Peripheral nerve injury evokes disabilities and sensory dysfunction in a subpopulation of rats: a closer model to human chronic neuropathic pain?

Chronic pain conditions for which treatment is sought are characterized usually by complex behavioural disturbances as well as pain. We review here evidence that although chronic constriction injury (CCI) of the sciatic nerve evokes allodynia and hyperalgesia in all rats, persistent social behavioural and sleep disruption occurs only in a subpopulation of animals. The finding that the 'degree of pain', as defined by allodynia and hyperalgesia, is the same in all animals suggests that the complex behavioural disabilities are independent of the level of sensory dysfunction.

Serotonin 5-HT2 and 5-HT1A receptors in the periaqueductal gray matter differentially modulate tonic immobility in guinea pig.

Tonic immobility (TI) is an inborn defensive behavior characterized by a temporary state of profound and reversible motor inhibition elicited by some forms of physical restraint. We have previously reported that cholinergic stimulation of the dorsal periaqueductal gray matter (PAG) decreases the duration of TI episodes, while stimulation of the ventrolateral region increases it. The ventrolateral PAG modulates this behavior via a similar neural circuit proposed to be involved in the antinociceptive system.

A subpopulation of rats show social and sleep-waking changes typical of chronic neuropathic pain following peripheral nerve injury.

Neuropathic conditions for which treatment is sought, the so-called chronic pain syndrome, are characterized usually by complex behavioural disturbances as well as pain. In this study we evaluated whether social behavioural and sleep disruptions occurred after nerve injury. Before and after chronic constriction of the sciatic nerve, resident-intruder and sleep-wake cycles, as well as mechanical and thermal allodynia/hyperalgesia, were quantified.