The ascending gustatory pathway: a Golgi analysis of the medial and lateral parabrachial complex in the adult hamster

This study examined the somal areas, dendritic features and orientations of neurons within taste responsive regions of the parabrachial complex, including the "waist" area that spans the brachium conjunctivum. The data were compared with those of a Golgi study of the gustatory zone of the nucleus of the solitary tract. Both fusiform and multipolar neurons were identified. Fusiform neurons had elongated somata that average 205 microns2 (range: 128-281 microns2) and generally possessed bipolar primary dendrites. Multipolar neurons had a stellate appearance and somal areas that averaged 230 microns2 (range: 109-443 microns2). These multipolar neurons possessed significantly more primary dendrites than fusiform neurons (4.0 versus 2.9 primary dendrites). Fusiform neurons were uncommon in the medial and lateral regions of the parabrachial complex but predominated in the solitary nucleus. Parabrachial neurons were usually larger and possessed more complex higher-order dendritic arborizations than solitary neurons. Computer-generated three-dimensional rotational analyses failed to demonstrate the strong orientation specificity in parabrachial neurons that characterizes gustatory solitary neurons. These Golgi studies described for the first time the morphological features of pontine neurons that could possibly receive ascending gustatory projections, and the morphological differences between neurons that receive direct peripheral input from taste receptors and the pontine targets of such neurons.     

Postnatal development of the rostral solitary nucleus in rat: dendritic morphology and mitochondrial enzyme activity

Morphological and metabolic development of the gustatory zone of the rostral nucleus of the solitary tract (NST) was examined in rat. Transganglionic transport of horseradish peroxidase (HRP) was used to visualize the organization of gustatory projections to the rostral gustatory NST in rats aged postnatal day 1 (P1) to P34. Golgi impregnation studies were performed to analyze morphological development of dendrites in regions of the rostral NST that were identified as anterior tongue terminal fields. Results demonstrate that afferent fibers of the anterior tongue project to the rostral NST in rats as young as P1. The volume of NST terminal fields increased from P1 to approximately P16-P20, and was adult-like after approximately P20. Developmental increases in terminal field volume resulted from a preferential expansion in the rostrocaudal plane. Planar length of first-order dendrites associated with fusiform, multipolar, and ovoid neurons, and second-order dendrites of fusiform and ovoid neurons, increased approximately three-fold between P4 and P16-20. First-order dendritic length for all morphological types was adult-like after approximately 20-25 days of age, whereas second-order dendritic length of multipolar neurons increased significantly between P30 and P60-70. Histochemical studies confirmed that activity of the mitochondrial respiratory enzymes cytochrome c oxidase (EC 1.9.3.1), succinate dehydrogenase (EC 1.3.99.1), and NADH-dehydrogenase (EC 1.6.99.3) increased monotonically during the developmental period in which planar growth of first-order dendrites was observed. The present results, in combination with results from previous studies, indicate that morphological and metabolic development fo the NST occurs concomitantly with morphological development of taste receptors and peripheral gustatory nerves.(ABSTRACT TRUNCATED AT 250 WORDS)     

Computer-generated rotation analyses reveal a key three-dimensional feature of the nucleus of the solitary tract

The dendritic processes of neurons within the nucleus of the solitary tract are oriented in the horizontal plane and often extend unusually long distances along the long axis of the brainstem. This preferred orientation is not predictable from a knowledge of the cytoarchitectonic organization of their somata within the various subnuclei of the nucleus of the solitary tract. Incoming peripheral afferent fibers, their collaterals and end-terminal ramifications are also oriented in the horizontal plane and are in alignment with the dendrites of second order neurons. These features enable single neurons to be influenced by a variety of widely distributed inputs that are related to vital autonomic functions and ingestional behavior.     

A golgi study of the class V cell in the visual thalamus of the cat

Golgi methods were used to study class V cells within the cat visual thalamus. Counterstaining was combined with Golgi staining to assess the distribution of dendrites relative to cytoarchitectural boundaries. Class V cells were encountered within all laminae of the lateral geniculate nucleus, the medial interlaminar nucleus, and the lateral posterior complex. The cells possess medium-sized perikarya and smooth and varicose or moniliform dendrites. Dendritic appendages are sparse and occur as single or serial swellings on thin processes. Many class V cells exhibit large, sparse dendritic arbors which span laminar or nuclear borders; dendrites were seen to lie within and to cross the interlaminar zones of the lateral geniculate nucleus, and extend beyond this nucleus into the perigeniculate nucleus and medial interlaminar nucleus. Class V cells of the lateral posterior complex send dendrites into the external medullary lamina. Indirect evidence favors the interpretation that the class V cells are thalamo-cortical relay cells.     

