Nucleus Reticularis Pontis Oralis Research Articles

Origins of serotonergic, and cholinergic neurons projecting to the nucleus reticularis pontis oralis in the cats

Origins of serotonergic, and cholinergic neurons projecting to the nucleus reticularis pontis oralis in the cats

Primate supplementary eye field: I. Comparative aspects of mesencephalic and pontine connections

WGA-HRP was used to examine projections to the brainstem from the supplementary eye field (SEF). The SEF was defined electrophysiologically in awake, behaving monkeys and connections were compared to those of the arcuate frontal eye field (FEF), area 6DC, and primary motor cortex. The SEF was found to have either direct or indirect connections with almost every known pre- and paraoculomotor structure of the brainstem. The SEF was found to project bilaterally to layers I and IV of a tangentially widespread region of the superior colliculus. Terminal label was evident in the pretectal olivary nucleus, nucleus of the optic tract, nucleus raphe interpositus (omnipause region), nucleus prepositus hypoglossi, the perioculomotor cap of the central gray, dorsal central gray, nucleus reticularis tegmenti pontis, nucleus reticularis pontis oralis, and to multiple nuclei of the basis pontis (most densely to the dorsomedial nucleus). Bilateral projections were found in the parvicellular red nucleus. Reciprocal connections were present in the nucleus limitans, the mesencephalic reticular formation, locus coeruleus, and the serotonergic nuclei of the raphe complex (dorsalis and central superior). Overall patterns of connectivity were similar to those of the FEF and markedly different from those of the contiguous dorsocaudal area 6 or primary motor cortex. It was concluded that observed patterns of SEF-brainstem connectivity further justifies viewing this region as a distinct eye field that is likely to serve preparatory and trigger functions in the generation of saccadic eye movements.

Supplementary eye field as defined by intracortical microstimulation: Connections in macaques

In macaques, the frontal eye field and the recently defined supplementary eye field play a role in the production of eye movements. Whereas the structure and function of the frontal eye field are well understood, little is known about the supplementary eye field. The goal of this study was to determine the connections of the physiologically defined supplementary eye field. In each case, the location of the supplementary eye field was determined by using intracortical microstimulation, the borders were marked with small electrolytic lesions, and horseradish peroxidase conjugated to wheat germ agglutinin was injected into the supplementary eye field. After the tissue was incubated with tetramethyl benzidine, it was determined that in three cases the injection site was confined to the physiologically defined supplementary eye field. The present results indicate that the supplementary eye field is reciprocally connected with the claustrum, ventral anterior nucleus, including pars magnocellularis, nucleus X, posterior subdivision of the ventral lateral nucleus, multiform, parvocellular, magnocellular, and densocellular subdivisions of the medial dorsal nucleus, central lateral nucleus, parafascicular nucleus, and suprageniculate-limitans complex. The supplementary eye field projects to the putamen, caudate, reticular nucleus of the thalamus, central densocellular nucleus, zona incerta, subthalamic nucleus, rostral interstitial nucleus of the medial longitudinal fasciculus, parvocellular part of the red nucleus, intermediate and deep layers of the superior colliculus, central gray, cuneiform nucleus, mesencephalic reticular formation, pontine gray, nucleus reticularis tegmenti pontis, and nucleus reticularis pontis oralis. The supplementary eye field is reciprocally and bilaterally connected with periprincipal and inferior prefrontal cortex, with periarcuate cortex, including the frontal eye field, the frontal ventral region, and with postarcuate premotor cortex, and cortex surrounding the supplementary eye field, including the supplementary motor area. The supplementary eye field is also reciprocally connected ipsilaterally with cortex in and around the cingulate sulcus and the intraparietal sulcus, whereas cortex within the superior temporal sulcus projects to the supplementary eye field. The connections of the physiologically defined supplementary eye field are compared to previously demonstrated connections of the supplementary motor region and of the physiologically defined frontal eye field. Comparisons between the connections of the frontal and supplementary eye fields reveal that both regions are connected with structures related to visuomotor functions, but the frontal eye field has more extensive connections with vision-related structures, and the supplementary eye field has more extensive connections with structures related to prefrontal and skeletomotor functions. Such connectional differences suggest functional differences between these two sensorimotor regions of the frontal lobe.

