TRPC-Mediated Current Is Not Involved in Endocannabinoid-Induced Short-Term Depression in Cerebellum

It has been reported that activation of metabotropic glutamate receptor 1 (mGluR1) can mediate endocannabinoid-induced short-term depression of synaptic transmission in cerebellar parallel fiber (PF)-Purkinje cell (PC) synapse. mGluR1 has signaling pathways involved in intracellular calcium increase which may contribute to endocannabinoid release. Two major mGluR1-evoked calcium signaling pathways are known: (1) slow-kinetic inward current carried by transient receptor potential canonical (TRPC) channel which is permeable to Ca2+; (2) IP3-induced calcium release from intracellular calcium store. However, it is unclear how much each calcium source contributes to endocannabinoid signaling. Here, we investigated whether calcium influx through mGluR1-evoked TRPC channel contributes to endocannabinoid signaling in cerebellar Purkinje cells. At first, we applied SKF96365 to inhibit TRPC, which blocked endocannabinoid-induced short-term depression completely. However, an alternative TRP channel inhibitor, BTP2 did not affect endocannabinoid-induced short-term depression although it blocked mGluR1-evoked TRPC currents. Endocannabinoid signaling occurred normally even though the TRPC current was mostly blocked by BTP2. Our data imply that TRPC current does not play an important role in endocannabinoid signaling. We also suggest precaution in applying SKF96365 to inhibit TRP channels and propose BTP2 as an alternative TRPC inhibitor.

Selective Neuronal Damage Produced by beta-fluoroethylacetate Intoxication in Rat Brain

Beta-fluoroethylacetate has been extensively used as the rodenticide in Korea. In some patients with acute poisoning, beta-fluoroethylacetate caused cerebellar dysfunction as a single and persistent neurologic sequela after a period of an acute neurological disorder which is characterized by mental deterioration, seizures, and respiratory failure. But there has been no report of pathological findings to explain neurological deficit. We tried to verify the histologic changes of the central nervous systems in beta-fluoroethylacetate poisoned rats. Silver staining(Gallyas) was used to evaluate the histology. In acute intoxication experiment with LD50(7mg/Kg), beta-fluoroethylacetate elicited acute onset of consciousness deterioration, generalized tonic-clonic seizures and large amplitude tremulous activity involving whole body with full recovery after 24 hours. There was no discernible pathologic change in CNS in acutely poisoned rats. However, when poisoned with sublethal dose(5mg/Kg) daily for five days, a moderate degree of nerve cell degeneration was found selectively in dentate nucleus, Purkinie cell layer, vestibulo-cochlear nucleus and striatum. This change was not seen in hippocampus, cerebral cortex or cerebellar cortex. These findings were well correlated with the previous reports of selective pathology in human 5-FU intoxication cases. Our preliminary results suggest that beta-fluoroethylacetate, a kind of cellular metabolism inhibitor may induce selective neuropathology mainly involving cerebellar output pathway in rats.

ABNORMAL EXPRESSION OF TYROSINE HYDROXYLASE IN THE CEREBELLUM OF NIEMANN-PICK TYPE C MICE / 解剖学报

Objective To investigate the time, location and relationship to clinical manifestation of abnormal expression of tyrosine hydroxylase(TH) in the cerebellum of Niemann\|Pick type C disease (NPC). Methods Immunohistochemical staining was applied, by using antibodies to TH, to brain sections from NPC and normal mice of various ages. Some adjacent sections were stained for calbindin D28k. Results There was no marked decrease in number of cerebellar Purkinje cells(PC), which were negatively stained for TH, in the NPC mice aged 1\|3 weeks. The PC were decreased in number starting from week 5. During postnatal weeks 8\|11, PC were significantly lost, but considerable number of PC in the nodulus and uvula vermis survived. Some survived PC and their dendritic trees were TH immunoreactive after week 8. These PC showed axonal spheroids and irregular dendrites that were bent, broken, locally enlarged or atrophied. Conclusion Mutation of NPC1 gene induces severe loss of cerebellar PC and survived PC have been damaged morphologically and show abnormal gene activity. These may be the pathogenic basis of movement disorders of NPC.