Microinjection of Gabazine and Kynurenic Acid into the PreBotzinger Complex Alter Cough Phase Durations in the Cat

Abstract

The preBotzinger complex (preBotC) is important in breathing rhythmogenesis, but its role in cough patterning is unknown. We previously microinjected an excitatory neurotransmitter, 5 mM DL‐Homocysteic acid (DLH), into the preBotC, which altered breathing phase timing, but not cough phase timing. To further understand the role of the preBotC in cough rhythmogenesis, we hypothesized that inhibiting the preBotC would also have no effect on cough phase timing but would inhibit coughing. To test this hypothesis, we bilaterally microinjected 50 mM kynurenic acid (KYN, n=6), a broad spectrum excitatory amino acid blocker, and separately 0.1 mM gabazine (GBZ, n=5), a GABA‐A receptor antagonist, into the preBotC in anesthetized, spontaneously breathing adult cats. We recorded electromyograms (EMG) from parasternal (PS), diaphragm (DIA) and internal oblique (ABD) muscles. Cough was elicited by mechanical stimulation of the tracheobronchial tree. KYN microinjection significantly increased breathing frequency (21±2 to 43±10 breaths/min, p<0.05) by changing both inspiratory (TI) and expiratory (TE) durations (TI 1.0±0.1 to 0.6±0.1, p<0.05; TE 1.8±0.3 to 0.9±0.2 s, p<0.05). DIA EMG magnitude and cough number did not change (4.5±0.6 to 3.9±1.4). However, inspiratory duration decreased (TI 1.1±0.1 to 0.7±0.06 s, p<0.05), and while active expiratory duration (TE1) did not change significantly (TE1 1.0±0.11 to 0.8±0.04 s, n.s.), passive expiratory duration (TE2) was altered but not until 2 hours after injection (TE2 baseline: 0.9±0.2; 20 min after injection: 0.6±0.3 s; 2 hrs after injection: 0.50±0.2 s, p<0.05). Both DIA (55±5 % of baseline) and ABD EMG (56±11 % of baseline) amplitudes decreased during cough. GBZ microinjection had the opposite effect on breathing compared to KYN, where breathing frequency decreased (21.0±4.0 to 12.0±1.0 breaths/minute, p<0.05) by altering both TI and TE (TI 1.1±0.1 to 2.1 ±0.3 s, p<0.05; TE 1.9±0.4 to 2.7±0.4 s, p<0.05). With respect to cough, GBZ decreased cough number (5.1±0.6 to 1.5±0.4, p<0.05) and ABD EMG magnitude (38±4 % of baseline, p<0.05), although PS EMG magnitude did not change significantly (147±34 % of baseline). Microinjection of GBZ increased the duration of all phases of cough (TI 1.1±0.1 to 2.1±0.4 s, p<0.05, TE1 0.9±0.05 to 1.8±0.2 s, p<0.05, TE2 1.1±0.70 to 2.4±0.9 s, p=0.06). These data indicate that the preBotC participates in the regulation of cough phase timing and magnitudes in the anesthetized cat. Disruption of excitatory amino acid neurotransmission with KYN primarily affected inspiratory duration whereas GBZ‐induced blockade of GABA‐A receptor transmission had a generalized effect on cough. These data support an important but more complex role for the preBotC in the regulation of the cough motor pattern than that for breathing.Support or Funding InformationSupported by OT2OD023854‐01, HL131716.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.