bluuebunny/crossref_metadata_2025 huggingface dataset:
On the “selectivity” of the Golgi‐Cox method
Authors: Pasternak Joseph F. , Woolsey Thomas A.
Published: January 2005

The randomness of the impregnation of layer IV cortical neurons by the Golgi‐Cox method (Van der Loos, 1956) has been assessed directly in Barrel C‐1 of the mouse SmI. All Golgi‐Cox impregnated neurons and unimpregnated neurons which were revealed with Nissl counterstain were counted and measured in ten cerebral hemispheres cut tangential to the pia overlying the barrel field. The percentage of Golgi stained neurons varied considerably in different preparations from 0.73% to 2.26% with an average of 1.29%. The size distributions of both the Golgi impregnated and Nissl stained cells are similar but the difference of the means is statistically significant. However, if the means are eqated there is no statistical difference in the two populations. When the Golgi precipitate is removed and the cells re‐measured following Nissl staining there is a systematic reduction of the perikaryal cross‐sectional area which is compatible with the differences in the means observed for the two populations as a whole. Finally, the frequency with which Golgi impregnated neurons are found in the barrel sides and hollows parallels the frequency with which Nissl stained neurons are observed in these two locations. We conclude that this variant of the Golgi method impregnates barrel neurons randomly. The value of this information for quantitative studies of cerebral cortex is discussed as is the potential of the system for elucidating some of the mechanisms responsible for Golgi impregnation.
Intensity and pattern discrimination after lesions of the pretectal complex, accessory optic nucleus and ventral geniculate in pigeons
Authors: Hodos William , Bonbright James C.
Published: January 2005

Pigeons were trained to discriminate between pairs of visual stimuli that differed in intensity or pattern. After completion of traianing, bilateral, stereotaxic lesions were made in various cell groups in the mesencephalon and diencephalon that receive terminals of the optic tract. The target regions were nucleus ectomamillaris (accessory optic nucleus), nucleus lentiformis mesencephali and area pretectalis (pretectal complex) and the nucleus geniculatus lateralis, pars ventralis (ventral geniculate). In some cases, combined lesions of nucleus lentiformis mesencephali and area pretectalis were made. Lesions of nucleus ectomamillaris, nucleus lentiformis mesencephali, area pretectalis, or ventral geniculate did not produce major impairments of discrimination performance nor did combined lesions of nucleus lentiformis mesencephali and area pretectalis.

A number of cases of intended destruction of the ventral geniculate also had extensive damage to the overlying nucleus rotundus. In several of these cases of combined destruction of nucleus rotundus and ventral geniculate, the previously reported discrimination deficits following nucleus rotundus lesions did not appear. In those cases in which the nucleus rotundus deficit was observed, the lesions were found to include the nucleus subpretectalis, which, like nucleus rotundus, receives tectofugal fibers via the brachium of the superior colliculus. The data of the ventral geniculate + rotundus cases and ventral geniculate + rotundus + subpretectalis cases suggest that sensory deficits following a lesion in a particular cell group may not necessarily indicate that the sensory information is processed in that cell group, but rather that the lesion had deprived other cell groups of the appropriate input necessary for their proper functioning.
Degeneration and phagocytosis of synaptic endings and axons in the medial trapezoid nucleus of the cat
Authors: Morest D. Kent , Jean‐Baptiste Michel
Published: January 2005

This study deals with the fine structure of the degenerative changes in the axonal calyces of the medial trapezoid nucleus after destruction of their cell bodies of origin in the contralateral cochlear nucleus. Two to four days after such lesions the main calycine processes which normally contain a core of neurofilaments, show a marked hyperplasia of neurofilaments, shrinkage, decrease in number of microtubules and mitochondria, swelling and decrease in number of synaptic vesicles, and the appearance of vesicular debris and coated vesicles. After seven days all of the calyces have degenerated. They are replaced by extracellular accumulations of neurofilaments, surrounded by phagocytic processes of proliferating astroglia and microglia. In contrast, the calycine appendages exhibit a dense mode of degeneration. Thus the different kinds of endings, arising from the very same fibers and synapsing on the very same cell bodies, exhibit two entirely different modes of degeneration. There is a correlation between the normal cytological features of the endings and their modes of degeneration. The preterminal calycine axons undergo filamentous hyperplasia in early degeneration.

The observations indicate that both microglia and astroglia may participate in phagocytosis of the preterminal fibers and their endings and that astrocytes undergo mitosis. The microglia in electron micrographs correspond to the classical microglial cells that appear in perivascular locations in Golgi preparations. The disintegration of the calyces is accompanied by mutual invaginations of thin axonal and glial processes, followed by the disappearance of the axolemma. Extracellular break‐up appears to be a regular feature of this process, which may involve the intercellular transfer of soluble breakdown products by calycine and glial vesicles and uptake by tubular elements of the smooth endoplasmic reticulum in the phagocytes. Incisures of Schmidt‐Lanterman occur in the large calyciferous fibers; these fibers are often invaded by phagocytes before the myelin sheath degenerates.
Demonstration of a pallido‐nigral projection innervating dopaminergic neurons
Authors: Hattori T. , Fibiger H. C. , McGeer P. L.
Published: January 2005

Afferents to the substantia nigra from the neostriatum and globus pallidus were studied in the rat by means of the autoradiographic tracing technique. 3H‐leucine was injected stereotaxically into either the globus pallidus or neostriatum. Twenty‐four hours later the axoplasmic transport of labelled proteins to the substantia nigra was studied by light and electron microscopic autoradiography. In animals used for electron microscopy, degeneration of dopaminergic cells in the substantia nigra was induced by intraventricular injection of 6‐hydroxydopamine 72 hours before sacrifice.

