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Biomedical subjects

H C Jones

Publications and source records attributed to H C Jones.

At least 73 records · Page 4Linked to original sources
PubMed1988

Brain fluid calcium concentration and response to acute hypercalcaemia during development in the rat.

1. In vivo measurements of plasma, cerebrospinal fluid (CSF) and brain interstitial fluid (ISF) ionic Ca2+ concentrations ([Ca2+]) have been made in anaesthetized rats aged between 19 days gestation and adult using calcium-selective microelectrodes. Total calcium concentration ([ Ca]) has also been determined in plasma and CSF samples by atomic absorption spectrometry. 2. Under control conditions, plasma, CSF and ISF [Ca2+] showed a small, but significant, decrease with age. Plasma and CSF, but not ISF, showed a transient hypocalcaemia at birth. After birth there were no significant differences between plasma, CSF and ISF [Ca2+], except in adult rats where CSF [Ca2+] was significantly lower than plasma [Ca2+]. The age-related changes in CSF and ISF [Ca2+] were small and it is uncertain as to whether they may have any functional significance. 3. Under control conditions, plasma and CSF [Ca] also declined with age. The fall in plasma [Ca] paralleled the changes in plasma [Ca2+]. The decrease in CSF [Ca] was steeper than that in [Ca2+] and indicated a higher proportion of protein-bound or complexed calcium in the CSF of young when compared to old rats. 4. Acute plasma hypercalcaemia was induced by intramuscular injections of calcium gluconate and consequent changes in CSF or ISF [Ca2+] were monitored in vivo. There was very weak regulation of CSF and ISF [Ca2+] at 21 days gestation, which may reflect placental control over fetal plasma calcium. Soon after birth there was good regulation in both ISF and CSF [Ca2+]. CSF [Ca] was also measured during hypercalcaemia in samples from post-natal rats and there was similar regulation to that in CSF [Ca2+]. 5. It is concluded that under control conditions, during rat development, CSF and ISF [Ca2+] closely follow changes in plasma [Ca2+], but that soon after birth homeostatic mechanisms develop to prevent large fluctuations in brain fluid calcium.

Aging↗
PubMed1988

Brain interstitial fluid calcium concentration during development in the rat: control levels and changes in acute plasma hypercalcaemia.

Age-related changes in brain interstitial fluid (ISF) ionic calcium, in ionic and total calcium in plasma and the effect of plasma hypercalcaemia on ISF calcium have been studied in rats aged between late gestation and adult. ISF ionic [Ca2+] decreased significantly with development from 1.6 mM to 1.2 mM. Plasma ionic [Ca2+] was not significantly different from ISF [Ca2+] apart from a transient hypocalcaemia at birth which was not reflected in the ISF. Plasma total calcium was around 2X ionic [Ca2+] and showed the same age-related decrease. In acute plasma hypercalcaemia induced by calcium gluconate injections, there was only weak regulation of ISF Ca2+ at 21 days gestation but a rapid improvement after birth resulted in excellent control by 5 days.

Aging↗
PubMed1987

Choroid plexus structure and function in young rats on a high-potassium diet.

Rats, 20 days old, were fed a diet containing 20% KCl for 10 days. At 30 days these rats had lower body, brain and choroid plexus weights than matched controls and plasma [K+] was increased to 7.5 mM compared to 4.1 mM for controls. Cerebrospinal fluid (CSF) [K+] and bulk fluid secretion were not changed by the high K+ diet but there was a mild metabolic acidosis. The fourth ventricle choroid plexus was prepared for transmission electron microscopy and the structure of the epithelium analysed by quantitative stereology. The high K+ rats had a large increase in the mitochondrial volume fraction of the epithelium due to a 36% increase in individual mitochondrial volume. The high-K+ rats also had a decrease in the apical surface density of the epithelium due to a 41% decrease in the height of the microvilli. It is concluded that the increase in mitochondrial volume may provide the additional energy required for the increased transport of K+ out of the CSF in hyperkalaemia. The reduction in height of the microvilli could be a means for maintaining a normal CSF bulk secretion rate despite the increase in K+ transport required to maintain normal CSF [K+] in hyperkalaemia.

