Brainstem projections from recipient zones of the anterior ethmoidal nerve in the medullary dorsal horn.

Stimulation of the anterior ethmoidal nerve or the nasal mucosa induces cardiorespiratory responses similar to those seen in diving mammals. We have utilized the transganglionic transport of a cocktail of horseradish peroxidase conjugates and anterograde and retrograde tract tracing techniques to elucidate pathways which may be important for these responses in the rat. Label was seen throughout the trigeminal sensory complex after the horseradish peroxidase conjugates were applied to the anterior ethmoidal nerve peripherally. Reaction product was most dense in the medullary dorsal horn, especially in laminae I and II. Injections were made of biotinylated dextran amine into the recipient zones of the medullary dorsal horn from the anterior ethmoidal nerve, and the anterogradely transported label documented. Label was found in many brainstem areas, but fibers with varicosities were noted in specific subdivisions of the nucleus tractus solitarii and parabrachial nucleus, as well as parts of the caudal and rostral ventrolateral medulla and A5 (noradrenergic cell group in ventrolateral pons) area. The retrograde transport of FluoroGold into the medullary dorsal horn after injections into these areas showed most neurons in laminae I, II, and V. Label was especially dense in areas which received primary afferent fibers from the anterior ethmoidal nerve. These data identify potential neural circuits for the diving response of the rat.

The central termination of sensory fibers from nerves to the gastrocnemius muscle of the rat.

Peripheral nerves innervating muscles have sensory fibers that relay information into the CNS information about proprioception, pain, and the metabolic state of the muscle. The present study shows the primary afferent projections into the spinal cord of the nerves innervating the gastrocnemius muscle of the rat using the transganglionic transport of a cocktail of horseradish peroxidase (HRP) conjugated to cholera toxin and wheat germ agglutinin; these markers have been shown to label large and small fibers, respectively. A dense projection into lamina I of the lumbar dorsal horn and a more moderate projection into lamina V were seen. Moreover, dense reaction product was found in the most medial aspect of lamina II, especially lamina II inner part, and less in lamina III and IV of levels L3-L5. Lamina VI had dense reaction product from the rostral sacral levels of the spinal cord that continued into Clarke's column at rostral lumbar levels. The nucleus gracilis also was labeled. Other nerves emerging from the popliteal fossa, including the tibial, peroneal, and sural nerves, also were injected with the HRP cocktail and their projections compared with those from the gastrocnemius muscle. Projections from the gastrocnemius muscle only partially overlapped with those from the tibial nerve, from which the nerves to the gastrocnemius muscle branch. However, the topology of projections from these nerves to laminae II-IV of the dorsal horn differed from that of the nerves of the gastrocnemius muscle, suggesting there was little spread to other nerves in the popliteal fossa. It was also noted that large labeled processes, presumably dendrites of retrogradely labeled motoneurons, entered the dorsal horn. These data provide information on the central projections of both the large and small fibers innervating the gastrocnemius muscle, and may aid in determining the circuitry utilized in the exercise pressor reflex as well as muscle pain.

Primary afferent projections from the upper respiratory tract in the muskrat.

