New patterns of intracortical projections after focal cortical stroke.

Cortical strokes alter functional maps but associated changes in connections have not been documented. The neuroanatomical tracer biotinylated dextran amine (BDA) was injected into cortex bordering infarcts 3 weeks after focal strokes in rat whisker barrel (somatosensory) cortex. The mirror locus in the opposite hemisphere was injected as a control. After 1 week of survival, brains were processed for cytochrome oxidase (CO)-, Nissl-, and BDA-labeled neurons. Cortex bordering the infarct (peri-infarct cortex) had abnormal CO and Nissl structure. BDA-labeled neurons were plotted and projections were analyzed quantitatively. Animals with small strokes had intracortical projections, arising from peri-infarct cortex, not seen in normal hemispheres: the overall orientation was statistically significantly different from and rotated 157 degrees relative to the controls. Compared to the controls, significantly fewer cells were labeled in the thalamus. Thus, after focal cortical stroke, the peri-infarct cortex is structurally abnormal, loses thalamic connections, and develops new horizontal cortical connections by axonal sprouting.

Collateral growth and angiogenesis around cortical stroke.

BACKGROUND AND PURPOSE: We tested the hypothesis that there are significant long-term local vascular changes after ministroke that could form a basis for functional recovery. METHODS: A 6- to 8-mm cranial window was opened over the barrel cortex, which was identified by an intrinsic optical signal during mechanical stimulation of the whiskers in anesthetized female Wistar rats. Branches of the middle cerebral artery (MCA) to this region were ligated. Fluorescein isothiocyanate (FITC) transits were recorded by videomicroscopy in each rat just before, immediately after, and 30 days after ligation. Changes in surface vessels and parenchymal perfusion were measured. In similarly prepared rats, angiogenesis was identified by 5-bromo-2-deoxyuridine labeling and immunohistochemistry for the integrin family member alpha(v)beta(3). RESULTS: The intrinsic optical signal disappeared immediately after MCA ligations. FITC injection just after ligation demonstrated 3 concentric regions: 1 region of unchanged perfusion, surrounding 1 region of reduced perfusion (the ischemic border) surrounding a central core with little observable perfusion. At 30 days, the following had taken place: (1) diameters and lengths of surface collaterals in the ischemic border had grown significantly, but no new surface vessels were detected, (2) FITC entered occluded MCA segments, (3) arteriocapillary latencies in the ischemic border were shortened compared with latencies just after ligation, and (4) small infarcts were virtually identical to the poorly perfused core. Angiogenesis was confined to the ischemic border. CONCLUSIONS: Arteriolar collateral growth and new capillaries support restored perfusion in the ischemic border after ministroke and could support long-term functional recovery.

Local cerebral blood flow during the first hour following acute ligation of multiple arterioles in rat whisker barrel cortex.

The objectives are to measure the early time-course of the flows of blood, red cells, and plasma in brain tissue destined to infarct following arterial occlusion. The flux of fluorescent red blood cells (fRBCs) through venules and the arteriovenous transit times (AVTT) of fluorescein-labeled plasma albumin were periodically monitored in anesthetized adult Wistar rats before and up to 60 min after permanent ligations of several small branches of the middle cerebral artery. Of note, fRBC is a function of venular erythrocyte flow and volume, whereas AVTT is a function of plasma flow and volume in visible arteriole-capillary-venule units. In another group of anesthetized rats, local cerebral blood flow (ICBF) was measured 1 h after permanent arterial occlusion by [14C]iodoantipyrine (IAP) autoradiography. With this model of focal ischemia, the lesion is highly reproducible and involves part of the whisker barrel cortex. Infarction of this area was observed in 12 of 13 rats. From 10 to 60 min after arterial occlusion, AVTT was nearly four times longer in the ischemic barrel cortex than at the same site before ligations, and fRBC flux was 25%. Neither parameter changed appreciably over this time. After 60 min of ischemia, ICBF on the ipsilateral barrel cortex was 18% of that on the contralateral side and 15% of the sham control value for the same area of the barrel cortex. Since whole blood flow in the ischemic barrel cortex was < 20% of normal at 60 min and AVTT and fRBC flux were essentially constant from 10 to 60 min, the rates of plasma and red cell flows were similarly depressed during the first hour of arteriolar occlusion. In conclusion, such lowering of red cell, plasma, and blood flows produced consistent infarctions in the barrel cortex.

