Spontaneous Synaptic Activity in Projection Neurons of Lamina I of the Isolated Rat Lumbar Spinal Cord: Effect of Peripheral Inflammation

Spino-cerebral (projection) neurons localized in lamina I of the spinal gray substance play an important role in the transmission of pain-related information to the brain. We examined spontaneous excitatory postsynaptic currents (sEPSC) recorded from lamina I spino-pontine neurons in isolated preparations of the rat lumbar spinal cord; the respective neurons were retrogradely labeled by a fluorescent dye. We tried to find out how experimentally induced peripheral inflammation affects the amplitude/time characteristics of these currents. It was found that, in preparations obtained from animals with inflammation of hind limb tissues, the frequency and (to a lesser extent) amplitude of sEPSC in projection neurons are, on average, higher than those measured in neurons of the control animals. It is belived that such changes result mostly from plastic modifications of neuron-to-neuron interactions in neuronal networks of lamina II, which form main synaptic inputs to neurons of lamina I. Increased frequency and amplitude of sEPSC in lamina I neurons should lead to some facilitation of transmission of nociceptive information to the cerebral structures. Such hyperexcitability of lamina 1 projection neurons can provide a notable contribution to the development of hyperalgesia in chronic inflammatory states and to facilitation of generation of pain-related emotions.