Abstract
Albeit lacking a sense of smell, anosmic patients maintain a reduced ability to distinguish different volatile chemicals by relying exclusively on their trigeminal system (TS). To elucidate differences in the neuronal representation of these volatile substances in the TS, we performed voltage-sensitive dye imaging (VSDI) in the rat trigeminal ganglion (TG) in vivo. We demonstrated that stimulus-specific patterns of bioelectrical activity occur within the TG upon nasal administration of ten different volatile chemicals. With regard to spatial differences between the evoked trigeminal response patterns, these substances could be sorted into three groups. Signal intensity and onset latencies were also dependent on the administered stimulus and its concentration. We conclude that particular compounds detected by the TS are represented by (1) a specific spatial response pattern, (2) the signal intensity, and (3) onset latencies within the pattern. Jointly, these trigeminal representations may contribute to the surprisingly high discriminative skills of anosmic patients.
Highlights
IntroductionThe trigeminal system (TS) provides facial mechanosensation (including discriminative touch), thermosensation, proprioception, chemoreception, and nociception (Lazarov, 2002; Viana, 2011)
The trigeminal system (TS) provides facial mechanosensation, thermosensation, proprioception, chemoreception, and nociception (Lazarov, 2002; Viana, 2011)
Chemical stimulation of trigeminal sensory afferents leads to different sensations that are triggered by activation of several polymodal receptors like transient receptors potential (TRP) channels that are activated by noxious stimuli e.g., harmful temperatures (Vay et al, 2012), various chemical ligands (Islam, 2011), and divalent cations (Ahern et al, 2005; Luebbert et al, 2010)
Summary
The trigeminal system (TS) provides facial mechanosensation (including discriminative touch), thermosensation, proprioception, chemoreception, and nociception (Lazarov, 2002; Viana, 2011). The TS fulfills important functions such as the detection and avoidance of potentially noxious stimuli within facial regions or sensing of the nasal air flow during breathing. Due to its chemosensory abilities, the TS contributes to overall gustatory and olfactory sensations and most odorants stimulate cells belonging to the trigeminal and the olfactory system (OS) (Tucker, 1971; Doty, 1975; Doty et al, 1978; Silver and Moulton, 1982). Chemical stimulation of trigeminal sensory afferents leads to different sensations (mostly stinging, burning, or cooling) that are triggered by activation of several polymodal receptors like transient receptors potential (TRP) channels that are activated by noxious stimuli e.g., harmful temperatures (Vay et al, 2012), various chemical ligands (Islam, 2011), and divalent cations (Ahern et al, 2005; Luebbert et al, 2010). Several studies addressed the question how volatile chemicals are represented in higher brain regions (for review see Boyle et al, 2007; Hummel et al, 2009; Albrecht et al, 2010; Lundström et al, 2011), nearly nothing is known about the impact of the trigeminal ganglia, housing the somata of trigeminal sensory neurons, on the overall representation of different volatiles
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