Search PubMed⌕ Search

Biomedical subjects

M E Rice

Publications and source records attributed to M E Rice.

At least 19 recordsLinked to original sources
PubMed1996

Water compartmentalization and extracellular tortuosity after osmotic changes in cerebellum of Trachemys scripta.

1. Water compartmentalization in the turtle cerebellum subject to media of different osmolalities was quantified by combining extracellular diffusion analysis with wet weight and dry weight measurements. The diffusion analysis also determined the tortuosity of the extracellular space. 2. Isolated cerebella were immersed in normal, oxygenated physiological saline (302 mosmol kg-1), hypotonic saline (238 mosmol kg-1) and a series of hypertonic salines (up to 668 mosmol kg-1). The osmolality was varied by altering the NaCl content. 3. Extracellular volume fraction and tortuosity of the granular layer of the cerebellum were determined from measurements of ionophoretically induced diffusion profiles of tetramethylammonium, using ion-selective microelectrodes. The volume fraction was 0.22 in normal saline, 0.12 in hypotonic medium and 0.60 in the most hypertonic medium. Tortuosity was 1.70 in the normal saline, 1.79 in the hypotonic and 1.50 in the most hypertonic saline. 4. The water content, defined as (wet weight-dry weight)/wet weight, of a typical isolated cerebellum (including granular, Purkinje cell and molecular layers) was 82.9%. It increased to 85.2% in hypotonic saline and decreased to 80.1% in the most hypertonic saline. 5. Measurements of extracellular volume fraction and water content were combined to show that hypotonic solutions caused water to move from the extracellular to the intracellular compartment while hypertonic solutions caused water to move from the intracellular to extracellular compartment, with only a relatively small changes in total water in both cases. 6. These results suggest the use of the isolated turtle cerebellum as a model system for studying light scattering or diffusion-weighted magnetic resonance imaging.

Animals↗
PubMed1995

Gender differences in cerebral ascorbate levels and ascorbate loss in ischemia.

Ascorbate and glutathione (GSH) are the primary water-soluble antioxidants in the CNS. Oxidative stress, sometimes indicated by loss of these antioxidants, has been linked to several clinical and experimental conditions, including cerebral ischemia. These conditions are also gender-linked, with greater incidence or severity in males than females. To test whether there are gender differences in oxidant/antioxidant regulation, we determined basal levels of ascorbate and GSH in rat brain and their loss after 1 h decapitation ischemia. We found that ascorbate levels in male rat brain were 7-10% higher than in females, depending on region, whereas GSH levels were gender-independent. Significant ascorbate loss (up to 12%) occurred in males during ischemia, with a regional pattern of cerebellum > hippocampus > prefrontal cortex. Loss of ascorbate in females was not significant in any region. By contrast, loss of GSH was significant in both males and females. Greater loss of GSH than ascorbate was in agreement with previous studies and was consistent with loss from enzymatic degradation, as well as oxidation. The significant gender difference in ascorbate loss, as a marker of oxidative stress, supports the hypothesis that inherent differences in oxidant/antioxidant regulation contribute to gender differences in response to ischemia and other pathological conditions.

Analysis of Variance↗
PubMed1995

Long distance pathways of diffusion for dextran along fibre bundles in brain. Relevance for volume transmission.

Texas Red-labelled dextran with a mol. wt of 3000 g mol-1, a marker for the extracellular space, was injected unilaterally into the neostriatum of adult rats (0.3-30 micrograms microliter-1) and its distribution evaluated 1 min to 5 h later. Diffusion in the neuropil was observed with clearance starting after 30 min. After 10-15 min strong labelling along the myelinated fibre bundles was observed in the entire neostriatum. After about 20 min the labelling along the fibres reached into the corpus callosum and the overlaying deep layers of the cerebral cortex. A marked cellular uptake and accumulation of labelled dextran was found in putative perivascular pericytes. Thus, in the living brain preferential extracellular fluid pathways for diffusion exist, especially along fibre bundles, which allow the exchange of chemical signals between two distant regions. These may represent extracellular fluid pathways for volume transmission.

Animals↗
PubMed1995

Salient victim suffering and the sexual responses of child molesters.

