Each canine tooth projects to all brain stem trigeminal nuclei in cat

The aim of this study was to determine in cats the precise sites of representation in the brain stem for specific teeth and their periodontal structures. Horseradish peroxidase was implanted in the pulpal chambers of either maxillary or mandibular canines and its transganglionic transport to the brain stem was studied light microscopically in tetramethyl benzidine preparations. The findings showed some differences between projections of maxillary and of mandibular canines, but a much more extensive ipsilateral central representation than previously reported for the individual teeth. The results are discussed in relation to previous anatomic and physiologic studies.     

Histochemical evidence for strictly ipsilateral innervation of maxillary canine teeth in cats

Substantial efforts by various investigators have not shown conclusively that there is a peripheral crossed innervation of feline maxillary canine teeth. In addition, the number and location of afferent cell bodies innervating these teeth has not been adequately determined. Horseradish peroxidase (HRP) was used as a retrograde neuronal marker of the afferent fibers innervating the maxillary canine teeth in 11 cats. Cavity preparations were made in the ipsilateral canine tooth and then HRP was deposited in the cavity preparation. After survival periods of 18 to 72 h, the anesthetized animals were perfused and both the ipsilateral and contralateral ganglia were processed histochemically for the localization of the HRP reaction product. Both ganglia were studied for labeled cell bodies and their locus within the ganglia. All labeled cell bodies were in the maxillary division of the ipsilateral trigeminal ganglion. The greatest number of labeled cell bodies, in excess of 200, occurred 18 h after injection of the HRP, and was higher than reported in previous studies. The results from this study clearly indicate that the primary afferent innervation of the maxillary canine teeth in the cat is strictly ipsilateral, which casts doubt on the previous claims of a crossed or “transmedian” innervation of the maxillary canine teeth in that species.     

Preganglionic innervation of the adrenal gland of the rat using horseradish peroxidase

Using the tetramethyl benzidine method for the demonstration of horseradish peroxidase, it was possible to label retrogradely spinal neurons whose axons project to the adrenal medulla in both young and adult rats. In both age groups, labeled neurons were found in the ipsilateral intermediolateral cell column of the T2 through T13 segments of the spinal cord, with most of the labeling in the T6 to T10 segments. The neurons labeled with horseradish peroxidase also demonstrated a strong acetylcholinesterase activity.     

Mesencephalic and pontine afferent fiber system to the facial neucleus in the cat: a study using the horseradish peroxidase and silver impregnation techniques.

The mesencephalic and pontine afferent fiber system to the medial or lateral part of the facial nucleus was examined in the cat by the horseradish peroxidase and the Fink-Heimer methods. The medial part of the facial nucleus was observed to receive afferent fibers mainly from the perioculomotor and the midbrain paralemniscal regions. The perioculomotor region, which included the oculomotor nucleus, the Edinger-Westphal nucleus, the interstitial nucleus of Cajal, the nucleus of Darkschewitsch, and the ventral part of the periaqueducatal gray, sent fibers to the facial nucleus bilaterally with a slight dominance of the ipsilateral distribution. The midbrain paralemniscal region, which was just medial to the dorsal part of the medial lemniscus at caudal levels of the superior colliculus, sent numerous fibers to the contralateral facial nucleus. In contrast, the lateral part of the facial nucleus received many afferent fibers from the ventral part of the parabrachial nuclei; the parabrachiofacial fibers were distributed bilaterally with a marked predominance of the ipsilateral distribution. The existence of crossed rubrofacial fibers was confirmed. Some neurons in the ventral part of the nucleus pontis centralis oralis were found to send fibers to the facial nucleus bilaterally with a predominance of the contralateral distribution.     

An inexpensive programmable stimulator for the study of thermal sensation

This report describes a simple thermal stimulator that uses a single-layer Peltier device to produce heating or cooling of the skin in the range 0-50 degrees C. The output temperature of the stimulator is determined by an external command voltage. The device incorporates a precision thermometer, and a novel feedback controller which employs out of phase gains to minimize oscillation of the stimulus temperature about the command value. Command waveforms are followed to within 0.05 degrees C for rates of up to 2 degrees C/s.     

