Ketamine treatment upon memory retrieval reduces fear memory in marmoset monkeys.

Emotionally arousing experiences are retained very well as seen in posttraumatic stress disorder (PTSD). Various lines of evidence indicate that reactivation of these memories renders them labile which offers a potential time-window for intervention. We tested in non-human primates whether ketamine, administered during fear memory reactivation, affected passive (inhibitory) avoidance learning. For the consolidation of contextual emotional memory, the unescapable foot-shock paradigm in a passive avoidance task with two compartments (dark vs illuminated) was used. After entering the dark compartment, marmoset monkeys received four random foot-shocks (1 mA, 4 s) within 15-min. This stressful exposure increased the saliva cortisol and heart rate and impaired REM-sleep (p<0.05). One week later the monkeys were re-exposed to the stressful situation for the reconsolidation of the fearful experience. During the re-exposure the monkeys were treated with ketamine (0.5 mg/kg) or saline. In week 3, the monkeys were placed in the experimental setting to test their memory for the fearful experience. In contrast to the vehicle-treated monkeys, who avoided the dark compartment, the ketamine-treated monkeys entered the dark compartment that was previously associated with the fearful experience (p<0.05). Post-mortem analysis of the hippocampus showed that ketamine-treated animals exhibited less doublecortin positive neurons and BrdU-labeled cells in the dentate gyrus. This study reveals that a single low dose of ketamine, administered upon fear retrieval in monkeys, reduce contextual fear memory and attenuate neurogenesis in the hippocampus. These are important findings for considering ketamine as a potential candidate to target traumatic memories in PTSD.

Acceleration of Amyloidosis by Inflammation in the Amyloid-Beta Marmoset Monkey Model of Alzheimer's Disease.

BACKGROUND: The immune system is increasingly mentioned as a potential target for Alzheimer's disease (AD) treatment. OBJECTIVE: In the present pilot study, the effect of (neuro)inflammation on amyloidopathy was investigated in the marmoset monkey, which has potential as an AD animal model due to its natural cerebral amyloidosis similar to humans. METHODS: Six adult/aged marmosets (Callithrix jacchus) were intracranial injected with amyloid-beta (Aß) fibrils at three cortical locations in the right hemisphere. Additionally, in half of the monkeys, lipopolysaccharide (LPS) was co-injected with the Aß fibrils and injected in the other hemisphere without Aß fibrils. The other three monkeys received phosphate buffered saline instead of LPS, as a control for the inflammatory state. The effect of inflammation on amyloidopathy was also investigated in an additional monkey that suffered from chronic inflammatory wasting syndrome. Mirror histology sections were analyzed to assess amyloidopathy and immune reaction, and peripheral blood for AD biomarker expression. RESULTS: All LPS-injected monkeys showed an early AD immune blood cell expression profile on CD95 and CD45RA. Two out of three monkeys injected with Aß and LPS and the additional monkey, suffering from chronic inflammation, developed plaques. None of the controls, injected with Aß only, developed any plaques. CONCLUSION: This study shows the importance of immune modulation on the susceptibility for amyloidosis, a hallmark of AD, which offers new perspectives for disease modifying approaches in AD.

Evaluation of ultrasonic vocalizations in common marmosets (Callithrix jacchus) as a potential indicator of welfare.

The vocal repertoire in common marmosets (Callithrix jacchus) has been assumed to consist not only of vocalizations audible to humans but also of ultrasonic vocalizations (USVs). The use of USVs to socially indicate distress has not been evaluated in this species, however. The authors analyzed the ultrasonic vocal repertoire of the common marmoset under normal housing conditions, under various experimental manipulations intended to elicit positive or negative emotional responses and during stressful experiences including blood draw and exposure to a perceived predator. Analysis of the recordings showed that marmosets produced vocalizations with ultrasonic components as part of their normal vocal repertoire, but these vocalizations all have audible components as well. Only 4 of the 13 types of vocalizations had ultrasonic components. These ultrasonic components were not reliably associated with responses to different experimental manipulations, suggesting that they are not used to indicate pain, discomfort or distress.