bluuebunny/crossref_metadata_2025 huggingface dataset:
Serotoninergic terminals: Ultrastructure and synaptic interaction with catecholamine‐containing neurons in the medial nuclei of the solitary tracts
Authors: Pickel Virginia M. , Joh Tong H. , Chan June , Beaudet Alain
Published: January 2005

The ultrastructural morphology of serotoninergic terminals and their synaptic relation with catecholaminergic neurons were examined in the medial nuclei of the solitary tracts (m‐NTS) using combined autoradiographic and immunocytochemical methods. Adult rats were pretreated with a monoamine oxidase inhibitor and subjected to a 2‐hour intraventricular infusion of 50 nM tritiated 5‐hydroxytryptamine (3H‐5HT). At the termination of the infusion, the brains were fixed by aortic arch perfusion with a mixture of 4% paraformaldehyde and 0.5% glutaraldehyde. Coronal Vibratome sections through the NTS and more rostral raphe nuclei were immunocytochemically labeled with specific antiserum to serotonin or tyrosine hydroxylase and then processed for autoradiography. By light microscopy, concentrations of reduced silver grains indicating uptake of 3H‐5HT usually paralleled the localization of peroxidase immunoreactivity for serotonin in neuronal perikarya of the rostral raphe nuclei and in varicosities in the brainstem. The 3H‐5HT‐containing varicosities were found throughout the medial and commissural portions of the NTS, where they were frequently associated with processes showing immunoreactivity for the catecholamine‐synthesizing enzyme tyrosine hydroxylase. Ultrastructural examination of the m‐NTS revealed that the silver grains for 3H‐5HT were accumulated over axon terminals. The 5HT‐labeled terminals contained a heterogeneous population of vesicles and formed both symmetric and asymmetric synapses with dendrites. The recipient dendrites were either unlabeled or showed immunoreactivity for tyrosine hydroxylase. These findings support a direct serotoninergic modulation of catecholaminergic neurons within the rat m‐NTS.
A study of the reciprocal connections between the septum and the entorhinal area using anterograde and retrograde axonal transport methods in the rat brain
Authors: Alonso Angel , Köhler Christer
Published: January 2005

The reciprocal connections between the septum and the entorhinal area (EA) was studied in the rat brain using antero‐ and retrograde axonal transport methods. After injections of large volumes (2 × 100 nl) of horseradish peroxidase (HRP) conjugated to wheat‐germ agglutinin (WGA) into the medial septum (MS) and the diagonal band of Broca (dbB), anterogradely transported HRP‐WGA was found primarily in layers II and IV of the medial and lateral EA. Injections of HRP‐WGA (50–100 nl) or fluorescent dyes (50–100 nl) into different parts of the retrohippocampal region resulted in labeling, by retrograde axonal transport, of cells in the MS and dbB, both ipsi‐ and contralateral to the injected hemisphere. The labeled cells were either small (long axis of soma: 10–15 μm), round, and oval, or medium (15–25 μm) to large (25–35 μm) of fusiform or multipolar shape. By using the method of retrograde fluorescent double labeling, the septal afferents to the EA were found to give off collaterals to other parts of the hippocampal region. A much smaller number of septal cells appeared to send bilateral projections to the EA of both hemispheres. Studies employing retrograde transport of HRP in combination with acetylcholinesterase (AChE) histochemistry on the same tissue section showed that, while a large number of cells projecting to the EA contain AChE, many projecting cells are devoid of AChE reaction products. These findings suggest that the septo‐entorhinal projection consists of a cholinergic as well as a noncholinergic component.

The entorhinal efferents to the septum were studied after injections of HRP‐WGA into different parts of the retrohippocampal region. Labeled fibers could be traced through the fimbria to their terminal fields in the intermediate parts of the lateral septal nucleus and to the most lateral aspect of the vertical limb of the dbB. The cells giving rise to this projection were situated in layer IV of the medial and layers II through V of the lateral EA. Taken together, the present findings demonstrate a close anatomical relationship between the septum and the entorhinal area, in addition to the better known connections between the septum and the Ammon's horn.
Somatotopy within the medullary electrosensory nucleus of the little skate, Raja erinacea
Authors: Bodznick David , Schmidt Anne W.
Published: January 2005

The dorsal octavolateral nucleus is the primary electrosensory nucleus in the elasmobranch medulla. We have studied the topographic organization of electrosensory afferent projections within the dorsal nucleus of the little skate, Raja erinacea, by anatomical (HRP) and physiological experiments.

The electrosensory organs (ampullae of Lorenzini) in skates are located in four groups on each side of the body, and each group is innervated by a separate ramus of the anterior lateral line nerve (ALLN). Transganglionic transport of HRP in individual rami demonstrated that electroreceptor afferents in each ramus project to a separate, nonoverlapping division of the central zone of the ipsilateral dorsal nucleus. These divisions, which are distinct areas separated by compact cell plates, are somatopically arranged. The volume of each division of the dorsal nucleus that is related to a single ramus is proportional to the number of ampullae innervated by the ramus, but not to the body surface area on which the receptors are distributed. Nearly one‐half of the nucleus is devoted to electrosensory inputs from the buccal and superficial ophthalmic ampullae concentrated in a small area on the ventral surface of the head rostral to the mouth. Multiple and single unit recordings demonstrated that adjacent cells in the nucleus have similar receptive fields on the body surface and revealed a detailed point‐to‐point somatotopy within the nucleus. With threshold stimuli most single units have ipsilateral receptive fields made up by excitatory inputs from 2–5 ampullary organs.

