ResearchCite this article: Chung D, Dzal YA, Seow A, Milsom WK, Pamenter ME. 2016 Naked mole rats exhibit metabolic but not ventilatory plasticity following chronic sustained hypoxia. Naked mole rats are among the most hypoxia-tolerant mammals identified and live in chronic hypoxia throughout their lives. The physiological mechanisms underlying this tolerance, however, are poorly understood. Most vertebrates hyperventilate in acute hypoxia and exhibit an enhanced hyperventilation following acclimatization to chronic sustained hypoxia (CSH). Conversely, naked mole rats do not hyperventilate in acute hypoxia and their response to CSH has not been examined. In this study, we explored mechanisms of plasticity in the control of the hypoxic ventilatory response (HVR) and hypoxic metabolic response (HMR) of freely behaving naked mole rats following 8-10 days of chronic sustained normoxia (CSN) or CSH. Specifically, we investigated the role of the major inhibitory neurotransmitter g-amino butyric acid (GABA) in mediating these responses. Our study yielded three important findings. First, naked mole rats did not exhibit ventilatory plasticity following CSH, which is unique among adult animals studied to date. Second, GABA receptor (GABAR) antagonism altered breathing patterns in CSN and CSH animals and modulated the acute HVR in CSN animals. Third, naked mole rats exhibited GABAR-dependent metabolic plasticity following longterm hypoxia, such that the basal metabolic rate was approximately 25% higher in normoxic CSH animals than CSN animals, and GABAR antagonists modulated this increase.

Naked mole rats ( Heterocephalus glaber ) are among the most hypoxia-tolerant mammals, but their physiological responses to acute and chronic sustained hypoxia (CSH), and the molecular underpinnings of these responses, are poorly understood. In the present study we evaluated the acute hypoxic ventilatory response and the occurrence of ventilatory acclimatization to hypoxia following CSH exposure (8–10 days in 8% O 2 ) of naked mole rats. We also investigated the role of excitatory glutamatergic signaling in the control of ventilation and metabolism in these conditions. Animals acclimated to normoxia (control) or CSH and then exposed to acute hypoxia (7% O 2 for 1 h) exhibited elevated tidal volume (V T ), but decreased breathing frequency (f R ). As a result, total ventilation ( E ) remained unchanged. Conversely, V T was lower in CSH animals relative to controls, suggesting that there is ventilatory plasticity following acclimatization to chronic hypoxia. Both control and CSH-acclimated naked mole rats exhibited similar 60–65% decreases in O 2 consumption rate during acute hypoxia, and as a result their air convection requirement (ACR) increased ∼2.4 to 3-fold. Glutamatergic receptor inhibition decreased f R , E , and the rate of O 2 consumption in normoxia but did not alter these ventilatory or metabolic responses to acute hypoxia in either the control or CSH groups. Taken together, these findings indicate that ventilatory acclimatization to hypoxia is atypical in naked mole rats, and glutamatergic signaling is not involved in their hypoxic ventilatory or metabolic responses to acute or chronic hypoxia.

Chronic upper gastrointestinal (GI) symptoms of unclear etiology are frustrating to patients and physicians alike. The integrative medicine procedures of acupuncture and neural therapy may provide treatment options. Tongue piercing, which is prevalent in 5.6% of the adolescent population, may be a contributing factor in upper gastrointestinal symptoms. The objectives of the study were as follows: (1) To demonstrate the usefulness of an integrative medicine treatment approach in two cases of patients with chronic abdominal pain, nausea, and vomiting of unclear etiology who had failed standard medical management. (2) To identify scars from tongue piercings as a possible contributing factor in chronic upper GI symptoms of unclear etiology. Two retrospective case studies are presented of young adult females who were seen in a private multi-physician integrative medicine practice in the US. The patients were treated with neural therapy and acupuncture. The desired outcome was the cessation or reduction of the frequency of abdominal pain, nausea, and vomiting. Both patients had resolution of their symptoms. From this study, we have concluded the following: (1) Tongue scars from tongue rings may be causes of chronic upper gastrointestinal symptoms. (2) Neural therapy and acupuncture may be helpful in the treatment of chronic upper GI symptoms related to tongue scars.

N-methyl-D-aspartate (NMDA) receptors (NMDARs), a principal subtype of excitatory neurotransmitter receptor, are composed as tetrameric assemblies of two glycine-binding GluN1 subunits and two glutamate-binding GluN2 subunits. NMDARs can signal nonionotropically through binding of glycine alone to its cognate site on GluN1. A consequence of this signaling by glycine is that NMDARs are primed such that subsequent gating, produced by glycine and glutamate, drives receptor internalization. The GluN1 subunit contains eight alternatively spliced isoforms produced by including or excluding the N1 and the C1, C2, or C2’ polypeptide cassettes. Whether GluN1 alternative splicing affects nonionotropic signaling by NMDARs is a major outstanding question. Here, we discovered that glycine priming of recombinant NMDARs critically depends on GluN1 isoforms lacking the N1 cassette; glycine priming is blocked in splice variants containing N1. On the other hand, the C-terminal cassettes—C1, C2, or C2’—each permit glycine signaling. In wild-type mice, we found glycine-induced nonionotropic signaling at synaptic NMDARs in CA1 hippocampal pyramidal neurons. This nonionotropic signaling by glycine to synaptic NMDARs was prevented in mice we engineered, such that GluN1 obligatorily contained N1. We discovered in wild-type mice that, in contrast to pyramidal neurons, synaptic NMDARs in CA1 inhibitory interneurons were resistant to glycine priming. But we recapitulated glycine priming in inhibitory interneurons in mice engineered such that GluN1 obligatorily lacked the N1 cassette. Our findings reveal a previously unsuspected molecular function for alternative splicing of GluN1 in controlling nonionotropic signaling of NMDARs by activating the glycine site.