Previous electrophysiological investigation shows that combinations of compounds classified by humans as umami-tasting, such as glutamate salts and 5'-ribonucleotides, elicit synergistic responses in neurons throughout the rodent taste system and produce a pattern that resembles responses to sweet compounds. The current study tested the hypothesis that a synergistic mixture of monopotassium glutamate (MPG) and inositol monophosphate (IMP) possesses perceptual similarity to sucrose in mice. We estimated behavioral similarity among these tastants and the individual umami compounds using a series of conditioned taste aversion (CTA) tests, a procedure that measures whether a CTA formed to one stimulus generalizes to another. Our primary finding was that a CTA to a synergistic mixture of MPG + IMP generalizes to sucrose, and vice-versa. This indicates umami synergistic mixtures are perceived as having a sweet, or at least sucrose-like, taste to mice. Considering other recent studies, our data argue strongly in favor of multiple receptor mechanisms for umami detection, and complexity in taste perception models for rodents.

This study investigated neural projections from the parabrachial nucleus (PBN), a gustatory and visceral processing area in the brainstem, to the ventral tegmental area (VTA) in the midbrain. The VTA contains a large population of dopaminergic neurons that have been shown to play a role in reward processing. Anterograde neural tracing methods were first used to confirm that a robust projection from the caudal PBN terminates in the dorsal VTA; this projection was larger on the contralateral side. In the next experiment, we combined dual retrograde tracing from the VTA and the gustatory ventral posteromedial thalamus (VPMpc) with taste-evoked Fos protein expression, which labels activated neurons. Mice were stimulated through an intraoral cannula with sucrose, quinine, or water, and PBN sections were processed for immunofluorescent detection of Fos and retrograde tracers. The distribution of tracer-labeled PBN neurons demonstrated that the populations of cells projecting to the VTA or VPMpc are largely independent. Quantification of cells double labeled for Fos and either tracer demonstrated that sucrose and quinine were equally effective in activating both pathways. These results indicate that information about both appetitive and aversive tastes is delivered to a key midbrain reward interface via direct projections from the PBN.

The purpose of this study was to investigate development and age‐specific novel alternative splicing patterns in the longevity genes age‐1 and clk‐1. The nematode Caenorhabditis elegans was used as the model organism, from which mRNA was harvested at different points in their developmental cycle (eggs, larval 3 (L3), dauer, adults, geriatrics). Reverse transcriptase polymerase chain reaction (RT‐PCR) analysis was performed to detect the presence of mRNA of different sizes at different genetic locations throughout the gene, which would suggest alternative mRNA isoforms. The fragments were sequenced (eggs L3, geriatrics) to verify actual splicing reactions. The results indicate novel instances of intron inclusion and exon exclusion with the latter being associated specifically with developmental stage L3.

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