Animals↗
PubMed1987

Morphological aspects of the development of hydrocephalus in a mouse mutant (SUMS/NP).

The SUMS/NP is a mouse mutant with a recessive gene for congenital hydrocephalus. The condition is detectable outwardly at 3 days after birth and affected animals die soon after weaning. The heads of fetuses from 14 to 20 days gestation and at 1, 4, 5, 12 and 18 days after birth have been sectioned for light microscopy and the volume of the lateral ventricles measured in all but the three oldest ages. At 16 days gestation and earlier all fetuses had a relatively large lateral ventricle volume. Hydrocephalus was first detected from volume measurements at 18 days gestation and generally became progressively more severe with age. Hydrocephalic animals, in addition to lateral and third ventricle dilatation, always showed a reduction in the cross-sectional area of the cerebral aqueduct or a total absence of the aqueduct. All hydrocephalics, with the exception of two fetuses, also had cystic cavitation of the forebrain around the lateral ventricles. Electron microscopy of animals with a reduced aqueduct showed the ventral part to be absent in hydrocephalics.

Age Factors↗
PubMed1987

Changes in cerebrospinal fluid pressure and outflow from the lateral ventricles during development of congenital hydrocephalus in the H-Tx rat.

Rats from the H-Tx strain develop hydrocephalus at 19 or 21 days gestation, and were used to measure cerebrospinal fluid pressure and resistance to absorption at different ages between 19 days gestation and 21 days after birth. The results were compared with earlier experiments on normal rats from a different strain. The resting pressure of cerebrospinal fluid in the lateral ventricles of hydrocephalic rats was not elevated above normal up to 10 days after birth, but by 21 days the pressure was nearly twice that of normal rats. Resting pressure measured from the cisterna magna was not significantly different from lateral ventricle pressure. In hydrocephalic rats the resistance to outflow from the lateral ventricles measured by constant-rate infusion, was the same as for normal rats at 19 days gestation but subsequently increased to a value above normal at 1 day after birth. This high resistance was maintained throughout the postnatal period without the postnatal decline seen in normal rats. Resistance to absorption from the cisterna magna, on the other hand, was similar to that in normal rats of the same age. Thus the results of these experiments showed that in the H-Tx strain, cerebrospinal fluid pressure increased only in the late stages of hydrocephalus and that the condition is associated with a reduction in outflow from the ventricular system.

Animals↗
PubMed1987

Developmental changes in cerebrospinal fluid pressure and resistance to absorption in rats.

Cerebrospinal fluid (c.s.f.) pressure and resistance to absorption have been studied in exteriorized fetuses (18 to 21 days gestation) from pregnant rats anaesthetised with pentobarbitone and in similarly anaesthetised postnatal rats at 1, 5, 10 and 30 days after birth and in adults. The resting c.s.f. pressure was low in fetuses (17-21 mm H2O) and it rose to 26-27 mm H2O at 1 and 5 days after birth. By 10 days after birth the pressure was 34 mm H2O after which time there was no further change. The plateau pressure response to different infusion rates was linear, but only up to pressures around 7-fold higher than the resting c.s.f. pressure. Hence, resistance to absorption was calculated for plateau pressures up to 140 mm H2O in fetuses, to 200 mm H2O in 1- and 5-day rats and to 240 mm H2O for 10-day, 30-day and adult rats. Resistance to absorption was not significantly different for the two measurement sites (lateral ventricle and subarachnoid space) at any age studied, showing that fluid can move freely through the ventricular system in young rats. The resistance to absorption was low in the fetuses, 10.8 and 16.3 mm H2O min/microliters at 18-19 and 20-21 days gestation, respectively. There was a sharp increase in resistance to 39.2 mm H2O min/microliters at 1 day after birth and thereafter there was a decrease to 6.8 mm H2O min/microliters at 30 days and this was similar to adult values. This decrease in outflow resistance from the first day after birth may be related to the increase in c.s.f. pressure and secretion rate that occur after birth in the rat.

Absorption↗
PubMed1987

The control of potassium concentration in the cerebrospinal fluid and brain interstitial fluid of developing rats.

