The neocortical projection to the inferior colliculus in the albino rat

Summary The purpose of the present study was to define the field of termination of the neocortical projection to the inferior colliculus in rat. The study was based on fiber degeneration following large lesions of the cerebral cortex, and anterograde transport of wheat germ agglutinin horseradish peroxidase ejected inotophoretically into more restricted neocortical loci. Neocortical fibers were found to supply the dorsal and external cortices of the inferior colliculus. The central nucleus, in contrast, did not receive such fibers. The results speak in favor of three separate projections, one partly bilateral to the deeper part of the dorsal collicular cortex, a second ipsilateral to the superficial part of this subdivision, and a third ipsilateral to the external collicular cortex.     

Retinotopic analysis of fiber pathways in amphibians. I. The adult newt Cynops pyrrhogaster

The possibility that pathways of retinal fibers within the optic tract and the tectum of the adult newt are retinotopic was examined by selective labeling of the retinal fibers with horseradish peroxidase.Within the optic tract fibers from the ventral, temporal and dorsal retinal quadrants were ordered from the dorsal to ventral edges of the optic tract. The nasal retinal fibers exhibited two different pathways. The fibers from the dorsonasal retina ran along the ventral edge of the optic tract, while the fibers from the ventronasal retina ran along the dorsal edge of the optic tract. Segregation of pathways within the optic tract was incomplete between the nasal and other retinal fibers. The dorsonasal retinal fibers were mixed completely with the dorsal retinal fibers, and the ventronasal retinal fibers were mixed partly with the ventral retinal fibers.Both the dorsal and dorsonasal retinal fibers preferentially entered the lateral tract, and finally projected onto the ventrolateral parts of the middle tectum and of the caudal tectum, respectively. The ventral and ventronasal retinal fibers entered the dorsomedial tract, and projected onto the dorsomedial parts of the middle tectum and of the caudal tectum, respectively. The temporal retinal fibers invaded the nasal tectum directly.Most dorsal, ventral, and nasal retinal fibers ran along the sub-tracts as far as to the level of their terminals, then sharply turned in a direction toward the tectum.     

Selective retinal reinnervation of a surgically created tectal island in goldfish. I. Light microscopic analysis

Through anatomical and physiological studies of the regenerating retinotectal projection of goldfish, we sought to determine whether the establishment of a topographic projection is attained through a refinement of an initially less precise pattern of innervation. A 1-mm-wide mediolateral strip of caudal tectum was removed so that a small island of tectal tissue was spared at the caudal pole, and the contralateral nerve was either crushed (TIX) or left intact (TI). The presence of regenerated axons in the ablated zone and the reinnervation of the caudal island were assessed with anterograde and retrograde labeling methods in the following postoperative intervals: early, 20-50 days; middle, 50-110 days; and late, more than 170 days. The anterograde radioautographic method revealed that the appropriate layers of the tectal island became reinnervated by optic axons during the early period. During the middle and late periods, one to several large, discrete bundles bridging the lesion zone along the surface of exposed subtectal structures were readily identified both by radioautography and by anterograde or retrograde labeling following application of horseradish peroxidase to the transected optic nerve or tectal island, respectively. In contrast, the anterograde horseradish peroxidase method did not reveal axon bundles extending caudal to the half-tectum in the absence of a tectal island. Among TIX cases, retrograde horseradish peroxidase labeling of the contralateral nasal retina was more widespread in the middle period than in the late period, a result we interpret as reflecting an improvement in topographical precision with time. The area of retinal labeling among TIX cases in the late period was similar to that following caudal tectal injection in cases with simple nerve crush, although it was still elevated above normal control values. Physiological maps indicated a focal representation of the nasal retina in the tectal island in both periods and did not reveal a transient extreme convergence of retinal input. These findings are discussed in relation to Sperry's chemoaffinity theory.     

Integration in descending motor pathways controlling the forelimb in the cat 15. Comparison of the projection from excitatory C3-C4 propriospinal neurones to different species of forelimb motoneurones

Summary In the preceding report (Alstermark and Sasaki 1986) it was shown that a stimulus of 500 A applied in the lateral reticular nucleus (LRN) evokes a maximal or near monosynaptic EPSP (LRN EPSP) in forelimb motoneurones. This EPSP which is assumed to be selectively mediated by C3-C4 propriospinal neurones (PNs), was used to estimate the strength of the excitatory projection from C3-C4 PNs. A systematic comparison was made of the size and time course of the maximal LRN EPSP in various species of forelimb -motoneurones innervating shoulder, elbow, wrist and digit muscles. The LRN EPSP was evoked in all investigated species of forelimb motoneurones. When either the peak amplitude or the underlying area of the LRN EPSP was compared, a three-fold range was found with some tendency for the size to vary in the order of wrist > shoulder elbow > digit > intrinsic paw motor nuclei. Generally, a positive correlation was found in each motor nucleus between the peak amplitude of the LRN EPSP versus the monosynaptic homonymous group Ia EPSP, input resistance and afterhyperpolarization duration respectively (cf. Alstermark and Sasaki 1986). It is therefore postulated, that the LRN EPSP peak amplitude is correlated with motor unit type. Comparison of the time course of the LRN EPSPs was made by measuring the time-to-peak (T-t-p) and half-width (H-w). The finding in the preceding report that the T-t-p and H-w is longer in slow than in fast motoneurones was confirmed and extended to all the investigated motor nuclei. The hypothesis that both fast slow motoneurones receive projection from a group of fast C3-C4 PNs, while slow motoneurones receive an additional projection from a group with lower conduction velocity, can therefore be applied to all forelimb motor nuclei. In addition, it is proposed that some slow shoulder, wrist and digit motoneurones receive projection from a special subpopulation of C3-C4 PNs with very slow conduction velocity.This work was supported by the Swedish Medical Research Council (project no. 94 and 6953)     

A simple,inexpensive technique to permit the half-axial projection in laboratories with single plane cineangiography

A simple inexpensive modification to permit x-ray beam angulation of a cineradio-graphic system consisting of a ceiling-suspended image intensifier and an under-the-table x-ray tube is described. This has permitted the incorporation of the half-axial projection into the routine evaluation of the proximal left anterior descending artery (LAD) with a minimum of patient discomfort.     

