Figure 4

Stimulated microglia, disruption of chloride homeostasis and bicuculline alter the sensory selectivity of nociceptive specific lamina I projection neurons. a. Rate meter records at the top show the response of an identified lamina I projection neuron to natural mechanical stimulation of the receptive field (B = Brush; T = Touch; P = Pinch). The inset shows antidromic spikes from the parabrachial nucleus following our protocol for identification of projection neurons (see methods and Fig. 1b). b. Graphs showing the population data (values indicate mean ± SEM). To avoid biasing the results because of heterogeneity in responses between cells, values are expressed as a percent of control response for each cell. While none of 30 nociceptive specific lamina I projection neuron tested showed occurrence of responses to innocuous input (neither brush or touch) in control conditions after up to 4 hours of recording, all four nociceptive specific cells tested showed a significant response to innocuous input (brush and touch) within 2–3 h of local administration of ATP-stimulated microglia on the surface of the lumbar spinal cord. c. Blockade of cation-chloride co-transporters with local spinal administration of DIOA, or blockade of GABA_A receptors with bicuculline unmasked innocuous input (brush and touch) to nociceptive specific lamina I projection neurons in control animals.