Effects of aging on current vocalization threshold in mice measured by a novel nociception assay.
BACKGROUND
Age-related changes in nociception have been extensively studied in the past decades. However, it remains unclear whether in addition to the increased incidence of chronic illness, age-related changes in nociception contribute to increased prevalence of pain in the elderly. Although a great deal of evidence suggests that nociception thresholds increase with aging, other studies yield disparate results. The aim of this investigation was to longitudinally determine the effect of aging on nociception.


METHODS
The authors developed a nociception assay for mice using electrical stimuli at 2,000, 250, and 5 Hz that reportedly stimulate Abeta, Adelta, and C sensory nerve fibers, respectively. A system was designed to automate a method that elicits and detects pain-avoiding behavior in mice. Using a Latin square design, the authors measured current vocalization thresholds serially over the course of mice's life span.


RESULTS
For 2,000-Hz (Abeta), 250-Hz (Adelta), and 5-Hz (C) electrical stimuli, current vocalization thresholds first decreases and then increases with aging following a U-shaped pattern (P < 0.001). In addition, average current vocalization thresholds at youth and senescence are significantly higher than those at middle age for the 250-Hz (Adelta) and 5-Hz (C fiber) electrical stimulus (P < 0.05).


CONCLUSIONS
Using a novel and noninjurious nociception assay, the authors showed that over the life span of mice, current vocalization threshold to electrical stimuli changes in a U-shaped pattern. The findings support the notion that age-related changes in nociception are curvilinear, and to properly study and treat pain, the age of subjects should be considered.
Finkel
Julia C
JC
Department of Anesthesia and Surgical Services, National Institutes of Health Clinical Center, National Institutes of Health, Bethesda, MD 20892-1512, USA.
Besch
Virginia G
VG
Hergen
Adrienne
A
Kakareka
John
J
Pohida
Thomas
T
Melzer
Jonathan M
JM
Koziol
Deloris
D
Wesley
Robert
R
Quezado
Zenaide M N
ZM
D000375:Aging / Q000502:physiology*; D000818:Animals; D001835:Body Weight / Q000502:physiology; D003627:Data Interpretation, Statistical; D004558:Electric Stimulation; D005260:Female; D051379:Mice; D009413:Nerve Fibers, Myelinated / Q000502:physiology; D036421:Nerve Fibers, Unmyelinated / Q000502:physiology; D009475:Neurons, Afferent / Q000502:physiology; D010146:Pain / Q000523:psychology; D010147:Pain Measurement / Q000379:methods*; D017288:Pain Threshold / Q000502:physiology*; D011930:Reaction Time / Q000502:physiology; D014828:Vocalization, Animal / Q000502:physiology*