After neostriatal injections, light microscopic analysis revealed heavy labelling of the globus pallidus and entopeduncular nucleus, but only background labelling of the subthalamic nucleus. There was preferential labelling of the zona reticulata of the substantia nigra, with significantly less labelling of the zona compacta.

After pallidal injections, light microscopic analysis showed very light labelling of those parts of the caudate‐putamen in the vicinity of the injection site. There was intense labelling of the subthalamic nucleus and heavy labelling of the entopeduncular nucleus. The zona compacta of the substantia nigra was also heavily labelled. There was considerably less labelling of the zona reticulata.

The electron microscopic analyses showed that after neostriatal injections, autoradiographic grains in the substantia nigra were located preferentially over boutons which terminated on normal dendritic processes. After pallidal injections, however, grains were preferentially located over boutons synapsing with degenerating dendritic processes. The degeneration produced in these dopaminergic processes by 6‐hydroxydopamine was invariably of the dark type. Except for the different association with degenerating vs. non‐degenerating dendrites, the subcellular distribution of autoradiographic grains in the substantia nigra was the same after injection into either the globus pallidus or caudate‐putamen. Approximately 80 percent of the grains were over axons or boutons which invariably made symmetrical synaptic contacts.

These observations demonstrate the existence of a pallido‐nigral projection which terminates preferentially on dopaminergic cells in the pars compacta of the substantia nigra. They also confirm previous studies indicating that the strionigral projection terminates mainly in the pars reticulata. These terminations appear to be principally to non‐dopaminergic cells.
Implications of genetic variation in mouse brain structure for electrode placement by stereotaxic surgery
Authors: Wahlsten Douglas , Hudspeth William J. , Bernhardt Kathryn
Published: January 2005

The spatial locations of several forebrain and midbrain fibre tracts have been compared across seven commonly used inbred, hybrid and outbred mouse strains using a series of electrolytic lesions of known postitions with respect to a stereotaxic instrument. Highly significant genetic variation was found in the positions of lambda, bregma and several major fibre tracts with respect to interaural zero; in the locations of fibre tracts with respect to bregma; and in the location of fibre tracts with respect to each other. It was demonstrated that stereotaxic coordinates of a structure for one strain could not be used for other strains. Errors resulting from improper alignment of the head in the instrument and histological artifact were also determined. These errors showed no significant group differences, but they revealed that within‐group variation was substantilly affected by such imperfections.
Neuroplasticity of primary afferents in the neo‐natal cat and some results of early deafferentation of the trigeminal spinal nucleus
Authors: Kerr Frederick W. L.
Published: January 2005

The plasticity of cervical primary afferents has been investigated in young adult cats in which the trigeminal root, together with most of the ganglion, had been excised via a new approach to these structures during the first week after birth.

Once degeneration debris had disappeared, bilateral ganglionectomies of the upper three cervical dorsal roots were done in five animals and the IXth and Xth roots transected on the side of the chronic trigeminal denervation in one instance; the degeneration pattern on the chronically denervated side was compared to that on the normal side.

There was mild evidence of increased degeneration of the cervical afferents in the C1 segment and in the medulla (subnucleus interpolaris of V) on the chronically denervated side. The proliferation was more apparent in the kitten operated at three days of age and was only vestigial in animals operated at six or seven days; it had no appreciable tendency to extend into the large contiguous pool of denervated trigeminal neurons. There was no evidence of sprouting of the IXth and Xth nerve afferents.

These observations indicate that primary afferents of the upper cervical roots and of the glossopharyngeal and vagus nerves have little neuroplastic potential even at early stages.

The literature on neuroplasticity is controversial and a brief review of this together with suggestions regarding the reasons for some of these conflicts is presented. Some structural and functional effects of chronic trigeminal denervation are briefly described.
Organization of retinocollicular pathways in the cat
Authors: Harting J. K. , Guillery R. W.
Published: January 2005

A direct pathway from the temporal retina to the contralateral superior colliculus has been demonstrated using anterograde degeneration methods. This observation of a crossed pathway to the most rostral pole of the colliculus confirms electrophysiological evidence that within each colliculus the whole eye, rather than just its hemiretina is represented.

