Comparison of Serial Blood Collection by Facial Vein and Retrobulbar Methods in C57BL/6 Mice.

Many biomedical research protocols for mouse models involve serial blood collection and analysis. Two common techniques for serial blood collection in this species are the retrobulbar (RB, also called retroorbital) and facial vein (FV) methods. However, previous studies comparing these methods typically evaluated collection at a maximum of 2 time points. Here we compared hematologic values, adverse clinical effects, and histopathologic lesions in mice bled either once or serially (6 times) by using the FV or RB method. Mice (n = 48) were divided into 4 groups: single FV, single RB, serial FV and serial RB. Mice in the single-collection groups underwent a single blood collection by the indicated method, whereas those in the serial-collection groups were sampled once weekly for 6 consecutive weeks. All animals were euthanized and necropsied 2 wk after their last blood collection. Compared with all other groups, the serial FV group experienced more serious clinical adverse events, including 33% mortality, convulsions, head tilt, and hemorrhage from the ear canal and nares. In addition, mice in the FV groups had a significantly greater acute body weight loss compared with mice in the RB groups. Histologically, mice in both serial-collection groups had an increased incidence of tissue lesions compared with their respective single-collection groups. Importantly, only mice in the serial FV group had life-threatening histopathologic lesions, including cerebral hemorrhage or ischemia. Given these data, we conclude that serial blood collection in mice causes increased incidence of tissue damage compared with single sampling, and serial blood collection by the FV method causes substantial morbidity and mortality compared with the RB method.

Functional magnetic resonance imaging of auditory cortical fields in awake marmosets.

The primate auditory cortex is organized into a network of anatomically and functionally distinct processing fields. Because of its tonotopic properties, the auditory core has been the main target of neurophysiological studies ranging from sensory encoding to perceptual decision-making. By comparison, the auditory belt has been less extensively studied, in part due to the fact that neurons in the belt areas prefer more complex stimuli and integrate over a wider frequency range than neurons in the core, which prefer pure tones of a single frequency. Complementary approaches, such as functional magnetic resonance imaging (fMRI), allow the anatomical identification of both the auditory core and belt and facilitate their functional characterization by rapidly testing a range of stimuli across multiple brain areas simultaneously that can be used to guide subsequent neural recordings. Bridging these technologies in primates will serve to further expand our understanding of primate audition. Here, we developed a novel preparation to test whether different areas of the auditory cortex could be identified using fMRI in common marmosets (Callithrix jacchus), a powerful model of the primate auditory system. We used two types of stimulation, band pass noise and pure tones, to parse apart the auditory core from surrounding secondary belt fields. In contrast to most auditory fMRI experiments in primates, we employed a continuous sampling paradigm to rapidly collect data with little deleterious effects. Here we found robust bilateral auditory cortex activation in two marmosets and unilateral activation in a third utilizing this preparation. Furthermore, we confirmed results previously reported in electrophysiology experiments, such as the tonotopic organization of the auditory core and regions activating preferentially to complex over simple stimuli. Overall, these data establish a key preparation for future research to investigate various functional properties of marmoset auditory cortex.

Audience affects decision-making in a marmoset communication network.

An audience can have a profound effect on the dynamics of communicative interactions. As a result, non-human primates often adjust their social decision-making strategies depending on the audience composition at a given time. Here we sought to test how the unique vocal behaviour of multiple audience members affected decisions to communicate. To address this issue, we developed a novel experimental paradigm in which common marmosets directly interacted with multiple 'virtual monkeys' (VMs), each of whom represented an individual marmoset with distinct vocal behaviour. This active social signalling paradigm provided subjects an opportunity to interact with and learn about the behaviour of each VM in the network and apply this knowledge in subsequent communicative decisions. We found that subjects' propensity to interact with particular VMs was determined by the behaviour of each VM in the audience and suggests that marmoset social decision-making strategies are highly adaptive to nuances of the immediate communication network.