bluuebunny/crossref_metadata_2025 huggingface dataset:
Angioarchitecture of the CNS, pituitary gland, and intracerebral grafts revealed with peroxidase cytochemistry
Authors: Broadwell Richard D. , Balin Brian J. , Charlton Harry M. , Salcman Michael
Published: January 2005

Blood vessels of the fetal, neonatal, and adult subprimate and primate CNS, including circumventricular organs (e.g., median eminence, pituitary gland, etc.), and of solid CNS and nonneural (anterior pituitary gland) allografts placed within brains of adult mammalian hosts were visualized with peroxidase cytochemistry applied in three ways: (1) to tissues from animals injected systemically with native horseradish peroxidase (HRP) or peroxidase conjugated to the lectin wheat germ agglutinin (WGA) prior to perfusion fixation; (2) to tissues from animals infused with native HRP into the aorta subsequent to perfusion fixation; and (3) to tissues from animals fixed by immersion and incubated for endogenous peroxidase activity in red cells retained within blood vessels. In neonatal and adult animals receiving native HRP intravascularly, non‐fenestrated vessels contributing to a blood‐brain barrier were outlined with HRP reaction product when tetrarnethyl‐benzidine (TMB) as opposed to diaminobenzidine (DAB) was used as the chromogen; fenestrated vessels of circumventricular organs were not discernible due to the density of extravascular reaction product. Fenestrated and nonfenestrated cerebral and ext racer ebral blood vessels exposed to blood‐borne WGA‐HRP were visible when incubated in TMB and DAB solutions. Native HRP infused into the aorta of fixed animals likewise labeled nonfenestrated vessels throughout the brain upon exposure to TMB or DAB but obscured fenestrated vessels of the circumventricular organs. Endogenous peroxidase activity of red cells, seen equally well with TMB and DAB, outlined blood vessels throughout the cerebral gray and white matter and all circumventricular organs in fetal, neonatal, and adult animals.

Application of the three peroxidase cytochemical approaches to study the development or absence of a blood‐brain barrier in intracerebral allografts demonstrated that the vascularization of day 16–19 fetal/1 day neonatal. Placement of the grafts. CNS allografts secured from donor sites expected to possess a blood‐brain barrier exhibited blood vessels that were not leaky to HRP injected intravenously in the host. Fenestrated blood vessels associated with anterior pituitary allografts were evident prior to 3 days posttransplantation within the host brain and permitted blood‐borne HRP in the host to enter the graft and surrounding host brain parenchyma.

The three peroxidase cytochemical approaches are useful for visualizing CNS blood vessels that contribute or do not contribute to a blood‐brain barrier in fetal, neonatal, and adult laboratory animals; the three approaches have potential application to cerebrovascular studies of stroke, trauma, and neoplasia.
Ultrastructure of synapses from the A‐laminae of the lateral geniculate nucleus in layer IV of the cat striate cortex
Authors: Einste Gillian , Davis Thomas L. , Sterling Peter
Published: January 2005

The morphology of synapses in layer IV of the cat striate cortex was studied by electron microscope (EM) autoradiography of serial sections following injection of tritiated amino acids into the lateral geniculate nucleus. Of the terminals in the neuropil, 22% had 2 or more silver grains in 10 successive sections and were labeled at 8–80 times the background level. These terminals were considered to be specifically labeled and to be derived from the lateral geniculate. Two forms of geniculate synapse were observed. One had medium‐size, round vesicles and a modest postsynaptic asymmetry (RA); the other had smaller, pleomorphic vesicles and hardly any postsynaptic opacity; that is, it appeared symmetrical (PS). The geniculate RA terminals were presynaptic to dendritic spines, fine processes, and cell bodies; the geniculate PS terminals were presynaptic to dendrites and cell bodies but not to spines. The possible sources of geniculate PS terminals are discussed.
Pattern of lateral geniculate synapses on neuron somata in layer IV of the cat striate cortex
Authors: Einstein Gillian , Davis Thomas L. , Sterling Peter
Published: January 2005

The distribution of geniculate synapses on neuron cell bodies in layers IVab and IVc of cat area 17 was studied. Electron microscope autoradiography was used to identify geniculate terminals that were labeled by antero‐grade transport of radioactivity injected into the A‐laminae of the lateral geniculate nucleus. Thirty‐eight cell bodies (19 in layer PVab and 19 in layer IVc) were examined in a series of 138 consecutive sections. Two pyramidal somas were studied and had no geniculate contacts. All of the other somas studied were nonpyramidal, and of these, 85% received geniculate contacts. The proportion of somas receiving somatic geniculate input differed in layers IVab and IVc. In layer IVab, 70% of the nonpyramidal somas received geniculate contacts; in IVc, 100%. Such high percentages indicate that geniculate afferents synapse with more types of layer IV neuron than the aspinous neurons that synthesize gamma‐aminobutyric acid (GABA) (Freund et al., '85b).