Autoradiographic tracing methods have been used to study the total tectal projection of each retina. Following intraocular injections of 3H proline, there is dense label in most of the superficial gray of the contralateral colliculus, but in this region there are several small areas of only relatively sparse label. In contrast, the superficial gray of the ipsilateral colliculus contains islands or patches of transported label. These patches are present throughout an extensive region of the colliculus and suggest that the ipsilateral retinocollicular pathway in the cat may be more substantial than earlier reports have indicated. There is no ipsilateral label within the most caudal parts of the colliculus which receives afferents from the monocular crescent of the visual field. In addition, a very small region of the rostral pole is free of ipsilateral input, and we suggest that this corresponds to the region receiving the crossed input from the temporal retina.
Changes in the magnocellular portion of the red nucleus following thoracic hemisection in the neonatal and adult rat
Authors: Prendergast Jocelyn , Stelzner Dennis J.
Published: January 2005

The spinal cords of newborn (0–3 day old) and adult rats were mid‐thoracically hemisected. Ninety days later a glial and connective tissue scar had formed at the lesion site in the adult hemisected rats while in neonatally lesioned animals only normal appearing regions of the contralateral spinal cord were found in the area of hemisection. Comparisons of the magnocellular portions of the red nucleus (MPRN) revealed a decrease in cell number in the MPRN contralateral (C‐MPRN) to the spinal lesion. However, only in the newborn operates was there massive cell loss accompanied by reduction in area and change in shape of the nucleus. These changes were most obvious in the caudal and ventrolateral portions of the C‐MPRN. Pooled data from each group of operates indicated that significantly more cells were lost in the C‐MPRN in the newborn than in the adult operates (p < 0.01).

Neurons of the C‐MPRN which are known to project to the lower cervical and upper thoracic segments of the spinal cord (Brown, '74; Gwyn, '71) remained undamaged after the mid‐thoracic hemisection in both groups. However, neurons of this region were enlarged in both groups when compared to a similar region of the ipsilateral MPRN. These neurons were found to be more enlarged in the newborn than in the adult operates (p < 0.01).

This result indicates that massive retrograde cell death takes place after a mid‐thoracic hemisection in the neonatal rat. The retrograde degeneration of axotomized neurons partially may explain why CNS regeneration is not found in the immature mammal even though many of the factors thought to limit regeneration in the adult mammal may not be apparent. The increase in cell size of C‐MPRN neurons which remain in the neonatal animals after mid‐thoracic hemisection may be related to the increase in axonal size found in the region of the rubrospinal tract rostral to the thoracic lesion reported earlier (Prendergast and Stelzner, '76a). Both the increase in axonal and perikaryal size are hypothesized to be related to the increased distribution of supraspinal axons found in the gray matter rostral to a hemisection of the neonatal rat spinal cord.
Neurogenesis in the visual system of the rat. An autoradiographic investigation
Authors: Brückner Gert , Mareš Vladislav , Biesold Dietmar
Published: January 2005

Rats of the BD III strain were injected with a single dose of 3 H‐thymidine on either the twelfth, fourteenth, sixteenth, eighteenth or twentieth day of gestation (ED 12…‥ED 20) or on the postnatal day one, three, or seven. Animals were killed at age 22 to 24 days. DNA synthesis, as an indicator of cell division, was studied in matrix precursors of nerve and glial cells in the visual centers, including the lateral geniculate body (LGB), the superior colliculus (SC) and the visual cortex (VC).

It was found that proliferation of matrix precursors of nerve cells destined for all the regions studied was in progress on ED 12. In the subcortical regions (LGB, SC) this process was substantially more advanced than in the VC. The first neuroblasts appeared in the SC (ED 12) and only later (ED 14) in the LGB and VC. In comparison with the LGB, VC neuroblasts were quite rare on ED 14 and were present only in layer VI. They appeared more frequently in this region only after injection of isotope on ED 16. Matrix cell proliferation and nerve cell formation ceased in the LGB between ED 16 and ED 18. The number of labeled cells arising after injection of the isotope on ED 16 indicates that neurogenesis ceased somewhat earlier in the dorsal nucleus of the LGB than in the ventral. In the SC the last neurons arose between ED 18 and ED 20, and in the VC, with the possible exception of a few granular neurons (which may continue division into the first few days postnatally), proliferation continued until the end of gestation.

The origin of neuroblasts initially followed a caudo‐rostral gradient. Later, the times of neurogenesis in the regions studied overlapped significantly. This is clear, for example, on ED 16, when neurogenesis in the mesencephalic SC continued for about two days longer than in the more rostral LGB, and coincided with that in the VC, especially in the deep layers. The end of neurogenesis in the LGB, especially in the ventral nucleus, coincided with the time of neurogenesis in the deep cortical layers.

In the VC, and partly also in the SC, an inside‐out pattern of proliferation and neuron formation was confirmed. The times of proliferation of precursor cells, with the exception of the very end of neurogenesis, substantially overlapped within both these regions. The degree of this overlapping, described in terms of Labeling Index values, decreased towards the end of the neurogenetic period.

