Diffuse Pleural Mesothelioma and Asbestos Exposure in the North Western Cape Province

TLDR

Adaptation has been studied in isolated olfactory receptor neurons, but its occurrence in the CNS during odorant stimulation remains poorly understood. The study aims to determine whether peripheral fast adaptation serves as a coding mechanism for high odor concentrations. Using two‑photon laser‑scanning microscopy and targeted extracellular recordings in freely breathing anesthetized rats, the authors examined peripheral adaptation at the first olfactory synapse in bulb glomeruli. Sustained high‑concentration odor stimulation produced rapidly adapting glomerular postsynaptic responses linked to decreased glutamate release from olfactory receptor neurons, a concentration‑dependent effect that persists despite blocking ionotropic glutamate or metabotropic GABA_B receptors, indicating peripheral fast adaptation encodes high odor concentration.

Abstract

Adaptation is a general property of sensory receptor neurons and has been extensively studied in isolated cell preparation of olfactory receptor neurons. In contrast, little is known about the conditions under which peripheral adaptation occurs in the CNS during odorant stimulation. Here, we used two-photon laser-scanning microscopy and targeted extracellular recording in freely breathing anesthetized rats to investigate the correlate of peripheral adaptation at the first synapse of the olfactory pathway in olfactory bulb glomeruli. We find that during sustained stimulation at high concentration, odorants can evoke local field potential (LFP) postsynaptic responses that rapidly adapt with time, some within two inhalations. Simultaneous measurements of LFP and calcium influx at olfactory receptor neuron terminals reveal that postsynaptic adaptation is associated with a decrease in odorant-evoked calcium response, suggesting that it results from a decrease in glutamate release. This glomerular adaptation was concentration-dependent and did not change the glomerular input–output curve. In addition, <i>in situ</i> application of antagonists of either ionotropic glutamate receptors or metabotropic GABA_B receptors did not affect this adaptation, thus discarding the involvement of local presynaptic inhibition. Glomerular adaptation, therefore, reflects the response decline of olfactory receptor neurons to sustained odorant. We postulate that peripheral fast adaptation is a means by which glomerular output codes for high concentration of odor.