Abstract
The present study investigated a subpopulation of neurons in the mouse parabrachial nucleus (PbN), a gustatory and visceral relay area in the brainstem, that project to the lateral hypothalamus (LH). We made injections of the retrograde tracer Fluorogold (FG) into LH, resulting in fluorescent labeling of neurons located in different regions of the PbN. Mice were stimulated through an intraoral cannula with one of seven different taste stimuli, and PbN sections were processed for immunohistochemical detection of the immediate early gene c-Fos, which labels activated neurons. LH projection neurons were found in all PbN subnuclei, but in greater concentration in lateral subnuclei, including the dorsal lateral subnucleus (dl). Fos-like immunoreactivity (FLI) was observed in the PbN in a stimulus-dependent pattern, with the greatest differentiation between intraoral stimulation with sweet (0.5 M sucrose) and bitter (0.003 M quinine) compounds. In particular, sweet and umami-tasting stimuli evoked robust FLI in cells in the dl, whereas quinine evoked almost no FLI in cells in this subnucleus. Double-labeled cells were also found in the greatest quantity in the dl. Overall, these results support the hypothesis that the dl contains direct a projection to the LH that is activated preferentially by appetitive compounds; this projection may be mediated by taste and/or postingestive mechanisms.
Highlights
In rodents, the parabrachial nucleus of the pons (PbN) is a critical brainstem relay for both gustatory and visceral sensory information
The present study investigated a subpopulation of neurons in the mouse parabrachial nucleus (PbN), a gustatory and visceral relay area in the brainstem, that project to the lateral hypothalamus (LH)
We examined the distribution of FG, Fos-like immunoreactivity (FLI), and double-labeled cells in PbN subnuclei across 6–7 sections per mouse
Summary
The parabrachial nucleus of the pons (PbN) is a critical brainstem relay for both gustatory and visceral sensory information (for reviews, see Lundy and Norgren, 2004a; Saper, 2004; Sewards, 2004). From the PbN, both gustatory and visceral sensory information are relayed to cortex via the thalamus; other PbN neurons project directly to limbic forebrain areas, including the central nucleus of the amygdala (CeA), bed nucleus of the stria terminalis (BNST), and lateral hypothalamus (LH; Norgren, 1974; Saper and Loewy, 1980; Fulwiler and Saper, 1984; Halsell, 1992; Karimnamazi and Travers, 1998; Yamamoto, 2006; Tokita et al, 2010). LH neurons project back to PbN (Moga et al, 1990; Saggu and Lundy, 2008; Tokita et al, 2009)
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