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D L Meyer

Publications and source records attributed to D L Meyer.

At least 73 records · Page 4Linked to original sources
PubMed1989

The nervus terminalis in larval and adult Xenopus laevis.

Nervus terminalis (nt) projections were studied by HRP injections into one nostril in adult Xenopus and in Xenopus tadpoles. Central nt targets are: medial septum, preoptic nucleus, nucleus of the anterior commissure, and hypothalamus (mainly ipsilaterally). In Xenopus tadpoles, additional fibers reach the ipsilateral dorsal thalamus and the mesencephalic tegmentum, bilaterally; furthermore, hypothalamic projections are bilateral. Xenopus tadpole nt connections resemble those of adult urodeles more closely than the projections of frogs. However, Xenopus tadpoles lack nt innervation of the medial septum.

Aging↗
PubMed1989

Thyroxine influences neuronal connectivity in the adult frog brain.

In contrast to results of earlier investigations the influence of thyroxine on CNS connectivity is not restricted to circum-metamorphic stages in frogs. Neuroanatomical findings in adult Xenopus treated with thyroxine reveal a spread of the ipsilateral retino-tectal projection. Sprouting fibers establish a tectal innervation pattern similar to the one found in primitive fish. The question arises, whether thyroxine also has morphogenetic effects in the mature CNS of other species.

Animals↗
PubMed1989

Isthmo-optic connections in congenitally monophthalmic chicks.

By means of retrograde transport of horseradish peroxidase, isthmo-optic projections were investigated in 1 to 9-day-old posthatching chickens. Some of the specimens were congenitally anophthalmic, others were monophthalmic. In contrast to a recent study, we did not detect significant differences in the one-eyed chicks. In particular, we find no indication for a retarded elimination of ectopic and aberrantly projecting isthmo-optic neurons during ontogeny. We tentatively suggest that more than one mechanism leading to monophthalmic deformities may exist.

Animals↗
PubMed1989

Central projections of the nervus terminalis in four species of amphibians.

The central projections of the nervus terminalis were investigated in two anuran and two urodele species by means of horseradish peroxidase injections into one nasal cavity. In anurans, the nervus terminalis projects to the medial septum, to the preoptic nucleus, to the nucleus of the anterior commissure and to the hypothalamus. In addition to these structures, the dorsal thalamus, the infundibulum and the mesencephalic tegmentum are innervated in urodeles. The structure containing the highest density of terminals in the amphibians investigated is the hypothalamus. In one anuran and one urodele species, the contralateral hypothalamus is primarily innervated, whereas in the other two species the majority of fibers remain ipsilateral. A comparison with other vertebrates shows that the terminalis system in urodeles has the greatest diversity of connections. Anurans, in contrast, lack some connections that are present in urodeles and fishes. These findings have implications for a possible relation of the nervus terminalis to an aquatic habitat.

Ambystoma mexicanum↗
PubMed1989

Reproductive and developmental toxicological evaluation of sanguinaria extract.

Reproductive and developmental toxicology studies were conducted with orally administered sanguinaria extract in rats and rabbits. Groups of animals which received no test article served as controls in all studies reported. No adverse effects on estrous cycling, male or female copulatory and fertility indices or gestation/lactation parameters were observed in rats given 10-100 mg/kg/day. Reduced body weights in the offspring during lactation were observed at the 100 mg/kg/day treatment level concomitant with maternal toxicity. No developmental toxicity, including teratogenicity, was observed on the fetuses of rats following maternal administration of 5-60 mg/kg/day. An increase in post-implantation loss was observed at maternally toxic dosage levels of 50 and 75 mg/kg/day in rabbits. Oral administration of sanguinaria extract in a perinatal and postnatal study in rats caused no adverse effects on litter size, parturition, or lactation of female rats nor on survival and growth of their offspring at dosage levels of 5-60 mg/kg/day. Maternal oral toxicity thresholds were 60 mg/kg/day in rats and 25 mg/kg/day in rabbits. It was concluded that the oral intake of sanguinaria extract has no selective effect on fertility, reproduction or fetal and neonatal development in rats or rabbits.

Alkaloids↗
PubMed1989

Contact-guidance of neurite growth: a direct or an indirect effect of physical environment?

Experiments with dissociated chick dorsal root ganglion cells cultured in different media revealed the significance of non-neuronal cells for neurite growth along a physical boundary. The evidence presented suggests that fibrillary fibronectin deposited by non-neuronal cells guides neurites, rather than the physical boundary itself. This guidance is not a consequence of preferential neurite growth on fibronectin deposits. Apparently fibronectin exerts different effects when present in a homogeneous vs. a fibrillary form. It is concluded, that these mechanisms account for the fact that elongating nerve fibers extend parallel to scratches in the culture dish surface and maintain a distance to it, when co-cultured with non-neuronal cells.

Animals↗
PubMed1989

Family conferences: reasons, levels of involvement and perceived usefulness.

