Morphological and electrophysiological properties of ACCx nociceptive neurons in rats.

A total of 33 neurons with cutaneous receptive fields were recorded from the anterior cingulate cortex (ACCx) and successfully injected with neurobiotin. All neurons were in area 24 of the ACCx. Neurons from the ACCx had large receptive fields (RFs), usually bilateral, and some had RFs covering the whole body surface. Most of the neurons were in the deep laminae and had a pyramidal soma with thick apical dendrites and many spines. Thirteen of 33 neurons were classified as pyramidal nociceptive specific (NS) neurons and 12 as noxious-tap neurons, 3 neurons received inhibitory input and were in lamina V. Two non-pyramidal noxious-tap neurons were located in lamina V and 1 pyramidal noxious-tap neuron was located in lamina VI, and 2 pyramidal NS neurons were in lamina III. Axon collaterals of NS neurons were mainly distributed around the soma, whereas those of noxious-tap neurons were also distributed far from the soma. A large number of varicosities were observed on the axon collaterals of both NS and noxious-tap neurons. Our results suggest that NS neurons in the ACCx send information locally to the vicinity of the soma, while noxious-tap neurons send information to a wider area of the ACCx.