| 1213 Effects of Synaptic Inputs on Properties of Trigeminal Sensory Neurons | ||
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D. VERDIER1, M. PAQUET1, J.P. LUND2, and A. KOLTA3, 1Université de Montréal, Canada, 2McGill University, Montreal, Canada, 3Université de Montréal, Montreal, Canada Objectives: Subthreshold membrane oscillations in large diameter primary afferent have been associated to the development of pathological pain conditions. The somata of the large diameter afferents innervating the jaw muscle spindles located in the trigeminal mesencephalic nucleus (NVmes) are contacted by boutons containing a variety of neurotransmitters. In this study, we investigated effects of synaptic inputs on the intrinsic properties of these neurons. Methods: Intracellular recordings were obtained using whole cell patch techniques or sharp glass electrodes in rat brainstem slices. The cells were labeled by prior injection of Dil into the masseter muscles. Synaptic responses were evoked by electrical stimulation. Transmitters were applied locally by pressure ejection. Results: NVmes neurons displayed high frequency oscillations (> 100 Hz) at RMP and depolarized potentials. Local synaptic inputs reset the rhythm and enhanced the amplitude of the oscillations, causing the cell to fire repetitively. These effects were blocked by DNQX. These neurons also displayed a bistable behavior under local application of KCl combined with hyperpolarization. The bistability was associated with a sudden drop of input resistance produced by downward, but not upward, current ramps at potentials between –40 and –70mV. This bistability was voltage dependent and could be triggered only in this narrow range. It persisted in presence of TTX, apamin, 4-AP and Cadmium, but was sensitive to TEA. Preliminary data indicate that the bistable behavior can be disrupted by several neurotransmitters (ATP, Ach, glutamate), that depolarize the cells but can be restored by injection of hyperpolarizing current. Conclusion: These results suggest that NVmes neurons have intrinsic properties that may be involved in either rhythmic pattern generation or development of hyperalgesic states and that these properties may be modulated by local synaptic inputs arising from neurons involved either in the masticatory CPG or trigeminal nociceptive pathways. CIHR grants #MT14392 and # 15716. | ||
| Seq #135 - Sensory, Motor, and Vascular Mechanisms 2:00 PM-4:00 PM, Thursday, 10 March 2005 Baltimore Convention Center Exhibit Hall E-F | ||
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