strychnine and Amyotrophic-Lateral-Sclerosis

Excitotoxic damage to motoneurons is thought to be an important contribution to the pathogenesis of amyotrophic lateral sclerosis (ALS), a slowly developing degeneration of motoneurons that, in most cases of sporadic occurrence, is associated with impaired glial glutamate uptake. Riluzole is the only drug licensed for symptomatic ALS treatment and is proposed to delay disease progression. As riluzole is administered only after full ALS manifestation, it is unclear if its early use might actually prevent motoneuron damage. We explored this issue by using, as a simple in vitro model, hypoglossal motoneurons (a primary target of ALS) of the neonatal rat brainstem slice preparation exposed to excitotoxic stress due to glutamate uptake block by DL-threo-β-benzyloxyaspartate (TBOA). TBOA evoked sustained network bursting, early (1 h) enhancement of the S100B immunostaining of gray matter astrocytes, and activated the motoneuronal stress ATF-3 transcription factor; 4 h later, loss (30%) of motoneuron staining ensued and pyknosis appeared. Riluzole (5 μM; applied 15 min after TBOA) inhibited bursting, decreased the frequency of spontaneous glutamatergic events, reversed changes in S100B immunostaining and prevented late loss of motoneuron staining. These results show that excitotoxicity induced by glutamate uptake block developed slowly, and was sensed by glia and motoneurons with delayed cell death. Our data provide novel evidence for the neuroprotective action of riluzole on motoneurons and glia when applied early after an excitotoxic stimulus.

Topics: Action Potentials; Amyotrophic Lateral Sclerosis; Animals; Aspartic Acid; Astrocytes; Bicuculline; Biomarkers; Convulsants; Excitatory Amino Acid Antagonists; GABA-A Receptor Antagonists; Glutamic Acid; Hypoglossal Nerve; Motor Neurons; Neuroprotective Agents; Patch-Clamp Techniques; Rats; Riluzole; Strychnine

Amyotrophic lateral sclerosis is a lethal, adult-onset disease characterized by progressive degeneration of motoneurons. Recent data have suggested that the disease could be linked to abnormal development of the motor nervous system. Therefore, we investigated the electrical properties of lumbar motoneurons in an in-vitro neonatal spinal cord preparation isolated from SOD1(G85R) mice, which is a transgenic model of amyotrophic lateral sclerosis. The study was performed on young animals at the beginning of their second week, between postnatal days 6 and 10. Measurements of resting membrane potential and action potential characteristics of motoneurons were similar in wild-type and SOD1(G85R) mice. However, the input resistance of motoneurons from transgenic mice was significantly lower than that of wild-type animals, whereas their membrane capacitance was increased, strongly suggesting larger SOD1(G85R) motoneurons. Furthermore, the slope of the frequency-intensity curve was steeper in motoneurons from wild-type pups. Interestingly, the input resistance as well as the slope of the frequency-intensity curves of other spinal neurons did not show such differences. Finally, the amplitude of dorsal root-evoked potentials following high-intensity stimulation was significantly smaller in SOD1(G85R) motoneurons. The superoxide dismutase 1 mutation thus induces specific alterations of the functional properties of motoneurons early in development.

Topics: Amyotrophic Lateral Sclerosis; Animals; Disease Models, Animal; Dose-Response Relationship, Radiation; Electric Stimulation; Glycine Agents; Lumbosacral Region; Membrane Potentials; Mice; Mice, Inbred C57BL; Mice, Transgenic; Motor Neurons; Patch-Clamp Techniques; Spinal Cord; Strychnine; Superoxide Dismutase; Superoxide Dismutase-1

Loss of motor neurons is the primary pathological hallmark of amyotrophic lateral sclerosis. Drug and neurotransmitter receptors are neuronal markers and can be indicators of neuronal connectivity. Knowledge of alterations in receptors in amyotrophic lateral sclerosis should contribute to our understanding of normal spinal cord neurotransmitter systems as well as of the pathophysiology of amyotrophic lateral sclerosis. We therefore used a sensitive, light microscopic in vitro labeling receptor autoradiographic technique to map and quantitate muscarinic cholinergic, glycinergic, and benzodiazepine receptors in three levels of spinal cord from six patients with amyotrophic lateral sclerosis and six age- and sex-matched control patients. In control tissues, the receptor distributions were similar in the three levels of spinal cord and also similar to those found in previous studies with animals. In amyotrophic lateral sclerosis, major reductions in receptor densities were noted in Rexed layer IX, the region containing motor neurons. Reductions were noted in other laminae as well, particularly for muscarinic receptors. The changes in muscarinic receptors were caused solely by changes in high-affinity agonist sites. Reductions in glycine and muscarinic receptors were highly correlated with the degree of motor neuron loss found in the amyotrophic lateral sclerosis patients. The findings in this study point out the usefulness of this receptor mapping technique in understanding the changes in neuronal populations that occur in the degenerative neurological diseases.

Topics: Adult; Aged; Amyotrophic Lateral Sclerosis; Autoradiography; Female; Flunitrazepam; Humans; Male; Middle Aged; Motor Neurons; N-Methylscopolamine; Nerve Degeneration; Neurotransmitter Agents; Receptors, Cell Surface; Receptors, GABA-A; Receptors, Glycine; Receptors, Muscarinic; Receptors, Neurotransmitter; Scopolamine Derivatives; Spinal Cord; Strychnine