Neuronal units linked to microvascular modules in cerebral cortex: response elements for imaging the brain.

How neuronal activity changes cerebral blood flow is of biological and practical importance. The rodent whisker-barrel system has special merits as a model for studies of changes in local cerebral blood flow (LCBF). Stimulus-evoked changes in neural firing and 'intrinsic signals' recorded through a cranial window were used to define regions of interest for repeated flow measurements. Whisker-activated changes in flow were measured with intravascular markers at the pia. LCBF changes were always prompt and localized over the appropriate barrel. Stimulus-related changes in parenchymal flow monitored continuously with H2 electrodes recorded short latency flow changes initiated in middle cortical layers. Activation that increased flow to particular barrels often led to reduced flow to adjacent cortex. Dye was injected into single penetrating arterioles from the pia of the fixed brain and injected into arterioles in slices of cortex where barrels were evident without stains. Arteriolar and venular domains at the surface were not directly related to underlying barrels. Capillary tufts in layer IV were mainly coincident with barrels. The matching between a capillary plexus (a vascular module) and a barrel (a functional neuronal unit) is a spatial organization of neurons and blood vessels that optimizes local interactions between the two. The paths of communication probably include: neurons to neurons, neurons to glia, neurons to vessels, glia to vessels, vessels to vessels and vessels to brain. Matching a functional grouping of neurons with a vascular module is an elegant means of reducing the risk of embarrassment for energy-expensive neuronal activity (ion pumping) while minimizing energy spent for delivery of the energy (cardiac output). For imaging studies this organization sets biological limits to spatial, temporal and magnitude resolution. Reduced flow to nearby inactive cortex enhances local differences.

Rapid optical imaging of whisker responses in the rat barrel cortex.

Videomicroscopy was used to image 'intrinsic' responses over the rat barrel cortex through a closed cranial window during controlled whisker stimulation. With a Macintosh IIfx running Image 1.49 VDM, video frames from a CCD camera were captured and averaged before, during and after whisker stimulation. The technique presented here is a functional imaging modality--using conventional videomicroscopic equipment, a small computer, and public domain NIH Image software--with a temporal resolution of 33 ms. Images can be obtained directly from the CCD camera or recorded to videotape for post hoc analysis. Pixel by pixel comparison of prestimulation images to images obtained during stimulation revealed changes in the reflectance characteristics of cortex and vessels overlying the barrel field. Imaged responses superimposed on barrel histology to map intrinsic signal matched barrels of the stimulated whiskers in every case. Video imaging of the rat barrel cortex provides a useful method for rapid targeting for other experimental protocols and has potential for analyzing localized responses to physiologic stimuli in vivo.

Cardiac output in Xenopus laevis tadpoles during development and in response to an adenosine agonist.

We test the hypothesis that the heart and arteries enlarge with increased cardiac output (CO) during development and volume overload. Transparent albino tadpoles of Xenopus laevis at stages 43-50 were anesthetized in 0.3-0.5 mM benzocaine. Areas and radii [maximum and minimum radius (Rmax and Rmin, respectively)] of the ventricle were measured in digitized video frames during the cardiac cycle. Stroke volume (SV) and CO were calculated from Rmax and Rmin. Maximal velocities of 3.4-microns fluorescent beads were measured in the aortic arches. Arterial pressure was estimated by the Landis method. During normal development, the radii of the ventricle and aortic arch diameters increased with lengths of tadpoles, and SV (0.7 microliters/g) and CO (70 microliters.g-1.min-1) with wet weights. Volume overload was induced by a vasodilatory adenosine agonist 5'-N-ethylcarboxamidoadenosine (NECA) in the aquarium water. Acute (0.5-4 h) NECA significantly increased Rmax and heart rate. Chronic (> 1 wk) NECA significantly increased both Rmax and Rmin. SV and CO increased more than two times, blood pressures decreased, and specific vascular conductances increased more than five times. It is concluded that NECA increases CO in Xenopus tadpoles through a combination of increased filling and accelerated growth.