1. In situ measurements of plasma, cerebrospinal fluid (CSF) and brain interstitial fluid (ISF) K+ concentrations have been made in anaesthetized rats aged between 19 days gestation and 30 days after birth using K+-selective micro-electrodes. 2. Under control conditions, plasma, CSF and ISF [K+] did not vary significantly with age, the over-all mean concentrations being 3.8, 3.1 and 3.2 mM respectively. The CSF and ISF [K+] were significantly lower than plasma [K+] at all ages. 3. It is concluded that young rats, from the age of 19 days gestation, can normally maintain plasma-to-CSF and plasma-to-ISF gradients similar to those in the adult, presumably by action of the blood-CSF and blood-brain barriers. 4. During acute plasma hyperkalaemia there was very little regulation of CSF [K+] at 21 days gestation, but after birth there was a gradual improvement in CSF K+ homeostasis until by 30 days after birth a normal CSF [K+] could be maintained. 4. There was no regulation of ISF [K+] during hyperkalaemia at 21 days gestation, although after birth there was a rapid improvement in ISF K+ homeostasis. 1-day-old neonates were able to maintain a normal forebrain ISF [K+] during hyperkalaemia. 6. It is concluded that the onset of both CSF and ISF K+ homeostasis takes place at around birth in rats. However, K+ homeostasis matures more rapidly in the ISF than in the CSF. This suggests that, at least in the neonatal period, the CSF is not essential for ISF [K+] regulation.

Animals↗
PubMed1987

Effect of chronic maternal hyperkalaemia on plasma, cerebrospinal fluid and brain interstitial fluid potassium in developing rats.

Plasma hyperkalaemia was induced in pregnant and lactating rats using a high potassium diet. Fetuses of high-K-diet mothers showed no increase in the potassium concentration [( K+]) of plasma, cerebrospinal fluid (CSF) and brain interstitial fluid, presumably due to placental control. Neonates from high-K-diet rats did show an increase in plasma [K+] but this increase was very small and there was no increase in CSF or interstitial fluid [K+]. Maternal milk [K+] was not affected by plasma hyperkalaemia. Weanling rats fed the high-K diet directly showed marked plasma hyperkalaemia but no increase in CSF or interstitial fluid [K+]. Thus, prior to weaning, a relatively stable plasma [K+] is maintained by maternal influence reducing the need for direct brain fluid K+ regulation.

Animals↗
PubMed1986

A morphometric analysis of the development of the fourth ventricle choroid plexus in the rat.

The choroid plexus from the rat fourth ventricle was investigated at ages from 16 days of gestation to 30 days after birth. Choroid plexus weights were measured and light and electron micrographs were analysed by quantitative stereological techniques at 4 levels of magnification. There was a 10-fold increase in plexus weight between 19 days of gestation and 30 days after birth which was largely due to an increase in epithelial weight, with little change occurring in the connective tissue core. Before birth, epithelial cell height decreased whereas between 10 and 30 days after birth cross-sectional area increased, both events being accompanied by corresponding changes in cell volume. Large intracellular stores of glycogen were present around birth, when they occupied up to 20% of the cell volume. After birth there were significant increases in apical microvillus height, the number of microvilli per cell and in the size of the mitochondria, suggesting that a large increase in choroid plexus secretory function, or the commencement of a new function, occurs after birth in the rat.

Animals↗
PubMed1985

The formation of cerebrospinal fluid in two amphibians, Rana catesbeiana and Rana pipiens.

The cerebrospinal fluid (CSF) system of two amphibians, Rana catesbeiana and Rana pipiens has been perfused from the lateral ventricle to a site in the subarachnoid space close to the roof of the fourth ventricle. The CSF production rate (Vf) was measured by the dilution method using a perfusion fluid containing [14C]dextran in artificial CSF. For Rana catesbeiana Vf was 1.43 microliter min-1 or 0.2 microliter min-1 mg choroid plexus-1 and for Rana pipiens Vf was 0.2 microliter min-1 or 0.1 microliter min-1 mg choroid plexus-1. These control values declined by 35% and 14% respectively in the second half of the experimental period. Ouabain (5 X 10(-5) M) in the perfusion fluid for the second half of the experiment resulted in a much greater reduction in Vf, viz. 65% for Rana catesbeiana and 71% for Rana pipiens. Acetazolamide (1 X 10(-4) M) in the perfusion fluid for the second half of the experiment gave no change in Vf values when compared with control 74.5 +/- 4.8 microliters.