Abnormalities of horizontal gaze. Clinical, oculographic and magnetic resonance imaging findings. II. Gaze palsy and internuclear ophthalmoplegia.

The site of lesions responsible for horizontal gaze palsy and various types of internuclear ophthalmoplegia (INO) was established by identifying the common areas where the abnormal MRI signals from patients with a given ocular-motor disorder overlapped. Patients with unilateral gaze palsy had lesions in the paramedian area of the pons, including the abducens nucleus, the lateral part of the nucleus reticularis pontis caudalis and the nucleus reticularis pontis oralis. Patients with abducens nucleus lesions showed additional clinical signs of lateral rectus weakness. Lesions responsible for bilateral gaze palsy involved the pontine tegmental raphe. Since this region contains the saccadic omnipause neurons, this finding suggests that damage to omnipause cells produces slowing of saccades rather than opsoclonus, as previously proposed. All INOs, regardless of the presence of impaired abduction or convergence, had similar MRI appearances. Frequently the lesions in patients with INO, were not confined to the medial longitudinal fasciculus (MLF) but also involved neighbouring structures at the pontine and mid-brain levels. There was a statistically significant association between the clinical severity of the INO and the presence of abnormal abduction or convergence. The findings suggest that the lesions outside the MLF, which may affect abducens, gaze or convergence pathways, are responsible for the presence of features additional to INO, depending on the magnitude of functional disruption they produce.

Lower brainstem afferents to the cat posterior hypothalamus: A double-labeling study

Using a double-immunostaining technique with cholera toxin (CT) as a retrograde tracer, the authors examined the cells of origin and the histochemical nature of lower brainstem afferents to the cat posterior hypothalamus. The posterior hypothalamus, in particular the lateral hypothalamic area, receives substantial afferent projections from: substantia nigra, peripeduncular nucleus, ventral tegmental area, periaqueductal grey, mesencephalic reticular formation, peribrachial region including the locus coeruleus complex, rostral raphe nuclei and the rostral part of the nucleus raphe magnus. In addition, a moderate number of retrogradely labeled neurons was found in: Edinger-Westphal nucleus, nucleus reticularis pontis oralis, nucleus reticularis magnocellularis, caudal lateral bulbar reticular formation around the nucleus ambiguus and lateral reticular nucleus and the nucleus of the solitary tract. The posterior hypothalamus receives: 1. 1) dopaminergic inputs from A8, A9 and A10 cell groups; 2. 2) noradrenergic inputs from A6 and A7 pontine, as well as A1 and A2 bulbar cell groups; 3. 3) adrenergic inputs from C1 cell group in the caudal medulla; 4. 4) serotoninergic inputs from the rostral raphe nuclei (B6, B7 and B8 cell groups); 5. 5) cholinergic inputs from the peribrachial region of the dorsal pontine tegmentum as well as from the nucleus reticularis magnocellularis of the medulla; 6. 6) peptidergic inputs such as methionin-enkephalin, substance P, corticotropin-releasing factor and galanin that originate mainly in the mesencephalic periaqueductal grey, the dorsal raphe nucleus and the peribrachial region of the dorsal pontine tegmentum.

Substance P-containing neurons in the pontomesencephalic tegmentum of the human brain

We have employed immunohistochemical and computerized morphometric procedures to study substance P-containing neurons in the tegmentum of adult humans. An estimated 192, 500±40,500 substance P-containing neurons were found in three main cytoarchitectural regions: the mesencephalic reticular formation, the central gray, and the pontine reticular formation. The morphology of the immunoreactive neurons varied according to the region in which they were found. On the basis of size alone two types of substance P-containing neurons, large and small, were readily distinguishable by eye and measurement. Within each of the three main regions it was possible to distinguish distinct subgroups using cell size, morphology and position. Large neurons were concentrated in the caudal midbrain (pedunculopontine tegmental nuclei), in the oral pontine reticular nucleus and in the lateral dorsal tegmental nucleus. In contrast, small neurons were concentrated in the rostral mesencephalic reticular formation (cuniform nuclei). Both small and large neurons were found in the midbrain and pontine raphe nuclei. In addition, small neurons were concentrated in discrete midline regions (the periaqueductal gray, the tegmental nuclei of the pontine central gray, and the interpeduncular nucleus). The findings suggest that the majority of neurons in the brainstem tegmental nuclei previously identified as cholinergic also contain substance P in humans.

