A method for determining the distribution of lithium in whole brain sections by use of 6 Li(n, ) 3 H reactions and radiographic dielectric track registration techniques

A method for demonstrating the distribution of lithium in whole brain sections of the rat by using radiographic dielectric track registration techniques is described. The method essentially involves freeze-drying coronal sections, overlaying them with dielectric films sensitive to alpha particles, bombarding the tissue and film with thermal neutrons and chemically etching the lithium (6Li(n,α)3H) tracks in the films. The tracks in the film are superimposed on the tissue and the distribution of the lithium is delineated by the alpha particle tracks. The method is extremely sensitive and suitable for any tissue where lithium-induced tracks are significantly greater than the background and should be useful in elucidating some of the biologic properties of lithium.

The response of ventral horn neurons to axonal transection

The morphological changes induced in the frog ventral horn neurons by axonal transection have been studied with the electron microscope. During the first 2 wk after axotomy the neuronal nucleus becomes more translucent and the nucleolus becomes enlarged and less compact. The cisternae of the granular endoplasmic reticulum vesiculate and ribosomes dissociate from membranes. Free ribosomes and polysomes are dispersed in the cytoplasmic matrix. Neurofilaments and neurotubules are increased in number. These structures appear to be important in the regeneration of the axon. It is proposed that neurotubules, neurofilaments, and axoplasmic matrix are synthesized by the free polyribosomes in the chromatolytic neuron. By the fourth postoperative week, the neurons show evidence of recovery. The cytoplasm is filled with profiles of granular endoplasmic reticulum and many intercisternal polysomes. The substances being manufactured by the newly formed granular endoplasmic reticulum are not clearly defined, but probably include elements essential to electrical and chemical conduction of impulses. The significance of these observations in respect to recent studies of axoplasmic flow is discussed.

Studies on the phrenic nerve and diaphragmatic plexus in rabbits and gerbils

Studies on nerve fibres within the phrenic nerve and in the diaphragmatic plexus were carried out in one species, the gerbil, a small desert rodent. The resistance of this small mammal to surgical insult enabled experimental intrathoracic transection of the phrenic nerve to be carried out so that the results in 10 animals could be observed within the diaphragmatic plexus, the phrenic nerve, and the phrenic nucleus. The findings in the diaphragmatic plexus and in the nerve trunk strongly resemble corresponding results for other animals with regard to `persisting' fibres. The phrenic nucleus, however, is much more extensive in this mammal than has been found in any other species; it is represented within the second to sixth cervical segment, its rostral extremity occupying the intermediolateral part of the spinal grey matter. The possible functional significance of these findings is discussed in the light of the mixed functions of the diaphragm, either voluntary or involuntary.