bluuebunny/crossref_metadata_2025 huggingface dataset:
The dorsal nucleus of the lateral leminiscus in the cat: Neuronal types and their distributions
Authors: Kane Eileen S. , Barone Leesa M.
Published: January 2005

The normal population of neurons and their distributions within the dorsal nucleus of the lateral lemniscus were studied in both Nissl‐stained celloidin and frozen sections and in Golgi impregnations from brains of mature cats. According to axial measurements of somata in Nissl‐stained material, neurons of the dorsal nucleus of the lateral leminscus (DNLL) were classified by width:length ratio (r) into round (0.80 ≤ r ≤ 1.0), ovoid (0.65 < r < 0.80), or elongate (r ≤ 0.65) types. These same neurons could also be classed by average diameter (Dm) as large (Dm ≥ 22), medium (12.0 ≤ Dm < 22.0), or small (Dm < 12.0). A combination of data on ratios (shape) and average diameters (size) provided the following possible categories of Nissl‐stained, DNLL neurons: large round (LR), large ovoid (LO), large elongate (LE), medium round (MR), medium ovoid (MO), medium elongate (ME), small round (SR), small ovoid (SO), and small elongate (SE). Very few small cells were found, however. Quantitative studies of the distributions of cell types within the whole DNLL showed (1) most medium‐sized and most LE cells in the caudal third of the DNLL and (2) most LO and LR cells dorsally located in the rostral third of the DNLL. There were progressively more large and more round types along the caudal‐to‐rostral axis. In Golgi impregnations of the DNLL, all medium and large cell types, but no small cell types (defined in the Nissl study) were found. Golgi material showed (1) subdivisions of the LO class into vertical (LOV) and horizontal (LOH) types, and (2) radiate (MRR) and oriented (MRO) subclasses of MR neurons according to dendritic arbor and cytology, orientation within the DNLL, and axonal morphology. Examples from all classes of large cells (particularly, LE cells) could have ventrally directed axons. These ventrally directed axons might be efferents to the cochlear nueleus, known from our previous work. A strong horizontal orientation of most DNLL cell somata and dendrites, shown in both our Nissl and Golgi material, is discussed in relation to known inputs to the DNLL. Correlations of our morphological findings with limited electrophysiological data on the DNLL are also discussed.
Laminar distribution of receptive field properties in the primary visual cortex of the mouse
Authors: Mangini Nancy J. , Pearlman Alan L.
Published: January 2005

We studied the receptive field properties of single neurons in the primary visual cortex (area 17) of the mouse and the distribution of receptive field types among the cortical laminae. Three basic receptive field types were found: (1) Cells with oriented receptive fields, many of which could be classified as simple or complex, were found in all layers of the cortex, but occurred with greater frequency in layers II and III and less commonly in Layer IV. (2) Cells with non‐oriented receptive fields had ON, OFF, or ON‐OFF centers; they were found in all layers but were predominant in layer IV. Two subclasses of non‐oriented receptive fields were characterized based on their responses to stationary and moving stimuli. One group of cells with non‐oriented receptive fields responded vigorously with sustained firing to stationary flashing stimuli, and also responded well to moving stimuli and over a wide range of stimulus velocities. A second group of non‐oriented cells, termed motion‐selective, responded poorly or not at all to stationary stimuli and responded optimally to moving stimuli over a restricted range of velocities. (3) A distinct group of neurons, termed large field, non‐oriented (LFNO) cells, were found almost exclusively in layer V. LFNO cells had receptive fields that were larger than those of the other two major classes at all visual‐field locations; they also had higher rates of spontaneous activity and responded to higher stimulus velocities than the other classes. In these respects, LFNO cells resembled the layer V cells of area 17 in the cat and the layer V and VI cells of area 17 in the monkey that project to the superior colliculus. We injected horseradish peroxidase into the superior colliculus, and determined that corticotectal cells in the mouse were also located in layer V, the layer where we recorded LFNO cells. Additional evidence that some LFNO cells project to the superior colliculus was provided by preliminary experiments in which we stimulated the superior colliculus and antidromically activated cortical cells with LFNO receptive fields. Neurons with LFNO receptive fields thus constitute a class that is functionally distinct, with cell bodies that are located in a single layer (V) of area 17 in the mouse.
Three groups of cortico‐geniculate neurons and their distribution in binocular and monocular segments of cat striate cortex
Authors: Tsumoto Tadaharu , Suda Kouhei
Published: January 2005

Among 409 neurons recorded from binocular and monocular segments of the cat striate cortex, 91 were identified as cells (C‐G cells) projecting to the dorsal lateral geniculate nucleus (LGN) on the basis of antidromic activation from LGN and of histological localization of cortical layer VI. The axonal conduction velocity of these C‐G cells was calculated from differences in latency between antidromic responses to electrical stimulation of LGN and the optic radiation. According to this velocity, 70 C‐G cells from the binocular segment could be classified as fast (13–32 m/sec), intermediate (3.2–11 m/sec) and slow (0.3–1.6 m/sec) cells. The fast cells (47% of the total) were spontaneously active and had receptive fields of complex type. Histologically they were located mostly in the upper half of layer VI. The intermediate cells (31%) were mostly simple. The slow cells (21%) were completely silent, not driven by visual stimuli, and located mostly in the lower VI. From the monocular segment of the cortex, the intermediate cells could not be recorded, while the other two groups of cells were sampled with the same frequency as from the binocular segment. These findings suggest an existence of three functionally distinct groups of C‐G cells and a possible participation of the intermediate cells in binocular vision.
Brain stem projections of sensory and motor components of the vagus complex in the cat: I. The cervical vagus and nodose ganglion
Authors: Kalia Madhu , Mesulam M‐Marsel
Published: January 2005

