Fimbria Fornix Research Articles

The effect of intrahippocampal kainic acid injections and surgical lesions on neurotransmitters in hippocampus and septum.

AbstractLocal injection of kainic acid (2 μg) was accompanied by destruction of intrinsic neurons in the dorsal part of hippocampus. The lesion was accompanied by a 75% reduction in glutamate decarboxylase activity, a 60% reduction in the high affinity uptake of l‐glutamate, a 40‐60% reduction in the endogeneous levels of aspartate, glutamate and GABA and no changes in the activities of choline acetyltransferase or aromatic amino acid decarboxylase in the dorsal hippocampus. Unilateral destruction of neurons in the dorsal hippocampus was followed by a 20‐40% reduction in the high affinity uptake of glutamate in lateral, but not in medial septum, on both sides. There was no reduction in choline acetyltransferase, glutamate decarboxylase or aromatic amino acid decarboxylase activities in the lateral or medial part of the septum. Transection of fimbria and superior fornix was accompanied by a severe reduction in choline acetyltransferase and aromatic amino acid decarboxylase activity in hippocampus, in the high affinity uptake of glutamate and in the endogenous level of glutamate in the lateral septum. The results are consistent with the concept that in the hippocampus kainic acid destroys intrinsic neurons and not afferent fibres. It seems therefore that all GABAergic fibres in the hippocampus belong to intrinsic neurons whereas glutamergic and aspartergic neurons belong partly to local neurons. The connection from the hippocampus to the lateral septum probably uses glutamate as a transmitter.

Commissural projection to the amygdala thourgh the fimbria fornix system in the cat.

Single shock stimulations have been applied stereotaxically and bilaterally in the region of the caudo-thalamic groove of the cat. These stimulations elicit diphasic potentials in the amygdala. Using combined methods of stimulation and lesion, it has been demonstrated that these electrical responses are due to the excitation of fibers projecting rostrally in the lateral border of the contralateral fimbria and caudally in the homologous part of the homolateral fimbria. A commissural path has been identified in the rostral part of the fimbria-fornix. Analysis of the experimental data has shown that the projection system consists of a discrete bundle of fibers which probably reaches the amygdala directly, in the dorsal part of the basal nucleus. The length of the explored portion of this pathway has been measured. The calculated conduction velocity of this amygdalopetal commissural component of the fimbria is 4.5 m/sec.

Histochemical mapping of the distribution of monoamine oxidase in the diencephalon and basal telencephalic centers of the brain of squirrel monkey ( Saimiri sciureus)

The activity of monoamine oxidase (MAO) was mapped at the macroscopic level using 50 μ thick fresh frozen sections arranged in a caudo-cranial series of sections through the diencephalon and basal telencephalic centers of the squirrel monkey brain. The various thalamic nuclei show a mild MAO reaction except the nuclei periventricularis and para- and subfascicularis, which show moderate MAO reaction. The hypothalamus, in general, shows a stronger MAO reaction than the thalamus, because of its involvement in various autonomic functions. The nuclei paraventricularis, supraopticus and ventromedialis hypothalami are particularly prominent because of the stronger MAO activity they show in contrast to other hypothalamic areas. The nucleus caudatus, putamen and globus pallidus show mild to moderate MAO activity. The fiber bundles of fimbria hippocampi, fornix, anterior commissure and internal capsule show a moderate to moderately strong MAO reaction. The nuclei of the amygdaloid complex differ little from one another and show negligible to mild MAO activity. The nuclei dorsalis, medialis and lateralis septi show a mild MAO reaction compared to the moderate activity in the nuclei fasciculi diagonalis Brocae and triangularis septi.