Trigeminal nerve and temporomandibular joint of the cat: A horseradish peroxidase study

The mesencephalic nucleus of the trigeminal nerve is considered to contain the cell bodies of the first-order neurons that have peripheral connections in the temporomandibular joint capsule. Through use of retrograde transport of horseradish peroxidase, this concept is challenged. The results indicate that a relatively specific region of the mandibular division of the trigeminal ganglion of the cat contains the first-order neurons innervating the temporomandibular joint capsule.     

Muscle units divided among retractor bulbi muscle slips and between the lateral rectus and retractor bulbi muscles in cat

Single muscle units of the retractor bulbi and lateral rectus muscles were activated with brief (0.5-ms) current pulses delivered through an intracellular micropipet penetrating single motoneuron cell bodies or axons in the principal abducens nucleus of the cat. Muscle unit mechanical characteristics were measured. A total of 40 retractor bulbi muscle units was studied. Thirty muscle units were contained in 2, 3, or all 4 retractor bulbi muscle slips. Three muscle units involved one retractor bulbi muscle slip and seven units were contained in the lateral rectus muscle plus one or both of the lateral retractor bulbi muscle slips. The largest percentage of muscle units (32.5%) was contained in the two inferior retractor bulbi muscle slips. The 33 retractor bulbi muscle units, having no muscle fibers in the lateral rectus muscle, caused the contraction of 76 retractor bulbi muscle slips. Twitch tension was measured in 58 slips and maximum tetanic tension in 27 slips. The average twitch tension per measured slip was 68.0 mg and the average maximum tetanic tension was 459.8 mg. The average retractor bulbi muscle unit contraction time was 10 ms and the lateral rectus average contraction time was 7.9 ms. We propose that peripheral branching of abducens nerve axons can account for the division of muscle unit components among the retractor bulbi muscle slips and between the lateral rectus and retractor bulbi muscles.     

Distribution and morphology of sacral autonomic neurons in the cat: peroxidase labeling of efferent neurons through transected ventral roots.

The distribution and morphologic characteristics of the nucleus intermediolateralis inferior, the cell group X of Onuf, and the medial border cell group of the ventral horn, the latter two of which are also possibly autonomic in function, were investigated in the cat by means of retrograde axonal transport of horseradish peroxidase through the cut end of the transected individual sacral ventral root. The nucleus intermediolateralis inferior contributes its axons chiefly to the S2 and S3 ventral roots, and the nucleus occupies a larger triangular area of the intermediate region than that described previously. The neurons of the intermediolateral group are arranged in horizontal fashion. Cell group X contributes its axons chiefly to S1, and this is composed of longitudinally arranged, medium-size neurons having very well-developed longitudinal dendritic bundles. The medial border cells of the ventral horn, which are chiefly of medium and small size, are also labeled by bathing the S1 through C×1 roots. Their neuronal characteristics suggest that they might be also autonomic in function.     

Cholinergic projections from the midbrain and pons to the thalamus in the rat, identified by combined retrograde tracing and choline acetyltransferase immunohistochemistry

The distribution of cholinergic neurons in the midbrain and pons which project directly to the thalamus was investigated in the rat using a procedure which allows the simultaneous detection of retrogradely transported horseradish peroxidase (HRP) and immunohistochemical demonstration of choline acetyltransferase (ChAT) in the same neurons. HRP injections were placed in the dorsal half of the anterior third of the thalamus on one side which included the anteroventral nucleus as well as portions of the rostral intralaminar and reticular nuclei. These thalamic nuclei showed the highest density of immunohistochemically detectable cholinergic fibers. Neurons containing both HRP and ChAT, which represented cholinergic neurons projecting directly to the thalamus, were found in the midbrain and pons in the lateral tegmental reticular formation, parabrachial region and lateral dorsal tegmental nucleus. Ipsilateral to the injection site over 91% of the HRP labeled neurons in all of these regions were cholinergic, while an average of 60% of the cholinergic neurons had transported HRP. Contralateral to the injection site 5-6% of the cholinergic neurons in these regions were also retrogradely labeled. These findings demonstrate direct cholinergic projections to the thalamus from neurons in several regions in the tegmentum and suggest that tegmental projections to the thalamus are predominantly cholinergic.     

