Evidence for a peripheral olfactory memory in imprinted salmon.

Abstract

The remarkable homing ability of salmon relies on olfactory cues, but its cellular basis is unknown. To test the role of peripheral olfactory receptors in odorant memory retention, we imprinted coho salmon (Oncorhynchus kisutch) to micromolar concentrations of phenyl ethyl alcohol during parr-smolt transformation. The following year, we measured phenyl ethyl alcohol responses in the peripheral receptor cells using patch clamp. Cells from imprinted fish showed increased sensitivity to phenyl ethyl alcohol compared either to cells from naive fish or to sensitivity to another behaviorally important odorant (L-serine). Field experiments verified an increased behavioral preference for phenyl ethyl alcohol by imprinted salmon as adults. Thus, some component of the imprinted olfactory homestream memory appears to be retained peripherally. Despite the extensive behavioral evidence linking olfactory imprinting to salmon homing, attempts to trace the neurobiological basis of homestream memory and recognition have proven inconclusive. Studies using electroolfactogram recordings have reported that imprinted fish show significantly greater responses to specific imprinted odorants than do nonimprinted fish (6, 7), but other researchers have claimed that these "imprinted" odorants consistently fail to elicit increased electrical activity at the level of the olfactory bulb in imprinted as compared to nonimprinted fish (8-10).In this study, we have combined patch clamp recording and behavioral imprinting assays to test directly the hypothesis that a change in the sensitivity of peripheral olfactory receptor cells contributes to establishing an olfactory memory in salmon. Our results demonstrate that plasticity in the peripheral olfactory system at the receptor cell level is linked to olfactory imprinting (11,12). METHODSAll investigations were performed on coho salmon spawned from the University of Washington's School of Fisheries stock. Details of imprinting paradigms, electrophysiological techniques, and behavioral methods are given below.Imprinting Procedures. Determination ofparr-smolt transformation. To achieve parr-smolt transformation by the first spring (0-age), fish were maintained at slightly elevated water temperatures (14-160C) and fed ad libitum. Fish were handculled to avoid exposing them to harsh drugs or other chemicals commonly used as disease preventatives in salmon culture. Parr-smolt transformation was determined by coloration changes, a behavioral tendency to orient downstream, and the ability of fish to maintain blood plasma Na+ levels to within 5% during a 48-hr exposure to salt water (freshwater exposure: 152.9 ± 1.2 meq of Na+ per liter of blood plasma, n = 10; saltwater exposure: 159.0 ± 1.7 meq ofNa+ per liter ofblood plasma, n = 8) (13-15). To determine plasma Na+ levels, salmon were transferred from their rearing hatchery (130C) to holding tanks containing either aerated fresh filtered hatchery or sea water (27 ppt; 120C). After 48 hr, blood was collected using heparinized capillary tubes and...

Cloning and characterization of an odorant receptor in five Pacific salmon

“…Fish olfaction is involved in wide ranges of behaviors including reproduction, homing, kin recognition, feeding and predator avoidance; all of which are paramount for their survival (Liley, 1982;Olsen and Liley, 1993;Nevitt et al, 1994;Hara and Zhang, 1996). In anadromous salmonids, olfaction is essential for successful completion of the homing migration (Hasler and Scholz, 1983).…”

Research on Captive Broodstock Programs for Pacific Salmon; Assessment of Captive Broodstock Technologies, Annual Report 2002-2003.

“…EOG responses reflect the summated responses of many receptor neurons in the olfactory epithelium (Ottoson 1971). Because the olfactory epithelium is apparently sensitized to specific odors during imprinting (Nevitt et al 1994, Dittman et al 1997, the EOG may provide a rapid, sensitive, and cost-effective method for assessing sensitization to imprinted odorants. In brief, the EOG technique involves placing a recording electrode near the medial surface of one lamellae within the olfactory rosette and monitoring electrical activity in response to perfusion of the rosette with odorants at different concentrations.…”

“…The alevins/emergent fry were continually exposed to a mixture of imprinting odorants (phenylethyl alcohol (PEA), L -arginine, L -threonine, and L -glutamate) at a final concentration of 100 nM each from February 1 to March 5, 2001. PEA has been used extensively as an odorant for studying imprinting (Hasler and Scholz 1983;Nevitt et al 1994;Dittman et al 1996Dittman et al , 1997. Amino acid odorants have also been used in imprinting studies (Morin et al 1989) and the three amino acids used in this study represent potent odorants that activate distinct receptor types in the olfactory epithelium (Hara 1992).…”

“…EOG responses reflect the summated responses of many receptor neurons in the olfactory epithelium (Ottoson 1971). Because the olfactory epithelium is apparently sensitized to specific odors during imprinting (Nevitt et al 1994, Dittman et al 1997, the EOG may provide a rapid, sensitive, and cost-effective method for assessing sensitization to imprinted odorants.…”

Behavioral Responses by Migratory Chum Salmon to Amino Acids in Natal Stream Water

“…Furthermore, the olfactory receptor cells of coho salmon that had been imprinted with PEA had a higher sensitivity to PEA than non-imprinted fish had (Nevitt et al, 1994), and only fish that were exposed to PEA or natural river odors during PST developed an imprinting memory . Using electrophysiological, behavioral, and gene-expression (a salmon olfactory-imprinting-related gene; Hino et al, 2007) experiments, we have previously demonstrated that 1-year-old lacustrine sockeye salmon were able to be imprinted using a single amino acid (Pro or Glu) for two weeks around PST, and that maturing and mature fish exposed to these test waters before and during PST in the previous two years had the ability to select the test waters .…”