An Inhibitory Medial Preoptic Circuit Mediates Innate Exploration

Excitation-inhibition imbalance in medial preoptic area circuits underlies chronic stress-induced depression-like states

Dysregulation of brain homeostasis is associated with neuropsychiatric conditions such as major depressive disorder. However, underlying neural-circuit mechanisms remain not well-understood. We show in mice that chronic restraint stress (CRS) and social defeat stress (SDS) are both associated with disruption of excitation (E)-inhibition (I) balance, with increased E/I ratios, in medial preoptic area (MPOA) circuits, but through affecting different neuronal types. CRS results in elevated activity in glutamatergic neurons, and their suppression mitigates CRS-induced depressive-like behaviors. Paraventricular hypothalamic input to these neurons contributes to induction but not expression of depressive-like behaviors. Their projections to ventral tegmental area and periaqueductal gray/dorsal raphe suppress midbrain dopaminergic and serotonergic activity, respectively, and mediate expression of divergent depressive-like symptoms. By contrast, SDS results in reduced activity of GABAergic neurons, and their activation alleviates SDS-induced depressive-like behaviors. Thus, E/I imbalance with relatively increased excitation in MPOA circuits may be a general mechanism underlying depression caused by different etiological factors.

Hypothalamic control of innate social behaviors

Sexual, parental, and aggressive behaviors are central to the reproductive success of individuals and species survival and thus are supported by hardwired neural circuits. The reproductive behavior control column (RBCC), which comprises the medial preoptic nucleus (MPN), the ventrolateral part of the ventromedial hypothalamus (VMHvl), and the ventral premammillary nucleus (PMv), is essential for all social behaviors. The RBCC integrates diverse hormonal and metabolic cues and adjusts an animal's physical activity, hence the chance of social encounters. The RBCC further engages the mesolimbic dopamine system to maintain social interest and reinforces cues and actions that are time-locked with social behaviors. We propose that the RBCC and brainstem form a dual-control system for generating moment-to-moment social actions. This Review summarizes recent progress regarding the identities of RBCC cells and their pathways that drive different aspects of social behaviors.

Neurocircuitry of Predatory Hunting

Predatory hunting is an important type of innate behavior evolutionarily conserved across the animal kingdom. It is typically composed of a set of sequential actions, including prey search, pursuit, attack, and consumption. This behavior is subject to control by the nervous system. Early studies used toads as a model to probe the neuroethology of hunting, which led to the proposal of a sensory-triggered release mechanism for hunting actions. More recent studies have used genetically-trackable zebrafish and rodents and have made breakthrough discoveries in the neuroethology and neurocircuits underlying this behavior. Here, we review the sophisticated neurocircuitry involved in hunting and summarize the detailed mechanism for the circuitry to encode various aspects of hunting neuroethology, including sensory processing, sensorimotor transformation, motivation, and sequential encoding of hunting actions. We also discuss the overlapping brain circuits for hunting and feeding and point out the limitations of current studies. We propose that hunting is an ideal behavioral paradigm in which to study the neuroethology of motivated behaviors, which may shed new light on epidemic disorders, including binge-eating, obesity, and obsessive-compulsive disorders.

Exploration driven by a medial preoptic circuit facilitates fear extinction in mice

Repetitive exposure to fear-associated targets is a typical treatment for patients with panic or post-traumatic stress disorder (PTSD). The success of exposure therapy depends on the active exploration of a fear-eliciting target despite an innate drive to avoid it. Here, we found that a circuit running from CaMKIIα-positive neurons of the medial preoptic area to the ventral periaqueductal gray (MPA-vPAG) facilitates the exploration of a fear-conditioned zone and subsequent fear extinction in mice. Activation or inhibition of this circuit did not induce preference/avoidance of a specific zone. Repeated entries into the fear-conditioned zone, induced by the motivation to chase a head-mounted object due to MPA-vPAG circuit photostimulation, facilitated fear extinction. Our results show how the brain forms extinction memory against avoidance of a fearful target and suggest a circuit-based mechanism of exposure therapy.

Neural and Genetic Basis of Evasion, Approach and Predation

Evasion, approach and predation are examples of innate behaviour that are fundamental for the survival of animals. Uniting these behaviours is the assessment of threat, which is required to select between these options. Far from being comprehensive, we give a broad review over recent studies utilising optic techniques that have identified neural circuits and genetic identities underlying these behaviours.