Changes in the Mitochondrial Enzyme Activity in Striatal Projection Areas after Unilateral Excitotoxic Striatal Lesions: Partial Restoration by Embryonic Striatal Transplants

It is well established that the activity of cytochrome oxidase (CO), a mitochondrial enzyme, reflects the long-term, steady-state levels of neuronal activity. The present study investigated the long-term effects of unilateral striatal lesions induced by quinolinic acid on CO activity in primary striatal targets, including the globus pallidus (GP), entopeduncular nucleus (EP), and substantia nigra pars reticulata (SNR) and a secondary striatal projection area, such as subthalamic nucleus (STN), in rats. The activity of CO was determined by measuring staining intensity on brain sections processed for CO histochemistry. We also examined whether intrastriatal transplants of embryonic striatal tissue could affect the lesion-induced changes in the CO activity of those brain structures. Unilateral striatal lesions were found to lead to increases in the CO activity of the GP, EP, and SNR ipsilateral to the lesions. By contrast, the activity of the ipsilateral STN was decreased following striatal lesions, probably due to the increased inhibitory effect of the GP on the STN. Intrastriatal implantation of the lateral ganglionic eminence (LGN), but not the medial ganglionic eminence (MGE), reversed the lesion-induced changes in the CO activity of the GP and STN with concomitant attenuation of apomorphine-induced rotational asymmetry. The grafts failed to affect the activity of either the EP or SNR. The present results indicate that striatal lesions induce changes in the functional activity of basal ganglia nuclei and that the LGE grafts placed in the damaged striatum partly reverse the alterations in the functional state of the basal ganglia circuitry.     

Responses of pallidal neurons to striatal stimulation in monkeys with MPTP-induced parkinsonism

Extracellular single unit activity was recorded from neurons of the internal (GPi) and external (GPe) pallidal segments, and from 'border cells' (Bor) which are part of the nucleus basalis, in 2 cynomolgus monkeys rendered parkinsonian by MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine). Cell counts showed that at least 90% of the nigral neurons of the compacta-type were degenerated. Electrical stimulation was applied to 3 sites bilaterally in the striatum: one in the caudate nucleus and 2 in the putamen. The results were compared to those obtained in intact monkeys. In the parkinsonians, more neurons of the 3 types responded to ipsilateral stimulation. The difference was even greater for contralateral responses, except in the case of Bor neurons. Greater proportions of the 3 types of neurons also responded to 2 and 3 sites and showed convergent responses to both the caudate nucleus and the putamen. The magnitude of the responses was larger. These results are in accordance with the excessive and unselective responses of the same neurons to passive limb movement, obtained in the same animals and described previously. The electrical stimulation allowed more detailed analyses of the responses. The major change in the responses of GPi and Bor neurons was the more frequent and larger late inhibitions, whereas the excitations were larger in GPe neurons. Long lasting oscillatory responses occurred frequently in the parkinsonians, mainly in GPi, and at frequencies close to the tremor displayed by the animals. Responses beginning with early inhibition were displayed by neurons located in the center of the pallidal zone of influence of each striatal stimulation site, as in intact animals, but in the GPi of the parkinsonians they were less frequently curtailed by excitation. Moreover, in the parkinsonians, the zones of influence were larger in both GPi and GPe, mainly because of the expansion of their periphery, where responses began with excitation and had lower thresholds than in intact animals. The dopamine agonist apomorphine normalized the responses in the parkinsonians. Thus, both the temporal and spatial magnitudes of inhibitions and excitations are abnormal at the output of the basal ganglia in parkinsonism.     

Behavioural recovery following transplantation of substantia nigra in rats subjected to 6-OHDA lesions of the nigrostriatal pathway. I. Unilateral lesions

The ability of embryonic substantia nigra transplants to compensate for behavioural deficits induced by unilateral destruction of the nigrostriatal dopamine pathway has been investigated in adult rats. Six days following unilateral 6-OHDA lesions of the nigrostriatal pathway, the adequacy of the lesion was assessed by measurement of the intensity of ipsilateral amphetamine-induced rotation. All rats then received surgical cavities in the cortex overlying the head of the caudate-putamen on the lesioned side. In 51 rats, transplants of embryonic substantia nigra were placed on the dorsal surface of the caudate-putamen, and the remaining 19 rats served as unilateral lesioned controls. Behavioural testing was conducted approximately 3 months after transplantation: (a) the transplant animals alone showed a marked reduction in ipsilateral rotation induced by 5 mg/kg amphetamine (‘compensation’); (b) although both transplanted and control rats expressed equal contralateral rotation at a dose of 0.25 mg/kg apomorphine, the transplant animals alone showed a marked reduction in rotation at a lower dose of 0.05 mg/kg; (c) the transplanted rats showed less asymmetry in spontaneous rotational behaviour than controls, and the asymmetry was further reduced by mild tailpinch; (d) when tested for spontaneous choice behaviour in a T-maze, control rats showed 97% selection of the arm ipsilateral to the 6-OHDA lesion, whereas the transplanted rats that were well compensated on the amphetamine rotation test turned to the contralateral side on 30–40% of choices; (e) no transplant-induced changes were found in contralateral sensory inattention on a sensorimotor test battery, whether tested spontaneously or under mild tailpinch-induced activation. The results support the conclusion that dopaminergic reinnervation of the dorsal neostriatum is capable of inducing functional recovery in many, but not all, behavioural tests which involve side choice or bias, not only after pharmacological activation but also in the spontaneous behaving animal.     

