Margarete Tigges

Melatonin synthesis and circadian tryptophan hydroxylase activity in chicken retina following destruction of serotonin immunoreactive amacrine and bipolar cells by kainic acid

The neurotoxic excitatory amino acid analog, kainic acid, was used to destroy serotonin-immunoreactive inner retinal neurons, bipolar cells and amacrine cells, in retinas of chickens. Tryptophan hydroxylase activity and melatonin content were examined in the kainic acid-lesioned retinas. Tryptophan hydroxylase activity was present in kainic acid-lesioned retinas and displayed a circadian rhythm. Nocturnal levels of activity in lesioned and control retinas were similar. Melatonin synthesis occurred in kainic acid-lesioned retinas in a diurnal cycle as in normal retinas. Dark-phase melatonin content of kainic acid-lesioned retinas exceeded that of controls. We conclude that most, if not all, circadian tryptophan hydroxylase activity and melatonin synthesis occurs in cells other than the cells that contain most of the serotonin in retina, serotonin-immunoreactive bipolar and amacrine cells.

Parvalbumin immunoreactivity of the lateral geniculate nucleus in adult rhesus monkeys after monocular eye enucleation

Immunocytochemical methods with antiserum to the calcium-binding protein parvalbumin (PV) were used to examine the effects of monocular enucleation on parvalbuminergic neurons and processes in the lateral geniculate nucleus (LGN) of adult rhesus monkeys. In the LGN of normal monkeys, numerous PV-positive neurons, including the largest neurons in the nucleus, and many PV-positive processes occur in all six laminae. After monocular enucleation, PV immunoreactivity is reduced in the neuropil of the denervated laminae compared to adjacent nondenervated and to normal laminae. PV immunoreactivity of somata in denervated laminae, however, appears to be indistinguishable from that of somata in nondenervated laminae, although neurons in the denervated laminae are smaller in size. Since LGN neurons in denervated laminae have lost their visual input, the functional role of PV in this nucleus may not relate directly to visual information processing.

Monocular enucleation reduces immunoreactivity to the calcium-binding protein calbindin 28 kD in the rhesus monkey lateral geniculate nucleus.

The calcium-binding proteins calbindin (CaBP) and parvalbumin (PV) are important in regulating intracellular calcium in brain cells. PV immunoreactivity is reduced by enucleation in the lateral geniculate nucleus (LGN) and by enucleation and visual deprivation in the striate cortex of adult monkeys. The effects of enucleation and visual deprivation on CaBP immunoreactivity in the LGN are not known. We therefore have studied cells and neuropil in the LGN that are labeled by antibodies to CaBP in normal and visually deprived Rhesus monkeys to determine if there is an effect on this calcium-binding protein. One group of monkeys had one eye removed 2 weeks to 4.3 years before sacrifice. A second group had one eye occluded with opaque lenses from infancy without enucleation. A final group had one eye occluded long-term followed by short-term enucleation 2 weeks before sacrifice. In normal monkeys, CaBP-immunoreactive neurons were found throughout the LGN. They were sparsely distributed within the six main laminae, and more densely distributed within layer S and the interlaminar zones (ILZ). The labeled ILZ neurons had a distinct morphology, with fusiform somata and elaborate dendritic trees that were confined primarily to the ILZ. Most CaBP-labeled neurons in the main layers had dendrites that radiated in all directions from the soma. ILZ and main layer cells labeled by CaBP thus probably represent two different cell types. Monocular enucleation with or without occlusion produced a significant reduction in antibody labeling in the deafferented laminae. Field measures revealed an average 11.5% reduction in optical density in each deafferented lamina compared to its adjacent, nondeprived layer. The differences in field optical density between deprived and nondeprived layers were statistically significant. CaBP neurons were still visible, but the optical density of antibody labeling in these cells also was reduced. Occlusion without enucleation had no effect. Thus, deafferentation, but not light deprivation, reduces concentrations of CaBP in monkey LGN. This effect is different than that seen in striate cortex of adult monkeys, where visual deprivation as well as enucleation alters CaBP immunoreactivity.

Efferents of area 4 in a South American monkey (Saimiri). I. Terminations in the spinal cord.

