Dorsomedial Group Research Articles

Motif structure for the four subgroups within the suprachiasmatic nuclei affects its entrainment ability

Circadian rhythms of physiological and behavioral activities are regulated by a central clock. This clock is located in the bilaterally symmetrical suprachiasmatic nucleus (SCN) of mammals. Each nucleus contains a light-sensitive group of neurons, named the ventrolateral (VL) part, with the rest of the neurons being insensitive to light, named the dorsomedial (DM) group. While the coupling between the VL and DM subgroups have been investigated quite well, the communication among the four subgroups across the nuclei did not get a lot of attention. In this article, we theoretically analyzed seven motiflike connection patterns to investigate the network of the two nuclei of the SCN as a whole in relation to the function of the SCN. We investigated the entrainment ability of the SCN and found that the entrainment range is larger in the motifs containing a link between the two VL parts across the nuclei, but it is smaller in the motifs that contain a link between the two DM parts across the nuclei. The SCN may strengthen or weaken connections between the left and right nucleus to accomodate changes in external conditions, such as resynchronization after a jet lag, adjustment to photoperiod or for the aging SCN.

Zebrafish crypt neurons project to a single, identified mediodorsal glomerulus

Crypt neurons are a third type of olfactory receptor neurons with a highly unusual “one cell type - one receptor” mode of expression, the same receptor being expressed by the entire population of crypt neurons. Attempts to identify the target region(s) of crypt neurons have been inconclusive so far. We report that TrkA-like immunoreactivity specifically labeled somata, axons, and terminals of zebrafish crypt neurons and reveal a single glomerulus, mdg2 of the dorsomedial group, as target glomerulus of crypt neurons. Injection of a fluorescent tracing dye into the mdg2 glomerulus retrogradely labeled mostly crypt neurons, as assessed by quantitative morphometry, whereas no crypt neurons were found after injections in neighboring glomeruli. Our data provide strong evidence that crypt neurons converge onto a single glomerulus, and thus form a labeled line consisting of a single sensory cell type, a single olfactory receptor and a single target glomerulus.

Morphological characteristics of C1 and C2 adrenergic neurone groups in marmoset monkey brainstem by using antibody against phenylethanolamine-N-methyltransferase.

This work describes a mapping study of phenylethanolamine-N-methyltransferase (PNMT) immunoreactive neurones and fibres in the medulla oblongata of the marmoset monkey, Callithrix jacchus. Two groups of PNMT-immunoreactive neurones were found in the marmoset monkey medulla oblongata: a ventrolateral (C1 group) and a dorsomedial PNMT-immunoreactive cells group (C2 group). The PNMT-immunoreactive cells in the ventrolateral group C1 were found to be located around the lateral reticular nucleus. The PNMT-immunoreactive somata within the ventrolateral medulla are round to oval, and mostly multipolar with branched processes. In the dorsomedial group C2, PNMT-immunoreactive cell bodies appeared near the obex. The majority of the dorsomedial PNMT-immunoreactive neurones were observed in the nucleus tractus solitarius; although some were present in the dorsal motor nucleus of the vagus. The PNMT-immunoreactive somata in the dorsomedial medulla were small and round or ovoid. These results provide information upon the adrenergic system in the medulla oblongata of a species that presents a useful model of a small primate brain, the marmoset monkey.

Functional organization of the suprachiasmatic nucleus of Xenopus laevis in relation to background adaptation.