Role of pontomedullary reticular formation neurons in horizontal head movements: an ibotenic acid lesion study in the cat

Single-cell recording, electrolytic lesion and electrical stimulation studies have indicated that the pontomedullary reticular formation (PMRF) plays a role in head movement (HM) control. However, recent studies utilizing excitotoxin lesions of the PMRF have reported no effect on HM. In the present study, we have examined the acute and chronic motor effects of injecting ibotenic acid (IBO) into the nucleus reticularis pontis oralis, nucleus reticularis potis caudalis and rostral medullary nucleus gigantocellularis of the feline PMRF. IBO injections in all of these regions induced tonic flexion of the head toward the ipsilateral side. This effect lasted 4–16 h. It was followed by a second phase in which head flexion and whole body circling were directed toward the contralateral side. Although this forced contralateral head turning disappeared within two days, the tendency to turn contralaterally and the impaired ability to make rapid ipsilateral HMs were present throughout survival periods lasting more than 4 months. Unilateral IBO PMRF lesions reduced the amplitude of vestibular induced quick phase (anti-compensatory) HMs toward the ipsilateral side and resulted in abnormally large and persistent slow compensatory HMs toward the contralateral side. Following IBO injections, the threshold intensity fof HMs evoked by electrical stimulation at the injection site was elevated, and the amplitude and velocity of evoked HMs reduced. Histological data indicated that the reticular area involved in HM control was relatively large and probably extended beyond the PMRF region examined here. However, lesions including the nucleus reticularis pontis caudalis (NRPC) produced more severe and persistent HM deficits than those including the nucleus reticularis gigantocellularis. These data together with available anatomical and electrophysiological evidence indicate that PMRF neurons play a critical role in the generation of fast horizontal HMs toward the ipsilateral side.

Afferent and efferent connections of the cholinoceptive medial pontine reticular formation (region of the ventral tegmental nucleus) in the cat

Following minor concussive brain injury when there is an otherwise general suppression of CNS activity, the ventral tegmental nucleus of Gudden (VTN) demonstrates increased functional activity (32). Electrical or pharmacological activation of a cholinoceptive region in this same general area of the medial pontine tegmentum contributes to certain components of reversible traumatic unconsciousness, including postural atonia (31, 32, 45). Therefore, in an effort to examine the neuroanatomical basis of the behavioral suppression associated with a reversible traumatic unconsciousness, the afferent and efferent connections of the VTN and putative cholinoceptive medial pontine reticular formation (cmPRF) were studied in the cat using the retrograde horseradish peroxidase (HRP), HRP/choline acetyltransferase (ChAT) double-labeling immunohistochemistry, and anterograde HRP and autoradiographic techniques. Based upon retrograde HRP labeling, the principal afferents to the VTN region of the cmPRF originated from the medial and lateral mammillary nuclei, and lateral habenular nucleus, and to a lesser extent from the interpeduncular nucleus, lateral hypothalamus, dorsal tegmental nucleus, superior central nucleus, and contralateral nucleus reticularis pontis caudalis. Other afferents, which were thought to have been labeled through spread of HRP into the medial longitudinal fasciculus (MLF), adjacent paramedian pontine reticular formation, or uptake by transected fibers descending to the inferior olive, included the nucleus of Darkschewitsch, interstitial nucleus of Cajal, zona incerta, prerubral fields of Forel, deep superior colliculus, nucleus of the posterior commissure, nucleus cuneiformis, ventral periaqueductal gray, vestibular complex, perihypoglossal complex, and deep cerebellar nuclei. In HRP/ChAT double labeling studies, only a very small number of cholinergic VTN afferent neurons were found in the medial parabrachial region of the dorsolateral pontine tegmentum, although the pedunculopontine and laterodorsal tegmental nuclei contained numerous single-labeled ChAT-positive cells. Anterograde HRP and autoradiographic findings demonstrated that the VTN gave rise almost exclusively to ascending projections, which largely followed the course of the mammillary peduncle (16, 21) and medial forebrain bundle, or the tegmentopeduncular tract (4). The majority of fibers ascended to terminate in the medial and lateral mammillary nuclei, interpeduncular complex (especially paramedian subnucleus), ventral tegmental area, lateral hypothalamus, and the medial septum in the basal forebrain. Labeling that joined the mammillothalamic tract to terminate in the anterior nuclear complex of the thalamus was thought to occur transneuronally. Some projections were also observed to nucleus reticularis pontis oralis and caudalis, superior central nucleus, and dorsal tegmental nucleus adjacent to the VTN. Only when the injections involved more extensive portions of the rostral mPRF were projections to the intralaminar complex and reticular nucleus of the thalamus observed. Only meager descending projections were observed to the nucleus reticularis pontis caudalis and nucleus reticularis gigantocellularis of the rostral medulla, and none were observed to the spinal cord. While no functional significance could be attributed to the predominantly ascending limbic connections of the VTN, the lack of descending spinal connections, and the failure of these studies to find a major cholinergic input to a region purported to be the cholinoceptive pontine inhibitory area (CPIA), are discussed in relation to the possible neuroanatomical bases of the complex functional roles of the medial pontine tegmentum in the etiology of behavioral consequences following traumatic brain injury. Taken together with previous reports, the study suggests that the spinal-projecting portion of the CPIA responsible for muscular atonia is located in the medial brainstem tegmentum caudal to the VTN.