A single injection of either tritiated proline or a mixture of proline and leucine was made in area 4 of 8 squirrel monkeys. The locus of the injection was systematically varied from medial to lateral among animals. Autoradiographs revealed a strong contralateral lateral corticospinal tract. A sparsely labelled ipsilateral lateral tract was also present in all animals. In 2 animals, a few labelled fibers indicative of an ipsilateral anterior tract were observed; the fibers terminated at lumbar levels. Grain counts over the cervical and lumbar gray showed that area 4 efferents terminated contralaterally in laminae IV--IX with a peak in lamina VII; only sparse input was seen in the vicinity of the large alpha-motoneurons of lamina IX. On the ipsilateral side, the terminals were largely confined to lamina VIII. This pattern was in accordance with that reported in other primates. The terminal fields at sacral and coccygeal levels were radically different in that large numbers of fibers recrossed to the ipsilateral side and ended in laminae V through IX; the functional significance of this strong bilateral termination was discussed.

Diffuser contact lenses retard axial elongation in infant rhesus monkeys

In each of five monkeys, one eye was fitted with a diffuser lens at birth. This lens allowed pattern vision, but also reduced contrast by about 1 log unit. In four out of five monkeys, the treated eyes were shorter and more hyperopic than the untreated fellow eyes. At 25 weeks of age, interocular differences (OD -- OS) of the experimental group were significantly greater than interocular differences of age-matched normal monkeys for both axial length (P < 0.05) and refractive error (P < 0.02). In addition, while the treated eyes were significantly different from normal eyes for both axial length measurements (P < 0.01) and refractive error (P < 0.01), there were no significant differences between the untreated fellow eyes and normal eyes. In primates less severe pattern deprivation appears to produce an effect on eye growth that is opposite to that of severe pattern deprivation (little or no pattern vision), which typically results in axial myopia.

Ultrastructural changes in the superficial layers of the superior colliculus in Galago crassicaudatus (primates) after eye enucleation.

SummarySeveral types of terminals were found in the three superficial collicular layers of Galago. At least two axon terminals with round vesicles (R1 and R2) could be distinguished on the basis of vesicle packing and electron density of the cytoplasmic and mitochondrial matrices. R1 axon terminals were characterized by aggregations of vesicles in an electron lucent cytoplasm and mitochondria with a relatively dark matrix, while in R2 axon terminals the vesicles were more evenly distributed in an electron dense cytoplasm and the mitochondrial matrix was pale. R2 endings occurred in clusters in the stratum griseum superficiale; they were absent in the stratum zonale. R1 endings were found in all three superficial collicular layers. Both types of R terminals made asymmetrical contacts with small dendrites, dendritic spines and F profiles. Profiles containing flattened vesicles and establishing symmetrical contacts were numerous, and many could be identified as dendrites by accepting as criteria for dendrites evenly spaced microtubules, clusters of ribosomes and the fact that these F profiles were postsynaptic to other terminals. F terminals were presynaptic to other F profiles, dendrites and somata; they were postsynaptic to R terminals and took part in serial synapses. Dendrodendritic contacts were frequent, somatodendritic contacts rare. After eye enucleation most R2 axon terminals underwent the electron dense degenerative reaction. The degeneration process was a lengthy one; many degenerating boutons were found 30 days after axotomy and some persisted up to 180 days postoperatively. There was strong indication that the superior colliculus received more crossed than uncrossed retinofugal fibers. The crossed and uncrossed retinocollicular axons terminated in two different substrata of the stratum griseum superficiale.

Enucleation demonstrates ocular dominance columns in Old World macaque but not in New World squirrel monkey visual cortex

The effect of monocular enucleation on basophilic and metabolic staining in primary (striate) visual cortex has been compared in Old and New World monkeys. Both species show a 30-40% shrinkage of neurons in the layers of dorsal lateral geniculate nucleus receiving axons from the enucleated eye. In striate cortex Old World macaque monkeys show alternating bands of increased and diminished staining in layers 3, 4 and 6, corresponding to ocular dominance columns. New World squirrel monkeys show staining patterns in all layers which are unchanged from normal cortex, suggesting that New World monkeys lack obvious ocular dominance columns.

Presynaptic dendrite cells and two other classes of neurons in the superficial layers of the superior colliculus of the chimpanzee.

