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Ciliary neurotrophic factor (CNTF) acts on immature astrocytes that express its trimeric receptor. In contrast, mature astrocytes do not significantly express the specific CNTFalpha receptor subunit, yet they respond to CNTF administration in vivo. Here we show that this controversy may be solved by a shift in astroglial sensitivity to CNTF over time, related to a change in the type of receptor bound by the cytokine on mature astrocytes. A convergent set of results supports the hypothesis that the CNTF effect is due to the illegitimate binding on the leukemia inhibitory factor receptor (LIFR): (i) it requires high concentration of recombinant rat CNTF; (ii) it involves the Jak/Stat and Ras-MAPK pathways; (iii) it is preserved in CNTFRalpha-/- cells; (iv) it is potentiated by soluble CNTFRalpha added to the medium; and (v) it is significantly decreased by a partial antagonist of LIFR. On these bases, we propose a mechanistic model in which, in the adult brain, a CNTF/LIFR interglial system may be modulated by neurons that synthesize CNTFRalpha., (Copyright 2001 Academic Press.)

Riluzole has been shown recently to increase life expectancy in patients with amyotrophic lateral sclerosis. A number of experimental studies also suggest that this compound may be a neuroprotectant. We have investigated in baboons whether riluzole would protect striatal neurons from a prolonged 3-nitropropionic acid (3NP) treatment and ameliorate the associated motor symptoms. In animals receiving 3NP and the solvent of riluzole, 12 weeks of high-dose 3NP treatment resulted in the appearance of persistent leg dystonia and significant increases in the incidence of three categories of abnormal movements and in the dyskinesia index in the apomorphine test (0.5 mg/kg i.m.). Quantitative assessment of these behavioral deficits using a video movement analysis system demonstrated a significant decrease in locomotor activity and peak tangential velocity in 3NP-treated animals compared to controls. Histological analysis showed the presence of severe, bilateral, striatal lesions, localized in both caudate and putamen. Cotreatment with riluzole (4 mg/kg i.p., twice daily) significantly reduced the dyskinesia index (-35%, P < 0.02) in the apomorphine test. In the quantitative behavioral analysis, riluzole significantly ameliorated the decrease in peak tangential velocity (P < 0.02) but not the decrease in locomotor activity observed after 3NP. Comparative histological analysis of the two groups of treated animals did not demonstrate a clear neuroprotective effect of riluzole. The present study suggests that one potential therapeutic interest for riluzole in neurodegenerative disorders may reside in the reduction of motor symptoms associated with striatal lesions.

Transplantation of human fetal neural cells has been used for several years as a treatment for Parkinson's disease. These therapeutic trials were based on a large number of rat allografts studies, and the species to species extrapolation appeared valid in many respects. One major difference between neurons of various species, however, is their rate of maturation; indeed, human neurons have been proven to grow much more slowly than rat neurons. This has been studied mostly, up to now, at the light microscope level. In an attempt to determine the fine structural correlates of this protracted development and to detail the schedule of morphogenesis and synaptogenesis, human fetal brain stem tissue (at 8 weeks of gestation) was transplanted into a previously lesioned brain area of immunosuppressed adult rats. Transplants, which were allowed to develop for 15 days to 3 months, were analyzed using the electron microscope. At 15 days, small cells containing a large nucleus were surrounded by wide extracellular spaces. At 1 month, grafted neurons displayed a thin rim of cytoplasm and few thin processes. At 2 months, extracellular spaces tended to diminish. Thin processes formed bundles and large processes extended from enlarged neurons. Major changes were observed at 3 months survival as the neuropile filled up with cells and processes and synaptogenesis began. Comparison with a similar ultrastructural study of thalamic rat allografts shows that human cells develop following a pattern similar to that in rat cells but that the duration of each maturation step is largely extended.