In phallometric testing, audiovisual stimuli in which the audio component depicted a child victim's suffering described from the child's point of view were compared with similar scenarios described from the adult male offender's point of view and to portrayals of consenting adult heterosexual activity. Fifteen male participants who had sexually assaulted girls and 15 nonoffenders were also administered questionnaire measures of empathy and opinions regarding sex with children. Consistent with predictions, maximal discrimination between groups was obtained using deviance indices based on stimuli that emphasized victim trauma. Also consistent with predictions, the questionnaire measures were related to sexual deviance. Recommendations are made regarding stimuli for phallometric testing. The results point to the relevance of changing deviant preferences and enhancing empathy for the victim in the treatment of child molesters.

Adolescent↗
PubMed1995

Violent recidivism: assessing predictive validity.

Until very recently, there has been little evidence of the ability of either clinicians or actuarial instruments to predict violent behavior. Moreover, a confusing variety of measures have been proposed for the evaluation of the accuracy of predictions. This report demonstrates that receiver operating characteristics (ROCs) have advantages over other measures inasmuch as they are simultaneously independent of the base rate for violence in the populations studied and of the particular cutoff score chosen to classify cases as likely to be violent. In an illustration of the value of this approach, the base rates of violence were altered with the use of data from 3.5-, 6-, and 10-year follow-ups of 799 previously violent men. Base rates for the 10-year follow-up were also altered by changing the definition of violent recidivism and by examining a high-risk subgroup. The report also shows how ROC methods can be used to compare the performance of different instruments for the prediction of violence. The report illustrates how ROCs facilitate decisions about whether, at a particular base rate, the use of a prediction instrument is warranted. Finally, some of the limitations of ROCs are outlined, and some cautionary remarks are made with regard to their use.

Actuarial Analysis↗
PubMed1995

High levels of ascorbic acid, not glutathione, in the CNS of anoxia-tolerant reptiles contrasted with levels in anoxia-intolerant species.

Ascorbic acid and glutathione (GSH) are antioxidants and free radical scavengers that provide the first line of defense against oxidative damage in the CNS. Using HPLC with electrochemical detection, we determined tissue contents of these antioxidants in brain and spinal cord in species with varying abilities to tolerate anoxia, including anoxia-tolerant pond and box turtles, moderately tolerant garter snakes, anoxia-intolerant clawed frogs (Xenopus laevis), and intolerant Long-Evans hooded rats. These data were compared with ascorbate and GSH levels in selected regions of guinea pig CNS, human cortex, and values from the literature. Ascorbate levels in turtles were typically 100% higher than those in rat. Cortex, olfactory bulb, and dorsal ventricular ridge had the highest content in turtle, 5-6 mumol g-1 of tissue wet weight, which was twice that in rat cortex (2.82 +/- 0.05 mumol g-1) and threefold greater than in guinea pig cortex (1.71 +/- 0.03 mumol g-1). Regionally distinct levels (2-4 mumol g-1) were found in turtle cerebellum, optic lobe, brainstem, and spinal cord, with a decreasing anterior-to-posterior gradient. Ascorbate was lowest in white matter (optic nerve) in each species. Snake cortex and brainstem had significantly higher ascorbate levels than in rat or guinea pig, although other regions had comparable or lower levels. Frog ascorbate was generally in an intermediate range between that in rat and guinea pig. In contrast to ascorbate, GSH levels in anoxia-tolerant turtles, 2-3 mumol g-1 of tissue wet weight, were similar to those in mammalian or amphibian brain, with no consistent pattern associated with anoxia tolerance. GSH levels in pond turtle CNS were significantly higher (by 10-20%) than in rat for several regions but were generally lower than in guinea pig or frog. GSH in box turtle and snake CNS were the same or lower than in rat or guinea pig. The distribution GSH in the CNS also had a decreasing anterior-to-posterior gradient but with less variability than ascorbate: levels were similar in optic nerve, brainstem, and spinal cord. The paradoxically high levels of ascorbate in turtle brain, which has a lower rate of oxidative metabolism than mammalian, suggest that ascorbate is an essential cerebral antioxidant. High levels may have evolved to protect cells from oxidative damage when aerobic metabolism resumes after a hypoxic dive.

Adaptation, Physiological↗
PubMed1994

Direct monitoring of dopamine and 5-HT release in substantia nigra and ventral tegmental area in vitro.