The motor and sensory connections of the cervical vagus nerve and of its inferior ganglion (nodose ganglion) have been traced in the medulla oblongata of 32 adult cats with the neuroanatomical methods of horseradish peroxidase (HRP) histochemistry and amino acid autoradiography (ARG). In 14 of these subjects, an aqueous solution of HRP was applied unilaterally to the central end of the severed cervical vagus nerve. In 13 other cases, HRP was injected directly into the nodose ganglion. Three of these 13 subjects had undergone infranodose vagotomy 6 weeks prior to the HRP injection. A mixture of tritiated amino acid was injected into the nodose ganglion in five additional cats. The retrograde transport of HRP yielded reaction product in nerve fibers and perikarya of parasympathetic and somatic motoneurons in the medulla oblongata. Furthermore, a tetramethyl benzidine (TMB) method for visualizing HRP enabled the demonstration of anterograde and transganglionic transport, so that central sensory connections of the nodose ganglion and of the vagus nerve could also be traced. The central distribution of silver grain following injections of tritiated amino acids in the nodose ganglion corresponded closely with the distribution of sensory projections demonstrated with HRP, thus confirming the validity of HRP histochemistry as a method for tracing these projections. The histochemical and autoradiographic experiments showed that the vagus nerve enters the medulla from its lateral aspect in multiple fascicles and that it contains three major components—axons of preganglionic parasympathetic neurones, axons of skeletal motoneurons, and central processes of the sensory neurons in the nodose ganglion. Retrogradely labeled neurons were seen in the dorsal motor nucleus of X(dmnX), the nucleus ambiguus (nA), the nucleus retroambigualis (nRA), the nucleus dorsomedialis (ndm) and the spinal nucleus of the accessory nerve (nspA). The axons arising from motoneurons in the nA did not traverse the medulla directly laterally; rather, all of these axons were initially directed dorsomedially toward the dmnX, where they formed a hairpin loop and then accompanied the axons of dmnX neurons to their points of exit. Afferent fibers in the vagus nerve reached most of the subnuclei of the nTS bilaterally, with the more intense labeling being found on the ipsilateral side. Labeling of sensory vagal projections was also found in the area postrema of both sides and around neurons of the dmnX. These direct sensory projections terminating within the dmnX may provide an anatomical substrate for vagally mediated monosynpatic reflexes. Following deefferentiation by infranodose vagotomy 6 weeks prior to HRP injections into the nodose ganglion, a number of neurons in the dmnX were still intensely labeled with the HRP reaction product. The axons of these HRP‐labeled perikarya may constitute the bulbar component of the accessory nerve.
Evidence for the existence of a sexually dimorphic nucleus in the preoptic area of the rat
Authors: Gorski Roger A. , Harlan Richard E. , Jacobson Carol D. , Shryne James E. , Southam Arthur M.
Published: January 2005

The volume of an intensely staining component of the preoptic area of the male rat is markedly larger than that of the female. Moreover, its volume in both sexes is altered by perinatal hormone exposure consistent with the view that this brain region undergoes hormone dependent sexual differentiation. The present study was carried out to determine if this sexually dimorphic area of the brain has a greater cell density than that of the surround, and if a unique population or distribution of cells, either within one sex or between males and females, characterized this region. A single coronal paraffin section (10 m̈m) through the approximate center of this sexually dimorphic area in four adult gonadectomized rats of each sex was evaluated systematically. Each cell was labelled as being inside or outside of the sexually dimorphic area. In addition to cell density per unit area the following parameters were evaluated through a closed circuit video system: cell size, staining intensity, shape, and the presence of processes and of a nucleolus. The presence of a nucleolus was further used to identify neurons within the total population of almost 5000 cells that was evaluated. In both sexes, the sexually dimorphic area was characterized by a significantly increased cell density per unit area compared to that of the surround. On this basis, the term, the Sexually Dimorphic Nucleus of the Preoptic Area (SDN‐POA) is proposed, for this region. Moreover, the SDN‐POA of the male was characterized by increased neuronal density per unit area. The SDN‐POA in the male was also found to contain larger cells and neurons, as determined by direct measurement of their greatest diameter, as well as a greater percentage of cells and neurons rated large on a three‐point scale (small, medium, and large). No consistent differences in frequency distribution by stain intensity, shape, or the presence of cell processes were found to characterize the SDN‐POA or contribute to the sexual dimorphism. It is concluded that the marked sex difference in the volume of the SDN‐POA is due principally to an increase in the male of the total area of higher cell and neuronal density. However, the present results do not eliminate the possibility that more subtle differences in neuronal characteristics may exist in the SDN‐POA.
Basal ganglionic pathways to the tectum: Studies in reptiles
Authors: Reiner Anton , Brauth Steven E. , Kitt Cheryl A. , Karten Harvey J.
Published: January 2005

