Biomedical subjects

D G Sperry

Publications and source records attributed to D G Sperry.

12 recordsLinked to original sources

PubMed1997

Organization of the hypobranchial motor column of the clearnose skate, Raja eglanteria, with comparisons to tetrapods.

Motoneurons that supply the clearnose skate's hypobranchial musculature, via the occipital nerve and first seven ventral spinal nerve roots, are located within a column that extends from a level just caudal to the obex through the corresponding rostral spinal cord segments. Individual muscle motoneuron pools within the column are considerably intermingled and overlap. Comparisons with tetrapods, particularly mammals, where the hypobranchial musculature is greatly modified, reveal general conserved features. The motor column's multisegmental organization is retained although, in mammals, the column begins rostrally at medullary levels, where hypobranchial muscle motoneurons are intimately associated with motoneurons to lingual muscles, and it is restricted caudally to fewer spinal cord segments. In addition, despite an intermingling of motoneurons that supply individual hypobranchial muscles there is a shared rostrocaudal sequence of the motor pools. Rostral most hypobranchial motoneurons supply the most ventral and anterior muscles (i.e., m. coracomandibularis, and likely m. coracohyoideus, of skate and the suprahyoid musculature, m. geniohyoideus, of tetrapods). Caudal hypobranchial motoneurons supply the skate's mm. coracohyomandibularis, coracoarcualis communis and coracobranchialis and the tetrapod's entire infrahyoid muscle complex. The intermingling of multisegmental motoneuron populations innervating different hypobranchial muscles might be attributed to intermixing of premuscle mesoderm derived from several postotic somites but the musculotopic organization along the rostrocaudal axis indicates that pre- and posthyoid muscle mesoderm may partially keep its identity during its migration to the floor of the pharynx and oral cavity.

Animals↗

PubMed1993

Organization of the vagus in elasmobranchs: its bearing on a primitive gnathostome condition.

The vagus nerve of the clearnose skate, Raja eglanteria, on the basis of its central and peripheral patterns and in light of the embryonic origin of its innervation fields, is viewed as a collector of separate elements. The peripheral elements include a series of branchial nerves to a segmented pharynx, an intestinal nerve to an unsegmented gut, a nerve or nerves to the heart, and an accessory nerve to a cucullaris muscle. The central elements include a sensory column, a dorsal motor column, and a ventral motor column. The dorsal motor column and sensory column are segmented in register with the branchial and intestinal nerves. Motoneurons that supply the branchial muscles of somitic origin are only located in the rostral segmented portion of the dorsal motor column. Preganglionic parasympathetics to the enteric plexus, presumably derived from circumpharyngeal crest, form the caudal portion of the dorsal motor column and are probably also present in the rostral segmented portion. Cardiac preganglionic parasympathetics to a visceral field of cardiac crest origin occur in the rostral portion of the ventral motor column as well as in the dorsal motor column. Accessory motoneurons that supply the cucullaris, likely a part of the general body musculature, are unrelated to other vagal motoneurons and form a separate nucleus (caudal ventral motor nucleus) located at spinal levels. The central and peripheral vagal nerve patterns of elasmobranchs suggest a highly conserved, ancestral gnathostome condition.

Animals↗

PubMed1992

Central location of the motoneurons that supply the cucullaris (trapezius) of the clearnose skate, Raja eglanteria.

