Lateral Cuneate Nucleus Research Articles

Distribution of vestibular afferents that innervate the sacculus and posterior canal in the gerbil.

The central distribution of afferents that innervate the macula of the saccule and the crista of the posterior canal was assessed in the gerbil following the direct injection of horseradish peroxidase (HRP) separately into the sensory neuroepithelia of each peripheral receptor organ. Ganglion cells innervating the posterior canal were located in the caudal part of the inferior ganglion, while those cells innervating the saccule were located in the rostral part of the inferior ganglion, scattered in the superior ganglion, and concentrated at the junction (isthmus) between the two. The paths of the central axons of these two groups of ganglion cells through the vestibular root and their division into ascending or descending pathways were similar. However, the distributions of their terminals were different. The posterior canal projected to medial parts of the vestibular nuclear complex. Terminals were found in the medial and superior vestibular nuclei. The posterior canal also projected to the uvula of the cerebellum. The saccule projected to more lateral-lying brainstem areas. Terminal fields were located in the lateral and descending vestibular nuclei and cell group y. Saccule projections outside the vestibular complex were observed to the lateral cuneate nucleus, the N. gigantocellularis, and the cerebellar cortex. Of the eight areas receiving primary afferent projections from these two organs, only within the medial and descending vestibular nuclei and the cerebellar cortex were overlapping projections observed.

Equine laryngeal hemiplegia part V. central nervous system pathology

Evidence of long central nerve fibre degeneration (axonal spheroids) in the lateral cuneate nuclei was found in all eight Thoroughbreds affected clinically and subclinically with equine laryngeal hemiplegia, but in only one of six control animals. It was considered that these spheroids may signify a central nervous component of the disease process of laryngeal hemiplegia although until further investigations are performed no firm conclusions regarding the relationship of these findings with laryngeal hemiplegia could be made. Examination of the left and right nucleus ambiguus of clinical and subclinical laryngeal hemiplegic horses revealed no pathological alterations.

Neck muscle afferent projections to the brainstem of the monkey: implications for the neural control of gaze.

Brainstem projections of first-order afferent neurons that innervate the suboccipital muscles of the monkey have been determined by using the technique of transganglionic transport of wheat-germ-agglutinin-conjugated horseradish peroxidase (WGA/HRP) and HRP. Neck muscle afferents distribute to several distinct regions located within the caudal brainstem and rostral spinal cord. Terminal labeling was heaviest within the ventral portion of the ipsilateral lateral cuneate nucleus. Muscle afferent terminals also distributed to ventrolateral portions of the pars triangularis division of the cuneate nucleus. Projections were consistent with the known somatotopic (i.e., both place and modality) organization of the cuneate nucleus. Moreover, neck muscle projections to the cuneate nucleus were, in part, coincident with those previously demonstrated for the extraocular muscles (Porter: J. Comp. Neurol. 247:133-143, '86). Sparse terminal projections were noted in the central cervical nucleus. In addition, light terminal labeling was present in group x of the vestibular complex and in an ill-defined region along the lateral margin of the brainstem. Present observations, which provide the first complete description of the central distribution of neck muscle afferent neurons in the primate, may contribute to the known substrate for eye/head coordination.

Progressive axonopathy: an inherited neuropathy of boxer dogs. 2. The nature and distribution of the pathological changes.

This report describes the neuropathology of progressive axonopathy (PA), an autosomal recessive inherited neuropathy of Boxer dogs, which affects CNS and PNS. The nerve roots contain numerous myelin bubbles and proximal paranodal axonal swellings containing vesicles, vesiculo-tubular profiles and disorganized neurofilaments. The myelin sheath overlying such swellings is often attenuated. As the disease develops there are progressive changes in the myelin sheath with thinning at paranodal and internodal locations, loss of myelin from lengths of axon and the formation of short internodes with disproportionately thin sheaths. The abnormalities show a very definite selectivity for nerve roots and proximal nerves. Conversely, the frequency of degeneration and regeneration is greater distally except in the cervical ventral roots which contain numerous regenerating clusters. In the CNS numerous axonal spheroids are found in the lateral and ventral columns of the spinal cord and in various brain stem nuclei, particularly the superior olives, accessory cuneate nuclei and lateral lemniscus and its nucleus. Axonal degeneration which occurs mainly in the cord shows no obvious tract or proximal/distal selectivity. The optic pathways are also involved, predominantly adjacent to the chiasma. The autonomic nervous system is affected and distal limb muscles show varying, but usually minor, degrees of neurogenic atrophy. The condition, which has no obvious direct parallel in human or veterinary medicine, shows gross disturbances of axon-glial inter-relationships in both CNS and PNS.

