The postnatal metabolic development of the nucleus commissuralis and nucleus medialis of the nucleus tractus solitarius

Maturation of kainic acid seizure-brain damage syndrome in the rat. I. Clinical, electrographic and metabolic observations

The maturation of the seizure/brain damage syndrome produced by parenteral administration of kainate was studied in the rat. The motor, electrographic and metabolic alterations are described in the present report, the maturation of the pathological abnormalities and of the specific kainate binding sites are described in the two following companion papers. Parenteral kainate produces tonico-clonic seizures until the end of the third week of age when limbic motor signs (wet-dog shakes, facial myoclonia, paw tremor etc.) were first produced. Using the 2-deoxyglucose autoradiographic method, we found that in animals of 3 days of age and until the third week of age, kainate produced a rise in metabolism restricted to the hippocampus and lateral septum. This was paralleled by paroxysmal discharges which were recorded in the hippocampus. Starting from the end of the third week of age approximately--i.e. when the toxin produced limbic motor seizures--there was a rise of labelling in other structures which are part of or closely associated to the limbic system i.e. the amygdaloid complex, the mediodorsal and adjacent thalamic nuclei, piriform, entorhinal and rostral limbic cortices and areas of projection of the fornix. These metabolic maps are thus similar to those seen in adults. Two main conclusions can be drawn from these experiments: kainate activates the hippocampus from a very early age probably by means of specific receptors present in this structure and the limbic syndrome will only be produced by the toxin once the limbic circuitry--including in particular the amygdaloid complex--is activated by the procedure i.e. after the third week of age.

Kainic acid seizure syndrome and binding sites in developing rats

In rats up to 16 days after birth, parenteral kainic acid (KA) produced tonico-clonic convulsions, metabolic activation limited to the hippocampus, and no brain damage. Starting with the 19th day after birth, KA produced limbic seizures associated with metabolic activation and subsequent damage in the hippocampus, the amygdala, and other limbic structures. Membranes prepared from hippocampi 10 days after birth bound [3H]KA with a high affinity component, which was localized in the mossy fiber region by slice autoradiography. In contrast, on amygdaloid membranes this component appeared only 17-19 days after birth. Our results further stress the crucial role of the amygdala in the KA seizure syndrome.

The development of two subnuclei of the nucleus tractus solitarius in spontaneously hypertensive rats

Changes in relative metabolic requirements and neuronal densities in the nucleus commissuralis (NC) and nucleus medialis (NM) of the nucleus tractus solitarius were studied in spontaneously hypertensive rats (SHR) during development. The changes in relative metabolic requirements in the two subnuclei of SHR between 2 and 12 weeks of age were similar to those previously reported for normotensive WKY at the same ages. However, the relative metabolic activity in the NC of 2- and 4-week SHR was significantly higher than in normotensive rats. The differences in metabolic requirements of the NC could not be explained by differences in the neuronal densities of this subnucleus in young SHR and may reflect abnormalities in developmental or functional activities in the pre-hypertensive rat. Neuronal densities in the NC of 8- and 12-week SHR and in the NM of 4-, 8- and 12-week SHR were significantly higher than in WKY controls. Differences in the neuronal densities in the NC and NM of SHR may be explained by a smaller brain size characteristic of this strain, but differences in the NC of SHR suggest that the alterations may underlie or result from the cardiovascular abnormalities associated with the spontaneous hypertension of this strain.