Fast-scan cyclic voltammetry with carbon fibre microelectrodes was used to detect endogenous dopamine (DA) and 5-hydroxytryptamine (5-HT) release from three distinct regions of guinea-pig mid-brain in vitro: rostral and caudal substantia nigra (SN) and the ventral tegmental area (VTA). Previous electrophysiological studies have demonstrated that cells of the caudal SN and the VTA have similar characteristics, whereas cells in the rostral SN have distinctly different properties. In the present study, we confirmed that each region has tyrosine hydroxylase-positive neurons and determined, using high-performance liquid chromatography, that DA levels were similar in rostral and caudal SN, but lower in SN than in VTA. In each region, application of veratrine, which was shown by intracellular recordings to have a reversible depolarising action, evoked a signal attributable to DA and distinguishable from that of 5-HT. Release signals were monitored every 250 ms with a spatial resolution of less than 50 microns.l DA release was calcium-dependent and was not detectable in a catecholamine-poor area such as the cerebellum, or in mid-brain tissue pre-treated with reserpine. Within the normal mid-brain, the amount of DA released was correlated with tissue content in that it was higher in the VTA than in either region of SN. It is concluded that DA released from somato-dendritic parts of mid-brain neurons exhibits site-specific variation. This is the first report of direct monitoring of DA and 5-HT release from these regions with in situ electrodes and demonstrates the utility of fast-scan cyclic voltammetry to investigate the mechanisms and possible non-classical functions of somato-dendritic DA release.

Animals↗
PubMed1994

Psychopathy as a taxon: evidence that psychopaths are a discrete class.

Taxometric analyses were applied to the construct of psychopathy (as measured by the Psychopathy Checklist) and to several variables reflecting antisocial childhood, adult criminality, and criminal recidivism. Subjects were 653 serious offenders assessed or treated in a maximum-security institution. Results supported the existence of a taxon underlying psychopathy. Childhood problem behaviors provided convergent evidence for the existence of the taxon. Adult criminal history variables were continuously distributed and were insufficient in themselves to detect the taxon.

Adolescent↗
PubMed1994

Ascorbic acid, but not glutathione, is taken up by brain slices and preserves cell morphology.

1. We have determined the ascorbic acid (ascorbate) and glutathione (GSH) content of cortical and hippocampal slices from rat brain after prolonged (6h) incubation and have correlated these levels with the histological quality of the slices. Ascorbate and GSH levels in control and sliced tissue were determined by high performance liquid chromatography (HPLC) with electrochemical detection. Cell morphology of incubated slices was compared with that of intact tissue in cresyl violet stained tissue sections. 2. Roughly 70% of tissue ascorbate and GSH was lost from slices during incubation in vitro. Normal in vivo levels of ascorbate (2-3 mumol g-1 tissue wet weight) could be maintained by including 200-400 microM ascorbate (typical extracellular concentration) in the incubation media. By contrast, the loss of GSH could not be prevented by incubation with GSH. 3. The morphology of cells in hippocampal slices incubated under conditions that maintained ascorbate content and compartmentalization were similar to those of intact tissue. Ascorbate protected pyramidal cells in CA1 and CA3 regions of the hippocampus from the degeneration that was seen in slices incubated in ascorbate-free media. 4. These data suggest that loss of endogenous antioxidants may be a major factor in neuronal loss in vitro and support the notion that ascorbate is an endogenous neuroprotective agent.

Animals↗
PubMed1994

Origin of the apparent tissue conductivity in the molecular and granular layers of the in vitro turtle cerebellum and the interpretation of current source-density analysis.

