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The goal of the Young Scientist Program (YSP) at Washington University School of Medicine in St. Louis (WUSM) is to broaden science literacy and recruit talent for the scientific future. In particular, YSP seeks to expose underrepresented minority high school students from St. Louis public schools (SLPS) to a wide variety of careers in the sciences. The centerpiece of YSP, the Summer Focus Program (SFP), is a nine-week, intensive research experience for competitively chosen rising high school seniors (Scholars). Scholars are paired with volunteer graduate student, medical student, or postdoctoral fellow mentors who are active members of the practicing scientific community and serve as guides and exemplars of scientific careers. The SFP seeks to increase the number of underrepresented minority students pursuing STEM undergraduate degrees by making the Scholars more comfortable with science and science literacy. The data presented here provide results of the objective, quick, and simple methods developed by YSP to assess the efficacy of the SFP from 2006 to 2013. We demonstrate that the SFP successfully used formative evaluation to continuously improve the various activities within the SFP over the course of several years and in turn enhance student experiences within the SFP. Additionally we show that the SFP effectively broadened confidence in science literacy among participating high school students and successfully graduated a high percentage of students who went on to pursue science, technology, engineering, and mathematics (STEM) majors at the undergraduate level.

original article abstract Axoplasmically transported proteins synthesized in neuronal somata labeled by radioactively labeled amino acids (tritium), following local targeted injections for tracing of pathways in the central nervous system using autoradiography. Results from a number of neuronal systems, including: the rat olfactory bulb; cortico-thalamic projections in the mouse; commissural connections of the rat hippocampus; and retinal projections in the monkey and chick are documented. Pathway origins are clear, as the number and distribution of the labeled cells and the normal structure of the injection site is preserved. Light and electron microscopic autoradiography shows that proteins are transported, at two rates: rapid transport (>100 mm/day) of fewer proteins accumulating in axon terminals; and, slow transport (1–5 mm/day) of the bulk of labeled proteins distributed along the length of axons. Different survival times can be selected to evaluate terminal projection field(s) or pathways from origin to termination. The clarity of autoradiographic labeling of pathways and their terminations is comparable to other techniques (such as the Nauta-Gygax and the Fink-Heimer methods and the electron microscopy of terminal degeneration). Labeled amino acids do not label molecules in fibers of passage and there is no retrograde transport of labeled material from the axon terminals. The functional polarity of fiber pathways can be easily established. We summarize the merits of this technique is based upon an established physiological properties of neurons that are summarized in contrast to currently used techniques dependent upon pathological changes in neurons, axons, or axonal terminals. Abstract The cytoarchitecture of layer IV in mouse SmI cerebral cortex was examined in.formalin-fixed, Nissl-stained and Cox-fixed, Golgi-Nissl-stained sections cut coronally and tangentially to the pia, A multicellular cytoarchitectonic unit is described in layer IV, roughly cylindrical, 100–400 um in diameter, and perpendicular to the pia. Because of their characteristic shape we call these structures barrels . Each barrel is a ring of neurons, the side , which surrounds a less cellular hollow . The nearly acellular reigion surrounding each barrel and separating adjacent barrels is the septum . Barrels are discussed in relation to observations reported in several earlier papers on the mouse cortex. The barrel field (all barrels) has remarkable constancy by all measures: from one hemisphere to the next and from one specimen to the next. A consistent part of the barrel field is the p ostero- m edial b arrel s ubield (PMBSF). Barrels in the PMBSF are larger, elliptical in shape, organized into five distinct rows and their numbers are constant. It is postulated that each barrel in the PMBSF is the cortical correlate of a contralateral mystacial vibrissa (whisker). On the basis of counts of barrels and of all facial sinus hairs a ‘one barrel-one vibrissa’ hypothesis is proposed. The general hypothesis is that barrels are the morphological manifestation in layer IV of the functional cortical columns discovered by physiologists. The barrels offer excellent opportunities for integrated studies of sensory cerebral cortex at a degree of resolution previously not possible. This article is part of a Special Issue entitled SI:50th Anniversary Issue .