Neuroaxonal dystrophy of the accessory cuneate nucleus in horses.

Data were collected from 37 horses with a neurologic disability and compared to a group of 34 normal horses. Affected horses had neuroaxonal dystrophy, gliosis, vacuoles, and sometimes pigment localized to the accessory cuneate nuclei with minimal or no changes in the spinal cord and no changes in the proximal peripheral nerves. The focal nature of the change and usual absence of significant light microscopic spinal cord or peripheral nerve changes are different than previously described equine neuropathologic conditions.

Distribution of primary vestibular fibers in the brainstem and cerebellum of the monkey

Attempts were made to determine the central projections of ganglion cells innervating individual semicircular ducts in the monkey by implanting or injecting tritiated amino acids (leucine and/or proline), or horseradish peroxidase (HRP), selectively into a single ampulla. Central transport via the vestibular ganglion in animals receiving isotope implants or injections fell into three categories: (1) transport from ganglion cells innervating all receptive elements of the labyrinth, (2) transport from ganglion cells innervating the three semicircular ducts, and (3) transport from cells of the inferior vestibular ganglion innervating the posterior semicircular duct. Transneuronal transport of isotope was observed in secondary vestibular fibers in animals where proline was used and survival exceeded 12 days. Transneuronal labeling of secondary auditory fibers was independent of the [ 3H]amino acid used, and occurred with survivals of 10 or more days. HRP implanted into the ampulla of the lateral semicircular duct in several animals produced retrograde transport to efferent vestibular and cochlear neurons, but did not result in transganglionic labeling of primary vestibular or auditory fibers. Primary vestibular fibers terminate throughout the superior (SVN) and medial vestibular nuclei (MVN). Within SVN, terminals are most pronounced in its central large-celled portion, but extend into peripheral parts of the nucleus, except for a small medial area near its junction with the oral pole of MVN. Primary projections to MVN are homogenously distributed throughout the nucleus excepting a small circular area of sparse terminals along its ventral margin. Primary vestibular afferents terminate mainly in rostral and caudal portions of the inferior vestibular nucleus (IVN), but do not reach cell group ‘f’. Projections to the lateral vestibular nucleus (LVN) are restricted to its ventral part. Primary projections to the accessory vestibular nuclei reach the interstitial nucleus of the vestibular nerve (NIVN) and cell group ‘y’. Fibers project beyond the vestibular nuclei (VN) to terminate ipsilaterally in the accessory cuneate nucleus (ACN), the subtrigeminal lateral reticular nucleus (SLRN), and well-defined portions of the reticular formation (RF). Projections to SVN and MVN are derived primarily from ganglion cells innervating the semicircular ducts, while projections to caudal IVN, cell group ‘y’ and ACN are related mainly to macular portions of the vestibular ganglion. NIVN receives both macular and duct afferents. Posterior duct afferents terminate in medial portions of SVN, in rostrolateral portions of MVN, and in rostral IVN. Transneuronal transport of isotope increases the volume of terminal label in the ipsilateral VN, but not in dorsal LVN, or cell groups ‘f’ or ‘x’. The quality of transneuronal transport in secondary vestibular fibers is dependent upon: (1) survival time, (2) proximity to the VN, and (3) the excitatory or inhibitory nature of the projection. Primary vestibulocerebellar fibers terminate heavily in the ipsilateral nodulus and ventral uvula. Lesser projections reach the flocculus, deep folia of vermal lobules V and VI, and the lingula. Primary vestibulocerebellar projections terminate as mossy fiber rosettes in the granular layer of these cortical areas. No primary vestibular fibers terminate in the primate fastigial nuclei.

Vestibular nerve input to neck and shoulder regions of lateral cuneate nucleus

Axonal transport of tritiated leucine by the vestibular nerve was observed in regions of the ipsilateral lateral cuneate nucleus (LCN) that were determined electrophysiologically to receive somatosensory input from the neck and shoulder and to respond to electrical stimulation of the vestibular nerve. Regions of the LCN receiving input from more distal musculature did not receive vestibular input.