LCBF changes in rat somatosensory cortex during whisker stimulation monitored by dynamic H2 clearance.

We evaluated increases in local cerebral blood flow (LCBF) localized to single activated cortical columns by H2 clearance methods. The rat whisker-barrel cortex is a model for cortical function and neural processing in active explorative behaviors. Up to four 30-40 microns Pt wire electrodes were inserted in or near the rat whisker-barrel cortex. Electrode positions were mapped by postmortem histology. H2 was generated electrochemically by constant current from one electrode and detected by one or more other electrodes 300-500 microns away. Changes in LCBF produced inverse changes in PH2. Shifts during steady H2 generation were calibrated against standard H2 inhalation clearance curves at rest and during inhalation of 7.5% CO2 for 1 min for quantitative estimates of LCBF. Contralateral whisker stimulation at 3 Hz, 1 min duration and delivered every 2 min produced the largest increases in LCBF. LCBF responses were detected in approximately 1 s. Stimulation of single whiskers produced the largest responses when an electrode was in the corresponding barrel. These results indicate that increased neural activity in a single cortical column produces blood flow responses primarily in that column.

Feeding and breathing in lampreys.

A basic problem faced by the agnathans in evolution was how to feed and breathe without jaws. Three solutions are represented by lampreys and their ammocoete larvae, reviewed here, and hagfishes. Lampreys feed upon fish with their suckers and breathe in and out of their branchial gill sacs. Parasitic species of lampreys can be flesh-feeders or blood-feeders, depending primarily on the structure of their teeth. Feeding behavior is characterized by rhythmic rasping, negative pressure pulses in the sucker, and swallowing of fluid into the gut. Ammocoete larvae use a velar pump for unidirectional ventilation and suspension feeding. In both lampreys and ammocoetes the branchial basket is actively compressed for exhalation; branchial expansion and inhalation is by passive elastic recoil, but in ammocoetes water is drawn from the mouth. Central pattern generators for respiration are distributed in the medulla, particularly lateral to Vm, and drive branchial motoneurons in VIIm-IXm-Xm. Trigeminal pattern generators in lampreys may be a holdover from the ammocoete stage, in which they drive nearby velar motoneurons as the primary pump for ventilation. Respiration in lampreys and ammocoetes is stimulated by hypoxia and modulated by reflexes. Metamorphosis from ammocoete to adult lamprey involves extensive remodeling of the head with regression and replacement of most muscles. Trigeminal motoneurons are probably preserved during metamorphosis, as inferred from constant maps of motoneurons in Vm. This hypothesis is supported by analogy with anuran metamorphosis in which V motoneurons are retained and remodeled. In Mallatt's current models, the earliest vertebrates breathed by branchial contractions and valves; jaws initially evolved for better ventilation and later were used for feeding.

Ministrokes in rat barrel cortex.

BACKGROUND AND PURPOSE: Many stroke models in rats are based on occlusion of the middle cerebral artery, which supplies a significant portion of multifunctional cortical and deep structures in the cerebral hemisphere. The purpose of this study was to develop a model for direct observation in real time of blood flow in and around focal ischemic regions of the cortex of known function. METHODS: Cranial windows were placed over the parietal cortex of adult Wistar and Sprague-Dawley rats anesthetized with ketamine and xylazine. Whisker barrel cortex responding to stimulation of the contralateral whiskers was identified by an intrinsic optical signal. Transits of vital dyes were recorded by videomicroscopy before and after ligation of three to six branches and major collaterals of the middle cerebral artery through the dura. Infarcts were demonstrated with triphenyl-tetrazolium chloride staining; their relation to barrel cortex was determined by Nissl and cytochrome oxidase histology. RESULTS: Reduced blood flow in small ischemic regions was outlined by patient blue violet in the surrounding nonischemic area; arteriovenous latencies increased more than four times in ischemic cortex. Infarcts,typically 3 mm or less, were seen at 24 hours in 8 of 16 Wistar and 9 of 9 Sprague-Dawley rats. The ministrokes were confirmed by histology to be in the somatosensory cortex. CONCLUSIONS: This model of local ischemia, produced deliberately in the functionally defined barrel cortex in rats, leads to ministrokes. Changes can be followed by videomicroscopy as they develop, and processes of recovery can potentially be monitored. Infarcts are confirmed by histology for their location and extent in the somatic representation.

