Robert B. Chronister

Sources of noradrenergic afferents to the hypoglossal nucleus in the rat

The sources of noradrenergic (NA) innervation to the hypoglossal nucleus (nXII) in the rat were investigated with double-labeling histochemical/immunocytochemical and lesion/degeneration techniques. Following injection of wheat germ-agglutinin conjugated to horseradish peroxidase into nXII, brain stem sections were reacted with tetramethylbenzidine, stabilized, and incubated in antiserum to tyrosine hydroxylase (TH). Double-labeled neurons were observed in three pontine sites bilaterally, although mainly ipsilaterally, that included the nucleus subceruleus (nSC; 68.75%) and the A7 (21.09%) and A5 (10.15%) cell groups. Confirmation of the above results and identification of the course taken by descending NA-nXII projections was accomplished by lesioning the rostral pons, the nSC, or the medullary catecholamine bundle (MB), the suspected route by which NA afferents reach nXII. Quantitative estimates of the reduction of TH immunoreactivity on the lesioned compared to nonlesioned side of nXII were made densitometrically. In each case, TH immunostaining was significantly decreased (75%) in the ipsilateral caudoventromedial district of nXII, the predominant target area of NA input. The results from this study establish that multiple NA sources in the pons project to nXII in the rat, the majority of NA-nXII afferents are derived from the nSC, and descending NA-nXII projections course in the MB. These data are discussed relative to tongue control.

The rodent neostriatum: a Golgi analysis.

In the adult rodent, coronal sections of Golgi impregnations of the neostriatum display a compact segregation of axon fascicles, neuronal clusters, and dendritic bundles thus forming an areolar configuration. Isolated neurons are rarely seen. The dorsomedial region of the neostriatum appears free of axon fascicles and dendritic bundles. Horizontal and sagittal sections of the neostriatum show clusters of cells parallel to axon fascicles. The neurons exhibit spine-laden dendrites with an initial spine-free segment. Neonatal impregnations exhibit a different configuration. Neonatally, cells tend to cluster but there is no bundling of dendrites. Neurons are spine-free or have protospines on the soma and the dendrites, including the initial segment. Transition from neonate to adult configuration is discernible at about 15 days after birth. The neostriatum of carnivores exhibits a different structure from the rodent neostriatum. This difference is associated with a developed anterior limb of the internal capsule in the carnivore. The axon fascicle-free portion of the carnivore neostriatum lacks dendritic bundles and pallisades. Portions near the capsule with axon fascicles appear similar to the rodent neostriatum with dendritic bundlings and pallisading. Such findings emphasize the importance of total neuronal configuration (neuronal-architectonics) in morphologic analyses.

Organization of projection neurons of the hippocampus

Abstract The origin of the fornix system was investigated by the horseradish peroxidase (HRP) technique. Small injections of HRP into the septal region resulted in labeling of neurons in both the pyramidal and nonpyramidal layers. Labeled neurons in the stratum pyramidale were seen in CA3 (bilaterally), CA2, CA1, and the adjacent subicular complex. Different patterns of uptake were observed in those hippocampal subfields. Numerous neurons in stratum oriens also displayed HRP positivity. These neurons were both polymorphic and spindle shape. The neurons were mainly restricted to the ventral portions of the hippocampus but labeled neurons were also seen in more dorsal levels. Furthermore, scattered neurons in stratum radiatum also displayed HRP positivity. These data demonstrate that some neurons generally considered to be interneurons are indeed projection neurons of the hippocampus.

Origin of the direct hippocampus-anterior thalamic bundle in the rat: A combined horseradish peroxidase-Golgi analysis☆

Abstract The origin of the direct fiber pathway from the hippocampus to the anterior thalamus was examined with the horseradish peroxidase technique and the resultant labeled neurons were compared with neurons impregnated by the Golgi technique. Injections of horseradish peroxidase into the anterior thalamus resulted in uptake of the compound by specialized areas of the subiculum and presubiculum. Labeled neurons in the subiculum were restricted to regions of subiculum distal to field CA1 and to cell laminae adjacent to the alveus. Presubicular labeled neurons were restricted to lamina principalis interna. The labeled neurons were characterized by exact position, dendritic orientation, and soma shape. Similarly appearing and located neurons were found in Golgi preparations. Based on an analysis of these types of neurons in the Golgi material, possible reciprocal connections between hippocampus and anterior thalamus are discussed.

