Isonicotinic hydrazide causes seizures in scrapie-infected hamsters with shorter latency than in control animals: a possible GABAergic defect

Analysis of RNA Expression Profiles Identifies Dysregulated Vesicle Trafficking Pathways in Creutzfeldt-Jakob Disease

Functional genomics applied to the study of RNA expression profiles identified several abnormal molecular processes in experimental prion disease. However, only a few similar studies have been carried out to date in a naturally occurring human prion disease. To better characterize the transcriptional cascades associated with sporadic Creutzfeldt-Jakob disease (sCJD), the most common human prion disease, we investigated the global gene expression profile in samples from the frontal cortex of 10 patients with sCJD and 10 non-neurological controls by microarray analysis. The comparison identified 333 highly differentially expressed genes (hDEGs) in sCJD. Functional enrichment Gene Ontology analysis revealed that hDEGs were mainly associated with synaptic transmission, including GABA (q value = 0.049) and glutamate (q value = 0.005) signaling, and the immune/inflammatory response. Furthermore, the analysis of cellular components performed on hDEGs showed a compromised regulation of vesicle-mediated transport with mainly up-regulated genes related to the endosome (q value = 0.01), lysosome (q value = 0.04), and extracellular exosome (q value < 0.01). A targeted analysis of the retromer core component VPS35 (vacuolar protein sorting-associated protein 35) showed a down-regulation of gene expression (p value= 0.006) and reduced brain protein levels (p value= 0.002). Taken together, these results confirm and expand previous microarray expression profile data in sCJD. Most significantly, they also demonstrate the involvement of the endosomal-lysosomal system. Since the latter is a common pathogenic pathway linking together diseases, such as Alzheimer's and Parkinson's, it might be the focus of future studies aimed to identify new therapeutic targets in neurodegenerative diseases.

The neurodegeneration sequence in prion diseases: evidence from functional, morphological and ultrastructural studies of the GABAergic system

Loss of the GABAergic system of neurons has been reported to be the first detectable neuropathological change in prion diseases, which features the accumulation of an aberrant isoform of the prion protein (PrP(Sc)). To determine the timing of GABAergic system dysfunction and degeneration and its relationship to PrP(Sc) accumulation during the course of prion disease in Syrian hamsters, we applied 3 approaches: i) quantifying GABA-immunopositive neurons and their processes by light and electron microscopy to test for selective loss; ii) measuring evoked [3H]-GABA release from synaptosomes to test for functional abnormalities; and iii) determining the kinetics of PrP(Sc) accumulation in subcellular fractions to correlate it with GABAergic dysfunction. At the terminal stages of disease, we found a significant increase in the number of GABA-positive and -negative presynaptic boutons with abnormally aggregated synaptic vesicles. At the same stage, we also found an equal degree of GABA-immunopositive and -immunonegative presynaptic bouton loss. In contrast, GABA-positive neocortical cell bodies increased, based on stereologic estimates in the terminal stage of scrapie. In the context of these abnormalities, evoked release of [3H]-GABA from cortical and thalamic synaptosomes was significantly decreased, which correlated well with the accumulation of PrP(Sc) in synaptosomes and cell membrane fractions.

Early destruction of the extracellular matrix around parvalbumin-immunoreactive interneurons in Creutzfeldt-Jakob disease

GABA-interneurons immunoreactive (IR) for the calcium-binding protein parvalbumin are lost during the early stages of Creutzfeldt-Jakob disease (CJD) and diminution in their number may partially account for the neurological disturbances manifested in patients suffering from this condition. The disease is characterized by a transformation of the prion protein, PrP(c)-a host-coded sialoglycoprotein-to its protease-resistant and putatively pathological form, PrP(CJD). And since this conversion is likely to take place at the cell surface, we were curious to know whether the "perineuronal net"-a characteristic accumulation of extracellular matrix in intimate contact with the surface of parvalbumin-IR neurons-is implicated in the early disappearance of the mantled cells. Using various lectins and antibodies as markers for the perineuronal net in brains of 21 CJD victims, we observed that this meshwork of extracellular matrix molecules is lost before the embraced parvalbumin-IR neurons themselves disappear. Hence, an interaction of PrP(c) and/or PrP(CJD) with components of the extracellular matrix around this subpopulation of nerve cells precipitates a sequence of as yet unknown events which culminates in the replacement of perineuronal nets by deposits of insoluble PrP(CJD). This change in the environment of the GABA-interneurons IR for parvalbumin may ultimately provoke their death.

