The rapid flow of cerebrospinal fluid from ventricles to cisterns via subarachnoid velae in the normal rat.

14C-sucrose in 0.5 microliter of buffered saline was infused over 30 sec into one lateral ventricle, and its subsequent distribution was determined in brain, meninges, cerebral blood vessels, and cerebrospinal fluid (CSF) by quantitative autoradiography. Within 3.5 min, infused radiotracer had moved into the third ventricle, the velum interpositum (an extension of the subarchnoid system that contains many blood vessels), the aqueduct, the mesencephalic and fourth ventricles, and the superior medullary velum (a part of the subarachnoid system that touches the mesencephalic and fourth ventricles). The CSF within both of these velae appears to empty into the quadrigeminal and ambient cisterns. Within 5 min radioactive sucrose was also found in the interpeduncular cistern. About 15% of the injected sucrose quickly left the ventricles and entered these large cisterns. In contrast to most CSF-brain interfaces, little sucrose moved from CSF into the medulla next to the lateral recesses and tissues such as the superior colliculus that lie adjacent to the large CSF cisterns. A thick, multilayered glia limitans visible on electron micrographs seemed to form a CSF-brain barrier at these interfaces. Some of the infused 14C-sucrose persisted in the perivascular spaces and walls of arteries and arterioles for more than 3.5 hr. These findings suggest that CSF may function to deliver various agents and factors to pial and parenchymal arteries and arterioles.

Rapid distribution of intraventricularly administered sucrose into cerebrospinal fluid cisterns via subarachnoid velae in rat.

The intracranial distribution of [14C]sucrose, an extracellular marker infused for 30 s into one lateral ventricle, was determined by autoradiography of frozen-dried brain sections. Within 3.5 min [14C]sucrose appeared in: (i) the third ventricle, including optic, infundibular and mammillary recesses; (ii) the aqueduct of Sylvius; (iii) the velum interpositum, a part of the subarachnoid space that runs along the roof of the third ventricle and contains many blood vessels; (iv) the mesencephalic and fourth ventricles; and (v) the superior medullary velum, a highly vascular extension of the subarachnoid space that terminates at the walls of the mesencephalic and fourth ventricles. Within 5 min, radioactivity was present in the interpeduncular, ambient and quadrigeminal cisterns, which encircle the midbrain. By 10 min, approximately 11% of the radioactivity had passed into the subarachnoid space via a previously undescribed flow pathway that included the velum interpositum and superior medullary velum. At many places along the ventricular system, [14C]sucrose appeared to move from cerebrospinal fluid into the adjacent tissue by simple diffusion, as reported previously (Blasberg R. G. et al. (1974) J. Pharmac. exp. Ther. 195, 73-83; Levin V. A. et al. (1970) Am. J. Physiol. 219, 1528-1533; Patlak C. and Fenstermacher J.D. (1975) Am. J. Physiol. 229, 877-884; Rosenberg G. A. and Kyner W.T. (1980) Brain Res. 193, 56-66; Rosenberg G. A. et al. (1986) Am. J. Physiol 251, F485-F489). Little sucrose was, however, taken up by: (i) circumventricular organs such as the subfornical organ; (ii) medullary and cerebellar tissue next to the lateral recesses; and (iii) the superior and inferior colliculi and cerebral peduncles. For the latter two groups of structures, entry from cerebrospinal fluid was apparently blocked by a thick, multilayered glia limitans. Although [14C]sucrose was virtually absent from the rest of the subarachnoid system after 1 h, it remained in the perivascular spaces and/or walls of pial arteries and arterioles for more than 3 h. Certain transport proteins, protease inhibitors, growth factors and other neurobiologically active materials are present in cerebrospinal fluid, and their distribution to the brain and its blood vessels may be important. The present work shows, in the rat, that the flow of cerebrospinal fluid and the disposition of its constituents is fairly complex and differs among regions. Flow was rapid throughout the ventricular system and into various subarachnoid velae and cisterns, but was surprisingly slow and slight over the cerebral and cerebellar cortices. The cerebrospinal fluid-to-tissue flux of material was relatively free at many interfaces, but was greatly restricted at others, the latter indicating that the old concept of a "cerebrospinal fluid-brain barrier" may hold at such places. Finally, radiolabeled sucrose was retained longer within the walls and perivascular spaces of pial arteries and arterioles than in other subarachnoid tissues; one function of the cerebrospinal fluid system or "third circulation" may thus be delivering factors and agents to these pial blood vessels.

Slightly altered permeability-surface area products imply some cerebral capillary recruitment during hypercapnia.

