The caudal subnucleus of the spinal trigeminal nucleus (medullary dorsal horn ; MDH) receives direct inputs from unmyelinated and thinly myelinated, small diameter primary afferent fibers. Thus, the MDH is implicated in the processing of nociceptive information in the orofacial region.
In this study, the types and characteristics of voltage-dependent ion currents were investigated in acutely isolated MDH neurons of postnatal rats by means of the whole cell patch clamp techniques. Coronal slice (400 pm) of the trigeminal caudal subnucleus region was sequentially treated with pronase 0.2 mgJui and thermolysin 1.2 mg/ml!, then single neurons were mechanically dissociated. Voltage-dependent sodium currents showed that the half-maximum activation potential was -41.8±1.8 mV and half-maximum inactivation potential was -62.4±3.0 mV. And the currents were blocked totally by application of lOOnM tetrodotoxin. In a Cat´ free solution, low-threshold transient (IA) and high-threshold sustained (IK) currents were recorded. The half-maximum activation and inactivation potential of IK were 2.5±1.9 mV and -37.1 ±2.3 mV, respectively. IA was activated and inactivated more rapidly than Ix. The half-maximum activation and inactivation potential were -21.6±6.3 mV and -84.5±5.0 mV, respectively. When a 4-aminopyridine of 5 mM was applied, IA was almost totally blocked.
These results reveal that MDH neurons express a variety of voltage-dependent ionic currents with distinct physiological and pharmacological properties, and they play an essential role in the transmission and modulation of sensation, especially pain, from trigeminal region.
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