Topography of locus ceruleus neurons projecting to the area dentata

The distribution of locus ceruleus neurons projecting to the dorsal and ventral area dentata was studied using the retrograde transport of horseradish peroxidase (HRP). Furthermore, the possibility that collaterals of single locus ceruleus neurons innervate both the dorsal and ventral area dentata was explored with a retrograde double-label technique using HRP and the fluorescent dye 4′,6-diamidino-2-phenylindole 2 HCl (DAPI). Fusiform and multipolar neurons of the pars dorsalis of the locus ceruleus (LC_d) were labeled after injection of HRP into the area dentata. The HRP-positive cells were found almost exclusively in the dorsal LC_d after dorsal area dentata injections whereas ventral injections labeled neurons throughout the LC_d. The highest density of LC_d neurons labeled from the ventral area dentata was observed in the dorsal half of the LC_d and thus overlapped with the distribution of neurons labeled from dorsal injections. Neurons containing both HRP and DAPI were observed in the dorsal LC_d suggesting that the topographic coincidence of neurons labeled from dorsal and ventral area dentata was in part a result of single neurons having terminals in both loci.     

Afferent projections to the dorsal and ventral respiratory nuclei in the medulla oblongata of the cat studied by the horseradish peroxidase technique

The central afferent projections to cells in the region of the dorsal and ventral groups of respiratory neurones of the medulla were studied in the cat using the retrograde axonal transport of horseradish peroxidase (HRP).HRP was injected electrophoretically either in the ventrolateral nucleus of the solitary tract (the dorsal group), or into the nucleus ambiguus and retroambigualis (the ventral group). Microelectrode recordings of the activity of the respiratory neurones in these locations were obtained prior to the iontophoretic injections of the enzyme.Projections from the parabrachial region of the pons (nucleus locus coeruleus and subcoeruleus, lateral and medial parabrachial nuclei, Kölliker-Fuse nucleus), nucleus reticularis pontis oralis, retrofacial nucleus, nucleus paragigantocellularis lateralis and ventrolateral nucleus of the solitary tract to the nucleus ambiguus and retroambigualis were identified.The ventrolateral nucleus of the solitary tract was found to receive an input from the retrofacial and lateral paragigantocellular nuclei, and to have strong reciprocal connections with the nucleus paragigantocellularis dorsalis of the medulla upon which pontine Kölliker-Fuse nucleus projects, and some of the primary respiratory and cardiovascular afferences are thought to converge.     

Origin of brain stem and temporal cortical afferent fibers to the septal region in the squirrel monkey

The origins of the brain stem and temporal cortical projections to the septal region in the squirrel monkey were investigated with the horseradish peroxidase (HRP) retrograde axonal transport technique. After HRP injections placed into the septal region, labeled cells were observed in brain stem sites which generally correspond to regions which are associated with known monoamine cell groups previously identified in the primate. These structures include the nucleus locus ceruleus, dorsal tegmental nucleus of Gudden, nucleus reticularis tegmenti pontis, nucleus annularis, ventral tegmental region, and the medial aspect of the lateral hypothalamus. Temporal cortical efferent fibers to the septal region arise principally from layers II and III of the perirhinal region, suggesting the presence of a second-order olfactory innervation of this structure.     

