The organization of cholinergic neurons in the mesencephalon of the eel,Anguilla anguilla,as determined by choline acetyltransferase immunohistochemistry and acetylcholinesterase enzyme histochemistry

Cholinergic systems in the midbrain of the eel were identified by using histochemical procedures for the demonstration of the enzymes choline acetyltransferase (ChAT) and acetylcholinesterase. Neurons detected by both methods are located in the stratum periventriculare of the tectum, cranial motor nuclei III and IV, nucleus isthmi, nucleus gustatorius secundarius, nucleus reticularis superior, and nucleus lateralis valvulae. Some projections of these cell groups were studied by injecting horseradish peroxidase into selected brain regions. Cholinergic neurons make up about 10% of the neurons in the stratum periventriculare of the tectum and are a subset of the type-XIV neurons. Neurons in n. isthmi project primarily to the ipsilateral tectum; some cholinergic isthmal neurons project to n. pretectalis superficialis. A few ChAT-positive axons, perhaps belonging to the tectopetal system, were observed in the optic nerve. The cholinergic neurons of n. gustatorius secundarious project to the inferior lobes of the hypothalamus. The neurons of the superior reticular nucleus are a cholinergic subset of the superior reticular formation. Their axons project rostrally, probably to the thalamus and pretectum. The findings are discussed in relation to functional features of the mesencephalon, particularly in relation to locomotory control.     

Connectivity of the salamander pretectum: an in-vitro (whole-brain) intracellular tracing study

The amphibian optic tectum and pretectum have been analyzed in detail anatomically and physiologically, and a specific model for tecto-pretectal interaction in the context of the visual guidance of behavior has been proposed. However, anatomical evidence for this model, particularly the precise pattern of pretecto-tectal connectivity, is lacking. Therefore, we stained pretectal neurons intracellularly in an in-vitro preparation of the salamanders Plethodon jordani and Hydromantes genei. Our results demonstrate that the projections of neurons of the nucleus praetectalis profundus are divergent and widespread. Individual neurons may project divergently to telencephalic (ipsilateral amygdala and striatum), diencephalic (ipsi-and contralateral thalamus, contralateral pretectum), and mesencephalic (ipsi- and contralateral tectum and tegmentum) centers, and to the ipsi- and contralateral medulla oblongata and rostral spinal cord. The projection of pretectal cells to the optic tectum is bilateral; axonal structures do not show discernible patterns and are present in all layers of the superficial white matter. A classification of pretectal neurons on the basis of axonal termination pattern or dendritic arborization has not been possible. Our results do not support the hypothesis that a distinct class of pretectal neurons projects to a particular subset of tectal cells. Rather, the pretectum appears to influence the tectum indirectly, acting either on retinal afferents or modulating inhibitory interneurons.     

Retinal projections in sockeye salmon smolts (Oncorhynchus nerka)

Summary The retinal projections in 2-year-old salmon smolt (Oncorhynchus nerka) are significantly different from those observed in other teleosts examined to date in that the projections are more extensive. Very noticeable are extensive projections to most of the dorsal thalamus, to all layers of the optic tectum, and into the periaqueductal gray of the torus semicircularis. The salmon smolt has bilateral retinal projections to the diencephalon and pretectum. A small retinal projection to the lateral habenular nucleus has not been described previously. Although these findings suggest striking differences in retinal projections among teleosts, this variation may relate to age differences since the previously studied teleosts were adults.     

Differences in the Neurons That Project from the Dorsal Column Nuclei to the Diencephalon,Pretectum, and Tectum in the Cat

The dorsal column nuclei (DCN) project to a number of targets in the nervous system besides the ventroposterolateral nucleus (VPL) of the thalamus. Recent evidence obtained using double-labeling techniques indicates that DCN's diencephalic-projecting neurons differ in their location and morphology from those that project to some of its other targets, such as the cerebellum and tectum. The purpose of the present study was to characterize anatomically the DCN neurons that project another of DCN's targets, the pretectum, and to determine if any of these neurons have collateral projections to the tectum or diencephalon.

The projections were studied using two double-labeling methods. One method made use of either tritiated inactivated horseradish peroxidase ([³H]apoHRP) or tritiated N-acetyl wheatgerm agglutinin ([³H]WGA) as a marker and HRP or WGA conjugated to HRP. The other method made use of the dyes Fast Blue and Nuclear Yellow. In each cat, one marker was injected into the DCN-recipient portions of the pretectum, tectum, or diencephalon, and the other marker was injected into another of these three targets.

