Effects of Preconditioning on the Resistance to Acute Hypobaric Hypoxia and Their Correction with Selective Antagonists of Nicotinic Receptors

Abstract

Hypobaric hypoxic preconditioning increased the resistance of low resistant and highly resistant rats to acute hypobaric hypoxia at a critical height. Intergroup differences in the resistance of rats to acute hypobaric hypoxia were not observed after hypobaric hypoxia and one variational series with a wide range of resistance (4.5-24.5 min) appeared. Methyllycaconitine, an antagonist of subtype α(7) nicotinic cholinergic receptors, abolished the influence of hypobaric hypoxia on low resistant rats, but had no effect on highly resistant animals. Mecamylamine, a preferential antagonist of subtype α(4)β(2) and α(3)-containing cholinergic receptors, did not modulate the effect of hypobaric hypoxia. By contrast, hypobaric hypoxia abolished the effect of mecamylamine on the resistance of rats that were not trained under conditions of hypobaric hypoxia (low resistant and highly resistant animals with low sensitivity to hypobaric hypoxia). We conclude that the same effect of hypobaric hypoxia is mediated by various mechanisms, which involve different nicotinic cholinergic receptors. They differ from the resistance mechanisms in non-trained rats.

Hypoxic Preconditioning Eliminates Differences in the Innate Resistance of Rats to Severe Hypoxia

“…Accordingly, HBH has a marked preconditioning effect on rats, increasing or restoring (in the case of the high-resistant rats) resistance to SHBH. This is consistent with the data for the low-resistant rats [22] [23] and confirms our previous data for the lowand high-resistant rats [29].…”

“…These results also confirm our previous data for high-and low-resistant rats [29]. The same HBH effect for the intact-and intermediate-resistant rat groups was revealed for the first time, and was unexpected for us with regard to the intact rats.…”

“…value [29]. At the same time, a significant decrease of T2 values in rats with T1 > 900 - in Nembutal-anesthetized rats with T1 > 900 s [28].…”

“…Systemic hypoxic preconditioning is achieved by short-term adaptation to a single one-three-hour moderate hypoxic continuous or intermittent exposure, in which hypoxia alternates with normoxia or hyperoxia [11] Using this pre-test, we found that a single session of moderate hypobaric hypoxia (HBH, 11% O 2 , 60 min) eliminated differences in the resistance to severe hypobaric hypoxia (SHBH, 4.5% O 2 ) between the high-and low-resistant rats [29]. However, it was unclear whether this is a consequence of SHBH pre-testing or HBH action only.…”

The Acoustic Sensorimotor Gating Predicts the Efficiency of Hypoxic Preconditioning. Participation of the Cholinergic System in This Phenomenon

“…Moderate one-off hypobaric hypoxia (HBH; 11% O 2 for 60 min) provokes preconditioning and increases the resistance to severe hypobaric hypoxia (SHBH; 4.5% O 2 ). In other words, it prolongs the time (T) before the onset of apnoea in SHBH conditions [5][6][7]. Recent rodent studies have shown high rat-to-rat variability in the SHBH resistance initiated by HBH and that the efficiency of HBH does not depend on the innate resistance to the direct action of SHBH (i.e.…”