Organization of GABA and GABA-transaminase containing neurons in the gustatory zone of the nucleus of the solitary tract

Previous cytoarchitectural and electron micrographic studies have indicated that the gustatory zone of the nucleus of the solitary tract (NST) may contain local circuit neurons. It is known that neurons of the caudal "visceroceptive" NST contain GABA, glutamic acid decarboxylase (EC 4.1.1.15), and GABA-transaminase (GABA-T; 4-aminobutyrate: 2-oxoglutarate aminotransferase; EC 2.6.1.19). The present study was conducted to determine whether or not neurons in the gustatory zone of the NST of rat contain GABA and the principle degradative enzyme of GABA, GABA-T. Transganglionic transport of horseradish peroxidase (HRP) was used to identify chorda tympani (CT) nerve terminal fields. Immunohistochemical studies were combined with transport experiments to evaluate the organization of GABA immunoreactive neurons in CT terminal fields. Results show that GABA immunoreactive neurons and puncta are located within CT terminal fields. These neurons evince small ovoid morphologies resembling Golgi interneurons, and comprise an average of 18% of total neurons in CT terminal fields. Independent histochemical studies reveal that approximately 82% of GABA immunoreactive neurons within CT terminal fields exhibit GABA-T activity. Retrograde transport of HRP was used in additional studies to evaluate whether or not axons of putative GABAergic neurons project to the second-order central gustatory relay located in the caudal parabrachial nucleus (PBNc), to the caudal NST, or to regions surrounding the rostral or caudal NST. Combined studies indicate that GABA immunoreactive neurons in the gustatory NST do not project axons to the PBNc, to the caudal NST, or to regions adjacent to the rostral or caudal NST.(ABSTRACT TRUNCATED AT 250 WORDS)     

The central organization of the vagus nerve innervating the stomach of the rat

We employed the neural tracers cholera toxin-horseradish peroxidase and wheat germ agglutinin-horseradish peroxidase to examine the organization of the afferent and efferent connections of the stomach within the medulla oblongata of the rat. The major finding of this study is that gastric motoneurons of the dorsal motor nucleus (DMN) possess numerous dendrites penetrating discrete regions of the overlying nucleus of the solitary tract (NTS). In particular, dendritic labelling was present in areas of NTS which also received terminals of gastric vagal afferent fibers such as the subnucleus gelatinosus, nucleus commissuralis, and medial nucleus of NTS. This codistribution of afferent and efferent elements of the gastric vagus may provide loci for monosynaptic vagovagal interactions. A small number of dendrites of DMN neurons penetrated the ependyma of the fourth ventricle and a few others entered the ventral aspect of the area postrema, thus making possible the direct contact of preganglionic neurons with humoral input from the cerebrospinal fluid and/or the peripheral plasma. Nucleus ambiguus neurons projecting to the stomach predominantly innervate the forestomach. The dendrites of these cells, when labelled, were generally short, and extended beyond the compact cluster of ambiguus neurons in a ventrolateral direction, parallel to the fascicles of vagal efferent fibers traversing the medulla.     

Pattern and field in cortical structure: the rabbit

Previous attempts at classification of cortical neurons have been based on a number of anatomical characteristics, some of doubtful physiological significance. In seeking a functionally more relevant scheme, we have based our classification on three neural attributes; (a) size and shape of the dendritic domain, (b) presence or absence of dendritic spines, and (c) intra or extra-cortical trajectory of the axon, as revealed in Golgi stained material. Our data indicate that neurons with extra-cortically projecting axons (long axons) invariably possess spine-rich dendrites forming domains with remarkably regular horizontal parameters (i.e. modular domains). Cells with axons limited to intra-cortical paths (short axons) are characterized by spine-poor or spine-free dendrites forming domains which are highly variable in size and shape. These two categories appear dependant on structural characteristics related both to input and output functions of cortical neurons, and are called Class I and II, respectively. The significance of synaptic arrangements along horizontal and vertical components of Class I dendritic modules are compared with those for Class II cells, and possible relationships between dendritic structure and temporo-spatial activity patterns are considered.     