Dopamine-rich transplants in rats with 6-OHDA lesions of the ventral tegmental area. I. Effects on spontaneous and drug-induced locomotor activity

In order to investigate the relative contribution of dopaminergic projections to the nucleus accumbens and prefrontal cortex in the regulation of spontaneous and drug-induced locomotor activity, separate groups of rats were prepared with 6-OHDA lesions of the ventral tegmental area alone, or additional grafts of dopamine-rich tissue reinnervating either the nucleus accumbens or medial prefrontal cortex. A fourth unoperated group served as normal controls. The lesions induced no change in spontaneous, daytime activity, but increased overnight activity. The lesioned rats were also hyperactive to apomorphine, while the activational effects of amphetamine were blocked. Grafts of dopamine-rich tissue, whether into the prefrontal cortex or nucleus accumbens, resulted in a significant normalization of both drug responses towards control levels. Neither graft influenced overnight hyperactivity, whereas spontaneous daytime activity was increased above both control and lesion levels by the accumbens grafts alone. The results are interpreted as suggesting that dopaminergic projections to prefrontal cortex and nucleus accumbens are similarly rather than antagonistically involved in the regulation of drug-induced locomotor activation.     

Extensive reinnervation of the hippocampus by embryonic basal forebrain cholinergic neurons grafted into the septum of neonatal rats with selective cholinergic lesions

Reconstruction of the septohippocampal pathways by axons extending from embryonic cholinergic neuroblasts grafted into the neuron-depleted septum has been explored in the neonatal rat by using a novel lesioning and grafting protocol. Neonatal ablation of the basal forebrain cholinergic projection neurons, accompanied by extensive bilateral cholinergic denervation of the hippocampus and neocortex, was produced at postnatal day (PD) 4 by 192 immunoglobulin (IgG)-saporin intraventricularly. Four days later, cholinergic neuroblasts (from embryonic day 14 rats) were implanted bilaterally into the neuron-depleted septum by using a microtransplantation approach. The results show that homotopically implanted septal neurons survive and integrate well into the developing septal area, extending axons caudally along the myelinated fimbria-fornix and supracallosal pathways that are able to reach the appropriate targets in the denervated hippocampus and cingulate cortex as early as 4 weeks postgrafting. Moreover, the laminar innervation patterns established by the graft-derived axons closely resembled the normal ones and remained essentially unchanged up to at least 6 months, which was the longest postoperative time studied. The reinnervating fibers restored tissue choline acetyltransferase activity (up to 50% of normal) in the dorsal hippocampus and the parietooccipital cortex. Retrograde labeling with Fluoro-Gold from the host hippocampus combined with immunocytochemistry confirmed that most of the projecting neurons, indeed, were cholinergic. The results suggest that the graft-host interactions that are necessary for target-directed axon growth are present in the septohippocampal system during early postnatal maturation. Thus, the present approach may contribute to overcome the functional limitations inherent in the use of ectopically placed intrahippocampal transplants. © 1996 Wiley-Liss, Inc.     

Fetal cortical transplants into neonatal rats respond to thalamic and peripheral stimulation in the adult. An electrophysiological study of single-unit activity

Plates of presumptive sensorimotor neocortex obtained from fetal rats at 14—16 days gestation were grafted into the cerebral hemisphere of 0- to 1-day-old newborn rats. The transplants were placed into small lesion cavities in the sensorimotor cortical area made immediately prior to grafting. At 4–5 months of age, single-unit activity in the transplants (TP) or normal cortex (NCX) was recorded under ketamine HCI anesthesia using standard electrophysiological techniques. Over 90% of cells in both the transplants (n = 63) and normal cortex (n = 39) responded to ventral thalamic stimulation. Their average response latencies were similar (11.48 ±0.56 ms in TP, 12.77 ±1.20 ms in NCX, mean ±S.E.M., no significant difference), as were their average responses of slightly more than 1 spike per thalamic stimulus (1.24±0.08 in TP, 1.07±0.01 in NCX, no significant difference). In addition, 64% (30/47) of transplant cells and 44% (14/32) of normal cells also responded to electrical stimulation of the contralateral forepaw, and here also the latencies were similar (16.11±0.67 ms in TP, 14.30±0.78 ms in NCX). The spontaneous neuronal activity obsserved within the transplants was also comparable to that seen in normal cortex, as measured by comparison of spontaneous interspike interval (ISI) histograms (median ISI of 84.5 for TP and 80.5 for NCX) and comparison of the burst index (% of intervals 5 ms, 14.7% for TP and 10.5% for NCX). These results are compared to those found in several recent studies where fetal cortex is grafted into adult hosts.     