[A comparison of the measurements of local cerebral blood flow by hydrogen clearance with hydrogen inhalation and by its electrochemical generation in brain tissue]. / Sopostavlenie izmerenii lokal'nogo mozgovogo krovotoka vodorodnym klirensom s ingaliatsiei vodoroda i s ego élektrokhimicheskoi generatsiei v tkani mozga.

The goal of the present investigation was to compare data received by modifications of H2-clearance method with inhalation (H2-Inh) and electrochemical generation in brain tissue (H2-Gen) of H2 from the same recording electrodes in acute experiments (urethane 1g/kgip) with Wistar rats (n = 39). Block of three or four Pt electrochemically sharpened electrodes to tip diameters of 20-40 mu, 0.3-0.5 mm apart and 0.8-1.0 mm in length were inserted through the dura into sensorimotor cortex. One electrode was used for H2 generation (DC current 3-5 microA) and the others for PH2 recordings by polarographical method. Durations of H2 inhalation and H2 electrochemical generation were 3 or 10s with similar amplitudes of PH2. Data was recorded with a MacLab analog-digital system and Macintosh 11si computer. Recordings of resting LCBF were made with H2-Gen and H2-Inh the beginning of the experiment and after 40-60 min. LCBF was stimulated with inhalation of 7.5% CO2 for 60s. In 6 preparations LCBF was measured 10-20 min. after occlusions of two branches of the middle cerebral artery. After experiments the brain was perfused with India ink and cut in frozen sections for morphological analyses. The mean values of resting LCBF measured by H2-Inh was 1.67 +/- 0.54 ml/g/min. (+/- SD, N = 149), and by H2-Gen 3.17 +/- 0.91 (N = 147). The diffusional component was estimated as 1.2-2.5 (equivalent units, ml/g/min.) in dead cortex. The ratio of clearances in H2-Gen to H2-Inh varied in different experiments from 1.0 up to 4.0.(ABSTRACT TRUNCATED AT 250 WORDS)

An adenosine agonist increases blood flow and density of capillary branches in the optic tectum of Xenopus laevis tadpoles.

OBJECTIVE: To test the hypothesis that adenosine can increase capillary densities in developing brain tissue. METHODS: Transparent tadpoles of albino Xenopus laevis were exposed to adenosine agonists, mainly 5'-N-ethylcarboxamidoadenosine (NECA), and to antagonists, mainly 8-phenyltheophylline (8PT) in aquarium water. After 2 weeks in drugs, networks of blood vessels on the dorsal surface of the optic tectum were scanned in vivo by videomicroscopy. Densities of surface capillaries and venules, of deep branches, and of deep perfused capillaries were calculated. RESULTS: NECA initially dilated brain blood vessels and chronically increased blood flow by a simple subjective index. 8PT diminished diameters and prevented the subjective flow increase. Chronic 3 microM NECA significantly increased densities of total deep branches from pial vessels into the tectum. CONCLUSIONS: In an in vivo amphibian assay, NECA dilated brain capillaries and venules and increased their flow and density. Adenosine was present chemically and increased during metabolic stress. These results are consistent with adenosine as a metabolic signal for growth of blood vessels during brain development. In addition, it appeared that short-term dilation and flow increase in tectal capillaries in acute NECA was followed over a period of weeks in chronic NECA by vascular remodeling and return of diameters to normal.

[Combinations of methods for the monitoring of the cerebral microcirculation]. / Kombinatsii metodov dlia monitoringa mikrotsirkuliatsii mozga.