Topographic analysis of the innervation of the rat neocortex and hippocampus by the basal forebrain cholinergic system

The basal forebrain-cortex connections of the rat were topographically mapped by retrograde tracer methods; and their contribution to the cholinergic innervation of the cortex was assessed by excitotoxin lesions placed in the rostral and caudal aspects of the complex. Discrete injections of tracer into frontal cortex labeled the prominent multipolar acetylcholinesterase (AchE)-positive cells of the ventromedial globus pallidus. Injections of tracer into the parietal cortex labelled cells in the ventral globus pallidus, the underlying substantia innominata, and the lateral hypothalamus. Separate injections of Fast Blue and Nuclear Yellow in the frontal and in the parietal cortex resulted in double-labeled cells in the ventral globus pallidus, which indicates that at least some of these cells may possess collateralizing axons. The cingulate cortex is innervated predominantly by neurons in the nucleus of the horizontal limb of the diagonal band. The occipital cortex was also shown to receive a projection primarily from the nucleus of the horizontal limb of the diagonal band. The hippocampal formation is innervated primarily by cells located in the vertical limb of the diagonal band and in the medial septum. Consistent with the results of the retrograde tracing studies, excitotoxin lesions affecting the diagonal band and medial septum decreased choline acetyltransferase (CAT) activity up to 40% on the occipital cortex and by 64% in the hippocampus, but did not affect CAT activity in the rostral neocortex. In contrast, ibotenate lesions of the caudal ventral globus pallidus and substantia innominata caused decreases in CAT activity in the frontal cortex of up to 65% without affecting enzyme activity in the hippocampal formation. The results of the present study provide details on the topographic organization of the cortical projections originating in the basal forebrain complex and indicate that these neurons are the predominant source of cortical cholinergic innervation.     

Magnetic resonance imaging in neonatal encephalopathy

Magnetic resonance imaging may provide invaluable information in the term born neonate with encephalopathy. However, both hardware and sequences may need adaptation from normal adult protocols. Sedation is often required to obtain good quality imaging, but anaesthesia is not necessary in this population. The perinatal history may predict the pattern of brain lesions, which, in turn, may be used to predict the neurodevelopmental outcome. Image interpretation is not easy and requires a full clinical history in addition to experience of both normal and abnormal neonatal brain appearances. Lesions evolve rapidly, and perinatally acquired leasions are at the most obvious 1-2 weeks from delivery. Early imaging in the first few days from presentation should always include diffusion-weighted sequences to identify early ischaemic change. Advanced techniques such as venography, angiography and perfusion-weighted imaging may be useful in certain situations, and serial imaging may help differentiate perinatal-acquired lesions from other pathologies.     

Dual, multilayered somatosensory maps formed by antennal tactile and contact chemosensory afferents in an insect brain

The antennae of most insects move actively and detect the physical and chemical composition of objects encountered by using their associated tactile sensors. Positional information is required for these sensory modalities to interpret the physical environment. Although we have a good understanding of antennal olfactory pathways, little is known about the destinations of antennal mechanosensory and contact chemosensory (gustatory) receptor neurons in the central nervous system. The cockroach Periplaneta is equipped with a pair of long, thin antennae, which are covered in bristles. The distal portions of each antenna possess about 6,500 bimodal bristles that house one tactile sensory and one to four contact chemosensory neurons. In this study, we investigated the morphologies of bimodal bristle receptor afferents by staining individual or populations of bristles. Unlike olfactory afferents, which project exclusively into the glomeruli in the ventral region of the deutocerebrum, both the presumptive mechanosensory and the contact chemosensory afferents projected into the posterior dorsal region of the deutocerebrum and the anterior region of the subesophageal ganglion. Each afferent showed multilayered segmentation and spatial occupation reflecting its three-dimensional position in the periphery. Presumptive contact chemosensory afferents, characterized by their thin axons and unique branching pattern, occupied more medioventral positions compared with the presumptive tactile afferents. Furthermore, projection fields of presumptive contact chemosensory afferents from single sensilla tended to be segregated from each other. These observations suggest that touch and taste positional information from the antenna is precisely represented in primary centers in a modality-specific manner.     

Standardized volume-rendering of contrast-enhanced renal magnetic resonance angiography

Purpose: To propose a technique for standardizing volume-rendering technique (VRT) protocols and to compare this with maximum intensity projection (MIP) in regard to image quality and diagnostic confidence in stenosis diagnosis with magnetic resonance angiography (MRA).

Material and Methods: Twenty patients were examined with MRA under suspicion of renal artery stenosis. Using the histogram function in the volume-rendering software, the 95th and 99th percentiles of the 3D data set were identified and used to define the VRT transfer function. Two radiologists assessed the stenosis pathology and image quality from rotational sequences of MIP and VRT images.

Results: Good overall agreement (mean κ = 0.72) was found between MIP and VRT diagnoses. The agreement between MIP and VRT was considerably better than that between observers (mean κ = 0.43). One of the observers judged VRT images as having higher image quality than MIP images.

Conclusion: Presenting renal MRA images with VRT gave results in good agreement with MIP. With VRT protocols defined from the histogram of the image, the lack of an absolute gray scale in MRI need not be a major problem.