Division of neuroglial cell precursors, started as early as on ED 14 in/for subcortical centers (LGB, SC), but not until ED 18 in/for the VC. A few labeled endothelial‐like cells were observed in all regions studied after isotope injection on ED 12.
Organization and development of brain stem auditory nuclei of the chicken: Ontogeny of N. magnocellularis and N. laminaris
Authors: Rubel Edwin W. , Smith Daniel J. , Miller Laurie C.
Published: January 2005

Nucleus magnocellularis (NM) and nucleus laminaris (NL) are, respectively, second‐ and third‐order auditory nuclei in the chicken brain stem. In this report the morphogenesis of these nuclei is examined. The times of origin of the cells of these nuclei were studied with 3H‐thymidine autoradiography. The number of cells in each nucleus and their rostro‐caudal distribution within each nucleus was determined in Nissl‐stained sections at 9, 11, 13, 15, 17, 19, and 21 days of incubation. For the above ages the volumes of NM and NL were also calculated planimetrically and the rostro‐caudal distribution of volume within each nucleus was studied.

The results indicate that the times of origin of NM and NL neurons do not overlap — the cells of NM are formed at around 60 hours of incubation, while those of NL are formed at around 84 hours. At nine days, both nuclei have a roughly equal complement of cells; however by 21 days (hatching) the number of NM neurons has decreased by 18%, while the number of NL neurons has decreased by 84%. In both nuclei most of the cell death occurs in the period between 11 and 13 days, during which time NL assumes a laminar appearance. A rostro‐caudal gradient of cell death was found for both nuclei. The times of volume increases in NM and NL commence at the end of the period of cell death, beginning at 13 days for NM and at 17 days for NL, whose cell death is more protracted. For both nuclei a rostro‐caudal gradient of volumetric expansion was also found.
A re‐examination of anatomical plasticity in the rat retina
Authors: Chernenko Garry A. , West Roger W.
Published: January 2005

Previous investigators have reported an increase in numbers of amacrine synapses in the inner plexiform layer (IPL) of the rat retina following light deprivation, and an increase in amacrine along with a decrease in bipolar synapses following light damage. Since there are several points of disagreement between the published reports on this subject we undertook a more detailed study of the effects of light deprivation and light damage on the retina.

Four groups of eight male albino rat pups (14 days old) were raised for eight weeks under different conditions: (1) unsutured, bright light reared (UB); (2) bilaterally lid‐sutured, bright light reared (SB); (3) unsutured, low light reared (UL); and (4) bilaterally lid‐sutured, dark reared (SD). The intensity of the light given the UL group was equated with that striking the corneas of the SB group.

Light microscopy showed that the retinas of the SB as well as the UB groups had almost complete degeneration of the outer retinal layers, indicating that even low intensity light, when continuous, causes severe retinal damage. The SD group was thicker in many of the retinal layers compared to the UL (control) group.

Electron microscopy revealed that there were no significant changes in the incidences of any type of synapse in the IPL following light deprivation or light damage when averaged over total depth. This is in contradiction to the reports of other investigators. However, when the IPL was analyzed by levels, the incidence of amacrine‐ganglion synapses was significantly greater (p < 0.05) in groups UB and SD, but only in the outer third of the IPL. Thus, extensive postnatal plasticity of IPL synapses in the rat retina did not occur under our experimental conditions. We found, at best, only limited effects which were confined to the amacrine‐ganglion synapses.
Categories of axons in mammalin rami communicantes
Authors: Coggeshall R. E. , Hancock M. B. , Applebaum M. L.
Published: January 2005

The present study is an electron microscope analysis of the rami communicantes and its purpose is to determine the functional categories of unmyelinated axons in these nerves. Our findings indicate that the grey rami of segments T7, T8, or T9 in the cat consist of approximately 5,000 unmyelinated axons and 20 myelinated axons, and that these axons are post‐ganglionic sympathetics. Although the numbers are new data, this conclusion confirms classic work. The white rami from the same segments contain approximately 3,200 unmyelinated axons and 1,600 myelinated axons. 80–90% of the myelinated axons are preganglionic sympathetics and the remainder are presumably sensory. This conclusion is also in confirmation of classic work. The new conclusions are that approximately 30% of the unmyelinated axons are preganglionic sympathetics, approximately 60% seem to be post‐ganglionic sympathetics and the surprisingly small remainder may be sensory.
Scanning electron microscopy of the subarachnoid space in the dog. IV. Subarachnoid macrophages
Authors: Malloy John J. , Low Frank N.
Published: January 2005

Young dogs of both sexes were used in this study. Transmission and scanning electron microscopy were utilized for the examination of the spinal cord and choroid plexus with emphasis on the study of free cells. These procedures were modified so that, in certain cases, the same cells observed in scanning electron microscopy could be analysed internally by transmission electron microscopy. One half of the animals were injected under anesthesia with horseradish peroxidase for observation of phagocytosis.

