The distribution of basal water between Antarctic subglacial lakes from radar sounding.

Antarctica's subglacial lakes have two end member geophysical expressions: as hydraulically flat, radar reflective regions highlighted in ice surface topography and radar sounding profiles ('definite lakes'), and as localized sites of elevation change identified from repeat elevation observations ('active lakes') that are often found in fast flowing ice streams or enhanced ice flow tributaries. While 'definite lakes' can be identified readily by high bed reflectivity in radar sounding, the identification and characterization of less distinct subglacial lakes and water systems with radar sounding are complicated by variable radio-wave attenuation in the overlying ice. When relying on repeat elevation observations, the relatively short times series and biased distribution of elevation observations, along with the episodic nature of 'active lake' outflow and replenishment, limit our understanding of how water flows under the ice sheet. Using recently developed methods for quantifying the radar scattering behaviour of the basal interface of the ice, we can avoid the problem of attenuation, and observe the plumbing of the subglacial landscape. In West Antarctica's Ross Sea Embayment, we confirm that extensive distributed water systems underlie these ice streams. Distributed water sheets are upstream in the onset regions of fast flow, while canal systems underly downstream regions of fast flow. In East Antarctica, we use specularity analysis to recover substantial hydraulic connectivity extending beyond previous knowledge, connecting the lakes already delineated by traditional radar sounding or surface elevation transients.

Connections of the nurse shark's telencephalon.

The extrinsic connections of the telencephalon of the nurse shark are very largely crossed and in this respect differ from those identified in all other vertebrate species so far examined. Studies with Nauta and Fink-Heimer methods have revealed telencephalic projections to the contralateral thalamus and optic tectum as well as to ipsilateral brainstem and rostral spinal cord.

Tectal projections of an infrared sensitive snake, Crotalus viridis.

Crotaline snakes have detectors for infrared radiation and this information is projected to the optic tectum in a spatiotopic manner. The tectal projections were examined in Crotalus viridis with the use of silver methods for degenerating fibers and the autoradiographic and horseradish peroxidase tracing methods. Large lesions included all of the tectal layers but not the underlying structures. Projections to the thalamus include a sparse input to the ipsilateral ventral and dorsal lateral geniculate nuclei, the ventromedial nucleus, and nucleus lentiformis thalami. Nucleus rotundus was not detected. The projections to the pretectal nuclei are primarily ipsilateral to the nucleus lentiformis mesencephali and pretectal nucleus. At the level of the mesencephalon, tectal efferents are bilateral to nucleus profundus mesencephali and the tegmentum. There is minimal input to the contralateral deep tectal layers. There are ipsilateral terminations in a nucleus identified as the posterolateral tegmental nucleus. Descending fibers include the two major tracts--the ventral tectobulbar tract that terminates in the ipsilateral lateral reticular formation and the predorsal bundle that distributes throughout the contralateral medial reticular formation. Two small descending tracts were noted--the intermediate and dorsal tectobulbar tracts. All of these descending tracts appear to terminate by the time they reach the caudal medulla. After superficial lesions terminals could be found in the ventral lateral geniculate nucleus, the nucleus profundus mesencephali, and the posterolateral tegmental nucleus; the two major descending tracts contained degenerated fibers as well. The areas receiving tectal input in Crotalus were compared to those of other reptiles and discussed.

Marginal neurons in the urodele spinal cord and the associated denticulate ligaments.

Marginal neurons have been described in the spinal cords of a variety of vertebrates including lamprey, reptiles, birds, and mammals but not in amphibians. There has been speculation about a motor function for these neurons but recent experimental evidence in lampreys indicates that they are intraspinal mechanoreceptor neurons. Additional evidence on reptiles and birds demonstrates that the marginal neurons are closely associated with the denticulate ligaments. In the present investigation, we have examined the spinal cords of Necturus, Ambystoma tigrinum, and A. mexicanum with light and electron microscopic techniques. Marginal nuclei were found in the ventrolateral position immediately internal to the pia and to the denticulate ligament. The marginal neurons were scattered in a continuous column of neuropil without segmental accumulation. They were approximately 30 to 50 microns in diameter and fusiform with dendrites extending from the poles, parallel with the length of the spinal cord. Neuronal fingerlike processes, like those found in peripheral mechanoreceptors and in the marginal nuclei of reptiles, were also found in the three species of urodeles studied. The structure of the denticulate ligaments, similar in the three different amphibians, was composed of collagen, elastin, and fibroblasts, all of which were concentrated in the segmental lateral processes.

