Neuronal populations in the spinal cord during ageing

The sensory and motor fibres of the spinal cord and the relative centres of integration were studied during ageing. Sections of spinal cord and ganglia from C8 to T12 of rats aged 6 and 24 months were treated using several techniques: Nissl, NADPH-diaphorase, and antibodies to enkephalins, substance P and neuropeptide Y. Nissl staining of the C8 segment showed that in the aged rat the dorsal horn was more oblique and narrow, the central canal was enlarged, the cellular density was reduced, and the neurons of the intermediolateral and ventral horns and of lamina IV were smaller. The total number of NADPH-diaphorase-positive cells of C8 segment was similar in the adult and in the aged rats. However, in the aged rat the number of cells was reduced in laminae I, II, III, VII and IX, remained the same in laminae V, VI and X, and was increased in laminae IV and VIII, and in the intermediolateral and intermediomedial horns. In the adult rat, we saw a greater number of cells with a lower expression of the enzyme. The area of the cells in laminae V and IX was reduced in the aged rat. In the C8 segment substance P was present in laminae I and II: in the aged rat the immunoreactivity was reduced and more diffuse. Enkephalins are present in laminae I, II and III, with a reduced immunoreactivity in the aged rat. NPY is present in the central canal in the adult rat and, is also present in laminae I and II in the aged rat.