Department of Pharmacological and Physiological Science, Saint Louis University School of Medicine, St. Louis, Missouri 63104-1028, USA.
J Appl Physiol (1985). 2010 Apr;108(4):811-20. doi: 10.1152/japplphysiol.00600.2009. Epub 2010 Jan 21.
Underwater submersion in mammals induces apnea, parasympathetically mediated bradycardia, and sympathetically mediated peripheral vasoconstriction. These effects are collectively termed the diving response, potentially the most powerful autonomic reflex known. Although these physiological responses are directed by neurons in the brain, study of neural control of the diving response has been hampered since 1) it is difficult to study the brains of animals while they are underwater, 2) feral marine mammals are usually large and have brains of variable size, and 3) there are but few references on the brains of naturally diving species. Similar responses are elicited in anesthetized rodents after stimulation of their nasal mucosa, but this nasopharyngeal reflex has not been compared directly with natural diving behavior in the rat. In the present study, we compared hemodynamic responses elicited in awake rats during volitional underwater submersion with those of rats swimming on the water's surface, rats involuntarily submerged, and rats either anesthetized or decerebrate and stimulated nasally with ammonia vapors. We show that the hemodynamic changes to voluntary diving in the rat are similar to those of naturally diving marine mammals. We also show that the responses of voluntary diving rats are 1) significantly different from those seen during swimming, 2) generally similar to those elicited in trained rats involuntarily "dunked" underwater, and 3) generally different from those seen from dunking naive rats underwater. Nasal stimulation of anesthetized rats differed most from the hemodynamic variables of rats trained to dive voluntarily. We propose that the rat trained to dive underwater is an excellent laboratory model to study neural control of the mammalian diving response, and also suggest that some investigations may be done with nasal stimulation of decerebrate preparations to decipher such control.
哺乳动物在水下浸没会引起呼吸暂停、迷走神经介导的心动过缓和交感神经介导的外周血管收缩。这些效应统称为潜水反应，可能是已知最强大的自主反射。虽然这些生理反应是由大脑中的神经元介导的，但由于以下原因，对潜水反应的神经控制的研究受到了阻碍：1）很难在动物水下时研究它们的大脑；2）野生动物通常体型较大，大脑大小不一；3）关于自然潜水物种的大脑仅有很少的参考资料。在麻醉的啮齿动物中刺激其鼻腔黏膜后，也会引发类似的反应，但这种鼻咽反射尚未与大鼠的自然潜水行为进行直接比较。在本研究中，我们比较了清醒大鼠在自愿水下浸没期间引发的血液动力学反应与在水面游泳的大鼠、被迫潜水的大鼠、麻醉或去大脑大鼠的反应，并通过氨气蒸气刺激鼻腔。我们发现，大鼠自愿潜水引起的血液动力学变化与自然潜水的海洋哺乳动物相似。我们还表明，自愿潜水大鼠的反应 1）与游泳时的反应明显不同；2）通常与受过训练的大鼠在水下“被迫”潜水时引起的反应相似；3）与在水下潜水的新生大鼠的反应通常不同。麻醉大鼠的鼻腔刺激与自愿潜水大鼠的血液动力学变量差异最大。我们提出，经过训练自愿潜水的大鼠是研究哺乳动物潜水反应的神经控制的优秀实验室模型，我们还建议，一些研究可以通过对去大脑准备进行鼻腔刺激来阐明这种控制。