The pattern of input to somas was so diverse that it was impossible to form groups of neurons based on only this criterion. We wondered if it would be possible to form groups of neurons based on a range of characteristics among which would be pattern of synaptic input. To this end, pyramidal neurons and neurons that contained, a cytoplasmic laminated body (CLB) (Winfield, '79; Einstein et al., '84) were treated as two separate classes. We found fair agreement among the features of these neurons within their own classes, with the CLB‐cells in layer IVab and IVc forming separate groups. Among the remaining neurons there was too little agreement within the range of features to enable us to treat them in this manner.

Geniculate somatic contacts in both sublayers were of 2 forms, those with round vesicles and asymmetric thickenings (RA) and those with pleomorphic vesicles and symmetric thickenings (PS) (Einstein et al., '87). The distribution of these forms varied: some cells received contacts exclusively from one form or the other; other cells received contacts from both. On one cell that bore 33 somatic geniculate terminals, 61% were RA and 39% were PS. Such substantial numbers of geniculate contacts located near the site of impulse initiation are likely to contribute significantly to the receptive field properties of this neuron, and the possible effects are discussed.
Neural induction of taste buds
Authors: Hosley Mark A. , Hughes Stephen E. , Oakley Bruce
Published: January 2005

Bilateral innervation allows more than 80% of the 610 vallate taste buds to survive removal of one IXth nerve in adult rats. Removal of both IXth nerves in neonatal or adult rats results in the absence of taste buds. In studying development, we found that removing or crushing one IXth nerve in three‐day‐old neonates profoundly decreased the number of vallate taste buds that subsequently developed. Specifically, after removal of one IXth nerve at 3 days, only 228 taste buds formed, compared with 496 taste buds that one nerve would maintain in adults. Thus, during normal development, the right and left IXth nerves interact synergistically, as at least 150 more taste buds develop than predicted by the sum of the independent action of each IXth nerve. This suggests that vallate taste buds are induced by the IXth nerve. A second example of synergism, representing evidence for the neural induction of taste buds, came from experiments in which we crushed the left IXth nerve 3 days after birth and found that these regenerated IXth nerve axons induced 4 times as many taste buds in the presence of the normal right IXth nerve (118 taste buds) as in its early absence (30 taste buds).

We conclude that taste buds are neurally induced and that axons of the IXth nerve interact synergistically in inducing them, rather than competing for targets. We propose that in development innervated progenitor cells form stem cells which lead to taste bud cells.
Corticotropin releasing factor‐like immunoreactivity in the rat brain as revealed by a modified cobalt‐glucose oxidase‐diaminobenzidine method
Authors: Sakanaka Masahiro , Shibasaki Tamotsu , Lederis Karl
Published: January 2005

A cobalt‐glucose‐oxidase diaminobenzidine (Co‐GOD) method, employing a specific antiserum against rat corticotropin releasing factor (CRF), was applied to determine immunohistochemically a widespread and detailed localization of corticotropin releasing factor‐like immunoreactivity (CRFI) in the rat brain.

Besides the CRFI cells in the paraventricular hypothalamic nucleus that project to the median eminence, CRFI cells were demonstrated in many brain regions, including the olfactory bulb, cerebral cortex, septal nuclei, hippocampus, amygdala, thalamic nuclei, medial hypothalamic nuclei, lateral hypothalamic area, perifornical area, central gray, cuneiform nucleus, inferior colliculus, raphe nuclei, mesencephalic reticular formation, laterodorsal tegmental nucleus, locus coeruleus, parabrachial nuclei, mesencephalic tract of the trigeminal nerve, pontine reticular formation, lateral superior olive, vestibular nuclei, prepositus hypoglossal nucleus, nucleus of the solitary tract, dorsal motor nucleus of the vagus, lateral reticular nucleus, nucleus of the spinal tract of the trigeminal nerve, external cuneate nucleus, inferior olive, and medullary reticular formation. CRFI‐reacting neural processes were also detected in these same areas. In particular, the median eminence, lateral septum, bed nucleus of the stria terminalis, mesencephalic reticular formation, parabrachial nuclei, and nucleus of the solitary tract contained large numbers of CRFI fibres.

The widespread localization of CRFI demonstrated in the present study strongly suggests that CRF, like many other neurohormones and peptides, may act as a neurotransmitter and/or neuromodulator in numerous extra‐hypothalamic circuits, as well as participate in neuroendocrine regulation.
Development of visual callosal connections in neonatally enucleated rats
Authors: Olavarria Jaime , Malach Rafael , Van sluyters Richard C.
Published: January 2005

The present report extends previous descriptions of the mature distributions of callosal cells and axonal terminations in rats monocularly or binocularly enucleated at birth. It also describes the time course of callosal development in these animals, and establishes the age at which eye removal ceases to alter the normal course of callosal development.

Although our results indicate that the callosal pattern is anomalous in adult, neonatally enucleated rats, the major features of the normal callosal pattern are nonetheless clearly recognizable in both monocularly and binocularly enucleated rats. Thus, as in normally reared rats, there are dense accumulations of callosal cells and terminations at the 17/18a border region, at the lateral border of area 18a, and within area 18b in enucleated rats. In addition, several narrow bands of callosal connections bridge the width of area 18a at several rostrocaudal levels, and a ring‐like callosal configuration is located anterolateral to area 17.

