Transection of Gustatory Nerves Differentially Affects Dietary Fat Intake in Obesity-Prone and Obesity-Resistant Rats

Abstract

The current prevalence of obesity has been linked to the consumption of highly palatable foods and may be mediated by a dysregulated or hyposensitive orosensory perception of dietary fat, thereby contributing to the susceptibility to develop obesity. The goal of the current study was to investigate the role of lingual taste input in obesity-prone (OP, Osborne-Mendel) and obesity-resistant (OR, S5B/Pl) rats on the consumption of a high-fat diet (HFD). Density of fungiform papillae was assessed as a marker of general orosensory input. To determine if orosensory afferent input mediates dietary fat intake, surgical transection of the chorda tympani and glossopharyngeal nerves (GLX/CTX) was performed in OP and OR rats and HFD caloric intake and body weight were measured. Fungiform papillae density was lower in OP rats, compared with OR rats. GLX/CTX decreased orosensory input in both OP and OR rats, as measured by an increase in the intake of a bitter, quinine solution. Consumption of low-fat diet was not altered by GLX/CTX in OP and OR rats; however, GLX/CTX decreased HFD intake in OR, without altering HFD intake in OP rats. Overall, these data suggest that inhibition of orosensory input in OP rats do not decrease fat intake, thereby supporting that idea that hyposensitive and/or dysregulated orosensory perception of highly palatable foods contribute to the susceptibility to develop obesity.

Keywords: Osborne-Mendel; S5B/Pl; chorda tympani; glossopharyngeal nerve; high-fat diet.

Figure 1.

Fungiform papillae in OP (n = 6) and OR (n = 5) rats were visualized and counted. (A) OP rats had significantly fewer fungiform papillae compared with OR rats. (B) Image of fungiform papillae following 0.5% methylene blue staining. Data shown as mean ± SEM; *P < 0.05.

Figure 2.

Quinine intake was measured in OP and OR rats with and without GLX/CTX. Following GLX/CTX, rats consumed more quinine solution than sham-operated rats. OR-SHAM (n = 5), OR-GLX/CTX (n = 5), OP-SHAM (n = 5), and OP-GLX/CTX (n = 4). Data shown as mean ± SEM; *P < 0.05.

Figure 3.

Caloric intake was measured daily for 20 days. (A) OR consumed more HFD than LFD. GLX/CTX significantly decreased caloric intake of HFD in OR rats in 13 out of 20 days beginning on Day 6. OR-SHAM-LFD (n = 10), OR-GLX/CTX-LFD (n = 8), OR-SHAM-HFD (n = 11), and OR-GLX/CTX-HFD (n = 10). (B) OP rats consumed more HFD than LFD. GLX/CTX did not affect HFD or LFD caloric intake in OP rats. OP-SHAM-LFD (n = 11), OP-GLX/CTX-LFD (n = 8), OP-SHAM-HFD (n = 10), and OP-GLX/CTX-HFD (n = 10). Data shown as mean ± SEM; *P < 0.05 between GLX/CTX and SHAM rats fed HFD.

Figure 4.

Change in body weight was assessed in OP and OR rats consuming HFD or LFD. (A) OR rats consuming HFD gained more weight than OR rats consuming LFD. OR-SHAM-LFD (n = 10), OR-GLX/CTX-LFD (n = 8), OR-SHAM-HFD (n = 11), and OR-GLX/CTX-HFD (n = 10). (B) OP rats consuming HFD gained more weight than OP rats consuming LFD. OP-SHAM-LFD (n = 11), OP-GLX/CTX-LFD (n = 8), OP-SHAM-HFD (n = 10), and OP-GLX/CTX-HFD (n = 10). Data shown as mean ± SEM.