Projections of nucleus caudalis and spinal cord to brainstem and diencephalon in the hedgehog (Erinaceus europaeus and Paraechinus aethiopicus): a degeneration study.

In the light of hypotheses related to the evolution of pain-carrying systems in mammals, terminal projection fields in brainstem and diencephalon of efferents of nucleus caudalis (NC) of the spinal trigeminal complex and spinal cord were determined in hedgehog by using Nauta-Gygax and Fink-Heimer silver techniques for degeneration. Unilateral NC lesions resulted in medullary degeneration in the ventral portion of NC contralaterally and bilaterally in cuneate nucleus (CU) and reticular formation. Pontine degeneration was noted ipsilaterally in medial (PBM) and lateral (PBL) parabrachial, facial motor (VII), and interpolar, oral, and main sensory trigeminal nuclei; degeneration in reticular formation was bilateral. Midbrain degeneration was seen bilaterally in caudal superior colliculus (SC), inferior colliculus (IC), periaqueductal gray, and tegmentum. In thalamus, projections to ventroposterior nucleus (VP) were contralateral and concentrated in a crescent extending along the lateral one-third-to-one-half and ventral border of the nucleus. Bilateral degeneration fields were noted in a dorsomedial sector of the "ventral nuclear field," posterior complex (PO), and mediodorsal nucleus (MD), the degeneration always heavier contralaterally in these nuclei. Sparse degeneration was noted in the medial most portions of the medial geniculate nuclei bordering PO and VP. In rostral diencephalon, bilateral degeneration was traced from the inferior thalamic peduncle to the lateral hypothalamic area (LH). Unilateral spinal cord lesions made between C7 and T1 vertebrae resulted in medullary degeneration in NC contralaterally, ipsilaterally in CU and lateral cuneate nucleus, and bilaterally in gracile nucleus, inferior olivary complex, and reticular formation. Pontine degeneration was limited to ipsilateral PBL and bilaterally to VII. Midbrain degeneration was found bilaterally in IC, SC, nucleus sagulum, and tegmentum; a minor projection was noted in interpeduncular nucleus. In thalamus, projections were confined to ipsilateral PO and zona incerta. In rostral diencephalon bilateral fields were noted in LH. NC terminations in PO and VP parallel results of research in hedgehogs on thalamic projections of the dorsal column nuclei (Jane and Schroeder, '71), and particularly the location in VP of most cells responsive to stimulation of the face (Erickson et al., '67). This suggests that somatic input from NC, some of which may be pain-specific, reaches thalamic areas, a portion of whose neurons are characterized as polymodal and at least partially convergent for somatotopy. These results are consistent with the thesis that specific sensory thalamic nuclei evolved from a diffuse sensory region. Response properties of neurons in the dorsomedial portion of the ventral nuclear field, an area which are also received NC efferents, are not known. Last, NC projections to MD and LH implicate the role of "limbic" aspects of nociception.

Motion-induced alterations in 2-deoxyglucose uptake in brainstem nuclei of squirrel monkeys: autoradiographic and liquid scintillation studies.

Each of 8 young adult female squirrel monkeys were injected via a femoral vein cannula with 167 microCi/100 g body weight of 2-(1,2-3H)-deoxy-D-glucose (2-DG) (New England Nuclear, 37.3 Ci/mmol) in 0.5 ml sterile saline. 4 additional female squirrel monkeys were injected in the same manner with 100 microCi/100 g body weight of the (3H)-2-DG. 2 h after this initial injection the original 8 animals were injected with 16.7 microCi/100 g body weight of 2-(1-14C)-deoxy-D-glucose (51.3 mCi/mmol) in 0.5 ml sterile saline. The 4 additional animals were injected with 25 microCi/100 g body weight of the (14C)-2-DG. Half of the animals each dose level were restrained in the upright position with Velcro straps and a nontraumatic moulded plastic head holder on a modified animal restraint board [Withrow and Devine, 1972] with the head in the sagittal plane but tilted forward about 20 degrees. They were then subjected to horizontal rotary motion at 25 rpm together with a vertical movement of 6 inches at 0.5 Hz for 1 h in a lighted room. The other half of the animals at each dose were restrained in the same manner and maintained in a quiescent state. At the end of this period each animal was anesthetized with ketamine, and the brain was quickly dissected out and frozen in isopentane cooled to -60 degrees C with dry ice. Transverse cryostat sections (-15 degrees C) of the brainstem were cut alternately at 200 and 20 microns from the nucleus gracilis caudally through the superior vestibular nucleus rostrally. Micropunch samples of the individual vestibular nuclei, and other brainstem nuclei and areas were obtained from the 200-microns sections with a modification of the method of Eik-Nes and Brizzee with a small stainless steel punch measuring 850 microns in diameter. The frozen punch samples were prepared for liquid scintillation counting (Beckman LS7500 system). Differential (3H) and (14C) counts (cpm) were made employing external standards. The 20-microns sections were prepared for 14C autoradiography by standard methods employing Kodak SB-5 X-ray film. The (14C) autoradiographs from the motion-stimulated animals revealed a selectively high uptake of 2-DG in all of the vestibular nuclei, the lateral cuneate nucleus and the lateral reticular nucleus as compared with the corresponding structures in the control animals.(ABSTRACT TRUNCATED AT 400 WORDS)

