The prevalence and cost of chronic pain is a major physical and mental health care problem in the United States today. As a result, there has been a recent explosion of research on chronic pain, with significant advances in better understanding its etiology, assessment, and treatment. The purpose of the present article is to provide a review of the most noteworthy developments in the field. The biopsychosocial model is now widely accepted as the most heuristic approach to chronic pain. With this model in mind, a review of the basic neuroscience processes of pain (the bio part of biopsychosocial), as well as the psychosocial factors, is presented. This spans research on how psychological and social factors can interact with brain processes to influence health and illness as well as on the development of new technologies, such as brain imaging, that provide new insights into brain-pain mechanisms.

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The Biopsychosocial Approach to Chronic Pain: Scientific Advances and Future Directions

Longitudinal study of 2 cohorts of children selected in the second or third year of life to be extremely cautious and shy (inhibited) or fearless and outgoing (uninhibited) to unfamiliar events revealed preservation of these 2 behavioral qualities through the sixth year of life. Additionally, more of the inhibited children showed signs of activation in 1 or more of the physiological circuits that usually respond to novelty and challenge, namely, the hypothalamic-pituitary-adrenal axis, the reticular activating system, and the sympathetic arm of the autonomic nervous system. It is suggested that the threshold of responsivity in limbic and hypothalamic structures to unfamiliarity and challenge is tonically lower for inhibited than for uninhibited children.

The Physiology and Psychology of Behavioral Inhibition in Children.

Background. Hypertension is a frequent complication of chronic renal failure, but its causes are not fully understood. There is indirect evidence that increased activity of the sympathetic nervous system might contribute to hypertension in patients with end-stage renal disease, but sympathetic-nerve discharge has not been measured directly in patients or animals with chronic renal failure. Methods. We recorded the rate of postganglionic sympathetic-nerve discharge to the blood vessels in skeletal muscle by means of microelectrodes inserted into the peroneal nerve in 18 patients with native kidneys who were undergoing long-term treatment with hemodialysis (of whom 14 had hypertension), 5 patients receiving hemodialysis who had undergone bilateral nephrectomy (of whom 1 had hypertension), and 11 normal subjects. Results. The mean (±SE) rate of sympathetic-nerve discharge was 2.5 times higher in the patients receiving hemodialysis who had not undergone nephrectomy than in the normal subjects (58±3 v...

https://www.nejm.org/doi/pdf/10.1056/NEJM199212313272704

Sympathetic overactivity in patients with chronic renal failure.

Hyperinsulinemia may contribute to hypertension by increasing sympathetic activity and vascular resistance We sought to determine if insulin increases central sympathetic neural outflow and vascular resistance in humans We recorded muscle sympathetic nerve activity (MSNA; microneurography, peroneal nerve), forearm blood flow (plethysmography), heart rate, and blood pressure in 14 normotensive males during 1-h infusions of low (38 mU/m2/min) and high (76 mU/m2/min) doses of insulin while holding blood glucose constant Plasma insulin rose from 8 +/- 1 microU/ml during control, to 72 +/- 8 and 144 +/- 13 microU/ml during the low and high insulin doses, respectively, and fell to 15 +/- 6 microU/ml 1 h after insulin infusion was stopped MSNA, which averaged 215 +/- 15 bursts/min in control, increased significantly (P less than 0001) during both the low and high doses of insulin (+/- 54 and +/- 93 bursts/min, respectively) and further increased during 1-h recovery (+152 bursts/min) Plasma norepinephrine levels (119 +/- 19 pg/ml during control) rose during both low (258 +/- 25; P less than 002) and high (285 +/- 95; P less than 001) doses of insulin and recovery (316 +/- 23; P less than 001) Plasma epinephrine levels did not change during insulin infusion Despite the increased MSNA and plasma norepinephrine, there were significant (P less than 0001) increases in forearm blood flow and decreases in forearm vascular resistance during both doses of insulin Systolic pressure did not change significantly during infusion of insulin and diastolic pressure fell approximately 4-5 mmHg (P less than 001) This study suggests that acute increases in plasma insulin within the physiological range elevate sympathetic neural outflow but produce forearm vasodilation and do not elevate arterial pressure in normal humans

/pdf/hyperinsulinemia-produces-both-sympathetic-neural-activation-1dip9pukph.pdf

Hyperinsulinemia produces both sympathetic neural activation and vasodilation in normal humans

Peripheral and central mechanisms of cutaneous hyperalgesia.

Somatosensory, proprioceptive, and sympathetic activity in human peripheral nerves

Synchronized bursts of efferent sympathetic impulses, appearing either spontaneously or triggered by various peripheral stimuli, were recorded with microelectrodes inserted percutaneously into skin nerve fascicles in alert, adult subjects. The signals were abolished by sympathetic ganglion blocking agents and by Lidocaine nerve blocks proximal to the recording site. Many of the sympathetic discharges were succeeded by skin resistance changes and plethysmographic vasoconstrictor responses within the innervation zone of the fascicle impaled. The sympathetic activity was not pulse synchronous as in muscle nerves and the spontaneous sympathetic volleys occurred largely independently of spontaneous blood pressure variations, indicating a relative lack of baroreflex control of the vasoconstrictor outflow to the skin. A loose coupling was observed, however, between the resting respiratory rhythm and the spontaneous sympathetic bursts in the skin nerves.

H. E. Torebjork

Papers

Somatosensory, proprioceptive, and sympathetic activity in human peripheral nerves

General Characteristics of Sympathetic Activity in Human Skin Nerves