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We investigated sound production and the sonic motor system in the Pineconefish, Monocentris japonica. The hand-held Pineconefish produced one type of sound (main frequencies: 100–600 Hz) in both water and air. The sonic organ consists of the swimbladder and a pair of extrinsic sonic muscles originating from exoccipital of the cranium and supracleithrum and inserting on the anterodorsal surface of the swimbladder and partly on vertebrae. The sonic muscle is innervated by occipital nerve branches, not the spinal nerves. Injections of wheat germ agglutinin-conjugated horseradish peroxidase into the sonic muscle resulted in labeled sonic motor neurons ipsilateral to the injections. The labeled neurons were located in the ventral zone of the caudal medulla oblongata, forming a column of sonic motor neurons (or the sonic motor nucleus) from the level of the vagal nerve root to the rostral part of the third ventral root of the occipital nerve. The total number of motor nerve fibers contained in the rig...

The descending control of respiratory-related motoneurones in the thoracic spinal cord remains the subject of some debate. In this study, direct connections from expiratory bulbospinal neurones to identified motoneurones were investigated using spike-triggered averaging and the strengths of connection revealed were related to the presence and size of central respiratory drive potentials in the same motoneurones. Intracellular recordings were made from motoneurones in segments T5–T9 of the spinal cord of anaesthetized cats. Spike-triggered averaging from expiratory bulbospinal neurones in the caudal medulla revealed monosynaptic EPSPs in all groups of motoneurones, with the strongest connections to expiratory motoneurones with axons in the internal intercostal nerve. In the latter, connection strength was similar irrespective of the target muscle (e.g. external abdominal oblique or internal intercostal) and the EPSP amplitude was positively correlated with the amplitude of the central respiratory drive potential of the motoneurone. For this group, EPSPs were found in 45/83 bulbospinal neurone/motoneurone pairs, with a mean amplitude of 40.5 μV. The overall strength of the connection supports previous measurements made by cross-correlation, but is about 10 times stronger than that reported in the only previous similar survey to use spike-triggered averaging. Calculations are presented to suggest that this input alone is sufficient to account for all the expiratory depolarization seen in the recorded motoneurones. However, extra sources of input, or amplification of this one, are likely to be necessary to produce a useful motoneurone output.

Investigators have demonstrated pressor areas in the medullas of various species. The present study precisely localized the pressor area in the caudal medulla of the rat and determined its projections to the caudal and rostral ventrolateral medulla. The caudal medulla first was mapped grossly in rats with injections (30 nl) of glutamate (30-, 15-, and 7.5-nmol doses) placed 0.5, 1.0, and 1.5 mm caudal to the calamus scriptorius, 1.0, 1.5, and 2.0 mm lateral to the midline, and 1.8, 1.7, and 1.6 mm ventral to the dorsal medullary surface, respectively, and their arterial pressures were recorded. One of these nine injections showed significant increases in arterial pressure. We micromapped this area with a total of 27 injections of glutamate (10 nl; 5 nmol) placed 300 μm apart at 3 different dorsoventral levels. This micromapping study pinpointed the precise location of caudal pressor area (CPA) neurons in a restricted region lateral to the caudal end of the lateral reticular nucleus and ventromedial to the medullary dorsal horn near the level of the pyramidal decussation. Injections of glutamate into this spot, 1.0 mm caudal to the calamus scriptorius, 2.0 mm lateral to the midline, and 1.7 mm ventral from the dorsal surface of the medulla, induced significant increases in arterial pressure. The neuroanatomic connections of neurons in the CPA to the ventrolateral medulla were then investigated with iontophoretic injections of either the anterograde tracer biotinylated dextran amine (BDA) made into the CPA or the retrograde tracer FluoroGold (FG) injected into either the caudal or rostral ventrolateral medulla. BDA injections resulted in bouton-laden fibers throughout both caudal and rostral portions of the ventrolateral medulla. Either of the FG injections resulted in numerous spindle-shaped neurons interspersed between the longitudinal fiber bundles running through the CPA area. The proximity of the CPA neurons to the A1 catecholaminergic cell group is discussed.