Altered GABA distribution in hamster brain is an early molecular consequence of infection by scrapie prions

Antibodies specific for GABA, glutamate and taurine were used to study the distribution of these amino acid neurotransmitters during the progression of scrapie in hamsters. Immunohistochemical distribution of glutamate and taurine were unaffected in scrapie hamsters compared with controls, but the distribution of GABA was altered by 21 days after inoculation. We found both a greater number of neurons showing GABA-like immunoreactivity and more intense staining in those neurons in scrapie-inoculated hamster brains, particularly in the hippocampus, inferior colliculus, frontal cortex and cerebellum. The overall concentrations of aspartate, GABA, glutamate and taurine, measured in seven different brain regions by PITC-amino acid analysis, were not significantly different between normal and scrapie-affected hamsters. The subtle alteration in GABA metabolism detected in this scrapie model suggests that PrPSc interacts directly with a component of the GABA system.

A study of GABAergic system in Scrapie-infected hamsters after striatal microinoculation of the agent

Experimental Scrapie in hamster is a simple, reproducible model of prion diseases that occur in humans and animals. Stereotaxic microinoculation (0.5 microliter) of the agent (263 K) into a specific cerebral structure (striatum) in hamster, previously developed in our group, gives the opportunity to further investigate the pathogenesis of these degenerative diseases and to more precisely define the brain areas and the groups of cells more vulnerable to the effects of the agent. In this model, early significant changes of glutamic acid decarboxylase (GAD) activity in striatum suggested a preferential alteration of the GABA system. The present study was focused on the effects of Scrapie agent directly injected into striatum on GABA neurons at the presynaptic level (GABA uptake) and at the postsynaptic level (GABAA receptors). The high-affinity [3H]GABA uptake is not changed in the Scrapie-injected striatum neither in the controlateral site and the kinetics (Km, Vmax) values are not statistically different for control and Scrapie-inoculated animals. The binding of [3H]GABA (Scatchard analysis) to cerebral membranes does not seem to be altered either at the local site of agent inoculation (striatum) neither at distance in the cerebellum: the affinity constant (Kd) to the ligand and the maximal number of receptor sites were of the same magnitude in control and Scrapie animals, but we do not have a statistical analysis. These effects are completely different of those of a neurotoxin. The present data suggest that the effects of prion agent may be very limited and very specific to some cellular mechanisms, without altering the whole cellular machinery, as recently shown in an in vitro model.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of stereotaxically injected scrapie on neurotransmitter systems of mouse cerebellum

The 22L strain of scrapie was injected stereotaxically into the cerebellum of C57BL/6J mice to determine its effect on several cerebellar neurotransmitter systems during the early clinical stages of the disease. In this model vacuolar lesions are restricted to the cerebellum with no evidence of vacuolization in other brain regions. Although vacuolar lesions develop throughout all cell layers of the cerebellum, they are most severe in the granule cell layer. Modest but significant (P less than 0.01) reductions in cerebellar weight, glutamate decarboxylase activity, and in the affinity of the N6-[adenine-2,8-3H]cyclohexyladenosine binding sites, were observed in scrapie affected mice. The densities of the high- and low-affinity adenosine receptors were unaffected. Adenosine receptors in the cerebellum are highly localized to the axon terminals of the glutamatergic, GABA receptive granule cells. GABA, benzodiazepine, glutamate, and muscarinic cholinergic receptors were not significantly altered. In addition, the high-affinity uptake of glutamate, and the activity of choline acetyltransferase were not significantly changed. GABA high-affinity uptake was slightly increased. Even though the granule cell layer of the cerebellum had undergone severe vacuolation, only modest neurotransmitter changes were apparent. Although these results suggest a tenuous relationship between scrapie pathology and the integrity of neurotransmitter systems, it is possible that compensatory neurochemical changes in uncompromised neuronal populations may have masked potentially specific neurotransmitter effects.

Impairment of the cortical and thalamic electrical activity in scrapie-infected rats

Cortical and thalamic EEG and somatosensory evoked potential (SEP) induced by stimulation of the somesthetic radiations were studied in scrapie-infected rats. Animals were inoculated intracerebrally with a rat-adapted strain (originating in the C506 M3 mouse scrapie strain). EEG and SEP were recorded from 9 to 17 months after inoculation (ti). Abnormalities (paroxysmal bursts, isolated spikes) first occurred in the cortex (parietal areas) and later in the thalamus, where they were usually less marked. Latencies of the postsynaptic components of the SEP increased at ti + 9 months. This effect became progressively more pronounced and at ti + 15 months, latencies of presynaptic components were also delayed. Nevertheless, marked alteration of the SEP occurred only at the terminal stage of the disease. These findings show that the scrapie-induced disturbances affect more especially the cortex. Decrease of inhibitory processes as well as electronic coupling between cells, resulting from the virus-induced membrane fusion, could produce paroxysmal activity of EEG and SEP impairments.