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L H Mathers

Publications and source records attributed to L H Mathers.

12 recordsLinked to original sources
PubMed1979

A critical period in the development of tectal neurons in the chick, as revealed by early enucleation.

To further study the existence of a critical trophic period in the development of the chick optic tectum, during which the presence of retinal synapses is essential to the continued growth of tectal neurons, we have unilaterally enucleated embryos between stages 14--20 and allowed survival until stages 35--43. If the critical trophic period is between stages 40--44, as previously reported, then we reasoned that early removal of the eye might not have any effect on tectal development until the critical period. We assessed tectal neuron survival by staining for degeneration in the efferent projections of tectal neurons. In early enucleates, degeneration was present from stages 37--43, and the severity of the degeneration was much reduced in comparison to animals enucleated during the critical period. These findings substantiate the proposition that there is a critical period late in chick tectal development. However, because the degeneration in tectal projections is less intense than in animals enucleated during the critical period, we suggest that the early enucleation has permitted axons from the remaining eye to be routed to the deafferented tectum, where they may help to sustain a portion of the tectal neurons through the critical period. Moreover, the somewhat earlier appearance of degeneration in tectal efferent pathways of early enucleates suggests that a subtle trophic relationship between retina and tectum may exist prior to stage 40, even though this relationship is not revealed when enucleations are performed later, as between stages 35--40 (ref. 17).

Age Factors↗
PubMed1979

Morphology of dissociated hippocampal cultures from fetal mice.

Dissociated hippocampal cultures from fetal mice (13--18 days gestational age) can be maintained for up to two months in culture. Cells grow as either isolated neurons or in small neuronal aggregates. Neurons remain small with a soma diameter of 15--20 micrometer even in mature cultures and develop extensively branched processes during the first two weeks in culture. After this time, processes become more difficult to visualize with phase-contrast optics because of a tendency to grow within the underlying non-neuronal cells. However, the presence of processes has been proved by silver-staining which demonstrates an organizational complexity ranging from a loosely reticulated neuropil to fascicles containing many fibers. More detailed study of individual neuronal morphology was carried out in cells filled with the fluorescent dye, Lucifer Yellow CH, in conjunction with the intracellular recording of synaptic and action potentials from dye-containing micropipettes. Dye-filled cells show a well-developed branching morphology. Process specializations include spines, beading, and basket-like endings. Processes tend to emanate from one side of the soma, either originating at the cell body or from a single trunk. Commonly there are 2--4 orders of branching, but up to 6 orders can occur (counted centrifugally from the soma). Electron microscopy revealed synapses distributed predominantly on dendrites with a smaller number on somata. Dendritic spines are present and are contacted principally by asymmetric synaptic junctions. Symmetric synapses are relatively more common on somata and proximal dendrites.

Action Potentials↗
PubMed1979

Postnatal dendritic development in the rabbit visual cortex.

Golgi preparations of rabbit visual cortex aged 1-25 days, as well as similar tissues from adults, were examined for the growth of the dendritic arbor, and in particular the development of dendritic spines. The layer 5 pyramidal neurons and layer 4 stellate neuron were chosen as representatives of larger classes of neurons in the visual cortex. It was determined that the growth of the dendritic arbor, determined by counts of total number of dendritic and total dendritic length, is quite similar for pyramidal and stellate neurons. Dendritic spine development, however, is more rapid in pyramidal neurons than in stellate. This disparity in the rate of dendritic spine development is discussed in the light of physiologic studies on the development of receptive field properties in the rabbit visual cortex.

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PubMed1979

Evidence for a critical period of neuronal trophism late in the development of the chick visual system.

Chick embryos and young hatchling chicks have undergone unilateral retinal ablation and the brains were subsequently prepared for modified Fink-Heimer staining to detect degenerating axoplasm. Additional animals have been injected with tritiated proline or combinations of tritiated proline and tritiated fucose. In examining the patterns of degeneration and labelling produced, it appears that during the stage 40-44 period of embryonic life there is a critical period during which damage to retinal axons produces degeneration not only in the direct targets of the optic tract (primary centers), but also in a number of nuclei not projected to by the optic tract (secondary centers). By examining various survival times following retinal ablation and animals of varying embryonic and post-hatch age, we have concluded that retinal ablation during the critical period causes a rapid and fulminant degeneration in the secondary centers because they are all targets of the projection from the optic tectum, itself a prime target of the optic projection. Presumably, interruption of the retino-tectal projection during the critical period disrupts some as yet undefined trophic relationship between these two sets of neurons. Our studies show that the observed degenerative reaction in the secondary centers occurs most strongly in chick embryos between stage 40 and stage 44. This period coincides with the onset of synaptogenesis in the retino-tectal system (Rager, '76a,b). We therefore hypothesize that during this period some property or influence is passing from the retinal to the tectal neurons such that interruption of this process leads to death of the tectal neurons.