1. We determined the origin of the apparent tissue conductivity (sigma 2) of the turtle cerebellum in vitro. 2. Application of a current with a known current density (J) along the longitudinal axis of a conductivity cell produced an electric field in the cerebellum suspended in the cell. The measured electric field (E) perpendicular to the cerebellar surface indicated a significant inhomogeneity in sigma a (= J/E) with a major discontinuity between the molecular layer (0.25 +/- 0.05 S/m, mean +/- SD) and granular layers (0.15 +/- 0.03 S/m) (n = 39). 3. This inhomogeneity was more pronounced after anoxic depolarization. The value of sigma a decreased to 0.11 +/- 0.03 and 0.040 +/- 0.008 S/m in the molecular and granular layers, respectively. The ratio of sigma a S in the two layers increased from 1.67 in the normoxic condition to 2.75 after anoxic depolarization. 4. This difference in sigma a across the two layers was present within the range of frequencies (DC to 10 kHz) studied where the phase of sigma a was small (less than +/- 2 degrees) and therefore sigma a was ohmic. 5. The inhomogeneity in sigma a was in part due to an inhomogeneity in the extracellular conductivity (sigma e) as determined from the extracellular diffusion of ionophoresed tetramethylammonium. Like sigma a, the value of sigma e was also higher in the molecular layer (0.165 S/m) than in the granular layer (0.097 S/m). The inhomogeneity in sigma e was due to a smaller tortuosity and a larger extracellular volume fraction in the molecular layer compared with the granular layer. 6. sigma a was, however, consistently higher, by approximately 50%, than sigma e. A core conductor model of the cerebellum indicated that these discrepancies between sigma a and sigma e were attributable to additional conductivity produced by a passage of the longitudinal applied current through the intracellular space of Purkinje cells and ependymal glial cells, with the glial compartment playing the dominant role. Cells with a long process and a short space constant such as the ependymal glia evidently enhance the effective "extracellular" conductivity by serving as intracellular conduits for the applied current. The result implies that the effective sigma e may be larger than sigma e for neuronally generated currents in the turtle cerebellum because the space constant for Purkinje cells is several times greater than that for the ependymal glia and consequently Purkinje cell-generated currents travel over a long distance relative to the space constant of glial cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1993

Extracellular dopamine concentration in the retina of the clawed frog, Xenopus laevis.

Dopamine reaches targets in the outer retina of the clawed frog (Xenopus laevis) by diffusion from a network of dopaminergic cells and processes located predominantly at the junction of inner nuclear and inner plexiform layers. We obtained values for the steady-state release, uptake, and extracellular concentration of dopamine in the retina by a combination of HPLC (with electrochemical detection), scintillation spectroscopy, and fast-scan cyclic voltammetry. Vitreal concentrations of dopamine varied from 564 +/- 109 nM in light-adapted eyes near the time of subjective dawn to 156 +/- 12 nM in dark-adapted eyes. The data are consistent with a simple model for steady-state dopamine diffusion from an appropriately sited thin-sheet source. This model was used to generate a profile of extracellular dopamine concentration as a function of retinal depth. The model predicted an increase in the dopamine concentration from the vitreous to the layer of dopaminergic cells, remaining constant from that layer to the distal tips of the photoreceptors. This prediction was borne out by comparing fast-scan voltammetric measures of dopamine at the distal tips of the receptors with the vitreal concentrations determined by HPLC using electrochemical detection.

Animals↗
PubMed1993

Transient extracellular volume reduction in neural lobe of rat hypophysis in response to neural stalk stimulation in vitro and its relationship to extracellular potassium.

1. Using ion-sensitive microelectrodes, a transient reduction in the local volume of neural lobe extracellular space was found to accompany the elevation in extracellular potassium induced by stimulation of the neural stalk. The volume decrease and potassium increase had similar stimulus-response curves when stimulus frequency was varied from 1 to 40 Hz, with maximal response at 20 Hz. The curves for stimulus duration diverged, as a near maximal potassium response was reached in 4-16 s with a 20-Hz stimulus, while the extracellular volume decrease was maximal at 64 s. 2. The volume decrease, but not the potassium increase, was strongly inhibited by lowering bath temperature and moderately inhibited by furosemide and by lowering extracellular chloride concentration. Both the volume and the potassium response were enhanced by ouabain. 3. In conclusion, shrinkage of the local extracellular space in neural lobe during nerve activity is mediated by a metabolically active process which is only partially dependent upon extracellular chloride concentration and anion-cation co-transport, but is relatively independent of Na(+)-K+ pump activity. A transient shrinkage in extracellular space during increased neurohypophysial nerve activity would be expected to play a role in hormone diffusion, ion buffering, and extracellular current flow.

Animals↗
PubMed1993

Anisotropic and heterogeneous diffusion in the turtle cerebellum: implications for volume transmission.

