Rhodes HJ and Amo M (2022), Electrophysiological responses to conspecific o...

XB-ART-59321

PLoS One 2022 Sep 07;179:e0273035. doi: 10.1371/journal.pone.0273035.

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Electrophysiological responses to conspecific odorants in Xenopus laevis show potential for chemical signaling.

Rhodes HJ, Amo M.

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The fully aquatic African clawed frog, Xenopus laevis, has an unusual and highly adapted nose that allows it to separately sample both airborne and waterborne stimuli. The function of the adult water nose has received little study, despite the fact that it is quite likely to receive information about conspecifics through secretions released into the water and could aid the frog in making decisions about social and reproductive behaviors. To assess the potential for chemical communication in this species, we developed an in situ electroolfactogram preparation and tested the olfactory responses of adult males to cloacal fluids and skin secretions from male and female conspecifics. We found robust olfactory responses to all conspecific stimuli, with greatest sensitivity to female cloacal fluids. These results open the door to further testing to identify compounds within cloacal fluids and skin secretions that are driving these responses and examine behavioral responses to those compounds. Understanding the role of chemical communication in social and reproductive behaviors may add to our rich understanding of vocal communication to create a more complete picture of social behavior in this species.

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Species referenced: Xenopus laevis

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	Fig 1. Location of the water nose and electrode placement. The medial cavity (MC, light blue) or water nose is a blind-ended compartment, opening only at the naris (N). The principal cavity (PC, dark blue) or air nose is a separate compartment that connects the naris to the oral cavity via the choana (C). The vomeronasal organ (VNO, purple) sits in the inferior aspect of the PC. Large black dots represent the animal’s eyes. (A) Schematic of olfactory anatomy, lateral view, as described by Reiss & Eisthen, 2014 [5]. (B) Schematic of experimental preparation, dorsal view. The EOG recording electrode is shown in red; it was placed along the medial wall of the MC. The profusion system that was used to deliver stimuli is represented in yellow.
	Fig 2. Sample experiment timeline. This timeline represents a short segment of an experiment, illustrating the order and timing of events. Stimuli were injected into a port in the perfusion line (colored dots), traveled down the perfusion line for several seconds, then washed across the olfactory epithelium (“stimulus exposure” period, marked on timeline). EOG responses were observed during this exposure time if evoked by the stimulus. Positive controls (shown in red; amino acids such as methionine and alanine) were used to elicit a strong EOG response at the start and end (not shown) of each recording block. After positive controls or test stimuli, a saline wash was administered to ensure the port and line were clean (white oval). Saline was also used as a negative control (blue). Test stimuli (green) at various dilutions were alternated with negative controls for the bulk of each recording block.
	Fig 3. Sample EOG recordings. EOG traces are shown in response to (A) amino acids, (B) female cloacal fluids, and (C) male cloacal fluids. The stimulus was injected into the perfusion line at the beginning of each trace (indicated with the black caret), creating a small stimulus artifact, with EOG response occurring 6–8 seconds later (large downward deflections). Stimuli and relative concentration are indicated to the right of each trace (A is 1 mM alanine; M is 1 mM methionine; C is cloacal fluid). Control in (A) was saline; controls in (B) and (C) were cloacal-specific controls (saline passed through the cloacal fluid collection process). Scale bar is 1 mV (vertical) and 3 s (horizontal). Data were from Frog 8; summary data can be found on subsequent figures.
	Fig 4. EOG responses to different concentrations of methionine. EOG amplitude, represented as z-score relative to control (saline) stimuli, are shown for 6 individuals across 6 concentrations, ranging from 1 mM to 0.01 μM L-methionine. EOG response declined at lower concentrations, with the detectability threshold (z ≥ 2) falling between 10 and 1 μM for most animals. Individual animals are shown with distinct symbols; light gray horizontal band from z = -2 to z = 2 indicates responses that may not be distinguishable from saline control.
	Fig 5. EOG responses to different concentrations of cloacal fluids from female and male conspecifics, represented as z-score relative to cloacal control stimuli. (A) EOG amplitudes in response to female cloacal fluids were robust at 10−2 concentration, and declined at lower concentrations, with the detectability threshold (z ≥ 2) falling between 10−3 and 10−5 for most animals. (B) EOG amplitudes to male cloacal fluids were far smaller, with a detection threshold between 10−2 and 10−3 for most animals.
	Fig 6. EOG responses to skin secretions from female and male conspecifics, represented as z-score relative to skin control stimuli. (A) EOG amplitudes in response to female skin secretions were well above the detection threshold at concentrations of 10−1 and 10−2, and may still have been detectable for some animals at 10−3 and 10−5. (B) EOG responses to male skin secretions were similar to those seen in A for the most concentrated stimuli, with a detection threshold between 10−2 and 10−3 for most animals.

References [+] :

Breunig, The endocannabinoid 2-arachidonoyl-glycerol controls odor sensitivity in larvae of Xenopus laevis. 2010, Pubmed, Xenbase