Ultrasonic Vocalizations and Oxidative Metabolism in Anhedonia Research

Abstract

Anhedonia, a key symptom of depression, manifests as a decreased interest in previously rewarding stimuli [2]. The sucrose preference test (SPT) is commonly used to validate anhedonia in animal models, often complemented with histochemical and physiological methods. Within my project, I delved into two such possible methodologies for detecting depressive states in rats - ultrasonic vocalizations (USV) and cytochrome oxidase (COX) activity staining, a measure of brain metabolic activity.

Rats have developed defensive adaptations against predators, including the ability to communicate using ultrasonic vocalizations. Adult rats emit two distinct types of ultrasonic calls: alarm calls (22 kHz) in dangerous and threatening situations, and appetitive calls (50 kHz) in non-aggressive behavioral contexts [3]. Both call types reflect heightened cholinergic or dopaminergic activity in the brain, serving as indicators of the rat's affective state. Disruptions in 50-kHz USVs are observed in preclinical depression models. Similar to reductions in sucrose preference, the number of USVs is generally decreased in multiple validated models of depression [3]. Additionally, some antidepressants restore sucrose preference and normalize baseline USV emission.

Despite their potential, anhedonia is rarely assessed through USVs. This study aimed to explore how USV vocalizations could provide insights into the stress sensitivity of animal models and their correlation with depressive states. I relied on a selected article [1] that combines both measuring USV vocalizations and oxidative metabolism through COX activity staining. The article examined the effect of chronic variable stress on depression and anxiety-related behavior in rats persistently expressing high or low vocal responses to tickling-like stimulation.

Following a literature review, I validated methodologies practically. Notably, I conducted COX activity staining. Utilizing frozen healthy rat brain, I coronally sectioned it (10 μm) and subjected it to staining with a prepared solution according to the established protocol [1]. The staining results were detected with optical densitometry and will be compared with the conclusions from the selected article [1] to understand how chronic stress affects COX activity.

The key findings of the project are that oxidative metabolism increases in several depression-related brain regions due to chronic stress [1], which can be investigated through COX activity staining. Additionally, USVs provide a unique perspective on stress sensitivity and predispositions to depression in animal models. Using both methods together can offer a more comprehensive understanding of depression and its mechanisms, potentially leading to more effective interventions.

References

[1] B. Tagliari et al., “Chronic variable stress impairs energy metabolism in prefrontal cortex and hippocampus of rats: prevention by chronic antioxidant treatment,” Metabolic Brain Disease, vol. 25, no. 2, pp. 169–176, May 2010, doi: https://doi.org/10.1007/s11011-010-9194-x.

[2] M. Heshmati and S. J. Russo, “Anhedonia and the Brain Reward Circuitry in Depression,” Current Behavioral Neuroscience Reports, vol. 2, no. 3, pp. 146–153, Jul. 2015, doi: https://doi.org/10.1007/s40473-015-0044-3.

[3] R. M. Rao and M. Sadananda, “Strain- and context-based 50 kHz ultrasonic vocalizations and anxiety behaviour in the Wistar-Kyoto rat,” Journal of Biosciences, vol. 40, no. 3, pp. 561–570, Jul. 2015, doi: https://doi.org/10.1007/s12038-015-9534-4.