Cortical projection of giant neostriatal neurons in the cat. Light and electron microscopic horseradish peroxidase study.

Following voluminous injections of horseradish peroxidase (HRP) in various neocortical fields, a small number of labeled large neurons are observed ipsilaterally in the putamen, striatal ponticuli, caudate nucleus, and nucleus accumbens septi. The bulk of the corticopetal cells are found in the putamen and in the striatal ponticuli. A more significant number of labeled neurons is encountered following injections in auditory and sensorimotor cortex, followed by the prefrontal and premotor cortex; very few cells project to the visual cortex. Ultrastructurally, the large HRP-labeled neurons display an eccentrically located, indented nucleus, abundant granular endoplasmic reticulum forming Nissl bodies, well developed Golgi zones, and numerous dense bodies. The simultaneous demonstration of retrogradely transported HRP and acetylcholinesterase (AChE) suggest that the large neurons are presumably cholinergic. These results provide evidence that at least some of the giant striatal neurons are efferent cells. The coincidence of cytological, histochemical, and hodological criteria invite the speculation that the giant corticopetal neostriatal neurons might be related to the magnocellular cholinergic groups of the basal forebrain (especially the Ch4 group).

Reciprocal connections between the claustrum and the auditory cortical fields in the cat. An experimental study using light- and electron microscopic anterograde degeneration methods, and the horseradish peroxidase retrograde axonal transport.

The reciprocal connections between the claustrum and the auditory cortical fields AI, AII and Ep were investigated by means of Nauta and Fink-Heimer selective silver impregnation procedures, electron microscopic identification of degenerated axons and synaptic boutons, and with the Mesulam horseradish peroxidase retrograde tracing technique. The course and termination of degenerating corticoclaustral axons were investigated following circumscript lesions of the AI, AII and Ep areas in 19 cats. The greatest amount of degeneration debris was observed following destruction of the AII area. The central third of the claustrum (stereotaxic level A13-A15) is filled with degenerating terminals (d. t.), with greatest concentration in the lateral wedge of the nucleus, and along its inferolateral border. Rostrally and caudally the density of degeneration diminishes but scattered d. t. were observed up to the rostral pole, and a moderate number - up to the caudal pole of the claustrum. Slightly lesser amount of d. t. was observed following Ep destruction. The caudal portion of the claustrum is filled with d. t. In the central third the degeneration field occupies mainly the ventrolateral zone of the nucleus. The rostral pole of the claustrum is free of degeneration. The projection from the AI field is considerably more moderate, and is diffusely organized. A substantial number of d. t. is encountered only in the lateral parts of the central claustral third. The crossed corticoclaustral connections mirror the ipsilateral ones but are far more modest. The AII area projects mainly to the central claustral third, the Ep area--to the caudal third. The projection of the AI area to the contralateral claustrum is very weak. The electron microscopic examination of the claustrum following auditory cortex destruction in 9 cats revealed an appreciable number of degenerating synaptic boutons. They undergo dark and more rarely light degenerative changes. The cortical terminals are classified in two types: "small round" (SR), comprising approximately 70 to 75% of the corticoclaustral boutons, and "large round" (LR)-25-30%, resp. The SR boutons measure 0.6-1.2 micron, contain tightly packed round synaptic vesicles (380-420 A), and form asymmetrical axodendritic contacts. The LR boutons measure 1-2.5 microns, contain round vesicles (400-500 A) and form asymmetrical axodendritic and (far more rarely) axosomatic contacts. The claustrocortical connection was investigated in 13 cats with selective injections of 30% HRP in the three subdivisions of the auditory cortex.(ABSTRACT TRUNCATED AT 400 WORDS)

Ribosome biogenesis and nucleolar ultrastructure in neuronal and oligodendroglial rat brain cells.