original article abstract Axoplasmically transported proteins synthesized in neuronal somata labeled by radioactively labeled amino acids (tritium), following local targeted injections for tracing of pathways in the central nervous system using autoradiography. Results from a number of neuronal systems, including: the rat olfactory bulb; cortico-thalamic projections in the mouse; commissural connections of the rat hippocampus; and retinal projections in the monkey and chick are documented. Pathway origins are clear, as the number and distribution of the labeled cells and the normal structure of the injection site is preserved. Light and electron microscopic autoradiography shows that proteins are transported, at two rates: rapid transport (>100 mm/day) of fewer proteins accumulating in axon terminals; and, slow transport (1–5 mm/day) of the bulk of labeled proteins distributed along the length of axons. Different survival times can be selected to evaluate terminal projection field(s) or pathways from origin to termination. The clarity of autoradiographic labeling of pathways and their terminations is comparable to other techniques (such as the Nauta-Gygax and the Fink-Heimer methods and the electron microscopy of terminal degeneration). Labeled amino acids do not label molecules in fibers of passage and there is no retrograde transport of labeled material from the axon terminals. The functional polarity of fiber pathways can be easily established. We summarize the merits of this technique is based upon an established physiological properties of neurons that are summarized in contrast to currently used techniques dependent upon pathological changes in neurons, axons, or axonal terminals. article abstract This article considers a heavily cited Brain Research article that reported an extremely important turning point in the ability to demonstrate neuroanatomical pathways in the central nervous system. Using radioactive leucine microinjections into the brain, neurons synthesized proteins from this amino acid that were transported down their axons to the terminal synapses on the target neurons. Tracing the transport of the labeled protein by autoradiography permitted quantitative analysis of projections and pathways. As a result, pathway analysis was transformed from studying the degenerating processes of lesioned neurons to the study of intact pathways in non-manipulated brains. The classical protocol has since been widely applied and used to investigate countless brain circuits. This article is part of a Special Issue entitled SI:50th Anniversary Issue .

The mouse trigeminal (V) system undergoes significant postnatal structural and functional developmental changes. Histological modules (barrelettes, barreloids and barrels) in the brainstem, thalamus and cortex related to actively moved (whisking) tactile hairs (vibrissae) on the face allow detailed studies of development. High-resolution [(3) H]2-deoxyglucose (2DG) emulsion autoradiography with cytochrome oxidase histochemistry was used to analyze neuronal activity changes related to specific whisker modules in the developing and mature mouse V system provoked by passive (experimenter-induced) and active (animal-induced) displacements of a single whisker (D4). We tested the hypothesis that neuronal activity patterns change in relation to the onset of active touch (whisking) on postnatal day (P)14. Quantitative image analyses revealed: (i) on P7, when whisker-like patterns of modules are clear, heightened 2DG activity in all appropriate modules in the brainstem, thalamus and cortex; (ii) on P14, a transitory activity pattern coincident with the emergence of whisking behavior that presages (iii) strong labeling of the spinal V subnucleus interpolaris and barrel cortex produced by single-whisker-mediated active touch in adults and (iv) at all above-listed ages and structures, significant suppression of baseline activity in some modules surrounding those representing the stimulated whisker. Differences in activity patterns before and after the onset of whisking behavior may be caused by neuronal activity induced by whisking, and by strengthening of modulatory projections that alter the activity of subcortical inputs produced by whisking behavior during active touch.