Mapping of forelimb afferents to the cuneate nuclei of the rat

Stumps of rat forelimb peripheral nerves were soaked in horseradish peroxidase solution. Impregnation of the median, ulnar, radial, and musculocutaneous nerves revealed that each nerve had definite projection zones in the cuneate nuclei. The radial nerve projected quite heavily to the lateral cuneate nucleus and to a narrow band along the dorsal edge of the main cuneate nucleus. Staining of the deep radial and superficial radial nerves showed that they projected heavily to the lateral and main cuneate respectively. The ulnar and median nerves projected primarily to medial and lateral portions of the main cuneate nucleus, ventral to the terminal field of the radial nerve. The rostral and caudal portions of the main cuneate nucleus were discriminable by cytoarchitectural characteristics and by terminal fibre orientation.

Projections of caudal fasciculus gracilis to nucleus gracilis and other medullary structures, and Clarke's nucleus in the rat

The extent of the projection of fasciculus gracilis from low thoracic (T12–13) spinal cord, to nucleus gracilis (NG) was studied by the Nauta-Gygax method in the rat in order to: (1) help define projection fields of fasciculus gracilis hindlimb and tail afferents along the longitudinal extent of NG; and (2) broaden the comparative data on the projection of the lower body to NG via fasciculus gracilis, already known in cat and monkey. Results showed that: (1) degenerated fasciculus gracilis axons are situated mainly dorsal to the corticospinal fibers, in the dorsal funiculus; (2) terminal projection fields were located at all levels of ipsilateral NG — caudal to the obex, terminal debris was confined to the medial two-thirds of NG — rostrad of the obex, in oral NG, degeneration was of finer caliber and projection fields more diffuse; and (3) ipsilateral degeneration was also seen at the level of a portion of Clarke's nucleus, and, in commissural and lateral cuneate nuclei and medial reticular formation in medulla.

The brainstem projection of the vestibular nerve in the cat.

The projection of the vestibular nerve to the brainstem of the cat was re-examined with silver degeneration methods after complete lesions of the vestibular ganglion. Whereas previous investigations emphasize that only parts of the major vestibular nuclei are innervated by the vestibular nerve, the present investigation shows that only the dorsal division of the lateral vestibular nucleus is uninnervated. Thus, the terminal field of the vestibular nerve extends to the cytoarchitectonic boundaries of the superior, medial, descending, and the ventral division of the lateral vestibular nuclei. Vestibular nerve fibers were also traced to discrete terminal fields in the reticular formation lateral to the abducens nucleus and in the rostral, lateral parts of the accessory cuneate nucleus. These observations indicate a more widespread distribution of vestibular nerve fibers in the brainstem of the cat than previously believed.

Organization of trigeminothalamic tracts and other thalamic afferent systems of the brainstem in the rat: Presence of gelatinosa neurons with thalamic connections

