transmission in substantia nigra and superior colliculus caused by ethanol and ethanol withdrawal

One of ethanol's actions after acute exposure is anticonvulsant activity whereas withdrawal from chronic ethanol exposure increases convulsant activity. An increase in neuronal transmission in the GABAergic pathways from striatum to the substantia nigra (SN) and a decrease in GABAergic transmission from SN to superior colliculus (SC) both appear to play a major role in inhibiting seizure propagation. If this is the case, then the changes in seizure sensitivity caused by ethanol may be expected to affect GABAergic transmission in opposite ways in SN and SC. We measured the effects of in vitro ethanol on pre- and postsynaptic indices of GABA transmission using SN and SC tissue from both ethanol-naive rats and rats given ethanol in their drinking water for 24 days and then withdrawn for 24 hr, a treatment that decreases seizure latency. While ethanol inhibited 3H-GABA release from slices of SC at low concentrations (20-100 nM), much higher concentrations were required to inhibit release from SN (100-500 mM). In fact, release from SN was increased by low concentrations of ethanol. Ethanol in vitro (20-1000 mM) also inhibited specific binding of 35S-TBPS to the GABAA receptor but this effect was similar in both potency and efficacy in SC and SN. Next, the in vitro effects of ethanol were measured in rats that had consumed an average of 9.8 g ethanol/kg body weight/day and were then withdrawn for 24 hr. Ethanol inhibition of 3H-GABA release from SC was significantly less in ethanol-treated rats compared to controls whereas the inhibitory effect of ethanol was increased in SN from ethanol-treated rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Subregions of the caudate nucleus and their in- and output channels in oro-facial dyskinesia: a behavioural and retrograde tracing study in the cat

Previous studies have shown that the feline caudate nucleus contains DPI-sensitive (caput nuclei caudati, anterodorsal part; r-CRM) and DPI-insensitive (caput nuclei caudati, rostromedial part; CRM) regions. Stimulation of dopamine receptors within the r-CRM by dopamine or DPI are known to elicit oro-facial dyskinesia (OFD), i.e. a syndrome of tic-like contractions of the facial muscles in combination with tongue protrusions. OFD is also elicited from the sub-commissural part of the globus pallidus (scGP), a first order output station of the r-CRM, but not from the CRM. On the basis of these data it has been hypothesized that (1) OFD is a specific feature of the r-CRM, but not the CRM; (2) effects elicited from the r-CRM are funneled via the scGP, and that (3) r-CRM and CRM are differentially innervated. Cats were bilaterally equipped with cannulas directed at the CRM or r-CRM and scGP. Following recovery from the operation the cats received bilateral injections of DPI into CRM (5 micrograms/5 microliter) or r-CRM (5 and 10 micrograms/5 microliter), the latter in combination with muscimol (50 and 100 ng/1 microliter) into the scGP or its solvent. Subsequently, behaviour was analyzed. OFD, quantified in number of tongue protrusions, was only elicited from the r-CRM, but not from the CRM confirming previously reported data in this respect. Furthermore the effect varied according to the dose used. The OFD elicited from the r-CRM was found to be blocked at the level of the scGP by local injections of muscimol, a GABA agonist.(ABSTRACT TRUNCATED AT 250 WORDS)

Behavioral correlates of a progressive dysfunctioning of the deeper layers of the colliculus superior: effects of picrotoxin

Intracaudate injections of relatively high doses of apomorphine produce a regression in motor behavior of cats collecting food pellets in a treadmill design (25). It has been hypothesized that this regression is partly due to functional disturbances in brain regions receiving (in) directly striatal output signals. In view of this hypothesis it was investigated whether experimentally induced changes in GABAergic activity within the deeper layers of the colliculus superior, which is a second order output station of the caudate nucleus, are also able to elicit a regression in motor behavior. Therefore, motor behavior of cats was tested in the treadmill paradigm before and after intracollicular injections of the GABA antagonist picrotoxin. Picrotoxin produced dose-dependently a regression in motor behavior which was comparable to that elicited by intrastriatally injected apomorphine. The noted effects were GABA-specific since muscimol attenuated the picrotoxin-induced regression. The present data are discussed in view of a model for a hierarchical organization of the brain.

Effects of intrastriatal apomorphine on changes in switching behaviour induced by the glutamate agonist AMPA injected into the cat caudate nucleus

Bilateral intracaudate application of the glutamate agonist DL-alpha-amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid (AMPA), viz. an agonist of quisqualate receptors, is known to produce the following effects in cats that had to climb on a small wooden bar and, subsequently, to switch to distinct patterns: it produces increases in switching from one pattern to another pattern (1) and it induces limb deficits, i.e. unilateral deficient placing of the fore- and/or hindlimb. In the present study, the effect of stimulating striatal dopamine receptors on behavioural changes induced by intracaudate injections of AMPA was investigated. Therefore, the dopamine agonist apomorphine was injected into the caudate nucleus 5 min before the striatal injection of 1.0 micrograms AMPA. AMPA-induced increases in switching behaviour were prevented by 0.6 micrograms, but not 0.3 micrograms, apomorphine. In contrast, AMPA-induced limb deficits were not prevented by pretreatment of apomorphine. In view of the notion that the dopaminergic caudate nucleus, its output station the substantia nigra, pars reticulata and the nigral output station the deeper layers of the colliculus superior are essential for switching behaviour, but not for the display of disturbances like AMPA-induced limb deficits, the present data strongly suggest that only AMPA-induced changes in switching, but not AMPA-induced limb deficits, are mediated by the caudato-nigro-collicular circuitry. The glutamate receptor-selectivity of the modulatory action of dopamine is discussed.

Local as well as remote functional and metabolic changes after focal ischemia in cats

Behavior and limb placing ability were analyzed acutely and subacutely (up to 21 days) following unilateral occlusion of the middle cerebral artery (MCA) in cats. Immediately following occlusion, all tested cats started to display a sequence of different behaviors, characteristic for 1) an ipsilateral inhibition of dopaminergic activity in the caudate nucleus (CN); 2) an inhibition of GABAergic activity in the reticular substantia nigra (SNR); 3) a stimulation of GABA receptors in the deeper layers of the colliculus superior (CSDL) (starting-time of these phases: about 4, 12 and 25 min, respectively). The latter behavior was also present subacutely. In addition, unilateral orofacial dyskinetic movements were observed acutely as well as subacutely. Contralateral limb placing was deficient in all cats 60 min postocclusion; it was at least partly restored subacutely. Twenty-one days after the occlusion, [14C]-2-D-deoxyglucose uptake was relatively reduced in the ipsilateral CN (especially in its posterior part), the ipsilateral SNR and the ipsilateral CSDL. The anterior CN appeared to be less affected than the posterior CN. Metabolism was relatively reduced in the sensorimotor cortex only in part of the tested cats. The data show that unilateral MCA occlusion produces consistent functional changes in all structures studied apart from the sensorimotor cortex, viz. the CN, the SNR and the CSDL.