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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.

A comparison was made of β-endorphin (B-END) concentrations versus post-translation products during the perinatal period in the hypothalamus and the caudal medulla oblongata. The concentration of B-END-like immunoreactivity did not differ statistically between embryonic day 21 (E21) and postnatal day 1 (P1) in either area. There were significant differences in forms, with a shift from larger precursors at E21 to smaller peptides at P1, with the predominant form of B-END being the 31 residue form at E21 in both regions. B-END varied between the two regions at P1, the 27-26 residue predominant in the hypothalamus, and the 31 residue in the caudal medulla.

During a 12-month period (1998–1999), microscopic evidence of neuroaxonal dystrophy (NAD) in medullae oblongata of raccoons ( Procyon lotor) was observed in 17/39 (47% prevalence in adults) from Iowa, USA. Three of the animals were kits (res in the brain were negative. Spongiotic areas often contained axonal spheroids. Degenerate neurons and axons occasionally contained amphophilic periodic acid-Schiff-positive granular material. There was a paucity of inflammatory cells in the affected areas. Since lesions were not present in kits, were either absent or mild in young adults, and were severe in older raccoons, the findings may be related to advancing age. Neuroaxonal dystrophy has not been previously reported in raccoons. Retrospective examination of raccoon brains from the eastern and northwestern areas of the country revealed very low prevalence of NAD. Because of the apparently high prevalence of this condition at this geographic location, factors other than age (genetic, nutritional, and/or environmental) may influence this degenerative process in the brains of raccoons in Iowa.

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.

In 1995, we discovered a new pathway in the cat, which originates from the nucleus retroambiguus (NRA) and terminates in a distinct set of lumbosacral hindlimb, axial, and pelvic floor motoneuronal cell groups [VanderHorst VGJM, Holstege G (1995) Caudal medullary pathways to lumbosacral motoneuronal cell groups in the cat: evidence for direct projections possibly representing the final common pathway for lordosis. J Comp Neurol 359:457-475]. The NRA is a compact group of interneurons located laterally in the caudal medulla oblongata. Its projection to lumbosacral motoneurons is thought to represent the final common pathway for male mounting and for female receptive or lordosis behavior. However, females only display lordosis behavior. However, females only display lordosis behavior when they are in estrus, which suggests that the NRA-lumbosacral pathway is only active during estrus. This raised the question of whether estrogen affects this pathway. The effect of estrogen on the NRA-lumbosacral projection was studied light microscopically, using wheat-germ agglutinin horseradish peroxidase (WGA-HRP) as a tracer. The rubrospinal pathway served as control. The density of labeled NRA fibers in their target hindlimb motoneuronal cell groups appeared abundant in estrous and very weak in nonestrous cats. Such differences were not found in the rubrospinal pathway. For electron microscopical study, the NRA projection to the semi-membranosus motoneuronal cell group was selected. In this cell group, an almost ninefold increase of labeled profiles was found in estrous versus nonestrous cats. Moreover, the semimembranous motoneuronal cell group contained labeled growth cones in estrous, but not in nonestrous, cats. The present study is the first to show that estrogen induces axonal outgrowth of a precisely identified pathway in the adult mammalian central nervous system. The possible mechanisms underlying this outgrowth are discussed.

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.

ALESSI, N. E. AND P. QUINLAN. Postnatal development of ACTH and a-MSH in the medulla oblongata of rat: a-MSH i.s the predominant peptide. PE PTIDES 6: Suppl. 2, 137-141, 1985.-ACTH and a-MSH levels were measured by radioimmunoassays in extracts of the caudal medulla oblongata of developing rats on postnatal (P) days 1-42 at 7 day intervals, and in adult rats. From PI to adulthood, ACTH increased > ! 1-fold from 7.2_ + 1.9 fmol to 82.4_+ 12.6 fmol per medulla section (mean_+ S.E.M.). In comparison, a-MSH increased >7-fold from 68.75_+ 11.0 fmol to 491 _+97.8 fmol during this time period. ACTH/p.g of soluble protein decreased during postnatal development from 0.006_+0.01 to 0.005_+0.001 fmol//zg of protein and a-MSH increased from 0.06_+0.01 fmol//zg of protein to 0.11 -+0.009 fmol//xg of protein between P1 and P7, decreased to 0.015_+0.003 fmol/#g of protein by P42 and increased to 0.03-+0.006 fmol/protein per unit protein by adulthood. These data indicate a significant shift in the levels of a-MSH detected during development with a decrease in the concentration of material occurring from early postnatal development (P1-P7) to adulthood, which does not appear to be solely related to a regional increase in protein. These studies, as well as radioimmunoassays for ACTH and a-MSH in combination with sizing chromatography of pooled extracts at P1. P7 and the adult, demonstrated the predominance of a-MSH at all ages. ACTH te-MSH Medulla oblongata Postnatal development Nucleus tractus solitarius

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.

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.

1. The medulla oblongata caudal to the obex was explored with glass capillary microelectrodes filled with fast green dye in urethan-chloralose-anesthetized cats. Concurrently, the trigeminal integument was mechanically stimulated. Two classes of units, which were activated by innocuous mechanical stimulation of the ipsilateral trigeminal integument, were identified. Both of them showed a somatotopic organization. 2. Units maximally activated by tactile stimulation of a small receptive field in the ipsilateral trigeminal integument were located in pars magnocellularis of the trigeminal subnucleus caudalis. Receptive field falling within, the mandibular distribution were found in the dorsomedial part of pars magnocellularis, maxillary fields occurred next, and ophthalmic fields were represented ventrolaterally. The rostrum (the mouth and nose) was represented just behind the obex, and the receptive field represented gradually shifted to the periphery of the face along the rostrocaudal axis, finally proceeding to dermatomes of cervical segments. At each transverse plane, tactile sensation of the most rostral segment of the represented integument projected onto the marginal zone of pars magnocellularis immediately adjacent to substantia gelatinosa, while the most peripheral segment projected onto the core of quasi-semicircular pars magnocellularis. The result is in contrast with the scheme proposed by previous investigators. 3. Within the lateral part of subnucleus reticularis dorsalis medullae oblongatae, which is ventromedially contiguous with pars magnocellularis, trigeminal units homologous with lamina V units in the spinal dorsal horn were identified. Typically, these units had a graded response in the center of the receptive field, but responded only to strong mechanical stimuli applied to the periphery of the receptive field. In the center of the receptive field, tactile stimulation of a small restricted area was effective, and the tactile receptive field showed a somatotopic organization. The mandibular distribution was represented dorsomedially, the maxillary distribution next to that, and the ophthalmic distribution laterally. Furthermore, a rostrocaudal differentiation similar to that observed with tactile units in pars magnocellularis was found. Hence, a double somatotopic representation of tactile sensation within the caudal medulla oblongata was indicated.

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.