Activation of the locus coeruleus after amygdaloid kindling

Purpose: Substnatia nigra (SN) and locus coeruleus (LC) neurons are implica ted in the propagation and suppression of amygdaloid seizures. Both structu res are activated concomitant with amygdaloid seizure discharges. Their mec hanisms of activation, however, remain to be elucidated. SN firing is not a ssociated with the induction of Fos immunoreactivity (ir), a marker of exci tatory neuronal activation. LC has not been studied. The purpose of this in vestigation was to determine if amygdala-kindled generalized seizures could induce Fos-ir in the LC. Methods: Female Sprague-Dawley rats were killed after generalized seizures induced by amygdala electrical stimulation and stained by using Fos immunoc ytochemistry. The number of Fos-ir neurons was compared between 15 animals with generalized seizures and four implanted, unstimulated controls. Results: LC-ir neurons were significantly (p < 0.05) more prevalent after s eizures than in control animals. Their numbers correlated very highly with Fos-ir in the central nucleus of the amygdala (p < 0.0001). No Fos inductio n was observed in LC in controls or in the SN in either group. Conclusions: Amygdala-induced generalized seizures result in Fos-ir in the LC but not in the SN. This is consistent with different mechanisms of activ ation possibly involving disinhibition in the SN and direct excitation in t he LC.