Relations between the basal ganglia and the tectum were investigated in two different orders of reptiles: turtles (Chrysemys scripta) and crocodilians (Caiman crocodilus). In both species, efferents from the paleostriatal complex, a telencephalic region considered comparable to the mammalian basal ganglia on the basis of topographic, histochemical, and hodological criteria, were found to project to a prominent pretectal cell group called the dorsal nucleus of the posterior commissure (nDCP). Cells within nDCP, in turn, were found to project extensively upon the optic tectum. This paleostriatal‐pretectal‐tectal pathway is comparable to a previously described paleostriatal‐pretectal‐tectal channel in birds that involves a relay in the pretectal nucleus, spiriformis lateralis (SpL). Neither the presently described paleostriatal‐pretectal‐tectal channel of reptiles nor that previously described in birds, however, appears comparable to the superficially similar basal ganglionic‐nigral‐superior collicular pathway of mammals. Rather, data from the present experiments indicate the existence of a second paleostriatal channel to the tectum, one which does appear comparable to the basal ganglionic‐nigral‐superior collicular pathway of mammals. This second paleostriatal channel to the tectum, relayed via a tegmental cell group termed the substantia nigra in turtles and the tegmentipedunculopontine complex in caiman, is of much lesser prominence in reptiles than the paleostriatal‐pretectal‐tectal channel.

The present results indicate the existence of at least two separate systems by which the basal ganglia in reptiles can influence the midbrain roof. These two channels, particularly the prominent paleostriatal‐prectectal‐tectal pathway, may represent major routes by which the basal ganglia influence motor functions in reptiles. Further, although previous research had only indicated the existence of a paleostriatal‐pretectal‐tectal pathway in birds and a basal ganglionic‐nigral‐collicular channel in mammals, existing data are consistent with the hypothesis that both presently described pathways in reptiles exist in birds and mammals, though only one of the two may be prominent in mammals.
The primate cochlear nuclei: Loss of lamination as a phylogenetic process
Authors: Kavanagh Moore Jean
Published: January 2005

In primates from prosimians to hominoids (lorisoid prosimians, marmoset and ceboid monkeys, cercopithecoid monkeys, and gibbon), there are differences in the location, depth, and extent of the granular layer of the cochlear nuclei. In the prosimians, the deep granular layer of the DCN is similar to that of other mammals, but there is, in addition, a superficial or subependymal layer of granule cells in the DCN. In ceboid and cercopithecoid monkeys, only a superficial or external granular layer is present in the DCN, and the granular layer over the VCN is much reduced. In the gibbon, there is no granular layer in either of the cochlear muclei. In conjunction with the progressive reduction of the cochlear granular layer in primates, fusiform cells lose their position as a radially oriented peripheral cell layer in the DCN and become located in the central region of the nucleus. These changes in primates are interpreted as resulting from failure of inward migration and increasing cell death in the ontogeny of the cochlear external granular layer, with concomitant changes occurring in the position and orientation of their target neurons, the fusiform cells.
Identification of parvocellular vasopressin and neurophysin neurons in the suprachiasmatic nucleus of a variety of mammals including primates
Authors: Sofroniew Michael V. , Weindl Adolf
Published: January 2005

The presence of parvocellular vasopressin‐ and neurophysin‐ containing neurons in the suprachiasmatic nucleus (SCN) was investigated in 13 mammalian species representing six mammalian orders (marsupials, rodents, lagomorphs, artiodactyls, carnivores, and primates), using specific antisera to vasopressin and neurophysin in the unlabelled antibody‐enzyme immunoperoxidase method. In all mammals examined, including man, parvocellular vasopressin and neurophysin neurons were found in the SCN. Only a portion of SCN neurons contain vasopressin and neurophysin, the number varying with species. Cell counts comparing the number of immunoreactive to Nissl‐stained neurons showed averages of 17% immunopositive neurons in the rat SCN, and 31% in the human SCN. No oxytocin‐containing SCN neurons were observed. These findings suggest that parvocellular vasopressin and neurophysin neurons are widely represented in mammals.
The organization of the extraocular motor nuclei in the atlantic stingray, Dasyatis sabina
Authors: Rosiles J. R. , Leonard R. B.
Published: January 2005

