How do rats go into hibernation? - briefly
When temperatures and daylight shorten, rats suppress metabolism, reduce body temperature and heart rate, and metabolize stored fat for energy. Hormonal shifts—elevated melatonin and lowered thyroid activity—initiate and maintain this torpid state.
How do rats go into hibernation? - in detail
Rats that undergo seasonal dormancy prepare through a cascade of physiological adjustments triggered by declining ambient temperature and shortening daylight. Photoreceptive cells in the retina convey reduced light exposure to the suprachiasmatic nucleus, which modulates melatonin secretion from the pineal gland. Elevated melatonin signals the hypothalamus to suppress thyrotropin‑releasing hormone, leading to a drop in circulating thyroid hormones and a consequent reduction in basal metabolic rate.
Concurrently, the hypothalamic–pituitary–adrenal axis releases corticosterone, promoting the mobilization of white adipose tissue. Lipolysis supplies free fatty acids that are stored in brown adipose depots. During the pre‑hibernation phase, rats increase food intake and accumulate fat reserves up to 30 % of body mass.
Thermoregulatory set‑point shifts downward; the hypothalamic thermoregulatory center lowers the target core temperature from approximately 37 °C to 20–25 °C. Peripheral vasoconstriction reduces heat loss, while shivering thermogenesis is suppressed. Brown fat mitochondria switch to uncoupled respiration, generating modest heat without raising metabolic demand.
When the environmental temperature falls below the species‑specific threshold (generally 5–10 °C), the animal seeks insulated microhabitats such as burrows or nest materials. The animal then enters torpor bouts characterized by:
- Core temperature decline to the new set‑point.
- Heart rate reduction from 300–400 bpm to 30–50 bpm.
- Respiratory frequency dropping from 80–100 breaths min⁻¹ to 5–10 breaths min⁻¹.
- Oxygen consumption decreasing by 80–90 % relative to active metabolism.
During torpor, glucose utilization is minimized; fatty acids become the primary fuel, oxidized via β‑oxidation in the liver and skeletal muscle. Ketone bodies circulate to supply the brain, preserving neuronal function despite low glucose availability.
Periodically, rats arouse spontaneously for brief intervals lasting 1–2 hours. Arousal involves rapid rewarming driven by brown fat thermogenesis, restoration of normal heart and respiratory rates, and brief feeding if food remains accessible. These intermissions prevent accumulation of metabolic waste and maintain tissue integrity.
The entire hibernation cycle, from onset of fat accumulation to final emergence in spring, may span several months. Successful completion depends on adequate pre‑hibernation nutrition, suitable shelter, and stable low temperatures that sustain the lowered metabolic state.