The process of background adaptation in the toad Xenopus laevis is controlled by neurons in the suprachiasmatic nucleus (SC) that inhibit the release of alpha-melanophore-stimulating hormone from the neuroendocrine melanotrope cells in the pituitary gland. We have identified the structural and functional organization of different neuropeptide Y (NPY)-containing cell groups in the Xenopus SC in relation to background adaptation. A ventrolateral, a dorsomedial, and a caudal group were distinguished, differing in location as well as in number, size, and shape of their cells. They also show different degrees of NPY immunoreactivity in response to different background adaptation conditions. In situ hybridization using a Xenopus mRNA probe for the exocytosis protein DOC2 revealed that melanotrope cells of black-adapted animals have a much higher expression of DOC2-mRNA than white-adapted ones. This establishes that the degree of DOC2-mRNA expression is a good parameter to measure cellular secretory activity in Xenopus. We show that in the ventrolateral SC group, more NPY-positive neurons express DOC2-mRNA in white- than in black-adapted animals. In contrast, NPY-positive neurons in the dorsomedial group have a high secretory activity under the black-adaptation condition. We propose that in black-adapted animals, NPY-positive neurons in the ventrolateral group, known to inhibit the melanotrope cells in white-adapted animals synaptically, are inhibited by NPY-containing interneurons in the dorsmedial group. NPY-positive neurons in the caudal group have similar secretory dynamics as the dorsomedial NPY neurons, indicating that they also play a role in background adaptation, distinct from that exerted by the ventrolateral and dorsomedial group.

Organization of projections from the inferior olive to the cerebellar nuclei in the rat.

The detailed organization of projections from the inferior olive to the cerebellar nuclei of the rat was studied by using anterograde tracing. The presence of a collateral projection to the cerebellar nuclei could be confirmed, and a detailed organization was recognized at the nuclear and subnuclear level. Olivary projections to the different parts of the medial cerebellar nucleus arise from various parts of the caudal half of the medial accessory olivary nucleus. The interstitial cell groups receive olivary afferents from the intermediate part of the medial accessory olive and from the dorsomedial cell column. A mediolateral topography was noted in the projections from the rostral half of the medial accessory olive to the posterior interposed nucleus. Olivary projections to the lateral cerebellar nucleus are derived from the principal olive according to basically inversed rostrocaudal topography. Projections from the dorsomedial group of the principal olive to the dorsolateral hump were found to follow a basically rostrocaudal topography. The anterior interposed nucleus receives olivary afferents from the dorsal accessory olive. Its rostromedial parts are directed to the lateral part of the anterior interposed nucleus and its caudolateral part reach the medial anterior interposed nucleus. No terminal arborizations in the cerebellar nuclei were found to originate from (1) the dorsal fold of the dorsal accessory olive, which resulted in projections to the lateral vestibular nucleus and (2) the dorsal cap of Kooy. It was noted that the olivary projection to the cerebellar nuclei is strictly reciprocal to the nucleo-olivary projection as described by Ruigrok and Voogd (1990). Moreover, it is suggested that the olivonuclear projection adheres to the organization of the climbing fiber projection to the cerebellar cortex and to the corticonuclear projection, thus, establishing and extending the detailed micromodular organization of the connections between inferior olive and cerebellum.

Direct projections from the dorsolateral pontine tegmentum to pudendal motoneurons innervating the external urethral sphincter muscle in the rat

Direct projections from the dorsolateral pontine tegmentum to pudendal motoneurons innervating the external urethral sphincter and the external and sphincter muscles were examined in the rat by the tract-tracing methods utilizing retrograde transport of cholera toxin B subunit and anterograde transport of biotinylated dextran amine. The dorsolateral pontine tegmental region, corresponding to the micturition reflex center of Barrington, was confirmed to send bilaterally, with an ipsilateral dominance, projection fibers to the spinal parasympathetic nucleus (inferior intermediolateral nucleus). The micturition reflex center of Barrington, however, did not seem to send many projection fibers to the ventral horn of the lumbosacral cord segments, whereas the region immediately ventral to the micturition reflex center of Barrington was found to send bilaterally, with a contralateral dominance, projection fibers to the dorsolateral group of pudendal motoneurons in both the male and female rats. In the female rat, the dorsolateral group of pudendal motoneurons are comprised primarily of motoneurons that innervate the external urethral sphincter muscle. The dorsomedial group of pudendal motoneurons, which contain motoneurons that innervate the external and sphincter and the bulbocavernosus muscles, did not seem to receive major projections from the dorsolateral pontine tegmental regions. It was also observed that the locus coeruleus sent some projection fibers bilaterally to the spinal parasympathetic nucleus but only a few to the ventral horn of the lumbosacral cord segments. Thus, the present results indicate that the dorsolateral group of pudendal motoneurons containing those innervating the external urethral sphincter muscle receive pontospinal projection fibers mainly from the dorsolateral pontine tegmental region immediately ventral to the micturition reflex center of Barrington.