After a number of reports indicating positive clinical outcome of intrastriatal transplantation of fetal ventral mesencephalic tissue into patients with Parkinson's disease, the time may have come to consider the possibility of using this technique to treat patients with Huntington's disease. On the basis of the available literature, the Network of European CNS Transplantation and Restoration has established a program aiming at defining the optimal conditions for such clinical trials. The present study, conducted within this framework, pursued the goal of providing information concerning the period of striatal neuronal ontogeny in humans, taking into account the technical and legal requirements imposed by the clinical procedure of neural transplantation using human tissue. On this basis, it aimed at establishing a reliable dissecting method for the intrastriatal grafting of human fetal striatal neurons. The ontogeny of medium-spiny neurons within the developing striatum was first studied in a series of human fetal brains, 5 to 10 weeks postconception, using immunocytochemical detection of DARPP-32. Immunoreactive neurons were observed in fetuses at 7 weeks of age and older. They were mostly localized in clusters, packed in the lateral ganglionic eminence. Over a 2-week-long period, DARPP-32 neurons increased in number. Their morphology remained poorly differentiated, however, with small cell bodies, few branched dendrites, and variable intensity of immunostaining. Based on these findings, selective dissection of the lateral ganglionic eminence was carried out. This tissue was stereotaxically implanted into the striatum of immunosuppressed adult rats previously lesioned. Two months postgrafting, DARPP-32 neurons were observed as discrete patches, embedded within areas of essentially DARPP-32-negative tissue. Up to 2 months after grafting, neurons remained poorly differentiated in general, with only a few neurons exhibiting a dense immunoreactivity and long processes. These results indicate that striatal DARPP-32-immunoreactive neurons are present in the lateral ganglionic eminence in fetuses as soon as 7 weeks postconception. The striatal tissue can be dissected out and successfully transplanted. Within the grafts, neuronal differentiation appears to be a very long process, suggesting that many months might be necessary for these neurons to become functionally integrated into an adult host brain.

We used MR imaging to locate and monitor in vivo the pathological events taking place 2 to 4 weeks after unilateral striatal injections of ibotenic acid (IA) in the Papio papio baboon. As early as 2 weeks after IA injections, excitotoxic lesions in the caudate and the putamen were directly visualized on T1-weighted images as small areas of low signal intensity. On T2-weighted images, the lesion sites were visualized as areas of high-intensity signal, spreading over larger areas than the corresponding regions in T1-weighted images. These alterations of T2-values in the lesioned striatum persisted 4 weeks after surgery. However, as the striatal degeneration progressed from 2 to 4 weeks after lesion, the size of the areas of high signal intensity on T2-weighted images decreased, whereas the same regions appeared essentially unmodified on T1-weighted images. A marked enlargement of the ipsilateral lateral ventricle (a characteristic of excitotoxic striatal lesions) could be detected 4 weeks after surgery, on both axial T1- and T2-weighted images. Comparisons of MR images with postmortem anatomical data indicated that areas of increased T1 values corresponded to regions of severe neuronal depletion (a direct result of the excitotoxic lesion), whereas areas of increased T2 values corresponded to regions of increased content in astrocytes and ferritin and probably in the early period following lesion (2 weeks) to a superimposed edema.

The functional status of the dopaminergic system following striatal excitotoxic lesions was studied in living baboons by positron emission tomography (PET) using 6-[18F]fluoro-L-dopa as specific tracer for the presynaptic dopaminergic terminals and [76Br]bromolisuride as selective dopamine D2-receptor marker. The glutamate receptor agonist ibotenic acid (IA) was injected into the right caudate-putamen of six baboons to induce a neuropathological and behavioral model of Huntington's disease (HD). In vivo PET studies performed 3 to 6 months after the IA injections showed that subtotal excitotoxic lesions of the CP were accompanied by changes in the kinetic of [76Br]bromolisuride binding indicating a dose-dependent reduction in binding sites in the lesioned striatum of all IA-injected animals. In the most severely lesioned animals, there was also a decrease in the uptake of the nigrostriatal dopaminergic marker. The loss of D2-receptors and decrease in striatal dopamine uptake are consistent with clinical and postmortem findings in HD. In addition, the decrease in 6-[18F]fluoro-L-dopa uptake confirms previous studies performed in a rat model of HD suggesting a continuous decline of nigral dopamine cell function following destruction of their intrinsic striatal target neurons. The results of our experience to date in PET studies of 6-[18F]fluoro-L-dopa and [76Br]bromolisuride binding in IA-lesioned primates indicate that PET can identify effects of cell loss on markers of pre- and postsynaptic function in the striatum of living subjects.

