Influence of asphyxia upon the responses of spinal motoneurons

Observations have been made upon asphyxial and postasphyxial changes in the electrical responses of motoneurons to antidromic stimulation. Analysis has been aided by the use of a simple method for locating conduction blocks in the circumstances of volume conduction. Asphyxiation has been produced by suspending artificial ventilation. Regular practice has been to restore ventilation immediately after complete conduction block is established. This has permitted study of the postasphyxial state, but not of the effects of prolonged asphyxiation with the latter of which this paper is not concerned. With asphyxiation produced in the manner outlined a latent period of approximately 1 minute precedes the onset of asphyxial change. The initial change, to judge by the work of others (6, 7), is beginning central depolarization. At the same time there is a severe loss of somatic after-potential (Fig. 1). Through this loss the dendrites acquire the ability to carry two volleys in rapid succession (Fig. 13). These changes appear to reach completion within approximately 30 seconds. There follows a period of convulsive activity during which reciprocal amplitude changes in the response of axons and dendrites prove that a fluctuation in somatic responsivity is taking place (Fig. 11). Intermittent impulse discharge in ventral roots is seen (Fig. 1). Conduction block may be developing slowly throughout the period of convulsive activity (Fig. 11). Frequently there is a rather definite instant at which convulsive activity ceases and a rapid development of block begins. Usually the recorded amplitude of the dendritic response then increases to a peak (the preterminal increment) before final disappearance (Figs. 9 to 11, 13 to 15). A variety of reasons has been advanced to show that this preterminal increment represents not increased response, but rather a developing block (Figs. 11 to 13). When fully established, asphyxial block is located at the junction of the initial and myelinated axon segments (Figs. 5 to 7). It is a depolarization or cathodal block. On restoring ventilation a latency of less than 20 seconds antecedes the onset of postasphyxial change. Within the span of a few seconds membrane potential recovers and overshoots the normal level. At a critical stage of repolarization motoneurons are capable of conducting impulses, but again lapse into block (Figs. 9, 10, 14, and 15). The newly established block is due to hyperpolarization and is anodal in type. It is a somatic rather than an axonal block. Final recovery from the postasphyxial block requires some 20 minutes. As soon as motoneurons perform the rapid transition from asphyxial block through normal to postasphyxial block they will, upon reasphyxiation, pass through a new and complete asphyxial cycle with the one difference that a marked phase of incrementing response is experienced due to asphyxial mitigation of the postasphyxial block (Fig. 14). Barbiturate narcosis depresses the response of dendrites in a manner that resembles anodal depression for it is relieved rather than reinforced by asphyxial depolarization (Fig. 15). Asphyxial augmentation of response may acquire spectacular dimensions when written upon a state of barbiturate depression. Blocking time of the spinal motoneurons is on the average about 3.5 minutes. It may be shortened by prior asphyxiation (Fig. 14) and is lengthened by cooling of the preparation. Narcotization has not been observed to alter survival time significantly (Fig. 15).     

Influence of intrauterine undernutrition on the development of hypercholesterolemia in an animal model

A low birth weight is a new risk factor for the development of premature atherosclerosis. The effect of intrauterine undernutrition on hypercholesterolemia in later life was studied in an experimental model using the Prague Hereditary Hypercholesterolemic (PHHC) rat. Compared to animals in the control group (Wistar rats), animals with an increased sensitivity to high-cholesterol diet (PHHC rats) display hypercholesterolemia. Only in PHHC animals, individuals undernourished in their intrauterine life (hypotrophic group, HG) had a significantly higher total cholesterol, compared with individuals without food restriction in pregnancy (eutrophic group, EG). Restricted food intake in pregnancy led to smaller nests and a decreased number of pups in each litter. We found no significant diferences in birth weight between HG and EG. In spite of similar birth weights in PHHC and Wistar rats, intrauterine undernutrition caused an increase in cholesterolemia in the HG group of the PHHC rats. The effect of intrauterine undernutrition on the development of hypercholesterolemia will most likely play a role in individuals with geneticaly determined increased susceptibility to a high-cholesterol diet. The use of this model of intrauterine undernutrition for the study of hypercholesterolemia has proved to be feasible.     

Histochemical observation of bovine spinal ganglia

Summary Morphologically, large oval cells, small oval cells and intermediate cells were distinguished among the nerve cells of the bovine spinal ganglion. — The nerve cells generally showed the prominent enzymatic reactions to SDH, NAD-, NADP-dependent MDH, GDH and NAD-dependent IDH.— Large cells reacted somewhat slightly to alpha-GDH, G-6-PDH and NADP-dependent IDH, while intermediate and small cells reacted strongly. LDH reaction of large and small cells was moderate and that of intermediate cells varying. — In general, to the dehydrogenases tested, intermediate cells were most stainable and small cells reacted in the varying degrees. Considerable reactions for dehydrogenases were present in the capsular cells especially in the case of NADP-dependent IDH and G-6-PDH. The nerve fibers were less stainable to the dehydrogenases. MAO activity was observed in the capsular cells, nerve fibers and a large number of the nerve cells. — AChE reaction of the nerve cells was various and that of the capsular cells negligible, while ChE activity was limited to the capsular cells. ACP activity in nerve and capsular cells was positive, and ALP activity was confined to the capsular cells and the capillary vessels. Intense ATPase activity was localized in the capsular cells, peripheral zone of the neuroplasm and the neurilemma.     

