The abilities of embryonic and adult rat sensory neurons to regenerate were compared when cultured on cryostat sections of normal and lesioned sciatic nerve tissues. Differences in neurite growth, visualized by GAP-43 immunolabelling, were most pronounced on substrata consisting of longitudinal sections of normal versus predegenerated sciatic nerve. Adult dorsal root ganglion (DRG) neurons grew only on the lesioned nerves. Neurites extended along these sections in a characteristically longitudinal orientation, and this growth was not dependent on nerve growth factor. Embryonic DRG neurons extended neurites on sections from both types of nerves. These results highlight important differences in the regenerative abilities of embryonic and adult DRG neurons when grown on physiologically appropriate substrata.

Undernutrition during early life is known to affect the morphology of the hippocampal formation. Recent advances in stereological techniques have made it possible to make relatively unbiased estimates of total cell numbers in well-defined brain regions. It was decided to use these methods to determine the effects of different levels of undernutrition during early postnatal life on the granule cells of the rat dentate gyrus. Male hooded Long Evans rats were undernourished between the 16th day of gestation and 30 postnatal days of age to two different levels. The daily food intake of level-1 and level-2 rats represented about 60 and 40%, respectively, of that eaten by well-fed, age-matched controls. Nutritional rehabilitation of the rats was commenced when they had reached 30 days of age by placing them on an ad libitum diet. Groups of control and experimental rats were killed at 70 and 212 days of age. The Cavalieri principle was used to determine the granule cell layer volume within the dentate gyrus, and the "dissector" method was used to determine numerical densities of these granule cells. These estimates were used to calculate the total numbers of granule cells. There were between 260,000 and 320,000 granule cells within the dentate gyrus of 70-day-old control and experimental rats. By 212 days of age, well-fed controls had an average of about 834,000 granule cells. The level-1 and level-2 previously undernourished rats had about 515,000 and 595,000 granule cells, respectively. Two-way analysis of variance procedures showed significant main effects of nutrition and age as well as a significant interaction between them.(ABSTRACT TRUNCATED AT 250 WORDS)

Alcohol taken regularly over a lengthy period of time has been claimed to cause the loss of neurons in both the adult and developing brain. However, it remains uncertain whether acute, as opposed to chronic, exposure to alcohol at specified periods can also cause disruption in the neuronal population of the developing brain. This question was investigated by exposing Wistar rat pups to 7.5 g/kg body weight of ethanol administered as a 10% solution via an intragastric cannula over an 8 hour period either on the 5th (PND5) or the 10th (PND10) postnatal day of age. Gastrostomy controls received a 5% sucrose solution substituted isocalorically for the ethanol. Another set of pups raised by their mothers was used as "suckle controls." All surgical procedures were carried out under halothane vapour anaesthesia. After the artificial feeding regimes, all pups were returned to the lactating dams and weaned at 21 days of age. Between 52 and 54 days of age, the rats were anaesthetised with an intraperitoneal injection with Nembutal and killed by intracardiac perfusion with 3% glutaraldehyde in 0.1 M phosphate buffer. The relatively unbiased stereological procedure known as the "fractionator" method was used to estimate the total number of Purkinje cells in the cerebellum of each animal. The Purkinje cell nucleolus was used as the counting unit; it was assumed that each Purkinje cell contained only one nucleolus. PND10 ethanol-treated rats and gastrostomy and suckle controls had between about 210,000-232,000 Purkinje cells in the cerebellum. However, the PND5 ethanol-treated rats had only about 137,000 Purkinje cells.(ABSTRACT TRUNCATED AT 250 WORDS)

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SUMMARY This paper provides additional experimental evidence that biological variation between individuals is likely to be the major factor influencing the overall precision and efficiency of nested sampling schemes for morphometric analysis of thin sections. Four distinct experimental systems (two based on nervous tissue and two on epithelia) have been investigated. Morphometric estimates were obtained from measurements made on micrographs generated by sampling tissues at several levels. Sources of sampling variation were isolated so that the contributions to overall variance made by inter‐animal differences could be evaluated. In each case, biological variation was the cardinal component of total observed variance between animals. Relative contributions ranged from 53% to 78%. Examining more animals would be the most efficient way of reducing the variance of the group mean in these sampling designs.

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