title: Hippocampal neuronal responses during signaled licking of gustatory stimuli in different contexts.
abstract: Neuroanatomical studies suggest that hippocampal formation (HF) receives information from all sensory modalities including taste via the parahippocampal cortices. To date, however, no neurophysiological study has reported that HF neurons encode taste information. In the present study, we recorded CA1 HF neurons from freely behaving rats during performance of a visually-guided licking task in two different triangular chambers. When a cue lamp came on, the rats were required to press a bar to trigger a tube to protrude into the chambers for 3 s. During this period, the rats could lick one of six sapid solutions: [0.1M NaCl (salty), 0.3M sucrose (sweet), 0.01 M citric acid (sour), 0.0001 M quinine HCl (bitter), 0.01 M monosodium L-glutamate (MSG, umami), and a mixture of MSG and 0.001 M disodium-5'-inosinate (IMP) (MSG+IMP)], and distilled water. Of a total 285 pyramidal and interneurons, the activity of 173 was correlated with at least one of the events in the task-illumination of cue lamps, bar pressing, or licking the solution. Of these, 137 neurons responded during licking, and responses of 62 of these cells were greater to sapid solutions than to water (taste neurons). Multivariate analyses of the taste neurons suggested that, in the HF, taste quality might be encoded based on hedonic value. Furthermore, the activity of most taste neurons was chamber-specific. These results implicate the HF in guiding appetitive behaviors such as conditioned place preference.
authors.affiliation: System Emotional Science, Graduate School of Medicine and Pharmaceutical Science, University of Toyama, Toyama, Japan.
authors.forename: Anh Son
authors.initials: AS
authors.lastname: Ho
authors.forename: Etsuro
authors.initials: E
authors.lastname: Hori
authors.forename: Phuong Hong Thi
authors.initials: PH
authors.lastname: Nguyen
authors.forename: Susumu
authors.initials: S
authors.lastname: Urakawa
authors.forename: Takashi
authors.initials: T
authors.lastname: Kondoh
authors.forename: Kunio
authors.initials: K
authors.lastname: Torii
authors.forename: Taketoshi
authors.initials: T
authors.lastname: Ono
authors.forename: Hisao
authors.initials: H
authors.lastname: Nishijo
mesh_terms: D000200:Action Potentials / Q000502:physiology*; D000818:Animals; D056547:CA1 Region, Hippocampal / Q000166:cytology / Q000502:physiology*; D003463:Cues; D005518:Food Preferences / Q000502:physiology*; D008297:Male; D009474:Neurons / Q000502:physiology*; D010775:Photic Stimulation / Q000379:methods; D051381:Rats; D017208:Rats, Wistar; D015398:Signal Transduction / Q000502:physiology*; D013649:Taste / Q000502:physiology*