The somatotopy within the mechanosensory medial nucleus, also revealed by the HRP fills of individual ALLN rami, appears less rigid than that in the dorsal nucleus, as extensive overlap is present in the terminal fields of separate ALLN rami.
Temporal pattern of HRP spread from an iontophoretic deposit site and description of a new HRP‐gel implant method
Authors: Fahrbach Susan E. , Morrell Joan I. , Pfaff Donald W.
Published: January 2005

In the course of examining afferents to ventromedial hypothalamic (VMH) neurons using horseradish peroxidase (HRP), we needed to know how close to an iontophoretic deposit site neurons could be proved to be retrogradely labeled. In evaluating cells near but clearly outside HRP deposit sites visualized after a 24‐hour survival period, for example, neurons which had been filled with HRP by somal or dendritic uptake could not be treated as retrogradely labeled and thus would not add to studies of intrahypothalamic connections.

Rats were given standardized iontophoretic applications of HRP into VMH (continuous positive current 0.25 μamp for 1 minute) and sacrificed after 5 or 15 minutes, 1, 4, 8, 12, or 24 hours in order to examine the pattern of HRP spread. The chromogen was tetramethylbenzidine. The volume of the application site visualized at 24 hours was less than 10% of maximum site size, which occurred at 1 hour. Since the cells located within the maximal spread boundary are candidates for nonretrograde labeling, HRP data on local connections obtained even from small iontophoretic deposits must be evaluated in the light of the demonstrated expansion and subsequent contraction of the application site. These results may also hold implications for the precision with which distant connections can be examined using the HRP retrograde method, as sites that appear discrete when visualized after 24‐hour survival may have overlapped at shorter times post‐iontophoresis.

Incorporation of retrograde tracers into polyacrylamide gels provides an effective alternative to pressure injection or iontophoresis of aqueous tracer solutions. We describe a method for filling micropipettes with HRP‐polyacrylamide gel. The pipettes are then implanted into brain sites to provide a confined pool of HRP. With postimplantation survival of 24 hour or longer, this method produces sites comparable in size to iontophoretic sites examined at 24 hours and results in improved retrograde labeling. Some results obtained with this method concerning the afferent connections of the dorsomedial hypothalamus are described.
Acetylcholinesterase‐immunoreactive axonal network in monkey visual cortex
Authors: Hedreen John C. , Uhl George R. , Bacon Sarah J. , Fambrough Douglas M. , Price Donald L.
Published: January 2005

Immunocytochemistry with antibodies to human erythrocyte acetylcholinesterase (AChE) was used to demonstrate axons containing this enzyme in the visual cortex (area 17) of macaques. AChE‐positive fibers were most dense in layers I, IIIB, IV, and VIB of Hassler and Wagner (I, IVA, IVC, and VIB of Brodmann) with three strata of more sparsely distributed fibers (layers II‐IIIA, IIIC, and V‐VIA of Hassler and Wagner [II‐III, IVB, and V‐VIA of Brodmann]). Layer I contained the most dense plexus of AChE‐positive axons, oriented horizontally. Horizontally oriented axons were also located in layers IIIB, IIIC, IV, and V of Hassler and Wagner (IVA, IVB, IVC, and V of Brodmann). Layer VIB contained axons of variable orientation, apparently afferent to cortex. Moderately stained neuronal perikarya were occasionally encountered in layer VIB and superficial white matter, but no intensely stained neurons were seen.
Neurohemal contact in the internal zone of the rabbit median eminence
Authors: Page Robert B. , Dovey‐Hartman Barbara J.
Published: January 2005

The concept of neurosecretion as the mechanism by which neural control of adenohypophyseal function is accomplished was based on the observation that long capillary loops penetrate deeply into the supra‐opticohypophyseal tract as it passes through the median eminence internal zone. However, neural contact upon these capillary loops has not been demonstrated in the mammalian median eminence. The present transmission electron microscopic investigation of the rabbit median eminence demonstrates neurohemal contact in the median eminence internal zone. Axons containing small lucent vesicles 53.3 ± 3.28 nm in diameter (mean ± SEM) or small lucent and large granular vesicles with a mean diameter of 122.4 (±3.28 nm) in their terminals make neurohemal contact with capillary loops in the internal zone and form a cuff about them. These terminals resemble terminals found in the external zone. Intravenous injection of the false neurotransmitter 5‐hydroxydopamine (5‐OH‐DA) renders small lucent vesicles granular in both the external and internal zone. The effect of 5‐OH‐DA injecting is abolished by concurrent reserpine administration. Whereas large granular vesicles in many terminals become lucent after reserpine administration, in others they remained electron dense. Viewed in the light of previous studies our findings suggest that the internal plexus arises from the external plexus and invaginates the neuropil carrying connective tissue and parvicellular axon terminals of aminergic and peptidergic systems from the external zone into the internal zone, that some elements making neurohemal contact with long capillary loops are terminals of the noradrenergic reticular infundibular tract arising outside the hypothalamus in the brainstem, and that long capillary loops form a system of repeating microvascular modules which markedly increase the surface available for neurohemal contact.
Region‐specific distribution of catecholamine afferents in primate cerebral cortex: A fluorescence histochemical analysis
Authors: Levitt Pat , Rakic Pasko , Goldman‐Rakic Patricia
Published: January 2005