Subdivisions and neuron types of the nucleus of the solitary tract that project to the parabrachial nucleus in the hamster

The solitary nuclear complex (NST) consists of a number of subdivisions that differ in their cytoarchitectonic features as well as in the amounts of inputs they receive from lingual afferent axons. In this study horseradish peroxidase (HRP) was injected into the parabrachial nucleus (PBN) of the hamster to determine which of these subdivisions contain cells that project to the pons. In the rostral, gustatory division of the NST, the rostral central subdivision contains the greatest number of labelled pontine-projection neurons. The rostral lateral subdivision contains moderate numbers of labelled cells; progressively fewer labelled cells are in the ventral, medial, and dorsal subdivisions. In the caudal, general viscerosensory division of the NST, the caudal central subdivision contains the majority of labelled cells, although fewer than its rostral counterpart. Progressively fewer cells are labelled in the medial, laminar, ventrolateral, and lateral subdivisions; none in the dorsolateral subdivision. Small horseradish peroxidase injections into the pons revealed that cells of the rostral central and rostral lateral subdivisions of the NST project to the medial subdivision of the PBN, predominantly to caudal and ventral parts of the subdivision. Cells of the caudal central and medial subdivisions of the NST project to the central lateral subdivision of the PBN, predominantly to intermediate and rostral-dorsal parts of the subdivision. Outside the NST, cells in the spinal trigeminal nucleus and parvicellular reticular formation were also labelled after PBN injections. Within the rostral central and rostral lateral (gustatory) subdivisions of the NST at least two types of neurons, distinguished on the basis of dendritic and cell body morphology, were labelled after HRP injections that included the medial PBN. Elongate cells have ovoid-fusiform somata and dendrites oriented in the mediolateral plane parallel to primary afferent axons entering from the solitary tract. Stellate cells have triangular or polygonal cell bodies and three to five dendrites oriented in all directions, although one or two often extend mediolaterally. These results indicate that cytoarchitectonic subdivisions of the NST are distinguished by their efferent ascending connections. For each subdivision within the rostral, gustatory NST there is a correlation between the density of lingual inputs it receives and the density of pontine-projection neurons it contains. Within the rostral central subdivision, which contains the densest lingual inputs and the largest collection of PBN-projection neurons, cell types previously identified in studies with the Golgi method were found to send their axons to the PBN. The presence of two types of pontine-projection cells in the rostral central subdivision provides a structural basis for parallel information processing in the ascending gustatory system. Projections to the PBN from regions outside the NST provide opportunities for convergence, at the level of the pons, between inputs arising from gustatory/general viscerosensory subdivisions of the NST and from trigeminal sensory nuclei and the reticular formation.     

Maturation of neuron types in nucleus of solitary tract associated with functional convergence during development of taste circuits

Late fetal through postnatal development in sheep is a period of increasing convergence of afferent taste fibers onto second-order neurons in the nucleus of the solitary tract (NST). To learn whether neuron morphology alters in concert with convergence and neurophysiological development in NST, three-dimensional neuron reconstructions were made of cells in a functionally defined region of gustatory NST from Golgi preparations of the brainstem. Elongate, multipolar, and ovoid neurons were studied in fetuses from 85 days of gestation through the perinatal period (term = 147 days of gestation), to postnatal stages. Somal size and form, and dendritic complexity and extent, increased markedly from 85 to about 110 days of gestation in both of the proposed NST projection neurons, elongate and multipolar. From 130 days of gestation to postnatal ages, growth of dendrites of elongate neurons plateaued or declined, whereas dendrites of multipolar neurons apparently continued to increase in size and extent. In addition, spine density decreased on elongate neurons but remained stable on multipolar neurons. Morphological variables of ovoid cells, proposed interneurons in NST, did not alter over this later period. The data suggest that multipolar, not elongate or ovoid, neurons are logical candidates to receive the increasing afferent fiber input onto NST cells during late gestation. Also, neural activity from taste afferent fibers is more likely to have a role in altering NST neuron morphology at later, rather than earlier, developmental periods. © 1994 Wiley-Liss, Inc.     