In monocularly enucleated rats, the most prominent anomaly develops in the hemisphere ipsilateral to the remaining eye, where a dense band of callosal connections runs rostrocaudally through the center of area 17. Periodic fluctuations in the density of labeling along the length of this extra band give it a beaded appearance. The callosal pattern in the hemisphere contralateral to the remaining eye in these rats appears normal. Binocular enucleation causes the appearance of discrete regions of reduced labeling within the 17/18a callosal band and several densely labeled tongue‐like regions that extend medially from this band well into area 17. The laminar distribution of callosal cells and terminations is not significantly altered by loss of one or both eyes at birth.

Our data indicate that enucleation does not affect the time course of callosal development. Thus, in enucleated pups, all features of the mature callosal pattern can be recognized by 6–7 days of age, and by 12 days of age the patterns appear virtually mature. Finally, our data reveal that monocular or binocular enucleations performed at 6 days of age or later allow the callosal pattern to develop normally, whereas enucleations performed between birth and 5 days of age produce anomalies similar to those observed in rats enucleated at birth. Thus, at about 6 days of age—just as the earliest features of the mature callosal pattern become discernible, and long before rats first open their eyes—the developing callosal pathway is no longer susceptible to disruptions of visual input.
The spinothalamic tract: An examination of the cells of origin of the dorsolateral and ventral spinothalamic pathways in cats
Authors: Jones M. W. , Apkarian A. V. , Stevens R. T. , Hodge C. J.
Published: January 2005

The locations of Spinothalamic neurons and the funicular trajectories of their axons were studied in cats by retrograde transport of horseradish peroxidase (HRP). Five animals were used as controls to determine the cervical and lumbar laminar distributions of neurons contributing to the Spinothalamic tract. An additional eight animals were used to determine the funicular trajectories of the Spinothalamic axons of lumbar neurons by utilizing a series of thoracic spinal cord lesions in conjunction with retrograde transport of HRP from the sensory thalamus. Three of these animals underwent midthoracic ventral quadrant lesions, four animals underwent midthoracic dorsolateral funiculus lesions, and one animal underwent total spinal cord transection sparing the dorsal columns. The locations of the cells containing the HRP reaction product were then determined after a 3– to 5– day survival time, and the patterns of labeled cell locations of the lesion groups were compared to the control group patterns. In the lesioned animals, the cervical Spinothalamic cell locations were used as a control to confirm the uniformity of the injection sites, transport and tissue processing.

The major finding of this study is that there exist two distinct components of the spinothalamic tract. The dorsolateral Spinothalamic tract (DSTT) is made up of axons originating in contralateral spinal cord lamina I and has negligible contribution from the deeper spinal cord laminae. The axons of lamina I cells cross segmentally and ascend exclusively in the dorsolateral funiculus (DLF). The DSTT comprises approximately 25% of the total spinothalamic input from the lumbar enlargement. The ventral Spinothalamic tract (VSTT) is made up of axons originating in spinal cord laminae IV–V and VII–X. Very few lamina I cells contribute axons to the VSTT. This crossed pathway ascends in the ventrolateral and ventromedial portions of the spinal cord. No cells contributing to the Spinothalamic tract were identified in spinal cord segments caudal to a dorsal column sparing lesion, indicating that there are no Spinothalamic tract axons traveling in the dorsal columns.

These results expand the classical concept of information processing by the Spinothalamic tract. The DSTT is made up of lamina I cell axons. All lamina I Spinothalamic cells respond exclusively to noxious peripheral stimuli. Hence the DSTT is a major nociceptive‐specific ascending spinal pathway, yet lies outside the confines normally assigned to the spinothalamic tract. In contrast, the spinothalamic tract axons ascending in the traditional ventral location originate predominantly from neurons of wide dynamic range as well as from low‐threshold neurons. These findings have novel implications concerning the relative importance, for nociception, of lamina I and deeper laminar input to the thalamus.
The neuronal composition of area 17 of rat visual cortex. IV. The organization of pyramidal cells
Authors: Peters Alan , Kara Daniel A.
Published: January 2005

In area 17 of the rat visual cortex, most of the apical dendrites of the large layer V pyramidal cells aggregate into oriented clusters, each containing three or more such dendrites. These clusters are not randomly distributed, but have a basic hexagonal packing distribution in which the mean center‐to‐center spacing is 55–60 microns. The majority of medium‐size pyramidal cells of layer V also add their apical dendrites to the clusters. As these clusters pass through layer IV they remain intact, and successively layer III and finally layer II pyramids add their apical dendrites to them. Perhaps because the pyramidal cells in layer II/III are so numerous, some of their apical dendrites form independent groups.

Apical dendrites of the small pyramidal neurons in layers VIa and IV seem not to specifically add to the clusters. Instead, apical dendrites of layer VIa pyramids form into contiguous fascicles and sheets, which pass around the groups of layer V pyramidal cell bodies to ascend to layer IV, where most of them form their apical tufts. Layer IV pyramidal cell apical dendrites behave somewhat similarly. These apical dendrites have to pass between the cell bodies of the lower layer III pyramidal cells. To do this, some join the clusters, but others form independent bundles.