OBJECTIVE: To use in vivo imaging methods in mice to quantify intracranial glioma growth, to correlate images and histopathological findings, to explore tumor marker specificity, to assess effects on cortical function, and to monitor effects of chemotherapy. METHODS: Mice with DBT glioma cell tumors implanted intracranially were imaged serially with a 4.7-T small-animal magnetic resonance imaging (MR1) scanner. MRI tumor volumes were measured and correlated with postmortem histological findings. Different nonspecific and specific positron emission tomography radiopharmaceuticals, [ 18 F]2 -fluoro-2-deoxy-D-glucose, [ 18 F]3 '-deoxy-3'- -fluorothymidine, or [ 11 C]RHM-1, a σ 2 -receptor ligand, were visualized with microPET (CTI-Concorde Microsystems LLC, Knoxville, TN). Intrinsic optical signals were imaged serially during contralateral whisker stimulation to study the impact of tumor growth on cortical function. Other groups of mice were imaged serially with MRI after one or two doses of the antimitotic N,N'-bis(2-chloroethyl)-N-nitrosourea(BCNU). RESULTS: MRI and histological tumor volumes were highly correlated (r 2 = 0.85). Significant binding of [ 11 C]RHM-1 was observed in growing tumors. Over time, tumors reduced and displaced (P≤ 0.001) whisker-activated intrinsic optical signals but did not change intrinsic optical signals in the contralateral hemisphere. Tumor growth was delayed 7 days after a single dose of BCNU and 18 days after two doses of BCNU. Mean tumor volume 15 days after DBT implantation was significantly smaller for treated mice (1- and 2-dose BCNU) compared with controls (P= 0.0026). CONCLUSION: Mouse MRI, positron emission tomography, and optical imaging provide quantitative and qualitative in vivo assessments of intracranial tumors that correlate directly with tumor histological findings. The combined imaging approach provides powerful multimodality assessments of tumor progression, effects on brain function, and responses to therapy.

Appoximately 110 colleagues attended a 2 day meeting from 21 to 22 October, 2004 in Carlesbad-by-the-Sea, CA USA. Summaries of the speakers’ presentations are followed by abstracts for the 44 posters shown. Barrels XVII will be held in the Washington, DC – Baltimore, MD area on 10–11 November 2005 prior to the Society for Neuroscience Annual Meeting. Please look to Volume 22, Number 3 of Somatosensory and Motor Research for location, housing options and a preliminary program. Inquires can be directed to Kathryn Diekmann, E-mail: somatosensory@prodigy.net

Intravenous MRI contrast agents are commonly used to improve the detection of intracranial tumors and other central nervous system (CNS) lesions for diagnosis and treatment planning. Two small-molecule, albumin-binding blood pool contrast agents (MP-2269 and MS-325) of potential clinical significance were evaluated at 1.5 Tesla in a mouse glioma model and compared with an extracellular contrast agent (OptiMARK). Tumor image contrast was significantly enhanced and long-lived following administration of 30 μmole/kg of the blood pool agents: specifically, contrast enhancement peaked slowly at 25–30 min following administration, remained constant for >3 hr, and returned to baseline within 20 hr. Comparable but “transient” enhancement was achieved using 100 μmole/kg OptiMARK: specifically, contrast enhancement peaked rapidly at 2–5 min following administration and then declined over 40 min. The blood pool contrast agents demonstrated an approximately threefold increased dose-effectiveness and a lengthened window of tumor contrast enhancement in comparison to commonly available extracellular contrast agents. This demonstrates the potential of alternative contrast-enhanced (CE) MRI examination protocols for tumor detection. Magn Reson Med 49:586–590, 2003. © 2003 Wiley-Liss, Inc.

Whereas ATP consumption increases with neural activity and is buffered by phosphocreatine (PCr), it is not known whether PCr synthesis by ubiquitous mitochondrial creatine kinase (uMtCK) supports energy metabolism in all neurons. To explore the possibility that uMtCK expression in neurons is modulated by activity and during development, we used immunocytochemistry to detect uMtCK-containing mitochondria. In the adult brain, subsets of neurons including layer Va pyramidal cells, most thalamic nuclei, cerebellar Purkinje cells, olfactory mitral cells and hippocampal interneurons strongly express uMtCK. uMtCK is transiently expressed by a larger group of neurons at birth. Neurons in all cortical layers express uMtCK at birth (P0), but uMtCK is restricted to layer Va by P12. uMtCK is detected in cerebellar Purkinje cells at birth, but localization to dendrites is only observed after P5 and is maximal on P14. Hippocampal CA1 and CA3 pyramidal neurons contain uMtCK-positive mitochondria at birth, but this pattern becomes progressively restricted to interneurons. Seizures induced uMtCK expression in cortical layers II–III and CA1 pyramidal neurons. In the cortex, but not in CA1, blockade of seizures prevented the induction of uMtCK. These findings support the concept that uMtCK expression in neurons is (1) developmentally regulated in post-natal life, (2) constitutively restricted in the adult brain, and (3) regulated by activity in the cortex and hippocampus. This implies that mitochondrial synthesis of PCr is restricted to those neurons that express uMtCK and may contribute to protect these cells during periods of increased energy demands.