Postnatal development of the parabrachial gustatory zone in rat: dendritic morphology and mitochondrial enzyme activity

Previous studies have shown that behavioral and neurophysiological responses to tastes develop during rat's postnatal life. The present experiments evaluated morphological and metabolic development of neurons in the gustatory zone of the caudal parabrachial nucleus (PBNc) of rat. Histological reconstruction studies were conducted to establish coordinate systems for PBNc gustatory zones in developing rats. Reliability of coordinate systems were evaluated in separate experiments following infusions of horseradish peroxidase in the thalamic taste area. Morphological and Golgi impregnation studies were performed to characterize neuronal and dendritic architecture in PBNc gustatory zones defined by coordinates. Conventional histochemical studies were performed for the mitochondrial respiratory enzymes cytochrome C oxidase (CO; EC 1.9.3.1) succinate dehydrogenase (SDH; EC 1.3.99.1), and NADH-dehydrogenase (NADH-DH; EC 1.6.99.3). Results show that two somatic morphologies can be statistically characterized in PBNc gustatory zones: Multipolar somatic types and fusiform somatic types. Multipolar and fusiform neurons of neonatal and adult rats project axons to the thalamic taste area, and dendrites of these neurons grow extensively between approximately 16 days after birth to approximately 35 days after birth. Activity of CO, SDH, and NADH-DH increases in the PBNc gustatory zones during the period of dendritic growth, and continues to increase slightly to approximately 45 days. These results provide the first demonstration of postnatal morphological and metabolic developmental in a central gustatory relay. Postnatal development of gustatory system therefore appears similar to that reported for other sensory systems, to the extent that morphological and metabolic development accompanies the ontogeny of taste responses.     

Synaptic relationships between the chorda tympani and tyrosine hydroxylase-immunoreactive dendritic processes in the gustatory zone of the nucleus of the solitary tract in the hamster

The toxic lectin ricin was applied to the hamster chorda tympani (CT), producing anterograde degeneration of its terminal boutons within the gustatory zone of the nucleus of the solitary tract (NST). Immunocytochemistry was subsequently performed with antiserum against tyrosine hydroxylase (TH), and the synaptic relationships between degenerating CT terminal boutons and either TH-immunoreactive or unlabeled dendritic processes were examined at the electron microscopic level. Degenerating CT terminal boutons formed asymmetric axodendritic synapses and contained small, clear, spherical synaptic vesicles that were densely packed and evenly distributed throughout the ending, with no accumulation at the active synaptic. The degenerating CT terminated on the dendrites of TH-immunoreactive neurons in 36% (35/97) of the cases. The most frequent termination pattern involved the CT and two or three other inputs in synaptic contact with a single immunoreactive dendrite, resulting in a glomerular-like structure that was enclosed by glial processes. In 64% (62/97) of the cases, the degenerating CT was in synaptic contact with unlabeled dendrites, often forming a calyx-like synaptic profile that surrounded much of the perimeter of a single unlabeled dendrite. These results indicate that the TH-immunoreactive neurons of the gustatory NST receive direct input from the CT and taste receptors of the anterior tongue and that the termination patterns of the CT vary with its target neuron in the gustatory NST. The glomerular-like structure that characterizes many of the terminations of the CT provides an opportunity for the convergence of several functionally distinct inputs (both gustatory and somatosensory) onto putative dopaminergic neurons that may shape their responsiveness to the stimulation of the oral cavity. J. Comp. Neurol. 392:78–91, 1998. © 1998 Wiley-Liss, Inc.     

Neurons of the lateral and basolateral amygdaloid nuclei: a Golgi study in the rat

Neurons in the lateral and basolateral nuclei of the rat amygdala were studied using Golgi-Kopsch and rapid Golgi techniques. According to differences in perikaryal, dendritic, and axonal morphology, three main neuronal classes are recognized. Class I neurons, the predominant cell type in both nuclei, are large, spiny neurons that vary in size in different subdivisions of the lateral and basolateral nuclei. These neurons often have a pyramidal shape, exhibiting one or two thick "apical" dendrites and several thinner "basal" dendrites. Axons of class I neurons, which appear to pass out of the nucleus of origin, usually give off several collaterals that arborize modestly in the vicinity of the cell. Class II neurons are smaller, ovoid cells that comprise approximately 5% of impregnated neurons. These neurons are characterized by spine-sparse dendrites and fairly dense local axonal arborizations. Class II neurons may be classified as multipolar, bitufted, or bipolar, depending on dendritic branching pattern. Another type of class II neuron, the amygdaloid chandelier cell, is recognized by virtue of its distinctive axon. The chandelier cell axon gives off numerous collaterals that form nestlike entanglements exhibiting clusters of axonal varicosities. Isolated chandelierlike axons of undetermined origin were observed forming multiple contacts with initial segments of class I axons. Several small, spherical class III neurons with short, varicose dendrites were observed. Axons branch profusely to form a dense tangle of collaterals in the vicinity of the cell. Both axons and dendrites establish numerous contacts with class I dendrites. This investigation, the first detailed Golgi study of the basolateral amygdala of the rat, reveals that the cytoarchitecture of this brain region in the rat is basically similar to that of the opossum and other mammals. Morphologic details described in this report should be useful in the interpretation of ultrastructural, immunocytochemical, and electrophysiological studies of the basolateral amygdala.     