The central projections of the ethmoidal, glossopharyngeal, and superior laryngeal nerves were determined in the muskrat by use of the transganglionic transport of a mixture of horseradish peroxidase (HRP) and wheat germ agglutinin (WGA)-HRP. The ethmoidal nerve projected to discrete areas in all subdivisions of the ipsilateral trigeminal sensory complex. Reaction product was focused in ventromedial portions of the principal nucleus, subnucleus oralis, and subnucleus interpolaris. The subnucleus oralis also contained sparse reaction product in its dorsomedial part. Projections were dense to ventrolateral parts of laminae I and II of the rostral medullary dorsal horn, with sparser projections to lamina V. Label in laminae I and V extended into the cervical dorsal horn. A few labeled fibers were followed to the contralateral dorsal horn. The interstitial neuropil of the ventral paratrigeminal nucleus was densely labeled. Extratrigeminal primary afferent projections in ethmoidal nerve cases involved the Kölliker-Fuse nucleus and ventrolateral part of the parabrachial nucleus, the reticular formation surrounding the rostral ambiguous complex, and the dorsal reticular formation of the closed medulla. Retrograde labeling in the brain was observed in only the mesencephalic trigeminal nucleus in these cases. The cervical trunk of the glossopharyngeal and superior laryngeal nerves also projected to the trigeminal sensory complex, but almost exclusively to its caudal parts. These nerves terminated in the dorsal and ventral paratrigeminal nuclei as well as lamina I of the medullary and cervical dorsal horns. Lamina V received sparse projections. The glossopharyngeal and superior laryngeal nerves projected to the ipsilateral solitary complex at all levels extending from the caudal facial nucleus to the cervical spinal cord. At the level of the obex, these nerves projected densely to ipsilateral areas ventral and ventromedial to the solitary tract. Additional ipsilateral projections were observed along the dorsolateral border of the solitary complex. Near the obex and caudally, the commissural area was labeled bilaterally. Labeled fibers from the solitary tract projected into the caudal reticular formation bilaterally, especially when the cervical trunk of the glossopharyngeal nerve received tracer. Labeled fibers descending further in the solitary tract gradually shifted toward the base of the cervical dorsal horn. The labeled fibers left the solitary tract and entered the spinal trigeminal tract at these levels. Retrogradely labeled cells were observed in the ambiguous complex, especially rostrally, and in the rostral dorsal vagal nucleus after application of HRP and WGA-HRP to either the glossopharyngeal or superior laryngeal nerves. In glossopharyngeal nerve cases, retrogradely labeled neurons also were seen in the inferior salivatory nucleus.(ABSTRACT TRUNCATED AT 400 WORDS)

Transient cerebrocerebellar projections in kittens: postnatal development and topography.

Orthograde and retrograde labeling techniques were used to study the ontogenesis of transient cerebrocerebellar projections in kittens. Tritiated amino-acid or horseradish peroxidase injections were made into the coronal gyrus of the primary somatosensory cortex of kittens 1-70 postnatal days old. Orthogradely labeled axons were observed bilaterally in the superior and inferior cerebellar peduncles in kittens between 6 and 49 postnatal days of age. Most cerebrocerebellar axons labeled on the ipsilateral side arise from the pyramidal tract as it courses through the pontine nuclei. These axons descend through the pontine tegmentum as a diffusely organized corticotegmental tract and enter the ipsilateral superior cerebellar peduncle. Fewer cerebrocerebellar axons leave the pyramidal tract caudal to the pontine nuclei and project into the contralateral superior cerebellar peduncle. Cerebrocerebellar projections through the superior cerebellar peduncles terminate primarily in the cerebellar nuclei, where they are localized in the interpositus nuclei and in immediately adjacent areas of the dentate and fastigial nuclei. More caudally, labeled axons exit from the pyramidal tract and take a superficial route around the ventrolateral brainstem into the inferior cerebellar peduncles bilaterally. These projections are more numerous contralaterally and are directed primarily to the internal granule cell layer of the posterolateral folia of the anterior lobe, the posteromedial simplex lobule, and the dorsal paramedian lobule. Horseradish peroxidase injections were made into the cerebellar posterior lobe and deep nuclei and the results from these cases showed that the cerebrocerebellar pathway originates from pyramidal neurons in layer V primarily in the coronal, the precoronal, and the anterior and posterior sigmoid gyri on both sides. In these gyri, many of the HRP-positive neurons were found in clusters of two to five neurons, aligned in anterior-posterior strips. The results from all experiments provide evidence about the ontogeny of cerebrocerebellar projections. Projections through the superior cerebellar peduncles generally develop at 6-8 postnatal days of age, whereas projections through the inferior cerebellar peduncles first are seen at 8-10 days postnatally. Cerebrocerebellar projections reach their maximum development in the second postnatal week but sharply decrease in density during the third postnatal week. No cerebrocerebellar projections were observed after the seventh postnatal week of development. Possible functional implications for this transient projection are discussed.