Microvascular decompression (MVD) of cranial nerves has become an established treatment for trigeminal and (vago)glossopharyngeal neuralgia and for hemifacial spasm. The authors present the case of a 64-year-old man who had a 3.5-year history of severe, drug-resistant hemibody pain with sensory and autonomic disturbance. The ipsilateral trigeminal, cochlear, and glossopharyngeal function also was affected. The contralateral posterior inferior cerebellar artery was seen on magnetic resonance imaging to be indenting the caudal medulla anterolaterally, causing displacement. After MVD of the medulla, there was an immediate and complete resolution of the pain and almost complete resolution of the sensory and autonomic disturbances. The pain later recurred mildly and transiently. The residual symptoms had resolved by 2 years.

Upbeat nystagmus (UBN) is typically increased with upward gaze and decreased with downward gaze. We describe a patient with acute multiple sclerosis who developed primary position UBN with a linear slow phase waveform, in which the velocity of nystagmus was intensified in downward gaze and decreased during upward gaze. Brain MRI showed high signal lesions in the paramedian dorsal area of the caudal medulla encompassing the most caudal part of the perihypoglossal nuclei. Clinicians should be aware of possibility of a caudal medullary lesion in a patient with UBN, especially when the velocity of the UBN is increased in downward gaze.

In experiment 1, quantitative regional comparisons of the antinociceptive and cardiovascular responses produced by electrical stimulation in the caudal medulla, including regions such as the nucleus tractus solitarius (NTS), nucleus reticularis ventralis (NRV), nucleus reticularis gigantocellularis (NRGC), nucleus reticularis paragigantocellularis (NRPGC), nucleus raphe obscurus (NRO), and medial portions of the lateral reticular nucleus (LRN), were made in the rat. Electrical stimulation in all of these regions resulted in inhibition of the nociceptive tail-flick reflex, although the threshold intensity for inhibition was greater for sites in NTS compared to many sites ventral to the NTS. Antinociception was generally accompanied by an increase in mean arterial blood pressure, with the exception of sites in the NRO, where depressor responses were evoked by stimulation. Detailed comparisons between the NTS and NRV revealed that greater intensities of electrical stimulation were required to produce antinociception for sites in the NTS as compared to the NRV. There were no significant differences in threshold intensities for antinociception as a function of rostrocaudal subdivisions of the NTS, but the lateral subdivision of the NTS was significantly more efficacious than the medial subdivision. This mediolateral difference within NTS was primarily due to stimulation in medial sites producing overt movements in some animals, probably due to stimulation of adjacent midline nuclei or pathways. Within the NRV, thresholds for inhibition of the tail-flick reflex were greater for sites in the dorsal subdivision as compared to the ventral subdivision, which contains spinopetal projections from the NRM. The slopes of the lines of recruitment for inhibition of the tail-flick reflex at stimulation sites in either the NTS or NRV were both very steep, similar to other forms of antinociception. In experiment 2, the pulse duration of electrical stimulation was varied for sites of stimulation in the lateral NTS and NRV to generate strength-duration curves. This experiment confirmed that stimulation sites in the lateral NTS required greater current intensities to inhibit the tail-flick reflex than sites in the NRV. However, the chronaxies derived from the strength-duration functions for the NTS or NRV were both approximately 170 μsec, indicating that the antinociceptive effects in these regions may not be exclusively due to the stimulation of fibers of passage. These results are discussed in terms of the role of the NTS, NRV, and caudal medulla in the modulation of nociceptive responses and cardiovascular function.

The nucleus retroambiguus (NRA) is a group of premotor neurons at the transition between brainstem and spinal cord. It projects to certain motoneuronal cell groups, among which is a distinct set of motoneurons in the lumbar enlargement innervating muscles including iliopsoas, adductor longus, and hamstrings. To find out whether these NRA-motoneuronal projections are monosynaptic, injections of wheat germ-agglutinin horseradish peroxidase (WGA-HRP) into the NRA were combined with injections of cholera toxin subunit b (CTb) into the hamstring muscles. Electron microscopical examination revealed that the NRA terminal profiles make monosynaptic contacts with dendrites of motoneurons innervating these muscles. The NRA terminal profiles formed asymmetrical synapses, and contained spherical and a few dense core vesicles. These findings provide evidence of monosynaptic NRA-hindlimb motoneuronal projections which are likely to be excitatory. (C) 1997 Elsevier Science Ireland Ltd.

