Neural Isolation of the Olfactory Bulbs Severely Impairs Taste-Guided Behavior to Normally Preferred, But Not Avoided, Stimuli

Abstract

Here we systematically tested the hypothesis that motivated behavioral responsiveness to preferred and avoided taste compounds is relatively independent of the olfactory system in mice whose olfactory bulbs (main and accessory) were surgically disconnected from the rest of the brain (bulbotomy; BULBx). BULBx was confirmed histologically as well as functionally with the buried food test. In brief access taste tests, animals received 10-s trials of various concentrations of a taste compound delivered quasi-randomly. BULBx C57BL/6 (B6) mice displayed severely blunted concentration-dependent licking for the disaccharide sucrose, the maltodextrin Maltrin, and the fat emulsion Intralipid relative to their sham-operated controls (SHAM B6). Licking for the noncaloric sweetener saccharin was also blunted by bulbotomy, but less so. As expected, mice lacking a functional "sweet" receptor (T1R2+T1R3 knockout, KO) displayed concentration-dependent responsiveness to Maltrin and severely attenuated licking to sucrose. Like in B6 mice, responsiveness to both stimuli was exceptionally curtailed by bulbotomy. In contrast to these deficits in taste-guided behavior for unconditionally preferred stimuli, BULBx in B6 and KO mice did not alter concentration-dependent decreases for the representative non-preferred stimuli, quinine and citric acid. Nor did it temper intake of and preference for high concentrations of affectively positive stimuli when presented in long-term (23-hr) 2-bottle tests, demonstrating that the surgery does not lead to a generalized motivational deficit. Collectively, these behavioral results demonstrate that specific aspects of taste-guided ingestive motivation are profoundly disturbed by eliminating the anatomical connections between the main/accessory olfactory bulbs and the rest of the brain.

Taste Impairments in a Parkinson’s Disease Model Featuring Intranasal Rotenone Administration in Mice

“…Olfaction can be partly involved in taste function. However, the bulbectomy mice, in which the OB was surgically disconnected from the brain, did not exhibit the blunted concentration-lick relationship for aversive taste such as QHCl [ 43 ]. The concept that mammals lick at a constant rate under a variety of conditions has been accepted [ 26 ].…”

Reduced menthol sensitivity in a prodromal Parkinson’s disease model induced by intranasal rotenone treatment

“…In our previous study, short-term intranasal rotenone-treated mice exhibited both olfactory and bitter taste impairments before motor deficits and neurodegeneration in the substantia nigra (SN) and the ventral tegmental area (VTA), implying a presumed animal model in the early-stage of PD ( Yin et al, 2022 ). The bitter taste impairment in this PD model mice occurred independently of olfactory impairments, because bitter taste sensitivity itself in mice was not changed by olfaction ( Inui-Yamamoto et al, 2020 ). However, it remains unclear whether this impairment is related to an altered intraoral temperature sensation.…”