Corneal and periocular representation within the trigeminal sensory complex in the cat studied with transganglionic transport of horseradish peroxidase.

The central projections of afferent fibers from the cornea, and the infraorbital, infratrochlear, frontal, lacrimal and auriculotemporal nerves were investigated by means of the transganglionic transport of horseradish peroxidase. Afferent projections to the dorsal horn of the medulla are organized along both the rostrocaudal axis and the ventrolateral to dorsomedial margin of the medullary dorsal horn. An inverted but discontinuous facial representation exists through the restrocaudal axis of the dorsal horn of the medulla with perioral and nasal receptive fields innervated by the infratrochlear nerves represented rostral to the progressively more posterior receptive fields innervated by the frontal, lacrimal and auriculotemporal nerves, respectively. The organization of the primary afferents is not uniform over the laminae of the dorsal horn of the medulla; the projections from the different nerves show the least overlap in lamina II, while overlap is most extensive in laminae I and V. The sensory projection from the cornea to the medullary dorsal horn is most dense in laminae I and II. All nerves, including those innervating the cornea, project to the interpolar, oral and principal trigeminal nuclei and are somatotopically organized. Projections to the reticular formation and the contralateral trigeminal sensory complex were not found in this study. These results support the organization of the dorsal horn of the medulla proposed by Déjerine ('14) and show that this organization is most evident for the primary afferent projections to lamina II.

Spinal projections from the medullary reticular formation of the North American opossum: heterogeneity.

Retrograde and orthograde transport techniques show that the nucleus reticularis gigantocellularis pars ventralis and the nucleus reticularis gigantocellularis project the entire length of the spinal cord. Double-labelling methods show that some of the neurons in each area innervate both cervical and lumbar levels. There is evidence, however, that neurons in the lateral part of the nucleus reticularis gigantocellularis pars ventralis and the dorsal extreme of the nucleus reticularis gigantocellularis project mainly to cervical and thoracic levels. The autoradiographic method shows that the above nuclei supply direct innervation to somatic and autonomic motor columns as well as to laminae V-VIII and X. The nucleus reticularis gigantocellularis pars ventralis provides additional projections to lamina I and the outer part of lamina II. Several areas of the medullary reticular formation project mainly, and in some cases exclusively, to cervical and thoracic levels. These areas include the nucleus reticularis parvocellularis, the nucleus reticularis lateralis, the nucleus retrofacialis, the nucleus ambiguus, the nucleus lateralis reticularis, caudal parts of the nuclei reticularis medullae oblongatae dorsalis and ventralis, and the nucleus supraspinalis. Autoradiographic experiments reveal that neurons in the ventrolateral medulla, particularly rostrally (the nucleus reticularis lateralis and neurons related to the nucleus lateralis reticularis), innervate sympathetic nuclei. Our results indicate that spinal projections from bulbar areas of the reticular formation are more complicated than previously supposed. Axons from separate areas project to different spinal levels and in some cases to different nuclear targets. These data are in conformity with the evolving concept of reticular heterogeneity.

Spinal projections from the mesencephalic and pontine reticular formation in the North American Opossum: a study using axonal transport techniques.

