Orosensory deprivation alters taste-elicited c-Fos expression in the parabrachial nucleus of neonatal rats

Abstract

In the present study we examined the effects of neonatal orosensory deprivation on taste-elicited gustatory activity in the rat parabrachial nucleus (PBN) using the functional anatomical marker c-Fos. Animals in three groups (GG, GO and GM) received gastric cannula implantation surgery on postnatal day 9 (P9). Animals in the fourth group (MR) did not receive any surgery. GG rats were fed by infusion of artificial milk directly into the stomach. GO rats were fed by intraoral infusion of artificial milk. GM and MR rats were reared by their mother with free access to mother's milk, water and rat chow. Rats from all groups were similar in body weight and length by P21. On P21 rats in all groups were intraorally presented with 0.5M sucrose solution and the brains were extracted and processed for c-Fos immunohistochemistry. Taste-elicited c-Fos expression in both the gustatory waist area, and the external lateral subnucleus of the PBN in rats in the GG group was significantly more robust than in the other three groups. These findings suggest a substantial alteration in orosensory-evoked neuronal response in this nucleus, due to sensory or motor deprivation during a critical developmental stage.

Figure 1

Schematic drawing of the procedures and timelines for each of the 4 experimental groups. GG, gastrostomy + intragastric infusion; GO, gastrostomy + intraoral infusion; GM, gastrostomy + mother rearing; MR, mother rearing.

Figure 2

Schematic diagram of the intraoral cannula used in the present study. The taste solution was presented through the cannula, which was fixed on the right cheek with dental adhesive resin cement. The stimulus was introduced into the oral cavity (vestibule) at about the first maxillary molar, similar to a conventional skull-fixed intraoral cannula.

Figure 3

Body weight (g) and size (length; mm) of rats in each group. A: Body growth as indicated by weight gain during P8 – P21 period. Post-hoc analysis revealed no significant difference on P21. B: There were no significant group differences in the mean (±S.E.) body length on P21.

Figure 4

Representative photomicrographs of the waist (gustatory) area located approximately 250 µm caudal to the contact of the inferior colliculus to the pons from individuals in each group. A: Nissl-stained section illustrating the location of the central medial (cms) and ventral lateral subnuclei (vls) relative to the brachium conjunctivum (BC). B: GG group; C: GO group; D: GM group; E: MR group. Scale bars = 200 µm.

Figure 5

Representative photomicrographs of the dorsal lateral (dls) and external lateral subnuclei (els) located approximately 50 µm caudal to the contact of the inferior colliculus to the pons from individuals in each group. A: Nissl-stained section illustrating the location of the dorsal lateral (dls) and external lateral subnuclei (els) relative to the brachium conjunctivum (BC). B: GG group; C: GO group; D: GM group; E: MR group. Scale bars = 200µm.

Figure 6

Mean (±S.E.) number of Fos-IR+ nuclei in the waist area (A), dorsal lateral (B), and external lateral subnuclei (C) in each of the 4 experimental groups. Fos-IR in the waist area and external lateral subnucleus in the GG group was significantly higher than in the other three groups. In the waist area Fos-IR of the GO group was also significantly higher than the MR group. *p < 0.05. **p < 0.01.