Contribution of postural muscle tone to full expression of posture and locomotor movements: Multi-faceted analyses of its setting brainstem-spinal cord mechanisms in the cat.

In this minireview, I have summarized and discussed our results concerning the neuronal mechanisms of postural suppression, and our thoughts about contribution of postural muscle tone to the full expression of locomotion. The identified brainstem-spinal cord system is schematically illustrated in Fig. 1 with its neuronal constituents (A). When cells of origin of this system (cells in the nucleus reticularis pontis oralis), or the pathway descending from these cells (DTF area) are tonically activated, cells in the nucleus reticularis gigantocellularis (gc cells) are also tonically activated, and with this process the system as a whole exerts generalized or non-reciprocal tonic inhibitory effects upon alpha-motoneurons innervating hindlimb extensor and flexor muscles. In consequence, postural muscle tone, especially that of the hindlimbs, is tonically suppressed and results in sustained suppression of postural support both in acute decerebrate cats (locomotor preparation) and in awake, freely moving cats, terminating locomotor movements. Since postural control and locomotor control are not separate phenomena, our results indicate that interaction of the above-described two control systems should be studied at each level of the brainstem and the spinal cord. In fact, contribution of brainstem neurons and of spinal interneurons has already been studied. It may also be interesting to elucidate supra-pontine structures which activate the identified brainstem-spinal cord inhibitory system. Such a study may elucidate the neuronal structures related not only to the termination of on going movements but also to the muscular atonia observed during active sleep. As demonstrated, even for the understanding of the brainstem-spinal cord system involved in postural suppression, multi-faceted and mutally related analytical approaches have been necessary as suggested by Brookhart, and these approaches allowed us to approach a much better understanding of the problem one faces. They were neuroanatomical analyses of plausible neuronal structures, electrophysiological analyses of their synaptic organizations, the neuropharmacological analyses of their putative neurotransmitters, and finally the most important, behavioral analyses. For a thorough understanding of the dynamics of postural and locomotor control systems, the problems we are now concerned with are to identify both the "hardware" and the "software" of these two systems. Understanding of the hardware requires an elucidation of the neuronal circuits including synaptic organizations, and that of the software an identification of the putative neurotransmitters that set the identified neuronal circuit to work, so that the systems as a whole exhibit a meaningful external manifestation.(ABSTRACT TRUNCATED AT 400 WORDS)

Neuronal origin of parallel suppression of postural tone and respiration elicited by stimulation of midpontine dorsal tegmentum in the decerebrate cat

This paper describes the possibility that rostal pontine neuronal structures cause the parallel suppression of postural tone and respiration evoked by stimulation of the dorsal tegmental field (DTF) of the pons in decerebrate cats. Stimulation of the DTF along the midline decreased both diaphragmatic activity and the bilateral tone of the hind-limb extensor muscles. Pontine neuronal structures located rostrally to the DTF, from which antidromically activated units could be recorded on stimulation of the DTF, were studied. Antidromic spikes were recorded in and near the nucleus reticularis pontis oralis. Tonic electrical stimulation of these sites caused parallel suppression of postural tone and respiration. These suppressive effects were almost similar to those elicited by the DTF stimulation.

