Figure 9
PB-CeA and not EC-CeA synapse is activated in response to peripheral inflammation. To investigate the specificity of the PB-CeA pathway output to the inflammation, the external capsule (EC) was stimulated while recordings were made from neurons present in the CeLC region of brain slices obtained from formalin treated animals. For these stimulus intensity experiments, the local anesthetic QX-314 (5 mM) was included in the pipette solution. (A) The enhanced current output induced by inflammation observed after stimulation of the PB afferents (middle panel, n = 5) did not occur when the EC was stimulated (lower panel, n = 5). Stimulation of the EC in the formalin brain slices yielded significantly lower current magnitude at the higher intensity compared to that obtained in untreated control brain slices (upper panel, n = 4). Injection (i.p.) of NAAG peptidase inhibitor ZJ43(150 mg/kg, n = 6, lower panel) 30 minutes before and 8 hours after formalin injection into the mouse's footpad significantly blocked the enhanced current output that would have occurred with stimulation of the PB afferents at the higher stimulus intensities in the formalin group (middle panel). Larger current output albeit not significant was observed in the CeLC region of brain slices obtained from the saline group (middle panel, n = 5) when compared to the untreated control group (upper panel, n = 5). (B) Average data showing the current output as a function of the stimulus intensity in all four animal groups (untreated control, saline treated, ZJ43- formalin treated, and formalin treated). For the treated groups the recordings were performed 24 hours post saline or formalin injection into the mouse's footpad. Afferents stimulation: (PB) indicates the parabrachial afferents, while (EC) indicates that the external capsule was stimulated. Data presented as mean ± SEM; *p ≤ 0.05 vs. control, #p ≤ 0.05 across group (Formalin 24 hr PB vs. ZJ43 Formalin 24 hr PB and Saline 24 hr PB), ◊p ≤ 0.05 across group (Formalin 24 hr PB vs. Formalin 24 hr EC),∞ p ≤ 0.05 across group (Formalin 24 hr EC vs. Control Untreated EC), unpaired Student's t-test. Recordings were in Mg2+ free ACSF.