The density, laminar distribution, spatial orientation, and intrahemispheric pathways of norepinephrine (NE)‐ and dopamine (DA)‐ containing axons were analyzed in a wide range of cytoarchitectonically distinct areas of cerebral cortex in the adult rhesus monkey by fluorescence histochemistry. Although the boundaries between most areas were rarely sharp, there were marked regional differences in density and distribution of monoamine afferents in different cortical regions. Fibers exhibiting typical DA‐like morphology were found only in the temporal and frontal lobes including motor and premotor areas as well as anterior cingulate and prefrontal cortices. In contrast, NE‐containing axons were present in all cerebral lobes, with notably high density in the somatosensory area and low numbers in primary visual cortex. Intracerebral distribution was characterized by a network of large preterminal axons coursing both anteroposteriorly and mediolaterally in layer VI and in the subjacent white matter. In most cytoarchitectonic regions examined, catecholamine (CA)‐containing axons exhibited a bilaminar distribution into one superficial and one deep fiber band. The location and width of the two dense bands, as well as the orientation and relative density of fibers within them, was region specific. Although fluorescent axons were found at all cortical depths, layers I, and IV usually contained relatively few fluorescent axons while layers II–III and IV–V were often densely innervated. An observation that may reflect a specialization in gyrencephalic brains is the particularly dense CA innervation around sulcal invaginations in all cerebral lobes. The present results confirm previous biochemical evidence of regional heterogeneity in the concentration of DA and NE in the primate neocortex (Brown and Goldman, '77; Brain Res. 124:576–550) and provide the first anatomical demonstration of corresponding differences in the pattern and density of CA innervation in diverse cytoarchitectonic areas in rhesus monkey. These findings raise the possibility of seletive targets and functions for CA fibers in different layers and regions of the primate cortex.
Ultrastructural localization of tyrosine hydroxylase in rat nucleus accumbens
Authors: Bouyer J. J. , Joh T. H. , Pickel V. M.
Published: January 2005

Immunocytochemical localization of tyrosine hydroxylase (TH) was used to determine the ultrastructural morphology and synaptic associations of catecholaminergic terminals in the nucleus accumbens of the rat. The brains were fixed by vascular perfusion with 4% paraformaldehyde and 0.2% glutaraldehyde. Coronal sections cut with a vibrating microtome were incubated with rabbit antiserum to TH then immunocytochemically labeled by the peroxidase‐antiperoxidase method. Immunoreactivity for the enzyme was found within unmyelinated axons and axon terminals. These terminals contained either all small clear or combined small clear and large dense core vesicles. Approximately 40% of the labeled terminals formed symmetric synapses with unlabeled proximal or distal dendritic shafts. The dendrites showed a sparse distribution of spines. Axosomatic synapses and axonal associations of the TH‐containing terminals also were detected. The recipient perikarya were usually 10–20 μm in diameter and contained an indented nucleus and abundant cytoplasm. The content of large dense vesicles and synaptic associations with somata and proximal dendrites suggest that a certain proportion of the TH‐containing terminals within the nucleus accumbens are morphologically distinct from catecholaminergic terminals within the dorsal striatum. These differences are discussed in relation to neuropeptides and functions of the dopaminergic mesolimbic and nigrostriatal pathways.
The effects of capsaicin applied to peripheral nerves on responses of a group of lamina I cells in adult rats
Authors: McMahon S. B. , Wall P. D. , Granum S. L. , Webster K. E.
Published: January 2005

In adult rats, the sciatic and saphenous nerves on one side were treated topically with capsaicin. The capsaicin treatment had the effect of increasing the latency for withdrawal of the foot from hot water; 11–22 days later, the animals were decerebrated, and cells in the superficial dorsal horn of the lumbar cord with axons projecting in the contralateral dorsolateral funiculus (DLF) were examined electrophysiologically on the treated and untreated sides of the cord. HRP was applied to cut axons of the DLF at C4, in other rats, and retrograde labelling of cells in the lumbar cord indicated that most or all of the recordings in the capsaicin‐treated animals were likely to originate from lamina 1. The dorsal horn cells, with receptive fields on the foot, showed decreased responses to electrically evoked afferent impulses in C fibres and grossly altered receptive fields.

After capsaicin treatment, the proportion of cells responding to C afferents fell from 83% to 14%. The proportion responding only to C afferents and not to A afferents fell from 9% to 0%.