Any single method for measuring changes in local cerebral blood flow (LCBF) or blood vessels during physiological stimuli has individual strengths and deficiencies. The coupling of multiple methods based on different physical principles permits simultaneous measurements and tests of interrelated cerebrovascular changes and mechanisms. The present paper describes combined recordings of LCBF by H2 clearance with inhalation (H2Cl-Inh) and with steady electrochemical generation (H2Cl-Gen), by laser Doppler flowmetry (LDF) and by dimensional changes in surface vessels with videomicroscopy through acute cranial windows in rats anesthetized with urethane 1g/kg or urethane (0.6 g/kg) plus chloralose (0.05 g/kg)ip. For H2Cl-Gen recordings paired or quadred Pt sharped block of electrodes (diameter 0.04-0.06 mm) with distance between single electrode 0.3-0.5 mm, was inserted to brain tissue in barrel cortex. One electrode was used for H2 generation and others for LCBF recordings and their position in brain tissue was examined morphologically. Increase local blood flow in barrel cortex and arterial dilation were stimulated by inhalation of 7% CO2 and mechanical stimulation of the contralateral whiskers. H2Cl-Inh was a "gold standard" for quantitative measurements of LCBF within a tissue radius 0.3-0.5 mm from the recording electrode during related tests during steady states at the same site. H2Cl-Gen was very sensitive to transient changes in flow and could record latencies. H2Cl-Gen was calibrated for quantitative measurements of changes in LCBF by pairing with H2Cl-Inh responses to CO2 inhalation. The laser Doppler miniature probe recorded the time course and normalized intensity changes within an approximate 1 mm3 volume of cortex but with more background noise and less sensitivity compared to H2Cl-Gen. Bright illumination of the cranial window increased LCBF by both methods in these experiments. The diameters of surface arterioles and venues were measured in single video frames with date-time markers for correlation with electrical recordings. Changes in diameter were small and were slower compared to H2Cl-Gen and LDF in the present recordings. Received data permit to conclude that there are two optimal combinations of methods were (1) H2Cl-Gen and H2Cl-Inh for both dynamic sensitivity and quantitative LCBF during systemic and neuronal stimulation, and (2) H2Cl-Gen, LDF, and videomicroscopy for multidimensional monitoring of cerebral circulation.

Localized dynamic changes in cortical blood flow with whisker stimulation corresponds to matched vascular and neuronal architecture of rat barrels.

The hypothesis that functional groups of neurons in whisker barrels are linked to a modular organization of cortical vessels was tested. Endovascular casts demonstrated cortical capillary networks resembling the whisker barrel pattern that were fed from the middle cerebral artery. In histological sections, dense capillaries apparently were confined to single barrels and were supplied by one or a few penetrating arterioles. The barrel field in cortical layer IV was localized in relation to surface arteriovenous patterns. Living vessels were imaged through a closed cranial window under anesthesia with a fluorescence microscope and SIT or ICCD cameras. After intracarotid injections of fluorescein isothiocyanatedextrans, saline, or 3 microns latex beads, changes in arteriolar diameter, arteriovenous transit times (AVTTs), and bead velocities were measured. When row C whiskers were stroked at 4-5 Hz for 1 min, blood flow increased in arterioles that supplied contralateral row C barrels as demonstrated by postmortem histology. AVTTs slowed significantly in vessels supplying adjacent cortex. We hypothesize that cerebral vascular units supply individual whisker barrels and are functionally linked to them for precise focal regulation of cerebral blood flow.

Blood flow in single surface arterioles and venules on the mouse somatosensory cortex measured with videomicroscopy, fluorescent dextrans, nonoccluding fluorescent beads, and computer-assisted image analysis.