Eighty-four neurons in the caudal ventrolateral medullary reticular formation were antidromically activated by the stimulation of the dorsolateral funiculus in 49 urethane-anesthetized rats. Of 76 neurons, 37 had no spontaneous discharge. Of the neurons that had spontaneous discharges, 80% had firing rates between 0.1 and 15 Hz. The average conduction velocity, determined among 70 neurons, was 15.20 ± 1.23 m/s, and 87% had conduction velocities within the range of 2–30 m/s. This study further confirms the existence of spinally-projecting neurons in the lateral reticular nucleus (LRN) of the caudal medulla, and some of them are probably responsible for the descending controls of nociception from the LRN.

Albrecht, U., Lametschwandtner, A., Adam, H. 1980. The vascularization of the anuran brain. Rhombencephalon and medulla spinalis. A scanning electron microscopical study of vascular corrosion casts. (Department of Zoology, University of Salzburg, Austria.) — Acta zool. (Stockh.) 61 (4): 239–246. The vascularization of the rhombencephalon and the medulla spinalis of Bufo bufo (L.) is demonstrated by scanning electron microscopy of vascular corrosion casts. The arterial supply of the rhombencephalon is performed by central arteries. The same is shown in the medulla spinalis. The venous pathways are represented by venae craniales occipitales and by a posterior and bulbar group of the encephaloposthypophysial portal vein, by veins draining into the venae craniales occipitales, by venae spinales ventrales (for the rostral regions of the medulla) and by venae spinales laterales (in the caudal medulla). In the regions examined so far a centrifugal course of the arterial vessels is reported.

Injections of tritiated l -leucine were placed in the reticular formation of the medulla, the spinal trigeminal and lateral reticular nuclei of cats and silver grain accumulations in the inferior olivary nucleus were demonstrated by autoradiography. Cells of the reticular formation located at the junction of nuclei reticularis magnocellularis and reticularis parvocellularis in the rostral medulla and within nucleus reticularis ventralis in the caudal medulla contribute four distinct projections to the olive. Three projections are distributed ipsilaterally in the caudal part of the medial accessory olive, at mid-level of the dorsal accessory olive and in the ventrolateral bend of the principal olive, at rostral levels. There is also a small contralateral projection to the caudal part of the medial accessory olive. The spinal trigeminal nucleus sends crossed projections to the rostral part of the dorsal accessory olive and adjacent ventral lamella as well as to the caudal part of the medial accessory olive. The lateral reticular nucleus sends an extensive ipsilateral projection to the caudal part of the medial accessory olive and provides a small contribution to the same subdivision, contralaterally. All these projections converge with other known afferents to the olive.

Using the retrograde tracer technique with horseradish peroxidase (HRP), attempts were made to determine the cells of origin and the descending pathway of the tegmentoreticular projections in order to give an anatomical substrate for the physiological phenomenon of the postural atonia observed during paradoxical sleep (PS) in the cat. The HRP was injected into various parts of the pontomedullary reticular formation (RF) including the caudal raphe nuclei, nucleus (n.) reticularis gigantocellularis (Gc), n. reticularis magnocellularis (Mc), and other pontomedullary structures adjacent to the Mc. The results indicated that the HRP injection into the Mc, particularly its caudal and lateral two-thirds, resulted in specific labeling of cells located in an area just medial to the LCα together with those in the most medial part of the LCα. Bilateral lesions of these pontine structures have been reported to suppress the atonia otherwise observed during PS in the normal cat. In addition to the HRP labeled cells, we have also observed HRP filled fiber bundles directed to labeled cells in the medial part of the LCα and immediately adjacent tegmental RF area. The same course of HRP labeled fiber bundles was also observed together with HRP labeled cells in the Mc after HRP injections into the medial part of the LCα area, indicating the existence of an interconnection between the LCα area and the Mc. The location of the tegmentoreticular pathway corresponded to that of the lesions effective to suppress the muscular atonia during PS. HRP injections into the caudal medulla caudal to the Mc, on the other hand, resulted in no or almost no HRP labeled cells in the area medial to the LCα, in spite of the presence of HRP containing neurons in other parts of the pontomedullary RF areas, showing that the tegmentoreticular projections as described above terminated almost exclusively in the Mc.

