The effect of chronic undernourishment on the synaptic depression of cutaneous pathways in the rat spinal cord

The aim of this study was to determine the effect of chronic undernourishment on the amplitude depression of the first negative component in the cord dorsum potentials (N1-CDPs) caused by the conditioning stimulation of sensory cutaneous nerves in the rat spinal cord. Single electrical pulses (1 Hz; 2 times threshold) applied to the sural (SU) nerve of control rats (n = 14) produced CDPs with a first negative component (N1-CDPs) larger in amplitude (14.2 ± 1.3%, p < 0.01) than those recorded in chronically undernourished rats (n = 14; 3 times threshold). The conditioning stimulation of the SP nerve (4 shocks at 300 Hz, 3 × T) in the control rats (n = 5) evoked a long-lasting (∼200 ms) depression of the N1-CDP (60.2 ± 7.2%). In contrast such depression was smaller in magnitude (42.5 ± 5.7%, p < 0.01) and time course (100–120 ms) in undernourished rats (n = 7). The systemic application of picrotoxin (PTX) reduced, but did not abolish the conditioned depression of the N1-CDPs and DRPs in both the control and undernourished rats. By assuming that the depression of the N1-CDPs is representative of presynaptic mechanisms, it is proposed that chronic undernourishment influence the activation of presynaptic neuronal pathways that regulate the transmitter release of cutaneous afferent fibers in the spinal cord and such effect could act as a compensatory mechanism that counterbalances the decreased activation of spinal neurons by the reduced afferent input in the rat.

► Undernutrition reduced the depression of cutaneous cord dorsum potentials. ► Picrotoxin reduced the depression of control and undernourished N1-CDPs and DRPs. ► Undernutrition depressed the spinal mechanisms generating presynaptic inhibition. ► This effect is considered as a compensatory mechanism against undernutrition.