By collecting the results of research from different laboratories it has been possible to picture the probable sequence in which the nervous system develops in certain mammalian species. As the present report is to be referred to current conceptions of the development of the nervous system, special attention will be pain to comparative aspects of the question. Mammalian forms vary greatly in degree of maturity at birth, ranging from the fetus-like newborn rat to the highly mobile, almost self-sufficient, guinea-pig. As identical sequences of development will be demonstrated in both categories of mammals attention will be devoted to discussing the criteria which condition our trusting this sequence of development. Lastly, Man will be considered. It is not easy to decide whether man is a true altricial species or in what sense he can be considered as a special case of precocial species. This point is discussed: Man is altricial from the motor point of view. He is precocial from the sensory point of view and sleep develops during embryonic life in this species.

Age Factors↗

PubMedDate not supplied

[Functional maturation of the somatosensory neocortex S1 in the rat. Electrophysiological and histochemical study (author's transl)].

The functional maturation of the somatosensory neocortex has been studied using the projection areas of the whiskers. Natural stimulation of the whiskers evokes global potentials and unitary responses from the 4th postnatal day on. From the 2nd postnatal week the characteristics of the unit responses approximate in latency, topographic organisation of the projections, coding of the directions and temporal characteristics of the stimulation those of the adult. The histochemical activity of succinyl dehydrogenase is demonstrated in layer IV a little before the first electrophysiological response but the typical massed organisation is only seen from the 5th postnatal day. During maturation optical densitometry shows a rapid rise in enzyme activity untill the 7th postnatal day then a slower rise up to the 21st day after which it stabilises.

Aging↗

PubMedDate not supplied

Cortical organization of the postero-medial barrel-subfield in mice and its reorganization after destruction of vibrissal follicles after birth.

The postero-medial barrel-subfield (PMBSF) of the SI cortex of normal adult mice contains clusters of cells called "barrels". Each barrel histochemically shows increased activity of succinate, lactate, and glucose-6-phosphate dehydrogenase and also GABA-T activity. Some neuronal perikarya in the barrel walls show GABA-T activity. Mitochondrial alpha-GPDH and AChE show equal activities in the hollows and in the walls of the barrels. On this cortical vibrissa field, the contralateral and ipsilateral vibrissae project somatotopically in a way which coincides with the barrels. The mystacial vibrissae and the common fur of the muzzle project to different loci. The cortical surface area for the normal fur is 0.025 mm2, whereas the cortical vibrissal area is 1.0 mm2. In mice with lesioned whisker pads the succinate-dehydrogenase activity of the IVth layer in the vibrissal area becomes a continuous sheet similar to the adjacent IVth layer, the thickness of the cortex is relatively preserved, and the total enzyme activities, biochemically assayed, are unchanged. These features can be explained by a functional substitution. In mice with whisker pads lesioned since birth, the vibrissal area can still be identified by the projections from ipsilateral vibrissae (undamaged side). This vibrissal area, and this alone, is found to be invaded by projections from the contralateral common fur of the muzzle. Experimental data suggest that the compensatory process may result from an invasion of the vibrissal area by a new set of ascending fibers, and not merely from axonal sprouting either at the periphery or at the cortical level.

4-Aminobutyrate Transaminase↗

PubMedDate not supplied