After intranasal instillation in the mouse, rabies virus (CVS strain) selectively infected olfactory receptor cells. In the main olfactory bulb (MOB), infection was observed in periglomerular, tufted, and mitral cells and in interneurons located in the internal plexiform layer. Beyond the MOB, CVS spread into the brain along the olfactory pathways. This infection is specific to chains of functionally related neurons but at the death of the animal some nuclei remain uninfected. CVS also penetrated the trigeminal system. The avirulent mutant AvO1, carrying a mutation in position 333 of the glycoprotein, infected the olfactory epithelium and the trigeminal nerve as efficiently as CVS. During the second cycle of infection, the mutant was able to infect efficiently periglomerular cells in the MOB and neurons of the horizontal limb of the diagonal band, which indicates that maturation of infective particles is not affected in primarily infected neuronal cells. On the other hand, other neuronal cells permissive for CVS, such as mitral cells or the anterior olfactory nucleus, are completely free of infection with the mutant, indicating that restriction is related to the ability of AvO1 to penetrate several categories of neurons. From these observations, we concluded that CVS should be able to bind several different receptors to penetrate neurons, while the mutant would be unable to recognize some of them.

Unilateral caudate-putamen (CP) lesions induced by the glutamate receptor agonist ibotenic acid in baboons produced a neuropathological and behavioral model of Huntington's disease (HD) in the nonhuman primate. Neuropathological evaluation of the lesioned caudate-putamen revealed a neurodegenerative pattern resembling HD. The ibotenic acid-infused CP areas showed a neuronal loss in Nissl-stained sections and a marked astrocytic gliosis by immunohistochemical staining for glial-fibrillary-acidic protein. Acetylcholinesterase fiber staining was severely reduced in the lesioned CP, while afferent dopaminergic fibers, as shown by tyrosine hydroxylase staining, were relatively spared. There was a moderate reduction of met-enkephalin staining in the globus pallidus-pars lateralis ipsilateral to the ibotenic acid lesion, indicating a partial denervation of this structure following the lesion. In the behavioral studies a dyskinetic syndrome with features in common with HD was provoked in the lesioned animals following dopamine receptor agonist administration (1-2 mg/kg apomorphine). The symptoms included hyperkinesia, chorea, dystonia, postural asymmetries, head, and orofacial dyskinesia. The apomorphine test was highly reproducible and individual animals responded with a similar set and incidence of dyskinesia in successive tests. Since the behavioral observations following excitotoxic caudate-putamen damage parallel symptoms in HD patients given dopamine stimulatory drugs, a hypothesis is presented for the observed abnormal movements suggesting that the CP lesions reduce movement thresholds while the activation of dopaminoceptive regions induces dyskinesias.