Thalamic projections from trigeminal and certain other nuclei of the brainstem of the rat have been investigated using the technique of retrograde transport of horseradish peroxidase (HRP). The pattern of trigeminothalamic projections is very specifically related to the individual subnuclei of the complex. The Main Sensory Nucleus (MSN) provides profuse cross connections to the ventrobasal thalamus (VB); these arise exclusively from medium and small-sized neurons, but never from the large cells. In addition to these crossed connections, a small ipsilateral dorsal trigeminothalamic tract arises from the dorsal third of the most rostral part of the MSN; this is the only ipsilateral connection to VB found in the trigeminal complex. Subnucleus Oralis has no projections to the thalamus; it is suggested that it may be concerned primarily with reflex activation of the facial nucleus, with which it is co-extensive in the rostro-caudal axis. Subnucleus Interpolaris has a well-defined crossed projection of moderate size which arises from the large, medium and some of the small neurons. Subnucleus Caudalis has a sparse output to the thalamus and differs in its projections from rostral to caudal. At the most rostral level, all layers (marginal, transitional gelatinosa and magnocellularis) contain neurons which project to the thalamus; particularly conspicuous in this respect are the marginal neurons, most of which are strongly labelled. The presence of gelatinosa neurons projecting to the thalamus emphasizes a point made in earlier reports, that these neurons do not form an homogeneous population. At caudal levels, the marginal neurons are the major source of thalamic projections, while connections to the thalamus form deeper lying neurons are infrequent. With a single exception, the medullary reticular nuclei contained no neurons with thalamic connections; a small number of reticulo-thalamic neurons were found in the ventral pontine area. Marked labelling of the medial cuneate nucleus and moderate labelling of the gracilis and lateral cuneate nuclei occurred contralaterally to the injection site. A small numebr of medial cuneate and gracile neurons project to the ipsilateral thalamus. Projections from the solitary nucleus were always ipsialteral. The boundaries of individual subnuclei of the lateral sensory trigeminal complex in the rat have been redefined on the basis of cytological criteria; these are in good accord with the corresponding thalamic projection patterns.

Nuclei of the solitary tract: efferent projections to the lower brain stem and spinal cord of the cat.

The efferent projections from the solitary complex to the lower brain stem and spinal cord were studied in the cat with the autoradiographic anterograde axonal transport and retrograde horseradish peroxidase (HRP) techniques. A revised cytoarchitectonic description of the caudal two-thirds of the complex is presented in which the complex was subdivided into six nuclei: lateral, ventrolateral, intermediate, medial, parvocellular, and commissural solitary tract nuclei. Following injections of 3H amino acids into electrophysiologically defined regions of the complex in which cardiac or respiratory units were recorded, labeled fibers could be traced to a number of sites in the caudal brain stem including the medial and lateral parabrachial nuclei, Kölliker-Fuse nucleus and the area ventral to this nucleus, lateral periaqueductal gray matter, ambiguus complex, which consists of the retrofacial, ambiguus and retroambiguus nuclei, ventrolateral reticular nucleus (in an area equivalent to the A1 cell group of Dahlström and Fuxe, '64), medial accessory olive, paramedian reticular formation, and lateral cuneate nucleus. Descending solitario-spinal projections have been traced bilaterally, but predominantly to the contralateral side, to the region of the phrenic motor neurons in the C4-C6 ventral horn, to the thoracic ventral horn, and intermediolateral cell column. Confirmatory evidence of some of these projections was obtained from a series of HRP experiments. Mainly small neurons of the parvocellular, medial and commissural solitary tract nuclei project to the region of the parabrachial and Kölliker-Fuse nuclei. The lateral solitary nucleus projects almost exclusively to the ipsilateral medial accessory olive. It was not possible to interpret conclusively the labeling seen in the medium and large neurons of the ventrolateral solitary nucleus after HRP injections made in the region of the ambiguus-retroambiguus complex due to the problem of fibers of passage. Following injections of HRP into the cervical, thoracic, lumbar, or sacral spinal cord, retrograde cell labeling was seen in the solitary complex. Cells in the intermediate and commissural nuclei were labeled after all four types of experiments. In the ventrolateral nucleus, medium sized neurons were predominantly labeled after the cervical spinal cord experiments, while large sized neurons were labeled mainly after the thoracic spinal cord injections. The potential physiological significance of these connections is discussed in terms of central control of cardiovascular and respiratory functions.

Cerebellar afferents in teleost catfish (Ictaluridae).

The cerebellar afferents in the bullhead catfish (Teleostei) were labeled by relying on the retrograde transport of horseradish peroxidase (HRP). Retrogradely labeled neurons were seen in: spinal cord, lateral cuneate nucleus, inferior olive, reticular nuclei, vestibular nuclei, nucleus subeminentialis, n. lateralis valvulae, locus coeruleus, n. mesencephalicus dorsalis, the basal optic nuclei, and a nucleus at the isthmic level which may be equivalent to the pontine nuclei of birds and mammals. Inputs to the molecular layer arise from the inferior olive, locus coeruleus and n. lateralis valvulae in addition to subjacent granule cells. No projections to cerebellum were seen to arise from either the optic tectum or from the inferior lobe. The so-called "lobo-cerebellar" tract in teleosts was reported by Goldstein, amongst many others, who mistook the superior secondary gustatory nucleus for a deep cerebellar nucleus.