Afferent fibers to the cingular vocalization region in the squirrel monkey

Three squirrel monkeys (Saimiri sciureus) received horseradish peroxidase injections in the anterior cingulate cortex at the level of the genu of the corpus callosum, a region yielding vocalization when electrically stimulated. Retrogradely labeled neurons were found at the cortical level within the dorsomedial and lateral prefrontal cortex (areas 9 and 10), orbital cortex (area 11), premotor cortex (areas 44, 6b, and 8), frontoparietal operculum, insula, cortex of the superior temporal sulcus, piriform cortex, subiculum, posterior cingulate, and retrosplenial cortex. Subcortical telencephalic projections came from the the claustrum, diagonal band of Broca, nucleus basalis Meynert, nuclei basalis lateralis and accessorius amygdalae, and cells at the periphery of globus pallidus. Diencephalic structures projecting to the anterior cingulate cortex were the thalamic nuclei anterior medialis, anterior ventralis, ventralis anterior, ventralis lateralis pars medialis, medialis dorsalis, pulvinaris medialis, centralis superior lateralis and limitans; the intralaminar nuclei paracentralis, centralis lateralis and parafascicularis; and the midline nuclei periventricularis, parataenialis, centralis superior, centralis inferior, centralis medialis, and reuniens. In the hypothalamus, projections came from the periventricular, lateral and posterior part, as well as the supramamillary nucleus. Midbrain afferent fibers came from the ventral tegmental area of Tsai, medial substantia nigra, reticular formation, area praerubralis, nucleus peripeduncularis, and periaqueductal gray. The most posterior labeled neurons were found in the locus ceruleus, dorsal tegmental nucleus of Gudden, nucleus annularis, nucleus centralis superior Bechterew, nucleus dorsalis raphae and the most dorsomedial part of the nucleus reticularis tegmenti pontis. Some of those projections have functional significance in the light of the hypothesis that the cingular cortex is involved in the volitional control of emotional reactions on the one hand and the influence of primary emotional reactions on intentional behavior on the other.     

Hypothalamic self-stimulation in rats with one hemisphere isolated anterior to the midbrain and the other hemisphere devoid of the telencephalon

The telencephalon was removed unilaterally in rats. In addition, the forebrain of the other hemisphere was isolated from its brain stem by a precollicular transverse cut. This preparation was then tested for self-stimulation via electrodes implanted in the region of the lateral hypothalamus and medial forebrain bundle (LH-MFB) of either hemisphere. Self-stimulation was found to be intact in both hemispheres. Possible pathways connecting the LH-MFB region of one hemisphere to the contralateral diencephalon were also investigated in the bilaterally detelencephalized rat. The technique of retrograde transport of horseradish peroxidase was used for this purpose. Some fibers from the LH-MFB of one hemisphere were found to decussate to the other hemisphere by way of the thalamic commissure. The supraoptic decussation as well as diffusely organized interdiencephalic connections provide additional routes for interhemispheric LH-MFB projections.     

Parabrachial nucleus neurons projecting to the lower brain stem and the spinal cord. A study in the cat by the Fink-Heimer and the horseradish peroxidase methods

Direct projections from the parabrachial nucleus (PBN) to the lower brain stem and the spinal cord were examined in the cat by the Fink-Heimer and the horseradish peroxidase (HRP) methods. After placing lesions in the PBN, many fine degenerated fibers were seen contralaterally in the ventromedial portions of the caudal pontine reticular formation, and ipsilaterally in the lateral portions of the facial nucleus, the regions around the hypoglossal nucleus, and the regions around the ambiguus nucleus; some degenerated fibers were traced ipsilaterally down to the spinal cord. Subsequently, HRP injections were attempted into these regions where many fine degenerated fibers were observed. In cats injected with HRP into the lateral portions of the facial nucleus, the regions around the hypoglossal nucleus, the regions around the ambiguus nucleus, or the first cervical cord segment, many HRP-labeled neurons were seen in the ventral portions of the PBN. The mean of the average soma diameters of the PBN neurons labeled with HRP injected into the regions around the hypoglossal nucleus or the first cervical cord segment was significantly larger than that of the PBN neurons labeled with HRP injected into the lateral portions of the facial nucleus or the regions around the ambiguus nucleus.     