Neurons labeled by pretectal or tectal injections were of all sizes, fusiform and multipolar in shape, and similarly located. They were scattered through the rostral zone of DCN, but were distributed at the periphery of and at the junction between the gracile and cuneate nuclei in DCN's middle and caudal zones.

In contrast to the pretectal-and tectal-labeled neurons, neurons labeled by diencephalic injections were round and large. They were found throughout the DCN complex, but were concentrated in DCN's middle and caudal zones. When both the pretectum and diencephalon were injected in the same cat, the two groups of neurons occupied similar locations in the rostral zone, but were distinct in the middle and caudal zones, with the pretectal-projecting neurons surrounding the clusters of diencephalic-projecting neurons. Very few neurons were double-labeled.

These results demonstrate that the projections to the pretectum, tectum, and diencephalon originate from different populations of neurons within specific domains in DCN. When these results are compared with the results of electrophysiological and other anatomical studies, it appears that the pretectal- and tectal-projecting neurons may be part of a previously unrecognized system originating in DCN. In contrast with the well-known lemniscal system, recognized for its function in tactile discrimination, and composed of DCN's VPL-projecting neurons together with VPL's projections to the cerebral cortex, this other system may serve some role in the regulation of posture or the coordination of movement.     

Primary retinal targets in the Atlantic loggerhead sea turtle,Caretta caretta

Summary Autoradiographic analysis distinguished twelve primary retinal targets in the diencephalon and the mesencephalon of the Atlantic loggerhead sea turtle, Caretta caretta. While the majority of fibers terminate contralaterally, sparse labelling is seen over ipsilateral thalamic nuclei. The dorsal optic nucleus is the most expansive retinal target in the dorsal thalamus. Four nuclei ventral and one dorsal, to the dorsal optic nucleus, receive retinal input. Before terminating in the optic tectum, labelled fibers pass through the pretectum terminating in four nuclei. Within the superficial zone of the optic tectum, three terminal zones are recognized. A distinct accessory tegmental tract separates from the main optic tract terminating in the basal optic nucleus.While such a multiplicity of retinal targets occurs among other reptiles, birds and mammals, it is presently impossible to accurately recognize visual homologies among amniotic vertebrates.     

Retinal projections in the chain pickerel (Esox niger Lesueur)

Summary The retinal projections inEsox niger, as determined with the aid of a modified cobalt-lysine method, are considerably more extensive in the diencephalon and pretectum than in other teleost fishes so far examined. Although most retinal axons terminate contralaterally, rare fibers can be traced to the same aggregates ipsilaterally. The retinohypothalamic projection appears larger than hitherto reported in teleosts, and the dorsomedial optic tract issues fibers to a series of cell clusters extending from the rostral thalamus to mid-torus levels. A retinal projection to a presumed ventrolateral optic nucleus (VLO) is described for the first time in a teleost. Other targets of retinal fibers include the nucleus geniculatus lateralis ipse of Meader (GLI), the pretectal nucleus (P), the cortical nucleus and a well-developed ventromedial optic nucleus (VMO). The projection to the optic tectum is principally to the stratum fibrosum et griseum superficiale (SFGS) and stratum marginale (SM), but a considerable number of axons also course through the stratum album centrale (SAC) before terminating there or piercing the stratum griseum centrale (SGC) and terminating in SFGS. Rare terminal arborizations of retinal fibers were also observed in stratum griseum centrale (SGS) and in the stratum griseum periventriculare (SGC) in restricted portions of the tectum. Because of the relatively large size of the visual structures inE. niger it is a potentially useful model for future experimental studies on the visual system.     

Retinal projections in the caecilian Ichthyophis kohtaoensis (Amphibia,Gymnophiona)

Summary The retinal projections of the caecilian Ichthyophis kohtaoensis were investigated by anterograde transport of HRP. The optic tract forms two bundles in the diencephalon, a narrow medial bundle in the optic tectum, and a basal optic tract consisting of few fibres. Terminal fields are in the thalamus, pretectum, tectum, and as a circum-scribed basal optic neuropile in the tegmentum. Thalamic, pretectal and tectal projections are contralateral as well as ipsilateral. The reduced but existing visual projection corresponds to a reduced but existing visually guided behaviour.     