It is suggested that the pyramidal cells whose apical dendrites are clustered represent vertically oriented neuronal modules whose activity is synchronized, and that different combinations of these modules are excited by afferents to the cortex to provide the bases for the various kinds of functional columns.
Distribution of acetylcholine and catecholamine neurons in the cat brainstem: A choline acetyltransferase and tyrosine hydroxylase immunohistochemical study
Authors: Jones Barbara E. , Beaudet Alain
Published: January 2005

The distribution of acetylcholine neurons in the brainstem of the cat was studied by choline acetyltransferase (ChAT) immunohistochemistry and compared to that of catecholamine neurons examined in the same or adjacent sections by tyrosine hydroxylase (TH) immunohistochemistry. The largest group of ChAT‐positive (+) neurons was located in the lateral pontomesencephalic tegmentum within the pedunculopontine tegmental nucleus and the laterodorsal tegmental nucleus rostrally and within the parabrachial nuclei and locus coeruleus nucleus more caudally. TH+ neurons were found to be coextensive and intermingled with ChAT‐h neurons in the dorsolateral pontomesencephalic tegmentum, where the number of ChAT+ cells (approximately 18,500) exceeded that of the TH+ cells (approximately 12,000). In the caudal pons, scattered ChAT+ neurons were situated in the ventrolateral tegmentum together with TH+ neurons. In the medulla, numerous ChAT+ cells were located in the lateral tegmental field, where they extended in a radial column from the dorsal motor nucleus of the vagus to the ventrolateral tegmentum around the facial and ambiguus nuclei, occupying the position of preganglionic parasympathetic neurons of the 7th, 9th, and 10th cranial nerves. TH+ cells were also present in this field. Neurons within the general visceral, special visceral, and somatic motor cranial nerve nuclei were all imrnunoreactive to ChAT. Scattered ChAT+ neurons were also present within the medullary gigantocellular and magnocellular tegmental fields together with a small number of TH+ neurons. Other groups of ChAT+ cells were identified within the periolivary nuclei, parabigeminal nucleus, prepositus hypoglossi nucleus, and the medial and inferior vestibular nuclei. Acetylcholine neurons thus constitute a heterogeneous population of cells in the brainstem, which in addition to including the somatic and visceral efferent systems, comprises many other discrete systems and represents an important component of the brainstem reticular formation. The proximity to and interdigitation with catecholamine neurons within these systems may be of important functional significance.
Prenatal growth of fine‐diameter primary afferents into the rat spinal cord: A transganglionic tracer study
Authors: Fitzgerald Maria
Published: January 2005

The aim of this study was to examine the growth of fine‐diameter, Aδ and C, primary afferents into the dorsal horn of the spinal cord. To do this, Aδ and C primary afferents were transganglionically labeled with wheat germ agglutinin‐horseradish peroxidase (WGA–HRP) in fetal rats at various ages and their growth was traced into the lumbar spinal cord. Sciatic or common peroneal nerves were injected with WGA–HRP at E18–E21.5 (just before birth) and the fetuses were returned to the uterus for 24 h before histochemical analysis. The results show fine‐diameter afferent fibers growing into the L4/L5 spinal cord at E19 when they reach the white matter overlying the dorsal horn and begin to penetrate lamina I. Twelve hours later at E19.5 terminals can be seen in lamina IIo and by E20 they are increasing in density and have reached Hi. By birth they have achieved the density in laminae I and II that is found in the neonate and young rat. Labeling of only the peroneal branch of the sciatic nerve, leaving the tibial unlabeled, demonstrated that the somatotopic specificity of central terminal fields is apparent from the time fine afferent fibers first grow into the spinal cord.
Central terminations of cutaneous mechanoreceptive afferents in the rat lumbar spinal cord
Authors: Woolf Clifford J.
Published: January 2005

The morphology in the dorsal horn of the lumbar spinal cord of the collateral branches and terminal arborizations of three different types of low‐threshold mechanoreceptor innervating the skin of the rat hindlimb has been studied by the intracellular injection of horseradish peroxidase into physiologically characterized afferent fibres. The central terminals of five rapidly adapting glabrous skin mechanoreceptors (RA), six hair follicle afferents (HFA), and four slowly adapting type I afferent fibres (SA I; two from glabrous and two from hairy skin) were recovered for detailed analysis. The number of collaterals per axon varied from eight to 12, and the length of axon stained from 3.5 to 4.7 mm. In each afferent, while the majority (52–67%) of the terminal arborizations displayed extensive branching with large numbers of en passant and terminal synaptic boutons, the arborizations at the caudal and rostral extremes of the terminal field tended to be much simpler and less profuse, with few and in some cases no boutons. This did not appear to be the consequence of inadequate filling.