A complex of three muscles (one lateral, one intermediate and one medial in position) in the clearnose skate, Raja eglanteria, is believed to be wholly, or in part, homologous to the cucullaris (trapezius). The retrograde transport of horseradish peroxidase was used to discover the central location of the motoneurons that supply each of these muscles. Motoneurons that project to the lateral muscle occupy the caudal part of the ventral nucleus of X. This nucleus is situated ventrolateral to the dorsal vagal motor column at caudal medullary levels, and lateral to the main ventral motor column of the rostral spinal cord. The axons of these motoneurons exit the medulla within the caudal vagal rootlets and course peripherally within the intestinal (visceral) ramus of the vagus nerve. Motoneurons that innervate the intermediate and medial muscles are located along the ventral border of the ventral column of gray at spinal cord segments 10-15. Their axons course peripherally within the ventral roots of spinal nerves. The caudal ventral nucleus of X, the nerve that supplies the lateral muscle, and the lateral muscle are likely homologues of the accessory nucleus, accessory nerve, and cucullaris (trapezius), respectively, among other fishes and tetrapods. Intermediate and medial muscles, based on the central location of motoneurons that supply them, are part of the longitudinal epaxial musculature and are not part of a trapezius complex.

Animals↗

PubMed1991

Lumbar lateral motor columns and hindlimbs of two Xenopus laevis chromosome mosaics.

Two chromosome mosaic Xenopus laevis, one tadpole and one metamorphic animal, both with different sizes of neurons on the left and right sides of their brains and spinal cords, have left and right lumbar lateral motor columns (L-LMCs) of equal lengths but composed of strikingly different numbers of motoneurons (40% fewer motoneurons on the side composed of larger cells). One portion of the lumbar cord in the metamorphic animal is bilaterally symmetrical; the cells on both sides are small and the numbers of motoneurons per section are the same. The mosaics demonstrate that column length and motoneuron density (number per section) are, or can be, regulated bilaterally and that changing cell size affects factors controlling cell density but not column length. Except for the peripheral nerves, there is no evidence of any side-to-side differences in the hindlimb tissues. Whether the side-to-side difference in L-LMC motoneuron number in the stage 66 mosaic corresponds to any feature of the hindlimbs is unknown, but similar side-to-side differences in an early and a late stage mosaic animal support the idea that whatever creates the initial number may also determine the final number of motoneurons.

Animals↗

PubMed1991

Topography and nerve supply of the cucullaris (trapezius) of skates.

Dissections of Sudan black B stained specimens reveal that, of a complex of medial, intermediate, and lateral muscles of skates, presumed homologous to the cucullaris of sharks, only the lateral muscle is innervated by a branch or branches of the vagus and is inserted, in part, to the fused pharyngobranchials of the caudal visceral arches. The medial and intermediate muscles are supplied by separate branches of rostral spinal nerves and do not attach to the branchial skeleton. The lateral muscle therefore is the most likely homologue of the cucullaris (trapezius) of sharks and perhaps other fishes and tetrapods. The medial and intermediate muscles appear to be part of the axial musculature.

Animals↗

PubMed1990

Variation and symmetry in the lumbar and thoracic dorsal root ganglion cell populations of newly metamorphosed Xenopus laevis.

The sizes of the lumbar and thoracic dorsal root ganglion cell populations in normally developing newly metamorphosed Xenopus laevis were measured in order to determine whether these neuron populations have the same characteristics as the hindlimb motoneuron population (i.e., large individual as well as sibling group differences, striking bilateral symmetry, and a rough correspondence between neuron number and body size that suggests some peripheral control of cell number during normal development (Sperry, J. Comp. Neurol. 264:250-267). Among animals from three sibling groups, the total numbers of thoracic and lumbar ganglion cells are highly variable and symmetrical, although symmetry is not uniformly present at the level of individual ganglion pairs. Significant sibling group differences in neuron number are also present. Metamorphic body size and cell number in the thoracic but not in the lumbar ganglia are significantly correlated. The motoneurons innervating the hindlimbs were also counted and measured in the same animals. While variable as well as symmetrical, motoneuron number and metamorphic body size are correlated in only two of the three sibling groups. Interestingly, the numbers of motoneurons and lumbar ganglion cells, two populations of neurons whose sizes one might predict would be significantly correlated in normally developing animals, are not correlated. The relationship between these observations and currently held views concerning how neuron numbers might be controlled during normal development is discussed.

Animals↗

PubMed1988

Lumbar lateral motor column development in triploid Xenopus laevis.