Notes on the Midbrain and Forebrain of Calamoichthys calabaricus Smith, 1865 (Polypteridae,Brachiopterygii)

The rostral parts of the brain in Calamoichtkys calabaricus, a brachiopterygian fish, show some similarities with actinopterygians, as well as with lungfishes and amphibians. This study includes a histological analysis of the optic tectum, pretectum, diencephalon and the olfactory system.     

Central projections of the pineal complex in the silver lamprey Ichthyomyzon unicuspis

Summary The central projections of the pineal complex of the silver lamprey Ichthyomyzon unicuspis were studied by injection of horseradish peroxidase. The pineal tract courses caudally along the left side of the habenular commissure, and a few fibers penetrate the brain through the caudalmost portion of this commissure. Most of the fibers, however, continue caudally and enter the brain through the posterior commissure. The pineal tract projects bilaterally to the subcomissural organ, the superficial and periventricular pretectum, the posterior tubercular nucleus, the dorsal and ventral thalamus, the dorsal hypothalamus, the optic tectum, the torus semicircularis, the midbrain tegmentum, and the oculomotor nucleus. A few fibers decussate in the tubercular commissure, but the course of these decussate fibers could not be followed owing to the bilateral nature of the projections. No retrogradely labeled cells were found in the brain. With the exception of the projections to the optic tectum and torus semicircularis, the pineal projections in the silver lamprey are similar to those reported in other anamniote vertebrates.     

The visual system of the guitar fish (Rhinobatos productus)

Summary The retinal projections in adult and juvenile guitar fish (Rhinobatos productus) were determined with the aid of the Nauta-Fink-Heimer techniques. The visual system was found to be more extensive and more differentiated than in any other elasmobranch studied to date. Massive projections exist to the dorsal and ventral thalamus, tectum and pretectum, in addition to the usual weak contributions to the hypothalamus and the ventral mesencephalic tegmentum. The projection to the lateral tectum is significantly less distinct than that to the medial part of this structure, suggesting that the ventral visual field has a smaller input, perhaps due to the fact that this visual field is normally aimed at the body of this flat fish.     

Cerebellar projections to the somatic pretectum in the cat

Neurons in the somatic pretectum receive input from the dorsal column nuclei (DCN) and project to a comparable "somatic" portion of the dorsal accessory nucleus of the inferior olive (DAO). This somatic DAO is reciprocally connected with the anterior interpositus nucleus of the cerebellum. One question that arises is whether this circuitry is further controlled by an output specifically from the anterior interpositus nucleus to the somatic pretectum. Wheatgerm agglutinin conjugated to horseradish peroxidase was injected into various parts of the cat pretectum. Injection sites were interpreted as including the somatic pretectum if neurons in the DCN were retrogradely labeled and if anterograde terminal labeling occurred in somatic DAO. The locations of retrogradely labeled neurons within the deep cerebellar nuclei were then compared in cases in which the injection sites included or excluded the somatic pretectum. In all cases in which the injection site included the somatic pretectum, retrogradely labeled neurons were observed in the anterior interpositus nucleus as well as in the lateral cerebellar nuclei. In some of these cases, neurons in the posterior interpositus and medial nuclei were also labeled. In contrast, in cases in which the pretectal injection site was located outside or at the border of the somatic pretectum, retrogradely labeled neurons were observed only in the lateral, posterior interpositus, and medial nuclei. Thus, the somatic pretectum appears to receive input primarily from neurons in the anterior interpositus nucleus, along with some input from neurons in the lateral nucleus. These results provide additional evidence for a pathway through the DCN in which sequentially processed somatic information has access to and is modulated by cerebellar circuitry. The existence of such a pathway supports the conclusion that neurons in the DCN convey somatic information important not only for cutaneous, kinesthestic, and other bodily sensations, but also for the control of movement.     

