Danielle Riche

Long-term effects of intrahippocampal kainic acid injection in rats: A method for inducing spontaneous recurrent seizures ☆

Kainic acid (KA) is known as a powerful convulsant and neurotoxic agent. When intracerebrally administered it causes repetitive seizures for about 1 or 2 days and brain damage both locally and in several remote brain regions. In the present paper the long-term effects of intrahippocampal KA administration are reported. Doses from 0.1 to 3.0 micrograms of KA were injected in the right hippocampus of Wistar rats and both the behaviour and EEG were observed during a period of about 3 months. Following KA doses of 0.8-2.0 micrograms, 4 distinct phases were observed: (1) acute phase which lasted 1-2 days and corresponded to the pattern of repetitive seizures as already described; (2) silent phase (5-21 days) which was characterized by a progressive return to apparently normal EEG and behaviour except for some aggressive behaviour in those animals receiving the highest doses; (3) phase of spontaneous recurrent seizures (these seizures started 6-22 days after KA injections and were mostly triggered upon handling and recurred approximately 2 times by day for about 30 days; usually they resembled the amygdaloid kindled seizures); and (4) post-seizure phase where no more seizures were observed but significant spiking activity in the amygdala recordings could be seen. Animals receiving KA doses of 0.1-0.4 microgram did not evolve beyond the acute phase whereas those receiving 3.0 micrograms died during this first phase. Neuropathological examination revealed dose-dependent alterations. These serial events offer a new method to induce spontaneous recurrent seizures with brain damage.

A primate model of Huntington's disease: Behavioral and anatomical studies of unilateral excitotoxic lesions of the caudate-putamen in the baboon

Unilateral caudate-putamen (CP) lesions induced by the glutamate receptor agonist ibotenic acid in baboons produced a neuropathological and behavioral model of Huntingtons 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.

Chronic MPTP treatment reproduces in baboons the differential vulnerability of mesencephalic dopaminergic neurons observed in parkinson's disease

Chronic administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to baboons was shown previously to result in a motor syndrome and a pattern of striatal dopaminergic fibre loss similar to those observed in idiopathic Parkinsons disease. In the present study, tyrosine hydroxylase-immunoreactive neurons were quantified in the mesencephalon of control (n = 4) and chronically MPTP-treated (n = 3) baboons. MPTP induced a significant reduction in neuronal cell density in the substantia nigra (63.8% reduction) and the ventral tegmental area (53.1%). Within the substantia nigra, obvious mediolateral and dorsoventral gradients of neuronal cell loss were observed. First, the pars lateralis was more affected than the lateral divisions of the pars compacta (89.6% vs 73.8% cell loss), which in turn were more depleted than the medial divisions (60.1% reduction). Second, the ventral regions of the pars compacta were more degenerated than the dorsal parts (82.4 vs 51.5% decrease). This regional pattern is strikingly similar to that observed in Parkinsons disease and indicates that two subpopulations of dopaminergic neurons are distinguishable on the basis of their differential vulnerability to MPTP. Finally, the present study confirms that chronic mitochondrial complex I inhibition using MPTP in primates is sufficient to reproduce the typical dopaminergic cell loss and striatal fibre depletion observed in Parkinsons disease.

Stable parkinsonian syndrome and uneven loss of striatal dopamine fibres following chronic MPTP administration in baboons.

The progressive degeneration of dopamine neurons observed in idiopathic Parkinsons disease was mimicked by injecting low doses of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to baboons, on a chronic basis. Five Papio papio baboons were treated on two different regimens (chronic intravenous administration at weekly intervals for 20-21 months or, daily MPTP treatment for five days followed five to six months later by chronic weekly injections for 5-21.5 months). All animals were assessed for motor symptoms during and after neurotoxic treatment. Both regimens invariably resulted in the appearance of a progressive and irreversible syndrome characterized by action and resting tremor, cogwheel rigidity, postural impairments, hypokinesia and bradykinesia. In some animals, symptoms of resting tremor and rigidity initially restricted to one side of the body became bilateral within a few months of treatment. Subtle abnormalities that may be found in idiopathic Parkinsons disease such as alterations of the blink reflex response were also noted. Neuropathological examination of caudate nucleus, putamen, substantia nigra and ventral tegmental area in brain sections stained for tyrosine hydroxylase showed a typical uneven striatal dopamine fibre loss and a neuronal depletion in the dopaminergic mesencephalic cell groups that reproduce those observed in idiopathic Parkinsons disease. Immunocytochemical observations and behavioural data show that chronic rather than acute MPTP injection regimens can replicate most of the neuropathological and the clinical features typical of idiopathic Parkinsons disease, possibly by increasing the ability of this neurotoxin to target specific subpopulations of mesencephalic dopaminergic neurons.