Recovery function of short latency components of surface and depth recorded somatosensory evoked potentials in the cat

Recovery functions of early components of surface and depth recorded somatosensory evoked potentials were studied in the cat. At interstimulus intervals of 50 msec or less differentiation of surface components was optimal. Component I showed less decrement at all ISI's than did component II and recovery curves of both were distinctly different from those of components III (anterior) and IV and the cortical SEP. The latter three potentials had similar recovery curves. Comparisons of latencies and recovery curves of surface recorded potentials with those of depth recorded potentials indicate that component I principally reflects activity in posterior column, that potentials in medial lemniscus, cuneate nucleus, and lateral cuneate nucleus contribute to component II, that the major generator for the contralateral component III is the ventral postero-lateral nucleus of the thalamus, and that component IV is largely due to activity in the sensory radiation. The results of this study support previous observations and conclusions about the origin of short latency, surface recorded somatosensory evoked potentials preceding the cortical SEP.

Projections of the superior cerebellar peduncle in rats and the development of new connections in response to neonatal hemicerebellectomy.

The normal distribution pattern of cerebellar efferents was determined using the Fink-Heimer technique in adult rats that sustained stereotaxic transection of the superior cerebellar peduncle. This pattern was found to be essentially similar to earlier studies and corroborated more recent reports of projections to the pontine gray and inferior olivary nuclei. Comparisons were made to a second group of animals that underwent neonatal hemicerebellectomy in addition to adult transection of the contralateral superior cerebellar peduncle. Abnormal projections to the ipsilateral red nucleus and ventral thalamus were observed in addition to evidence suggestive of axonal sprouting within the oculomotor complex. These animals also demonstrated an absence of cells in the pontine gray and inferior olive on the side contralateral to the hemicerebellectomy and in the lateral reticular and lateral cuneate nuclei on the ipsilateral side.

Dorsal column nuclei in a prosimian primate (Galago senegalensis). II. Cuneate and lateral cuneate nuclei: morphology and primary afferent fibers from cervical and upper thoracic spinal segments.

The morphology and brachial cord primary afferent projections of the cuneate and lateral cuneate nuclei have been studied in the lesser bushbaby. The cuneate nucleus was divided into three regions. From caudal to rostral these were the large cell, cell column and rostral regions. Primary afferents from C2, C4, C6, C7, C8, T1 and T3 terminated within distinct partially overlapping terminal zones in the ipsilateral large cell and cell column regions of the cuneate nucleus (CN) and the lateral cuneate nucleus (LCN). Segmentotopic was the greatest in the rostal region of the CN due to a more diffuse projection pattern. In the LCN, the transverse terminal fields appeared as curved mediolaterally oriented laminae. In each case, ascending fibers of passage from C4, C6, and C7 in the cuneate fasciculus were organized so that two distinct fiber laminae were present. The separation of fibers and the formation of the two ascending laminae were completed either within two segments rostral to their respective level of entry (for C6 and C7 lesions) or in the caudal medulla (for C4 lesion). For each of these segments, the laminae consisted of a small dorsomedial one and a large lateral one. The organization of primary afferents from one segment into two ascending fiber laminae in the cuneate fasciculus was reflected in a differential termination pattern within both the CN and LCN. The results of this study were discussed relative to earlier anatomical and physiological studies on the DCN in other animals.

Descending hypothalamic pathways with cardiovascular function in the cat: A silver impregnation study