The general pattern of the terminal arborizations was one of mediolaterally compressed, rostrocaudally oriented sheets. In the case of the RA afferents there was no overlap between the adjacent terminal arborizations; a few of the arborizations of the SA I afferents overlapped; most, but not all, of the HFA terminal arborizations overlapped. The terminal arborizations of the HFAs had a distinctive morphology identical to the flame‐shaped arbors described in earlier Golgi studies and included synaptic boutons extending from inner lamina II to lamina IV. The morphologies of the RA and SA terminal arborizations were similar to each other, but the former tended to be concentrated in lamina IV with branches in III and V, whereas the latter tended to V with few branches more superficial than lamina IV. There were also differences in the intercollateral spacing between these two types of afferent fibre.

While there are similarities between the morphology of the central terminals of cutaneous low‐threshold mechanoreceptors in the rat and those previously described in the cat (for example, the longitudinally continuous arrangement of the mediolaterally restricted flame‐shaped HFA arborizations and the discontinuous RA arborizations arising from a dorsally located axon), there are also some major differences: the large number of HFA arbors extending to lamina Hi and to lamina IV rather than being restricted to lamina III, the deeper location of the RA arbors (in laminae IV and V rather than lamina III), and the absence of a regular lateral convexity in the collateral axon of the SA type I afferents.
Anatomy and electrophysiology of neurons terminating in the corpora allata of the cockroach Diploptera punctata
Authors: Thompson C. S. , Lococo D. J. , Tobe S. S.
Published: January 2005

Intracellular recording and dye injection were used to study the structure and electrophysiological properties of individual neurons that project to the corpora allata of the cockroach, Diploptera punctata. Neurons in the pars intercerebralis generate long‐duration, tetrodotoxin‐sensitive action potentials. Dye injection revealed two cell types. One type extends axons to the contralateral nervi corporis cardiaci I, some of which innervate the corpora allata, and another type extends a major axon down each of the circum‐oesophageal connectives. Neurons in the pars lateralis also generate long‐duration action potentials. These neurons extend axons to the ipsilateral nervi corporis cardiaci II, which continue on to terminate in the corpora cardiaca and the corpora allata. Small groups of all the above neuronal types are dye and electrically coupled. Penetration and dye injection into nerve terminals in the corpora allata and corpora cardiaca confirmed the innervation of the corpora allata by neurons located in the pars intercerebralis and pars laterally and revealed a third class of neurons that have terminals in the corpora allata: intrinsic neurons of the corpora cardiaca.
Axonal arborization in the developing chick retinotectal system
Authors: Thanos Solon , Bonhoeffer Friedrich
Published: January 2005

The growth and arborization of chicken retinal ganglion cell axons have been investigated by means of an intraaxonally transported fluorescent marker in the developing retinotectal system. The fluorescent dye D282 or diI from the carbocyanine group of dyes is taken up by ganglion cells and labels the axon as well as the axonal growth cones and the terminal arborizations on the tectum.

Branching and arborization start in the chick retinotectal system on embryonic day 9 (E9). At this stage retinal axons leave the stratum opticum (SO) and invade the stratum griseum et fibrosum superficiale (SGFS), where arborization takes place. On day E12 several axons were found to arborize in the SGFS. At this stage arbors appear to have small branches with less than 4 branching points. The extension of terminal arbors in the anterior/posterior (A/P) and in the dorsal/ventral (D/V) direction was determined for 50 axonal trees at days E13–14 and for 24 arbors at days E15–16. Few axonal terminals were investigated at day E18. The mean A/P extent of axonal terminal trees increases from 0.23 ± 0.12 to 0.36 ± 0.22 mm from E13–14 to E15–16 and seems to stay at this order of magnitude on E18. The mean D/V extent increases from 0.23 ± 0.17 to 0.30 ± 0.18 mm in the same embryonic period of development. The number of branching points calculated from the same number of axonal trees increases from 7.50 ± 2.98 at E13–14 to 11.70 ± 4.10 at E15–16. This number seems to increase further after day E16 achieving values of about 20 to 25 at E18. This was, however, not quantifiable by the technique used here and represents an approximate value estimated from 6 completely labeled terminal fields at E18.

The data presented here suggest that the modeling of the final branching pattern in the chick retinotectal system takes place within a relatively short period of embryonic development. Prior to the beginning of terminal arborization two important events contribute to the formation of a retinotopic projection. One event is the change of the D/V position by a minority of axons lying ectopic in terms of retinotopy. Some axons turn at right angles and change their D/V position. The other event is the appearance of side branches along the A/P axis.
GABA immunoreactive neurons in rat visual cortex
Authors: Meinecke Douglas L. , Peters Alan
Published: January 2005

An antiserum to γ‐aminobutyric acid (GABA) was used in a light and electron microscopic immunocytochemical study to determine the morphology and distribution of GABA‐containing neurons in the rat visual cortex and to ascertain whether all classes of nonpyramidal neurons in this cortex are GABAergic. The visual cortex used for light microscopy was prepared in such a way that the antibody penetrated completely through tissue sections, and in these sections large numbers of GABA immunoreactive neurons were apparent. The labeled neurons could be identified as being either multipolar, bitufted, bipolar, or horizontal neurons. In layers II through Via, GABA immunostained cells were distributed uniformly and accounted for approximately 15% of all neurons, but in layer I all neurons appeared to be immunostained.