The receptive fields (RFs) of these cells showed two gross abnormalities; 32% of the cells on the treated side had no apparent RF or an ill‐defined, intermittent RF, whereas such cells were rare on the untreated side or in intact animals. By contrast 49% of the cells had grossly expanded RFs with an average area of 430 mm2 against the normal average size of 130 mm2.

The antidromic conduction velocity of the axons of the cells was measured, and while there was no significant change in the number of cells with axons conducting above 3 m/second, an increased number of cells with lower velocities were recorded. It is suggested that the capsaicin treatment induced dendritic changes in cells with small axons allowing antidromic spikes to invade these cells.
Selective loss of neurites during differentiation of cells in the leech central nervous system
Authors: Wallace Bruce G.
Published: January 2005

The arborizations of annulus erector (AE) motoneurons in the central nervous system of the leech, Hirudo medicinalis, have been examined during embryogenesis to determine how segmental differences in their branching patterns arise. Early in development AE motoneurons all along the ganglionic chain had a similar central arborization, with major branches extending both rostrally and caudally along the connectives that link adjacent ganglia. As the embryo grew, the processes in the connectives elongated but failed to increase significantly in caliber and eventually atrophied and were lost. This sequence of events did not occur uniformly along the cord, however. AE motoneurons in midbody ganglia lost both anterior and posterior branches, cells near the head lost only their posterior branch, while cells near the tail lost only their anterior branch. In this way, the selective atrophy of neurites during development produced a systematic segmental difference in the morphology of homologous cells.
Further studies of the secretory process in hypothalamo‐neurohypophysial neurons: An analysis using immunocytochemistry, wheat germ agglutinin‐peroxidase, and native peroxidase
Authors: Broadwell Richard D. , Cataldo Anne M. , Balin Brian J.
Published: January 2005

The axonal endoplasmic reticulum (ER) and synaptic‐like (micro)vesicles within axon terminals of the neurohypophysis and their contribution to the secretory process in hypothalamo‐neurohypophysial neurons have been investigated cytochemically in normal mice and in mice given 2% salt water to drink for stimulation of hormone synthesis in and release from these neurons. Cytochemical techniques included the peroxidase‐antiperoxidase (PAP) immunocytochemical method for localization of neurophysin, wheat germ agglutinin‐horseradish peroxidase (WGA‐HRP) as a tracer for the anterograde axonal transport of membrane from within the perikaryon, and blood‐borne native horseradish peroxidase (HRP) as a tracer for internalized axon terminal membrane. The primary antiserum employed was directed against neurophysins I and II, the carrier proteins for the peptide hormones oxytocin and vasopressin, respectively. PAP reaction product was observed over neurosecretory granules but never over the endoplasmic reticulum, microvesicles or other organelles in axons and terminals of the neurohypophysis WGA‐HRP was delivered extracellularly to cell bodies of paraventricular neurons by cerebral ventriculocisternal perfusion. Internalized perikaryal surface membrane tagged with WGA‐HRP was recycled through the innermost Golgi saccule (GERL) from which neurosecretory granules were formed. The anterograde axonal transport of membrane‐bound WGA‐HRP was manifested within the neurosecretory granules; WGA‐HRP did not label the axonal reticulum or terminal microvesicles in the neurohypophysis. Blood‐borne native HRP endocytosed into neurohypophysial terminals was associated with a plethora of microvesicles measuring 40–70 nm in diameter and vacuoles similar in size to the 100–300‐nm‐wide neurosecretory granules. The microvesicles contributed to the formation of numerous vacuoles. The internalization of axon terminal membrane as microvesicles incorporating HRP was quantitatively greater than vacuoles in both salt‐stressed and control mice. The results suggest that in the hypothalamo‐neurohypophysial system of the mouse the axonal ER and terminal microvesicles are not involved in the transport, storage, and exocytosis of neurosecretory material and perhaps other molecules processed through the innermost Golgi saccule. Nevertheless, a prominent population of the microvesicles within axon terminals of the neurohypophysis does participate in the secretory process. These vesicles are involved directly in the internalization of the terminal surface membrane subsequent to release of secretory granule content. The recapture of neurohypophysial terminal membrane in toto may be represented as endocytic structures ranging in size from 40 through 300 nm in diameter.
Rostral ventrolateral medulla: Selective projections to the thoracic autonomic cell column from the region containing C1 adrenaline neurons
Authors: Ross Christopher A. , Ruggiero David A. , Joh Tong H. , Park Dong H. , Reis Donald J.
Published: January 2005

Anterograde, retrograde, and combined axonal transport methods were used to describe the descending efferent projections of a region of rostral ventrolateral medullary reticular formation important in cardiovascular control. We have termed this region, which contains C1 adrenaline‐synthesizing neurons, the nucleus reticularis rostroventrolateralis (RVL).

Efferent projections from the RVL innervate all segmental levels of the thoracic intermediolateral and intermediomedial columns as shown using retrograde transport of lectin‐conjugated horseradish peroxidase (HRP) or fast blue dye, and anterograde transport of either HRP or labeled amino acids. The projection is highly specific in that there are no projections to thoracic dorsal or ventral horns. This innervation corresponds to the distribution of preganglionic sympathetic neurons in the intermediolateral column. In particular, terminals surround neurons projecting to the adrenal medulla, as demonstrated by combined anterograde and retrograde transport methods at the light level.