Efferent neurons to the macula lagena in the embryonic chick

The lipophilic dye, DiI, was placed into the macula lagena of paraformaldehyde-fixed embryonic chicks. Retrogradely labeled cells were found bilaterally in the pontine reticular formation (RF) between the dorsal facial nucleus and the abducens nerve root. This location is similar to that of the dorsomedial group of efferent cells that project to the basilar papilla. No lagenar efferent neurons, however, were found near the superior olivary nucleus where the ventrolateral group of cochlear efferents is located. Whether efferent neurons in the pontine RF send collaterals to both the basilar papilla and to the macula lagena has yet to be determined.

Choline acetyltransferase-immunoreactive cochlear efferent neurons in the chick auditory brainstem.

Cholinergic neurons in the chick auditory brainstem were studied with the aid of an antiserum to choline acetyltransferase (ChAT), the biosynthetic enzyme for acetylcholine. ChAT-immunoreactive (ChAT-I) neurons were found in a ventrolateral and a dorsomedial cell group. The ventrolateral group is a rostrocaudally directed column of cells that surround the superior olive (SO), are ventromedial to the ventral facial nucleus (VIIv), and are lateral to the nucleus pontis lateralis (PL) as far rostrally as the nucleus subceruleus ventralis. Cells in the dorsomedial group were found in the pontine reticular formation medial to the dorsal facial nucleus and lateral to the abducens nerve root. Occasionally, small ChAT-I cells were found in the crossed dorsal cochlear tract and in the medial vestibular nucleus near the dorsal border of the caudal nucleus magnocellularis (NM). No ChAT-I neurons or fibers were observed in NM, nucleus angularis, nucleus laminaris, in the nuclei of the lateral lemniscus, or in the nucleus mesencephalicus lateralis pars dorsalis. To determine which cholinergic neurons project to the cochlea, a double-labeling technique was used combining ChAT-I and the retrograde transport of biotinylated dextran amine (BDA) from the inner ear. Double-labeled cells were found bilaterally in both the ventrolateral and dorsomedial cell groups, with the exception of large ChAT-I cells dorsal to the SO, which do not appear to project to the cochlea. Cholinergic cells that project to the cochlea were classified into three morphological groups: multipolar, elongate, and round-to-oval. Both the ventrolateral and the dorsomedial cell groups appear to have a mixture of these different cell types. The average somal area of cholinergic cochlear efferents was 246 microns 2. Only about 70% of the cochlear efferent neurons, however, are cholinergic.

Cerebellar nucleo‐olivary projections in the rat: An anterograde tracing study with Phaseolus vulgaris‐leucoagglutinin (PHA‐L)