Thalamic projections from the caudal medulla of the cat were examined using the method of retrograde axonal transport of horseradish peroxidase (HRP). Injections were made unilaterally in various thalamic regions. Large injections labeled cells in the subnuclei: zonalis (Vcz), gelatinosus (Vcg), magnocellularis (Vcm), reticularis dorsalis (Vcrd) and ventralis (Vcrv) medullae oblongatae. The largest number of labeled cells were in Vcz, Vcrd and Vcrv. Most of the labeled cells in Vcz and Vcrd were contralateral to the injection site, although the labeled cells in the Vcrv were bilateral. Small injections were made into the medial, lateral and dorsal regions of the nucleus ventralis posteromedialis (VPM), rostral regions of the posterior nuclei (POm and PO1), caudal POm, the nucleus centralis lateralis (CL) and the center median-parafascicular nuclear complex (CM-Pf). Most of the neurons in Vcz were found to project to the medial VPM and some to the caudal POm. A small number of cells in the Vcrd project to the medial VPM, but a large number project to the caudal POm and CM-Pf complex. The largest number of neurons projecting to the CM-Pf complex was present in Vcrv, where the labeled cells were bilateral. The types of trigeminothalamic projecting cells and the sizes of their somata were observed for different subnuclei and a considerable difference was found to exist among the subnuclei. This anatomical differentiation of the trigeminothalamic projections probably reflects a functional specialization of neuronal location since the functional properties of neurons vary according to their locations.

The subdiencephalic rat brain was mapped for sites capable of mediating prostaglandin-induced pyrexia. In conscious rats, PGE 1 , 200 ng in a volume of 1 ωl, was injected unilaterally into 412 sites between the midmesencephalon and the caudal medulla. Injections into only 12 sites caused a reproducible, short-latency core temperature increase of at least 0.5°C. None of these was located in the paramedian brainstem, which was considered a likely site of PGE 1 action because of the presence there of thermosensitive and pyrogen-sensitive neurons. Rather, the reactive loci were found in the hippocampus (5 sites) and in the vicinity of the cochlear nuclei (7 sites). Injections into only 2 sites in the latter region failed to produce pyrexia. In the hippocampus, however, injections at 31 sites in the same frontal planes as the reactive loci produced no effect. The possibility that the active hippocampal sites were associated with a distribution of injectate to PGE 1 -sensitive neurons located within hippocampal cleavage planes rather than in a circumscribed region is discussed.

The mode of termination of primary afferent fibers within the cat trigeminal nucleus caudalis was investigated by means of the transganglionic transport of horseradish peroxidase (HRP). Several types of laminar-related labeling were observed, depending upon the survival time after HRP application. At the earliest survival time (28–34 h) the highest density of labeling was found in laminae I and II. At 2 and 3 days survival laminae III and IV were heavily labeled, in addition to laminae I and II where the amount of labeling was greatly increased in lamina I, but not in lamina II. At 5 days survival time an abrupt drop of labeling occurred in laminae I and II, while this pattern was not predominant in laminae III and IV. In lamina V the pattern of labeling was less intense and not changeable through all survival times observed. These findings indicating a differentiation of the primary afferent terminals have good correspondence with a functional specialization of neuronal locations since the functional properties of neurons vary according to their locations.

The reticular formation of the brain stem is the most ancient part of the brain and the one part that is absolutely necessary to the life of the organism. It consists of large numbers of neurons and fibers, and exclusive of the adjacent cranial nerve nuclei, long ascending and descending tracts, and a few large nuclear masses such as the olives, nucleus ruber, and substantia nigra, it constitutes the core of the brain stem. It is generally thought of as extending from the caudal medulla to the interface between mesencephalon (midbrain) and diencephalon (thalamus-hypothalamus). However, a series of cell masses clustered in the medial portions of the thalamus continue forward, forming the thalamic nonspecific system and, as such, can be thought of as the reticular formation of the thalamus.

Experiments were conducted in urethan-anesthetized rabbits to determine whether vasomotor effects elicited by activation or inhibition of the caudal ventrolateral medulla depend on gamma-aminobutyric acid (GABA)ergic, glycinergic, or alpha-adrenergic receptors in the region of the rostral ventrolateral medulla, which contains the bulbospinal sympathoexcitatory neurons. Bilateral injection of bicuculline methiodide into the rostral medulla caused a dose-related reduction in the fall in arterial pressure and in the inhibition of renal sympathetic nerve activity normally elicited by chemical stimulation of neurons in the caudal medulla using local injection of L-glutamate. When both bicuculline and muscimol were injected into the rostral medulla at the same time, resting arterial pressure was maintained at base-line levels, and the sympathoexcitatory neurons remained normally excitable by local injection of L-glutamate into the rostral medulla. In the presence of this mixed antagonist-agonist GABAergic blockade, both decreases and increases in arterial pressure elicited by excitation or inhibition of neuronal function in the caudal medulla were abolished. Similar effects were not observed after blockade of glycinergic or alpha-adrenergic receptors in the rostral ventrolateral medulla. Results suggest that the depressor neurons in the caudal ventrolateral medulla alter peripheral sympathetic vasomotor activity almost entirely by an action on GABAergic receptors in the rostral ventrolateral medulla.