Trigeminal projections in snakes possessing infrared sensitivity.

The first order of projections of the trigeminal nerve were studied in four species of snakes, three of which are infrared sensitive, utilizing silver degeneration and cobalt iontophoresis techniques. The trigeminal nerve projected ipsilaterally to a main sensory nucleus, descending spinal nucleus, ventral trigeminal field and solitary nucleus with a contralateral projection to the base of the descending spinal nucleus in all four species. A major additional projection to the lateral nucleus of the trigeminal was present in all three infra-red sensitive species but absent in the other. Iontophoresis of cobalt chloride into a trigeminal branch composed entirely of infrared sensitive fibers and into a trigeminal branch containing no infrared fibers indicated that the lateral nucleus of the trigeminal nerve was the sole first target of the infrared system.

Cytoarchitecture of the optic tectum in the nurse shark.

The cytoarchitecture of the optic tectum of the nurse shark is described and related to the arrangements of afferents from retina, telencephalon and contralateral tectum. Its lamination is not pronounced when compared to tecta of most other non-mammalian species but more comparable to those of mammals. The absence of highly differentiated cells such as pyramidal and true horizontal cells is perhaps correlated with the poor differentiation in general, including the apparent partial overlap of inputs. Some neurons near the midline were found to possess dendrites extending into the contralateral tectum.

Cytoarchitecture of the tectum mesencephali in two types of siluroid teleosts.

The cytoarchitecture of the tectum mesencephali in the siluroid teleosts Bagrus and Ictalurus was studied by means of the Golgi method. These animals are known to have a restricted visual system and it seemed important to study whether this fact would affect the existence or the shape of the main neuron types which have been described for highly visual teleosts. It had been shown for a variety of teleosts that the retinotectal axons and terminals occupy almost exclusively the stratum opticum and the stratum fibrosum et griseum superficiale. The thickness of these strata in Bagrus and Ictalurus was found to be reduced. However, the main types of especially the vertically oriented neurons, such as the pyramidal, fusiform, large pyriform and periventricular neurons which have been described for highly visual species of teleosts, were also found in Bagrus and Ictalurus. Although their shape was somewhat distorted, these neurons, nevertheless, showed processes distributed to the same tectal layers as in highly visual teleosts and are accessible to horizontally distributed fiber systems such as marginal, telencephalotectal and commissural tectal fibers, as well as the retinotectal fibers. Nonvisual inputs appear to be considerably involved in the maintenance of the main neuron types in the siluroid tectum. For example, the pyramidal neuron's apical dendritic tree, which receives the excitatory input from the marginal fibers, is as well developed in siluroids as in highly visual teleosts.

Cytoarchitecture of the optic tectum of the squirrelfish, Holocentrus.

The Holocentrus has large eyes and a well-developed optic tectum. Nissl and fibers stains and various Golgi techniques show that the optic tectum of Holocentrus has six strata which can be subdivided into 14 alternating cell and fiber layers, some of which have additional organization. The stratum marginale (SM) is especially impressive in this fish and contains dendrites of pyramidal neurons, marginal fibers from torus longitudinalis, and axon-like processes (the SM ascending axons) from cells located in the stratum griseum centrale (SGC). Stratum opticum (SO) and stratum fibrosum et griseum superficiale (SFGS) have many small neurons with limited dendritic fields. The large, so-called pyramidal cell of SFGS has an extensive dendritic tree in SM and descending dendrites and axon to SGC. The latter has a variety of neurons with large dendritic fields in various layers of the tectum; the most distinctive, however, is the large fusiform neuron with its shepherd's crook axon. This stratum also has a dense layer of neuropil, the internal plexiform layer. Stratum album centrale (SAC) is primarily a fibrous layer, and stratum periventriculare (SPV) is a dense cellular area with the upper portion containing neuronal types also found in SGC and different from the typical neurons found in SPV. The latter have a major ascending branch with various dendritic patterns, and often do not have an identifiable axon; however, some of these cells have extensive branches throughout SFGS with an axon-like appearance. Some general conclusions were made about the functional significance of the various tectal layers and cell types.