Retrograde transport of HRP was used to determine the location and organization of the motor nuclei innervating the extrinsic eye muscles of the stingray, an elasmobranch fish. Oculomotor neurons are located both medial to and immediately ventrolateral to the MLF in the rostral midbrain. A ventral oculomotor nucleus was found among the IIIrd nerve rootlets close to the base of the midbrain. The dendrites of cells in the dorsal nucleus appear to be preferentially oriented in the transverse plane penetrating the MLF. Motoneuron pools innervating individual muscles are incompletely segregated in the dorsal group. However, the ventral nucleus innervates only the inferior oblique muscle. Dorsally, motoneurons innervating a single muscle are found on both sides of the MLF. In the caudal midbrain, the majority of trochlear motoneurons are located immediately ventrolateral to the MLF. Abducens motoneurons are scattered in the medulla from a ventrolateral position resembling the location of the nucleus in teleost fish to a dorsomedial position close to the MLF as in most other vertebrates. In contrast to other vertebrates, the medial rectus muscle is innervated by the contralateral oculomotor nucleus. Motoneurons innervating the other muscles have the same laterality as found in other vertebrates.
Topography of retinal representation in the rabbit cortex: An experimental study using transneuronal and retrograde tracing techniques
Authors: Holländer Horstmar , Hälbig Wolfgang
Published: January 2005

The cortical representation of the retina in rabbits was studied autoradiographically using transneuronal transport of tritiated proline and tritiated fucose. Injection of one eye produced cortical labelling on both sides. There was no indication of ocular dominance columns. On the contralateral side, the labelling was found in cortical layers II–IV, and partly also in layer VI of area striata and the caudal part of area peristriata, and in layer IV of most of area occipitalis. In addition, there was a patch of labelling in layers II–IV of the temporal cortex. On the ipsilateral side, the labelling was restricted to layer IV in a strip of cortex comprising area striata and area occipitalis along their common border. The cortical labelling in area striata and occipitalis was interpreted as evidence for a direct geniculo‐cortical projection. This was confirmed by demonstration of retrogrately labelled nerve cells in the lateral geniculate nucleus produced by small injections of horseradish peroxidase into area occipitalis and area striata. In experiments with intraocular injections of tritiated adenosine, transneuronal cortical labelling was much weaker and more diffuse. In addition to the neuropil, nerve cell bodies and glial cells were also labelled.
Gliogenesis of astrocytes and oligodendrocytes in the neocortical grey and white matter of the adult rat: Electron microscopic analysis of light radioautographs
Authors: Kaplan Michael S. , Hinds James W.
Published: January 2005

The identification of newly formed glial cells in the normal adult cerebral cortex is unresolved, since the identification of cells incorporating [H3] thymidine has not been demonstrated in the adult by electron microscopy. In the present study, this problem has been studied by combining the resolution of the electron microscope with radioautography of 1‐μm sections. Four normal male rats were injected at 90 days of age with [H3] thymidine and allowed to survive for 30 days. Labeled cells were found in 1‐μm sections of the visual cortex of these adult rats, and electron micrographs of selected cells from these same sections demonstrated clearly two types of cells labeled, astrocytes and oligodendrocytes, in both grey and white matter. The few cells that were tentatively identified as labeled microglia in the light microscope proved to resemble oligodendrocytes when examined in the electron microscope. In 1‐μm sections of the cortical grey matter, heavily labeled astrocytes (13 or more silver grains over the nucleus) represent about 0.08% of the total astrocytic population, and heavily labeled oligodendrocytes also were about 0.08% of their population. In the cortical white matter, about 0.03% heavily labeled astrocytes were observed, compared to about 0.07% heavily labeled oligodendrocytes. For all neuroglial cells in both white and grey matter, the average percent heavily labeled cells was 0.066%, a value large enough to suggest a slow turnover of neuroglial cells during the lifespan of the rats.
Functional and morphological studies of peptide‐containing neuroendocrine cells in goldfish hypothalamus
Authors: Reaves Troy Albert , Hayward James N.
Published: January 2005

We report the development of a double‐label method which combines intracellular recording, dye‐marking, and immunocytochemistry for the study of functional and morphological aspects of peptide‐containing neurons in the magnocellular preoptic nucleus of the goldfish hypothalamus. Using multiple techniques, we distinguish three types of peptide‐containing neurons: enkephalin (27%), isotocin (49%), and vasotocin (24%). Drawings of serial sections containing the dye‐injected cells were the basis for subsequent reconstruction. These peptidecontaining cells measure 14‐56 μm in somata diameter, are unipolar, bipolar, or multipolar in somata shape and lie 6–244 μm from the ependymal lining of the preoptic recess of the third ventricle. Their electrophysiological properties match those of other mammalian and fish magnocellular neuroendocrine cells. This report confirms the one neuron, one hormone (peptide) hypothesis, supports synaptic over electrotonic coupling between peptidergic and adjacent hypothalamic neurons, and suggests that chemical and functional classification of single electrophysiologically and neuroanatomically studied central neurons is feasible technologically.
Fine structure of rat locus coeruleus
Authors: Groves Philip M. , Wilson Charles J.
Published: January 2005

Locus coeruleus of the rat was studied in material prepared by aldehyde‐osmium fixation. Cell bodies of locus coeruleus neurons possess large nuclei with a prominent nucleolus, a homogeneous karyoplasm of moderate density, and occasional indentations of the nuclear membrane. The cytoplasm is rich in organelles, including an extensive network of endoplasmic reticulum which forms well organized Nissl bodies. The highly developed Golgi apparatus surrounds the nucleus and extends into large dendritic trunks. In coronal section, cell bodies appear elongated along an approximate dorso‐ventral axis, and most dendrites as well as axons appear in cross‐section. In parasagittal sections the cells are very elongate, with dendrites and axons in the neuropil mostly cut longitudinally. Thus, locus coeruleus neurons possess disc‐shaped dendritic fields parallel to the anterior‐posterior axis of the brainstem, with predominantly longitudinal axo‐dendritic synaptic configurations.