Reduced nicotinamide adenine dinucleotide phosphate-diaphorase histochemistry in the pontomesencephalic region of the human brainstem

Reduced nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-diaphorase), which is specifically localized in neurons, has been histochemically demonstrated in human brain by using a perfusion-fixation procedure. With such fixed human brainstem, it was possible to study the topographic organization of NADPH-diaphorase-containing neurons that were visualized in fine detail for the first time. In the pontomesencephalic region, positive neurons were observed in nuclei around the decussation and arm of the superior cerebellar peduncle. These nuclei included the pedunculopontine tegmental, lateral parabrachial and oral pontine reticular nuclei. The positive somata were mainly multipolar in shape and medium to large in size. The positive neurons appeared to correspond to cholinergic neurons, at least partly in the brainstem, in terms of both the patterns of distribution and the cellular morphology.

Neuronal structures of the brainstem participating in postural suppression in cats

Two histochemical tracer techniques (a horseradish peroxidase and a Phaseolus vulgaris leucoagglutinin axonal flow technique) were employed to determine the cells of origin, axonal trajectories and terminals of fibers of passage through the dorsal tegmental field (DTF) in the pons along the midline (Horsley-Clarke coordinates, P 3 to P 7, LR 0, H - 4.5 to H - 6.0). Stimulation of the DTF area results in the postural suppression in both acute decerebrate, reflexively standing cats and freely moving awake cats. With these techniques, we have been able to demonstrate that in addition to pontine reticular cells, many cells in the dorsolateral pontine tegmentum, including the LC-complex, project their axons to the rostral part of the midline DTF area, and that descending axons from the nucleus reticularis pontis oralis pass through the DTF area and terminate on cells in the nucleus reticularis pontis caudalis and the nucleus reticularis gigantocellularis. Among those cells in the nucleus reticularis gigantocellularis, a great number of giant cells project to the lumbar spinal cord. The functional roles of these neuronal structures are discussed in relation to the results obtained by chemical stimulation of the pontine structures.

Glycine potentiates diazepam anticonvulsant activity in electroshock seizures of rats: Possible sites of interaction in the brainstem

The effect of orally or intracerebrally injected glycine on the anticonvulsant actions of intraperitoneal diazepam was examined using a tonic-clonic electroshock seizure model in the rat. Orally administered glycine (1.125 g/kg) potentiated the anticonvulsant effect of diazepam (DZP) to convert tonic-clonic electroshock seizures to less severe subthreshold clonic seizures. Oral glycine by itself had no effect on the tonic-clonic seizure response. Bilateral substantia nigra (SN) microinjections of glycine (125 μg/site) failed to potentiate intraperitoneal DZP when compared with the most appropriate control, animals treated with DZP and intranigral saline. It was not possible to determine whether bilateral glycine microinjections into the inferior olivary nucleus (IO) potentiated anticonvulsant effects of DZP since glycine alone converted all tonic-clonic seizures to the clonic response. Finally, bilateral glycine microinjection alone into the nucleus reticularis pontis oralis (PNO) produced an anticonvulsant effect when compared to untreated control responses but did not potentiate the anticonvulsant actions of DZP. Although these results may indicate that the glycinergic potentiation of DZP involves a direct pharmacodynamic interaction between these two compounds at specific brain sites, these sites have not yet been demonstrated conclusively.

Afferent connections of the nuclei reticularis pontis oralis and caudalis: A horseradish peroxidase study in the rat

