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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.

The characteristics of acoustic reflex adaptation were studied in human subjects. Contralateral stapedial reflex measurements were made by monitoring changes in acoustic conductance and susceptance with a 220-Hz probe. The reflex activators included four tonal stimuli (500, 1000, 2000, and 4000 Hz) and broadband noise presented for 180 s at 96, 104, and 112 dB SPL. The data are presented as change in acoustic admittance and in percent of maximum admittance change. The static admittance of the ear was found to drift systematically toward lower admittance values in the absence of contralateral stimulation. All stimulus conditions demonstrated some reflex adaptation. The half-life and time of onset of adaptation were found to vary directly with intensity and inversely with frequency. The effects of stimulus parameters on the rates of reflex adaptation are discussed. A previously described exponential model of reflex adaptation provided a reasonable first approximation to the data.

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.

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.

Cerebrospinal fluid plateau pressures and transverse sinus plateau pressures were measured in response to a series of constant-rate infusions into the CSF in 10-day-old control and hydrocephalic H-Tx rats. In control rats the venous pressure increased with CSF pressure but to a lesser extent and around 60% of the total resistance to absorption was due to the concurrent rise in venous pressure with a hydrostatic gradient maintained between CSF and venous blood. In hydrocephalic rats the same infusion rates resulted in an increase in venous pressure which was the same magnitude as the rise in CSF pressure, resulting in zero hydrostatic gradient from CSF to blood. This suggests that CSF drainage does not take place by this route in hydrocephalic rats and that alternative drainage routes must be operating.

The H-Tx rat has inherited hydrocephalus which is present at birth. In order to investigate the onset and early stages of hydrocephalus, the heads of fetuses from 16 to 21 days gestation and at 1 day after birth, were serially sectioned using conventional wax histology. Lateral and third ventricle volumes were measured with a graphics tablet and microcomputer. Hydrocephalus was first detected at 18-20 days gestation by enlarged lateral ventricles and it was sometimes accompanied by a large third ventricle. Most hydrocephalics had a non-patent cerebral aqueduct between the third ventricle and the posterior collicular recess and the remainder (about 25%) had an aqueduct which was patent but with a smaller lumen than in non-hydrocephalic littermates. Some fetuses prior to 18 days gestation with normal lateral ventricles also had non-patent aqueducts. Abnormal aqueducts were lined by ependymal cells which were ventrally displaced by thickening of the overlying midbrain; also the subcommissural organ was foreshortened. Infusion with fluorescent markers confirmed that the flow pathway through the aqueduct was obstructed in many hydrocephalic rats. It is concluded that the hydrocephalus may be the result of abnormal brain development in the midline region of the dorsal mesencephalon, leading to aqueduct closure.

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.

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.

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.

In order to study cerebrospinal fluid (CSF) absorption across the dural sinus wall, the effect of CSF pressure (recorded from the cisterna magna) on dural venous pressure (recorded from the transverse sinus) was investigated in groups of rats at 2, 10, 20, and 31 days after birth and in adulthood. At normal resting pressures there was no positive pressure gradient between the CSF and sinus venous blood in 2-, 10-, and 20-day-old rats, but in 31-day-old and adult rats there was a positive gradient of 16 and 12 mm H2O, respectively. A series of constant-rate infusions of artificial CSF was made into the cisterna magna, and subsequent plateaus in both CSF and venous blood were recorded. The gradient of a plot of plateau pressure against infusion rate gave the overall resistance to absorption of the CSF for each age group, which was higher in 2- and 10-day-old rats than at three older ages. The effect on dural venous pressure was age-related, with the largest increase at 2 days, the smallest at 20 days, and no effect at 31 days or in adults. The pressure difference between CSF and sinus blood has been used to calculate resistance to absorption across the sinus wall. This showed that the high overall resistance to drainage in young rats can be largely accounted for by the rise in sinus pressure. It is concluded that drainage of CSF into the sinuses is greatly restricted in young animals.

Medicaid claims data for a 35% random sample (n = 146,167) of persons receiving benefits from Aid to Families with Dependent Children, and who were eligible for Medicaid in Texas in 1980 are used to examine the impact of outpatient department (OPD)/emergency room (ER) care. Average cost is estimated for OPD/ER and private physician (MD) visits. Persons are also classified by primary source of care. Data on age, race, sex, residence, and months eligible in 1980 permitted prediction of statistically adjusted differences between OPD- and MD-oriented persons for number of ambulatory visits, probability of hospitalization, 1980 total costs, and both hospital episode institutional amount paid and length of stay. OPD/ER visits were found to be $23 more expensive than MD visits. OPD-oriented persons had fewer ambulatory visits, slightly more hospitalizations, greater total and episode costs, and longer lengths of stay than did MD-oriented persons. Potential cost savings are projected.

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.

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.