The results from several experimental approaches lead to the following conclusions. The nucleus cuneiformis projects to at least lumbar levels of the spinal cord. Its axons course through the ipsilateral sulcomarginal and ventral funiculi to distribute within lamina VIII and adjacent portions of lamina VII. Neurons within the nucleus reticularis pontis (RP), particularly within more medial parts of the nucleus, project through comparable routes to the same laminae. In addition, however, neurons within the lateral and dorsolateral RP relay through the lateral and dorsolateral funiculi, ipsilaterally, and the dorsolateral funiculus, contralaterally. Axons could be traced from the dorsolateral tracts to laminae IV through VII, lamina X and, in some instances, to laminae I and II. Injections of the dorsolateral pons also label the intermediolateral cell column and an area presumed to be the sacral parasympathetic nucleus. Many of the neurons which contribute to the contralateral bundle are located adjacent to the ventral nucleus of the lateral lemniscus. The nucleus reticularis gigantocellularis projects mainly via the sulcomarginal, ventral and lateral funiculi to laminae VIII and adjacent portions of lamina VII. The nucleus reticularis gigantocellularis pars ventralis innervates the same laminae; but, in addition, projects heavily to laminae I and II, to lateral portions of laminae IV through VII; to laminae IX and X and to the intermediolateral cell column. Axons destined for laminae I and II, as well as IV through VII and X, traverse the dorsolateral funiculi as described for the cat by Basbaum et al. ('78). Neurons within the nucleus reticularis parvocellularis project to cervical levels, mainly through the ventral funiculi. In general our results show that reticulospinal projections are more complex than suggested by degeneration methods and that laminae I, II. lateral parts of laminae IV-VII, laminae IX and X, as well as the intermediolateral cell column and sacral parasympathetic nucleus are targets of axons from specific areas.

Projections from the paratrigeminal nucleus and the medullary and spinal dorsal horns to the peribrachial area in the cat.

The projections from the medullary and spinal dorsal horns to the dorsolateral pons were investigated in the cat utilizing both the retrograde and anterograde transport of a wheat germ agglutinin-horseradish peroxidase complex and the retrograde transport of the fluorescent dyes Fast Blue and Nuclear Yellow. After injections of wheat germ agglutinin-horseradish peroxidase into the area surrounding the brachium conjunctivum, numerous neurons were labeled ipsilaterally near levels of the obex in the paratrigeminal nucleus. Such neurons were located in connected pockets of neuropil located within the spinal trigeminal tract and along its medial edge. Most of the neurons labeled in the dorsal horns after such injections were found in lamina I. Those found in the medullary dorsal horn were mostly ipsilateral to the injection while those in the spinal dorsal horn were found bilaterally. Some labeled neurons were also found in lamina V of both the medullary and spinal dorsal horns bilaterally. When the injection was centered in either the medial parabrachial nucleus or the Kolliker-Fuse nucleus, a greater number of neurons were labeled ipsilaterally in lamina V of the medullary dorsal horn. Since neurons in lamina I of the medullary dorsal horn also project to the medial thalamus, fluorescent dyes were used to determine if the same neuron might project to both targets. Fast Blue was first injected into either the peribrachial area or the medial thalamus. After an appropriate period, Nuclear Yellow was injected into that target not injected first with Fast Blue. The injection of Nuclear Yellow was always placed on the side of the brain opposite to the first injection. Both dyes were transported retrogradely and were found in neurons located in lamina I of the medullary dorsal horn. However, no double-labeled neurons were seen. In general those labeled after injections of the medial thalamus were more superficial than those labeled after injections of the dorsolateral pons. The anterograde transport of wheat germ agglutinin-horseradish peroxidase was used to determine the termination of the projections from neurons in the medulary dorsal horn and the cervical spinal cord to the peribrachial area. After injections into these areas a moderate to sparse labeling of the lateral parabrachial nucleus and the Kolliker-Fuse nucleus was seen. It was mostly ipsilateral in cases with injections of the medullary dorsal horn but was bilateral following injections into the cervical enlargement.(ABSTRACT TRUNCATED AT 400 WORDS)

Fos immunohistochemical determination of brainstem neuronal activation in the muskrat after nasal stimulation.