This study confirms that the free cells observed in the subarachnoid space with the scanning and transmission electron microscopes are identical. The internal morphology of these cells corresponds to that of macrophages. This is further subtantiated by the ability of these cells to localize horseradish peroxidase in discrete vacuoles within their cytoplasms. Both pial macrophages and epiplexus cells localize peroxidase in an identical manner in the same animal after one injection. In addition macrophages on the surface of the pia mater respond to extravasated red blood cells in a characteristic manner including phagocytosis. The plentiful population of macrophages on the surface of the pia mater supports the concept that these cells are of major importance in maintaining asepsis in the subarachnoid space.
Synaptogenesis in the ventromedial hypothalamus of the prenatal mouse
Authors: Beals Jacquelyn K.
Published: January 2005

Mouse embryos from day 13 to day 19 of gestation (E13 through E19) were removed by Caesarean section and their brains were prepared for electron microscopy. Coronal sections were examined in three planes through the ventromedial hypothalamus: anterior, the level at which the optic tracts pass posterolaterally to become partially enclosed in the major brain mass; middle, the level at which the floor of the third ventricle begins to widen and flatten; posterior, the level at which the most anterior infundibulum appears.

Three types of junctional complexes were examined.

Close junctions are identified as straight, parallel areas of two apposed membranes which appear more electron‐dense than immediately adjacent regions. The membranes are separated by a clearly visible cleft. Unlike synapses, no clear synaptic vesicles are found in either of the adjacent profiles unless randomly distributed and accompanied by ribosomes or glycogen. Close junctions are seen most frequently on day E15, then decrease in number through E19. Their participation in synaptogenesis is discussed from temporal, morphological, distributional and quantitative perspectives and is provisionally rejected.

Immature synapses show only the minimal membrane specialization found in close junctions, but vesicles are present, ribosomes absent in at least one of the adjacent cytoplasms. Their appearance peaks on E17–E18, paralleling and slightly preceding that of the mature synapses. Their evolution from close junctions has only weak temporal support.

Mature synapses display the cytoplasmic densities which immature synapses lack. They attain their greatest prenatal numbers on E18, then decrease in number on E19.

The conclusion is advanced that synaptogenesis does—or at least can—occur without the prior appearance of avesicular regions of increased membrane density.
The organization and postnatal development of the commissural projection of the rat somatic sensory cortex
Authors: Wise S. P. , Jones E. G.
Published: January 2005

Anterograde and retrograde tracing experiments have been used to demonstrate the origin and terminal distribution of commissural fibers in the first somatosensory cortex (SI) of the rat. The commissural fibers originate from pyramidal cells of all layers, but predominantly from layers III and V. The fibers terminate in a series of approximately vertical bands. In each of these there are concentrations of terminals extending from the inner portion of the molecular layer to the deep portion of layer III as well as in the superficial part of layer V, and in layer VI. Discrete vertical bands of cortex are reciprocally connected across the midline to give both the origin and terminal regions of the projection a patchy or “columnar” appearance. The commissural fibers arise from and terminate in areas of the cortex that lie between and alongside the aggregations of granule cells that distinguish SI of the rat. No commissural fibers terminate within the aggregations of layer IV cells themselves but the more superficial terminal ramifications may come to overlie these aggregations. A heterotopic projection to the contralateral second somatosensory cortex has been observed and is similar in form to the homotopic projection to SI.

Many commissural fibers have crossed the midline in the corpus callosum by the day of birth but lie in the underlying white matter and do not enter the cortical plate until at least the third postnatal day. During the first postnatal week these fibers grow somewhat diffusely into the maturing cortex and their topographic and laminar pattern of distribution attains its adult characteristics by the end of the first week. Commissural axons, thus, arise from immature cells but the maturation of cell form seems to precede the ingrowth of these axons and the acquisition of commissural synapses.
Histochemical mapping of dopamine neurons and fiber pathways in dog mesencephalon
Authors: Shimada Shozo , Ishikawa Masatsune , Tanaka Chikako
Published: January 2005

A topographic mapping of dopamine (DA)‐containing neurons and fibers was done mainly in the mesencephalon of the dog using the fluorescent histochemical technique of Falck and Hillarp. The extensive DA neuron system was found to be located in the ventral and medial regions of the mesencephalon; the pars compacta of the substantia nigra, the area almost corresponding to the ventral tegmental area of Tsai (hich consists of three groups, a caudal, the nucleus parabrachialis pigmentosus, a ventral, the nucleus paranigralis and a rostral, the caudal part of the nucleus tegmentalis gventralis of Tsai), the nucleus linearis of the raphe, and the mesencephalic reticular formation.

The nigro‐neostriatal projection can be traced in the non‐treated or nialamide plus L‐dopa treated puppies without the lesion‐degeneration technique. Most fibers arising from these DA cell groups assemble at the prerubral area and ascend just dorsal to the medial forebrain bundle. Most fibers turn laterally at the lateral hypothalamus and enter the neostriatum via the dorsal part of the subthalamic nucleus, the zona incerta and the capsula interna. These findings show that the distribution of DA neurons and the nigro‐neostriatal pathway are fundamentally similar to those in other mammals. In this study, the processes of the nigral and paranigral DA neurons have been demonstrated to project into the pars reticulata in the dog.
Electron microscopic autoradiographic studies of gliogenesis in rat optic nerve. II. Time of origin
Authors: Skoff Robert P. , Price Donald L. , Stocks Adelaine
Published: January 2005

The time of origin for astrocytes and oligodendrocytes in rat optic nerve was studied by 3H‐thymidine autoradiographic techniques similar to those used in dating the time of origin for neurons. This study shows that astrocytes are formed throughout late embryonic and all of postnatal development, while oligodendrocytes are generated only during the postnatal period.