A method was developed to quantitate the volume of brain inactivated by muscimol focally injected. Tritiated muscimol was injected into the cerebellum and closely spaced sequential microelectrode recordings made at different depths by penetrations in an X-Y pattern centered at the injection site to evaluate changes in spontaneous activity in the tissue volume. Animals were euthanized after survivals from 40 min to 6 h, the cerebellum sectioned in the sagittal plane, and the sections dried onto glass slides. The slides were dipped in photographic emulsion, exposed in the dark and developed. Silver grain densities were quantitated by light microscopy from measured standards. The extent and concentration of bound, labeled muscimol co-varied with the observed reduction in recorded spontaneous activity. For future studies, the distribution and density of silver grains alone can serve as an accurate spatial indicator of the area of muscimol inactivation at high spatial resolution.

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 α v β 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.

Surprisingly little is known about the development of connections within a functional area of the cerebral cortex. We examined the postnatal growth of connections in mouse barrel cortex during the second and third weeks after birth, coinciding with the period of rapid synaptogenesis that occurs just after the barrels first form. A barrel is a group of neurons in layer 4 of somatosensory cortex that is part of a cortical column. Each whisker/barrel column is linked anatomically and functionally to a homotopic whisker on the contralateral face. Radial groups of cortical neurons were labeled with the neuronal tracer biotinylated dextran amine in mice ranging in age from postnatal day 8 (P8; P0 is the date of birth) to adulthood. The spatial distributions of retrogradely labeled neurons in different laminae were analyzed. The barrel map in layer 4 was used as a template to compare quantitative data from different animals and to account for substantial changes in barrel and barrel field size during development. Intrinsic projections 1) innervate increasingly more distant targets within barrel cortex up to 3 weeks of age; 2) continue to form in targets after 3 weeks, effectively strengthening existing connections; 3) follow a timetable for growth that is layer-specific; 4) link more distant barrel columns in layer 4 from neurons that are found preferentially in the barrel side and the septa between barrels; and 5) form over the shortest distances between the barrel columns. These data indicate that intrinsic connections in mouse barrel cortex develop by the progressive addition of neuronal connections rather than by sculpting preliminary connections. We describe statistically significant changes in connectivity during development that may be applied to model and assess the development of connections after a variety of experimental perturbations, such as to the environment and/or the genome. J. Comp. Neurol. 436:17–31, 2001. © 2001 Wiley-Liss, Inc.

The effect of chronic hypobaric hypoxia (28 days, 455 Torr) on the organization of brain vessels was studied in Balb/c mice. In comparison to age-matched controls kept at sea level, emulsion-perfused capillaries in hypoxic mice showed marked dilation in all brain areas studied. Capillary length per unit volume of tissue ( L v) was increased in the cerebellar granular layer, the caudate nucleus, the globus pallidus, the substantia nigra, the superior colliculus, and the dentate gyrus. There was a selective increase of L v in the hippocampus (CA1 strata pyramidale and lacunosum and CA3 strata pyramidale and oriens) and in somatosensory cortex layers V and VI, motor cortex layers II, III, V, and VI, and auditory cortex layers II and III. An increase in capillary surface area per unit volume of tissue was also determined in several brain areas, including layer IV of somatosensory cortex, where L v was not significantly increased. The O2diffusion conductance and [Formula: see text] in the tissues were estimated with a mathematical model. The remodeling of capillary diameter and length during chronic hypoxia accounts for the significant increase of O2conductance to neural tissues. Also the estimated tissue[Formula: see text] in chronic brain hypoxia is markedly increased in the caudate nucleus and the substantia nigra compared with acute hypoxia. These results suggest that formation of new capillaries is an important mechanism to restore the O2 deficit in chronic brain hypoxia and that local rates of energy utilization may influence angiogenesis in different areas of the brain.