The absolute amounts of precursor to ribosomal RNA (pre-rRNA) and ribosomal RNA (rRNA) in isolated rat brain neuronal and oligodendroglial nuclei were determined. The amount of the major pre-rRNA and rRNA species in neuronal nuclei was about twofold higher than in oligodendroglial nuclei. The relative rate of pre-rRNA synthesis in vivo was 2.3- to 2.7-fold higher in neuronal as compared with oligodendroglial nuclei. This corresponds to a 2.7-fold higher activity of the "template-bound" RNA polymerase I in isolated neuronal nuclei, whereas the activity of the "free" enzyme in both neuronal and glial nuclei was almost identical. The higher transcription rates of rRNA genes correlated with the markedly more prominent fibrillar component in neuronal nucleoli. The turnover times of the major pre-rRNA and rRNA species in neuronal and oligodendroglial nuclei were similar, except for 45S pre-rRNA, which turned over at an approximately 1.5-fold slower rate in neuronal nuclei. The relative rates of processing of pre-rRNA and of nucleocytoplasmic transport of rRNA in neuronal cells were approximately 2.7-fold higher than in oligodendroglial cells and corresponded to the differences in rRNA gene transcription rates. The established ribosome formation features correlated with an abundant (neurons) or exceedingly scarce (oligodendrocytes) nucleolar granular component. The turnover rate of cytoplasmic ribosomes in rat brain neurons was twofold slower than in oligodendrocytes, largely because of the about fivefold higher amount of ribosomes in the cytoplasm of neurons. We conclude that ribosome formation and turnover in neuronal and oligodendroglial cells are adapted to the protein synthetic levels in these two types of brain cells.

Electron microscopic localization of silver staining NOR-proteins in rat liver nucleoli upon D-galactosamine block of transcription.

The method for electron microscopy of the Ag-staining of NOR-specific proteins was adapted to tissue sections from solid organs. The distribution of the Ag-staining proteins in rat liver nucleoli after complete block of transcription caused by D-galactosamine was investigated. In control animals, the Ag-staining proteins are associated with the fibrillar components of nucleoli. After block of transcription, positive Ag-staining is observed in the condensed fibrillar components of segregated nucleoli and later in the derived dense nucleolar fibrillar remnants. The granular components and the spherical bodies in segregated nucleoli are negative. It is concluded that in interphase nucleoli the Ag-staining NOR proteins are associated with the fibrillar components and with the derived nucleolar fibrillar remnants. The positive Ag-staining does not reflect the actual transcription of rRNA genes since it is present in both transcribed and non-transcribed r-chromatin.

Changes in the mitochondria in the initial part of the axon during regeneration.

The initial part of the axon including the axon hellock, the initial unmyelimated segment and the beginning of myelinated axon was studied electron microscopically during regeneration, 1--30 days following a crush lesion of the rat hypoglossal nerve. Large mitochondria reaching 1.1 mum in diameter, with abundant cristae and dense granules in the matrix were observed between days 3--21. They formed clusters in the initial myelinated segment of the axon. End-to-end contacts and ribosomes around them were very often visible. The large mitochondria exhibited strong succinate dehydrogenase and NAD - H2 diaphorase activities. The relationship between the appearance of large and active mitochondria in the initial part of the axon and the elevated axonal transport during regeneration of the peripheral nerve is also discussed.

[Ultrastructure of the proliferation of astrocytes and microglia]. / Données ultrastructurales sur la prolifération des astrocytes et de la microglie

Glial cell proliferation was studied during axonal reaction of hypoglossal nerve, and around stab wound in the brain cortex of the rat. The cytoplasm and chromosomes of astroglial mitoses were pale. Lipid droplets, few sparse dense bodies with heterogenous structure were present in the cytoplasm. The mitotic astrocytes had irregular outlines. The ultrastructure of "light microglial" cells was described; it was found that these cells divided and gave rise to microglial cells. The cytoplasm and the chromosomes of microglial mitoses were dense; the cytoplasm contained always groups of dense bodies and lipfuscine granules. The outlines of mitotic microglial cells were more regular.