Lack of thyroid hormones but not their excess affects the maturation of olfactory receptor neurons: a quantitative morphologic study in the postnatal rat.
To study quantitatively actions of thyroid hormones on maturation of olfactory receptor neurons (ORN), surface density and total number of receptor knobs (1 knob/ORN) were measured in 1 mu sections from septal olfactory epithelium of newborn, 12- and 25 day normal, hypo- and hyperthyroid rats. Hypothyroidism was induced by adding to drinking water n-propylthiouracil (0.1% w/v) from birth. Hyperthyroidism was induced by daily injection of pups with T4 (1-thyroxine, 0.3 microgram/g b.w., s.c.). Experimental pups showed all the signs of hypo- and hyperthyroidism. Between days 1-25, normal pups showed marked increase in surface area of septal olfactory epithelium (6x), total number (12x) and surface density (#/mm2, 2x) of mature ORNs. Thyroid deficient rats showed, by day 12, marked reductions in epithelial surface area and total number of mature ORNs; these and the surface density deficits became very pronounced by 25 day (30% area, 27% density, 47% # mature ORNs). Hyperthyroid rats, however, did not show an increase in any of these parameters over controls. Although total number of ORNs (mature and immature), as measured by number of nuclei, was also reduced in hypothyroid pups, surface density was not altered, indicating that maturation of ORNs, but not their local accretion is altered in thyroid deficiency. The results indicate that thyroid hormones are essential for normal proliferative expansion of olfactory epithelium and for maturation of ORNs postnatally. These actions of thyroid hormones are not increased or accelerated by excess T4 suggesting saturation of the hormone receptor system at the normal plasma level.
Paternostro
M A
MA
Department of Physiology and Biophysics, University of Illinois, Urbana 61801.
Meisami
E
E
D000818:Animals; D000831:Animals, Newborn / Q000502:physiology; D002455:Cell Division / Q000187:drug effects / Q000502:physiology; D002467:Cell Nucleus / Q000648:ultrastructure; D003712:Dendrites / Q000648:ultrastructure; D005260:Female; D006980:Hyperthyroidism / Q000503:physiopathology; D007037:Hypothyroidism / Q000139:chemically induced / Q000503:physiopathology; D009297:Nasal Mucosa / Q000187:drug effects / Q000294:innervation / Q000648:ultrastructure; D009475:Neurons, Afferent / Q000502:physiology* / Q000648:ultrastructure; D011247:Pregnancy; D011441:Propylthiouracil; D051381:Rats; D011919:Rats, Inbred Strains; D012903:Smell / Q000502:physiology*; D013963:Thyroid Hormones / Q000172:deficiency / Q000502:physiology*; D013974:Thyroxine / Q000494:pharmacology
D013963:Thyroid Hormones; D011441:Propylthiouracil; D013974:Thyroxine