1. Measurements of extracellular diffusion properties were made in three orthogonal axes of the molecular and granular layers of the isolated turtle cerebellum with the use of iontophoresis of tetramethylammonium (TMA+) combined with ion-selective microelectrodes. 2. Diffusion in the extracellular space of the molecular layer was anisotropic, that is, there was a different value for the tortuosity factor, lambda i, associated with each axis of that layer. The x- and y-axes lay in the plane parallel to the pial surface of this lissencephalic cerebellum with the x-axis in the direction of the parallel fibers. The z-axis was perpendicular this plane. The tortuosity values were lambda x = 1.44 +/- 0.01, lambda y = 1.95 +/- 0.02, and lambda z = 1.58 +/- 0.01 (mean +/- SE). By contrast, the granular layer was isotropic with a single tortuosity value, lambda Gr = 1.77 +/- 0.01. 3. These data confirm the applicability of appropriately extended Fickian equations to describe diffusion in anisotropic porous media, including brain tissue. 4. Heterogeneity between the molecular and granular layer was revealed by a striking difference in extracellular volume fraction, alpha, for each layer. In the molecular layer alpha = 0.31 +/- 0.01, whereas in the granular layer alpha = 0.22 +/- 0.01. 5. Volume fraction and tortuosity affected the time course and amplitude of extracellular TMA+ concentration after iontophoresis. This was modeled by the use of the average parameters determined experimentally, and the nonspherical pattern of diffusion in the molecular layer was compared with the spherical distribution in the granular layer and agarose gel by computing isoconcentration ellipsoids. 6. One functional consequence of these results was demonstrated by measuring local changes in [K+]o and [Ca2+]o after microiontophoresis of a cerebellar transmitter, glutamate. The ratios of ion shifts in the x- and y-axes in the granular layer were close to unity, with a ratio of 1.04 +/- 0.08 for the rise in [K+]o and 1.03 +/- 0.17 for the decrease in [Ca2+]o. In contrast, ion shifts in the molecular layer had an x:y ratio of 1.44 +/- 0.14 for the rise in [K+]o and 2.10 +/- 0.42 for the decrease in [Ca2+]o. 7. These data demonstrate that the structure of cellular aggregates can channel the migration of substances in the extracellular microenvironment, and this could be a mechanism for volume transmission of chemical signals. For example, the preferred diffusion direction of glutamate along the parallel fibers would help constrain an incoming excitatory stimulus to stay "on-beam."

Animals↗
PubMed1991

Anoxia-resistant turtle brain maintains ascorbic acid content in vitro.

The isolated turtle brain maintains intra- and extracellular concentrations of ascorbate when incubated in ascorbate-free physiological saline for as long as 24 h. After incubation for 1 h, total tissue content of ascorbate in the turtle cerebellum was the same as in unincubated controls. After 20-24 h, tissue ascorbate content remained at 65% of control levels, while extracellular ascorbate concentration, measured with carbon fiber voltammetric microelectrodes, was 56% of the initial value. For an intermediate incubation period of 6 h, reduced ascorbate content was maintained at about 80% of control levels, regardless of whether incubation was under normal conditions or in the absence of glucose or oxygen. By contrast, only 4% of the ascorbate content of guinea pig brain slices remained after a 6 h incubation. Maintenance of high levels of ascorbate by the anoxia-resistant turtle brain could be an important factor in the amelioration of oxidative injury in this tissue. Inclusion of ascorbate in media used for in vitro studies of mammalian brain tissue is recommended.

Animals↗
PubMed1991

Extracellular alkaline-acid pH shifts evoked by iontophoresis of glutamate and aspartate in turtle cerebellum.

The effect of glutamate and aspartate iontophoresis on extracellular pH was investigated in the turtle cerebellum in vitro. Both amino acids produced a rapid alkaline transient, typically followed by a prolonged acidification. These responses could be evoked in all layers of the cerebellum. Transition from bicarbonate to N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid-buffered media amplified the pH shifts. Similar alkaline-acid transients could be evoked in the molecular layer by electrical stimulation of the parallel fibers or the ipsilateral peduncle, or by superfusion of glutamate or aspartate. However, no alkaline shifts were evoked in the granular layer by either parallel fiber or peduncle stimulation. In contrast, the iontophoretically induced alkaline shifts were largest in the granular layer. Compared with the stimulus-evoked alkalinizations, the iontophoretic alkaline shifts were relatively insensitive to Mn2+ or Cd2+. These data suggest that the activity-dependent alkalinization of brain extracellular space is generated by a bicarbonate-independent mechanism related to excitatory synaptic transmission. The results are consistent with a flux of hydrogen ions through cationic channels, but do not support a direct role for voltage-dependent Ca2+ channels. In view of the sensitivity of ion channels to changes in external pH, and the magnitude of the amino acid-induced pH shifts, these results indicate that extracellular pH could play an important modulatory role in excitatory synaptic transmission.

Animals↗