We studied the effects of chronic (7 day) infusions of GABA (100 and 20 micrograms/microliter, 10 microliter/h) applied in different cerebral structures of baboons made photosensitive by a subconvulsant dose of allylglycine. The GABA infusion has partial anticonvulsant effects when applied to the motor cortex, reticular magnocellular nucleus (RMC), or substantia nigra (SN), but when directed to the prefrontal cortex (area 8) it has no effect. These anticonvulsant effects of GABA infusion are more important when GABA is infused into the motor cortex, where paroxysmal discharges (PDs) originate, than when it is infused into the RMC. In contrast, the anticonvulsant effects on light-induced generalized seizures are more pronounced when GABA is infused into the RMC than when it is infused into the motor cortex. GABA infusion into the SN has no effect on PDs and myoclonia and blocks seizures less effectively than the RMC infusion. These results are in accordance with the role of the motor cortex as a generator of PDs and of RMC in the generalization of seizures. Focal paroxysmal EEG and clinical activities, previously reported to appear at the end of the motor cortex GABA infusion, were not observed after RMC or SN infusions. However, behavioral hyperactivity occurring at the end of subcortical GABA infusions was observed. These behavioral signs could correspond to the clinical expression of a GABA withdrawal syndrome.

The effects of intracerebral injection of folic acid are still controversial. We studied the electroencephalographic, behavioral, and histopathologic consequences of the seizures induced by intra-amygdala administration of various doses of FA in freely moving cats. The severity of the seizures was dose-dependant. For doses of 25 and 50 nmol, single low-amplitude spikes appeared in the amygdala 15 to 20 min after injection and a typical amygdala symptomatology was observed. From doses of 100 nmol recurrent limbic seizures occurred 40 to 80 min after injection. Finally, from doses of 150 nmol secondarily generalized seizures were induced, which could be followed by death 4 to 6 h after injection. The severity of the cerebral lesions was related to both the dose and the paroxysmal manifestations. In cases with short survival time (6 h) and few seizures the pathology was restricted to a lymphocytic and glial reaction with some ischemic cells at the injected site. In cases with status epilepticus, edema and neuronal degeneration was observed in the hippocampus, amygdala, thalamic nuclei of the midline, entorhinal cortex, and cerebellum. No neuronal alteration at the injected site was observed. For longer survival times (8 days) edema was less severe, but hyperchromatic cells were still numerous. These results, compared with those of intra-amygdala administration of kainic acid, suggest that pathologic lesions induced in cats by folic acid more closely resemble those described in man after some status epilepticus.

The behavioral and electrographic effects of chronic (7 days), localized infusion of GABA (100 micrograms/microliter) into the somatomotor cortex of fully amygdala-kindled rats is reported. The animals were stimulated once daily until a stage 5 (generalized clonic seizure) was obtained for five consecutive days. After determination of a stable seizure triggering threshold, the rats were implanted with osmotic minipumps (1 microliter/h for 7 days) connected to previously implanted bilateral cannulae. Amygdala stimulation was continued for 14 successive days. GABA infusion reduced the motor seizure without significantly modifying the limbic afterdischarge. This effect lasted until termination of drug application, with recovery of stage 5 convulsions on the following 3 to 5 days. No effects were observed in saline-infused animals or in rats with unilateral GABA treatment. Upon cessation of GABA treatment (removal of the osmotic devices by day 7 postimplantation), spontaneous epileptic discharges localized to the infusion sites appeared. In some animals, the abnormal activity was accompanied by behavioral signs of myoclonus. This cortical hyperexcitability lasted 2 to 24 h, with complete recovery afterward. These data indicate that two types of focal epilepsy may coexist independently in the same animal and provide confirmation of previous observations in the monkey on the existence of a "GABA-withdrawal syndrome" after chronic, focal infusion of the amino acid.

Forebrain-bisected cats underwent kindling at primary and secondary amygdala sites. The behavioral effect of amygdala kindling was then examined according to the extent of the surgical lesion in the forebrain commissures. Bisection of the corpus callosum with or without lesion of the hippocampal commissure modified both kindling and kindled symmetrical generalized seizure into a lateralized and asymmetrical form. Lesion of the hippocampal commissure was correlated with the loss of the expected positive transfer effect at the secondary amygdala site. These results suggest that whereas the corpus callosum plays a major role in patterning convulsive generalization and generalized convulsion, the hippocampal commissure is involved in mediation of the transhemispheric positive transfer effect. Evidence of a callosal inhibitory influence on amygdala kindling was not obtained.