Stimulation of the nasal passages of muskrats with either ammonia vapours or retrogradely-flowing water produced cardiorespiratory responses (an immediate 62% decrease in heart rate, 29% increase in mean arterial blood pressure, and sustained expiratory apnoea). We used the immunohistological detection of Fos, the protein product of the c-fos gene, as a marker of neuronal activation to help elucidate the brainstem circuitry of this cardiorespiratory response. After repeated ammonia stimulation of the nasal passages, increased Fos expression was detected within the spinal trigeminal nucleus (ventral laminae I and II of the medullary dorsal horn, ventral paratrigeminal nucleus, and spinal trigeminal nucleus interpolaris), an area just ventromedial to the medullary dorsal horn, the caudal dorsal reticular formation and the area of the A5 catecholamine group compared to control animals. Repeated water stimulation of the nasal passages produced increased Fos expression only in the A5 catecholamine group. There was an increase in the number of Fos-positive cells in the ammonia group in the ventral laminae I and II of the medullary dorsal horn and the ventral paratrigeminal nuclei compared with the water group. We conclude that ammonia stimulation of the nasal passages produces a different pattern of neuronal activation within the brainstem compared with water stimulation. We also conclude that Fos immunohistochemistry is a good technique to determine functional afferent somatotopy, but that immunohistochemical detection of Fos is not a good technique to identify the medullary neurons responsible for the efferent aspects of an intermittently produced cardiorespiratory reflex.

Trigeminal projections to the peribrachial region in the muskrat.

The anterograde and retrograde transport of wheat germ agglutinin-horseradish peroxidase was used to study the trigeminoperibrachial pathway in the muskrat after injections of tracer into either the medullary dorsal horn or the dorsolateral pons. After injections into the medullary dorsal horn, labeled fibers ascended into the ipsilateral dorsolateral pons via the spinal trigeminal tract, within the neuropil of the trigeminal sensory complex and within the reticular formation adjacent to the spinal trigeminal nucleus. At caudal levels of the ipsilateral peribrachial area, dense terminal-like label distributed in the Kölliker-Fuse nucleus continued into the lateral parabrachial nucleus. At intermediate levels ipsilaterally, the Kölliker-Fuse nucleus again was labeled densely, as were areas analogous to the external lateral and external medial subnuclei of the parabrachial nucleus in the rat. A thin band of label along the ventral spinocerebellar tract outlined an unlabeled area in the central portion of the lateral parabrachial nucleus. Rostrally near the pontomesencephalic junction, the area designated the superior lateral subnucleus in the hamster was labeled, while sparser label was present more dorsally. Contralateral to the injections, caudal and intermediate levels of the peribrachial area contained only scant reaction product. However, the rostral area of the superior lateral subnucleus was labeled densely via fibers ascending in the trigeminothalamic tract. Injections made just rostral to the obex and either centered in or including the dorsal or ventral paratrigeminal nuclei produced similar labeling at caudal and intermediate levels of the peribrachial area. An exception, however, was that the caudal medial parabrachial nucleus was also labeled after the dorsal paratrigeminal injection. Also, only scant label was found in the rostral third of the dorsolateral pons on either side after these injections. Both trigeminothalamic and trigeminolemniscal pathways were labeled contralaterally after these injections. These trigeminal projections to the dorsolateral pons were compared to the projections from the nucleus tractus solitarii and the ventrolateral medulla. Numerous trigeminal neurons were labeled retrogradely after injections of wheat germ agglutinin-horseradish peroxidase into the dorsolateral pons. In the medullary dorsal horn, they were found almost exclusively in laminae I and V. Labeled neurons in lamina I were especially prominent in rostral ventral levels of the medullary dorsal horn. Labeled cells in lamina I were continuous with others found in the displaced band of substantia gelatinosa at the interface of the subnucleus caudalis and subnucleus interpolaris, as well as with those found in the ventral and dorsal paratrigeminal nuclei.(ABSTRACT TRUNCATED AT 400 WORDS)

The persistence of a normally transient cerebrocerebellar pathway in the cat.

