Expression Of Interleukin-6 Receptors In Cerebellar Interpositus Nuclei And Effect Of Interleukin-6 On Neuronal Discharge Of Interpositus Nuclei

Objective: The recent studies in our laboratory have showed the expression of cytokine interleukin-6 (IL-6) and IL-6 receptor (IL-6R) in the neurons of cerebellar cortex. Also we have revealed that IL-6 can protect cultured cerebellar granule neurons against glutamate-induced neurotoxicity. However, whether the neurons in the cerebellar deep nuclei also express IL-6R and what effect IL-6 has on the neurons have been less known. Thus, in the present study we on the one hand investigated the expression of IL-6R in the cerebellar interpositus nucleus (IN), and on the other hand explored the effect of IL-6 on neuronal discharge of IN and the receptor mechanism mediating the IL-6 effect, so as to extend our knowledges and comprehensions on roles of cytokines in neuroimmunomodulation. Methods: An immunohistochemical technique (avidin biotin horseradish peroxidase complex, ABC) was used to detect IL-6R immunoreactive neurons in the IN. IL-6R mRNA and gp130 mRNA, an intracellular signaling subunit of IL-6R, in neurons of IN were measured by the method of reverse transcription-polymerase chain reaction (RT-PCR). The cerebellar slices were prepared and spontaneous discharges of single cerebellar IN neuron were recorded by extracellular recordings. The responses of single neuronal discharges were observed when the slices were superfused by IL-6. Results: Many IL-6R immunoreactive neurons were found in the IN. The neurons in the IN could express IL-6R mRNA and gp130 mRNA. Forty-one IN neurons with a tonic discharge were recorded. The spontaneous firing rate of the cells ranged from 16.0 to 85.3 spikes/s and the mean firing rate of the cells was 42.4±14.6 spikes/s. Of the 41 recorded IN neurons, 17 neurons (41.4%) were excited by the IL-6 stimulation (10 ng/ml), and the other 24 neurons (58.6%) failed to respond to the IL-6 stimulation during the recording time (3 h). The average onset latency was 5.1±1.6 min and the response reached a maximum about 41.0±7.8 min after the IL-6 application. Of the 3 IN recorded neurons randomly selected, the spontaneous firing rate of the cells showed no change by the anti-IL-6R antibody application (0.2 ug/ml). Of the other 3 IN neurons that showed an excited response by IL-6 (10 ng/ml) stimulation, the anti-IL-6R antibody (0.2 ug/ml) could block the IL-6 induced excitation. Conclusions: IN neurons express both the IL-6R and gp130 (intracellular signaling subunit of IL-6R). IL-6 can excite a proportion of neurons in IN and the excitatory response to the IL-6 stimulation may be potential through a direct activation of IL-6R expressed by this neuronal type. Objective: Effects of glutamate on the discharges of neurons in cerebellar interpositus nucleus were investigated in rat cerebellar slices. Methods: The cerebellar slices were prepared and spontaneous discharges of single cerebellar interpositus nuclear neurons were recorded by using extracellular recording technique. Results: Glutamate evoked a significant increase in firing rate of the cerebellar interpositus nuclear neurons. A low-Ca²⁺/high-Mg²⁺ medium did not block the excitatory response of cerebellar interpositus nuclear neurons to glutamate. Conclusions: The excitatory effect of glutamate on the discharge of interpositus nuclear neurons in cerebellar slices may be directly mediated by glutamate receptors on interpositus nuclear neurons.