In this study, family conferences conducted in a family practice model clinic were prospectively monitored. Study goals were (1) to identify the distribution of clinical situations for which family conferences were being conducted, (2) to test whether the levels of physician involvement typology developed by Doherty and Baird represented a hierarchy of skills, at least in their frequency of application in conferences, and (3) to generate clinicians' estimates of conference utility. During a 1-month period 57 conferences were held, primarily for medical management problems. Sixty-one percent took place in the model clinic (3% of office visits) and 23% in the hospital (20% of admissions). A hierarchy of levels of involvement was found: the clinicians indicated that medical information and advice was most often provided "a lot," emotional support was provided "some," systematic assessment and intervention were provided "a little," and family therapy skills were usually not used. Clinicians perceived the conferences to be usually useful to the patient, almost always useful to the family, and always useful to themselves. These results can provide information for future training, practice, and research.

Adolescent↗
PubMed1988

Odor stimuli modulate retinal excitability in fish.

Recording electroretinograms (ERGs) of fish prior to olfactory stimulation and after application of odor substances to the nostrils revealed a modulatory effect by chemoreceptive afferents on retinal responsiveness. The b-wave amplitude was increased in animals previously stimulated with dissolved food extracts. It is suggested that this phenomenon is related to well known behavioral effects of chemoreceptive stimulation on visually guided postural control mechanisms. The result for the first time suggests a behaviorally significant function of efferent optic nerve fibers.

Animals↗
PubMed1988

Primary olfactory projections and the nervus terminalis in the African lungfish: implications for the phylogeny of cranial nerves.

Primary olfactory and central projections of the nervus terminalis were investigated by injections of horseradish peroxidase into the olfactory epithelium in the African lungfish. In addition, gonadotropin-releasing hormone (GnRH) immunoreactivity of the nervus terminalis system was investigated. The primary olfactory projections are restricted to the olfactory bulb located at the rostral pole of the telencephalon; they do not extend into caudal parts of the telencephalon. A vomeronasal nerve and an accessory olfactory bulb could not be identified. The nervus terminalis courses through the dorsomedial telencephalon. Major targets include the nucleus of the anterior commissure and the nucleus praeopticus pars superior. some fibers cross to the contralateral side. A few fibers reach the diencephalon and mesencephalon. No label is present in the "posterior root of the nervus terminalis" (= "Pinkus's nerve" or "nervus praeopticus"). GnRH immunoreactivity is lacking in the "anterior root of the nervus terminalis," whereas it is abundant in nervus praeopticus (Pinkus's nerve). These findings may suggest that the nervus terminalis system originally consisted of two distinct cranial nerves, which have fused-in evolution-in most vertebrates. Theories of cranial nerve phylogeny are discussed in the light of the assumed "binerval origin" of the nervus terminalis system.

Animals↗
PubMed1988

Central projections of the nervus terminalis in lampreys, lungfishes, and bichirs.

Central projections of the nervus terminalis were investigated in a cyclostome (Lampetra planeri), in a sarcopterygian (Protopterus dolloi), and in an actinopterygian fish (Polypterus palmas), following the injection of horseradish peroxidase into the olfactory epithelium. Despite differences in forebrain morphology (inversion versus eversion of the hemispheres), projections of the terminal nerve are similar in the species investigated. The nervus terminalis courses through the subpallium (septum) and mainly innervates periventricular nuclei in the telencephalon and diencephalon. In lampreys, the majority of labeled fibers terminate in the hypothalamus, while in bony fishes the main projection is to periventricular nuclei of the anterior commissure. The course of the nervus terminalis through the dorsomedial telencephalon in lungfishes supports the interpretation that this part of the brain constitutes the septum, and not a pallial structure. Nervus terminalis projections are compared with those in teleosts and in amphibians. The presumed lack of gonadotropin-releasing hormone in the nervus terminalis of lampreys is discussed.

Animals↗
PubMed1987

Comparative neurology of the optic tectum in ray-finned fishes: patterns of lamination formed by retinotectal projections.

Retinotectal projections were studied in 33 different species of Actinopterygii, the ray-finned fishes, with horseradish peroxidase and cobalt tracing techniques. The distribution of retinorecipient layers in the contralateral optic tectum was analyzed. In addition, the degree of differentiation of the stratum periventriculare, and the presence of ipsilateral retinotectal projections was examined. Retinofugal fibers are labeled in the stratum opticum (SO), stratum fibrosum et griseum superficiale (SFGS), stratum griseum centrale (SGC), stratum album centrale (SAC) and stratum periventriculare (SPV). Some species lack the projection to the SO, others lack the projection to the SGC, and a third group of fishes lack both projections. Five different patterns of retinorecipient tectal strata are distinguished. These patterns correlate with the species' taxonomic position. Evolutionary trends of tectal lamination and retinotectal innervation are described. The retinotectal projection patterns provide a useful indicator of phylogenetic relationships. Some of our data suggest different relationships between actinopterygian species than hitherto believed.

Animals↗
PubMed1987

The nervus terminalis also exists in cyclostomes and birds.

