Odor blocking of stress hormone responses

Area of Science:

• Neuroscience
• Olfactory system research
• Stress response mechanisms

Background:

• The use of scents to alleviate stress is ancient, yet the underlying biological mechanisms remain largely unelucidated.
• Stress and fear trigger hormonal responses mediated by specific neural circuits, including corticotropin-releasing hormone neurons (CRHNs).

Purpose of the Study:

• To investigate the neurobiological mechanisms by which common odorants can mitigate stress responses in a mammalian model.
• To identify the specific neural pathways and neuronal populations involved in scent-mediated stress reduction.

Main Methods:

• Utilized mouse models exposed to common odorants and potent stressors (physical restraint, predator odor, social confrontation).
• Measured stress hormone levels and monitored neuronal activity in key brain regions, including the bed nucleus of the stria terminalis (BNSTa) and the ventromedial hypothalamus (VMH).
• Employed optogenetic techniques to selectively silence inhibitory neurons in the VMH to assess their role.

Main Results:

• Two common odorants significantly blocked stress hormone increases induced by physical restraint, predator odor, and social confrontation.
• One odorant inhibited the activation of excitatory neurons in the BNSTa that project to CRHNs.
• Both odorants activated inhibitory neurons in the VMH, and silencing these neurons impaired the stress-blocking effect of odors.

Conclusions:

• Odorants can attenuate stress hormone responses through at least two distinct neural mechanisms.
• Mechanism 1: Inhibition of excitatory stress-transmitting neurons upstream of CRHNs (e.g., in BNSTa).
• Mechanism 2: Activation of inhibitory neurons (e.g., in VMH) that suppress CRHN activation, either directly or indirectly.