Effects of vasopressin on the somatic membrane of spinal ganglia neurons

Intracellular recording from the soma of 68 sensory neurons was performed during experiments on perfused cerebrospinal ganglia (CSG) isolated from 22- to 36-day-old rats. Application of vasopressin (VP) to the CSG produced a response in 59 cells (or 87.76%). Depolarization was noted in 67.8% of those responding, two-stage response in 16.95%, and hyperpolarization in 15.25%. All responses were dose-dependent and reversible. Membrane resistance (R_m) following depolarization declined but increased following hyperpolarization. Application of VP produced a lengthening of action potentials (AP) and a decline both in AP amplitude and after-hyperpolarization. A correlation was revealed between the biophysical properties of CSG neurons and the pattern of their response to VP. Neurons with a slow velocity of axonal conductance, protracted AP, and high R_m (small cells) had the lowest sensitivity threshold to VP at a concentration of 1·10^–11 M and responded with prolonged high-amplitude depolarizing potentials. Cells with a high velocity of axonal conductance, short-lasting AP, and low R_m responded to VP at a concentration of 1·10^–8 M, although response was occasionally lacking even at a concentration of 1·10^–6 M. Depolarization was more short-lived in these neurons and characterized by lower amplitude; cases of hyperpolarization were sometimes observed. Findings from our study would indicate that VP exerts an effect on the soma or primary sensory neurons, acting preferentially on small CSG cells.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 20, No. 6, pp. 801–808, November–December, 1988.     

The two prolongations of spinal ganglia neuroblasts: an ultrastructural study during chick embryo development

Peripheral and central prolongations of chick embryo spinal ganglia neuroblasts were studied and compared at an ultrastructural level during development. Important differences in the terminal tracts of the prolongations and their endings were demonstrated. The possibility of environmental influences being responsible for structural differences in the two prolongations is suggested. It was not possible, at any stage of development, to demonstrate significant polarization of any cytoplasmatic structure in the emerging cones.     

Influence of intrauterine infections and follicular development on the response to GnRH administration in postpartum dairy cows

The effects of intrauterine infections and prior follicular development on the response to gonadotropin releasing hormone (GnRH) administration in postpartum dairy cows were studied. Fifty lactating Holstein cows were assigned at random to one of two groups after calving. Group I (control) consisted of 25 cows given a single intramuscular injection of saline on Day 15 postpartum. Group II (treated) consisted of 25 herdmates given a single i.m. injection of 100 mug of GnRH on Day 15 postpartum. Palpation per rectum and real-time ultrasonography were used to monitor ovarian activity, and endometrial swabs were cultured to determine the presence of uterine infection. Blood samples were collected for progesterone (P(4)) and luteinizing hormone (LH) analysis. Fourteen cows (control, n = 5; treated, n = 9) did not ovulate during the first 60 d postpartum. Ovaries in these cows contained 4 to 8-mm size follicles and both P(4) and LH remained at basal concentrations. Fourteen other cows (control, n = 6; treated, n = 8) ovulated by Day 15 postpartum. Follicles >/= 10 mm were demonstrable in the ovaries of these cows before or by Day 12 postpartum. GnRH treatment had no effect on the lifespan of the existing corpus luteum in these cows. In the remaining cows, 7 of 14 Control and all 8 Treated cows ovulated within 3 d of treatment. All cows ovulating within this period were free of uterine infection and the ovaries contained follicles 相似文献   

Development of satellite-neuron relations in the spinal ganglia of the rat

Cerebrospinal ganglia of 11-, 13-, 15-, 18- and 20-day-old embryos have been studied light- and electron-microscopically. On the 11th day of anlage the ganglia are presented exclusively as neuroblasts: the satellite-cells are formed later from lemmoblasts that install into the ganglion on the 13th-15th days both from the surrounding mesenchyme and from the developing roots and trunklets of the cerebrospinal nerves. In the ganglion they undergo proliferation and further differentiation. On the 15th day simple satellite-neuron interrelationships are formed: one satellite-cell is tightly connected with perikaryons of some neuroblasts and young neurons. On the 18th day around some neurons a double layered capsule is formed from the satellite-cells. Multilayered tunics are formed only on the 10th-15th day after birth. During the process of the capsule formation an unusual reactive character of the satellite-neuron interrelationships is revealed, it is manifested as, performed by the satellite-cells, an active microphagocytosis of the perikaryon cytoplasmic processes and the initial segment of the sensitive neuron main process. In embryogenesis the lemmocyte-axon interrelationships develop earlier than the satellite-neuronal ones.