SummaryIn the superior colliculus of chimpanzee, three classes of neurons can be identified by ultrastructural criteria. They are 1) marginal cells located in the stratum zonale, 2) collicular relay cells in the stratum griseum superficiale and 3) presynaptic dendrite (PSD) cells, i.e., neurons with presynaptic specializations in soma and/or dendrites. PSD cells are the smallest neurons in the stratum griseum superficiale; they have a relatively large, deeply infolded nucleus and a small rim of cytoplasm rich in free ribosomes. PSD cells are sufficiently different from the two other classes of neurons to be reliably identified at the ultrastructural level. They closely resemble presynaptic neurons as described in the lateral geniculate nucleus of other mammalian species. Presynaptic dendrites in continuity with PSD cells are rich in organelles, especially ribosomal clusters, and establish en passage contact with other dendrites. Another type of presynaptic dendrite, poor in organelles, except for bundles of microtubules, could not be traced back to its parent neuron. Homoor heterogeneity of PSD cells is discussed. No axon was traced from a PSD cell.

Developmental study of neuropeptide Y-like immunoreactivity in the neurohypophysis and intermediate lobe of the rhesus monkey (Macaca mulatta)

SummaryThe purpose of this study was to examine the development and distribution of neuropeptide Y-immunoreactive fibers in the neurohypophysis of the rhesus monkey (Macaca mulatta) throughout life and the relationship of these fibers to the hypothalamo-hypophyseal portal vasculature. In rhesus monkeys, which varied in age from fetal life to 34 years, neuropeptide Y-immunoreactive fibers were present at all ages examined. In adult monkeys, varicose neuropeptide Y-labeled fibers were concentrated in the upper infundibular stem in association with capillary loops of the portal vasculature and the long portal vessels. Other fibers travelled down the infundibular stem and were distributed at the junction of the lower infundibular stem and infundibular process in the vicinity of the short portal vessels. In the infundibular process, neuropeptide Y-immunoreactive fibers were concentrated along the border of the intermediate lobe. Other stained fibers were sparsely distributed in the infundibular process and were often associated with small vessels. Neuropeptide Y-immunoreactivity was also located in a few fibers and cells of the intermediate lobe. Very few labeled fibers were seen in the fetal neurohypophysis, but their number increased gradually during the first postnatal year. At two years of age, a high density of stained fibers was observed, especially in the infundibular process. The number of axons in the infundibular process was lower at 12 years and continued to decline until 34 years of age. Neuropeptide Y may modulate hormone release at these sites and may also be released directly into vessels in the infundibular process. The close association of neuropeptide Y-labeled fibers with capillaries of the portal vasculature strongly suggests that neuropeptide Y is released into the portal blood of monkeys throughout life and may influence hormone secretion from the anterior pituitary gland.

Types of degenerating geniculocortical axon terminals and their contribution to layer IV of area 17 in the squirrel monkey (Saimiri).

SummaryRadiofrequency lesions were made in the lateral geniculate nuclei of six squirrel monkeys. The resulting degenerating terminals and their postsynaptic structures in layer IV of area 17 were quantitatively categorized on photomontages covering large areas of neuropil. Two to five days after the lesion, numerous axon terminals were affected by a variety of degenerative changes, i.e., enlargement and distortion of synaptic vesicles, neurofilamentous hyperplasia, electron-lucent and electron-dense reactions. Based on the aggregation of electron-dense material beneath the postsynaptic membrane, the degenerating terminals were considered to be of the asymmetric type. Among the degenerating boutons were the largest axon endings that occur in layer IV. Three days postoperatively, degenerating boutons contributed an average of 16.2% to the total synapse population; five days postoperatively, the average had increased to 19.3 %. The percentage of degenerating boutons on individual montages, however, amounted to as much as 29%. This amount probably reflects more closely the actual contribution of the geniculocortical fiber system to layer IV of striate cortex. The postsynaptic structure most frequently contacted by degenerating axon endings was the dendritic spine, followed by dendrites of small diameter. To account for the diversity of degenerative changes in the same fiber system, we offer the tentative suggestion that heterogeneously degenerating axon terminals arise from a heterogeneous population of neurons in the lateral geniculate nucleus, i.e., from magnocellular versus parvocellular laminae.