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GM1 ganglioside, thyroxine and hydrocortisone were tested for their ability to improve the survival and growth of fetal locus coeruleus noradrenergic neurons in the transected, adult spinal cord. GM1 alone was also tested for its effect on fetal mesencephalic dopaminergic neurons implanted into a small dorsolateral cavity at the L2 region of the cord previously transected at the T9-T10 region. None of the substances tested had any measurable effect on either of the fetal implants. However, in the GM1- and thyroxine-treated animals the somatic dendrites of the axotomized, noradrenergic, coerulospinal neurons appeared more robust, and more intensely fluorescent, compared to their appropriate controls. GM1 also caused a pronounced sprouting of the axotomized monoaminergic (catecholaminergic and serotonergic) fibres in the rostral region of the cord adjacent to the transection site. All of the mesencephalic dopaminergic implants survived in both the GM1-treated animals and their saline-injected controls. However, their development was apparently not influenced by GM1. The results indicate that GM1 and thyroxine can enhance those aspects of the reactive mechanisms of mature, axotomized, noradrenergic coerulospinal neurons that promote their regeneration. As such, GM1 could become a useful tool in current attempts to foster the regeneration of damaged monoaminergic neurons in the mammalian CNS.

The development of the optic tectum and the establishment of retinotectal projections were investigated in the quail embryo from day E2 to hatching day (E16) with Cresyl violet-thionine, silver staining and anterograde axonal tracing methods. Both tectal cytodifferentiation and retinotectal innervation occur according to a rostroventral-caudodorsal gradient. Radial migration of postmitotic neurons starts on day E4. At E14, the tectum is fully laminated. Optic fibers reach the tectum on day E5 and cover its surface on day E10. 'Golgi-like' staining of optic fibers with HRP injected in vitro on the surface of the tectum reveals that: growing fronts are formed exclusively by axons extending over the tectal surface; fibers penetrating the outer tectal layers are always observed behind the growing fronts; the penetrating fibers are either the tip of the optic axons or collateral branches; as they penetrate the tectum, optic fibers give off branches which may extend for long distances within their terminal domains; the optic fiber terminal arbors acquire their mature morphology by day E14. The temporal sequence of retinotectal development in the quail was compared to that already established for the chick, thus providing a basis for further investigation of the development of the retinotectal system in chimeric avian embryos obtained after xenoplastic transplantation of quail tectal primordia into the chick neural tube.

The neuronal properties of separate dissociated cell cultures of dorsal and ventral halves of the embryonic mouse spinal cord (E 13.5) were investigated. Ventral-half cultures grew on a variety of substrates and in a variety of media; dorsal-half cultures required a non-neuronal feeder layer and supplemented medium for survival. The two types of cultures differed in their morphological and biochemical properties. Ventral-half neurons remained well separated on the culture plate, whereas dorsal-half neurons tended to aggregate. Lucifer yellow fills showed that ventral-half neurons were substantially larger and had more processes than dorsal-half neurons. Because of the large size and good separation of the neurons, ventral-half cultures provide an especially attractive system for electrophysiologic and morphologic studies. Ventral-half cultures were highly enriched for choline acetyltransferase (ChAT) activity and had more neurons that stained for intracellular acetylcholinesterase (AChE); dorsal-half cultures were enriched for glutamic acid decarboxylase (GAD) activity, and high-affinity gamma-aminobutyric acid (GABA) uptake. The clear differences between the two cultures indicate that many morphological and biochemical properties are already specified on embryonic day 13.5.