Repeated microdialysis from the nucleus tractus solitarii of chronically instrumented, unsedated piglets

Normal development of respiratory rhythm and control, and perturbations thereof, likely relate to neuromodulators in brainstem regions. To assess the feasibility of repeated neurochemical sampling by in vivo microdialysis from the respiratory-related nucleus tractus solitarii (NTS) during development. 19-24 day-old piglets (n = 7) were implanted under anesthesia with chronic microdialysis guides near NTS around obex. Unsedated piglets then underwent in vivo microdialysis twice, 3 days apart, through probes inserted acutely via the guides to abut against the NTS. The probe tips, surrounded by normal neurons and only diffuse gliosis, either intersected, or were within < or = 300 microns from the NTS. Thirty-min microdialysates were collected for 120 min in normoxia, HPLC-fractionated, and assayed for substance-P (SP), a respiratory excitatory neuropeptide. SP levels stabilized within 90 min from probe placement, and did not differ between the 2 experimental days. Thus, repeated in vivo microdialysis from NTS of conscious piglets is feasible, and can illuminate respiratory-related normal and pathological neurochemical processes during development.