Madge E. Scheibel

Organization of spinal motoneuron dendrites in bundles

Abstract In the spinal ventral horn of the mature cat and monkey, most motoneuron dendrites show high degrees of organization along the rostrocaudal axis. Horizontal sagittal sections of Golgi-impregnated cord indicate that the majority of these dendrites are organized in densely packed bundles. Each bundle consists of dendrite shafts from neurons of different motor cell columns representing different functional groups. It is suggested that these dendrite bundles, utilizing both synaptic and extrasynaptic mechanisms, constitute subcenters for the integration of motor output.

Progressive dendritic changes in the aging human limbic system

Abstract The methods of Golgi have been used in histological evaluation of tissue from the limbic lobe of nine aged patients, six of whom showed clinical signs and symptoms of senility. Special attention was paid to the pes hippocampus and dentate gyrus as prototypic exampes of archicortex and to entorhinal cortex serving as an example of transitional cortex. Sequences of degenerative changes with aging and senescence were found in all the regions studied. Although there were general similarities among the pathological patterns, changes appeared idiosyncratic to the regions involved. The severity of pathological changes appeared to correlate more closely with the amount of antecedent psychomotor loss than with the chronologic age of the patient. Dendritic systems showed progressive deteriorative changes in all three regions. Entorhinal cortex also appeared characterized in at least three of the more severely affected patients by the appearance of spindle-shaped thickenings along the apical shafts, frequently clustered at specific distances throughout the depth of cortex. Some suggestions are made as to the possible significance of this type of dendritic lesion, and of the putative consequences of patchy lesions in pes hippocampus.

Maturation of reticular dendrites: loss of spines and development of bundles.

Abstract Dendrite systems of most neurons in the brain stem reticular core undergo two significant changes between birth and maturity. The shaggy spinelike excrescences (heteromorphic protospines) which cover each dendrite and soma at birth, are lost completely, resulting in smooth, spineless reticular dendrites in the adult nervous system. It is suggested that these spinelike structures and their associated presynaptic terminals are concerned with primitive needs of the internal milieu and are replaced by a secondary system of terminals which provide substrate for more complex core functions. In contrast to the familiar radiative aspect of reticular dendrites in newborn organisms, dendrite shafts are rearranged into bundles which surround the fascicles of axons running longitudinally through the reticular formation. The bundles of dendrites are marked by closeness of apposition of the shafts and continuous change in the dendritic elements comprising them. On the basis of previous work, it is suggested that these bundles are the repository for central programs mediating certain stereotyped repetitive output patterns such as respiration and the rest-activity cycle.

Developmental relationship between spinal motoneuron dendrite bundles and patterned activity in the hind limb of cats

Most dendrites of motoneurons in the spinal cord of mature cats and monkeys have been shown to be grouped in tightly packed bundles. In the lumbosacral cord, bundles begin to appear at postnatal day, 12 to day 14 coincident with the earliest appearance of reciprocal activity in flexor-extensor muscle pairs and development of stepping-walking-weight-bearing capability in the hind limb. We suggested that the central program responsible for controlling integrated patterns of limb activity may be generated in motoneuron dendrite bundles. In the kitten, treading motions of the front legs associated with suckling appear almost immediately after birth. In addition to a generally more advanced state of development in cervical cord, motoneuron dendrite bundles can be identified in the neonatal cervical ventral horn. This can be interpreted as offering further support to the view that dendrite bundles provide the central program for reciprocal activity of leg muscle pairs in coordinated motor activity.

Specialized organizational patterns within the nucleus reticularis thalami of the cat

Abstract Structural analysis of the nucleus reticularis thalami in the adult cat, using variations of the rapid Golgi method, reveals significant differences between anterior pole and dorsolateral portions of the nucleus. The former is characterized by a dense presynaptic neuropil plexus and long, pleomorphic appendages on most of the dendrites. The latter is notable for its smooth-surfaced dendrites, a large proportion of which are arranged in tightly packed bundles, reminiscent of similar structural complexes previously noted in the spinal ventral horn. These structural differences underline the heterogenic nature of the nucleus reticularis and suggest the possibility of more than one functional role for this nuclear complex. We suggest that the dendrite bundles may represent a structural motif causally related to the burst type discharges characteristic of reticularis neurons.

The aging human betz cell

Abstract The methods of Golgi in conjunction with cresyl violet and Bielschowsky techniques have been used to study the precentral gyri of seven patients aged 74 to 102 years, with special reference to the giant pyramidal cells of Betz. These large neurons appear especially vulnerable to the process of aging and senescence. Age-related changes include irregular swelling of the cell body and principal dendrite shafts with progressive loss of dendrite spines; shortening, disruption, and progressive disappearance of the numerous circumferential (basilar) dendrites which characterize these cells during the period of vigorous adult life; the frequent engulfing of these cells during their senescent phase by astroglia; and the eventual loss of all dendrite shafts including the apical element prior to disappearance of the cell body. A semiquantitative survey of our material indicates that 75% or more of Betz cells show age-related changes by the eighth decade of life compared to less than 30% of the more numerous surrounding non-Betz pyramids. The function of these giant cells increasingly appears to be one of temporary relaxation of extensor muscle tone across weight-bearing joints preceding a specific motor action. Because of the very limited total number of Betz neurons, we suggest that their high incidence of age-related pathology and loss results in a clinically significant decrease in the capacity for rapid initial lysis of antigravity tone in extensors. Symptoms and signs of pain, stiffness, and slowing in activities affecting the lower extremities and hips, so common in aging and senescent individuals, may be, in part, a function of this loss of extensor inhibition and the resulting necessity to force motor patterns upon weight-bearing muscle systems in some degree of constant, unrelieved muscle tone.

