Paper Information

Title: 

CONGENITAL HYPOTHYROIDISM ALTERS FORMALIN-INDUCED PAIN RESPONSE IN WEANLING RATS

Type: PAPER
Author(s): BEHZADI ZH.,ROUHANI M.H.*
 
 *NEUROSCIENCE RES. CTR., PHYSIOLOGY DEPT, FAC. MED., SHAHEED BEHESHTI MED. SCI. UNIV., TEHRAN, IRAN
 
Name of Seminar: IRANIAN CONGRESS OF PHYSIOLOGY AND PHARMACOLOGY
Type of Seminar:  CONGRESS
Sponsor:  PHYSIOLOGY AND PHARMACOLOGY SOCIETY, MASHHAD UNIVERSITY OF MEDICAL SCIENCE
Date:  2007Volume 18
 
 
Abstract: 

Introduction: It is known that postnatal maturation of the CNS is critically dependent on the thyroid hormone levels. The present study attempted to investigate the development of nociceptive circuits following induction of the formalin pain in congenitally hypothyroid pups at the time of weaning.
Methods: Timed pregnant rats received PTU from 16th day of gestation until 23rd postnatal day in their drinking water. Control pups received tap water. Control and hypothyroid offspring pups were received different formalin solution (2.5%, 5% and 10%) in right hind paw at 23 day of age.
Results: Significant reduction in weight gain was evident in PTU-treated offspring from postnatal days 15 up to 23 (P<0.001). In control pups, formalin injection in all concentrations produced the typical biphasic nociceptive responses. Hypothyroid pups showed slightly biphasic pattern of pain behavior compared to controls. However they kept a persistency of higher pain behavior intensity until the end of the session with different formalin concentrations. During the first part of the second phase (15-40 min post injection) in control pups the mean number of licking was significantly higher than in hypothyroid pups. In the last part of the test (40-60 min) the mean number of lifting and shaking in hypothyroid rats was significantly higher than in control rats. The pain intensity increased significantly in relation to formalin concentrations in control pups for all phases. However the increase in formalin concentrations did not change the pain intensity scores in hypothyroid pups at any phases.
Conclusion: Our findings suggest that thyroid hormone deficiency impairs the developmental profile of nociceptive circuitry at the level of central inhibitory mechanisms.

 
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