Effects of early postnatal receptor damage on dendritic development in gustatory recipient zones of the rostral nucleus of the solitary tract.

The rostral gustatory zone of the nucleus of the solitary tract (NST) exhibits extensive anatomical development during the first 3 weeks of postnatal life, and this development requires the presence of intact gustatory receptors during a critical period. We have previously shown that unilateral damage induced to fungiform papillae of the anterior tongue at postnatal day 2 (P2) alters normal migration and ramification of chorda tympani (CT) axons in the rostral NST. In addition to alterations of axonal development, P2 receptor damage decreases the intraneuronal distance between neurons that project axons to the second-order central gustatory relay, located in the caudal parabrachial nucleus (PBN). This observation suggested that P2 receptor damage may alter both axonal development and dendritic development in the rostral gustatory NST. The present study evaluated potential changes in dendritic development of PBN projection neurons following either P2 or P10 receptor damage. Morphological studies were first conducted to quantitatively define somatic characteristics of neurons that project axons to the PBN. Independent experiments used fluorescent labeling combined with subsequent Golgi-impregnation to study dendritic architecture of identified PBN projection neurons. Results confirmed that P2 receptor damage alters dendritic development of PBN projection neurons located in CT terminal fields. Anterior tongue receptor damage at P2 (1) reduces planar length of first- and second-order dendritic branches, (2) reduces the mean number of second-order branches per neuron, and (3) reduces the density of spine processes on second-order dendritic branches. A critical period exists for these effects, similar to that reported for axonal development, insofar as P2 receptor damage alters dendritic development of PBN projection neurons, whereas P10 receptor damage does not. Dendrites of identified PBN projection neurons located in regions of the NST that receive primary afferent axons from the glossopharyngeal nerve are not affected by anterior tongue damage at P2. These results show that early postnatal receptor damage influences both pre- and postsynaptic development in the rostral gustatory NST. These anatomical changes are undoubtedly related to alterations in taste-guided behaviors that are observed following P2 receptor damage.     

Structural characteristics of cell and fiber populations in the optic tectum of the frog (Rana catesbeiana)

In the optic tectum Cajal's method II for neurofibrils reveals two major fiber systems in which the fibers are oriented perpendicular to one another. The outer fiber system, composed of seven laminae, lies in the superficial zone with its fibers oriented in the anteroventral to posterodorsal direction; Golgi preparations show that optic tract fibers enter the outer system laminae at the tectal margin, run within single laminae, and end in arborizations that are elongated in the dominant fiber direction. The intermediate fiber system is composed of bundles of fibers in lamina 7 of Ramón and the superficial zone; its fibers are oriented in the anterodorsal to posteroventral direction. A third deep fiber system, forms fibrous laminae in the region between lamina 7 and the ependyma. In Golgi impregnations the deep cells are of two major classes: pyramidal cells with relatively narrow dendritic arbors in the superficial zone and candelabra cells with broad arbors. Many pyamidal cell dendrites have lamellar branching patterns such that terminal bushes occur within one or another of the outer system laminae. The multipolar cells within lamina 6 and lamina 7 of Ramón send large, unbranched axons directly into the deep medullary lamina and appear to be the major efferent neurons. Near the pia the perikarya of superficial granule cells give rise to single processes that branch repeatedly within the superficial zone.     