A direct, although transient, projection from the sensorimotor cortex to the cerebellum has been described previously in the neonatal kitten. The present report demonstrates that this pathway can be induced to persist into juvenile stages of the cat by partially denervating the deep cerebellar nuclei. Most of the cerebellar cortex on one side was removed in kittens within the first week after birth, but the deep cerebellar nuclei were preserved, in an effort to destroy most of the input into the deep nuclei. After 6-11 weeks the remaining white matter and deep nuclei on the lesioned side were injected with WGA-HRP in most of the animals, while a few received injections of either WGA-HRP or HRP in the sensorimotor cortex ipsilateral to the lesion. Results from these experiments showed that the normally transient cerebrocerebellar pathway persisted to some degree in young adults lesioned as neonates. However, the functional significance of this pathway, as well as other transient pathways, is still unknown.

Trigeminal mediation of the diving response in the muskrat.

Stimulation of the nasal cavity elicits powerful cardiorespiratory responses similar to the diving response. In the present study, bradycardia and apnea were elicited in muskrats by stimulation of the nasal cavity with ammonia vapors. These responses could be blocked by injections of 2% lidocaine made bilaterally into the medullary dorsal horns of the trigeminal sensory complex. However, the bradycardia due to activation of the baroreceptor reflex with intravenous phenylephrine was retained. These data implicate trigeminal neurons in the medullary dorsal horn as modulators of autonomic activity, especially in the cardiorespiratory adjustments after nasal stimulation.

The transience of cerebrocerebellar projections is due to selective elimination of axon collaterals and not neuronal death.

Fluorescent dyes were used to determine firstly if the transience of cerebrocerebellar projections in neonatal kittens is due to the selective elimination of axon collaterals or to neuronal death; and secondly, if the cerebrocerebellar projection neurons lived, did any maintain a projection to the brainstem or spinal cord. Injections of Fast Blue were made into the cerebellar cortex and deep nuclei in 7-9 postnatal days old kittens, the age in which cortical axons grow into the cerebellum. Later, at 31-71 postnatal days of age, when the transient cerebrocerebellar projections have disappeared, injections of Nuclear Yellow were made into the brainstem or the spinal cord. In the frontoparietal cortex, numerous neurons were labeled with Fast Blue suggesting that the disappearance of cerebrocerebellar projections is due primarily to the selective elimination of axon collaterals and not neuronal death. Moreover, many of the cortical neurons labeled with Fast Blue also were labeled with Nuclear Yellow which shows that many of the cortical neurons with transient collateral projections to the cerebellum in the neonate maintain a projection to brainstem or spinal targets in older animals.

Enkephalin-immunoreactive neurons in the nucleus tractus solitarius project to the parabrachial nucleus of the cat.

Enkephalin immunoreactive neurons within the nucleus tractus solitarius (NTS) were found to project to the parabrachial nucleus of the cat with the use of a combination of immunohistochemistry and retrograde transport of horseradish peroxidase. Double labelled neurons were located in the medial, parvocellular and commissural subdivisions of the NTS and were present predominantly ipsilateral to the injection site within the parabrachial nucleus. Only a few double labelled neurons were found in the contralateral NTS. The presence of neurons containing enkephalin immunoreactivity suggests that the role of enkephalin in the regulation of autonomic functions may be, in part, by circuits between the NTS and the parabrachial nucleus.

Heterogeneity of neurons in the subnucleus interpolaris of the cat.

Fluorescent dyes were used to determine if neurons in the feline subnucleus interpolaris of the spinal trigeminal nucleus project to more than one target via axon collaterals. Either Fast Blue or True Blue was injected into the ventrobasal thalamus while Nuclear Yellow later was deposited into either the principal trigeminal nucleus or the cerebellum. In general, numerous neurons in the subnucleus interpolaris were labeled by a single dye after these injections, but only a few were labeled with two dyes, and the latter only after the combination of injections were into the thalamus and the principal nucleus on the opposite side. These data suggest that independent populations of neurons in the subnucleus interpolaris project to these targets.