Terminals containing phenylethanolamine‐N‐methyl transferase (PNMT) were mapped using immunocytochemical techniques. PNMT‐labeled terminals were present at all levels of thoracic intermediolateral column, in a distribution similar to that of the descending projections from the RVL. We have previously shown using double label techniques (Ross et al, '81–'83), that many of the spinal projections of the RVL originate from C1 neurons.

These data support our suggestion that certain bulbospinal neurons within the RVL, in particular the C1 neurons, are crucial for tonic vasomotor control.
Cortical projections to nuclei adjacent to oculomotor complex in the medial dien‐mesencephalic tegmentum in the monkey
Authors: Leichnetz G. R. , Spencer R. F. , Smith D. J.
Published: January 2005

Cortical projections to cell groups surrounding the oculomotor complex were studied by using the retrograde and anterograde capabilities of the horseradish peroxidase (HRP) technique in old and new world monkeys. Fluid HRP injections or transcannular solid polyacrylamide HRP gel implants were made into the oculomotor nucleus (OMN) and adjacent nuclei to label retrogradely corticofugal neurons that project to this region, and cortical HRP gel implants were made in various areas of the frontal lobe to label anterogradely the trajectories and terminations of cortico‐paraoculomotor projections and thus to confirm the retrograde findings. Projections to the paraoculomotor cell groups in the medial dien‐mesencephalic tegmentum originate almost exclusively from the frontal lobe. Both retrograde and anterograde studies confirmed that the prearcuate cortex in the concavity of the arcuate sulcus, including the frontal eye field, and, to a lesser extent, suprarcuate rostral dorsal area 6 cortex and the dorsomedial convexity (area 9), project to the rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF) in the dorsal region of the prerubral field, nucleus of Darkschewitsch (ND), medial accessory nucleus of Bechterew (NB) and dorsomedial parvocellular red nucleus (dmPRN). The premotor area 6 and motor area 4 cortex, on the other hand, give rise to projections that target a larger portion of the parvocellular red nucleus, extending rostrally into the ventral region of the prerubral field, and a rather intense projection to the ND. The interstitial nucleus of Cajal (IC) was distinguished more by its light, or lack of, projections from the frontal cortex. The inferior parietal lobule (IPL, area 7) which has certain common physiological properties with the frontal eye field (FEF area 8) related to the oculomotor system, lacked retrogradely labeled neurons in all cases where transcannular gel implants into the OMN eliminated the possibility of HRP uptake in the corpus callosum or other structures traversed in needle injections, suggesting that the IPL affects eye movement primarily through its rostrally directed corticocortical associational connections with the FEF. In additional cases, the NDNB‐dmPRN configuration of cells that receives FEF input is shown to project to the inferior olivary complex (i.e., is pre‐olivo‐cerebellar), whereas riMLF and IC give rise to descending projections in the MLF, which target extraocular muscle motor nuclei, vestibular complex, and spinal cord. The results are discussed in terms of the potential role of the cerebral cortex in eye movement mechanisms.
Thalamocortical and other synapses involving nonspiny multipolar cells of mouse SmI cortex
Authors: White Edward L. , Benshalom Gadi , Hersch Steven M.
Published: January 2005

Golgi‐impregnated and ‐deimpregnated neurons having somata in layer IV of mouse posteromedial barrel subfield (PMBSF) cortex were identified with the light microscope and then extensive portions of them were examined with the electron microscope. Dendrites of nine nonspiny multipolar cells and eight of their cell bodies were reconstructed from serial thin sections to determine the numbers and types of symmetrical, asymmetrical, and thalamocortical synapses they formed. Results of this analysis show that cells of the same general morphological class may form widely different patterns of synaptic connections: some nonspiny multipolar cells had dendrites that formed a high proportion of their synapses with thalamocortical axon terminals, whereas dendrites belonging to other cells formed only very small proportions of thalamocortical synapses. A similar diversity characterized the synaptic connections of cell bodies: some formed more symmetrical than asymmetrical synapses, others the reverse. Some formed high proportions of thalamocortical synapses, others much less. Comparisons of thalamocortical synaptic input to cell bodies and dendrites showed that one cell formed about the same proportions of thalamocortical synapses with its cell body as with its dendrites. For two other cells the proportions of thalamocortical synapses formed with their somata was about double that formed with their dendrites. The remaining five cell bodies examined formed far higher proportions of thalamocortical synapses than did their dendrites. That different nonspiny multipolar cells form such contrasting synaptic patterns suggests that included within this morphological classification are cells which are likely to have very different functional roles.
A comparison of the ultrastructure of substance P and enkephalin‐immunoreactive elements in the nucleus of the dorsal lateral funiculus and laminae I and II of the rat spinal cord
Authors: Bresnahan Jacqueline C. , Ho Raymond H. , Beattie Michael S.
Published: January 2005