The one-to-one correspondence of whiskers to barrels in layer IV of rodent somatosensory cortex can be demonstrated by a precise match between columns of heavy 2-deoxyglucose (2DG) label in layer IV barrels and other layers which correspond to stimulated whiskers. While there is specificity of peripheral-to-central mapping, the extent to which integration and/or modulation are generated by circuitry within or interactions between the barrel-defined whisker columns is not clear. Following stimulation of selected whiskers, large cells at the layer IV-V boundary throughout the barrel field are heavily labeled by 2-deoxyglucose (2DG) at high resolution. Many of these cells are outside the barrel columns of the stimulated whiskers. Further, the number of cells labeled is not directly related to the number of activated barrel columns. These neurons are not labeled in animals anesthetized before 2DG injection and are not as heavily labeled in barrel fields of somnolent animals. Most of the heavily labeled neurons immunolabel for glutamate decarboxylase (GAD) and are presumed to be inhibitory, while a smaller number of labeled neurons, presumed to be excitatory, immunolabel for glutamate (Glu). Similar populations of large, heavily 2DG-labeled neurons are found in other cortical areas. These relatively few neurons are exceptionally active and may modulate integrative functions of cerebral cortex.

We followed developmental changes in "barreloid" thalamocortical relay cell (TCR) dendritic arbors between postnatal day 5 (P5; birth = P0) and adulthood. Single neurons in 150- to 250-microns coronal or oblique slices through the somatosensory thalamus in mice of different postnatal ages were injected with lucifer yellow (LY) under direct visualization. Filled cells in the ventroposterior medial nucleus (VPM) were imaged with a confocal microscope, and rendered and analyzed on a computer workstation with special-purpose software. The whisker representation in the thalamus, as revealed by the pattern of barreloids, was demonstrated by oblique illumination of the slices and/or later cytochrome oxidase (CO) staining. VPM cross-sectional area trebles from P5 to adulthood. Barreloids (single-whisker representations) are well delineated in unstained sections until P10-P11; thereafter, barreloids can only be recognized with difficulty with the CO stain. Thalamocortical relay cell (TCR) somal volumes increase rapidly in the first 2 weeks. The number of primary dendrites does not change, nor does the length of the primary dendritic segments, from P5 to adulthood; however, distal dendritic segments elongate and increase in number. Dendritic arbors are confined on P5 to single barreloids; in adults they extend to adjacent barreloids. The postnatal transformation of dendritic arbors by process growth to adjacent barreloids is mainly completed by P18. A change in the developmental role of these cells, from instructing whisker pattern formation to integrating sensory information from more than one whisker, thus occurs after the whisker pattern in the barrel cortex is established. It coincides with the age at which animals are known to begin exploratory whisking behaviors. The mechanism appears to be by growth and remodeling of distal dendrites rather than by oriented growth and regression, as has been reported for stellate cells in cortical whisker barrels.

We evaluated increases in local cerebral blood flow (LCBF) localized to single activated cortical columns by H 2 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 μm Pt wire electrodes were inserted in or near the rat whisker-barrel cortex. Electrode positions were mapped by postmortem histology. H 2 was generated electrochemically by constant current from one electrode and detected by one or more other electrodes 300–500 μm away. Changes in LCBF produced inverse changes in PH 2 . Shifts during steady H 2 generation were calibrated against standard H 2 inhalation clearance curves at rest and during inhalation of 7.5% CO 2 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 ≈ 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.

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 triphenyltetrazolium 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 patent 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 case of ocular duplication with complex craniofacial and central nervous system anomalies is described. The anomaly is termed triopia because the child's most overt and distinguishing feature was three eyes: the left orbit contained two globes with independent ocular adnexa; the right orbit contained one normal appearing and functioning globe. Computer assisted medical imaging was used to define, in vivo, the intra- and extracranial soft and hard tissue anomalies: the cerebral hemisphere ipsilateral to the ocular duplication was also duplicated. Possible bases for this anomaly include duplication of primordia for the eye and secondary prosencephalon.

