Behavioural evidence for enhanced olfactory and trigeminal perception in congenital hearing loss.

Sensory deprivation, especially hearing loss (HL), offers a valuable model for studying neuroplasticity in the human brain and adaptive behaviours that support the daily lives of those with limited or absent sensory input. The study of olfactory function is particularly important as it is an understudied aspect of sensory deprivation. This study aimed to compare the effects of congenital HL on olfactory capacity by using psychophysical tasks. Methodological concerns from previous studies regarding the onset of HL and cognitive assessments were addressed. We recruited 11 individuals with severe-to-profound sensorineural HL (SNHL) since birth and 11 age- and sex-matched typical hearing non-signers. We used standardized neuropsychological tests to assess typical cognition among participants with SNHL. We evaluated olfactory functions by assessing olfactory detection threshold, odour discrimination and odour identification. Hearing-impaired participants outperformed their typical hearing counterparts in olfactory tasks. We further evaluated the accuracy and response time in identifying and localizing odours to disentangle olfactory sensitivity from trigeminal system sensitivity. Participants with SNHL demonstrated higher sensitivity to both the identification and localization tasks. These findings suggest that congenital SNHL is associated with enhanced higher-level olfactory processing and increased trigeminal sensitivity.

Lipophilic antioxidants and lipid peroxidation in yellow perch subjected to various anthropogenic influences along the St. Lawrence River (QC, Canada).

In Lake Saint-Pierre (LSP), the last great widening of the St. Lawrence River (province of Québec, Canada), the yellow perch has been experiencing a significant decline since the mid-1990s. The combined effect of several stressors (deterioration of habitats appropriate for reproduction and growth, invasive species and poor water quality) seems to exert considerable influence on the yellow perch population in LSP, characterized by low recruitment. To better understand possible stressor effects at the biochemical level, LSP yellow perch were compared with other sites along a gradient of increasing human influences from upstream to downstream along the St. Lawrence River. Morphometry (size, weight, circumference and Fulton's condition factor) and biomarkers associated to the peroxidation of lipids, lipophilic antioxidants (α-tocopherol and carotenoids), along with retinoids (vitamins A1and A2) and proteins were compared between sites at the larval, juvenile and adult stages. Fulton's condition factor was similar between sites for juveniles but was significantly lower in LSP adults, suggesting a weakened physiological condition. In most contaminated sites as LSP, lipid peroxidation tended to be higher in juveniles and adults whereas the lipophilic antioxidant lycopene and proteins content were lower. Retinyl esters were significantly lower for LSP fish compared to other sites, not only in larvae but also in the livers of juveniles and adults. These results are consistent with possible altered metabolism in the retinoid system of LSP yellow perch. The overall results reflect the "pressure" gradient tested, where the yellow perch from the most affected sites located downstream had impaired physiological and biochemical conditions compared to the upstream sectors.

Interactive effects of neonicotinoids and natural ultraviolet radiation on yellow perch (Perca flavescens) larvae.

Neonicotinoids (NEOCs) are insecticides that are widely used worldwide in the culture of maize and soya. Whereas they specifically target terrestrial insects by acting as agonists of the neurotransmitter acetylcholine in their nervous system, their effects on the cholinergic system of vertebrates is still unclear. Moreover, there is an increasing concern about their effects on aquatic biota because of their high leaching potential. In the agricultural watershed of Lake St. Pierre (LSP) (St. Lawrence River System, Québec, Canada), for example, NEOC concentrations considered toxic for aquatic biota (>8.3 ng L-1) have frequently been detected. These conditions may affect the yellow perch (Perca flavescens) population in LSP, which collapsed in the mid 1990s and is now experiencing poor recruitment. Moreover, because their larvae are found in shallow waters (<80 cm) near agricultural land, they are also exposed to ultraviolet radiation (UVR), with unknown potential interactions with NEOCs. The objective of this study was to test the synergistic effects of two commonly used NEOCs (imidacloprid and thiamethoxam) with natural UVR on yellow perch larvae using survival analysis and biomarkers to better quantify lethal and sublethal effects. Three common garden experiments were conducted with thiamethoxam and/or imidacloprid and natural UVR following a factorial design. Our results showed an interaction between UVR and thiamethoxam in terms of larval mortality. At the sublethal level, imidacloprid was associated with increased protein content and, in the presence of UVR, with increased acetylcholinesterase activity, thus indicating a cholinergic perturbation like that found in insects. Finally, we also found unexpected reduced lipid peroxidation associated with imidacloprid. A reduction in the overall lipid accumulation is suspected to be behind this puzzling result. These results will open new research avenues related to the effects of NEOCs on proteins and lipid accumulation.

Integrated spatial health assessment of yellow perch (Perca flavescens) populations from the St. Lawrence River (QC, Canada), part B: cellular and transcriptomic effects.

Multi-biological level assessments have become great tools to evaluate the health of aquatic ecosystems. Using this approach, a complementary study was designed to evaluate the health of yellow perch (Perca flavescens) populations in the St. Lawrence River (Quebec, Canada). In the present study, stress responses were compared at the transcriptomic, cellular, and tissue levels in yellow perch collected at six sites along the river: Lake St. François, Lake St. Louis (north and south), Beauregard Island and Lake St. Pierre (north and south). These results complement the physiological and chemical parameters as well as pathogen infection investigated in a companion paper published in the present issue. Thiobarbituric acid reactive substance (TBARS) analyses indicated the presence of oxidative stress in fish collected in the southern part of Lake St. Louis and at the downstream sites of Lake St. Pierre. High lipid peroxidation levels were found in the muscle of yellow perch caught at Beauregard Island, located downstream of the Montreal's wastewater treatment plant, suggesting an impact of the municipal effluent on redox homeostasis. Transcriptomic results indicated the down-regulation of genes related to lipid, glucose, and retinoid in southern Lake St. Pierre as well as a decrease in retinoid storage. Overall, biochemical and molecular markers indicated that the health status of yellow perch followed a decreasing gradient from upstream to downstream of the St. Lawrence River. This gradient is representative of the cumulative negative impacts of human activities on water and habitat quality along the river.