Somatosensory properties of spinoreticular neurons in the cat

(1) Spinal cord neurons projecting to the brain stem were studied in cats prepared by decerebration or anesthetized with barbiturate or nitrous oxide and halothane. Antidromic stimulation from the medial pontomedullary reticular formation (MDRF) and midbrain (MB) was used to identify the site of projection. (2) Receptive fields were mapped using adequate stimuli. A variety of noxious stimuli was employed to establish the capacity of these neurons to transmit nociceptive input. (3) Neurons were found to project bilaterally to the MPRF. Of 46 units tested for a more rostral projection, only 13 were activated from the MB electrode. (4) Neurons fall into three categories based on receptive fields: cutaneous, restricted (SR); deep, restricted (DR); and complex, extensive (CE). All 16 SR neurons were located in the dorsal horn and had low thresholds to mechanical stimulation of the skin. Seven discharged maximally to nociceptive inputs. The 34 DR neurons were widely distributed in the spinal gray and responded to pressure upon subcutaneous structures. Although 13 neurons increased their firing rate as the stimulus intensity was increased into the noxious range, nociceptive input could only be established with confidence in 4 neurons. The 38 CE neurons were located ventrally in the spinal gray and had highly convergent inputs from cutaneous and deep receptors. Ten responded maximally to noxious stimulation.