Animals↗
PubMed1978

Physiological and morphological identification of a nonpyramidal hippocampal cell type.

In intracellular recordings from the CA1 region of the hippocampal slice preparation, an infrequent cell type different from the predominant pyramidal cell has been characterized. The cells have very brief spikes, hyperpolarizing after-potentials, and tend to fire at a high spontaneous rate; unitary synaptic potentials are visible in the baseline. Stimulation in stratum radiatum evokes an EPSP which often triggers a short burst of spikes; an IPSP invariably follows the initial excitation. Intracellular injection of HRP into these cells shows them to be a non-pyramidal cell type with extensive local axon ramification; however, they do not resemble the classical basket cell. These cells are, nevertheless, candidates for an interneuron in hippocampus.

Animals↗
PubMed1978

Synaptic development in the rabbit superior colliculus and visual cortex.

The development of synapses in the visual cortex (VC) and superior colliculus (SC) of the rabbit has been examined with the electron microscope. In both areas, the number of synapses reaches adult levels by 20--25 days of postnatal age, but the development in the visual cortex is delayed in comparison to that in the superior colliculus. When S synapses (spheroidal vesicles, asymmetric thickening) are compared with F synapses (flattened vesicles, symmetric thickening), even greater differences are seen. In both the VC and SC, S synapses develop earlier than F synapses, though there is considerable overlap. Of interest is that fact that synapses in the visual cortex seem to overshoot their adult levels late in development, suggesting that an excess of synapses may be formed in this system. Multiple synapses, probably of retinal origin, increase in the first 3 weeks of synaptic development in the SC, but never are present in significant proportions in the VC. Synapse formation most often is characterized by formation of a junction and a postsynaptic thickening, followed by acquisition of synaptic vesicles. After 15 days, there is only a small number of such "non-vesicle synapses" in either the SC or VC.

Age Factors↗
PubMed1977

Postnatal maturation of neurons in the rabbit superior colliculus.

The superior colliculi of Dutch-belted rabbits aged 1 to 30 days were prepared according to Nissl and Golgi techniques and examined in comparison to the neuronal populations in the adult. It was found that the laminar dimensions of the adult are attained at 15 to 20 days, presumably due to glial and dendritic enlargement. The largest neuron in the superficial gray, the vertical cell, was found to mature earliest and to display the least evidence of dendritic development postnatally. Its dendrites do elongate from 0 to 15 days, but there are no growth cones or other unusual dendritic configurations. The intrinsic neurons of the superficial gray, the piriform and stellate cells show more evidence of postnatal dendritic development. Particularly in the case of stellate cells, there are dendritic growth cones present at birth, and early in development spines are found on the soma and large dendrites. Only at 15 to 20 days do the dendritic arbors of these cells assume normal adult shapes and sizes. These and other observations suggest that there are two phases of postnatal cellular maturation in the upper layers of the superior colliculus, one involving the smaller "interneurons." This phased maturation is compared with the known sequence of physiological maturation as studied by the method of receptive-field mapping.

Animals↗
PubMed1977

Anatomical studies of a temporal visual area in the rabbit.

Using Fink-Heimer, autoradiographic and horseradish peroxidase techniques, the connections of a temporal visual cortical region of the rabbit were explored. The temporal visual area covers portions of areas T1 and T2, and is reciprocally connected with the posterior nucleus and suprageniculate nuclei of the thalamus. It was also shown that the temporal visual area projects to a similar region in the opposite hemisphere, and to intermediate laminae of the superior colliculus. The temporal visual area is discussed in comparison to other similar regions in the cortex of primate species. It is pointed out that recent evidence indicates visual areas in the occipital cortex of non-primate species may be no less numerous and complex than those in primate species.

Animals↗
PubMed1975

Ontogenesis of receptive field characteristics in the dorsal lateral geniculate nucleus of the rabbit.

The responses of rabbit dorsal lateral geniculate neurons to light or optic nerve shock were tested for 415 units in 43 rabbit pups 2--20 days of age. Units were driven by optic nerve shock at the youngest ages tested, but could not be driven by light until postnatal day six. Examples of each of the three prominent categories of receptive fields found in the adult were first observed at 8 days of age. Cells with receptive field properties not characteristic of the dorsal lateral geniculate nucleus of the adult were encountered until 17 days of age. The percentage of neurons with uniform and motion sensitive receptive fields approached adult levels soon after eye opening (11--12 days) but the percentage of cells with concentric receptive fields showed a steady increase throughout the neonatal period studied. The relevance of our data to the development of the visual response in the dorsal lateral geniculate nucleus and striate cortex is discussed.

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