Effects of hypergravity on the morphological properties of the vestibular sensory epithelium. II. Life-long exposure of rats including embryogenesis.

Rats were exposed to a hypergravity (HG) level of 2.5 x g from conception until the age of 14 weeks. The vestibular epithelia of four of these animals and four control animals were immunohistochemically labeled for actin and tubulin. The apical cross-sectional area of epithelial cells of HG exposed rats appeared to be larger in all end organs. Area increase was 7.0% in the utricle (p<0.005) and 8.2% in the crista (p<<0.001). Hair cells and supporting cells appeared to be intact. The cellular arrangement and the proportion of different cell types within the epithelia was normal.

Effects of hypergravity on the morphological properties of the vestibular sensory epithelium. I. Long-term exposure of rats after full maturation of the labyrinths.

The effect of prolonged exposure to hypergravity on the morphology of vestibular epithelia of rats was investigated. At the age of 1 month, i.e., when vestibular end organs are fully maturated, three rats were transferred to a hypergravity environment of 2.5 g inside a large radius centrifuge. After 9 months, vestibular epithelia of these animals and of three control animals were immunohistochemically labeled for actin and tubulin. The apical cross-sectional area of epithelial cells of hypergravity exposed rats appeared to be smaller in all end organs. Area reduction was 1.9% in the saccule (not significant), 5.0% in the utricle (p < 0.005), and 11.6% in the crista (p<<0.001). No indications for a deterioration of vestibular functioning were observed.

Effects of selective antagonism or depletion of the cholinergic system on visual discrimination performance in rats.

A two-lever simultaneous visual discrimination task was used to study the effects on performance in Long-Evans rats of the muscarinic antagonists scopolamine (0.0125, 0.05, 0.2 and 0.8mg/kg s.c.), the M(1) antagonist pirenzepine, the M(2) antagonist AF-DX 116, the M(3) antagonist UH-AH 37 (each 3.2, 10, 32µg/rat, i.c.v.), and the cholinergic depleting agent, hemicholinium-3 (0.04, 0.2, 1.0 and 5.0µg/rat i.c.v.). Scopolamine dose-dependently decreased accuracy, increased the number of trials on which the rats failed to respond, and significantly lengthened latency to respond. Only the highest doses of hemicholinium-3, pirenzepine and AF-DX 116 reduced accuracy and increased errors of omission as well as response latency. UH-AH 37 reduced overall task performance at 10 and 32µg, suggesting that antagonism of both M(3) and other muscarinic receptors (including M(1)) had a greater effect on performance than selective antagonism of the M(1) or M(2) receptors. These data indicate that the disruptive effects of cholinergic antagonism on attentionally demanding tasks are strengthened by activity at multiple subtypes of the receptor.