SPECIFIC AIMThe sensor of blood flow need in conditions as diverse as brain activation, exercise, high altitude, and diabetes mellitus is unknown. Our first aim was to test the hypothesis that accumulation of electrons in cytosolic free NADH, the reduced form of nicotinamide adenine dinucleotide (NAD), functions as this sensor. The rationale for testing this hypothesis was based on the near equilibria between extracellular and intracellular lactate/pyruvate (L/P) and free cytosolic NADH/NAD+ ratios; NADH was increased or decreased by injecting lactate or pyruvate, respectively. Our second aim was to identify components of the signaling cascade that mediate increased flows.PRINCIPAL FINDINGS1. Increasing L/P increases blood flow in numerous tissues at restBolus injection or brief infusion of lactate increased blood flows in all tissues examined except heart and brain: retina 50%, sciatic nerve 65%, epitrochlearis and gastrocnemius skeletal muscles 30%, soleus muscle 86%, and kidney 40%. Flow increases afte...

The processes underlying development, refinement, and retention of the intracortical connections critical for the function of the mammalian brain are unknown. Horseradish peroxidase-labeled fibers in mouse somatosensory barrel cortex, which is patterned like the whiskers on the contralateral face from which it receives inputs, were evaluated by automated image analysis. The sensory nerve to the whiskers was sectioned on postnatal day 7, after the whisker map is set. The deprived barrel cortices, examined in adults, showed drastically diminished intracortical projections relative to normal controls, although the map of the whiskers in the cortex was unchanged. This demonstrates anatomically that the normal pattern of intracortical connections, like the normal sensory map, is dependent upon the sensory periphery four synapses away.

We studied thalamocortical afferent (TCA) growth into somatosensory cortex as the whisker barrels emerge in postnatal mice. Ingrowing fibers from the ventrobasal (VB) thalamus were selectively labeled by two means. Under direct vision, individual axons and populations of axons were labeled in vitro with HRP, or in fixed tissue with Dil (1,1'-dioctodecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate), in pieces of brain containing both the source nucleus in the thalamus and its cortical target. Many simple thalamocortical afferents are already within the upper cortical plate at birth [postnatal day one (PND1)]. Initially, TCAs from each point in the thalamus distribute in the cortex as two-dimensional "Gaussians," which overlap laterally to constitute a uniform projection pattern. The projection is topographic, because adjacent focal injections within VB label adjacent cortical loci. Subsequent development of barreloids (thalamic representations of the whiskers) partitions the TCA projection into a set of whisker-related Gaussians, centered on cortical targets whose collective topography reflects that of the source pattern. After barreloids form on about PND3, but before barrels appear in cytoarchitecture on about PND5, the overlapping TCAs segregate into dense terminal clusters in layer IV, around which barrels later mature. Time series of single fibers traced with camera lucida explain this transformation that is so noticeable at the population level. As early as PND1, individual TCAs emit multiple ascending collaterals on their horizontal run through white matter and oblique ascent into upper cortex. Subsequently, by PND4, and proceeding at least through PND7, there is accelerated terminal arborization of selected appropriate collateral branches and pruning back of other inappropriate ones. The selection mechanism appears to result from within-group reinforcement events that are stronger for branches toward the center of each whisker-related Gaussian distribution.

Introduction The barrel cortex is a remarkable structure. Its form has captured the imagination of researchers for decades and its versatility has ensured that it finds a place in each new wave of neuroscience research. Since its discovery by Woolsey and Van der Loos in the early 1970s, researchers have used barrel cortex to study some of the most pressing questions in neuroscience. How does the cortex develop? How does active touch work? What makes neurons plastic? In each case, the value of the barrel cortex has been to help neuroscientists to relate structure with function through its unique and easily defined form. In order to understand how these questions are being addressed currently, it is useful to understand some of the basic structural and functional features of the barrel cortex. The first three chapters of this book address some of the fundamental anatomy and physiology of the barrel cortex. For the expert in the field, most of what is written in these chapters will probably be quite familiar but will hopefully still serve as a useful reference to the original studies. While most of the original anatomical studies span the 1970s and 1980s, new neuroanatomical findings are still being described into the current century. Curiously, a review of this anatomical literature has not previously been written. For those less familiar with barrel cortex, the anatomical pathways linking the periphery to barrel cortex are described in Chapter 2 along with the intracortical connections, the study of which, at the time of writing, is still an active area of research.