To test the capillary recruitment hypothesis in brain, cerebral blood flow was raised markedly in rats by exposure to 8% CO2 (hypercapnia), and capillary permeability-surface area (PS) products were measured. Local cerebral blood flow (LCBF), volume of radiolabeled blood in parenchymal microvessels (also referred to as the blood space or Vb), plus the local capillary influx rate constants (K1) and PS products of [14C]antipyrine and 3-O-[14C]methyl-D-glucose (3OMG) were estimated in 44 brain areas. Hypercapnia raised PaO2 to 140 mm Hg, elevated LCBF by two- to threefold through out the brain, and increased Vb from 5 to 33% (mean = 22%) in 42 of 44 brain areas; hypercapnia did not, however, alter microvessel hematocrit. With hypercapnia, the influx of antipyrine was increased by 40-65% in all brain areas, and the PS products of antipyrine were elevated from 0-35% (mean = 17%). The PS products of antipyrine plus the parenchymal blood spaces suggest modest (< 30%) capillary recruitment in most brain areas as well as some microvessel dilation, mainly in forebrain gray matter and white matter areas. In contrast, hypercapnia did not appreciably alter K1 nor PS of 3OMG; it slightly but not significantly raised the blood levels of glucose. In view of the blood space and antipyrine evidence for modest capillary recruitment and vasodilation, the lack of change in PS of 3OMG implies that glucose transporter activity was lowered by hypercapnia, an effect similar to that reported for high-dose pentobarbital. Finally, the microvessel hematocrit and 3OMG data suggest that cerebral capillary permeability (P) was not increased by hypercapnia. Overall, hypercapnia seems to increase LCBF mainly by raising the velocity of blood flow; capillary recruitment and dilation appear to play relatively minor roles in this flow increase.

Parenchymal microvascular systems and cerebral atrophy in spontaneously hypertensive rats.

Spontaneously hypertensive rats (SHR) are hypertensive, hyperactive, and hydrocephalic; furthermore SHR have smaller brain volume and weight than age-matched, normotensive Wistar-Kyoto rats (WKY). At 6-7 months of age, local cerebral glucose is sizably lower in SHR than WKY. The hypothesis that these several abnormalities of SHR lead to variations in cerebral microvascular bed morphology was tested in 6-7-month-old SHR and WKY by quantitating various parameters of small, intermediate, and large parenchymal microvessels (grouped by luminal diameter) in 21 brain areas. Within each rat strain, the microvascular bed properties such as vessel profile frequency (density) varied considerably among the 21 brain areas. In opposition to the hypothesis, mean luminal diameter as well as profile frequency, surface area, and luminal volume of the microvascular beds per unit tissue mass were virtually identical in each brain area of SHR and WKY for the three groups of microvessels. These findings coupled with the reports of less tissue per structure but similar density of neurons throughout the brain of SHR and WKY indicate that there are fewer neurons and less vascular tissue per brain structure in 6-7-month-old SHR than WKY; in addition, they suggest a linkage between the size of parenchymal microvascular beds and the surrounding nervous tissue.

Smaller local brain volumes and cerebral atrophy in spontaneously hypertensive rats.

Spontaneously hypertensive rats (SHR) have enlarged cerebral ventricles from 8 weeks of age onward and smaller brains than age-matched, normotensive Wistar-Kyoto (WKY) rats (controls). At 6-7 months of age local cerebral glucose utilization is apparently lower in many brain areas of SHR relative to WKY rats. These observations led to the hypothesis that there are morphological differences between these two strains of rats in many, if not all, brain areas. This hypothesis was tested in 6-7-month-old SHR and WKY rats by quantitating 1) the volumes of the ventricular system, whole brain, six gray matter structures, and two white matter areas; 2) the thickness of two regions of the cerebral cortex; and 3) the frequency of neuronal nuclei (neuronal frequency) in nine brain areas. Ventricular volume was twofold greater in SHR than in control rats. The volumes of the entire brain and all six gray matter structures plus the thickness of the two cortical regions were 11-25% less in SHR. Neuronal frequency was, however, similar in the two rat strains. The latter finding coupled with the smaller regional tissue volumes indicates appreciably fewer neurons per brain structure in young adult SHR than in controls. These results indicate significant cerebral structural differences between young adult SHR and WKY rats and suggest that structure as well as metabolism are abnormal in the SHR brain.

A perspective of dental education in the twenty-first century.

With the beginning of the twenty-first century only twelve years away, it is clearly not too early for dental educators to be planning for it. If one compares the practice of dentistry and the nature of dental education in 1888 with that of 1988, and then tries to project what they will be like in the year 2088, we have a difficult task indeed. As Alvin Toffler has pointed out in his book Future Shock, we are in an ever escalating period of change. Dentistry and dental education will change much more in the next one hundred years than they have in the last one hundred years.

Particle generation, transport, and characterization at the First International Workshop on light absorption by aerosol particles.