Structure and function of neurons in the complex of the nucleus electrosensorius of the gymnotiform fish Eigenmannia: Detection and processing of electric signals in social communication

Summary The complex of the diencephalic nucleus electrosensorius (nE) provides an interface between the electrosensory processing performed by the torus semicircularis and the control of specific behavioral responses. The rostral portion of the nE comprises two subdivisions that differ in the response properties and projection patterns of their neurons. First, the nEb (Fig. 1 B), which contains neurons that are driven almost exclusively by beat patterns generated by the interference of electric organ discharges (EODs) of similar frequencies. Second, the area medial to the nEb, comprising the lateral pretectum (PT) and the nE-acusticolateralis region (nEar, Fig. 1 B-D), which contains neurons excited predominantly by EOD interruptions, signals associated with aggression and courtship. Neurons in the second area commonly receive convergent inputs originating from ampullary and tuberous electroreceptors, which respond to the low-frequency and high-frequency components of EOD interruptions, respectively. Projections of these neurons to hypothalamic areas linked to the pituitary may mediate modulations of a fish's endocrine state that are caused by exposure to EOD interruptions of its mate.Abbreviations a axon - ATh anterior thalamic nucleus - CCb corpus cerebelli - CE central nucleus of the inferior lobe - CP central posterior thalamic nucleus - Df frequency difference between neighbor's EOD and fish's own - DFl nucleus diffusus lateralis of the inferior lobe - DFm nucleus diffusus medialis of the inferior lobe - DTn dorsal tegmental nucleus - EOD electric organ discharge - G glomerular nucleus - Hc caudal hypothalamus - Hd dorsal hypothalamus - Hl lateral hypothalamus - Hv ventral hypothalamus - JAR jamming avoidance response - LL lateral lemniscus - MGT magnocellular tegmental nucleus - MLF medial longitudinal fasciculus - nB nucleus at the base of the optic tract - nE nucleus electrosensorius - nEar nucleus electrosensorius-acusticolateral region - nEb nucleus electrosensorius-beat related area - nE nucleus electrosensorius, area causing rise of EOD frequency - nE nucleus electrosensorius, area causing fall of EOD frequency - nLT nucleus tuberis lateralis - nLV nucleus lateralis valvulae - PC posterior commissure - Pd nucleus praeeminentialis, pars dorsalis - PeG periglomerular complex - PG preglomerular nucleus - PLm medial division of the perilemniscal nucleus - Pn pacemaker nucleus - PPn prepacemaker nucleus - PT pretectal nucleus - PTh prethalamic nucleus - R red nucleus - Sc suprachiasmatic nucleus - SE nucleus subelectrosensorius - TAd nucleus tuberis anterior-dorsal subdivision - TAv nucleus tuberis anterior-ventral subdivision - TeO optic tectum - TL torus longitudinalis - TSd dorsal (electrosensory) torus semicircularis - TSv ventral (mechanosensory and auditory) torus semicircularis - tTB tecto-bulbar tract - VCb cerebellar valvula - VP valvular peduncle - VPn nucleus of the valvular peduncle     

Anatomy,neurophysiology and functional aspects of the nucleus isthmi in salamanders of the family Plethodontidae

Summary Tongue-projecting plethodontid salamanders have massive direct ipsilateral retinal afferents to the tectum opticum as well as a large and well developed nucleus isthmi. Retrograde staining revealed two subnuclei: A ventral one projecting to the contralateral tectal hemisphere and a dorsal one projecting back to the ipsilateral side. The isthmic nuclei show a retinotopic organization, which is in register with that of the tectum. Electrophysiological recordings from nucleus-isthmi neurons revealed response properties that are very similar to those found in tectal neurons. Thus, there is no substantial processing of tectal neural activity in the nucleus isthmi. Measurements of peak latencies after electrical and light stimulation suggest the continuous coexistence of 4 representations of the visual field in the tectum mediated by (1) the contralateral and (2) the ipsilateral direct retinal afferents, (3) the uncrossed and (4) the crossed isthmo-tectal projection. (1) and (2) originate at the same moment in the retina and arrive simultaneously in the tectum. It is assumed that in plethodontid salamanders with massive ipsilateral retino-tectal projections depth perception based on disparity cues is achieved by comparison of these images.Representations mediated by (3) and (4) arriving in the tectum at the same time as (1) and (2) originate 10–30 ms earlier in the retina. It is hypothesized that these time differences between (1)/(2) and (3)/(4) are used to calculate three-dimensional trajectories of fast-moving prey objects.Abbreviations EL edge length - FDA fluoresceine dextranamine - RDA tetramethylrhodamine dextranamine - RF receptive field     