To identify descending pathways with cardiovascular function originating in the hypothalamus, unilateral electrolytic lesions were made in adult cats at hypothalamic sites from which arterial hypertension and cardioacceleration were elicited by electrical stimulation. After a survival period of 5 to 11 days, histological sections of the hypothalamus, midbrain, pons, medulla, and spinal cord were stained using modifications of the Nauta techniques for degenerating axons and terminals. The main caudal projection from lesions in the dorsal hypothalamic region could be traced ipsilaterally into the periaqueductal gray and was found to continue in the region of the dorsal longitudinal fasciculus throughout the midbrain, pons, and medulla. Fibers terminated primarily in the Edinger-Westphal nucleus, in the inferior colliculus, in a region dorsolateral to the superior olivary nucleus, and in the parahypoglossal region. The degeneration patterns resulting from lesions in the posterior hypothalamic region and in the ventrolateral hypothalamic-medial forebrain bundle regions were essentially similar. Lesions in these regions demonstrated the existence of dorsomedial and ventrolateral descending pathways (i) through the medial hypothalamus and periaqueductal gray and (ii) through the medial forebrain bundle and ventrolateral mesencephalic reticular formation. The projection through the periaqueductal gray was similar to that traced in animals with lesions in the dorsal hypothalamic region, but dense terminal degeneration was seen bilaterally in the caudal aspect of the accessory cuneate nucleus and the medial aspect of the nucleus tractus solitarius. The medial forebrain bundle partially decussated just rostral to the red nucleus and descended bilaterally into the region of the ventral tegmental area of Tsai, where some fibers terminated. The pathway continued through and around the lateral reticular nucleus in the medulla and into the spinal cord. Dense terminal degeneration was noted in the intermediomedial nucleus primarily in segments from C8 to T3, but extended to the lower thoracic segments as low as T12. No terminal degeneration was observed in the upper cervical, lumbar, or sacral cord, or in the intermediolateral nucleus of the thoracolumbar cord. These results suggest the existence of two distinct descending pathways that may be involved in the mediation of cardiovascular responses elicited by stimulation of the hypothalamus.

Morphological characteristics of acetylcholinesterase-containing neurons in the CNS of DFP-treated monkeys: Part. 3. Brain stem and spinal cord

The distribution of acetylcholinesterase (AChE, EC 3.1.1.7) was studied in the lower brain stem and spinal cord of 4 monkeys following the i.m. administration of bis-(1-methylethyl) phosphorofluoridate (di-isoprophylfluorophosphate: DFP). In 1 animal that received 0.43 mg/kg of DFP 4 hr prior to death, AChE was virtually absent in all structures. In the other 3 animals sacrificed 10, 12 and 18 hr after the injection of 0.20 mg/kg of DFP, AChE activity was considerably lighter in the neuropil of different structures normally displaying a moderate to intense AChE activity in pharmacologically unmanipulated monkeys. As a consequence of the lighter background activity several groups of neurons were easily identified and their cell bodies and processes were sharply outlined. Brain stem and spinal cord groups of neurons that show an intense AChE activity include the nuclei of the somatic motor column (cranial nerves III, IV, VI and XII, and ventral horn cells) and of the special visceral (cranial nerves V and VII and nucleus ambiguus) and general visceral (Edinger-Westphal and salivatory nuclei, dorsal nucleus of the Xth nerve and intermediomedial and intermediolateral spinal nuclei) motor columns. Other neurons of the midbrain that display intense AChE activity include the rostral division of nucleus linearis, the magnocellular division of the red nucleus, perirubral giant neurons, the nucleus of the mesencephalic root of V, the substantia nigra and the subnucleus compactus of the pedunculopontine tegmental nucleus. Midbrain neurons with a light to moderate AChE activity are located in the periaqueductal gray, the parvocellular division of the red nucleus, the interstitial nucleus of Cajal, and the magnocellular nucleus of the posterior commissure. Other intensely stained groups of neurons at isthmus and pontine levels include the intermediate and caudal divisions of nucleus linearis, all divisions of the dorsal nucleus of the raphé, the laterodorsal nucleus, nucleus annularis, nucleus centralis superior, neurons of the loci coeruleus and subcoeruleus and of the mesencephalic root of V, the few and large neurons of nuclei pontis oralis and pontis caudalis and nuclei paraabducens and paramedianus dorsalis. Other groups of neurons with a light to moderate AChE activity at isthmus and pons levels include the pontine and reticulotegmental nuclei. The neurons of the cerebellar fastigial nucleus are intensely stained and those of nucleus interpositus and nucleus dentatus, as well as the cell bodies of the Golgi cells of the cerebellar cortex, are moderately stained. At medulla and spinal cord levels the neurons of the lateral vestibular nucleus, the gigantocellular nucleus, the dorsal nucleus of Clarke and the lumbo-sacral border cells are intensely stained. Other neurons with lightly to moderately stained cell bodies include the superior and medial vestibular nuclei, nucleus praepositus, the lateral cuneate and lateral reticular nuclei, and the principal inferior and accessory olivary nuclei.