The posterior tela of the rhombencephalon, the overlying arachnoid mater, and the pial surface of the medulla were examined by transmission electron microscopy in the frog, Rana pipiens. The arachnoid mater and the pia mater have, with minor exceptions, similar ultrastructural characteristics to the same structures in mammals. The posterior tela, on the other hand, is an unusual membrane, the ependymal cells of which are modified to form numerous intercellular pores. These cells are pleomorphic (round, columnar or squamous) and have relatively few surface specialisations while their cytoplasm in electron-dense due to numerous microfilaments. Ependymal cells at the edges of pores are characterised by dense coils of basal lamina inserted into indentations of the lateral plasmalemma and, near the apical surface, by small specialised attachments to adjacent ependymal cells which are otherwise in a different plane.

Scanning electron microscopy of the caudal end of the roof of the fourth cerebral ventricle in four amphibian species shows that numerous pores occur between the ependymal cells. These pores have diameters ranging from 5--100 micron; they permit bluk flow of cerebrospinal fluid out of the ventricular system into the subarachnoid space.

Two tape-slide sequences in general pathology were used in an experiment to assess the value of self-test items and to determine whether it is better to intersperse the self-test items in the programme or place them all at the end of the sequence. The programmes were presented to a random sample of thirty-six students from a class of 149 in one of three forms: version 1, tape-slide programme without self-test items; version 2, tape-slide programme with self-test items interspersed between sections of the sequence; and version 3, tape-slide programme with all self-test items at the end of the sequence. Each student worked a pre-test before studying versions 1, 2 or 3 of a programme. A week later they worked through the post-test which was identical to the pre-test. At the same time they filled in a short attitude questionnaire on the teaching method. All students learned from the programmes. There was improvement in the post-test on the mean pre-test scores for all versions of both programmes. For one programme there was no significant difference between the mean post-test scores for students studying versions 1, 2 or 3, but for the other programme there was a significant difference between the versions. In this case the inclusion of self-test items was better for learning than no self-test items, and it was better if the self-test items were placed at the end of the sequence. A highly favourable attitude to the method is reported.

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.

The hindbrains and meninges of the pigeon and chick have been examined by light and electron microscopy. Serial section histology of the skull with the brain and meninges intact has shown that the caudal end of the roof of the fourth ventricle consists of an extensive membranous pouch which projects caudally and dorsally into the subarachnoid space. Electron microscopy of selected areas of the membranous pouch in pigeon has shown it to consist of two components: ependymal cells and pial tissue. The membrane ependymal cells are squamous, adjacent cells being linked by intermediate junctions. At the junction with the surface of the medulla the ependymal cells are continuous with the ventricular ependyma, and at the choroid plexus they are continuous with the choroid plexus epithelium. These results are discussed in relation to the fluid spaces in and around the hindbrain.

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.

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.

The effect of hydrocephalus on cerebral glucose utilization as reflected by deoxyglucose uptake has been examined in rats with inherited hydrocephalus at 10, 20, and 28 days after birth using a semiquantitative method. Injection of [14C]deoxyglucose intraperitoneally was followed by freezing the brain, sectioning, and quantitative autoradiography of 10 brain regions. Brain [14C] concentration, cortical thickness, and plasma glucose concentrations were measured. Maximal thinning of the cerebral cortex had already occurred by 10 days after birth, although obvious symptoms such as gait disturbance developed after 20 days. In control rats, the cerebral isotope concentration was lower and more homogeneous at 10 days than at 20 or 28 days, which may be a reflection of the use of metabolic substrates other than glucose in younger animals. In order to make comparisons between control and hydrocephalic groups, tissue isotope concentrations were normalized to cerebellar cortex which was not affected by the hydrocephalus at any age. In hydrocephalic rats at 10 and 20 days, the concentration of [14C] was lower in all areas except the inferior colliculi and pons but the reduction was only significant in the sensory-motor cortex at 10 days and in the caudate nuclei at 20 days. By 28 days after birth, all areas except the cerebellum (six cortical regions, inferior colliculi, pons, and caudate) had significantly lower isotope concentrations in the hydrocephalic group. It is concluded that cerebral glucose metabolism is significantly reduced by 28 days after birth in H-Tx rats with congenital hydrocephalus and that less marked reductions occur prior to 28 days.

Continuity between the ventricular and subarachnoid cerebrospinal fluid has been investigated in Rana pipiens. The structure of the posterior tela, a deficient membrane situated at the extreme caudal end of the roof of the fourth ventricle, has been studied using whole membrane mounts and by light microscopy of resin embedded tissue. The ependymal component consists of columnar and rounded cells which form a regular 'syncytium' enclosing round and oval fenestrations. Small fenestrations are covered on the subarachnoid side by elongated pial cells and thus do not give total continuity between the fourth ventricle and the subarachnoid space. Large fenestrations, on the other hand, are accompanied by equivalent pial fenestrations giving direct access between the fluid compartments. Towards the caudal end the fenestrations break up and the numbers of ependymal and pial cells decrease, the caudal end itself being characterised by a small remaining clump of ependyma and pia or of pia alone. Flow through the tela has been studied using fluorescein-labelled dextran placed in the intraventricular space. Infusion into the lateral ventricle and subsequent localisation by fluorescence microscopy shows the marker to be in the fourth ventricle, in the fenestrations of the posterior tela and in the subarachnoid space overlying the tela. Infusion of the marker followed by freezing and examination of the cut heads on a freezing microtome, shows fluorescence throughout the ventricular system, in the subarachnoid space adjacent to the posterior tela and also along the dorsal subarachnoid space of the spinal cord.

