Association between Novel Object Recognition/Spontaneous Alternation Behavior and Emission of Ultrasonic Vocalizations in Rats: Possible Relevance to the Study of Memory

Rats emit ultrasonic vocalizations (USVs) in situations with emotional valence, and USVs have also been proposed as a marker for memories conditioned to those situations. This study investigated whether USV emissions can predict and/or be associated with the behavior of rats in tests that evaluate unconditioned memory. To this end, rats were subjected to “tickling”, a procedure of heterospecific play that has emotional valence and elicits the emission of USVs, and afterwards evaluated in the novel object recognition test (NOR) and in the single trial continuous spontaneous alternation behavior (SAB) test in a Y-maze. The number of 22-kHz USVs (aversive) and 50-kHz USVs (appetitive) emitted in response to tickling and during NOR and SAB tests were scored, and the correlations among them and with rats’ behavior evaluated. Rats emitted 50-kHz USVs, but not 22-kHz USVs, during the NOR and SAB tests, and such calling behavior was not linked with the behavioral readouts indicative of memory function in either test. However, rats that prevalently emitted 22-kHz USVs in response to tickling displayed an impaired NOR performance. These findings suggest that measuring the emission of USVs could be of interest in studies of unconditioned memory, at least with regard to 22-kHz USVs.

Comparison between the timing of the occurrence of taste sensitivity changes and short-term memory decline due to aging in SAMP1 mice

Several studies have suggested that cognitive impairment affects taste sensitivity. However, the mechanism behind this is still unclear. In this study, we focused on short-term memory. Using senescence-accelerated mouse prone 1 (SAMP1) mice, we compared whether the effects of aging are observed earlier in taste sensitivity or short-term memory. We used 8-week-old mice as the young group, and 70- and 80-week-old mice as aged groups. Taste sensitivity was evaluated using a 48-hour two-bottle preference test, and short-term memory was evaluated using the Y-maze test. SAMP1 mice showed apparently changes in taste sensitivity at 70-weeks-old. However, the influence of aging on spontaneous alternation behavior, which is indicative of short-term memory alterations, was not observed in 70-week-old mice. At 80-weeks-old, the influence of aging was observed, and spontaneous alternation behavior was significantly decreased. This suggests that age-dependent changes in taste sensitivity occur prior to short-term memory function decline. In addition, there was no significant influence of aging on the mRNA expression of long-term potentiation-related genes in the hippocampus of 80-week-old mice. Therefore, the age-related decline of short-term memory may not affect taste sensitivity.

Nitrous Oxide-induced Impairment of Spatial Working Memory Requires Activation of GABAergic Pathways

Background: Previous research from our laboratory implicated opioid and benzodiazepine- GABA mechanisms in other effects of N2O (antinociception and anxiolysis), so a decision was made to study these as potential mechanisms of N2O-induced dysfunction of spatial working memory. Objective: to explore potential mechanisms of N2O in reducing spatial working memory in mice. Methods: we monitored spontaneous alternation behavior (SAB) in male NIH Swiss mice exposed to N2O during a T-maze spontaneous alternation task (T-SAT). Results: mice that were exposed to 70% N2O (in O2) exhibited severely and significantly reduced spontaneous alternation behavior in the T-SAT. Mice in this environment alternated their route only 33% of the time, in comparison to the control (room air) rate of alternation at approximately 70%. Mice pretreated with the benzodiazepine antagonist, flumazenil exhibited a dose-dependent restoration of spatial working memory under 70% N2O in the T-SAT. Alternatively, pretreatment with neither the GABAA antagonist gabazine nor the opioid antagonist naloxone had any appreciable effect on the N2O-reduced SAB. Conclusion: this study verified that 70% N2O can reduce spatial working memory in mice, which appears to involve benzodiazepine mechanisms in the brain.