Tyrosine hydroxylase-positive fibers and neurons in transplanted striatal tissue in rats with quinolinic acid lesions of the striatum

Using the quinolinic acid (QA) animal model of Huntington's disease (HD) the dopaminergic afferent input to intrastriatal striatal grafts was examined. After bilateral striatal lesions with QA (15 nmol), 4 microliters of fetal (E17) striatal tissue were delivered into the lesioned striata. Twenty-eight weeks posttransplantation the tissue was processed for TH immunocytochemistry and cresyl violet staining. In addition fetal intact brains (E17) were also processed for TH immunocytochemistry and cresyl violet staining. Viable striatal grafts were located within the host striatum and in some cases within the lateral ventricles. TH-positive fibers were present within the graft and also groups of TH-positive cell bodies were seen in some of the grafts. TH immunocytochemistry on E17 fetuses revealed several groups of TH-positive neurons one of which was placed immediately ventral to the developing striatal ridge. The origin of TH-positive innervation within the graft is discussed.     

Sexually dimorphic effects of neonatal immune system activation with lipopolysaccharide on the behavioural response to a homotypic adult immune challenge

Research has shown that acute immune activation during the early postnatal period with the Gram-negative endotoxin, lipopolysaccharide (LPS), alters a variety of physiological and behavioural processes in the adult animal. For example, neonatal LPS exposure affects disease susceptibility later in life, though these effects appear to be modulated by time of exposure, sex, and immune stimulus. The current study examined sex differences in the effect of neonatal LPS treatment on the locomotor activity response to adult LPS administration. Male and female Long-Evans rats were treated systemically with either LPS (50 microg/kg) or saline (0.9%) on postnatal days 3 and 5. Later in adulthood (postnatal day 92), all animals were subjected to an adult LPS challenge and were injected (i.p.) with 200 microg/kg LPS. Two hours after injection, animals were placed in a non-novel open-field and locomotor activity was assessed for 30 min. Body weights were determined both at the time of injection and 24h later to examine LPS-induced weight loss. Adult males treated neonatally with LPS exhibited significantly less horizontal and vertical activity in response to the LPS challenge relative to males treated neonatally with saline. This effect was not observed in females. Thus, the current study provides important evidence of sexual dimorphism in the long-term effects of neonatal LPS exposure on the responses to an adult homotypic immune challenge in rats. These findings have potential clinical significance given that neonatal exposure to pathogens is a fairly common occurrence and Gram-negative bacteria are a common cause of neonatal bacterial infections.     

Chronic, systemic treatment with a metabotropic glutamate receptor 5 antagonist produces anxiolytic-like effects and reverses abnormal firing activity of projection neurons in the basolateral nucleus of the amygdala in rats with bilateral 6-OHDA lesions

Although 2-methyl-6-(phenylethynyl)-pyridine (MPEP), a selective metabotropic glutamate receptor 5 antagonist, improves the motor symptoms of Parkinson's disease (PD), the effects of MPEP on the psychiatric symptom of PD and the mechanism involved are still unclear. In the present study, we examined the effects of MPEP in anxiolytic-like behavior and firing activity of projection neurons in the basolateral nucleus of the amygdala (BLA) in rats with 6-hydroxydopamine (6-OHDA) injected bilaterally into dorsal striatum. Rats were divided into three groups, sham-operated group, 6-OHDA lesion with vehicle treatment group and 6-OHDA lesion with MPEP treatment group. Injection of 6-OHDA (10.5 μg) into the dorsal striatum produced 31.5% loss of tyrosine hydroxylase immunoreactive (TH-ir) neurons in the SNpc. The 6-OHDA-lesioned rats showed anxiety behavior and the firing rate of BLA projection neurons decreased significantly compared with sham-operated rats, and no difference was found in the firing pattern of these neurons. Whereas chronic, systemic treatment of MPEP (3 mg/kg/day, i.p.; 14 days) attenuated loss of TH-ir neurons, produced anxiolytic-like effect and normalized the abnormal firing rate of projection neurons of the BLA in rats with the bilateral lesions. Systemic administration of cumulative apomorphine (10-160 μg/kg, i.v.) inhibited the firing rate of BLA projection neurons in sham-operated, 6-OHDA lesion with vehicle-treated and MPEP-treated rats, but the 6-OHDA lesion decreased the response of BLA projection neurons to apomorphine stimulation, while MPEP reversed the reactivity of these neurons. These data demonstrate that the partial lesion of the nigrostriatal pathway causes anxiety symptom and decreases firing rate of BLA projection neurons in the rat. Furthermore, chronic, systemic MPEP treatment has the neuroprotective and anxiolytic-like effects, and reverses the abnormal firing rate of BLA projection neurons, suggesting that MPEP has important implication for the treatment of PD.