The ultrastructure of substance P (SP)‐ and enkephalin (ENK)‐immunoreactive elements in the nucleus of the dorsal lateral funiculus (NDLF) and in laminae I and II of the spinal cord was examined in the rat using the peroxidate‐antiperoxidase (PAP) technique. Electron‐microscopic observations were made of a large number of immunolabelled terminals (n = 428; many followed in serial sections), axons, and immunoreactive cell bodies and dendrites which were occasionally encountered. Morphometric analysis was used to describe and compare the fine structural features of immunolabelled elements. Both SP‐ and ENK‐immunoreactive terminals contained clear synaptic vesicles and dense‐cored vesicles of similar size but the ENK‐immunoreactive profiles contained significantly more dense‐cored vesicles than SP‐immunolabelled profiles. Both SP‐ and ENK‐immunoreactive profiles in the dorsal laminae of the dorsal horn contacted mainly smaller dendritic elements. Only rarely were axo‐axonic interactions noted. The NDLF contains widely scattered cell bodies dispersed within a neuropil which is rich in synaptic complexes and is interdigitated between fascicles of myelinated and unmyelinated axons. Numerous SP‐ and ENK‐immunoreactive profiles were observed in the NDLF, many of which made asymmetric synaptic contacts with NDLF neurons. Although both the dorsal gray and NDLF contain large numbers of SP‐ and ENK‐immunoreactive elements which are similar in morphology in both regions, the NDLF can be distinguished from laminae I and II by a number of criteria, including the nature of the neuropil, principle sources of SP innervation, and the termination patterns of ascending projections.
Midbrain tegmental projections of nucleus reticularis thalami of cat and monkey: A retrograde transport and antidromic invasion study
Authors: Parent A. , Steriade M.
Published: January 2005

The projections of reticularis thalami (RE) neurons to midbrain reticular formation (MRF) and superior colliculus (SC) were studied in cat and monkey by using retrograde transport techniques and antidromic identification. The projections to MRF arise in rostral parts and lateral extent of RE nuclear complex whereas RE fibers to SC predominantly originate in the RE poster‐oventral district, Following injections of horseradish peroxidase (HRP) or fluorescent tracers into the MRF territory, retrogradely labeled neurons were always more numerous in the lateral hypothalamus and zona incerta than in the continuing RE wing. There were only very few doubly labeled RE cells following injections of fluorescent tracers into the midbrain tegmentum and thalamic nuclei, despite the fact that numerous doubly labeled cells occurred in the internal part of globus pallidum and pars reticulata of substantia nigra in the same animals. Control injections in the pons showed that RE labeling after midbrain injections was not due to uptake by fibers coursing more caudally. Antidromic identification experiments in cat confirmed the existence of a descending RE input to midbrain and further indicated that RE‐midbrain projections consist of slow‐conducting (≏1 m/second) axons.
Projections from C2 and C3 nerves supplying muscles and skin of the cat neck: A study using transganglionic transport of horseradish peroxidase
Authors: Abrahams V. C. , Richmond F. J. , Keane J.
Published: January 2005

Transganglionic transport of HRP has been used to trace the pathways and termination sites of cutaneous and muscle afferent axons entering from the C2 and C3 dorsal rami. The muscle afferent projection in the spinal cord is restricted and (apart from the ventral horn) largely confined to the intermediate gray matter. There is a muscle afferent projection to the ventrolateral main cuneate nucleus and a complex pattern of projection through the extent of the external cuneate nucleus. In contrast, the cutaneous spinal projection is abundant with extensive filling of axons in the tract of Lissauer and many termination sites in the lateral substantia gelatinosa. Axons enter the lateral gray matter of the cervical spinal cord from the dorsal columns and the dorsolateral funiculus and terminate in the lateral one‐third of the dorsal horn as far rostral as the spinomedullary junction. Axons of the tract of Lissauer form a complex web around the dorsal horn and many penetrate rostrally to the region of the spinomedullary junction, where they terminate among clusters of interstitial cells on and close to the dorsal medullary surface. Cutaneous afferent axons from the dorsal columns turn into the main cuneate nucleus and enter a dense mass of HRP‐reaction product which occupies the most ventrolateral part of the nucleus for its entire length.
The organization of immature callosal connections
Authors: Innocenti Giorgio M. , Clarke Stephanie
Published: January 2005

In newborn kittens, the anterograde transport of horseradish peroxidase, alone or bound to wheat‐germ agglutinin, indicates that callosal axons have entered selectively the restricted portions of the neocortical gray matter (e.g., the area 17/18 border) which receive callosal afferents in adults. The callosal axons do also reach regions where they lack in the adult, but there they seem not to penetrate far into the gray matter.

Neonatal injections of retrograde fluorescent tracers restricted to the gray matter in areas 17, 18, and posteromedial lateral suprasylvian area (PMLS) label neurons in the contralateral hemisphere only when the tracers were directed into regions known to receive callosal axons. In particular, injections near the 17/18 border label neurons in the contralateral hemisphere at the homologous site and at restricted, retinotopically corresponding locations in other visual areas: a pattern similar to the adult one.