Aerosol particles with a wide range of light absorption properties were generated, transported, and characterized to permit meaningful intercomparisons of all the major types of light absorption instruments. The particles were generated in concentrations of ~1 mg m(-3) and 50 microg m(-3) for periods up to 2 h. The particle characteristics ranged from highly absorbing carbonaceous to nearly transparent ammonium sulfate, from submicron ammonium sulfate to supermicron Arizona road dust, and from spherical ammonium sulfate to chain-aggregate carbonaceous and irregular ambient particles.

Aerosol generation to simulate specific industrial fine particle effluents.

Techniques were developed for generating large quantities of fine particle metal oxide aerosols. The aerosols were generated by burning flammable solutions containing appropriate soluble compounds (nitrates, for example) of the desired elements. In the flame these compounds generally decomposed to oxides. The generated aerosol flow rates were as high as 42 m3 per minute (1500 cfm); the mass concentrations were as high as 16.8 g per m3 at STP. For most aerosols the particle concentrations were of the order of 10(9) particles per cm3. Electron microscopic pictures (SEM and TEM) of precipitated particles show that many of the larger particles (20 microm) are hollow and that the smaller particles (0.01 microm) are aggregated. Specific aerosols were generated to simulate the fine particulate effluents generated by combustion of pulverized coal (electricity generation) electric arc and basic oxygen furnaces (iron and steel production) and zinc smelters. Methods were developed to vary the sulfur dioxide concentration and the electrical resistivities of the simulants for coal combustion.

Results of surgical intervention in the symptomatic multiply-operated back patient. Analysis of sixty-seven cases followed for three to seven years.

Sixty-seven of seventy-three patients who had had multiple operations on the back with an initial diagnosis of lumbar-disc disease were reevaluated as to relief of pain two and four years after the most recent operation. More than 80 per cent of the patients had gained enough relief to deem the procedure worth while. A diagnosis of fibrosis, preoperatively or intraoperatively, portended a poor result, while the opposite was true with diagnoses of mechanical compression (disc fragment or stenosis) and instability (pseudarthrosis after fusion or spondylolisthesis). The presence of a pain-free interval lasting one year from the date of the previous operation correlated highly with the presence of a surgically remediable lesion.

Byssinosis and chronic respiratory disease in U.S. cotton gins.

A pilot study of cotton gin workers was undertaken in the ginning industry so as to determine if a definitive study could be undertaken and to make some first order estimates of byssinosis and chronic respiratory disease and to compare the findings to those reported in the African and European gins. Baseline medical data were collected on 203 gin workers and 260 controls, consisting of a medical symptom questionnaire, a chest x-ray and the forced expiratory spirogram pulmonary test. Results revealed a prevalence of functional reactors equal to that found in the textile industry and other gin studies (44%) as determined by spirometric testing, without any association to smoking history. The major reaction group within the ginning population was those working in the baling press area. These same workers demonstrated evidence of chronic depressions in their spirometry data. No excess of chronic respiratory disease as determined by the questionnaire was detected within the gin worker population.

Temporal and thermal effects on deformation potentials in bone.

There were 44 freshly excised adult rat femora subjected to mechanical deformation in a 4-point bending jig while the load/deformation curves and the electrical potentials generated were recorded simultaneously. Serial testing was repeated after storage of specimens up to 30 days at 25 degrees C and -15 degrees, and after heating for 1 h at 70 degrees, 80 degrees, and 85 degrees C. The amplitude of the potential decreased shortly after the femora had been excised until, by 4-7 days, it reached a plateau which was 10-20% of the initial value. In some cases polarity reversal occurred. These changes were not prevented by freezing or drying nor were they accompanied by increased stiffness. It is presumed that they are related to more subtle changes in the mechanical properties of bone or to alterations in the generating or conducting mechanisms. Heating caused a significant increase in potential without a change in the waveform. A corresponding increase in the deformation occurred due to softening of the bone which could, in itself, be responsible for the increased potential without a basic alteration in the transducer mechanism.

Complete spondylolisthesis in an infant. Treatment with decompression and fusion.

A grade 4 spondylolisthesis at the level of L-4 and L-5 was detected in a 3-year-old girl who had a spastic gait and focal sensory deficit. There was no history or objective evidence of substantial spinal trauma. A deformity over the lower part of the spine had been noted at 1 year of age and the radiological lesion was more extensive than that found in classical spondylolysis. Consquently, a diagnosis of congenital spondylolisthesis is most acceptable. Treatment via combined posterior and posterolateral fusion following anterior decompression has yielded gratifying results.

Mechanism for multiplication of atmospheric ice crystals: apparent charge distribution on laboratory crystals.

Replication of ice crystals with vapor of methyl 2-cyanoacrylate has produced evidence of whiskers on them; an additional mechanism for the necessary multiplication of ice crystals in the atmosphere is suggested. This replication technique also confirms crystal clustering in the atmosphere and appears to confirm the distribution of electrical charge on ice crystals.