The effects of increasing ploidy on the development of the lumbar lateral motor column (L-LMC) in Xenopus laevis were investigated in order to determine how early events contribute to producing the significant difference in the average number of motoneurons present in diploid and triploid animals after cell death (Sperry: J. Comp. Neurol. 277:499-508, '88). From naturally occurring diploid and experimentally produced triploid siblings at two stages prior to significant amounts of neuronal cell death, at one stage during the peak period of cell death, and at one stage after cell death, the L-LMC motoneurons were counted and nuclear cross-sectional areas were measured. At stages before and after cell death, the average nuclear cross-sectional areas of motoneurons and of other cells that were also measured were greater in the triploids, while the average number of motoneurons and motoneuron density (the mean number of cells per section) were less. Average body size and average motor column length in diploid and triploid animals were equal at each of the stages. The general characteristics of L-LMC development that have been widely noted in diploids, an increase in cell size accompanied by a decrease in cell number, were also observed in the triploid animals. However, not only were these general features present in the triploids, but the increase in average motoneuron size and the decrease in average motoneuron number in diploids and triploids were roughly equal when scaled to the general differences in nuclear size or to the difference in the average number of motoneurons present prior to cell death.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1988

Effects of increasing ploidy on the lumbar lateral motor column and hindlimb of newly metamorphosed Xenopus laevis: a comparison of diploid and triploid siblings.

This study was undertaken to determine how increasing ploidy in Xenopus laevis affected the size of the lumbar lateral motor column (L-LMC) motoneuron population, the size of representative hindlimb muscles, and the relationship between these features in animals at the completion of metamorphosis. Triploids were produced by exposing fertilized diploid eggs to increased hydrostatic pressure. In the triploids, L-LMC motoneuron number was significantly reduced and motoneuron nuclear cross-sectional area was significantly increased. Both L-LMC length and the total L-LMC size (neuron number x mean nuclear size) were roughly equal in diploids and triploids. No ploidy-related differences in fiber number were observed in two representative thigh muscles. In diploid animals, motoneuron number is significantly correlated with both muscle fiber number and with body size. The latter two variables are also significantly correlated with one another, making it possible that a feature related to muscle fiber number or one related to body size or both are significant in determining motoneuron number. In triploid animals, motoneuron number was significantly correlated with body size but not with muscle fiber number. This suggests that the feature significant in determining motoneuron number may be one related to body size rather than to muscle fiber number. If a feature related to muscle fiber number were the primary determinant of motoneuron number, one would have expected in addition similar average changes in the two variables in comparing diploids and triploids. That this was not observed provides further reason to suspect muscle fiber numbers may not be a primary determinant of motoneuron number. In both diploids and triploids, total L-LMC size (a value combining neuron number and neuron size) was highly correlated with body size, but again, not with muscle fiber number. The average total L-LMC size and the average body size were equal in diploids and triploids while average motoneuron number was significantly different. What this suggests is that in discussing possible mechanisms to account for correspondences between central and peripheral sizes, the relevant variable for the former may be total L-LMC size rather than motoneuron number.

Animals↗

PubMed1987

Relationship between natural variations in motoneuron number and body size in Xenopus laevis: a test for size matching.

During normal development, tadpoles of Xenopus laevis demonstrate large variations in body size that are carried through metamorphosis. This variation in size exists at the stages when lumbar lateral motor column (L-LMC) motoneurons are produced and when neuronal cell death in this neuron population occurs. Body size, hindlimb size, motoneuron number, and motoneuron size (i.e., neuron nuclear cross-sectional area) were measured in animals from three developmental stages: one prior to significant amounts of cell death, one at the peak rate of cell death, and one after cell death. The hypothesis that neuron population size is matched to peripheral size was tested by using the natural size variation found at each of these stages. The ranges of values for the measurements at the three stages were large. Significant correlations between body size and motoneuron number, as well as between motoneuron number and muscle fiber number, were present after cell death. Since these correlations emerged as cell death reduced neuron numbers, size matching may have occurred and cell death may have adjusted the L-LMC motoneuron population's size to variation in body size. In addition to the correlations between body size and motoneuron number at the end of cell death, neuron numbers before and after cell death were significantly correlated among groups of siblings. The possibility that the number of neurons after cell death was also influenced by differences in the number of L-LMC progenitors is discussed.