The ascending projection of the nucleus of the lateral descending trigeminal tract: a nucleus in the infrared system of the rattlesnake, Crotalus viridis.

The efferent projections of the nucleus of the lateral descending trigeminal tract (LTTD) in the rattlesnake (Crotalus viridis) were studied by anterograde tracing techniques. The LTTD, a brainstem trigeminal nucleus, is the sole projection site of the infrared-sensitive trigeminal fibers that innervate the pit organs in these snakes. The efferent fibers exit from the ventromedial edge of the LTTD and course medially and caudally toward the central grey area of the medulla. Upon reaching the central region of the medulla these fibers turn and move laterally and rostrally, eventually forming a tract on the ventrolateral surface of the brainstem. Embedded in this tract and slightly overlapping the LTTD in the rostrocaudal axis, is a population of large (20-45 micrometer) multipolar neurons that forms the nucleus reticularis caloris. Heavy terminal and preterminal degeneration in this area indicates that many of the efferent fibers of the LTTD terminate in this nucleus. A small bundle of degenerating fibers turn dorsally from the ventrolateral tract and ascend to terminate in a nucleus associated with the cerebellum, the lateral tegmental nucleus. No projection was found to any other nuclei or areas in the brain. This study demonstrates that the infrared-sensitive snakes, along with developing peripheral specializations (the pit organs), have developed specialized nuclei to handle this additional sensory information. The direct projection from the LTTD to the nucleus reticularis caloris provides a pathway linking the infrared-sensitive neurons of the LTTD with neurons of the same modality in the optic tectum. The second LTTD projection, to the lateral tegmental nucleus, suggests a connection between the infrared system and the cerebellum in these animals.

Visual discrimination following partial telencephalic ablations in nurse sharks (Ginglymostoma cirratum).

An instrumental conditioning task was used to examine the role of the nurse shark telencephalon in black-white (BW) and horizontal-vertical stripes (HV) discrimination performance. In the first experiment, subjects initially received either bilateral anterior telencephalic control lesions or bilateral posterior telencephalic lesions aimed at destroying the central telencephalic nuclei (CN), which are known to receive direct input from the thalamic visual area. Postoperatively, the sharks were trained first on BW and then on HV. Those with anterior lesions learned both tasks as rapidly as unoperated subjects. Those with posterior lesions exhibited visual discrimination deficits related to the amount of damage to the CN and its connecting pathways. Severe damage resulted in an inability to learn either task but caused no impairments in motivation or general learning ability. In the second experiment, the sharks were first trained on BW and HV and then operated. Suction ablations were used to remove various portions of the CN. Sharks with 10% or less damage to the CN retained the preoperatively acquired discriminations almost perfectly. Those with 11-50% damage had to be retrained on both tasks. Almost total removal of the CN produced behavioral indications of blindness along with an inability to perform above the chance level on BW despite excellent retention of both discriminations over a 28-day period before surgery. It appears, however, that such sharks can still detect light. These results implicate the central telencephalic nuclei in the control of visually guided behavior in sharks.

A methodology for determining the patch-matrix compartmental location of extracellular single-unit recordings in the striatum of freely moving rats.

A methodology was developed to combine extracellular electrophysiological recording techniques in awake, behaving rats with immunohistochemical protocols to determine the placement of recording sites in the patch (striosome) or matrix (extrastriosome) regions of the striatum. The recording system includes a 3-barrel glass micropipette, which can be used to deposit Pontamine Sky Blue to mark a small number of neurons at the recording site. Subsequent immunostaining for calbindin allows the site to be localized within the patch-matrix organization. Other dyes or neuroanatomical probes can be ejected from other barrels of the recording pipette to label afferent and efferent structures. The methodology can be applied to many brain regions, providing for integrative studies of behavior and nervous system structure and function.

The nucleus dorsalis myelencephali of snakes: relay nucleus between the spinal cord and the posterior colliculus (paratorus).

Nucleus dorsalis myelencephali is in the dorsolateral area of the caudal medulla in snakes. The parvocellular area projects bilaterally to the paratorus and receives ipsilateral projections from the spinal cord. The magnocellular area projects bilaterally to the spinal cord. This nucleus has been only briefly described in snakes but not in any other reptilian group.