In contrast, an injection reaching the white matter of areas 17 or 18 labels a wider, continuous territory extending mediolaterally over most visual areas from 17 to posterolateral lateral suprasylvian area (PLLS) and including regions which later become acallosal; in addition, labeled neurons are found in the limbic cortex medial to area 17 and in the auditory cortex lateral to PLLS, none of which is known to project to either 17 or 18 in the adult. In flattened reconstructions of the cortex, the shape of the territory labeled by each of these injections is characteristically, although somewhat irregularly, crescent shaped; its rostrocaudal position varies with that of the injection. An injection extending into the white matter of more lateral visual areas (19, 21a, PMLS) labels callosal neurons over a similar territory, which extensively overlaps that labeled by the 17/18 border injections and likewise includes regions which are acallosal in the adult.

In spite of the overlapping distribution of labeling obtained from separate injection sites, as in adults, each cytoarchitectonically (or retinotopically) defined area seems to receive from a different set of neurons, although a few neurons send bifurcating axons to more than one area.

In conclusion, injections restricted to the cortical gray matter reveal a topographic organization of juvenile callosal connections similar to that of the adult. In contrast, injections extending into the white matter and adequate to reach the transitory callosal axons which appear to be confined there reveal what appears to be an earlier organization. These two organizations probably reflect different morphogenetic factors.
Cortical connections of area 17 in tree shrews
Authors: Sesma M. A. , Casagrande V. A. , Kaas J. H.
Published: January 2005

In order to better understand the organization of extrastriate cortex in tree shrews, injections in area 17 of wheat germ agglutinin or tritiated proline were used to reveal an intrinsic pattern of connections, ipsilateral connections with area 18 and two other subdivisions of cortex, and callosal connections with areas 17 and 18 of the opposite cerebral hemisphere. Areal patterns of connections were best seen in sections cut parallel to the surface of flattened cortex. Within area 17, periodic foci of labeled terminations and cells extended from and surrounded injection sites as described by Rockland et al. ('82). Single injections produced multiple foci of labeled terminations and cells in area 18. The foci tended to fuse into short bands that sometimes crossed the width of area 18. Double injections produced more foci, and multiple injections tended to produce more continuous regions of label. An overall retinotopic pattern was evident with rostral area 17 connected to rostral area 18 and caudal area 17 connected to caudal area 18. Terminations extended through layers II–VI, with some increase in density in layer IV. Cells in area 18 projecting back to area 17 were in layers III and V. The injections also allowed identification of previously undefined subdivisions of visual cortex in temporal cortex immediately adjoining area 18. Dense reciprocal connections were observed in a 13 mm2 oval of cortex on the lateral border of the middle section of area 18 that we define as the temporal dorsal area, TD. Connections indicate a crude topographic organization with lower field represented rostrally and upper field caudally. Inputs were most dense in the middle cortical layers, and labeled cells were supragranular, and less frequently, infragranular. A 10‐mm2 oval of cortex near the posterior edge of the hemisphere, the temporal posterior area (TP), contained labeled cells after area 17 injections, but terminal labeling was only obvious in the dorsal part. Single injections sometimes produced quite separate dorsal and ventral zones of label in TP, suggesting a small separate dorsal division. A crude retinotopic order appears to exist within ventral TP, with the lower field most ventral. Labeled cells were largely supragranular. A fourth zone of ipsilateral connections was in posterior limbic cortex bordering area 17 on the ventromedial surface of the cerebral hemisphere. The callosal connections were reciprocal and included regions 1 mm wide on either side of the area 17 and area 18 border. Callosal connections were roughly homotopic. Callosal terminations included superficial layers, and projecting cells were both supragranular and infragranular. We conclude that extrastriate cortex in tree shrews contains at least three subdivisions, one of which (TD) may be the homologue of the middle temporal visual area of primates.
The development of synapses and “spoon” synaptic terminal space in the tangential vestibular nucleus: A quantitative electron microscope study
Authors: Peusner Kenna D.
Published: January 2005

This developmental study focuses on the quantitation of synapses and synaptic terminal space belonging to one identifiable population of synaptic endings, the spoon endings. Spoon endings contact only one cell type, the principal cells of the chick tangential nucleus. The tangential nucleus is an interstitial nucleus of the vestibular nerve, comprising part of the avian lateral vestibular complex. In addition to the spoon endings formed by the vestibular fibers, the principal cell bodies receive synaptic contacts from small endings of vestibular and non‐vestibular inputs.

