11: Cingulate Noradrenaline Release Scales With Pain Behaviour Across the Rat Oestrous Cycle

Topic: Basic Science
Subtopic: Non-specific to any diagnosis (including studies in healthy animals), Assessment and Measurement of Pain/Nociception, Animal imaging (includes Ca2+ imaging, fluorescence microscopy), Behavioral studies

Background and Aims: Noradrenaline is a key neuromodulator in pain processing and acts across the central nervous system, including the anterior cingulate cortex (ACC). The ACC is important in the affective component of pain. ACC noradrenaline levels increase in response to noxious stimuli (1)(2). In rodents, pain affect is reflected in pain-related coping behaviours following noxious stimulation, such as paw licking. Pain sensitivity fluctuates across the rodent oestrous cycle(3); however, how these behavioural changes relate to ACC noradrenergic signalling is poorly understood. Defining how ACC noradrenaline dynamics vary with pain behaviours and ovarian hormones may provide new insight into sex-specific mechanisms of pain.

Methods: Adult female rats (n= 10, 170–200g) received noxious thermal stimuli of pseudorandomised intensities (2.0–2.75 J) delivered to the hind paw using an Nd:YAP infrared laser. The protocol was conducted across 5 consecutive days and the oestrous cycle was tracked. Pain-evoked behaviours were scored into five categories (0-4) where a higher score corresponded to a greater degree of pain-related behaviour. In vivo noradrenaline release in the ACC was recorded using GRAB-NE1m fibre photometry(4). Pain behaviours and noradrenergic signals were analysed for scaling relationships, and all data were subsequently grouped according to oestrous cycle stage.

Results: Pain behaviour varied across the oestrous cycle, with animals in the proestrus phase consistently displaying higher pain behaviour scores than those in oestrus or dioestrus at all laser intensities. ACC noradrenaline release scaled proportionally with pain behaviour regardless of laser intensity. The greatest noradrenergic response was seen when animals engaged in prolonged grooming of the stimulated paw. This graded increase in noradrenaline release was evident across all oestrous cycle phases. Additionally, during the proestrus phase, there was more sustained elevation in ACC noradrenaline following the noxious stimulus.

Conclusions: These findings demonstrate that ACC noradrenergic release scales with pain-related behaviour independent of laser intensity. Noradrenaline levels are highest when animals display sustained coping behaviours that reflect the affective dimension of pain, consistent with the established role of the ACC in processing pain affect rather than sensory intensity. Pain behaviour is consistently elevated during proestrus, and the sustained elevation of noradrenergic release during this phase suggests a modulatory influence of oestrous state on pain-evoked noradrenaline. These results highlight ACC noradrenaline as a neural marker of affective pain behaviour and reveal oestrous cycle–dependent modulation of pain-related noradrenergic dynamics.

References: Reference List

1. Johansen JP, Fields HL. Glutamatergic activation of anterior cingulate cortex produces an aversive teaching signal. Nature Neuroscience. 2004;7(4):398-403.
2. Koga K, Yamada A, Song Q, Li XH, Chen QY, Liu RH, et al. Ascending noradrenergic excitation from the locus coeruleus to the anterior cingulate cortex. Mol Brain. 2020;13(1):49.
3. Averitt DL, Hornung RS, Murphy AZ. Role of Sex Hormones on Pain. Oxford University Press; 2019.
4. Feng J, Zhang C, Lischinsky JE, Jing M, Zhou J, Wang H, et al. A Genetically Encoded Fluorescent Sensor for Rapid and Specific In Vivo Detection of Norepinephrine. Neuron. 2019;102(4):745-61.e8.

Presenting Author: Annie McShane
Submitting Author: Annie McShane

Senior Author: Dr Robert Drake

IASP 2026 Global Year theme of Neuropathic Pain: No