Compensatory Rapid Switching of Binasal Inputs in the Olfactory Cortex

Abstract

Odors are inhaled through the nostrils into two segregated nasal passages and detected by sensory neurons in the bilateral olfactory epithelia. Airflow through the two nasal passages is usually asymmetrical because of alternating changes in nasal mucosal congestion. Here we show that neurons in the anterior olfactory nucleus (AON) of the adult rat olfactory cortex are ordinarily dominated by ipsi-nasal inputs and that binasal neurons in the AON respond to ipsilateral and contralateral nasal inputs with nearly equivalent odorant category selectivity. Deprivation of ipsilateral nasal inputs by unilateral nostril obstruction greatly enhanced the response to contralateral odor stimulation, in a reversible manner, in ϳ33% of AON neurons within only several minutes. In 27% of AON neurons that showed spike responses induced by the inspiration of room air, ipsilateral nasal obstruction initially suppressed respiration phase-locked spike discharges and, several minutes later, induced respiration phase-locked discharges with longer delays between inspiration and response. Recordings from AON neurons in rats with anterior commissure (AC) transection indicated that the resumed respiration phase-locked discharges with longer delays were mediated by the contralateral pathway via the AC. The ipsi-nasal occlusion-induced switching of nasal inputs to individual AON neurons shows that a subset of AON neurons in the adult rat has neuronal mechanisms for rapid nostril dominance plasticity, which may enable both right and left olfactory cortices to preserve their responsiveness to the external odor world, despite reciprocal changes in nasal airflow.

Neurons in the anterior olfactory nucleus pars externa detect right or left localization of odor sources

“…A thermoplastic external nasal septum that fitted the external shape of the rat nose was used to prevent odors delivered in front of one nostril from spreading to the contralateral nostril (Fig. 1A), which enabled the selective stimulation of either the ipsilateral or contralateral olfactory epithelium (6). We examined spike responses of individual neurons in the rostral part of the AON (Fig.…”

“…1B) to ipsinostril-only and contranostril-only stimulation with the panel of odorants (52 cells in 36 rats). AON neurons that showed excitatory spike responses to ipsinostril stimulation with an odorant category showed three types of responses to contranostril stimulation with the same odorant category: excitatory responses (ipsi-excitatory and contraexcitatory response, or an E-E-type response), no response (ipsi-excitatory and contranull response, E-0-type response), and suppressive responses (ipsi-excitatory and contrainhibitory response, E-I-type response) (6).…”

“…Because the two passages are relatively well isolated, odorants inhaled through one nostril activate olfactory sensory neurons only in the ipsilateral olfactory epithelium (6). Therefore, to detect the right or left localization of odor sources, the central olfactory system needs only to compare afferent odor signals originating from the right and left olfactory epithelia (OEs).…”

Odor representations in the olfactory bulb evolve after the first breath and persist as an odor afterimage

“…Blocking the nostril nearly silenced neurons (37). When we applied odorants, only 4/423 cell-odor pairs responded during the first breath, showing that feedback alone is insufficient to drive OB activity for almost all neurons (38).…”

Sensory Deprivation Disrupts Homeostatic Regeneration of Newly Generated Olfactory Sensory Neurons after Injury in Adult Mice

“…Airflow through the contralateral (open) side increases after ipsilateral nostril occlusion (Kikuta et al, 2008). Therefore, increased airflow in the open side may facilitate OSN regeneration and result in differences in the thickness and number of OSNs between the open and closed sides.…”