FUNCTIONAL RELATIONSHIPS BETWEEN NEURONS OF MARGINAL AND SUBSTANTIA GELATINOSA LAYERS OF PRIMATE DORSAL HORN

The purpose of this study was to examine the functional role of substantia gelatinosa neurons in the transmission of nociceptive and nonnociceptive input to spinothalamic neurons in the marginal layer of the spinal cord dorsal horn. One hundred thirty neurons in layer I (marginal layer) and Rexed's layer II (substantia gelatinosa, subdivided into an outer zone, a, and an inner zone, b) of L7-S1 were studied in rhesus monkeys lightly anesthetized with sodium pentobarbital. The response properties of 51 pairs of neurons recorded successively in the same microelectrode track were compared; the dorsal neuron of each pair was a layer I spinothalamic or nonprojection neuron and the ventral neuron, located with 200 μm, was a layer II neuron. The location of all neurons in layer II was determined histologically from small lesions made at the sites of maximum spike amplitudes. In addition, an anatomical analysis of common neuron types and their connections in layers I and II was performed using the Golgi method.