Hyperspectral interferometric microscopy uses a unique combination of optics and algorithm design to extract information. Local brain activity rapidly changes local blood flow and red blood cell concentration (absorption) and oxygenation (color). We demonstrate that brain activity evoked during whisker stimulation can be detected with hyperspectral interferometric microscopy to identify the active whisker-barrel cortex in the rat brain. Information about constituent components is extracted across the entire spectral band. Algorithms can be flexibly optimized to discover, detect, quantify, and visualize a wide range of significant biological events, including changes relevant to the diagnosis and treatment of disease.

We tested the hypothesis that glutamate receptor mediated activity is required for the postnatal development of intracortical connections in layers II/III of rodent barrel cortex. To block glutamate receptors, a slow release polymer (elvax) loaded with a glutamate receptor antagonist (D-AP5) was targeted subdurally over the future rat barrel cortex on P0 (day of birth). On P14-16 biotinylated dextran amine (BDA) was injected under the elvax into all layers to label neurons retrogradely. A BDA injection was made stereotactically at the mirror site of the untreated hemisphere of each animal. The animals survived to P22-24. Injection sites and retrogradely labeled cell bodies were identified in tangential sections in relation to the barrel map. D-AP5 treated and untreated hemispheres were matched according to the location of the injection site in the barrel map. Glutamate receptor blockade did not prevent the growth of intrinsic projections, but altered their organization. The normal row-like asymmetry of connections in untreated hemispheres was lacking in the D-AP5 treated cortex (ANOVA, p =0.02). Cortical activity mediated through glutamate receptors contributes to the correct development of connections between barrel columns in layers II/III.

The authors evaluated representations of discretely activated, neighboring brain regions using real-time optical intrinsic signals by transcranial imaging with 540-nm and 610-nm broadband illumination of the mouse barrel cortex. Iron filings were glued to two neighboring whiskers (C2 + D2) that were stimulated magnetically, singly and together. Real-time images were collected, averaged, and analyzed statistically. Postmortem filling of arteries with fluorescent beads was shown in relation to histochemical staining of barrels to accurately relate surface changes to functional cortical columns. Significant optical intrinsic signal changes are related to overlapping distributions of arterioles that feed the two separate areas. Activation of adjacent and interacting cortical columns leads not only to increased magnitude of vascular responses in those columns, but also to wider spatial extent of absorption changes occurring principally in areas of cortex fed by vessels upstream of the active cortex. The localization of changing hemoglobin absorption around upstream blood vessels and their vascular domains suggests that propagated vasodilation of upstream parent vessels is greater when vasodilatory signals from separate areas of active cortex converge on common arterioles that feed them.

This chapter reviews techniques used to study the dynamic realtime changes in local cerebral blood flow (LCBF) by direct observation of the brain surface in experimental animals. One of the techniques— Doppler effect— can be used to estimate mean velocities and the magnitude of moving objects. With optical laser-Doppler flowmetry, frequency shifts in coherent light in the near infrared to which tissue is relatively transparent can be used to estimate red blood cells (RBCs) velocity and volume of moving RBCs. Direct observation of cerebral vessels requires magnification. Low-magnification systems with appropriate macro lenses and dissecting microscopes for modest magnification can be used to view changes over wide areas of exposed brains of larger animals, including humans. Electrophysiological recording of evoked responses is the traditional way to determine the location of sensory cortical areas. It takes considerable time to generate detailed “maps” point by point for accurate localization representation within a map, even with surface electrodes. Angiographers use the timing of movement of radio-opaque dyes to estimate flow abnormalities. Transits have been measured in animals with carbon particles and dilution of RBCs with saline or dye.

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.

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.

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Neural plasticity is one of several mechanisms used by the nervous system to assure that information for efficient and effective actions necessary for survival is coherent. In mammals, if not all animals, plasticity is related to different processes and components in the brain that vary in their

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.