Mapping of the human lambda immunoglobulin variable gene subgroup 1

We describe the cloning and mapping of 20 putative members of the IGLV subgroup 1. These gene segments are contained on 26 phage clones which fall into 7 contigs plus one solitary phage. This represents approximately 240 kilobases (kb) of cloned DNA. Like IGLC gene segments, the IGLV gene segments were found to be oriented proximal to distal on the chromosome, indicating IGL somatic rearrangement is by deletion. The gene segments were placed on a long-range map of the IGL locus, which covers at least 800 kb. Clones were further ordered by pulsed field gel electrophoresis analysis of B-cell lines known to produce IGL-containing immunoglobulins. DNA deletions ranged from 120 to 570 kb.     

Enkephalin-immunoreactive cells in the mesencephalic tegmentum project to the optic tectum of the teleosts Salmo gairdneri and Salmo salar

Summary Immunocytochemistry using antibodies against Met-enkephalin and Leu-enkephalin has demonstrated a group of large enkephalin-immunoreactive neurons in the nucleus of the rostral mesencephalic tegmentum (mRMT) of two teleost fish, Salmo gairdneri and Salmo salar. Injections of cobalt-lysine in the medial optic tectum retrogradely labeled the above group of tegmental neurons. Tegmental neurons were labeled only ipsilaterally to the injection site. This indicates that enkephalinergic neurons in the nRMT project to the optic tectum, and that at least some of the enkephalinergic axons observed in the optic tectum belong to a tegmento-tectal pathway. Comparable enkephalinergic pathways have been described in reptiles and birds, where pretectal-mesencephalic nuclei contribute to the enkephalin-containing fibers that project to the optic tectum.     

Bilateral retinal projections in the black piranah (Serrasalmus niger)

Summary The retinal projections were studied in the black piranah (Serrasalmus niger) with degeneration and autoradiographic methods. The projections are bilateral to the hypothalamic optic nucleus, the dorsomedial optic nucleus, corpus geniculatum ipsum of Meader (1934) and the optic tectum. Unilateral, crossed projections were traced to the pretectal nucleus and the cortical nucleus. The visual system of the black piranah is exceptionally well developed but has retained many primitive features including the extensive bilateral projections.     

Afferent connections of the optic tectum in channel catfish Ictalurus punctatus

Summary Horseradish peroxidase was injected unilaterally into the optic tectum of the channel catfish, Ictalurus punctatus. The sources of tectal afferents were thereby revealed by retrogradely labeled neurons in various brain centers. Retrogradely labeled cells were seen in both the ipsilateral and contralateral telencephalon. The superficial pretectal area was labeled on both sides of the brain. Ipsilateral projections were also observed coming from the entopeduncular nucleus. Both the anterior thalamic nucleus and the ventro-medial thalamic nucleus projected to the ipsilateral optic tectum. Cells in the ipsilateral nucleus of the posterior commissure were seen to project to the tectum. Labeled fibers were visualized in the lateral geniculate nucleus ipsilateral to the injected tectum, however, no labeled cell bodies were observed. Therefore, tectal cells project to the lateral geniculate nucleus, but this projection is not reciprocal. No labeled cells were found in the cerebellum. Labeled cells occurred in both the ipsilateral and contralateral medial reticular formation; they were also observed in the ipsilateral nucleus isthmi. A projection was seen coming from the dorsal funicular nucleus. Furthermore, labeled cells were shown in the inferior raphe nucleus.Abbreviations AP Area pretectalis - C Cerebellum - DPTN Dorsal posterior tegmental nucleus - H Habenula - IRF Inferior reticular formation - LI Inferior lobe - LGN Lateral geniculate nucleus - LR Lateral recess - MB Mammillary body - MRF Medial reticular formation - MZ Medial zone of the telencephalon - NC Nucleus corticalis - NDL-M Nucleus opticus dorsolateralis/pars medialis - NI Nucleus isthmi - NPC Nucleus of the posterior commissure - OPT Optic tectum - OT Optic tract - PC Posterior commissure - PN Pineal organ - PrOP Preoptic nucleus - PT Pretectum - TBt Tectobulbar tract - TEL Telencephalon - TL Torus longitudinalis - TS Torus semicircularis - VC Valvula cerebelli - VLTN Ventrolateral thalamic nucleus - VMTN Ventromedial thalamic nucleus     

Projections to the midbrain tectum in Salamandra salamandra L.

