No abstract

Rats of the BD III strain were injected with a single dose of 3H-thymidine on either the twelfth, fourteenth, sixteenth, eighteenth or twentieth day of gestation (ED 12. . . . .ED 20) or on the postnatal day one, three, or seven. Animals were killed at age 22 to 24 days. DNA synthesis, as an indicator of cell division, was studied in matrix precursors of nerve and glial cells in the visula centers, including the lateral geniculate body (LGB), the superior colliculus (SC) and the visual cortex (VC). It was found that proliferation of matrix precursors of nerve cells destined for all the regions studied was in progress on ED 12. In the subcortical regions (LGB, SC) this process was substantially more advanced than in the VC. The first neuroblasts appeared in the SC (ED 12) and only later (ED 14) in the LGB and VC. In comparison with the LGB, VC neuroblasts were quite rare on ED 14 and were present only in layer VI. They appeared more frequently in this region only after injection of isotope on ED 16. Matrix cell proliferation and nerve cell formation ceased in the LGB between ED 16 and ED 18. The number of labeled cells arising after injection of the isotope on ED 16 indicates that neurogenesis ceased somewhat earlier in the dorsal nucleus of the LGB than in the ventral. In the SC the last neurons arose between ED 18 and ED 20, and in the VC, with the possible exception of a few granular neurons (which may continue division into the first few days postnatally), proliferation continued until the end of gestation. The origin of neuroblasts initially followed a caudo-rostral gradient. Later, the times of neurogenesis in the regions studied overlapped significantly. This is clear, for example. on ED 16, when neurogenesis in the mesencephalic SC continued for about two days longer than in the more postral LGB, and coincided with that in the VC, especially in the deep layers. The end of neurogenesis in the LGB, especially in the ventral nucleus, coincided with the time of neurogenesis in the deep cortical layers. In the VC, and partly also in the SC, an inside-out pattern of proliferation and neuron formation was confirmed. The times of proliferation of precursor cells, with the exception of the very end of neurogenesis, substantially overlapped within both these regions. The degree of this overlapping, described in terms of Labeling Index values, decreased towards the end of the neurogenetic period. Division of neuroglial cell precursors, started as early as on ED 14 in/for subcortical centers (LGB, SC), but not until ED 18 in/for the VC. A few labeled endothelial-like cells were observed in all regions studied after isotope injection on ED 12.

To test the hypothesis that cortical reorganization depends on acetylcholine and one or more of the monoamines, the hindpaw cortex was mapped in eight different groups of mature rats: (1) untreated; (2) after sciatic nerve transection; (3) after intraperitoneal injections of reserpine, to reduce the level of cortical monoamines; (4) after ibotenic acid lesion of the nucleus basalis of Meynert (NBM), to destroy cholinergic cells projecting to the cortex; (5) after reserpine treatment and transection; (6) after ibotenic acid lesion and transection; (7) after reserpine treatment and ibotenic acid lesion; and (8) after reserpine treatment, ibotenic acid lesion, and transection. Four days after transection, the cortex had reorganized in the transected group. However, this process of reorganization was prevented in transected animals with NBM lesions. Treatment with reserpine alone did not inhibit the process of reorganization, nor did it enhance the effect of NBM lesion. Nonetheless, the animals treated with reserpine and transected had higher response thresholds in the reorganized cortex than did the animals that were treated but not transected. These data suggest that acetylcholine plays an important role in the early reorganization that follows deafferentation, and that one or more of the monoamines may have other influences on reorganization of the primary somatosensory cortex of adult rats.

Graded hypoxia (FETo2 14-6%) and hypercapnia (FETC2 6-10%), which were applied for 45 s and 2 min, respectively, to urethane anesthetized and artificially ventilated rats produced an increase in adrenal sympathetic efferent nerve activity in parallel with increases in adrenaline and noradrenaline secretion measured in the adrenal venous effluent. Percentage increases in adrenaline and noradrenaline were almost equal. In rats whose carotid sinus nerves (CSN) were bilaterally cut, hypoxia did not produce any effect on adrenal sympathetic nerve activity or catecholamine secretion. In contrast, excitatory adrenal nerve and catecholamine secretory responses to hypercapnia remained unchanged in CSN denervated rats. After severing a splanchnic nerve whose branches innervated the adrenal gland, while maintaining the resting level of catecholamine secretion by low-frequency stimulation of the peripheral end of the splanchnic nerve, hypoxia did not produce any increase in catecholamine secretion. Hypercapnia (FETCo2 8 and 10%), however, induced catecholamine secretion from denervated adrenal medulla, although the magnitude of the response was significantly lower than that in animals with adrenal nerve intact. It is concluded that hypoxia stimulates the adrenal medulla via the carotid chemoreceptor reflex whereas hypercapnia acts mainly via mechanisms besides carotid chemoreceptors such as central chemoreceptors with some direct stimulatory effect on the adrenal medulla. The functional significance of these dual mechanisms of sympathoadrenal excitation during hypoxia and hypercapnia is discussed.

No abstract

Changes in the glycogen content and patterns of deposition in the developing rat brain were studied using a light microscopic periodic acid-Schiff method on embryonic days (ED) 14, 16, 18, 20 and postnatal days (PD) 1, 3, 7, 12, 16 and 21. Regional and temporal differences were quantified with an automatic image analyser by estimation of stained material in subpial regions of cerebral cortex, thalamus, superior colliculus and medulla. The cellular localization of glycogen particles was investigated by electron microscopy on ED 18, ED 20 and PD 2. On ED 14 the first signs of glycogen storage were found in parts of the immature choroid plexus and in radial glial cells in the midbrain and medullary raphé. With advancing foetal age these structures retained their high capacity for glycogen storage but, in addition, an increasing number of radial fibres in most of the brain stem regions and in the cerebral cortex of older foetuses (ED 18-20) showed significant amounts of glycogen. The storage of glycogen in cerebral cortex was relatively low at all foetal age intervals studied. In new born animals the distribution of glycogen particles was similar to that found in the late foetal brain. A decrease of glycogen content commenced from PD 1 to 3 and reached the pattern of the adult brain between PD 7 and 21. Glycogen storage by radial glial cells in the developing rat brain might indicate their possible role as an energy source in perinatal carbohydrate metabolism.

No abstract

Electrophysiological recordings were made at a large number of sites in the primary somatosensory cortex of six anesthetized raccoons. A high density of penetrations (110-229 per animal), within or near the representation of the fourth digit, allowed identification of three cortical regions with different physiological properties: a glabrous zone, containing a highly detailed, somatotopically ordered representation of the glabrous surface of the digit; rostral to this a claw-dominant zone, in which the neurons at most penetrations respond to stimulation of the claw of the fourth digit, but may also receive input from the hairy skin or surrounding glabrous skin; and a more rostral multidigit zone, in which the neurons respond to stimulation of two to five digits, with the dominant digit usually being the one represented caudally (i.e., the fourth digit at most of the sites sampled here). Claw-dominant zones with receptive fields restricted to digit three or five are also found rostral to the representations of the glabrous skin of the corresponding digit. The glabrous and claw-dominant zones constitute a complete map of the fourth digit. The multidigit region presumably is a separate map, since its neurons have different spatial convergence, higher thresholds, and a lower incidence of slowly adapting inputs than those in the claw-dominant and glabrous zones. A comparison between animals with lesions of the basal forebrain and intact animals found no differences in the organization of these zones or in the responses to peripheral input, suggesting that cholinergic inputs to the cortex are not essential to these properties. The detailed description of these regions and the proposed terminology should resolve some inconsistencies in the use of the term "heterogeneous zone" in this species.