Serotonin-containing axon terminals in the hypoglossal nucleus of the rat. An immuno-electronmicroscopic study

The morphology and distribution of serotonin-containing axon terminals in the rat hypoglossal nucleus (XII) was investigated immunocytochemically at the electron microscopic level. Serotonin-positive profiles were found throughout all regions of XII and included unmyelinated axons, varicosities and axon terminals. Most labeled profiles (68.1%) were nonsynaptic unmyelinated axons and varicosities, while synaptic profiles, ending on dendrites and somata, were seen less frequently (28.7%). The majority of labeled axon terminals (76.9%) ended on small-to-medium-sized dendrites. Most axodendritic terminals contained small, round agranular vesicles (20-55 microns), several large (60-100 microns) dense core vesicles, and were associated with a pronounced asymmetric postsynaptic specialization. By contrast, labeled axosomatic terminals were seen less often than those ending on dendrites (23.0%). Axosomatic terminals typically contained small, round, agranular and large dense core vesicles and were associated with a symmetric or no postsynaptic specialization. These results provide the structural substrates for elucidating the functional role of serotonin in tongue control.

The pattern of termination of ventral tegmental afferents into nucleus accumbens: An anterograde HRP analysis

The input pattern from the ventral tegmental area (VTA) to the nucleus accumbens was examined using the anterograde transport of HRP. Following an injection of HRP into the VTA, marked heterogeneity was seen in accumbens especially in caudal regions. Here, the terminals were restricted for most part in the dorsal portions of accumbens. In rostral accumbens, the pattern was more uniform across accumbens. Glyoxylic acid induced histofluorescence supported these findings. The present results demonstrate considerable complexity in the rostral-caudal termination pattern of A10 afferent within the nucleus accumbens.

Catecholamine innervation of the rat hypoglossal nucleus

The catecholamine innervation of the hypoglossal nucleus (XII) was investigated immunocytochemically by comparing the distribution patterns of tyrosine hydroxylase (TH), dopamine-beta-hydroxylase (DBH) and phenylethanolamine N-methyltransferase (PNMT) in the rat. Numerous TH- and DBH-positive profiles were found throughout XII, while only occasional PNMT immunoreactivity was observed. Significantly, the distribution patterns of TH and DBH immunoreactivity were coextensive with the most intense staining found ventromedially along the caudal half of XII. We conclude, therefore, that the catecholamine innervation of XII is largely noradrenergic, and that motoneurons innervating the genioglossi muscles, the principal protrusors of the tongue, are the primary targets of this input.

Interconnections between substantia Nigra reticulata and medullary reticular formation

Injections of wheat germ agglutinin-HRP into the medullary reticular formation (MRf) or the substantia nigra reticulata (SNr) revealed the presence of reciprocating fiber connections between the two areas. Large injections in the MRf demonstrated the existence of labeled neurons in the lateral portions of the SNr. Isolated injections into the parvocellular nuclei of the MRf resulted in the presence of terminal fields in the SNr particularly its lateral portions. Injections in the SNr resulted in the presence of labeled cells in the parvocellular nuclei. The significance of these findings is discussed in terms of oro-facial dyskinesias.

Effects of CCK-8 in the nucleus accumbens

The electrophysiological effects of CCK-8 were studied in the rabbit nucleus accumbens. CCK-8 was found to influence neurotransmitter (modulator) systems so as to enhance their action. For example, CCK-8 enhanced the effects of stimulation of the glutaminergic pathways, the fimbria. In addition, when CCK-8 was co-administered with dopamine and acetylcholine, their suppressive effect on the fimbria evoked response was enhanced. Therefore, CCK-8 appears to be capable of enhancing the influence of multiple neurotransmitter (modulator) systems.

The Septo-Hippocampal System: Significance of the Subiculum

The hippocampal formation has been a favorite area of anatomic investigation for a number of years. Excellent descriptions of its morphology can easily be found in the classical anatomical literature. For example, Meynert (19,20,21) divided the area into a fascia dentata, a cornu ammonis (synonomous with ammonshorn or hippocampus proper), and a subiculum or sigmoid process (this latter area included more than what is now referred to as subiculum). As the concept of a hippocampal lobule or hippocampal gyrus became elaborated, considerable confusion remained in the definition of subiculum. Some statements can be found that appear to equate subiculum with the whole so-called hippocampal gyrus. (This confusion can still be found in a modern medical dictionary (11). However, close examination of this literature reveals that the subiculum as used by many authors, referred to the areas now called subiculum, presubiculum and parasubiculum.