Electron microscopy of GABA immunostained visual cortex prepared to ensure good fine structural preservation confirmed the presence in layers II through Via of numerous immunoreactive bipolar neurons, both small and large varieties, as well as multipolar and bitufted neurons. Additionally, electron microscopy reveals that astrocytes are frequently GABA immunoreactive.

From a correlated light and electron microscopic evaluation of neurons in GABA immunostained visual cortex, it was possible to confirm which kinds of neurons are GABAergic and what proportion of the neuronal population they represent. Thus, from an analysis of some 950 neurons, it was found that pyramidal neurons were never immunoreactive and that except for 20% of the bipolar cell population, all examples of other types of nonpyramidal neurons encountered in this material were GABA immunoreactive.
Regionally selective elimination of cutaneous thermal nociception in rats by neonatal capsaicin
Authors: Doucette R. , Theriault E. , Diamond J.
Published: January 2005

We have studied thermal and mechanical nociception in anesthetized adult rats that had received subcutaneous injections of capsaicin as neonates. This treatment appeared not to have impaired mechanonociception in any of the body regions that were examined. In contrast, thermal nociception was present in some locations and absent in others. Its total disappearance from back skin correlated with the loss of C fiber responsiveness in the dorsal cutaneous nerves (DCNs); electrical excitation of these nerves now failed to evoke the delayed component of the cutaneus trunci muscle reflex, although the early reflex response, elicited by excitation of the mechanosensitive Aδ axons, was unaffected. Heat nociception was similarly eliminated from the nonpad glabrous skin of the paws. When the stimulus was applied selectively to the pads, however, a normal foot‐withdrawal response was evoked. The probable basis of this differential heat responsiveness in the paws was revealed by the use of the Evans Blue technique in untreated animals; antidromic activation of the paw nerves to excite their C fiber population led to dye extravasation in the glabrous skin around the pads but to almost none in the pads themselves, indicating a relative absence in the pads of a nociceptive C fiber innervation. In capsaicin‐treated animals, the tail‐flick test revealed a significantly reduced responsiveness to noxious heat in the tail. These results may explain some of the anomalies among the reports of the effects of neonatal capsaicin. It appears that in strategically exposed locations exemplified by the paw pads and tail, capsaicin‐resistant axons that could be the relatively fast‐conducting Aδ ones are involved in the signalling of noxious heat. The heat‐nociceptive C fibers that seem to be solely responsible for such signalling from back skin and nonpad glabrous skin of the paws probably contribute to heat nociception in the tail but not to that in the paw pads.
Normal and precocious sprouting of heat nociceptors in the skin of adult rats
Authors: Doucette R. , Diamond J.
Published: January 2005

The ability of intact cutaneous thermonociceptive C fibers to sprout into adjacent denervated skin, and the effects on this of electrical activity in the axons, were studied in adult rats. The presence of heat‐sensitive endings in the back skin was assessed physiologically by the ability of a hot probe to elicit the reflex contraction of the underlying cutaneus trunci muscle; sensory C fibers were detected both by the Evans Blue technique, in which antidromic excitation of the C fibers causes a visible extravasation of dye in the skin it supplied, and by direct electron microscope (EM) examination of skin. The field of an identified branch of a selected dorsal cutaneous nerve (DON) was “isolated” by eliminating all the nerves supplying the surrounding skin.

The heat‐sensitive area began to expand between 10 and 14 days after its isolation and reached a maximum (approximately doubling the initial value) by about 24 days. When the isolated nerve was antidromically excited, the borders within which dye extravasation now occurred had extended; the area of discoloration correlated well with that of the (enlarged) heat field, showing that its expansion was indeed attributable to C fiber sprouting. Electron microscopic examination showed that some of the “empty” Schwann tubes, routinely observed in the subepidermal horizontal fiber system of insensitive skin following denervation, had acquired unmyelinated axons when heat sensitivity had returned. A precocious expansion of the heat field, which was obvious by 10 days after its isolation, was produced if the heat stimulus was applied randomly throughout the field at the time of the adjacent denervations; this expansion too was shown to be due to sprouting of C fibers. Precocious sprouting of heat‐nociceptive fibers also occurred if, immediately following the field isolation, the C fibers in the spared DCN were electrically excited, and also if pinches were applied throught its field, i.e., the C fibers involved seemed to be polymodal, responding both to heat and to noxious mechanical stimulation. Precocious sprouting did not occur when tetrodotoxin was used to block central conduction of the “conditioning” impulses in the isolated DCN. Peripheral nerve damage often occurs in a situation likely to cause activation of nociceptive nerves; we suggest that the accelerated sprouting of spared axons could be important in reducing the period during which atrophic changes might occur in denervated target regions, in addition to hastening the provision of a nociceptive innervation. The various experimental approaches now available for producing differential innervation of selected regions of back skin are summarized.
Amygdaloid connections with posterior insular and temporal cortical areas in the rat
Authors: McDonald Alexander J. , Jackson Thomas R.
Published: January 2005

