Biology subjects

Torchia, S.

Publications and source records attributed to Torchia, S..

3 recordsLinked to original sources

bioRxiv2026

Reciprocal feedback inhibition and divergent intrinsic firing properties between behaviorally defined classes of neurons in the mouse ventromedial hypothalamus

The capacity to orchestrate appropriate defensive behaviors in response to threatening stimuli is essential for the survival of organisms. Flight, freezing, appeasement, and attack, for example, are common defensive responses evoked depending upon the nature of the threat, the immediate context, and past experiences. Multiple brain regions have been implicated in regulating such responses, with the medial hypothalamus playing a key role in mediating innate responses to social and predator threats. The ventrolateral subdivision of the ventromedial hypothalamus (VMHvl) has been shown to mediate both avoidance and aggression towards conspecific threats in mice, suggesting that it serves as a circuit for context-appropriate defensive responses to social threats. Previous in vivo calcium imaging in VMHvl identified cells whose activity encodes either approach toward or escape from a social threat (Assessment+ and Flight+ cells, respectively), but it remained unclear how the switch in neural encoding from approach to avoidance occurs. Here, we use in vivo single-unit electrophysiology recordings coupled to channelrhodopsin-assisted circuit mapping (optrodes) to explore the functional and structural connectivity basis of the approach-avoidance switch. We confirm the presence of Assessment+ and Flight+ neurons in VMHvl and demonstrate that they are interconnected through feedback excitation and reciprocal feedback inhibition. Moreover, we discover that Assessment+ and Flight+ neurons exhibit a pronounced difference in their intrinsic firing properties. We hypothesize that this asymmetry in intrinsic responsivity coupled to reciprocal feedback inhibition underlies the nonlinear firing changes at the approach-to-avoidance transition and plays a role in triggering escape behavior.

neuroscience↗

bioRxiv2026

Excitatory and inhibitory neurons in the dorsal periaqueductal gray encode decisions to assess and escape natural threats

Prey species are able to engage hardwired neural pathways to rapidly escape from an imminent predator attack. However, when predator threat is less probable they typically show a stereotypical sequence of approach toward the threat aimed at gathering more information, followed by escape to safety when the threat threshold is reached. The brainstem dorsal periaqueductal gray (dPAG) is required for the expression of escape behavior to predator threats and stimulation of dPAG elicits goal-directed flight. However, in vivo neural recordings in dPAG have identified separate populations of neurons that are tuned to either the approach or escape phase of the behavior suggesting that the structure may also be involved in threat assessment. The genetic identity and connectivity of these Assessment+ and Escape+ neurons have not been defined, although optogenetic activation of glutamatergic, but not GABAergic neurons elicits high-speed flight, suggesting that Escape+ neurons might be exclusively excitatory in nature. Moreover, it is not clear whether non-predator threats such as those elicited by conspecific or other animate threats are encoded by independent or overlapping neurons in dPAG. Here we report the activity pattern of ensembles of glutamatergic and GABAergic dPAG neurons during approach and escape from predator, social, and prey threats. Unexpectedly, we found that both glutamatergic and GABAergic neurons harbor Assessment+ and Escape+ neurons, suggesting that both cell-types are engaged in the approach-to-avoidance transition. Consistent with the functional involvement of both cell-types in approach-to-avoidance behavior, optogenetic activation of GABAergic cells elicited a reduction of risk assessment behavior towards the predator. Finally, we found that exposure to predator, social or prey threat recruited largely overlapping neurons in dPAG, demonstrating a convergence of threat processing in this structure. These findings point to a tightly coordinated role for dPAG excitatory and inhibitory neurons in the generalized control of innate threat assessment and avoidance behavior.

neuroscience↗

bioRxiv2024

Induction of territorial behavior and dominance hierarchies in laboratory mice

Territorial behaviors comprise a set of coordinated actions and response patterns found across animal species that promote the exclusive access to resources. House mice are highly territorial with a subset of males consistently attacking and chasing competing males to expel them from their territories and performing urine marking behaviors to signal the extent of their territories. Natural variation in territorial behaviors within a mouse colony leads to the formation of dominance hierarchies in which subordinate males can reside within the territory of a dominant male. While the full repertoire of such territorial behaviors and hierarchies has been extensively studied in wild-derived mice in semi-natural enclosures, so far they have not been established in the smaller enclosures and with the genetically-defined laboratory strains required for the application of neural recording and manipulation methods. Here, we present a protocol to induce an extensive repertoire of territorial behaviors in small enclosures in laboratory mice, including a method for the simultaneous tracking of urine marking behavior in mouse pairs. Using this protocol we describe the emergence of robust dominant-subordinate hierarchies between pairs of CD1 outbred or CD1xB6 F1 hybrid mice, but unexpectedly not in C57BL/6 inbred animals. Our behavioral paradigm opens the door for neurocircuit studies of territorial behaviors and social hierarchy in the laboratory.

animal behavior and cognition↗