Activation of substantia nigra pars reticulata neurons: role in the initiation and behavioral expression of kindled seizures.
Numerous studies have implicated the substantia nigra pars reticulata (SNR) in the initiation and behavioral expression of kindled seizures. In immobilized, amygdala-kindled animals, SNR neurons have been shown to enter an intense burst-firing pattern during afterdischarge (AD). Taken together these findings raised the possibility that the SNR facilitates the expression of kindled seizures by directly propagating seizure activity into target structures. In this study we examined the relationship between activation of SNR neurons and the electrical (EEG) and behavioral (clonic motor) expression of kindled seizures using both immobilized and unrestrained animals. The principal findings were that: (1) in both immobilized and unrestrained animals the SNR neurons of kindled, but not control, animals were recruited into a burst-firing pattern during AD; (2) the onset of burst-firing was delayed until after the onset of AD; and (3) the onset of burst-firing was not correlated with the onset of rhythmic motor seizure activity. These findings support the idea that the development of kindling is associated with recruitment of SNR neurons into a seizure propagating network. However, these data suggest that activation of SNR neurons is not necessary for the expression of clonic motor activity and does not lower seizure threshold.