Animals↗

PubMed1985

Regulation of neuron numbers in Xenopus laevis: effects of hormonal manipulation altering size at metamorphosis.

Xenopus laevis tadpoles reared in a 0.01% solution of 6-n-propyl-2-thiouracil (PTU) are blocked in their development at larval stage 54 but continue to increase in size. When released from the effects of PTU they metamorphose into frogs of sizes significantly larger than those of their untreated siblings. Using this size difference to examine the hypothesis that neuron numbers are matched to the size of their postsynaptic targets during neuronal cell death, we measured the following on stage 66 frogs metamorphosing from PTU-treated and untreated tadpoles: lumbar lateral motor column (L-LMC) motoneuron number and mean nuclear cross-sectional area; thoracic and lumbar dorsal root ganglion (DRG) cell number and mean nuclear cross-sectional area; and muscle fiber number in two representative thigh muscles. A few measurements of neuron number and cell size were also made on untreated and PTU-treated stage 54 tadpoles. The most striking correlations observed were not between peripheral size and neuron numbers but between peripheral size and neuron size. Motoneuron numbers were not increased in the PTU-treated animals, perhaps because the increase in peripheral size involved an increase in muscle fiber diameter rather than an increase in muscle fiber number. Thoracic DRG cell number, but not the sum of thoracic and lumbar DRG cell numbers, was increased. In general, our findings do not support the hypothesis that neuron numbers are matched to peripheral size by a process regulating the amount of cell death that occurs during metamorphic stages in Xenopus laevis.

Animals↗

PubMed1983

Postmetamorphic changes in the lumbar lateral motor column in relation to muscle growth in the toad, Bufo americanus.

Motoneuron number and size (nuclear cross-sectional area) were measured from serially sectioned spinal cords of Bufo americanus to investigate the relation between changes in the lumbar lateral motor column (L-LMC) and postmetamorphic increases in hindlimb muscle fiber number. Previous studies of neuron number in a variety of anuran species reported a correlation between number and body size, suggesting the possible addition of neurons during growth. Our results show a poor correlation between motoneuron number and body size with at most a 25% increase in neuron number occurring over the body size range where previous work had shown a hindlimb muscle fiber increase of ten to 20-fold. Thus, most new muscle fibers must be incorporated into motor units that exist at metamorphosis. Motoneurons, but not ependymal cells, showed a significant size increase with increasing body size; this is perhaps related to an increased motor unit size that results from axonal sprouting. The range of variation of L-LMC cell numbers in newly metamorphosed toads was nearly equal to that of all other toads examined. This suggests that the weak correlations between motoneuron number and size observed in this and previous studies may be due to differential survival of individuals with larger neuron populations rather than to postmetamorphic addition of motoneurons. Our findings also show a strong bilateral correlation of motoneuron numbers, a finding suggesting that factors other than peripheral size may be important in regulating motoneuron number.

Animals↗

PubMed1976

A proposed function for microridges on epithelial cells.

Microridges (MR), also called microvillar ridges, microplicae and cytoplasmic folds, have been noted on many epithelial surfaces. Several functions have been proposed for these structures. In the present study we examine the mechanical role that microridges may play in holding mucus to the lumenal surface to the esophagus in the trout Salmo gairdneri. Our findings support the hypothesis that the microridges help hold a protective coat of mucus to the epithelium. In addition, the complex curved or whorled arrangement of microridges appears to facilitate the spread of mucus away from goblet cells.

Animals↗