The spoon ending's synaptic space on the target cell diminishes significantly at or around the time of hatching. This diminution is expressed in quantitative terms. The spoon ending covers 34.8% of the somatic linear surface in the embryo, 10.9% in the hatchling, and 9.8% in the 3 year old. Although the spoon ending's vesicular synapses become rare after hatching, the spoon‐ending interface exhibits a significant increase in gap‐junction density during development. Neither the spoon endings nor their target cells exhibit a constancy in synaptic junction covering during development, although the spoon endings show a constant covering of attachment plaques. In the light of the present findings, the role of very large endings in the formation of synaptic connections and the control of developmental changes in junctional complexes is discussed.
Morphology of lumbar motoneurons innervating hindlimb muscles in the turtle Pseudemys scripta elegans: An intracellular horseradish peroxidase study
Authors: Ruigrok T. J. H. , Crowe A. , Donkelaar H. J. Ten
Published: January 2005

Motoneurons in the turtle lumbar spinal cord, electrophysiologically identified as innervating a muscle belonging to a functional group, were injected with horseradish peroxidase by electrophoresis. A total of 45 motoneurons were reconstructed from transverse sections. Eleven motoneurons were identified as innervating knee extensor muscles, eight as innervating hip retractor and knee flexor muscles, 14 as supplying ankle and/or toe extensors, and 12 as innervating ankle and/or toe flexor muscles.

The cell bodies were elongated and spindle‐shaped in the transverse plane. The mean equivalent soma diameter was calculated to be 33.4 μm. The mean axon conduction velocity was 15.7 m/second. Significant, though rather weak, positive correlations were found between soma diameter, axon diameter, and axon conduction velocity. The axons of the reconstructed motoneurons did not reveal a recurrent axon collateral. However, a few unidentified motoneurons did possess such collaterals.

The dendritic trees were restricted to the ipsilateral side of the cord, but reached out in lateral, ventral, and ventromedial directions to the subpial surface. Easily recognizable and characteristic dendrites were found both in the dorsal dendritic tree and in the dorsomedial dendritic tree. Correlations were calculated between the soma diameter and (1) the number of first‐order dendrites, (2) the mean diameter of the first‐order dendrites, and (3) the combined diameter of the first‐order dendrites. In each case no correlations or only weak correlations were found. Fair correlations were observed between the diameter of a first‐order dendrite and the number of terminal dendritic branches (r = .61) and the combined dendritic length (r = .78). However, correlations between the combined diameter of all first‐order dendrites per neuron and the total number of terminal dendritic branches and the total combined dendritic length of a neuron were extremely weak.

The overall appearance of turtle spinal motoneurons is comparable to that observed in other “lower” vertebrates such as frog and lizard. However, similarities are also observed between certain morphometric parameters in turtle and cat lumbar motoneurons.
Optic axons ignore foreign denervated sites in goldfish tectum even after removal of some of their normal termination sites
Authors: Marotte J. R.
Published: January 2005

Previous experiments have shown that optic axons ignore foreign denervated territory in the goldfish tectum and preferentially reinnervate their normal layers of termination. In the present experiments ultrastructural morphometry was used to test whether this was still the case if optic axons were deprived of some of their normal termination sites. The stratum fibrosum marginale (SFM) of the tectum was partially denervated to provide foreign synaptic sites and the caudal half of the tectum was ablated at the same time. This removed approximately half the normal sites of optic termination. In the majority of cases optic axons grew into the SFM but there was no evidence of any significant formation of synapses by them in the SFM. Instead they synapsed in their normal layers. Myelinated optic axons in the SFM were present in significantly higher numbers in fish operated on in spring than in fish operated on in autumn after similar survival times. Although removal of some of the normal sites of termination promoted growth of optic axons into foreign denervated territory, the axons did not synapse there. Instead they passed through the foreign region and reinnervated their normal layers even though this meant reorganizing the optic projection within the reduced tectal space.
Bilateral cerebral metabolic alterations following lesion of the ventromedial thalamic nucleus: Mapping by the 14C‐deoxyglucose method in conscious rats
Authors: Girault Jean‐Antoine , Savaki Helen E. , Desban Marcel , Glowinski Jacques , Besson Marie‐Jo
Published: January 2005

The functional role of the ventromedial thalamic nucleus (VM) was investigated by means of the quantitative autoradiographic 14C‐deoxyglucose method. Local cerebral glucose utilization (LCGU) was measured bilaterally in 53 discrete brain areas of conscious rats 1 week and 1 month following electrolytic lesion of the VM. There was no difference observed in the LCGU values between the two groups of lesioned animals. In the VM‐lesioned rats glucose consumption was decreased in several ipsilateral (prefrontal, frontal, cingulate, sensorimotor, visual) and in some contralateral (cingulate, sensorimotor, visual) cortical areas. Furthermore, LCGU values were depressed bilaterally in the striatum, hippocampus, dentate gyrus, substantia nigra compacta, superficial layers of the superior colliculus, oculomotor complex, and cerebellar dentate nuclei. Glucose utilization was diminished also in the deep layers of the superior colliculus and in the fastigial nucleus ipsilateral to the lesion. Within the thalamus, glucose metabolism was decreased in several nuclei either bilaterally (reticular, intralaminar, paralamellar mediodorsal) or ipsilaterally (lateroposterior, ventrobasal, ventrolateral, ventroanterior, and medioventral) to the lesion. A significant correlation between the percentage of injured VM and the regional metabolic depression was demonstrated in the areas displaying the most pronounced decrease in LCGU. These results support a widespread influence of the VM on brain function extending beyond the limits of purely motor systems and reveal the consequences of a unilateral lesion of the thalamus on metabolic activity in several contralateral structures.