Serotonin alters multi-segmental convergence patterns in spinal cord deep dorsal horn and intermediate laminae neurons in an in vitro young rat preparation.
Each spinal neuron has a receptive field that corresponds to stimulation of a specific area of skin or subcutaneous tissue. Receptive fields are plastic and can be altered during development and injury but the actions of neuromodulators, such as serotonin (5-hydroxytryptamine, 5-HT) on receptive field properties are not well known. We used stimulation of multiple adjacent dorsal root spinal segments as a measure of "receptive field size" to determine the effects of 5-HT on multi-segmental convergent input onto neurons in laminae IV-VII. Whole-cell patch-clamp recordings were undertaken in the in vitro hemisected thoracolumbar spinal cord of rats aged 8-10 days old. Based on synaptic responses, neurons could be divided into two predominant groups and 5-HT exerted different effects on these groups. The first group received excitatory post-synaptic potentials (EPSPs) from the homonymous dorsal root but inhibitory post-synaptic potentials (IPSPs) with increasing amplitude from more distant dorsal roots. In this group, 5-HT preferentially depressed the IPSPs from adjacent nerve roots while leaving the EPSP intact. The second group received short-latency EPSPs from all segments stimulated and 5-HT potently depressed all synaptic input. In both populations the depressant actions of 5-HT increased with dose (0.1-10.0 microM). Bicuculline and strychnine did not affect the 5-HT induced short-latency synaptic depression. These results suggest that descending serotonergic systems depress spinal sensory convergence in a graded and differentiated manner. The findings are discussed in relation to the modulation of nociceptive signaling.
Shay
Barbara L
BL
University of Manitoba, Winnipeg, Canada R3E 3J7.
Hochman
Shawn
S
D000818:Animals; D000831:Animals, Newborn; D004305:Dose-Response Relationship, Drug; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology; D016166:Free Radical Scavengers / Q000494:pharmacology; D020671:Posterior Horn Cells / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012701:Serotonin / Q000494:pharmacology / Q000502:physiology*; D013116:Spinal Cord / Q000187:drug effects / Q000502:physiology; D013126:Spinal Nerve Roots / Q000187:drug effects / Q000502:physiology; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology
D016166:Free Radical Scavengers; D012701:Serotonin