Organization of anterior dorsal ventricular ridge in snakes

Anterior dorsal ventricular ridge (ADVR) is a major telencephalic structure in reptiles. The intrinsic, efferent, and afferent connections of ADVR were studied in water snakes (Natrix sipedon) and garter snakes (Thamnophis sirtalis) using orthograde degeneration and Golgi techniques. ADVR in these snakes contains four zones oriented concentric with the ventricular surface and named zones A, B, C, and D, with zone A being the most peripheral. Each zone contains a characteristic population of neurons. Zone A neurons have dendrites which extend obliquely through zone A and into zone B. Zone B neurons have dendrites with a high density of dendritic spines and axons which ramify in zone A concentric with the ventricle, typically bearing large varicosities about 5 μ in length. Zone C neurons have dendrites with a low density of dendritic spines and axons which ramify within about 300 μ of the soma, typically bearing small varicosities about 3 μ in length. Zone D neurons resemble those in zone C, except that their axons may course ventrally out of ADVR into the subjacent striatum. Lesions placed superficially in ADVR produce terminal degeneration which is restricted to ADVR in Fink-Heimer preparations. Lesions which damage the ventral part of ADVR produce degeneration in striatal nuclei (medial striatal nucleus, intrapeduncular nucleus, and perifascicular complex) as well as in the ventral two-thirds of the posterior dorsal ventricular ridge. Unilateral transections of the midbrain produce degeneration in a system of thick caliber axons, with thin collaterals, which enters ADVR caudally behind the anterior commissure and rostrally through the lateral forebrain bundle. These fibers are oriented primarily along the radii of ADVR and confined predominantly to zones B, C, and D. Lesions of the dorsal thalamus produce degeneration in a system of thin caliber axons which enters ADVR rostrally through the lateral forebrain bundle. These fibers course radially through zones C and D and then turn to run concentric with the ventricle in zone B. These observations suggest that snake ADVR consists of two fundamentally different parts. Neurons in zones A and B interact strongly with neighboring neurons through somatosomatic and axodendritic contacts and participate in connections which run concentric with the ventricle. Neurons in zones C and D participate in connections which run radially. Some of the neurons in zone D, and possibly some in zone C, project to the striatum. Neurons situated near the ventral border of ADVR are the only source of ADVR efferents. Neurons in each zone interact with those in neighboring zones.     

The dendritic architecture of the visual pretectal nuclei of the rat: a study with the Golgi-Cox method

The dendritic architecture of the neurons of the visual pretectal nuclei in the rat was studied with the Golgi-Cox method. The olivary pretectal nucleus (PO) is characterized by distinctive neurons with a gnarled, tufted, richly branched dendritic arbor forming a dense neuropil within the nucleus. The distinct dendritic morphology of the olivary pretectal neurons enables this nucleus to be identified at all levels of the pretectum in Golgi-impregnated preparations. Rostromedially, the PO is surrounded by peripheral neurons whose dendrites wrap around the surface of the PO. The nucleus of the optic tract (NTO) contains three types of cells: (1) superficial horizontal cells whose dendrites extend out transversely; (2) large multipolar neurons whose dendrites spread out predominantly in a transverse plane, and (3) small to medium multipolar neurons with varying dendritic architecture. The posterior pretectal nucleus (PP) is composed predominantly of (1) multipolar cells with horizontally and vertically oriented dendrites extending out transverse to the optic axons; (2) piriform cells with dendrites extending dorsally toward the brachium; and (3) small multipolar neurons. The presence of superficial horizontal and large multipolar neurons in the NTO distinguishes the NTO from the PP in Golgi preparations. The horizontally oriented dendrites of many of the multipolar neurons in the PP give this nucleus an appearance distinct from that of the NTO. The differences in dendritic morphology between the visual pretectal nuclei in the rat permit identification of these nuclei at all levels within the pretectum. The boundaries of these nuclei, as determined in the Golgi-Cox preparations, correlate quite well with the boundaries defined by studying retinal projections (Scalia and Arango, '79).     

Golgi study on neurons and fibers in Nucl. rotundus of the thalamus in chicks.

The structural arrangement of nucleus rotundus was studied by Golgi method. Large, multiangular principal neurons, their dendrites and dendritic terminals were observed. The long dendrites and their side-branches course parallel and/or perpendicular to each-other and they are arranged about in dorso-ventral latero-medial and rostro-caudal directions. The dendrites and their side-branches develop characteristic terminal branchings. These dendritic terminals overlap each-other and the area is called dendritic terminal field. The tecto-rotundal fibers traverse the nucleus in large bundles and the final sections of fibers join to the dendrites of principal neuron and terminate in dendritic terminal fields.     