Presynaptic profiles in locus coeruleus neuropil were classified according to the characteristics of their vesicle populations and other features. The most frequently encountered synaptic ending was characterized by small, round, densely packed synaptic vesicles, and comprised approximately 41% of the total sample of 775 synapses. Another group having large, rounded synaptic vesicles, which could be traced in a number of instances to large myelinated axons, accounted for 20% of the sample. Synaptic endings having large, flattened vesicles were also numerous, comprising 23% of the total. Another category of presynaptic endings was identified as those possessing numerous, small, flattened vesicles and comprising about 11% of the sample. Presynaptic endings having many vesicles of mixed sizes accounted for 2% of the total, and another group of the same proportion having small, rounded synaptic vesicles but also an unusually large number of larger, dense‐cored vesicles was also present. Two other categories of synaptic endings were encountered, each comprising less than 1% of the total. One of these was derived from small, unmyelinated axons and contained clusters of pleomorphic synaptic vesicles. The other consisted of dendro‐dendritic synapses between locus coeruleus neurons and also displayed small clusters of pleomorphic synaptic vesicles near the zone of synaptic apposition. Quantitative analysis revealed that most afferents to the nucleus synapse onto dendrites ranging between 0.5 and 2.5 micrometers in diameter and onto spine‐like appendages derived from somata and dendrites. There were no significant differences between different categories of afferent terminals and their spatial distribution onto various postsynaptic targets of locus coeruleus neurons.
Monoaminergic presynaptic axons and dendrites in rat locus coeruleus seen in reconstructions of serial sections
Authors: Groves Philip M. , Wilson Charles J.
Published: January 2005

Locus coeruleus was studied in rats pretreated with intraventricularly administered 5‐hydroxydopamine ½ to 3 hours prior to conventional aldehydeosmium fixation. Presynaptic profiles in locus coeruleus neuropil were classified according to the characteristics of their vesicle populations and other features, as in our previous report. Similar categories of endings were observed, and the sites of postsynaptic innervation were identical to those described previously, that is, a majority of synapses were made with dendrites between 0.5 and 2.5 micrometers in cross‐sectional diameter, a significant proportion was seen ending onto somatic and dendritic spines, with a relative paucity of synapses made with spine‐free membrane of somata and large dendritic trunks. There were no significant differences between different morphological categories of afferent terminals and their spatial distribution onto various postsynaptic targets on locus coeruleus neurons.

In addition to various membrane‐bound compartments of the cytoplasm, three categories of synaptic endings were labelled by the synaptic marker, while all others were unlabelled. One of these was identified previously as containing small, rounded synaptic vesicles and an unusually large number of large, dense core vesicles. The synaptic vesicles were lightly labelled with scattered, small, eccentrically placed opaque cores inside the synaptic vesicles, apparently randomly distributed throughout the terminal. This terminal is thought to be serotonergic. A second category of labelled synapse has been previously identified as that derived from small, unmyelinated axons having clusters of pleomorphic synaptic vesicles in which the vesicles are heavily labelled by 5‐hydroxydopamine. These are believed to represent catecholaminergic synaptic endings derived from recurrent collaterals as well as extrinsic catecholaminergic innervation of locus coeruleus. A final category of heavily labelled profile was identified as presynaptic dendrites, which, along with recurrent catecholaminergic axon collaterals, probably play an important part in the intrinsic regulation of nucleus locus coeruleus. When 59 labelled synapses were examined in adjacent serial sections, every vesiclecontaining profile was associated with a synaptic contact having characteristic membrane specializations. A similar result was obtained when 132 other unlabelled terminals of different categories were examined in serial sections.
A stereological analysis of the cerebellar granule and purkinje cells of 30‐day‐old and adult rats undernourished during early postnatal life
Authors: Bedi K. S. , Hall R. , Davies C. A. , Dobbing J.
Published: January 2005

Male rats undernourished from birth to 30 days of age were nutritionally rehabilitated till 160 days of age. Quantitative stereological procedures at the light microscope level were used to estimate, among other things, the numerical densities of cerebellar granule and Purkinje cells on a “per unit volume of cortex” basis. These were subsequently used to calculate granule‐to‐Purkinje cell ratios.

The 30‐day‐old undernourished rats had a mean ± S.E. of 290 ± 27 granule cells for every Purkinje cell present, compared to 395 ± 34 for the controls. This was a deficit of about 27% (p<0.05). At 160 days of age, the previously undernourished rats still showed a persisting deficit of about 25% (p<0.05) in this ratio, despite the lengthy nutritional rehabilitation. There were no statistically significant age‐related changes in this ratio.

The numerical density of Purkinje cells but not that of granule cells, was significantly greater in the previously undernourished rats than in controls, for both age groups. Increasing age caused a fall in the numerical density of both cell types.

Granule and Purkinje cell nuclear diameters were unaffected by nutrition. However, Purkinje cell nuclei decreased in size by between 7%–13% with increasing age.