The afferent connections of the nuclei reticularis pontis oralis and caudalis were studied experimentally in the rat by the aid of either free horseradish peroxidase or horseradish peroxidase conjugated with wheat germ agglutinin used as retrograde tracers. The results suggest that the nucleus reticularis pontis oralis receives its main input from the zona incerta and field H 1, of Forel, the superior colliculus, the central gray substance, and the mesencephalic and magnocellular pontomedullary districts of the reticular formation. Many other structures seem to represent modest additional sources of projections to the nucleus reticularis pontis oralis; these structures include numerous cortical territories, the nucleus basalis, the central amygdaloid nucleus, hypothalamic districts, the anterior pretectal nucleus, the substantia nigra, the cuneiform, the accessory oculomotor and the deep cerebellar nuclei, trigeminal, parabrachial and vestibular sensory cell groups, the nuclei raphe dorsalis and magnus, the locus coeruleus, the dorsolateral tegmental nucleus, and the spinal cord. While the afferentation of the rostral portion of the nucleus reticularis pontis caudalis appears to conform to the general pattern outlined above, some deviations from that pattern emerge when the innervation of the caudal district of the nucleus reticularis pontis caudalis is considered; the most striking of these differences is the fact that both spinal and cerebellar inputs seem to distribute much more heavily to the referred caudal district than to the remaining magnocellular pontine reticular formation. The present results may contribute to the elucidation of the anatomical substrate of the functionally demonstrated involvement of the nuclei reticularis pontis oralis and caudalis in several domains that include the regulation of the sleep-waking cycle and cortical arousal, somatic motor mechanisms and nociceptive behavior.

The cerebellar projection from the reticular formation of the brain stem in the rabbit

By retrograde transport of horseradish peroxidase the reticulocerebellar projections were examined in twenty-six rabbits. After injections in the cerebellum retrogradely labeled neurons were more numerous in the caudal reticular formation (ventral and gigantocellular reticular nuclei) than in its rostral part (caudal and oral pontine reticular nuclei). The labeled cells were of all sizes, large, medium-sized and small. Giant cells were labeled only after injections in the posterior lobe vermis. After injections in the anterior lobe, the posterior vermis, the fastigial nucleus and the flocculus, retrogradely labeled neurons were found bilaterally in the ventral reticular nucleus, the gigantocellular reticular nucleus and the caudal pontine reticular nucleus. Some cases with posterior vermal and fastigial injections in addition showed labeled neurons bilaterally in the oral pontine reticular nucleus. There were no major side differences. The cases with injections in the anterior part of the paramedian lobule gave rise to only a few labeled cells in the gigantocellular reticular nucleus. Negative findings were consistently made in the mesencephalic reticular formation.

The fiber projections from the dentate nucleus to the reticular formation of the brain stem in the rabbit.

The projections from the dentate nucleus to the reticular formation of the brain stem in rabbit have been examined by means of the Fink-Heimer technique. The fibers arising from the dentate nucleus primarily project to the reticular formation via the contralateral and ipsilateral descending limbs of the brachium conjunctivum. The descending fibers project bilaterally to the parvocellular reticular nucleus, the ventral reticular nucleus, the gigantocellular reticular nucleus, the nucleus raphe magnus, the oral and caudal pontine reticular nuclei, and the reticulo-tegmental nucleus.

Pontine urine storage center in the dog.

Electrical stimulation of the presumptive pontine urine storage center, areas ventral to and/or lateral to the pontine micturition center, elicited an increase in threshold volume at which reflex micturition occurred in response to bladder filling with physiological saline, suggesting a facilitatory effect on the urine storage function. The electrolytic lesions made in the stimulated areas were histologically identified to distribute at the nucleus reticularis pontis oralis, Kölliker-Fuse nucleus and subcoeruleus. These nucleus seemed to work as a pontine urine storage center and to perform a reciprocal action with the pontine micturition center.

Dorsolateral pontine tegmentum and the classically conditioned nictitating membrane response: analysis of CR-related single-unit activity.

Previous investigations have suggested that the dorsolateral pontine tegmentum (DLP) may be part of a system essential for classical conditioning of the nictitating membrane response. The present study examined CR-related firing patterns of extracellularly-recorded single units in the DLP. Differential conditioning, using tonal CSs and periocular electrostimulation as the US, was employed so that firing patterns on CR and non-CR trials could be compared. Cells that exhibited CR-related increases in firing (excitatory cells) were found in reticular formation surrounding the motor trigeminal nucleus (zone h), including the supra-trigeminal region, and in a region dorsal and dorsomedial to the brachium conjunctivum. Cells that exhibited CR-related decreases in firing (inhibitory cells) were observed in subcoeruleus/medial parabrachial regions and dorsal nucleus reticularis pontis oralis and caudalis. A third class of cells (temporal cells) exhibited CR-related shifts in the temporal distribution of spikes; these cells were located in various brain stem regions. The firing of many of the excitatory, inhibitory, and temporal cells preceded the behavioral CR by an amount of time sufficient for causal involvement. In light of evidence indicating that the cerebellum is critically involved in conditioning, the present study suggests that two systems, the cerebellum and the DLP, may be in control of CRs. The relationship of the two systems and their possible roles in conditioning are discussed.