Golgi studies of the neurons in layer I of the dorsal horn of the medulla (trigeminal nucleus caudalis)

Two kinds of pyramidal neuro ns and two kinds of multipolar neurons have been identified in layer I in the adult cat on the basis of thier dendritic morphology. The spiny pyramid emits an apical dendrite which beings dividing within 50 μm of the cell body and gives rise to an extensive dendritic arbor in which some second and third order branches extend for over 100 μm. The primary branches of the basal dendrites divide into secondary branches within 20 μm of the cell body. At each of these divisions, one daughter secondary branch will turn 180° and course in the direction of the apical dendrite. It then undergoes further branching and becomes intermingled in the apical dendritic arbor. These recurrent basal dendrites and the apical dendrites are charcterized by numerous long-necked spines. The other secondary basal branch either courses at right angles to the apical dendrite or droops basally away from it. Many of these basal dendrites are not as robust and extensive as the other dendritic branches. They may end without further branching or when they do branch they tend to be thinner and shorter with some showing signs of stunting. Smooth pyramids differ from the spiny pyramids in several respects. Their dendritic arbors contain fewer, more widely spaced spines and are more expansive than those of the spiny pyramids. While they still send branches into the apical arbors many branches run basally away from the cell body for considerable distances to give the entire dendritic field a more circular appearance. The compact multipolar neuron is found in the inner half of layer I. The long axis of its compact dendritic arbor (～ 50 μm wide) is oriented in the rostrocaudal axis of the layer. Most of its dendritic branches lie to one side of the cell body squeezed between the axon bundles of the inner half of layer I. The loose multipolar neuron in found throughout the layer. Its loose dendritic arbor is at least 200 μm wide and, like the spiny pyramid, gives rise to several dendrites which terminate abruptly with little branching and without much change in diameter. The dendrites of all four layer I neurons are confined within layer I and its extensions into the spinal V tract. These four layer I neurons are considered to be Golgi type I projection neurons on the basis of the morphology of their initial axonal segment. Golgi type II inteneurons are not found in layer I.     

Neurokinin-1 receptor immunoreactivity in the nucleus of the solitary tract in the hamster.

Substance P (SP) modulates the activity of taste-responsive neurons in the gustatory zone of the nucleus of the solitary tract (NST) in the hamster. The distribution of the neurokinin-1 (NK1) receptor (i.e. the SP receptor) was mapped and compared with the distribution of SP immunoreactivity to identify the sites of ligand-receptor interactions. NK1-immunoreactive puncta and somata were located mostly in the rostral lateral, upper half of the rostral central and medial NST subnuclei. These subnuclei also contained intense SP-immunoreactive puncta, and are known to receive substantial inputs via gustatory and somatosensory afferent fibers. The ventral subnucleus, which is involved in visceromotor reflexes accompanying ingestion, contained little NK1 or lighter SP-immunoreactivity. These findings suggest that SP modulates taste activity destined for the ascending gustatory pathway at the level of the first central synapse in the gustatory pathway.     

Morphological characterization of slow and fast pyramidal tract cells in the cat

In adult cats the morphology of slow and fast pyramidal tract (Pt) neurons was studied following intracellular HRP injections and Golgi impregnation. Both types of neurons are pyramidal cells and their soma are all located in the fifth layer of the motor area. As a rule, fast Pt neurons have large somata and their basal and apical dendrites occupy a larger territory in the tangential plane. In layer I, terminal apical dendrites of fast Pt neurons are smooth and divide poorly while those of slow Pt neurons bear a moderate amount of spines and branch profusely. Midway between the pia and layer V, in the third layer, the apical shafts of both types of Pt cells run upward with little branching. These shafts are more numerous in fast Pt cells (7 to 16) and they are almost devoid of spines. Those of slow Pt cells in layer III number between 5 and 9 and are densely covered with spines. Oblique and horizontal branches of slow and fast Pt neurons extend in layer V and some of them invade the lower part of layer III. It is suggested that this zone corresponds to a true fourth layer in the motor area. In both types of cells oblique and lateral branches bear numerous spines. Within the basal dendritic territory of Pt cells, one has to distinguish two dendritic systems: a short and a long one. The former spreads downward obliquely and appears to remain within layer V. The latter is made up of long descending vertical (antiapical) and oblique dendrites (tap root). While both types of cells may have long antiapical dendrites that run down radially to the lower part of layer VI, tap root dendrites which expand laterally below the cell body for considerable distances are a distinctive feature of fast Pt neurons. Though basal dendrites of all Pt cells bear spines, their number, distribution and shape are very variable in fast Pt cells.