Preoptic area unit activity during sleep and wakefulness in the cat

The spontaneous discharge of 86 preoptic area (POA) neurons was recorded extracellularly in chronically prepared cats during wakefulness (W), slow-wave sleep (SWS), and REM sleep. Of these, the percentage of units exhibiting maximal discharge rates in SWS and REM sleep (84%) was significantly greater than that of those exhibiting a maximal discharge rate in W (16%). Furthermore, those neurons that discharged rapidly in sleep (fast units) generally had a reduced discharge rate in W. Sixteen of the 86 units showed a strong tendency to discharge in bursts during SWS but not during W or REM sleep. The mean coefficient of variation and the mean discharge rate for these bursting cells in SWS were significantly greater than the corresponding values for the same cells in W and REM sleep, and for the nonbursting cells in SWS. Because POA stimulation is known to initiate behavioral and electrocortical signs of sleep, it is suggested that "fast units" in SWS with reduced discharge rates in W, may be "hypnogenic" cells.     

Cells of origin of propriospinal connections to cat lumbosacral gray as determined with horseradish peroxidase

Propriospinal cells projecting to the lumbosacral spinal cord of cat were identified using the technique of retrograde transport of horseradish peroxidase (HRP). An injection technique was used to preferentially label cells via their terminals rather than through damaged axons of passage. Large volumes (1 to 5 μl) of 35% HRP were slowly ejected from a micropipet penetrating the cord dorsum midway between the dorsal root entry zone and the midline, while the pipet was slowly withdrawn from a depth of 1500 to 2000 μm below the cord surface. This technique resulted in diffusion of HRP throughout the gray matter on the side of the injection and, usually, sperad to the contralateral gray matter. HRP-labeled cells were observed from C1 to S3 after injections in segments L3-S3. Significant differences were seen in the rostrocaudal distributions of labeled cells after injections at different lumbosacral levels: specifically, L6-L7 injections resulted in less labeling of cells at cervical and high thoracic levels than injections that included segments L3-L5 or S1-S3.     

Ultrastructural identification of physiologically recorded neurons in the cat cerebellum

Neurons from the cerebellar cortex of cats were examined in electron microscopic preparations after intracellular recording and pressure injections of horseradish peroxidase (HRP). Neurons that contained HRP reaction product within dendrites were identified as either Purkinje or Golgi II cells. This identification was based on specific ultrastructural criteria that included the presence of synapses on the surfaces of dendritic shafts or spines, the identification of the presynaptic component of these synapses, and the presence of certain visible intracellular organelles. In addition, we examined specimens that contained two types of labeled dendrites after a single HRP injection. These dendrites were identified as arising from Purkinje and Golgi II cells and were shown to interdigitate with each other in a dendritic glomerulus. Dendritic appendages or sheet-like spines emanated from the Purkinje cell dendrite and sent small finger-like protrusions that surrounded and invaginated the Golgi II cell dendrite. In this glomerulus, the dendrites were shown to approach each other, and preliminary results suggest the presence of a gap junction at this site of direct apposition. This finding supports physiologic data which suggest electrical coupling between Purkinje and Golgi II cells. In addition, the results of this study demonstrate the usefulness of combining intracellular electrophysiology with HRP staining for the ultrastructural identification of recorded neurons.     

Morphological and functional evaluation of the superior salivatory nucleus in rabbits

Horseradish peroxidase (HRP) was applied to the submandibular ganglion of the rabbit to determine the locus of the parasympathetic preganglionic neurons in the medulla. Labeled cells were recognized in the ipsilateral bulbar reticular formation at the level between the caudal end of the facial genu and the caudal part of the root of the facial nerve. The size of the labeled cells were distributed from 150 to 1150 μm² with a variety of forms such as spindle shape, triangular, and polygonal. Moreover, these cells of different sizes and forms were evenly scattered in the superior salivatory nucleus. To evaluate the physiologic functions of the bulbar salivatory nucleus, electrical stimulation was applied to the medulla, and salivary secretion and thermal change of the submandibular gland were measured simultaneously after bilateral cervical sympathectomy. A very good parallelism between the volume of salivary secretion and the magnitude of temperature change at each stimulating point suggests that secretory and vasodilator cells are intermingled with each other in the salivatory nucleus.