Stephen Johnson

Associate Professor, Comparative Biosciences

stephen.m.johnson@wisc.edu

School of Veterinary Medicine

Lab Webpage:
Johnson Lab

Research

Gestational intermittent hypoxia (GIH) alters breathing of neonatal offspring

Sleep disordered breathing (SDB) and obstructive sleep apnea (OSA) during pregnancy are growing health concerns because these conditions are associated with adverse outcomes for newborn infants. SDB/OSA during pregnancy exposes the mother and the fetus to intermittent hypoxia. Direct exposure of adults and neonates to intermittent hypoxia causes neuroinflammation and neuronal apoptosis, and exposure to intermittent hypoxia during gestation (GIH) causes long-term deficits in offspring respiratory function. However, the role of neuroinflammation in CNS respiratory control centers of GIH offspring has not been investigated. To address this question, pregnant rats are exposed to daily intermittent hypoxia during gestation (G10-G21). Neuroinflammation in brainstem and cervical spinal cord is evaluated in P0-P3 pups that are injected with saline or lipopolysaccharide (LPS; 0.1 mg/kg, 3 h). In CNS respiratory control centers, GIH attenuates the normal CNS immune response to LPS challenge in a gene-, sex-, and CNS region-specific manner. GIH also alters normal respiratory motor responses to LPS in newborn offspring brainstem-spinal cord preparations. These data underscore the need for further study of the long-term consequences of maternal SDB on the relationship between inflammation and the respiratory control system, in both neonatal and adult offspring.

• Johnson SM, Randhawa KS, Epstein JJ, Gustafson E, Hocker AD, Huxtable AG, Baker TL, Watters JJ. Gestational intermittent hypoxia increases susceptibility to neuroinflammation and alters respiratory motor control in neonatal rats. Respir Physiol Neurobiol Epub ahead of print, 2017.

Respiratory Rhythm Generation and Neuroplasticity – How does neuroinflammation alter breathing?

Breathing is a rhythmic motor behavior produced throughout our entire lifetime, but how neurons in the brainstem generate this behavior is not known. Also, breathing is highly modulated and can undergo long-lasting changes in rhythm frequency and motor output following activation of specific neurotransmitter receptors (respiratory neuroplasticity). We study isolated brainstems from neonatal rats and induce long-lasting increases in respiratory frequency (frequency plasticity) and long-lasting increases in spinal motor output (long-term facilitation). To test whether neuroinflammation alters respiratory neuroplasticity, neonatal rat pups are injected with lipopolysaccharide (LPS) to induce inflammation, and then isolated brainstems are tested to determine if respiratory neuroplasticity is altered.

Reptile Analgesia Without Respiratory Depression

In collaboration with Dr. Kurt Sladky (Surgical Sciences, UW School of Vet Med), our goal is to test and develop pharmacological approaches for providing pain relief in reptiles with minimal or no respiratory depression. To test for analgesic effects of drugs, noxious thermal stimuli are applied to the hindlimbs of awake turtles or to the ventral surface of snakes before and after drug administration. Breathing in awake turtles and snakes is measured to quantify any respiratory depression. Our major findings are that tramadol given orally produces long-lasting analgesia (up to 3 days after drug administration) with only modest respiratory depression in turtles. Surprising, snakes (corn snakes, ball pythons) are remarkably resistant to opioid drugs with respect to analgesia and possibly respiration. Snakes show no increase in noxious thermal withdrawal latencies with high dosages of morphine (40 mg/kg). When fentanyl patches were used to provide long-lasting therapeutic fentanyl levels, there was no increase in thermal withdrawal latencies, but modest respiratory depression was observed. Fortunately, dexmedetomidine (alpha2-adrenergic agonist) increases thermal withdrawal latencies without obvious anesthetic effects (several python behaviors were not altered by dexmedetomidine). However, dexmedetomidine also caused respiratory depression. Current studies are focused on testing whether co-administration of respiratory stimulant drugs with dexmedetomidine can induce analgesia without respiratory depression in snakes.