The terminal nerve has been described in all vertebrate classes, with the exception of cyclostomes and birds. With regard to this question, we have examined representatives of these two classes using tracer techniques, and found a terminal nerve in larval lampreys and young domestic mallards. Horseradish peroxidase or cobaltous lysine was injected into the olfactory mucosa, which is known to be innervated by peripheral branches of the terminal nerve. The brains were then searched for labeled, centrally directed fibers of the terminal nerve that project further caudally than the glomerular layer of the olfactory bulb. In larval lampreys, centrally projecting fibers of the terminal nerve were found in the tel-, di- and mesencephalon. Termination of labeled fibers was observed in the hypothalamus. Some fibers of the terminal nerve cross to the contralateral side via the commissure of the posterior tuberculum. In young ducks, the terminal nerve projects ipsilaterally along the medial edge of the telencephalon.

Animals↗
PubMed1986

Central connections of the olfactory bulb in the bichir, Polypterus palmas, reexamined.

Central connections of the olfactory bulb of Polypterus palmas were studied with the use of horseradish peroxidase and cobalt-tracing techniques. The olfactory bulb projects to subpallial and pallial areas in the ipsilateral telencephalon; a projection to the contralateral subpallium is noted via the habenular commissure. A further target of secondary olfactory fibers is a caudal olfactory projection area in the ipsilateral hypothalamus. No labeling was seen in the anterior commissure and in the contralateral olfactory bulb. The medial and the lateral pallium receive secondary olfactory fibers in distinct areas. Neurons projecting to the bulb are found in the ipsilateral subpallium, mainly in one dorsal longitudinal nucleus. The main connection with the tel- and diencephalon is mediated via the medial olfactory tract. This tract also contains fibers to the contralateral telencephalon, and to the hypothalamus. The smaller lateral olfactory tract mediates fibers to the lateral pallium. The organization of pathways of secondary olfactory fibers in the telencephalon is described. The present findings are compared to those obtained in species possessing an inverted forebrain.

Animals↗
PubMed1986

Tracing of single fibers of the nervus terminalis in the goldfish brain.

Central projections of the nervus terminalis (n.t.) in the goldfish were investigated using cobalt- and horseradish peroxidase-tracing techniques. Single n.t. fibers were identified after unilateral application of cobalt chloride-lysine to the rostral olfactory bulb. The central course and branching patterns of individual n.t. fibers were studied in serial sections. Eight types of n.t. fibers are differentiated according to pathways and projection patterns. Projection areas of the n.t. include the contralateral olfactory bulb, the ipsilateral periventricular preoptic nucleus, both retinae, the caudal zone of the periventricular hypothalamus bilaterally, and the rostral optic tectum bilaterally. N.t. fibers cross to contralateral targets in the anterior commissure, the optic chiasma, the horizontal commissure, the posterior commissure, and possibly the habenular commissure. We propose criteria that differentiate central n.t. fibers from those of the classical secondary olfactory projections. Branching patterns of eight n.t. fiber types are described. Mesencephalic projections of the n.t. and of secondary olfactory fibers are compared and discussed with regard to prior reports on the olfactory system of teleosts. Further fiber types for which the association with the n.t. could not be established with certainty were traced to the torus longitudinalis, the torus semicircularis, and to the superior reticular nucleus on the ipsilateral side.

Animals↗
PubMed1986

A light- and electron-microscopic study of mesencephalic neurons projecting to the ganglion of the nervus terminalis in the goldfish.

After application of various neuronal tracers (horseradish peroxidase, cobalt-chloride lysine, true blue) to the ganglion of the nervus terminalis a small number of neurons was retrogradely labeled in the mesencephalon. As revealed by combined horseradish peroxidase and catecholamine-fluorescence techniques these neurons are located in the isthmic area immediately rostral to, but not within the locus coeruleus. Cobalt-labeled axons of the mesencephalic neurons were traced individually in serial sections. Neurons projecting contralaterally cross in the horizontal commissure. Tracing of single fibers provided no evidence for axon collaterals within this pathway. Retrograde labeling reveals two different types of isthmic neurons afferent to the ganglion of the nervus terminalis: One smaller-sized type is located bilaterally and consists of four to six neurons; another type possessing many dendritic processes was consistently found as only one single cell located contralateral to the side of injection. The existence of two types of neurons was confirmed by their cytological differences: The small-sized type receives only sparse perisomatic input, while the large-sized type shows heavy somatic and dendritic, probably monoaminergic innervation.

Animals↗
PubMed1986

Anatomical basis for repair of ulnar and median nerves in the distal part of the forearm by group fascicular suture and nerve-grafting.

The topography of the intraneural fascicular groups must be understood if the treatment of acute lacerations of the major nerves in the forearm is to be successful. Most lacerations in the upper extremity occur at the wrist and in the distal half of the forearm. With microsurgical longitudinal dissections and serial sections, we studied the intraneural topography of the fascicular groups of the median and ulnar nerves utilizing forty-five fresh frozen or refrigerated specimens. We devised a new technique of light photography to demonstrate the distinct boundaries of the fascicular groups. The intraneural fascicular groups provide the anatomical basis for the recommended surgical techniques of group fascicular repair and nerve-grafting.

Cadaver↗