A few astroglia undergo their final cell division as early as 15.5 days of gestation, but most astrocytes are not generated until the first week of postnatal development. Although the final cell division for more than half of the astrocytes takes place before the end of the first postnatal week, fully mature, fibrous astrocytes are not observed in electron micrographs until after 14 days of age. This time lag implies that the differentiation of these early generated cells takes place gradually over a 2‐to 3‐week interval.

Oligodendroglia begin their final division a day or two before the onset of myelination (6–7 days postnatal), but the vast majority are produced during the period of myelinogenesis. After almost all of the axons have been myelinated, oligodendrocytes are still being generated in small numbers. These late forming cells are generally less differentiated in appearance than those formed earlier; this suggests that the degree of differentiation of oligodendrocytes may be dependent upon the number of axons available for myelination. As with astrocytes, oligodendrocytes show a lag of about two weeks from the time of final cell division until they transform into morphologically differentiated cells.

In transverse sections of the optic nerve heavily labeled neuroglia are randomly distributed, indicating there are no temporal‐radial gradients for the individual cell types. This observation taken together with the other information obtained from the present and the previous study (Skoff et al., '76) strongly suggest that the factors controlling gliogenesis are different from those governing neuronogenesis.
Recovery from deafferentation by cricket interneurons after reinnervation by their peripheral field
Authors: Murphey R. K. , Matsumoto S. G. , Mendenhall B.
Published: January 2005

The physiological and morphological recovery of cricket (Acheta domesticus) abdominal giant interneurons following varying periods of deafferentation and subsequent regeneration was examined. The principal afferent input to two identified interneurons was removed by surgically ablating an abdominal sensory appendage, the cercus. Deafferentation restricts the growth of the dendrites of the medial giant interneuron. Reinnervation by the peripheral sensory field leads to recovery of the dendrite length which is dependent on the time allowed for recovery. The response properties of the reinnervated neurons never completely recovers irregardless of how short the period of deafferentation. Reinnervated neurons respond more weakly to standard tones than do control neurons. This is due in part to faciliation of an inhibitory synaptic input which is activated by the control cercus. The results suggest that the balance between the excitatory and the inhibitory synaptic inputs to these interneurons is irrevocably altered by brief periods of deafferentation early in life.
The efferent connections of the ventromedial nucleus of the hypothalamus of the rat,
Authors: Saper C. B. , Swanson L. W. , Cowan W. M.
Published: January 2005

The efferent connections of the ventromedial nucleus of the hypothalamus (VMH) of the rat have been examined using the autoradiographic method. Following injections of small amounts (0.4–2.0 μCi) of tritium labeled amino acids, fibers from the VMH can be traced forward through the periventricular region, the medial hypothalamus and the medial forebrain bundle to the preeoptic and thalamic periventricular nuclei, to the medial and lateral preoptic areas, to the bed nucleus of the stria terminalis and to the ventral part of the lateral septum. Some labeled axons continue through the bed nucleus of the stria terminalis into the stria itself, and hence to the amygdala, where they join other fibers which follow a ventral amygdalopetal route from the lateral hypothalamic area and ventral supraoptic commissure. These fibers terminate in the dorsal part of the medial amygdaloid nucleus and in the capsule of the central nucleus. A lesser number of rostrally directed fibers from the VMH crosses the midline in the ventral supraoptic commissure and contributes a sparse projection to the contralateral amygdala.

Descending fibers from the VMH take three routes: (i) through the medial hypothalamus and medial forebrain bundle; (ii) through the periventricular region; and (iii) bilaterally through the ventral supraoptic commissure. These three pathways are interconnected by labeled fibers so that it is not possible to precisely identify their respective terminations. However, the periventricular fibers seem to project primarily to the posterior hypothalamic area and central gray, as far caudally as the anterior pole of the locus coeruleus, while the medial hypothalamic and medial forebrain bundle fibers apparently terminate mainly in the capsule of the mammillary complex, in the supramammillary nucleus and in the ventral tegmental area. The ventral supraoptic commissure fibers leave the hypothalamus closely applied to the medial edges of the two optic tracts. After giving off their contributions to the amygdala, they continue caudally until they cross the dorsal edge of the cerebral peduncle to enter the zona incerta. Some fibers probably terminate here, but others continue caudally to end in the central tegmental fields, and particularly in the peripeduncular nucleus.

