Selective effects of kainic acid on diencephalic neurons.

Injections of kainic acid (KA) into the lateral hypothalamus (LH) produce neuronal loss in this region without apparent damage to medial forebrain bundle fibers passing through the area. Cellular destruction is not limited to the LH; the neuronal loss in the thalamic reticular nucleus, the subthalamic nucleus and zona incerta is more extensive than that in the LH. Since all of the nuclei of ventral thalamic origin except the ventral lateral geniculate nucleus (VLGN) were destroyed by LH injections of KA, we sought to determine whether this nucleus also is sensitive to KA. Injections directly into the VLGN produce total neuronal loss here as well as in the thalamic reticular nucleus, zona incerta and subthalamic nucleus. Other areas showing cell loss are the dorsal LGN, medial geniculate, lateral portion of the ventrobasal complex and midline thalamic nuclei. Injections of KA into medial hypothalamus adjacent to the suprachiasmatic nucleus produced no neuronal degeneration. In addition, no neuronal loss was noted in medial hypothalamic nuclei lying adjacent to areas of LH in which KA was injected. Therefore, the sensitivity of diencephalic nuclei appears to range from highly sensitive regions such as derivatives of ventral thalamus and midline thalamic nuclei to regions of moderate sensitivity such as the LH, geniculate nuclei and ventrobasal thalamic nucleus, to regions resistant to KA toxicity such as the suprachiasmatic nucleus and other nuclei and areas of medial hypothalamus.