Acetazolamide↗
PubMed1985

Cerebrospinal fluid pressure and resistance to absorption during development in normal and hydrocephalic mutant mice.

Hydrocephalic mutant mice and matched siblings at different ages were used to measure the pressure and the resistance to drainage of the cerebrospinal fluid (CSF) from the lateral ventricles and from the cisterna magna with glass micropipets. The resting CSF pressure in normal mice increased between 1 to 2 and 4 to 8 days after birth and subsequently decreased between 4 to 8 and 14 days after birth. In hydrocephalic mice the resting pressure was not significantly different from normal in the 1st week after birth, but by 14 days the pressure was significantly higher in hydrocephalic mice. For normal mice, the resistance from the lateral ventricles at 1 to 2 days after birth was 143.9 mm H2O min microliter-1 and it decreased rapidly to 62.0 at 4 to 8 days, and to 21.2 mm H2O min microliter-1 at 14 days. The resistance to absorption from the cisterna magna in normal mice declined from 94.9 to 44.4 and to 26.8 mm H2O min microliter-1 at 1 to 2 days, 4 to 8 days, and 14 days after birth, respectively, suggesting that the absorptive capacity of the subarachnoid outflow sites increased during that period. Thus resistance measured from the lateral ventricles was significantly higher than that from the cisterna magna in the 1st week after birth, suggesting that in immature mice there is a resistance to flow of CSF through the ventricular system. In hydrocephalic mice the resistance measured from the lateral ventricles was higher than for normal animals at 181.5, 106.4, and 103.7 mm H2O min microliter-1 for 1 to 2 days, 4 to 8 days, and 14 days, respectively. Resistance from the cisterna magna in hydrocephalic animals was not significantly different from normal at any age. Thus it is concluded that the hydrocephalus is associated with an obstruction to the flow of CSF from the ventricles.

Absorption↗
PubMed1985

Earphone-coupling technique for measuring the temporal characteristics of aural acoustic-immittance devices.

This research note describes an earphone-coupling technique that can be used to measure the temporal characteristics of acoustic-immittance instruments. The primary advantage of the earphone-coupling procedure in comparison with the procedure described by Popelka and Dubno (1978) is that the temporal measures are not contaminated by delays and irregularities in the coupler sound-pressure level associated with the pressure system. The latencies of two instruments (Grason-Stadler, Model 1723) were compared using this earphone-coupling procedure and the Popelka-Dubno procedure. The latency measures were in good agreement following a correction for the delay associated with the pressure tubing in the latter procedure. The technique described is offered as an alternative to the Popelka-Dubno procedure in the absence of a modified 2-cm3 coupler, particularly for instruments with complex pressure systems.

Acoustic Impedance Tests↗
PubMed1984

Word recognition with segmented-alternated CVC words: a preliminary report on listeners with normal hearing.

Consonant-vowel-consonant (CVC) monosyllabic words were segmented at the approximate phoneme boundaries and were presented to subjects with normal hearing in the following sequence: (a) the carrier phrase to both ears, (b) the initial consonant segment to one ear, (c) the vowel segment to the other ear, and (d) the final consonant segment to the ear that received the initial consonant. A computer technique, which is described in detail, was used to develop the test materials. The digital editing did not alter appreciably the spectral or temporal characteristics of the words. A series of four experiments produced a list of 50 words on which 10% correct word recognition was achieved by listeners with normal hearing when the vowel segment or the consonant segments of the words were presented monaurally in isolation. When the speech materials were presented binaurally--that is, the vowel segment in one ear and consonant segments in the other ear--word-recognition performance improved to 90% correct.

Adult↗
PubMed1984

The development of congenital hydrocephalus in the mouse.