The collateral origin of a transient cerebrocerebellar pathway in kittens. A study using fluorescent double-labeling techniques.

A transient pathway from the sensorimotor neocortex to the cerebellum recently has been described in the kitten which appears late in the first postnatal week, develops maximally at days 9 and 10 and then gradually disappears. The transience of this pathway has been investigated in the present study using the retrograde transport of fluorescent dyes. In one set of experiments Fast Blue was injected into the caudal medulla of neonatal kittens while Nuclear Yellow was injected into the opposite cerebellum 3-10 days later. Neurons labeled with Fast Blue were found bilaterally throughout lamina V of the frontoparietal cortex. Neurons labeled with Nuclear Yellow also were found in lamina V. However, their distribution was predominantly ipsilateral to the cerebellar injection and generally was limited to the anterior and posterior sigmoid gyri, and the coronal gyrus. Most importantly, many neurons were labeled with both dyes, indicating that at least part of the transient cerebrocerebellar projection is derived from collateral branches of corticobulbar axons. A second set of experiments was done to determine if the transience of the cerebrocerebellar pathway is due to a retraction of collaterals of corticofugal axons or due to the death of the cortical neurons themselves. In these experiments True Blue was injected into the cerebella of kittens 8-10 days after birth and allowed to survive for 40-75 days. No neurons were labeled with True Blue in the frontoparietal cortex, although numerous neurons were labeled in the precerebellar nuclei of the brainstem. In a control set of experiments, True Blue was injected into the caudal medulla in animals at 7 postnatal days.(ABSTRACT TRUNCATED AT 250 WORDS)

Midbrain projections to the trigeminal, facial and hypoglossal nuclei in the opossum. A study using axonal transport techniques.

It has been proposed (see Berntson and Micco for review) that circuits intrinsic to the midbrain play an important role in the elaboration and control of behaviors involving the motor nuclei of the trigeminal, facial and hypoglossal nerves (e.g. defense, threat, attack); but because of technical problems, it has been difficult to analyze their organization. Using the horseradish peroxidase technique we have localized those midbrain neurons which project to each of the above nuclei and by using the autoradiographic method we have plotted the intranuclear distribution of their axons. Using both techniques, we have seen that mesencephalic projections to oral-facial motor nuclei strongly favor the nucleus of the facial nerve. Cells ventral to the cerebral aqueduct, including the ventral periaqueductal gray, the interstitial nucleus of Cajal, the nucleus of Darkshchewitsch and the rostral oculomotor nucleus provide major midbrain-facial projections in the opossum. Their axons terminate densely and bilaterally within areas innervating auricular muscles and to a lesser extent, the platysma sheet. The projection to the caudal auricular area of the facial complex is particularly dense. Neurons within and dorsal to the red nucleus project to regions of the contralateral facial nucleus reported to supply buccolabial, zygomatic and cervical musculature. There is also a minor tectal projection to the facial nucleus. Direct projections to the hypoglossal nuclei also arise within the periaqueductal gray and interstitial nucleus, but if such regions influence the motor trigeminal nucleus, it is mainly by way of dendrites that extend outside the nucleus or by at least one synaptic delay. The mesencephalic nucleus of the trigeminal nerve, however, projects strongly to the motor trigeminal nucleus. These data are discussed in light of their possible functional significance.

A medullary dorsal horn relay for the cardiorespiratory responses evoked by stimulation of the nasal mucosa in the muskrat Ondatra zibethicus: evidence for excitatory amino acid transmission.