These results indicate that undernutrition during early life can cause a permanent distortion of the relative number of the various cell types in the cerebellum.
Development of the brain stem in the rat. I. Thymidine‐radiographic study of the time of origin of neurons of the lower medulla
Authors: Altman Joseph , Bayer Shirley A.
Published: January 2005

Groups of pregnant rats were injected with two successive daily doses of 3H‐thymidine from gestational days 12 and 13 (E12+13) until the day before birth (E21+22). In adult progeny of the injected rats the proportion of neurons generated on specific days was determined quantitatively in the major nuclei of the lower medulla. The earliest generated cells form two motor nuclei: the hypoglossal and dorsal vagal nuclei. The bulk of hypoglossal neurons are produced on day E12, with a small proportion earlier; the bulk of dorsal vagal neurons are produced, likewise, on day E12, with a small proportion on day E13. The neurons of the third motor nucleus of the region, the ambiguus, are generated later, with a peak on day E15. Neurons of the sensory relay nuclei, the gracilis, cuneatus, and solitarius are produced over a more extended period, with peaks on day E13; the exception was the external cuneate nucleus in which peak generation time was on day E15. In the caudal nucleus of the trigeminal complex, neurons of the subnucleus magnocellularis arise earliest, with a peak on day E14, and those of the subnucleus marginalis last, with a peak on day E15, and extending into day E16. The neurons of the nuclei raphe pallidus and obscurus, and of the dorsal and ventral portions of the caudal medullary reticular formation, are produced between days E12 and E15, without any obvious peaks. The neurons of the nucleus parasolitarius and the nucleus of Roller are produced relatively late, and the area postrema contains a germinal cell population throughout the embryonic period, presumably supplying cells to the choroid plexus of the fourth ventricle. On the basis of absolute datings, duration of neuron production, intranuclear and internuclear gradients, and other criteria, it is postulated that the neurons of the lower medulla are derived from at least eight different cytogenetic zones.
Development and degeneration of retina in rds mutant mice: Light microscopy
Authors: Sanyal S. , De Ruiter A. , Hawkins R. K.
Published: January 2005

Changes during the development and degeneration of the retina in 020/A mice, which are homozygous for the newly reported rds (retinal degeneration slow), gene were studied by histological and enzyme‐histochemical methods with Balb/c mice carrying the normal allele as control. During normal development the total thickness of the retina grows from the time of birth till the age of 21 days and thereafter gradually diminishes, while the thicknesses of the component layers show a characteristic and differential change in course of their histogenesis. In the normal retina the perikarya of the cones are more frequent in the central than in the peripheral areas. The cone frequency in the central retina, but not in the periphery, increases with age and implies selective loss of rod cells in older animals.

In the homozygous rds mice, the receptor layer remains rudimentary, but the other retinal layers show a normal trend of growth during the first 2 weeks after birth. Thereafter the morphological layers containing visual cell structures—the receptor, the outer nuclear, and the outer plexiform layers—begin to reduce. The loss of visual cells is readily marked by the reduction of the outer nuclear layer and is first evident at 2 weeks after birth. Degeneration is more rapid up to the age of 2–3 months, when the outer nuclear layer is reduced to half of its original thickness; thereafter degeneration progresses more slowly. The receptor and the outer plexiform layers are also simultaneously reduced. At 9 months, the peripheral parts of the retina, and at 12 months, the entire retina is completely lacking in visual cells. In the central retina of the mutant, rod and cone cell populations are equally affected up to the age of 6 months, as their relative frequency remains similar to the normal. In the peripheral retina, where cell loss is more pronounced, and in the central retina at 9 months an increase in relative frequency of cones is recorded and indicate increased susceptibility of the rods to later degenerative changes. The inner parts of the retina, including inner nuclear, inner plexiform, and ganglion cell layers, remain morphologically unaffected until irregular vascularization follows total loss of visual cells. The pigment epithelium is also affected at this late stage and appears depleted and patchy.

In the normal retina, macrophages which are positively stained for the enzyme N‐acetyl‐β‐glucosaminidase appear in the inner layers with the growth of the retinal vasculature. In the mutant, increased frequency and stainability of the macrophages are discernible in the inner retina at 11 days. The macrophages migrate outwards and are observed in the outer nuclear layer and in the optic ventricle during the period of degeneration.

These findings are compared with the observations in the other retinal degeneration mutants in rodents, and in retinitis pigmentosa in humans. The suitability of the rds mice as an animal model system for the human disease is emphasized.
Interhemispheric connections of visual cortex in the owl monkey, Aotus trivirgatus, and the bushbaby, Galago senegalensis
Authors: Newsome William T. , Allman John M.
Published: January 2005