Within the hypothalamus, the VMH appears to project extensively to the surrounding nuclei. However, we have not been able to find evidence for a projection from the VMH to the median eminence. Isotope injections which differentially label the dorsomedial or the ventrolateral parts of the VMH have shown that most of the long connections (to the septum, amygdala, central tegmental fields and locus coeruleus) originate in the ventrolateral VMH, and there is also some evidence for a topographic organization within the projections of this subdivision of the nucleus.
Cerebellar corticonuclear and corticovestibular fibers of the anterior lobe vermis in a prosimian primate (Galago senegalensis)
Authors: Haines Duane E.
Published: January 2005

Efferent projections of the anterior vermis were studied in a prosimian primate (Galago senegalensis). Cerebellar corticonuclear and corticovestibular fibers of the anterior lobe vermis are, in toto, ipsilateral. Two additional main points emerge. First, evidence is given which suggests that the cortical area defined as vermis converges, in a rostral direction (from lobules V to I + II), as the hemispheres of these lobules become latero‐medially foreshortened. The anterior vermis is a cortical region reflected by its efferent projections and not an arbitrary median strip of cortex which is either constant in width or morphologically separated from adjacent paravermal areas. Secondly, two patterns of organization emerge concerning cortical efferents, one suggestive of longitudinal zones and a second which shows that individual lobules project mainly to specific areas of the ipsilateral NM and into portions of the vestibular complex. Three zones are recognized. A very narrow midline area which appears to project bilaterally to the NM, a wider intermediate area (homologous to zone A) related to the ipsilateral NM, and a lateral area (homologous to zone B) related mainly to the ipsilateral vestibular complex, primarily its lateral nucleus. Within this overall zonal organization individual lobules project to specific areas of the NM and vestibular complex. Lobules V and IV project to rostrodorsal and rostrocentral NM respectively and into the dorsal LVN. Lobules III and II + I project to rostroventral‐medial and rostroventral‐lateral NM respectively, throughout the LVN and minimally into the SVN and SpVN. The specificity of corticonuclear terminations in the NM from the anterior vermis, heretofore not described for any primate, are similar, in terms of a general pattern, to that recently reported for the cat (Courville and Diakiw, '76).
Single unit studies on the dorsal and intermediate acoustic striae
Authors: Adams Joe C.
Published: January 2005

Studies were made of the fiber composition and of single unit discharge characteristics in the dorsal and intermediate acoustic striae. Counts of fibers and cells revealed more than twice as many fibers as cochlear nucleus cells of the types known to contribute axons to these tracts. Recordings were made in the striae to confirm the classes of discharge patterns which are transmitted from the posterior cochlear nucleus to more central structures and to seek evidence for descending activity entering the cochlear nucleus through the striae. Discharge patterns of the majority of units resembled those seen in previous studies when recordings were made from regions of the cochlear nucleus which are known to contribute fibers to the striae. Some patterns, however, were unlike any which have been reported in the cochlear nucleus on the same side as the recording site, but resembled activity of other auditory structures, suggesting that these were descending inputs. To confirm the presence of descending activity, recordings were made in the dorsal acoustic stria at a point medial to where the stria had been completely severed. Recordings made under these conditions demonstrated the presence of descending activity. The physiological findings help explain the disparity between the counts of fibers and cells, and point out a need for more detailed descriptions of the origins of descending inputs through the striae.
Some quantitative results on golgi impregnated axons in rat visual cortex using a computer assisted video digitizer
Authors: Paldino A. M. , Harth E.
Published: January 2005

Axonal fiber distributions of pyramidal cells in the visual cortex of the albino rat have been investigated using the rapid Golgi method and modern data collecting techniques. Three dimensional coordninate information was extracted from Golgi‐impregnated axonal networks using a computer‐assisted video digitizer. Computer programs used this data to generate various statistical distributions. In particular, angular distributions of the initial collateral segments and their endpoints were examined and found to reveal anisotropies. Inspection of the spatial distributions of the endpoints indicated a clustering at two distinct levels with respect to the pyramidal cell from which they orignate. Dynamic graphic displays of the three dimensional data have been obtained and presented in the form of computer tracings of various orthogonal projections.
The pigmented‐rat optic nerve: Fibre count and fibre diameter spectrum
Authors: Hughes A.
Published: January 2005

A well distributed electron microscopic sample of 52,000 fibres from the pigmented rat optic nerve cross section indicates a total count of 120,000±1,600 (S. E. M.) fibres ranging from 0.437μ to 5.2μ in diameter. The fibre diameter spectrum is essentially unimodal with a peak at 1.0μ with a well developed “tail”. These results are identical to those available in the literature for the albino rat.
Morphometric analysis of the effects of exenteration and enucleation on the development of third and sixth cranial nerves in the rat
Authors: Bronson Roderick T. , Hedley‐Whyte E. Tessa
Published: January 2005