Stimulation of the upper respiratory tract, including the nasal mucosa, with water, vaporous irritants, or gases, induces a collation of several cardiorespiratory responses including an apnea and bradycardia and often some change in arterial blood pressure. Since the nasal mucosa is innervated by branches of the trigeminal nerve, it implies that some part of the trigeminal system within the central nervous system mediates the autonomic responses induced by nasal stimulation. In the present study, respirations, heart rate and arterial pressure were monitored in muskrats anesthetized with a mixture of chloralose-urethane. We induced a bradycardia and apnea by stimulating the nasal mucosa of muskrats with brief (5 s) transnasal application of vapors of ammonia hydroxide. In an effort to determine the central site where the trigeminal mediation of the cardiorespiratory responses occurs, small nanoliter injections of 2% lidocaine were made bilaterally into the subnucleus caudalis of the spinal trigeminal nucleus (referred to as the medullary dorsal horn) to determine if the responses could be blocked. The responses could be blocked when the lidocaine injections on both sides were placed in the rostral, ventral parts of the medullary dorsal horn, but persisted when the injections were placed elsewhere. Since lidocaine blocks both neurons and fibers of passage, nanoliter injections of kynurenate, a general excitatory amino acid antagonist, were used in a similar paradigm to circumvent the problem of blocking only fibers of passage.(ABSTRACT TRUNCATED AT 250 WORDS)

Negative chronotropism of the heart is inhibited with lesions of the caudal medulla in the rat.

Neurons in the ventrolateral medulla are essential for cardiorespiratory regulation. It has been suggested that neurons in the caudal ventrolateral medulla are responsible for the negative chronotropic effect of the heart, at least in carnivores, because injection of glutamate into this area decreases heart rate significantly. In the present study, we monitored heart rate both before and after injections of the excitotoxin ibotenic acid into the most caudal part of the ventrolateral medulla in rats. We found that resting heart rate increased significantly by more than 53% (P<0.0001) after the ibotenic acid injections. This result suggests that neurons located in the caudal ventrolateral medulla are responsible for the negative chronotropic effect of the heart in the rat, especially its most caudal part.

Brainstem projections to the facial nucleus of the opossum. A study using axonal transport techniques.

The horseradish peroxidase and autoradiographic techniques have been used to determine the origin and intranuclear termination of brainstem axons projecting to the facial nucleus of the opossum and to define networks which could be utilized in some oral-facial behaviors. Two regions of the midbrain have dense projections to the facial nucleus. One region is the ventral periaqueductal gray and adjacent interstitial nucleus of the medial longitudinal fasciculus which project bilaterally to those areas of the facial nucleus supplying auricular and cervical musculature. A second is the paralemniscal zone of the caudolateral midbrain which innervates the same areas of the contralateral facial nucleus. The red nucleus and/or the adjacent tegmentum send a less dense projection to those regions of the contralateral facial nucleus which innervate buccolabial and zygomatic muscles. The dorsolateral pons (the parabrachial complex, the nucleus locus coeruleus, pars alpha, and the nucleus sensorius n. trigemini, pars dorsalis) projects densely to those areas of the ipsilateral facial nucleus which innervate buccolabial and zygomatic musculature. In contrast, the nucleus reticularis pontis, pars ventralis, projects bilaterally to parts of the facial nucleus supplying auricular and cervical muscles. There was evidence of some rostral to caudal organization in the latter projection. Neurons in medial parts of the lateral reticular formation project bilaterally to the facial nucleus. Those within the nucleus reticularis parvocellularis and the rostral nucleus reticularis medullae oblongatae ventralis innervate areas supplying buccolabial and zygomatic muscles. Neurons in the nucleus reticularis medullae oblongatae ventralis located caudal to the obex favor regions of the facial nuclei which supply auricular and cervical muscles. Neurons in the nucleus reticularis medullae oblongatae dorsalis and lamina V of the medullary and spinal dorsal horns project ipsilaterally to the facial nucleus in a manner suggesting that information from specific cutaneous areas reaches neurons supplying the muscles deep to them. The brainstem-facial connections are discussed in relation to the functionally diverse roles served by the facial nucleus in oral-facial behavior.