PARENT SESSION
PM25 - Agrochemicals
Monday, 18 November 2002
8:00 AM to 6:30 PM
Exhibit Hall

(P444) Distribution of choline acetyltransferase (ChAT) in the salmon olfactory system: Implications for mechanisms of pesticide-induced impairment.

Jarrard, Hugh^*,1, Lee, Rick¹, Kennedy, Chris¹, ¹ Dept. Biol. Sci., Simon Fraser University, Burnaby, BC, Canada

ABSTRACT- Previously we have shown that sublethal exposure of coho salmon to carbamate pesticides impairs olfactory capabilities, as measured by electroolfactograms (EOGs; Jarrard et al., SETAC 2001). This impairment appears mediated by acetylcholinesterase (ACh), as dose-dependant carbamate reduction of EOG amplitude can be mimicked with known ACh inhibitors such as physostigmine. Little, however, is known about the distribution or function of cholinergic neurons in the salmonid primary olfactory system. Here we describe the olfactory distribution of ACh through immunohistochemistry with goat polyclonal antibody against human placental ChAT, the enzyme catalyzing ACh production and a marker for cholinergic neurons in rainbow trout brain (Perez et al [2000] J. Comp. Neurol 428:450-474). Cyrostat cut sections (14m) of olfactory tissues from 4% paraformaldehyde-fixed juvenile coho (n=5) were incubated in -ChAT for 40 hrs. at 4°C, then biotin-anti-goat secondary, avidin-biotin-peroxidase, and diaminobenzidine. In results, discrete regions of the salmon olfactory rosette exhibit strong -ChAT-like immunoreactivity (-ChAT-ir): nonsensory distal-most tips and secondary folds of olfactory lamellae contained numerous strongly-labeled goblet cells, nonsensory ciliated cells, and putative neuronal fibers. Histochemistry on alternate sections with periodic acid-schiff staining for mucopolysaccharides confirmed the identity of -ChAT-ir goblet cells as mucus-secreting. Surprisingly, the olfactory bulb appeared absent of -ChAT-ir. We are currently carrying out Western blots on olfactory homogenates to confirm that -ChAT-ir is confined to proteins of an appropriate molecular weight for ChAT. These results provide supporting evidence that pesticide-induced olfactory impairment is due in part to ACh-mediated hypersecretion of mucus in the salmon periphery.

Key words: salmon, olfaction, pesticides, immunohistochemistry