Characteristics of projections from the nucleus ventralis lateralis to the motor cortex in the cats: An anatomical and physiological study

SummaryThe properties of neurons in the nucleus ventralis lateralis (VL) of thalamus were examined by anatomical and electrophysiological methods and the following results were obtained:1.There were two types of projection fibers from VL to the motor cortex. One type projected to a limited area of the cortex, the other arborized extensively and projected to a wide area of the cortex.2.The widely arborizing projection fibers, i.e., wide projection fibers, showed a special terminal bush which was different from that of the specific projection fibers of VPL and spread as widely as 1.0 mm2 within the III layer of the motor cortex.3.Neither narrow nor wide projection fibers carried specific information from the periphery but rather diffuse information arising from deep structures such as joints and periosts.4.Both types of projection fibers branched somewhere in the white substance and projected to different areas of the motor cortex.5.The chronaxie of these fibers was about the same as that of PT cells but considerably longer than spinal interneurons. The excitability of these fibers was lower than that of PT cells indicating that weak intracortical microstimulation (ICMS) does not excite these fibers.6.The possible functional role of wide projection fibers was discussed in relation to the cortical efferent zones.

Neuropil organization in the superior olive of the cat

Abstract Golgi studies of the sagittally sectioned brain stem of the cat show that the longitudinal organization of the superior olive (medial or accessory, and lateral or S segment) differs markedly from that revealed by cross sections. Olivopetal fibers from the cochlear nuclei terminate in sheets of neuropil arranged parallel to the long axis of the stem. Each sheet appears to be made up of the terminal elaborations of several afferent fibers, partially overlapped. Olivary neurons lie embedded in these sheets, their longitudinally elaborated dendrite systems densely covered by plexus terminals. The characteristic flame-shaped arbors and elongated bipolar neurons familiar from previous histological studies, appear to represent the end-on view of an essentially two-dimensional neuropil system. Some putative functional consequences of this organizational pattern are discussed.

Some Structural and Functional Substrates of Development in Young Cats

Publisher Summary The material presented in this chapter is developed within the framework of a long-term study of neuropil patterns in the brain stem reticular core and related structures, and is geared toward elucidating certain aspects of the problems of inhibition and facilitation. Three general topics are considered here: (1) some structuro-functional correlates of brain wave maturative patterns with particular reference to cerebral cortex, cerebellum, and reticular formation, (2) the maturation of cortical activation mechanisms, including cortical “following” reactions, and (3) the development of certain discriminative conditional responses, including habituation-like phenomena. The data discussed in this chapter are drawn from a large body of material gathered over several years from a group of approximately 80 kittens chronically implanted within a few hours to a few days of birth. Although the neurophysiological material and related structural correlative data are derived from this source, a larger body of structural information rests on some 12 years of experience with several thousand brains of laboratory animals examined by Golgi and related techniques. Wherever possible, kittens were operated within 3 to 12 h of birth. Minute amounts of intraperitoneal Nembutal (30 mg/kg) in saline were used as basal anaesthesia and supplemented by open drop ether as needed. Under sterile precautions, animals were placed in a specially constructed head-holder, which was suspended within the frame of a standard Johnson stereotaxic apparatus. Three adjustable arms shaped to the bridge of the nose and the mastoid prominences held the head motionless without injury to sensitive tissue of mouth, eyes, or ears.

Neuronal changes in the aging mouse. Spinal cord and lower brain stem.

Abstract In view of the marked changes which we have recently described in the Golgi-stained nerve cell bodies and dendrites of cerebral neocortex in senescent human subjects, we have attempted a similar study of the very old (26 to 30 months) mouse for comparative purposes. Although neocortical changes in this species seemed unimpressive, marked and apparently progressive agerelated changes were found in most neurons of spinal cord and lower brain stem. Early changes included irregular swelling and “lumpiness” of cell bodies and initial portions of the dendrites, followed by increasing nodularization of the dendrite tree and loss of whatever spines or postsynaptic specializations may have been present in the young adult. Zones of constriction along dendrite shafts seemed to result in complete breaks with loss of the distal segment and shrivelling of the proximal segment. Irregularly swollen neurons with “amputation stumps” replacing principle dendrites appeared the penultimate phase before eventual cell loss. The remarkably widespread occurrence of such changes throughout sensory and motor systems is considered in relation to the consequent loss of functional neuropil and the possible embarrassment of coping behavior in the senile mouse.