c-fos expression after formalin injection into the face in the cat

Area of Science:

• Neuroscience
• Pain Research
• Molecular Biology

Background:

• The c-fos gene is a marker for neuronal activity.
• Understanding central nervous system (CNS) responses to pain is crucial.
• Previous studies have investigated pain pathways, but specific feline facial pain responses require further elucidation.

Purpose of the Study:

• To examine the expression of the c-fos gene in the CNS of cats following facial formalin injection as a pain stimulus.
• To identify specific brain regions activated by acute facial pain in a feline model.

Main Methods:

• Cats were subjected to formalin injection into the face (experimental group) or anesthesia only (control group).
• Immunohistochemistry was used to detect Fos-positive neurons, indicating gene expression.
• Brain sections were analyzed for labeled neurons in various CNS regions.

Main Results:

• Fos-positive neurons were observed bilaterally in the cerebral cortex (anterior cingulate, anterior insula), thalamic nuclei, hypothalamus, and brainstem in both groups.
• Distinctly, the experimental group showed Fos-positive cells in the primary somatosensory cortex (SI), secondary somatosensory cortex (SII), and trigeminal subnucleus caudalis.
• A significant increase in Fos-positive cells was noted in areas 24, 23, and the anterior agranular insular cortex in cats receiving formalin.

Conclusions:

• Facial formalin injection in cats induces c-fos gene expression in specific CNS areas related to pain processing.
• The findings highlight the activation of somatosensory and pain-related pathways, including SI, SII, and trigeminal nucleus caudalis.
• These results contribute to understanding the neurobiological basis of complex pain experiences and align with human PET findings, with noted differences in laterality.