Cingulate cortex stimulation drives distinct pupillary responses in rat via recruitment of noradrenergic neurons in the locus coeruleus

The organization of the cingulate cortex has been the subject of intensive studies, concluding to its central role in motor control, cognition, and arousal. One of the key anatomical pathways through which the cingulate cortex influences behavior is its efferent connection to the locus coeruleus (LC). This brainstem region is responsible for noradrenaline (NA) release and is critical for various cognitive and behavioral functions. However, the specific impact of cingulate subregions on the LC-NA system remains unexplored. This study investigated how the different cingulate cortex areas affect LC-NA activity by measuring pupil-evoked responses (PERs) as an index of LC-NA activity. Using intra-cortical stimulation across the eight cingulate areas in rats, we found that anterior cingulate cortex and midcingulate cortex subregions evoked rare autonomic responses but significant pupil dilations whose amplitude increased along the caudo-rostral and dorso-ventral axes. By using the DSP-4, a neurotoxin-selective ablation of the LC-NA system, we suppressed PER and confirmed the role of LC-NA activity in this response. The differential influence of cortical areas on the PER demonstrates that each subregion of the rat cingulate cortex has the potential to differentially activate the LC-NA system, suggesting a clear parcellation of the rodent cingulate cortex, likely corresponding to functional specialization.