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Biomedical subjects

B Cragg

Publications and source records attributed to B Cragg.

6 recordsLinked to original sources
PubMed1979

Cell growth in the monocular segment of the lateral geniculate nucleus following the opening or closing of one eye.

Both eyes were closed in 12 kittens soon after birth, and one eye was reopened at 23 days. From 14 to 26 days later, the cells in the monocular segment of the LGN connected to the open eye became significantly larger than the corresponding cells on the other side of the brain that were connected to the eye that was still closed. Up to 26 days after eye opening, the response of the monocular segment was similar to that of the binocular segment, so the latter may not be dependent on mutual inhibition or competition between sets of cells connected to each eye. From 30 to 60 days after eye opening, however, there were no differences between the monocular segments, but marked differences between the binocular A laminae where mutual inhibition and competition can occur. In seven more kittens both eyes were untouched until 23 days, when one eye was closed. Between 3 and 31 days later the deprived cells in the monocular segment of the LGN were not more than 8% smaller than those on the other side of the brain, and the measurements were not significantly different in any one cat. Within the binocular part of lamina A, cell growth is retarded by eye closure in two phases. Neither the early phase from 4--6 days nor the later phase from 21 days onwards occurred in the monocular segment, so both may be dependent on mutual inhibition of competition between the sets of cells connected to each eye. Two possible explanations of this difference between the effects of eye opening and eye closing are discussed.

Animals↗
PubMed1979

Brain extracellular space fixed for electron microscopy.

Adult mammalian brain contains 17--20% extracellular space, but fixatives cause the cellular elements to ingest the extracellular fluid so that the space is reduced to less than 5% with all conventional methods of fixation. This can be prevented by washing out the extracellular fluid with isotonic sucrose, which does not penetrate cells. Subsequent fixation with aldehydes and osmium and conventional processing leads to the preservation of extracellular space in electron micrographs. Extracellular space was found to be unevenly distributed, widely separating some cellular processes while leaving other groups of processes contiguous.

Animals↗
PubMed1976

The effect of age on the reversibility of cellular atrophy in the LGN of the cat following monocular deprivation: a test of two hypotheses about cell growth.

Monocular closure soon after birth is known to reduce the growth of the deprived cells in the LGN provided that there are competing cells with normal input. When the closed eye was opened and the open eye closed after three of six weeks of monocular closure, the originally deprived cells in the LGN were able to recover their normal size. However, it was found that after 14 weeks of monocular closure there was no recovery. The ability of the initially closed eye to excite cells in the visual cortex is known to depend on the age when eye closure is reversed in a similar manner. Thus the growth of cells in the LGN is correlated with the possession of effective synapses upon cortical cells. This result is compatible with the possession of effective synapses upon cortical cells. This result is compatible with the hypothesis that competition occurs at the cortical level. It is argued that the alternative hypothesis of competition within the LGN predicts reversibility at any age. In some kittens, the closed eye was opened and the opposite optic nerve crushed. Some evidence was then found of structural recovery even after 14 weeks of deprivation. The hypothesis of cortical competition predicts functional recovery in such kittens, but this remains to be tested.

Age Factors↗
PubMed1976

Cell growth in the lateral geniculate nucleus of kittens following the opening or closing of one eye.

Closing one eye of kittens at 23 days after birth resulted in paler Nissl staining of the deprived cells in the lateral geniculate nucleus (LGN) that was detectable two days later. Differences between the two sides of the brain in mean cell area increased to a peak in binocular lamina A at 4--6 days after eyelid suture, and then fell to a trough at eight days before rising progressively to a higher level at 31 days. In lamina A1 the peak and trough were later. Opening one eye of kittens after 23 days of binocular closure from birth resulted in more intense Nissl staining of the stimulated cells in the LGN that was detectable four days later. The stimulated cells grew faster than the cells connected to the eye that remained closed, and this differential growth reached a peak at 17 days in binocular lamina A and at 21 days in lamina A1 before falling to a trough at 26--31 days. These results are compared with the time course of anabolic changes that have been measured in other neurons during stimulation. The coefficient of variation of cell size was computed and found to be slightly decreased for deprived cells and increased for stimulated cells. This suggests that larger cells changes their sizes proportionately more than smaller cells. The cells were measured in fronzen sections without shrinkage, and the areas are at least 25% larger than those reported previously after paraffin or celloidin embedding.

Animals↗
PubMed1976

Behavioral, biochemical and histological effects of prenatal administration of progesterone in the rat.

Pregnant Wistar rats were injected with progesterone (1.5 mg/kg) between Days 8 and 21 of gestation and the behavioral, biochemical and histological effects of this treatment were observed in the offspring. The progesterone offspring weighed less than the control animals during this weaning and were retarded on one measure of exploratory activity in the open field. None of the other 29 tests used showed any significant difference apart from a 9% increase in the amount of brain DNA in the progesterone animals. It was concluded that these differences were fortuitous and that progesterone has no consistent or significant effects on brain development in rodents following prenatal administration.

Animals↗