A comparison of cell size changes in central and pericentral representations within the primate lateral geniculate nucleus following early monocular deprivation

Mean cell areas have been measured in the most posterior part of the lateral geniculate nucleus containing the representation of central retina in 8 normal monkeys (Macaca mulatta) and in 5 monkeys following monocular closure from birth. Comparisons with cell size changes at a more anterior level, where pericentral retina is represented, show that size changes of parvocellular cells at the posterior level are significantly less, being only between half and two-thirds of those more anteriorly. The undeprived cells undergo less initial hypertrophy than cells at a more anterior level and subsequently the deprived cells show less shrinkage. There is no comparable difference for magnocellular cells.     

Shrinkage of cells in undeprived laminae of the monkey lateral geniculate nucleus following late closure of one eye

Measurements of mean cell area have been made in the lateral geniculate nuclei of 16 normal rhesus monkeys as a control for changes following visual deprivation. There is little variability between animals and no significant growth between 8 days of age and adulthood in the parvocellular laminae. The magnocellular laminae show more variability and some continuing growth after 8 days of age.     

Effect of methotrexate on the immune response in children with acute lymphatic leukaemia

Lymphocyte count, lymphocyte subpopulations identified by monoclonal antibodies and mitogen stimulation assays with phytohaemagglutinin, concanavalin A, pokeweed mitogen and staphylococcal protein A, were used to quantitate the effect of methotrexate on the immune response in children with acute lymphatic leukaemia on maintenance therapy. Methotrexate exerted a profound but apparently short-term effect on these parameters as it is prescribed in current maintenance schedules for childhood acute lymphatic leukaemia. A significant drop in lymphocyte count, affecting all subpopulations, was observed 4 h after oral or intramuscular administration of methotrexate which had reverted to pre-methotrexate values one week after the drug was given. Lymphocyte function was markedly affected, with a major decrease in mitogen responsiveness 1 h after methotrexate and a reversion to pre-methotrexate values by 48 h. A selectivity of suppressor T cells to methotrexate is proposed as being responsible for early recovery. Scheduling of methotrexate in current maintenance programmes would therefore appear to allow adequate time for recovery of immunoresponsiveness between doses.     

Effect of reopening an eye after a period of monocular deprivation on sizes of neurons in the primate lateral geniculate nucleus

Following monocular closure shortly after birth the deprived eye of 4 rhesus monkeys was reopened at different times. Following long-term recovery, cells in the undeprived laminae of the lateral geniculate nucleus of these animals were of normal size and those in the deprived laminae were markedly shrunken. Comparisons with animals monocularly deprived for similar periods indicate, however, that in 3 of these animals the undeprived parvocellular cells would have been markedly hypertrophied at the time of reopening the deprived eye, and in two of the animals, little shrinkage of the deprived parvocellular cells would have occurred by this time. Both undeprived and deprived parvocellular cells have therefore undergone marked shrinkage after the deprived eye had been reopened. The parallel shrinkage of deprived and undeprived parvocellular cells which occurs following closure at birth thus appears to be a consequence of the initial abnormalities produced by monocular closure rather than a direct result of the continuing lack of visual input to one eye.     

Effects of monocular closure at different ages on deprived and undeprived cells in the primate lateral geniculate nucleus

This study has examined the effects of monocular visual deprivation on cells in the lateral geniculate nucleus of the primate by comparing the sizes of cells in deprived and undeprived LGN laminae of experimental rhesus monkeys with those of cells in the corresponding laminae of normal animals. A number of conclusions may be drawn from this comparison: monocular visual deprivation has major effects on cells in the undeprived LGN laminae and these vary with age at closure; the initial effect of monocular closure from birth is to cause marked hypertrophy of undeprived parvocellular cells with little shrinkage of the deprived parvocellular cells, whereas late monocular closure (after 2 months of age) causes marked shrinkage of both undeprived and deprived parvocellular cells; following monocular closure at birth, the LGN abnormality continues to evolve until at least 3 months of age, with a marked parallel shrinkage affecting both deprived and undeprived parvocellular cells. The initial hypertrophy of the undeprived cells is reversed and the deprived cells become smaller than normal; cells in the monkey LGN are sensitive to visual deprivation until about 1 year of age, much later than previously thought. Visual experience, however, modifies this sensitivity so that the effects of monocular visual deprivation are both qualitatively and quantitatively different at different ages; there are important differences between the susceptibility of cells in the magnocellular and parvocellular laminae to visual deprivation; and actual shrinkage of cells to markedly below normal size occurs and the smaller size is not simply failure of growth.