The connections of the amygdala with the insular and temporal cortices were examined by injecting wheat germ agglutinin conjugated to HRP (WGA‐HRP) into the rat cortex. Following injections into the posterior agranular insular area (AIp) or perirhinal cortex (PR), bands of labeled neurons extending across nuclear boundaries were observed in the amygdala. These neuronal bands involved cells in the lateral, basolateral, and basomedial nuclei as well as the periamygdaloid cortex. Other nuclei of the corticomedial amygdala and the ventral endopiriform nucleus also exhibited retrogradely labeled cells. Anterograde label was observed in nuclei containing labeled neurons and in the central nucleus. Injections into gustatory, somatosensory, and auditory neocortical areas located dorsal to AIp and PR labeled small numbers of cells in the lateral and basolateral nuclei. Injections into AIp, PR, and, to a lesser extent, dorsally adjacent neocortical areas produced both retrograde and anterograde labeling in the contralateral amygdala. The main nuclei with contralateral insular and temporal projections are the basomedial nucleus, ventral endopiriform nucleus, and nucleus of the lateral olfactory tract. The contralateral central nucleus and to a lesser extent the lateral nucleus exhibited anterograde labeling.

The pattern of retrograde labeling seen with injections at different rostrocaudal levels of the AIp‐PR continuum indicates that amygdalocortical projections to these areas exhibit an overlapping topographical organization. Comparison of the results of this study with findings on amygdaloprefrontal cortical efferents suggests that amygdaloid projections to the entire fronto‐insulo‐temporal mesocortical field are topographically organized.
Sources of projections to subdivisions of the inferior colliculus in the rat
Authors: Coleman James R. , Clerici William J.
Published: January 2005

Brainstem and forebrain projections to major subdivisions of the rat inferior colliculus were studied by using retrograde and anterograde transport of horseradish peroxidase. Retrograde label from injection into the external cortex of the inferior colliculus appears bilaterally in cells of the inferior colliculus, as well as in other brainstem auditory groups including the ipsilateral dorsal nucleus of the lateral lemniscus and contralateral dorsal cochlear nucleus. The external cortex is the only collicular subdivision where an injection labels cells in the contralateral cuneate nucleus, gracile nucleus, and spinal trigeminal nucleus. Other projecting cells to the external cortex are found in the lateral nucleus of substantia nigra, the parabrachial region, the deep superior colliculus, the midbrain central gray, the periventricular nucleus, and area 39 of auditory cortex. Injection of the dorsal cortex of inferior colliculus heavily labels pyramidal cells of areas 41, 20, and 36 of the ipsilateral neocortex. Anterograde label from a large injection of auditory cortex is densely distributed in the dorsal cortex, lesser so in the external cortex., and only slightly in the central nucleus. Labelled cells appear in the central nucleus, dorsal cortex, and external cortex, primarily ipsilaterally, following dorsal cortex injection. Relatively few cells from other brainstem auditory groups show projections to the dorsal cortex. Injection of the central nucleus of the inferior colliculus results in robust labelling of nuclei of the ascending auditory pathway including the anteroventral, posteroventral, and dorsal cochlear nuclei (mainly contralaterally), and bilaterally the lateral superior olive, lateral nucleus of the trapezoid body, dorsal nucleus of the lateral lemniscus, and the central nucleus, dorsal cortex, and external cortex of the colliculus. The medial superior olive, superior paraolivary nucleus, and ventral nucleus of the trapezoid body essentially show ipsilateral projections to the central nucleus. The differential distribution of afferents to the inferior colliculus provides a substrate for functional parcellation of collicular subdivisions.
Defects of the fetal forebrain in mice with hereditary agenesis of the corpus callosum
Authors: Wahlsten Douglas
Published: January 2005

Inbred BALB/c mice are genetically the same, yet less than half of adults show absent or small corpus callosum. Is this because only a minority has prenatal defects of the sling at the telencephalic midline, or do most fetuses have a defective sling but some are able to form a corpus callosum via some other substrate pathway? This question was addressed by comparing large samples of BALB/c fetuses at 17, 18, and 19 days after conception with a series of normal C57BL/6 and hybrid fetuses matched for body size.

At 17 days postconception almost all BALB/c fetuses show an unusual widening or bulge in the interhemispheric fissure anterior to the hippocampal commissure. Furthermore, formation of the hippocampal commissure is greatly retarded, although it eventually attains a normal size in adult mice. At 17 days, when mice of normal strains all have a corpus callosum at midplane, almost every BALB/c fetus lacks the structure, but 1 day later 67% of fetuses show delayed formation of this structure and by 19 days all but 7% of fetuses have some callosal axons crossing the midsagittal plane. Many BALB/c fetuses are able to form a corpus callosum without the benefit of a normal sling. The degree of delay of axon crossing is strongly correlated with the severity of sling defects. An unusually small adult corpus callosum occurs because fetal axons are able to follow unusual pathways and actively compensate for absence of the sling, not because of arrested midline development.
Extra‐ and intracellular HRP analysis or the organization of extraocular motoneurons and internuclear neurons in the guinea pig and rabbit
Authors: Evinger Craig , Graf Werner M. , Baker Robert
Published: January 2005