Anatomical techniques have been used to map within visual cortex the pattern of degenerating axonal terminals produced by surgical section of the splenium of the corpus callosum in the owl monkey, Aotus trivirgatus, and the bushbaby, Galago senegalensis. Previous studies in other species have shown that callosal inputs terminate preferentially in regions where the vertical meridian of the visual field is represented. Such a correspondence can serve as a useful aid for locating the boundaries of visual areas. The goals of this study have been (1) to assess the degree of correspondence between callosal inputs and previously identified vertical meridian representations in the owl monkey and bushbaby, and (2) to gain information from the pattern of callosal inputs concerning the existence and organization of as yet unidentified extrastriate visual areas. In both the owl monkey and the bushbaby, a discrete band of degenerating axonal terminals corresponds precisely to the vertical meridian representation at the V1‐V2 border, and a less precise increase in the density of degenerating axonal terminals corresponds to the vertical meridian representation of extrastriate area MT. A well‐defined band of degeneration on the ventral surface of the owl monkey's cerebral hemisphere corresponds to a previously unknown vertical meridian representation which is shared by two newly identified extrastriate visual areas. Elsewhere in visual cortex the pattern of callosal connections is more complex. Although this pattern may still reflect visual topography, it is not immediately useful for distinguishing areal boundaries.
The paraventricular nucleus of the hypothalamus: Cytoarchitectonic subdivisions and organization of projections to the pituitary, dorsal vagal complex, and spinal cord as demonstrated by retrograde fluorescence double‐labeling methods
Authors: Swanson L. W. , Kuypers H. G. J. M.
Published: January 2005

Experiments using two retrogradely transported fluorescent dyes (bisbenzimide‐true blue, and Evans blue‐granular blue) were performed in order to determine whether the same or different populations of neurons in the paraventricular nucleus of the hypothalamus (PVH) project to the pituitary gland, dorsal vagal complex, and spinal cord in the rat. The results suggest that cells projecting to the pituitary gland are concentrated in the magnocellular core of the nucleus, while the descending connections arise primarily from the surrounding parvocellular division. The occurrence of neurons double‐labeled with both dyes further indicate that at least 10–15% of the labeled cells in the parvocellular division send divergent axon collaterals to the dorsal vagal complex and to the spinal cord. Cell counts suggest that at least 1,500 cells in the PVH project to the medulla and/or spinal cord. These results, combined with a cytoarchitectonic analysis, show that the PVH consists of eight distinct subdivisions, three magnocellular and five parvocellular. The lateral hypothalamic area and zona incerta also contain a large number of cells projecting to the dorsomedial medulla and spinal cord; approximately 15% of such cells are double‐labeled following injections of separate tracers into these two regions of the same animal.
The efferent projections of the central nucleus and the pericentral nucleus of the inferior collculus in the cat
Authors: Anderse Richard A. , Roth G. Linn , Aitkin Lindsay M. , Merzenich Michael M.
Published: January 2005

The efferent projections of the central nucleus of the inferior colliculus (ICC) and the pericentral nucleus of the inferior colliculus (ICP) were examined by placing restricted injections of anterograde tracers at electrophysiologically defined loci in the inferior colliculus (IC) of the cat.

It was found that single loci in the ICC projected bilaterally onto the ventral division of the medial geniculate body (MGB) in the form of caudorostrally oriented sheets of terminals. The ICC loci also projected bilaterally onto the MGB In the form of caudorostrally oriented columns of terminals; these columns had their caudal aspects located in the medial division and their rostral aspect of the sheets of terminals in the ventral division was folded and passed though both pars lateralis and pars ovoidea of the ventral division. Every component of the ICC‐to‐MGB projection was cochleotopically ordered. Periodic discontinuties of two types were noted in the projections of the ICC onto pars lateralis (VI) of the ventral division. The on type of periodic discontinuity sometimes approximated bands oriented caudorostrally in the caudal aspect of VI. The second type of discontinuity was of very thin parallel columns of more intense Labeling oriented roughly discontinuity and oblique or normal to the first type of discontinuity.

Injections in the ICP produced autoradiographic labeling in the caudal dorsal nucleus (Dc) of the dorsal division of the MGB. Thus the ICC‐to‐MGB and ICP‐to‐MGB projection are segregated.

The efferent connections of the IC with other brainstem auditory structures were noted.
Non‐specific esterase activity in reactive cells in injured nervous tissue labeled with 3H‐Thymidine or 125Iododeoxyuridine injected before injury
Authors: Schelper Robert L. , Adrian Erle K.
Published: January 2005

Tritiated thymidine (3H‐TdR) injected before a stab wound of the spinal cord or transection of the hypoglossal nerve has resulted in many labeled reactive cells in the CNS after injury, most of which have the ultrastructural features of microglia. To test for the possible origin of these labeled cells from monocytes, we examined them for the presence of sodium, fluoride‐ (NaF) sensitive non‐specific esterase (NSE), an enzyme characteristic of monocytes. Some of the labeled cells in stab wounds had NaF‐sensitive NSE, but no such cells were found in the nucleus of the injured hypoglossal nerve. To test for the possibility that the NSE‐negative labeled cells had been labeled by reutilization of 3H‐TdR, we used 125I‐5‐iodo‐2'deoxyuridine (125I‐UdR), a thymidine analogue with a much lower rate or reutilization, to label blood mononuclear cells prior to either a spinal cord stab wound or hypoglossal axotomy. The number of labeled cells was decreased in the spinal cord wound, but more than half were NSE‐negative. No labeled blood mononuclear cells were found in the hypoglossal nucleus, although there was no decrease in the hyperplasia of unlabeled non‐neuronal cells. When 125I‐UdR was injected on the fourth day after hypoglossal axotomy, or when both 3H‐TdR and 125I‐RdR were injected simultaneously before hypoglossal axotomy, many labeled cells were found in the hypoglosaal nucleus, indicating that 125I‐UdR can be used by the reactive cells and that it did not inhibit their proliferation. Therefore, the microglial cells that proliferate in response to peripheral nerve injury are not recently derived from any type of circulating large blood mononuclear cell. The most likely explanation for the presence of the 3H‐TdR‐labeled cells in the nucleus of the injured hypoglossal nerve in that they were proliferating intrinsic labeled by reutilization of 3H‐TdR.
Development of the mossy fibers of the dentate gyrus: I. A light and electron microscopic study of the mossy fibers and their expansions
Authors: Amaral David G. , Dent Judith A.
Published: January 2005