Following unilateral iontophoretic application of HRP into the optic tectum of Salamandra salamandra, retrogradely HRP-filled cells were found bilaterally in the pretectum, tegmentum isthmi, the reticular formation, pars medialis, and in the nucleus vestibularis magnocellularis. The area octavo-lateralis projects only to the caudal part of the tectum. Ipsilateral projections were noted from the dorsal gray columns of the cervical spinal cord, the dorsal tegmentum, the thalamus dorsalis pars medialis, thalamus dorsalis, pars anterior (to the rostral one-third of the tectum), the thalamus ventralis (in its entire rostro-caudal extent), and the preoptico-hypothalamic complex. Retrogradely filled cells were identified in deeper layers of the contralateral tectum. There are two telencephalic nuclei projecting ipsilaterally to the tectum via the lateral forebrain: the ventral part of the lateral pallium, and the posterior strioamygdalar complex.     

Dynamics of process formation during differentiation of tectal neurons in embryonic zebrafish

Neurons acquire their distinct shapes after passing through many transitional stages in early development. To reveal the dynamics and spatiotemporal sequence of process formation in situ, the growth of neurons in the optic tectum of live zebrafish embryos (54 to >100 h old) was monitored using time-lapse videorecordings. Neurons were labeled by injecting the fluorescent vital dye DiO into the cell-rich layer of the developing tectum in 50- to 70-h-old embryos. In phase 1, tectal neurons possess an apical “primary process” which reaches to the ventral aspect of the tectal neuropil. The primary process produces at its tip short transitory branches, some with growth cones, over a period of roughly 6 h. One of the growth cones then elongates rapidly and grows toward the caudal tectum via a route characteristic of efferent axons. After retraction of excess branches and growth cones, branching activity resumes at the tip of the primary process to form the dendritic tree (phase 2). The dendritic tree develops in the tectal neuropil through emission and retraction of many branches during a period of >20 h (our longest continuous time-lapse movie). The tectal territory “explored” in this way is larger than the area finally covered by the tree resulting from growth and loss of branches. The dynamics observed here directly are probably characteristic for dendrite formation in vertebrates. Moreover, consistent with the sequence of neuronal differentiation observed in vitro, the growth of the axon precedes that of the dendrites, although both emerge from a common primary process in this type of tectal neuron. © 1997 John Wiley & Sons, Inc. J Neurobiol 32: 627–639, 1997     

Physical location of the human immunoglobulin lambda-like genes, 14.1, 16.1, and 16.2

The human immunoglobulin lambda-like (IGLL) genes, which are homologous to the human immunoglobulin lambda (IGL) light chain genes, are expressed only in pre-B cells and are involved in B cell development. Three IGLL genes, 14.1, 16.1, and 16.2 are present in humans as opposed to one, 5 (Igll), found in the mouse. To precisely map the location of the human IGLL genes in relation to each other and to the human IGL gene locus, at 22q11.1–2, a somatic cell hybrid panel and pulsed field gel electrophoresis (PFGE) were used. Hybridization with a -like gene-specific DNA probe to somatic cell hybrids revealed that these genes reside on 22q11.2 between the breakpoint cluster region (BCR) and the Ewing sarcoma breakpoint at 22q12 and that gene 16.1 was located distal to genes 14.1 and 16.2. Gene 14.1 was found by PFGE to be proximal to 16.2 by at least 30 kilobases (kb). A 210 kb Not I fragment containing genes 14.1 and 16.2 is adjacent to a 400 kb Not I fragment containing the BCR locus, which is just distal to the IGL-C (IGL constant region) genes. We have determined that the IGLL genes 14.1 and 16.2 are approximately 670 kb and 690 to 830 kb distal, respectively, to the 3-most IGL-C gene in the IGL gene locus, IGL-C7. We thus show the first physical linkage of the IGL and the IGLL genes, 14.1 and 16.2. We discuss the relevance of methylation patterns and CpG islands to expression, and the evolutionary significance of the IGLL gene duplications. Consistent with the GenBank nomenclature, these human IGLL genes will be referred to as IGLL1 (14.1), IGLL2 (16.2), and IGLL3 (16.1), reflecting their position on chromosome 22, as established by this report. Correspondence to: B. B. Blomberg.