Cortical surface vessels were monitored through closed cranial windows with an epifluorescence microscope and SIT or ICCD cameras. Fluorescent dextrans or 1.3 microns latex beads were injected into the contralateral jugular vein for plasma labeling and for vascular transits. For close arterial transits, these tracers or physiological saline were injected into the ipsilateral external carotid artery. AVTTs were calculated from intensity differences of tracers between a branch of the MCA and a vein draining the same cortical region over time. AVTTs for saline dilutions of RBCs were significantly shorter (0.73 times) than for dextrans. Both dextrans and beads distributed with plasma. With FITC-dextran, inner diameters of arterioles and venules averaged 6 microns larger than hemoglobin under green light. This difference was likely due to the segregation of red blood cells and plasma during flow. Velocities of individual fluorescent beads were measured in pial vessels by strobe epi-illumination. Plots of bead velocities against radial position in arterioles were blunted parabolas. Peak shear rates in the marginal layer next to the vessel walls were determined directly from bead tracks in arterioles (D = 21-71 microns) and were 1.32 times the Poiseuille estimate. The calculated peak wall shear stress was 39 +/- 14 dyn/cm2 (mean +/- SD) for these arterioles but was probably severalfold greater in the smallest terminal pial arterioles. Vmax near the axes of arterioles increased with D+0.5. The calculated peak wall shear rate was highest in small arterioles and decreased with D-0.5. The calculated flow Q increased with D+2.5. These methods permit direct, simultaneous, dynamic measurements on multiple identified cerebral microvessels.

Development and remodeling of cerebral blood vessels and their flow in postnatal mice observed with in vivo videomicroscopy.

Changes of blood vessels in the mouse somatosensory (barrel) cortex were assessed from birth (P0) to adulthood. Surface vessel anatomy and flow were observed directly with videomicroscopy through closed cranial windows and with intravascular fluorescent tracers. Histology was used to determine the internal capillary density. At birth, arterioles had numerous anastomoses with each other, pial capillaries formed a dense surface plexus, and pial venules and veins were relatively small and irregular. Morphological changes over the next 2 weeks included (a) fewer arteriolar anastomoses, (b) formation and growth of venules, (c) more uniform diameters of all types of vascular segments, (d) increase in intraparenchymal capillary length density (Lv), and (e) decreases in superficial capillary density and diameters. A simple morphological test showed that wall shear rates at arteriolar branch points were matched on average in neonates and adults. Flow characteristics in single vessels were evaluated. In arterioles of like diameters, (a) Vmax, (b) peak wall shear rates, and (c) peak flows were similar at all ages; (d) velocity was very high in occasional arteriovenous (AV) shunts in newborns; and (e) flow in arteriolar anastomoses was slow and variable. Although flow was heterogeneous in all types of vessel, the marked similarities in newborn and adult mice of average peak velocities and calculated wall shear rates in arterioles of the same size suggest that blood flow regulates in part the remodeling of blood vessels during development (Rovainen et al., 1992). The rodent barrel cortex undergoes major neuronal and vascular development, functional differentiation, and remodeling during the first weeks after birth. It provides special opportunities for testing how blood vessels grow and adapt to supply the local metabolic requirements of neural modules in the brain.

Labeling of developing vascular endothelium after injections of rhodamine-dextran into blastomeres of Xenopus laevis.

The goal of this work has been to label endothelial cells with fluorescent marker and to record their behavior during angiogenesis in vivo. Single blastomeres in 16-128-cell-stage embryos of pigment-deficient Xenopus laevis were injected intracellularly with 5% tetramethyl-rhodamine dextran. Subsequently, the embryos and tadpoles were examined with an epifluorescence microscope, a silicon-intensified target (SIT) camera, and video recordings. Clones that would include endothelium could be selected as early as stages 33-36 on the basis of heavy labeling in the ventral mesodermal core of the tail. Strands of fluorescent cells and early vessels appeared in the tail at stages 39-41. Subsequently, groups of endothelial cells were followed in case histories in the tail and in the aortic arches and gills of tadpoles. Two main results were that the patterns of fluorescent endothelial cells were stable in established arteries, veins, and capillaries for at least 2-12 days, and that labeled endothelial cells migrated distally in elongating sprouts. In addition, it was inferred that endothelium was derived from multiple blastomeres, probably in the ventral vegetal regions. Only small fractions of total endothelium were labeled from any single blastomere. None of the early blastomeres produced exclusive clones of vascular endothelium; other labeled cell types in various clones included muscle fibers, lymphatics, mesodermal stellate cells, blood cells, gut, proctodeum, and some epidermis, in addition to endothelial cells. The method of intracellular marking of blastomeres is recognized as a direct approach for charting lineage and fate tables in embryos of Xenopus and other species. The present study extends the period of observation in vivo for up to 2 weeks in the growing tadpole and focuses on endothelial cells during angiogenesis. Even though fluorescent dextran was apparently packaged in vesicles and metabolized, individual cells and small groups could be identified and followed with time. This method provides excellent opportunities for addressing problems in vascular development in the living animal.

