Conditioning Slowed Breathing for Relaxation in the Rat Open Access

Noble, Donald (2015)

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In humans, exercises involving slowed respiratory rate (SRR) have been found to counter autonomic sympathetic bias and engage the relaxation response. This state of deep rest reduces responses to stressors, including in individuals with various degrees of autonomic dysfunction. This thesis aimed to develop an animal model of the SRR-induced relaxation response. In the rat, we used operant conditioning procedures to train SRR and examined whether conditioned reductions in respiratory rate (RR) altered the physiological and behavioral responses to stressors in a manner consistent with the relaxation response. To condition SRR, we continuously monitored RR during 20 two-hour sessions using whole-body plethysmography, with feedback provided via a customized interface in LabVIEW. Conditioned rats, but not yoked controls, were able to turn off aversive visual stimulation (intermittent bright light) by slowing their breathing. Conditioned rats decreased their average resting RR by 10.6 breaths per minute, and maintained a reduced RR during intermittent retention sessions. Subsequent testing addressed the impact of conditioned slow breathing on stress reactivity and nociceptive responses. Compared to controls, conditioned rats showed i) decreased latency to enter the center of an open field, ii) decreased RR under acute restraint, and iii) decreased mechanical sensitivity to Von Frey hairs 75 minutes after formalin injection, possibly indicating alleviated hyperalgesia. In conclusion, rats could be trained to reduce their RR, rate reductions were maintained in the absence of training, and additional behavioral changes seen following conditioning were consistent with the development of an animal model of the relaxation response. In parallel, we developed a technological approach using electric field sensors for non-contact recordings of cardiorespiratory and behavioral variables. When strategically positioned, sensors accurately recorded rat RR and heart rate, overall motor activity, and various rhythmic motor behaviors including sniffing, rearing, grooming, and chewing. We forward the view that new generation sensor technologies can be linked to subsequent respiratory conditioning studies to provide continuous home cage assessment of cardiorespiratory and behavioral changes throughout an animal's lifespan. In sum, these studies establish the use of feedback-based conditioning of RR to investigate the physiological principles of stress reduction in a well-controlled animal model.

Table of Contents

CHAPTER 1: Decreased respiratory rate as a physiological trigger of relaxation. 1

Abstract. 2

Introduction. 3

Physiology of the Respiratory System. 6

Baroreceptor Resonance and Cardiorespiratory Synchronization at 0.1 Hz. 10

Respiration in Health and Disease: Human Research. 20

Respiration in Health and Disease: Animal Research. 24

Specific Aims of this Dissertation. 27

CHAPTER 2: Aversive bright light can be used to condition reduced respiratory rate. 31

Abstract. 32

Introduction. 33

Materials and Methods. 37

Results. 48

Discussion. 62

Acknowledgements. 71

CHAPTER 3: Operantly conditioned slow breathing in the rat modifies baseline respiration and induces behavioral changes consistent with the relaxation response. 72

Abstract. 73

Introduction. 74

Materials and Methods. 77

Results. 84

Discussion. 94

Acknowledgements. 104

CHAPTER 4: Plessey EPIC sensors permit remote monitoring of respiration, heart rate, and stereotyped behavior in the rodent. 105

Abstract. 106

Introduction. 107

Materials and Methods. 110

Results. 117

Discussion. 132

Acknowledgements. 136

CHAPTER 5: General Conclusions and Future Directions. 137

Summary. 138

The Neural Basis of Conditioned SRR: Review and Proposal. 139

Chapter 2 Future Directions. 145

Chapter 3 Future Directions. 148

Chapter 4 Future Directions. 152

Developing an Animal Model of Psychophysiological Coherence. 159

APPENDIX 1: Isolating a role for deep breathing in reducing activation of stress-related limbic circuits. 161

Abstract. 162

Introduction. 162

Materials and Methods. 164

Results. 169

Discussion. 170

Acknowledgements. 173


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