Neurobiology最新文献

125-I-NGF was found to associate with embryonic chick dorsal root ganglia (DRG) through two processes. A time-saturable process included the binding of NGF to surface receptors with an apparent affinity constant in the range of 10(-7)M minus 1 and at a level of 4 f moles/mug tissue protein. The second process was time-linear, temperature-sensitive, and included both bound and non-competable NGF. While metabolic inhibitors had little effect, histone and insulin considerably increased the uptake. A comparison of 125-I-NGF and 125-I-peroxidase uptake suggested that the time-linear uptake of 125-I-NGF must include only bound NGF and incubation medium. Sequestration of the proteins taken up was indicated by the lack of release of radiolabeled material at 4 degrees C, even in the presence of native proteins. All these characteristics are consistent with an interpretation that DRG cells can take up NGF and other proteins by a pinocytotic process. Similar NGF binding and uptake properties were found to occur in cells from a variety of other embryonic chick tissues.

Cultures of chick dorsal root ganglia were examined with the scanning electron microscope. Fibroblasts, Schwann cells and neurites with their characteristic terminal filamentous growth cones were identified and their surface ultrastructure and inter-relationships described. Although exploratory filopodia of nerve growth cones were observed to pass both over and underneath the edges of wandering fibroblasts present at the periphery of the outgrowth, it was noted that the nerve bundles ultimately came to overlie sheets of fibroblasts. The neurites appeared generally bare along their lengths but were sometimes attached to the substrate or underlying fibroblastic sheet by small lateral projections. Some Schwann cells were observed to migrate freely between the neurites whilst others appeared to have wrapped around the nerve bundles in a manner suggestive of early myelination.

Explants of 10-12-day-old embryonic chick spinal cord were cultured for up to 20 days by the "coverslip-roller" method. Morphological development of neurons as shown by the presence of mature neurons, myelinated axons and synaptic structures, was demonstrated by light and electron microscopy. Two important enzymes associated with acetylcholine transmitter metabolism, choline acetyltransferase (ChAc) and acetylcholinesterase (AChE), were assayed in cultures at selected time intervals. The activity of ChAc and AChE exhibited an increase of 60 per cent and 80 per cent, respectively, over a 20-day period. It is concluded that organotypic cultures of embryonic chick spinal cord show differentiation not only in morphological aspects, but also in biochemical terms through progressive development of ChAc and AChE.

In order to determine the chemical changes which might occur during post-tetanic potentiation, amino acids from the motor regions of the ventral horn of the spinal cord (potentiated and unpotentiated sides) of 10 different cats were analyzed. The intermittent tetanic stimulation of the Nn. gastroc. (only on the potentiated side) was carried out until a maximum of potentiation was reached (3--4 min). The monosynaptic reflexes were obtained from the ventral roots (L7 or S1) of both sides. The amino acids of the potentiated side were compared to those of the unpotentiated side (control) using a 14-C-dansyl chloride procedure. The two main amino acids considered to be excitatory neurotransmitters, glutamic acid and aspartic acid, showed a more than 20 per cent increase on the potentiated side as compared to the control side. Glycine, which plays an inhibitory role, especially in the spinal cord, reacted with 6 per cent decrease, whereas GABA which is also considered as an inhibitory neurotransmitter showed a change of + 11 per cent on the potentiated side as compared to the unpotentiated side. The importance of the potentiation time for those changes is pointed out.

A morphologic study of the postnatal development of cerebellum in normal and pre- and postnatally undernourished rats was initiated in order to evaluate the effect of undernutrition. Defined areas of the cerebellar hemisphere were studied light-microscopically. Parallel to this study a histochemical investigation was performed on the same cerebellar areas (see part II). It was found that pre- and postnatal undernutrition causes a retarded outgrowth of the apical dendritic tree of the Purkinje cells. Furthermore, undernourished rats displayed a delayed persistence of the external granular layer and a retarded differentiation and migration of presumed basket, stellate and internal granular cells which is in accordance with previous studies on cerebellar development in experimental undernutrition.

Rat cerebral cortex neuronal nuclei were isolated by a mild technique utilizing sucrose; citric acid was not used in the isolation of the nuclei. These nuclei in 0.0145 M NaC1, 4.5 per cent sorbitol, and 0.6 mM NaHCO3 with pH 7.2 plus or minus 0.1 at 25 degrees C had an electrophoretic morbidity of minus 2.01 mum-s(-1)-V(-1)-cm(-1). The mobility curves for the brain nuclei indicated that the surface had an acid-dissociable group of pK APPROXIMATELY 2.7. Nuclei treated with 50 mg neurominidase/mg particle protein had a mobility of minus 1.4 mum-s(-1)-V(-1)-cm(-1). DNase or RNase at 50 mug/mg protein had no effect on the mobility of the isolated nuclei. Concanavalin A at 50 mug/mg protein decreased the nuclei electrophoretic mobility to minus 1.82 mum-s(-1)-V(-1)-cm(-1). The results are interpreted to mean that the brain nuclear external surface contains terminal sialic acid residues, but it is completely devoid of nucleic acids, and it binds canavalin A.

Dibutyryladenosine 3'-5' monophosphate (DBcAMP) induces ultrastructural transformations in clonal rat nerve and glia. Cells cultured in the presence of DBcAMP contain large numbers of aligned microtubules and microfilaments in their elongated processes, while control cultures without DBcAMP are relatively devoid of these structures. In addition, the cells exposed to DBcAMP contain 2000 A to 6000 A vesicles which are not observed in control cells.

The postnatal growth in diameter of corticospinal nerve fibres was studied in the medullary pyramid of the rabbit in order to make comparisons with the development of functional properties, which has been demonstrated by previous workers. During the first postnatal days the as yet unmyelinated fibres underwent a distinct increase in size. The first signs of myelin ensheathment were seen in 5-day-old animals, the ensheathed fibres varying between 0.4 and 0.7 mu in diameter. The growth in size of the largest myelinated fibres was more rapid during the second week and thereafter continued at a slower rate to a final size of 4--5 mu. The number of myelinated pyramidal fibres increased most rapidly during the first postnatal month and reached around 90,000 (unilaterally) in the adult. The vascular density initially increased, reaching a peak at 3 weeks and thereafter decreased. Comparison with physiological data showed that the initiation of myelination does not coincide in time with any striking decrease in response latency but rather seems to allow for a continued steady decrease. At a size of 3.5-4 mu the fibres appear to have attained the capability to follow rapid rates of stimulation.

The specific activity of the lysosomal glycosidase N-acetyl-beta-D-glucosaminidase was determined in Purkinje cell bodies and granule cells isolated in bulb from cerebella of 13-, 15- and 18-day-old rats, and somewhat higher values were found for the enzyme in the Purkinje cell bodies. Although the pH profile of N-acetyl-beta-D-glucosaminidase in both neuronal types was similar, the activity in the granule cells exhibited two "pH optima". The glycosidase could be readily solubilized from both neuronal types by repeated freezing and thawing and, upon sedimentation in sucrose density gradients, the solubilized activity appeared as two distinct molecular components. The findings demonstrate the feasibility of detailed and direct comparative studies of neuron-specific patterns of enzymatic development and the excellent suitability of bulk-isolated cells for this purpose.