The distribution of extraocular motoneurons and abducens and oculomotor internuclear neurons was determined in guinea pigs by injecting horseradish peroxidase (HRP) into individual extraocular muscles, the abducens nucleus, the oculomotor nucleus, and the cerebellum. Motoneurons in the oculomotor nucleus innervated the ipsilateral inferior rectus, inferior oblique, medial rectus, and the contralateral superior rectus and levator palpebrae muscles. Most motoneurons of the trochlear nucleus projected to the contralateral superior oblique muscle although a small number innervated the ipsilateral superior oblique. The abducens and accessory abducens nuclei innervated the ipsilateral rectus and retractor bulbi muscles, respectively. The somata of abducens internuclear neurons formed a cap around the lateral and ventral aspects of the abducens nucleus. The axons of these internuclear neurons terminated in the medial rectus subdivision of the contralateral oculomotor nucleus. At least two classes of guinea pig oculomotor internuclear interneurons exist. One group, located primarily ventral to the oculomotor nucleus, innervated the abducens nucleus and surrounding regions. The second group, lying mainly in the dorsal midline area of the oculomotor nucleus, projected fee the cerebellum.

Intracellular staining with HRP demonstrated similar soma‐dendritic organization for oculomotor and trochlear motoneurons of both guinea pigs and rabbits. Dendrites of oculomotor motoneurons radiated symmetrically from the soma to cover approximately one‐third of the entire nucleus, and each motoneuron sent at least one dendrite into the central gray overlying the oculomotor nucleus. In both species, a small percentage of oculomotor motoneurons possessed axon collaterals that terminated both within and outside of the nucleus. The dendrites of trochlear motoneurons extended into the medial longitudinal fasciculus and the reticular formation lateral to the nucleus.

Our data on the topography of motoneurons and internuclear neurons in the guinea pig and soma‐dendritic organization of motoneurons in the guinea pig and rabbit show that these species share common organizational and morphological features. In addition, comparison of these data with those from other mammals reveals that dendritic complexity (number of dendrites per motoneuron) of extraocular motoneurons exhibits a systematic increase with animal size.
Viscerotopic representation of the upper alimentary tract in the medulla oblongata in the rat: The nucleus ambiguus
Authors: Bieger Detlef , Hopkins David A.
Published: January 2005

The nucleus ambiguus has been reported to innervate various thoracic and abdominal viscera in addition to the musculature of the upper alimentary tract. However, the literature is contradictory as to how different regions of the nucleus ambiguus innervate specific organs. Therefore, a systematic investigation of the viscerotopic organization of the nucleus ambiguus was undertaken. In 102 rats, 0.5–10.0 μl of HRP, WGA‐HRP, cholera toxin‐HRP or fluorescent tracers were injected into the IXth, Xth, and XIth cranial nerves and the major branches of the Xth as well as organs supplied by them.

The results demonstrate that the nucleus ambiguus in the rat is made up of two major longitudinal divisions: a dorsal division comprised of three rostrocaudally aligned subdivisions representing the special visceral efferent component, and a ventral division comprised of at least two subdivisions representing the general visceral efferent component. The dorsal division corresponds to the nucleus ambiguus in the narrow sense and comprises a rostral esophagomotor compact formation, an intermediate pharyngolaryngomotor semicompact formation, and a caudal laryngomotor loose formation. Each of these formations displays a characteristic dendroarchitecture. The stylopharyngeal and cricothyroid motoneurons are displaced rostrad from the main pharyngeal and laryngeal motoneuronal pools. Thyropharyngeal (lower constrictor) motoneurons occupy the rostral half of the semi‐compact formation and hyopharyngeal (middle constrictor) motoneurons its entire length. The ventral division of the nucleus ambiguus corresponds to the external formation, extends along the entire length of the medulla oblongata, and contains preganglionic neurons innervating the heart and supradiaphragmatic structures innervated by the glossopharyngeal and the superior laryngeal nerves.
Alpha ganglion cells in the rabbit retina
Authors: Peichl Leo , Buhl Eberhard H. , Boycott Brian B.
Published: January 2005

In the rabbit retina a distinctive morphological class of large ganglion cells was demonstrated by a combination of intracellular staining with Lucifer Yellow and the quantification of reduced silver‐stained preparations. The class is called alpha because of the qualitative and quantitative resemblance to the alpha cells of the cat's retina. Rabbit alpha cells change their size with location on the retina. In the high ganglion cell density region of the visual streak, their somata are about 15 μ in diameter, and their dendritic fields have diameters as small as 180–220 μm. The largest alpha cells in the inferior periphery have soma diameters of 30 μm and dendritic field diameters of 960 μm. There is a considerable scatter of sizes at any retinal location. Alpha cell density changes from about 55/Inm2 in the streak to about 3/mm2 in far periphery, and the cells make up 1–1.4% of the ganglion cell population. Dendritic trees stratify in either an inner or an outer sublamina of the inner plexiform layer, suggesting an on/off dichotomy in the response to light. Each of the inner and outer branching subtypes is distributed in a regular mosaic, and the dendritic trees cover the retina completely and economically. The possibility is discussed that the alpha cells are the brisk transient/Y cells of physiology.