The cholinergic system of the human hindbrain studied by choline acetyltransferase immunohistochemistry and acetylcholinesterase histochemistry

A map of cholinergic cells of the human brainstem identified by immunohistochemistry of choline acetyltransferase (ChAT) is presented, along with a map of acetylcholinesterase (AChE)-containing cells and fibers. ChAT-positive structures belong to 4 brainstem systems: the cranial motor nuclei; the parabrachial complex; the reticular system; and the vestibular system. All motor nuclei of the cranial nerves, as well as the nucleus supraspinalis, are ChAT-positive. The positively staining structures of the parabrachial system include the nucleus tegmentali pedunculopontinus, and the nuclei parabrachialis medialis and lateralis. Nuclei of the reticular system containing some ChAT-positive cells include the nucleus reticularis pontis oralis and caudalis, the nucleus reticularis tegmenti pontis, the nucleus reticularis gigantocellularis, the nucleus reticularis lateralis and the formatio reticularis centralis (medulla). Structures of the vestibular and auditory systems which contain some ChAT-positive cells include the nucleus vestibularis lateralis, and the nuclei olivaris superioris medialis and lateralis. All ChAT-positive structures stain strongly for AChE. AChE-positive, ChAT-negative structures were noted in several sensory systems. The substantia nigra, locus coeruleus and raphe nuclei, known to contain non-cholinergic cells, also stain positively. The significance of the AChE-positive, ChAT-negative staining in most structures remains to be determined. A knowledge of the cholinergic systems of human brain may be important to an understanding of the pathology of a number of diseases.

Connections of the pigeon dorsomedial forebrain studied with WGA‐HRP and 3H‐proline

The afferent-efferent connections of the pigeon dorsomedial forebrain, which is composed of the "hippocampus" (Hp) and "parahippocampus" (APH), presumed homologues of the mammalian hippocampal complex, were studied. Afferent projections were identified by wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP) and efferent projections were identified by 3H-proline and WGA-HRP. In addition to identified intrinsic connections within Hp and APH, both Hp and APH were found to be in receipt of ipsilateral forebrain afferents from each other, the hyperstriatum accessorium, nucleus of the diagonal band, nucleus taeniae, and area corticoidea dorsolateralis. Only Hp received input from the contralateral Hp while only APH received input from the ipsilateral hyperstriatum dorsale and archistriatum, pars ventralis. Both Hp and APH received ipsilateral diencephalic afferents from the nucleus mamillaris lateralis, stratum cellulare internum, nucleus lateralis hypothalami, and nucleus paramedianus internus thalami. Only APH received bilateral input from the nucleus superficialis parvicellularis (this nucleus may send a small projection to Hp) and nucleus dorsolateralis anterior thalami, pars medialis, and an ipsilateral projection from the nucleus subrotundus. Brainstem afferents to Hp and APH included ipsilateral projections from the area ventralis (Tsai) nucleus reticularis pontis oralis, nucleus raphes, nucleus subceruleus dorsalis, and nucleus centralis superior of Bechterew, and bilateral projections from the nucleus linearis caudalis and locus ceruleus, of which the nucleus subceruleus dorsalis, nucleus centralis superior of Bechterew, and locus ceruleus projected to APH only. Forebrain efferents from both Hp and APH were found to project ipsilaterally to the septum, the area of the fasciculus diagonalis Brocae, nucleus taeniae, and area corticoidea dorsolateralis. Only Hp appeared to send efferents to the contralateral septum and Hp, while only APH sent efferents to the hyperstriatum dorsale and the archistriatum. A hypothalamic projection from Hp and APH was found to partially terminate near the nucleus mamillaris lateralis. At the level of pathway connections, the results demonstrate a striking similarity between the avian dorsomedial forebrain and the dorsomedial cortex of reptiles and the mammalian hippocampus.