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Identification of carbonic anhydrase activity in bullfrog olfactory receptor neurons: histochemical localization and role in CO2 chemoreception.

Authors
Type
Published Article
Journal
Journal of comparative physiology. A, Sensory, neural, and behavioral physiology
Publication Date
Volume
182
Issue
2
Pages
163–174
Identifiers
PMID: 9463917
Source
Medline
License
Unknown

Abstract

The objectives of this study were to determine: (1) the frequency and distribution of carbonic anhydrase (CA) activity in the bullfrog nasal cavities, and (2) whether inhibition of nasal CA affects the olfactory receptor response to CO2 or other odorants. It was found, using Hansson's staining technique, that some olfactory receptor neurons exhibited CA activity and that these CA-positive receptors were distributed throughout the nasal cavity with peak densities in the dorsal and ventral sensory epithelial regions. To test for the role of CA in olfactory transduction, electro-olfacto-grams (EOGs) were recorded from the surface of the ventral sensory epithelium in response to 2-s pulses of 5% CO2 and amyl acetate before and after topical CA inhibition with acetazolamide (10(-3) mol.l-1). In 52 bullfrogs, 1222 sites on the ventral epithelium were tested resulting in 23 locations that exhibited a response to 5% CO2. Inhibition of CA caused an immediate 65% reduction in the EOG response to CO2 while the response to amyl acetate was not affected. These results, along with the histochemical localization of CA in some olfactory receptor neurons, indicate that CA plays a role in the detection of CO2 in frog olfactory neurons and that only a small population of olfactory receptor neurons are CO2 sensitive.

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