The postnatal development of the axons of the dentate granule cells—the so‐called mossy fibers—was studied at the light microscopic level in Timm and Golgi preparations and also by transmission electron microscopy. In the Timm‐stained material, there was a distinctive coloration in the hilus and incipient stratum lucidum, indicating the presence of mossy fibers, on the first postnatal day. Over the next two weeks, the stained areas became more extensive, the size and density of the stained particles increased, and the particles became more intensely stained. These signs of progressive development of the mossy fibers appeared to reflect, temporally and topographically, the developmental gradients followed by their parent granule cells.

The Golgi material confirmed the presence of mossy fibers in the hilus on the first postnatal day. Fasciculi of mossy fibers were observed in the stratum lucidum of the 3‐day‐old hippocampus, and although these immature axons were devoid of large synaptic expansions, they did have prominent growth cones at their termini. Small expansions along the lengths of the axons first appeared on day 7 and these grew to approximately an adult size and complexity by about day 14. The postsynaptic component of the mossy fiber synapse, the “thorny excrescence,” did not begin to emerge from the proximal portion of the pyramidal cell dendrites until sometime after day 9.

At the electron microscopic level we observed, on the first postnatal day, small, immature mossy fiber expansions which made both symmetric and asymmetric contacts directly with dendritic shafts. These profiles, which were only one tenth the size of mature expansions, grew rapidly between postnatal days 1 and 9 and increased their mean area by a factor of five. On or about day 9, as the “thorny excrescences” emerged, the asymmetric synapses came to be associated with these spinous processes.

Taken together, the Golgi and electron microscopic analyses support the suggestion that mossy fibers establish synaptic contact with pyramidal cell dendrites early in the postnatal period, several days before there is any indication of spine development. Furthermore, the “thorny excrescences” develop after the more typical, pedicellate spines have appeared on the distal pyramidal cell dendrites. Finally, while it is clear that the mossy fibers in our 21‐day‐old material are, for the most part, fully matured, a more subtle and protracted development of the system, long into adulthood, is indicated by the increased area and density of stained particles in the Timm preparations from adult animals.
Thalamocortical synapses involving identified neurons in mouse primary somatosensory cortex: A terminal degeneration and golgi/EM study
Authors: Hersch Steven M. , White Edward L.
Published: January 2005

Synapses involving thalamocortical afferents and hitherto unexamined neuron types of the posteromedial barrel subfield (PMBSF) of the mouse have been identified using a combined degeneration and Golgi/EM technique (Peters et al., '77). Degeneration of thalamocortical axon terminals was produced with electrolytic lesions of the nucleus ventralis posterior, pars lateralis thalami, and the nucleus posterior thalami. Four days after receiving lesions, the animals were perfused, and blocks of cortex containing the PMBSF were processed by the Golgi method. The blocks were tissue‐chopped at 125 μm and examined with the light microscope. Sections containing neurons of interest were gold‐toned and deimpregnated in preparation for electron microscopy (Fairén et al., '77). Portions of selected neurons contained in layers III‐V were serially thin‐sectioned and examined with an electron microscope to determine if they were involved in synapses with degenerating thalamocortical axon terminals. Results showed thalamocortical synapses on the apical dendrites of five different sized pyramidal cells whose somata occurred in layers V and VI, and on dendrites of one spiny bitufted neuron and one non‐spiny multipolar neuron with somata in layer V. A non‐spiny bitufted neuron of layer IV which was not impregnated also received thalamocortical synapses.

Although every neuron examined formed at least one thalamocortical synapse, some formed very few, whereas others formed many. Of the pyramidal cells, small layer V and VI pyramidal cells and a large deep layer V pyramidal cell were involved in small numbers of thalamocortical synapses, while a medium superficial layer V pyramidal cell and a large layer VI pyramidal cell each formed many. The spiny bitufted neuron formed a small number of thalamocortical synapses, while the non‐spiny bitufted neuron formed very many. The non‐spiny multipolar neuron was involved in a moderate number of thalamocortical synapses. The findings suggest that, whereas any type of neuron with a dendrite in layer IV likely receives some synaptic input from the thalamus, individual neurons were involved in very different quantities of thalamocortical synapses.