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.

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.

Solutions of fluorescein-labelled dextran or Evans blue-albumin were infused into the lateral cerebral ventricle of Rana pipiens. The subsequent distribution in the cerebrospinal fluid (CSF) was investigated between 2 and 24 h after infusion by freezing and examination of the cut blocks of the head and vertebral column of the stage of a freezing microtome. These marker substances move out of the ventricles into the subarachnoid space at the caudal end of the fourth ventricle and spread rapidly along the subarachnoid space of the spinal cord. The spreading of marker substances is slower into the brain subarachnoid space, When the marker is infused into the subarachnoid space of the forebrain, it becomes distributed throughout the subarachnoid space of the brain and spinal cord but not in the ventricles. Partial clearance of markers from the ventricles takes place within 5 h and total clearance within 8 h. Clearance from the brain and cord subarachnoid space is somewhat slower and can only be detected in experiments lasting 10 h or more. Absorption of the markers from the CSF occurs via the intervertebral foramina of the spinal cord. Fluorescence microscopy of sections of the cord show that the fluorescence leaves the subarachnoid space at the point where the spinal nerves traverse the arachnoid membrane.

There have been consistent reports in the psychosomatic literature indicating that a patient's perception of tinnitus as well as differential response to various treatment modalities may be affected by personality variables. The present study examined several personality correlates of subjective tinnitus in forty-five male patients referred to the Audiology Clinic of a large VA Medical Center with constant tinnitus of at least six months duration. Information was also collected on etiology, onset and chronicity, medications, prior treatment and related medical problems. Four standard psychological tests (MMPI, Cattel's 16 PF, Rotter's Locus of Control and Holmes and Rahe Life Stress Scale) were administered to all patients in the study, in addition to a comprehensive audiologic and otologic evaluation. Correlational analyses were used to examine the relationship between personality profiles and the demographic, medical and audiologic data. The expected psychosomatic characteristics of this patient population did not emerge as had been predicted from previous reports in the literature. Findings suggest that tinnitus may have an unwarranted reputation as a psychopathological disorder. Therefore, conventional psychotherapy may be of limited efficacy whereas standard audiologic treatment approaches may be more promising.

Potassium and calcium have been measured in cerebrospinal fluid (CSF), brain interstitial fluid (ISF) and in plasma of congenitally hydrocephalic rats (H-Tx strain) and the results compared with a previous study on control, non-hydrocephalic, rats (CFY strain). Ion-selective microelectrodes were used to determine [K+] at 1-2 and 5 days and [Ca2+] at 1-2, 5, 10 and 20 days after birth. Total [Ca] was measured in plasma and CSF samples with atomic absorption spectrometry. In addition, K+ homeostasis has been studied in CSF and ISF during plasma hyperkalaemia at 5 days after birth. Apart from a raised [Ca2+] immediately after birth, hydrocephalic rats had similar CSF and ISF potassium and calcium concentrations to those found in control rats at the same age. The degree of CSF and ISF K+ homeostasis was also similar in hydrocephalic and control rats.

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.

Sucrose concentrations of 3, 10, 20, and 30% in Czapek Dox broth served as the carbon source for growth, aflatoxin production, and sporulation for Aspergillus parasiticus NRRL 2999 and A. flavus NRRL 3557, 5862, and 5013. All cultures produced mycelial growth and sporulated in all sucrose concentrations during the 12-day growth period. The area of mycelial mat coverage per hour increased directly with increased sugar concentrations. The 20 and 30% sucrose concentrations inhibited mycelial growth for 5862. The 30% sucrose cultures of 3557 and 5862 failed to produce detectable levels of aflatoxins. All other isolates produced B1 and G1 in an approximately 4:1 ratio in all sucrose concentrations. Only 2999 was a substantial producer of aflatoxin in all 4 sucrose cultures, ranging from 72 to 96 micrograms/mL medium. A. flavus 5013 produced the most toxin, 144 and 126 micrograms/mL medium in the 10 and 20% sucrose cultures, respectively. The 10 and 20% sucrose cultures were most conducive to aflatoxin production. Since these sucrose levels correspond closely to the levels in many food and drink products, especially home-made products, care and attention should be taken to keep them free of aflatoxigenic spores. Extensive mycelial growth and sporulation, even in aflatoxigenic strains, do not necessarily result in comparably high aflatoxin levels. Routine extraction and quantitation procedures for aflatoxin were applicable and provided satisfactory results.

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.