A primate model of Huntington's disease: cross-species implantation of striatal precursor cells to the excitotoxically lesioned baboon caudate-putamen

SummaryIbotenic acid was injected unilaterally into the baboon caudate-putamen (CP) to achieve a neural degeneration model in the primate, with a neuropathology similar to Huntingtons disease. Four to six weeks later injections of cell suspensions of striatal precursor cells, obtained by dissection of the fetal rat striatal region (13–15 days gestational age), were made into the excitotoxically lesioned CP of 3 baboons immunosuppressed by Cyclosporin A. Morphological analysis indicated that in one of the baboons, which had the largest lesion of the CP and the shortest survival time (6 weeks after implantation), there was a surviving striatal implant. The implanted neurons grew in high densities in cellular aggregates within the host gliotic CP. These neurons had a neuronal size phenotypical for rat striatum, i.e. on average about a 25% smaller neuronal cell diameter than a similar population in the baboon caudate-putamen. Glial-fibrillary-acid-protein immunoreactivity was present on large astrocytes within the striatal implant, with a distinct border towards the lesion-induced astrogliosis of the host. Neuronal markers for acetylcholinesterase and Leu-enkephalin were distributed in a typical patchy manner in the striatal implants along with fiber staining for tyrosine-hydroxylase-like immunoreactivity (TH) possibly derived from afferent host dopaminergic axons. Some of these fibers in the implants came from intrinsic TH-positive neuronal somata, probably of neocortical fetal origin and transiently expressing the enzyme. In conclusion, the results indicate that neuronal replacement can be achieved by crossspecies implantation of fetal striatal precursor cells to the previously neuron depleted primate CP under immunosuppression but that the survival and growth of such implants may be variable and subject to unfavourable trophic conditions.

The GABA-withdrawal syndrome: a new model of focal epileptogenesis.

A novel model of focal, cortical epilepsy is described. Chronic (6 h to 14 days), localized application of gamma-aminobutyric acid (GABA) into the somatomotor cortex of rats induces, upon withdrawal, the appearance of epileptogenic activity with maximal electrographic expression circumscribed to the infused site. This GABA-withdrawal syndrome (tested for a 100 micrograms/microliter/h dose) lasted from 24 to 168 h (mean values). A significant correlation was found between infusion time and duration of the excitability rebound, with the longer duration corresponding to the shorter infusion time. A distant lesion effect was observed in the thalamic area of cortical projection. The potential use of this neurotransmitter-induced phenomenon in the study of brain plasticity in general, and of epilepsy in particular, is discussed.

Effects of localized, chronic GABA infusions into different cortical areas of the photosensitive baboon, Papio papio

The effects of chronic (7 days) intracortical GABA infusions were investigated in both naturally photosensitive and non-photosensitive baboons. Bilateral and unilateral infusions into motor and occipital regions blocked photosensitivity, while premotor and prefrontal cortex infusions had no effect on the electro-clinical manifestations of this type of reflex epilepsy; the monkeys with prefrontal GABA infusions, however, showed selective attention deficits, detected with the delayed response test. In all cases a GABA withdrawal syndrome, appearing as epileptogenic spontaneous activity localized to the infused sites, was found at the cessation of GABA application. We conclude that GABAergic systems localized at discrete cortical areas play an important role in photosensitivity and in the modulation of cognitive processes in the monkey.

Theophylline reduces cerebral hyperaemia and enhances brain damage induced by seizures

Hippocampal and neocortical blood flows and tissue pO2 were investigated by mass spectrometry in unanaesthetized spontaneously breathing rats during kainic acid-induced seizures to determine whether adenosine is involved in the coupling of cerebral blood flow to metabolism during enhanced metabolic demand. The possible involvement of adenosine in the neuronal damage induced by seizures was also analyzed. The intrinsic effects of theophylline and the duration of the adenosine receptor blockade by this xanthine were first tested in 8 rats. Two groups of rats were then compared: one (n = 6) received kainic acid, and the other (n = 10) theophylline 15 min prior to kainic acid administration. An additional group of 10 rats was taken for classical histology 48 h after kainic acid treatment. Theophylline significantly reduced the hyperaemia observed during seizures, prevented any tissue hyperoxia and enhanced brain damage. This strongly suggests that adenosine is partly responsible for the increase in cerebral blood flow during kainic acid-induced seizures and has neuroprotective properties.

A primate model of Huntington's disease: functional neural transplantation and CT-guided stereotactic procedures.

In this article, we show that 1) computed tomographic (CT)-guided stereotactic infusion of an excitotoxin into the striatum of a nonhuman primate provides a useful neuropathologic and behavioral model for Huntingtons disease. 2) High-resolution positron emission tomography (PET) can be used to image the decreased glucose utilization and the preservation of dopaminergic terminals in the lesioned striatum by using 2-fluoro-deoxy-D-glucose (2FDG) and N-(C-11)-methyl-2-beta-carbomethoxy-3-beta-phenyl tropane (CPT) as tracers. 3) Transplantation of crossspecies striatal fetal tissue into the lesioned caudate-putamen reduces many of the abnormal motor movements and behavioral changes seen in the Huntingtons disease primate model. 4) Graft rejection results in the return of the abnormal signs of the pregrafted state. These results indicate that treatment of the neuronal deficit in Huntingtons disease can involve intervention at the local neuronal circuit level. CT-guided stereotactic implantation of cells that might protect or replace this defective circuitry may eventually provide an effective treatment for Huntingtons disease.

Cortical hypometabolism and its recovery following nucleus basalis lesions in baboons: a PET study

The cerebral metabolic rate for glucose was measured serially with positron emission tomography and [18F]fluorodeoxyglucose in five baboons with stereotactic electrocoagulation of the left nucleus basalis of Meynert (NbM). Four days after lesion, a significant metabolic depression was present in the ipsilateral cerebral cortex, most marked in the frontotemporal region, and which recovered progressively within 6–13 weeks. These data demonstrate that adaptive mechanisms efficiently compensate for the cortical metabolic effects of NbM-lesion-induced cholinergic deafferentation. Moreover, unilateral NbM lesions also induced a transient reduction in contralateral cortical metabolic rate, the mechanisms of which are discussed. Explanation of these effects of cholinergic deafferentation in the primate could further our understanding of the metabolic deficits observed in dementia of the Alzheimers type.