| Objective:There is a high incidence of neonate experiencing procedural pain, causing a series of short-term and long-term impacts. Nowadays, the assessment and treatment of neonate pain are still faulty. And the underlying pathogenesis of neonatal pain is the same. Substantia gelatinosa(SG) of spinal dorsal horn is the first relay station transmitting nociceptive information, so SG neurons play a key role in pain transmission. However, morphological classification and electrophysiological property of SG neurons are still elusive. Consequently, we use whole-cell patch-clamp and immunohistochemical techniques in spinal parasagittal slices to study its morphology and electrophysiology properties. Methods:7-10 days old Sprague-Dawley rats were anesthetized with cold ices(about 4 °C). After transcardial perfusion and extraction of the lumbosacral spinal cords(L1-S3), the pia-arachnoid membrane as well as all dorsal and ventral roots were removed with fine forceps. Spinal cords were then cut into 300 μm thick parasagittal slices. Whole-cell patch clamp technique was applied to record passive membrane properties(resting membrane potential, membrane capacitance, and membrane resistance) and positive membrane properties(action potential, involving firing pattern, threshold, height, and half-width). Meanwhile, with neurobiotin 488 permeating through the recording neuron, at least 10 minutes during holding state, we can record and analyze SG neurons’ morphology properties.Neonatal rats SG neurons(n=129),according to their morphology,are classically categorized as follows: islet, central, radial, vertical and unclassified neurons; and according to their electrophysiology, are classically categorized as follows: tonic-firing、delayed-firing、initial-burst、single-spiking、phasic-bursting、gap-firing、reluctant-firing. Results:1. Neonatal rats SG neurons are classically categorized as follows: islet, central, radial, vertical and unclassified neurons;2. Neonatal rats SG neurons with different morphology have different soma diameter and rostral, caudal, dorsal and ventral dendritic field span;3. Neonatal rats SG neurons with different morphology have different passive membrane properties, including resting membrane potential, membrane capacitance, and membrane resistance;4. Neonatal rats SG neurons with different morphology have different AP threshold, AP height and AP half-width;5. Neonatal rats SG neurons’ firing pattern are classically categorized as follows: tonic-firing、delayed-firing、initial-burst、single-spiking、phasic-bursting、gap-firing and reluctant-firing;6. Neonatal rats SG neurons with different firing pattern have different passive and positive membrane properties;7. Neonatal rats SG neurons with different morphology have different firing pattern;8. Neonatal rats SG neurons with different firing pattern have different morphology. Conclusions:The morphological categories and passive and positive membrane properties have their own characteristics in neonatal SG neurons. These data illustrated that there exists a relationship between morphology and electrophysiology properties of SG neurons. And SG neurons with the same morphology properties share the same electrophysiology properties. Obviously, the research on neonatal SG neurons may provide theory evidence for neonatal pain. |