Is the intimate relationship between ligaments and marginal specialized cells in the snake's spinal cord indicative of a CNS mechanoreceptor?

Large neurons at the ventrolateral edge of the snake's spinal cord are intimately associated with ligaments that closely adhere to the whole length of the spinal cord. Ultrastructural studies show close similarities of these cells and their processes with those of other mechanoreceptors. Furthermore, the ligaments undergo changes within the intervertebral areas that would enhance focusing the stimulus to the receptor area.

Localization of motor- and nonmotor-related neurons within the matrix-striosome organization of rat striatum.

Striatal neurons can be classified as movement- and nonmovement-related depending on their ability to change firing rate in close temporal association with spontaneous movement in an open-field arena. The present study assessed the location of these cell types within the compartmental organization of the striatum by combining single-unit recording techniques in freely moving rats with calbindin immunohistochemistry. Movement-related neurons were found predominately either in the matrix or along the matrix-striosome border. Most of these neurons were nonselective in that they increased activity whenever the animals changed from a quiet resting posture to any form of behavioral activation (e.g., grooming, locomotion, rearing). The remaining neurons in this group responded exclusively to movements of the head. Nonselective units discharged at a significantly slower rate than head-movement units during both quiet rest and periods of actual movement. Nonmovement-related neurons, which failed to show a reliable change in activity to overt behavior, comprised a relatively small portion of the neuronal sample but were also located in either the matrix or along the matrix-striosome border. Collectively, these results suggest that even though striatal neurons can be distinguished on the basis of their responsiveness to ongoing behavior in an open-field paradigm, such distinctions are not clearly linked to sites within the matrix or its striosomal borders.

Breast cancer worry and screening: some prospective data.

Breast cancer concerns were measured among 353 women, ages 40-75, from North Dakota. One year later, participants were recontacted and asked about their screening behavior during the previous year. Greater concern about breast cancer, even the highest level of concern, was related to a higher likelihood that women performed breast self-examination, had a mammography screening, and had a clinical breast examination. These data do not support the idea that worry inhibits action; instead, they suggest that nonpathological worry motivates self-protective behavior.

What is the relationship between breast cancer risk and mammography screening? A meta-analytic review.

This meta-analytic review addresses the issue of how a woman's risk of breast cancer relates to the likelihood that she will obtain mammography screenings. Studies that compared women with or without a family history of breast cancer (n = 19) showed that women with a family history were more likely to have been screened. Studies that measured perceived risk (n = 19) showed that feeling vulnerable to breast cancer was positively related to having obtained a screening. Studies that compared women who did or did not have a history of breast problems (n = 10) showed that those with a positive history were more likely to have been screened. Finally, studies that measured worry (n = 6) showed that greater worry was related to higher screening levels. Taken together, these data suggest that increasing perceptions of personal vulnerability may increase screening behavior for breast cancer.

Retinal afferents and efferents of an infrared sensitive snake, Crotalus viridis.

The retinal afferents and efferents were examined in Crotalus viridis. Retinofugal fibers were traced by injecting horseradish peroxidase (HRP) or tritiated leucine into the eye, or by removing the eye and staining degenerating axons with silver methods. Terminations were seen contralaterally in the suprachiasmatic nucleus, the dorsal and ventral lateral geniculate nuclei (extensive), the pretectal nuclei, including the nucleus posterodorsalis (a very heavy input), the nucleus lentiformis mesencephali, nucleus geniculatus pretectalis, and nucleus pretectalis, the superficial layers of the optic tectum, including the stratum zonale, the stratum opticum, the stratum griseum et fibrosum centrale and the upper portion of stratum griseum centrale, and the basal optic nucleus. Ipsilateral input reaches the intermediate portion of the dorsal lateral geniculate nucleus, a small portion of the pretectal nucleus and nucleus posterodorsalis, and the basal optic nucleus (very minimally). Retinopedal fibers were traced with the HRP method. The cell bodies lie in the ventral thalamus within the nucleus of the ventral supraoptic decussation. These neurons project primarily to the contralateral retina, but some more rostrally located neurons project to the ipsilateral retina.