The effects on rat cranial nerve growth of removing various amounts of extraocular muscle was studied using morphometric techniques. Growth in the third cranial nerves was found to be severely retarded when most of the muscle tissue was removed. By contrast, removal of the eye alone, leaving extraocular muscles relatively intact, was found to have little or no effect on the subsequent growth of third and sixth cranial nerve fibers and of extraocular muscle fibers. This conclusion could be drawn only through the application of statistical methods which take into account several generally unrecognized facts: frequency distributions of axon circumference and myelin sheath thickness are highly variable from nerve to nerve even in normal rats, which often have more large fibers in left than in right nerves. The bimodal nature of peripheral nerve fiber distributions precludes the use of such parametric tests as the commonly and inappropriately used t‐test, but a non‐parametric test such as the Kolmogorov‐Smirnov test, extensively used in these studies, is inadequate for data comprising several sets of distributions to be compared. The application of the analysis of variance to some of the data and the merits of the procedure are discussed.
Neuroanatomy of spastic, a behavior mutant of the mexican axolotl: Purkinje cell distribution in the adult cerebellum
Authors: Ide Charles F. , Tompkins Robert , Miszkowski Nancy
Published: January 2005

The spastic mutant, found in the Mexican axolotl, shows swimming coordination and equilibrium deficiencies. Histological analyses of wildtype and spastic mutant cerebella previously characterized in physiological studies revealed changes in Purkinje cell location in the mutant auricle or vestibulo‐cerebellum. Purkinje cells are “translocated” ventrally correlated with a similar translocation of vestibular single units described previously (Ide, '77). Where wild‐type Purkinje cells are distributed from the surface to a depth of 250 micrometers, mutant Purkinje cells are “crowded” between 250 and 350 micrometers. Although mutant granule cells are present, boundaries between granule cell and Purkinje cell zones are less precise in mutants. Cerebellar nucleus cells are translocated medially, failing to organize into the discrete cell group appearing in wild‐type. Cerebellar white matter tracts and fibers show changes, both in orientation with respect to the underlying tegmentum, and in fascicular organization. Obvious changes in the gross anatomy of the cerebellum are confirmed in reconstructions which define cell and fiber translocations. Thus, the spastic gene is compatible with differentiation of all cerebellar elements, but appears to alter interactions between cells, or between cells and the external milieu. Although all cell types are present in the mutant cerebellum, they fail to attain their proper positions along all three body axes.
Experimental analysis of embryogenesis of cerebellum in rat. II. Morphogenetic malformations following X‐ray irradiation on day 18 of gestation
Authors: Das Gopal D.
Published: January 2005

Rat embryso of 18 days gestation were exposed in utero to 170 R of X‐ray irradiation. Embrysos were collected six hours, 1, 2 and 3 days after irradiation, and animals of 2‐, 6‐, 15‐ and 30–day‐old postnatal age were sacrificed. Six hours after irradiation pyknosis of cells was noticed in the external granular layer along the posterior aspect of the cerebellum. Neuroblasts, destined to differentiate into Purkinje cells, were found arrested in their migratory path. During subsequent peoiods of embryogenesis the external granular layer was found recovered, and clustering of the neuroblasts was disorganized and fragmented. This abnormal clustering of neuroblasts was permanent, and the external granular layer followed the same abnormal pattern in its growth. During postnatal development the internal granular layer also was found to follow the abnormal pattern of Purkinje cell layer. These abnormal developmental events were seen to lead to malformed folia in the anterior regions of the cerebellum. In addition to it the cerebellum of X‐ray irradiated animals appeared smaller than the normal. Issues having abearing on the differential radiosensitivity of different cells, factors determining the small size of the cerebellum, and cellular events determining the morphogenetic malformations are discussed.
Indoleamine neurons and their processes in the normal rat brain and in chronic diet‐induced thiamine deficiency demonstrated by uptake of 3H‐Serotonin
Authors: Chan‐Palay Victoria
Published: January 2005

Indoleamine structures in the brains of normal, pair‐fed control, and thiamine deficient rats are selectively localized by autoradiography following monoamine oxidase inhibition and simultaneous intraventricular infusion of 3H‐5HT (10−5 m) and cold d–1 norepinephrine (10−4 m). The locations of indoleamine neurons and their plexuses are comparable in the normal and control animals and are enumerated and mapped in detail. In addition to numerous labeled neurons in the raphe and reticular formation of pons and medulla, there are indoleamine neurons in several hypothalamic nuclei, in the mammillary, habenular, and interpeduncular nuclei. Labeled axonal plexuses occur in almost all areas of the brain but certain regions in spinal cord, medulla, midbrain, diencephalon, basal ganglia, and hippocampus are particularly rich. Thiamine deficiency causes lack of label in almost all indoleamine neurons and their processes in the midbrain and medulla; only a few dystrophic cells with hypertrophied axons are seen. In the diencephalon more indoleamine neurons and their axonal plexuses are visualized in these uptake studies. The periventricular regions of spinal cord, medulla, midbrain and diencephalon, the mammillary nuclei, habenular nuclei, and cerebellum – areas richly innervated by indoleamine axons in the normal brain – are the most severely affected. The ventricular and leptomeningeal indoleamine structures are preserved, however, and individual axons may hypertrophy. It remains to be resolved whether these changes reflect disturbances in the ability of certain indoleamine neurons to take up and retain 3H‐5HT or true neuronal degeneration.