Fluorescent imaging in vivo of developing blood vessels on the optic tectum of Xenopus laevis.

The growth and development of individual living capillaries, venules, and endothelial sprouts on the pial surface of the brain were examined with video microscopy and intravascular FITC-dextran in anesthetized tadpoles of pigment-deficient Xenopus laevis, stages 42-50. The fluorescent tracer, injected intracardially through glass micropipets, was well tolerated by the tadpoles and improved the visibility of vessels compared to transmitted light. Case histories of vascular development on the optic tectum confirmed the sprouting of new capillaries during angiogenesis. The caudal tectum and its vascular domains grew faster than the rostral, but the densities of caudal surface vessels were at least as high as rostral densities, indicating that angiogenesis was well matched to neural development. Internal capillary branches were further elaborated and pial venules increased in diameter in premetamorphic tadpoles and in Xenopus frogs.

Angiogenesis on the optic tectum of albino Xenopus laevis tadpoles.

Developing blood vessels were observed directly on the dorsal surface of the optic tectum of anesthetized, transparent albino Xenopus laevis tadpoles, stages 41-54. Case histories of individual tadpoles indicated that pial capillaries developed by the classical mechanism of sprouting of endothelial cells from existing blood vessels. 'Deep sources' appeared on the tectal surface during development. These were sites of upwelling blood cells from capillaries within the nervous tissue of the tectum into vessels on the surface. Few 'deep sinks' were observed in the dorsal tectum of normal tadpoles. The earliest deep sources were probably formed by sprouts from the surface vessels through the basement membrane and into the nervous tissue; later ones may also have formed from internal sprouts back to the surface. Maps of deep sources and of surface vessels in case histories indicated that neural tissue and blood vessels in the caudal half of the tectum grew faster than in the rostral half. The medial venules on the dorsal tectum originated as ordinary-sized rostrocaudal capillaries. They enlarged in diameter as they drained the increasing flow of blood from the tectum into the choroid plexus over the 4th ventricle. Some capillaries disappeared or regressed during development. Our observations on the tectum were consistent with the classical sequence of loss of flow, narrowing, collapse of the lumen, and retraction of endothelial cells into adjacent vessels. Likely sites for regression were upstream from a deep source and at crosslinks between transverse vessels on the lateral tectum. Morphometric parameters for tectal angiogenesis were (a) surface density (mm-1) calculated as total length of surface vessels divided by the dorsally projected surface area, and (b) density of deep sources (mm-2) calculated as total number divided by surface area. From stages 41/42 to 50 average surface density approximately doubled, and average density of deep sources increased about 5-fold. Some of the factors which might be expected to alter brain angiogenesis include nervous activity, availability of O2, and metabolic rate. Removal of one eye deprived the contralateral tectum of direct retinal inputs, while the ipsilateral side was a control in the same animal. Anterograde labeling of retinal axons with diI18 from the remaining eye confirmed projections only to the opposite side. No significant differences in densities of surface vessels or of deep sources were observed between the contralateral and ipsilateral sides of the tectum.(ABSTRACT TRUNCATED AT 400 WORDS)

Feeding behavior by parasitic phase lampreys, Ichthyomyzon unicuspis.

Feeding behavior was initiated in juvenile and adult lampreys, Ichthyomyzon unicuspis, by attachment to goldfish or by injection of saline extracts of goldfish skin and muscle into the sucker cavity. Feeding was confirmed by the apparent swallowing of fish extract plus food dye by lampreys. Distinctive characteristics of feeding behavior included low frequency cycles, long duration (hours), variable biphasic pressure changes in the sucker cavity, and protraction of the tongue-like apicalis. In contrast, pumping behavior was used to move excess fluid from the sucker through the pharynx and out the gill pores; it was characterized by transient, high-frequency, monophasic suctions, simple retraction of the apicalis, and lack of swallowing.