Activation of the laryngeal mucosa results in
apnea that is mediated through, and can be elicited via electrical stimulation of, the superior laryngeal nerve (SLN). This potent inhibitory reflex has been suggested to play a role in the pathogenesis of
apnea of prematurity and
sudden infant death syndrome, and it is attenuated by
theophylline and blockade of
GABA(A) receptors. However, the interaction between
GABA and
adenosine in the production of SLN stimulation-induced
apnea has not been previously examined. We hypothesized that activation of
adenosine A(2A) receptors will enhance
apnea induced by SLN stimulation while subsequent blockade of
GABA(A) receptors will reverse the effect of A(2A) receptor activation. The phrenic nerve responses to increasing levels of SLN stimulation were measured before and after sequential intracisternal administration of the
adenosine A(2A) receptor agonist CGS (n = 10) and
GABA(A) receptor blocker
bicuculline (n = 7) in ventilated, vagotomized, decerebrate, and paralyzed newborn piglets. Increasing levels of SLN stimulation caused progressive inhibition of phrenic activity and lead to
apnea during higher levels of stimulation. CGS caused inhibition of baseline phrenic activity,
hypotension, and enhancement of
apnea induced by SLN stimulation. Subsequent
bicuculline administration reversed the effects of CGS and prevented the production of
apnea compared with control at higher SLN stimulation levels. We conclude that activation of
adenosine A(2A) receptors enhances SLN stimulation-induced
apnea probably via a GABAergic pathway. We speculate that SLN stimulation causes endogenous release of
adenosine that activates A(2A) receptors on GABAergic neurons, resulting in the release of
GABA at inspiratory neurons and subsequent respiratory inhibition.