Mouse brain circuits separate pain responses from anxiety-like behavior
Experiments in mice separate the effects of two nerve pathways leaving the lateral hypothalamus. One pathway altered anxiety-like behavior and, when inhibited after nerve injury, reduced pain indicators. The other mainly changed responses to painful stimuli on the opposite side of the body. The findings concern neural circuits in animals, with no human treatment established.
Science··Morning
Two routes from the same region
Pain responses and anxiety-like behavior changed differently when researchers manipulated two brain pathways in mice. Both start in the lateral hypothalamus, a region involved in motivated behavior. Their destinations differ: a nucleus in the thalamus for one, the brainstem’s lateral parabrachial nucleus for the other. The peer-reviewed November 5 study used anatomical tracing, electrical measurements and light-based control of nerve activity to distinguish these pathways. Male and female mice supplied the evidence; the experiments do not establish a treatment for humans.[1]
Anxiety depends on the animal's condition
Activating the pathway to the thalamus increased anxiety-like behavior in healthy mice and in mice with experimentally induced nerve injury, without changing pain sensitivity. Inhibiting it had a different pattern: pain indicators and anxiety-like behavior fell in nerve-injured animals, while healthy animals showed no clear behavioral change. The researchers measured responses to mechanical and thermal stimuli alongside behavior in open-field and elevated-maze tests. These assays track observable animal responses rather than people's subjective descriptions of pain or anxiety.[1]
A separate effect on pain thresholds
The brainstem pathway mainly affected the opposite side of the body. Activating it increased sensitivity to painful stimuli in the contralateral paw. Inhibiting it raised pain thresholds in both healthy and nerve-injured mice, without clearly changing general anxiety measures. Additional experiments supported a local mechanism: the projection inhibits inhibitory nerve cells, allowing excitatory cells to become more active. The two pathways therefore showed different combinations of sensory and behavioral effects under the tested conditions.[1]