The development of hydrocephalus has been investigated in a strain of mice with an autosomal recessive gene for hydrocephalus. The hydrocephalus is apparent in histological sections by 1 day after birth as a dilatation of the lateral ventricles and cavitation of the surrounding brain. Infusion experiments show that the flow pathway out of the ventricles is obstructed in 4 day hydrocephalic animals or older but not in newborn animals. The resistance to absorption of the cerebrospinal fluid from the lateral ventricles is high in normal animals at 1-2 days after birth and it falls to adult values at 14 days. Resistance from the cisterna magna is lower than from the lateral ventricles in animals less than 14 days suggesting that, in the first week or two after birth, there is a resistance in the flow pathway through the ventricular system. In hydrocephalic animals the resistance of the flow pathway was higher than normal. There was no defect in the capacity for fluid absorption from the subarachnoid space in hydrocephalic animals.

Animals↗
PubMed1984

Absorption of the cerebrospinal fluid and intracranial compliance in an amphibian, Rana pipiens.

Experiments have been carried out to investigate the absorption of the cerebrospinal fluid (c.s.f.) and the intracranial compliance in an amphibian, Rana pipiens, using infusions into the c.s.f. system through glass micropipettes. Resistance to absorption of the c.s.f. was estimated by the constant rate infusion technique. Mean absorption resistance for infusions of artificial c.s.f. into the lateral ventricles and into the cerebral subarachnoid space were 15.48 and 16.52 mmH2O min microliter-1 respectively. This difference was not significant and it is concluded that the pores in the posterior tela situated in the roof of the fourth ventricle do not offer any resistance to the flow of c.s.f. out of the ventricles. The resistance to drainage of the c.s.f. in this amphibian is higher than that found for mammals. Mean resting c.s.f. pressure, estimated from the intercept of the regression line with the pressure axis at zero infusion rate was 18.0 mmH2O. Absorption resistance was measured from the cerebral subarachnoid space before and after injection of 4 microliter Indian ink solution. There was a 3-fold increase in resistance following ink injection. Two-way analysis of variance showed the difference to be significant (P less than 0.01) suggesting that the outflow sites can become partially blocked by particulate matter. During a continuous 3 h infusion of artificial c.s.f. containing [14C]dextran or [125I]-labelled human serum albumin (RISA) into the lateral ventricles, the mean percentage uptakes into the systemic circulation after the first 0.5 h of a 3 h period were 74.1 and 61.9% respectively. The difference is not significant. The rapid and high uptake into blood suggests there is a direct communication between c.s.f. and blood in amphibians. During continuous infusion of RISA into the lateral ventricles, simultaneous blood samples were taken from the femoral artery and the internal dorsal vertebral vein. Radioactivity was found to be 13.2% higher in venous samples. This suggests that at least some c.s.f. drainage takes place directly into the spinal venous system. Intracranial compliance was investigated by recording the peak pressure in response to a series of bolus injections of artificial c.s.f. into one lateral ventricle. Compliance was estimated to be 0.11, 0.10 and 0.09 microliter mmH2O-1 for injection rates of 12.74, 16.62 and 25.10 microliters min-1 respectively. The difference between these values is not significant. The results suggest that for injection volumes over 5 microliters the c.s.f. system behaves elastically.

Absorption↗
PubMed1983

The development of interependymal pores in the rhombencephalic posterior tela in late embryonic, larval and metamorphosing stages of Rana pipiens.

The structure of the roof of the fourth cerebral ventricle has been studied by scanning and transmission electron microscopy in Rana pipiens from the late embryonic stages, through the larval stages to metamorphosis. Stage 20 and 21 post-hatching embryos have a rhombencephalic roof consisting of undifferentiated embryonic cells. From embryonic stage 22-25 there is progressive differentiation into choroid plexus and posterior tela ependymal cells. Between 1 and 3 interependymal pores occur in the posterior tela and there is a small incipient subarachnoid space dorsal to the posterior tela. During the larval stages, total pore number increases with larval length in a curvilinear manner, with the steepest increase occurring in the latter part of the larval stages. By metamorphosis, total pore number (50-100) approaches that found previously in the adult amphibian. The diameter of individual pores ranges from 1 to 200 microns. Small pores are more numerous than large pores at all stages and both small and large pores become more numerous as development proceeds. Large pores may form by the fusion of two or more smaller pores. It is concluded that pore formation is a gradual process with its onset in the late embryonic stage and concurrent with the onset of choroid plexus and subarachnoid space development. It is suggested that the onset of CSF secretion and circulation may take place shortly after hatching.

Animals↗