Structure–function analysis of rhythmogenic inspiratory pre-Bötzinger complex networks in “calibrated” newborn rat brainstem slices

Inspiratory pre-Bötzinger complex (preBötC) networks remain active in perinatal rodent brainstem slices. Our analysis of (crescendo-like) inspiratory-related population and cellular bursting in novel histologically identified transversal preBötC slices in physiological (3 mM) superfusate [K+] revealed: (i) the preBötC extent sufficient for rhythm in thin slices is at most 175 μm. (ii) In 700 μm thick slices with unilaterally exposed preBötC, a <100 μm kernel generates a eupnea-like inspiratory pattern under predominant influence of caudally adjacent structures or thyrotropin-releasing hormone-like transmitters, but a mixed eupnea-sigh-like pattern when influence of rostral structures or substance-P-like transmitters dominates. (iii) Primarily presynaptic processes may underlie inhibition of rhythm by opioids or raising superfusate [Ca2+] from lower to upper physiological limits (1–1.5 mM). (iv) High K+ reverses depression of rhythm by raised Ca2+, opioids and anoxia. In summary, distinct activity patterns of spatiochemically organized isolated inspiratory networks depend on both an extracellular “Ca2+–K+ antagonism” and slice dimensions. This explains some discrepant findings between studies and suggests use of “calibrated” slices and more uniform experimental conditions.