To Vocalize or Not to Vocalize, That Is the Question

Imagine you were an adult male mouse. Do you vocalize when you are in a safe environment with a female? (Duh of course) Do you vocalize when you face a male intruder mouse? (Well, gotta vocalize when appropriate to get the intruder away) What if there is a cat present? (Hmm…better off staying quiet) How would you weigh things out if there is a female and a cat present? (Ughh…Let me check with my brain)

The Mooney Lab is particularly interested in the neurobiology of hearing and communication. This summer, the two projects that I’m involved with focus on the production and perception of vocalization in mice.

Vocalization is crucial to communication and social functioning for many mammalian species. Humans, for instance, rely on complex speech to convey emotions and various information; mice, for another example, produce ultrasonic vocalizations (USVs) for purposes such as courtship and defense (Holy et Guo, 2005; Portfos, 2007). In our society, producing speech appropriately in different social contexts is essential for individuals’ social survival. Similarly, to survive and reproduce, mice vocalize in a context-specific fashion, and thus serve as a model system for studying mammalian vocal control (Chabout et al., 2012; Weiner et al., 2016). In mammals, the neural circuitry for vocalization production is a complex network across the forebrain and brainstem, obligated to integrate cues from social contexts, determine the appropriateness of vocalization and finally signal motor neurons to generate sounds through larynx (Tschida et al., unpublished). However, despite its critical role, understanding of the vocalization network has remained limited at the neuronal level.

Previously, Katie and Valerie (my mentor, wohoo!!) have worked extensively on an area within the midbrain called periaqueductal gray (PAG). PAG is a highly heterogeneous structure, pertaining to nociception, defensive, reproductive and maternal behaviors as well as autonomic regulation (Basbaum et Fields, 1978; Carrive, 1993; Tovote et al., 2016; Tschida et al., unpublished). It has also been shown to be an essential node in the vocalization circuitry, since when PAG is lesioned, individuals exhibit mutism (Esposito et al., 1999; Jurgens, 1994; Jurgens, 2002). Using CANE (capturing activated neuronal ensembles) (Sakurai et al., 2016), a viral genetic tagging method, the lab has been able to characterize distinct subpopulations of PAG neurons that are activated during USVs of male mice to females. Nevertheless, these selective subsets were only characterized in the context of male-female interactions. My first project thus examines two social contexts––courtship with females and defensive behaviors against intruding juvenile males––, and studies whether the same subpopulations of PAG-USV neurons are activated for vocalization in both scenarios.

In the last two weeks, we have performed CANE tagging brain surgery on two mice. I’ve also been practicing doing histology. I’m still very slow carrying out each step during the surgery (special thanks to my mentor for being so patient), but I’ll try my best to getting better at it with every more step I do (and to ALWAYS ALWAYS remember to check how fast the mouse is breathing).

The second project studies mouse’s auditory perception of his own vocalization. Such acoustic feedback has a significant role in vocal production as well, as changes in this feedback could elicit compensatory alterations in what the animal vocalizes (Eliades et Wang, 2002; Houde et Jordan, 2002). A previous study on marmosets showed that cortical neural responses in these primates are suppressed as a result of vocalization, and that this suppression takes place hundreds of milliseconds before the vocalization onset (Eliades et Wang, 2002). To investigate how the auditory neurons in mice respond to the animals’ vocalizations, I was tasked to habituate mice to a head-fixation device in order to obtain clearer electrophysiological recordings.

Working with mice this week, I had quite some philosophical moments, and thought more deeply about biology and my relationship with living things. While more will come in next week’s post on the interview with my PI, I want to thank all in the lab and in BSURF who discussed this big topic of life with me. I’ve learned so much so far, and I can’t wait to find out what comes next!

Mice Love! (weekend sketches)

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