After trigeminal tractotomy, neurons within the trigeminal subnucleus caudalis and adjacent subnucleus reticularis dorsalis failed to respond to mechanical stimulation of the trigeminal integument, but neurons responsive to noxious stimulation of the trigeminal region were found within subnucleus reticularis ventralis (SRV) of the caudal medulla oblongata. Neurons antidromically excited by electrical stimulation of the ipsi- or contralateral SRV were found within the reticular formation adjacent to the trigeminal subnuclei oralis and interpolaris. These neurons were also responsive to noxious stimulation of the ipsilateral trigeminal region. It was concluded that neurons relaying trigeminal nociceptive input onto SRV are located within this part of the reticular formation.

In an investigation of the origin of tonic descending inhibition of dorsal horn neurones by impulses in unmyelinated primary afferents, brainstem regions were electrolytically lesioned. With each neurone studied, tonic descending inhibition was measured before and after brainstem lesions by cooling a segment of spinal cord cephalic to the recording site. Such inhibition was not reduced by lesions of areas which, when stimulated, produce analgesia. These included the periqueductal grey and the rapheareas of the midbrain and pons-medulla. Tonic descending inhibition was reduced by bilateral lesions of the ventrolateral caudal medulla in the region of the lateral reticular nuclei. Lateral reticular areas may have a functional role in the control of pain.

By studying cross-section autoradiograms of the spinal cord with dark field microscopy we demonstrated a ventral uncrossed corticospinal tract in the rat. Corticospinal fibers were labeled by the slow axoplasmic flow of a minute volume of high specific activity tritiated proline injected directly into the motor sensory cortex. The uncrossed ventral corticospinal tract was small but easily identifiable in the cervical region. More caudally the tract became less distinct and could not be traced below midthoracic levels. Only two corticospinal tracts were identified in this study: the well-known crossed dorsal corticospinal tract and the ventral uncrossed corticospinal tract described in this study. The corticospinal tract in the rat has been described as an easily identified group of fibers situated in the most ventral portion of the dorsal white funiculus of the spinal cord (1, 3, 5). Aside from a single abstract (2), we know of no report of ancillary corticospinal tracts in the rat spinal cord. Other reports indicate that the corticospinal tract in the rat spinal cord is completely crossed at the level of the caudal medulla oblongata and lies in the most ventral portion of the dorsal white columns. In the course of study of transport of tritiated proline by corticospinal axons in the rat (6), we discovered a constant ventral corticospinal tract which was easily identified by dark field illumination of cross-section autoradiographs of the spinal cord.

HISTOCHEMICAL mapping of monoamine-containing neurones in the spinal cord has established the course and terminations of abundant descending neurones that contain either noradrenaline (NA) or 5-hydroxytryptamine (5-HT). Although these neurones terminate throughout the spinal grey matter, the intermediolateral columns receive the most dense terminations of both NA and 5-HT neurones that appear to make intimate synaptic contact with sympathetic preganglionic neurones1,2. The possibility that sympathetic outflow is influenced by these monoaminergic neurones is strengthened by the locations of their cell bodies in areas of the caudal medulla oblongata that are involved in central vasomotor control3.

The distribution of catecholamine varicosities within the brainstem reticular formation of the immature cat was determined by means of the formaldehyde-induced fluorescence technique. A continuous pattern of intense, green, medium-sized varicosities exists at nearly all brainstem levels. At most of these levels the varicosities appear within the boundaries of reticular formation nuclei. However, in rostral mesencephalon, some of the varicosities of the pattern lie in proximity to perikarya of the red nucleus. In addition, numerous varicosities in caudal medulla appear to extend from the pattern into nonreticular formation nuclei. A comparable pattern of reticular formation fluorescence is absent in the rat and this finding is believed to represent a true interspecies difference.