Glutamate-mediated astrocyte-to-neuron signalling in the rat dorsal horn - PubMed

A–D, behavioural tests. A, zymosan (30 μl, 35–40 mg ml⁻¹) causes a significant increase of paw volume (oedema), compared with control animals injected with the same volume of saline (Mann–Whitney U test, P < 0.05; mean baseline paw volume ranged from 281 to 301 μl in both groups). B, zymosan induces thermal hyperalgesia evaluated as a significant decrease of paw withdrawal latency to a thermal stimulus during the plantar test (Mann–Whitney U test, P < 0.01 for both sets of data). C, mechanical allodynia assessed using von Frey filaments on the right paw of animals receiving zymosan or saline (Mann–Whitney U test, P < 0.01). Zymosan causes a significant decrease of paw withdrawal threshold. D, mechanical allodynia tested by performing the von Frey test on the right (injected with zymosan) and left paw (non treated) of each animal. The injected paw exhibits a significant decrease of withdrawal threshold compared to the untreated one (Mann–Whitney U test, P < 0.01). Data are expressed as means ±

s.e.m.

of 5–6 rats for each group. E–G, patch-clamp recordings of SICs in lamina II neurons, obtained from non-treated rats (control) and animals injected with zymosan or saline. Recordings were performed at −60 mV in basal conditions (i.e. zero extracellular Mg²⁺ and 1 μ

m

TTX). E, representative traces of SICs recorded from an inflamed animal, in basal conditions. F, traces recorded in a different lamina II neuron, from a treated animal, showing the presence of a spontaneous SIC in control, abolished by the subsequent application of 100 μ

m d

-AP5. G, mean frequency of SICs determined from all cells obtained from the 3 animal groups. Zymosan causes a significant increase of SIC frequency compared to control and saline (P < 0.001 and P < 0.05, respectively), while no significant difference is observed between control and saline (Kruskal–Wallis test followed by Dunn's method for multiple comparisons). The application of 100 μ

m d

-APV during recording from treated animals completely abolishes SICs (control: n= 50; zymosan: n= 47; saline: n= 46, zymosan +

d

-APV: n= 10).