In order to evaluate the reciprocity of olivo-cerebellar and cerebello-olivary connections, a detailed description of the cerebellar nucleo-olivary projection in the rat is presented using small, iontophoretic injections of the anterograde tracer Phaseolus vulgaris-leucoagglutinin. Sparse projections were found to arise from the rostral part of the medial cerebellar nucleus toward the lateral part of the caudal medial accessory olive. Its medial parts receive a projection from the dorsolateral protuberance of the medial cerebellar nucleus. Caudal and lateral regions of the medial cerebellar nucleus project to the "beta" group and dorsomedial cell column. Heavy olivary projections to circumscribed parts of the inferior olive were found after injections in the remaining cerebellar nuclei. The medial part of the posterior interposed nucleus connects to caudolateral areas of the rostral half of the medial accessory olive, whereas lateral areas project to more rostromedial parts. The most ventromedial part of the lateral cerebellar nucleus projects to the ventrolateral outgrowth. Adjacent medial, ventral, and caudal regions connect to the ventral leaf of the principal olive. The cerebellar origin of the projection to its dorsal leaf is located in lateral, dorsal, and rostral parts of the lateral cerebellar nucleus. The dorsolateral hump projects to the dorsomedial group of the rat inferior olive. Rostromedial projections to the dorsal accessory olive originate from the lateral part of the anterior interposed nucleus, whereas its medial parts project to more lateral and caudal regions of this olivary subnucleus. The dorsal fold of the dorsal accessory olive does not receive a projection from the cerebellar nuclei but from the lateral vestibular nucleus. No cerebellar projections were found to the dorsal cap. Relatively strong ipsilateral projections, which were the mirror images of the contralateral projections, were observed in the dorsomedial group, rostral medial accessory olive, and ventral leaf of the principal olive. When both the inferior olive and the cerebellar nuclei are considered as folded but continuous sheets of grey matter, the complete nucleo-olivary projection can be described as a simple transformation.

Brainstem projections to the rat cuneate nucleus

Neurons in the pontomedullary tegmentum have been proposed as a final common pathway subserving descending inhibition in the dorsal column nuclei. To investigate the anatomical substrate for these descending effects, brainstem projections to the cuneate nucleus of rats were studied with injections of lectin-conjugated horseradish peroxidase. In rats with iontophoretic tracer injections in this nucleus, many labeled neurons were detected near the injection site, especially ventral and caudal to it. Intrinsic reciprocal projections were observed after injections in caudal, middle, or rostral levels of the cuneate nucleus. Neurons were labeled in the red nucleus, in agreement with previous anatomical studies, and also in the trigeminal, vestibular, and cochlear nuclei. An ipsilateral dorsomedial group of neurons was labeled in the upper cervical segments and scattered neurons were also labeled bilaterally near the central canal. Sparse retrograde labeling in the tegmentum was focused in the lateral paragigantocellular nucleus and caudal raphe. Consistent with the retrograde experiments, anterograde labeling after pressure injections of lectin-conjugated horseradish peroxidase in the pontomedullary tegmentum was very sparse within the dorsal column nuclei; labeling was dense, however, in the region immediately ventral to these nuclei. These results confirm previous work indicating that the activity of cuneate neurons is modulated by brainstem sensory nuclei. However, it appears that direct projections to the cuneate nucleus from pontine and rostral medullary regions are sparser than previously suggested. The last link of a polysynaptic descending inhibitory pathway may include GABAergic neurons immediately adjacent to the dorsal column nuclei and/or intrinsic to these nuclei.

Galanin-like immunoreactivity is present in human substantia innominata and in senile plaques in Alzheimer's disease

Galanin immunoreactivity has been shown to be present in cholinergic magnocellular basal forebrain neurons in both rat and monkey brain. In the present study galanin immunoreactivity in human substantia innominata was found in both the magnocellular neurons of the nucleus basalis of Meynert and in a dorsomedial group of intensely immunoreactive parvocellular neurons. Scattered galanin-immunoreactive fibers, but no immunoreactive neurons, were found in normal human cerebral cortex. Galanin-immunoreactive neurites were found in a small number of senile plaques in the hippocampus and temporal isocortex of Alzheimer's disease patients. The existence of galanin immunoreactivity in human magnocellular basal forebrain neurons which are depleted in Alzheimer's disease suggests that galanin may be similarly affected.

Morphology and distribution of nicotinamide adenine dinucleotide phosphate (reduced form) diaphorase reactive neurons in human brainstem

Nicotinamide adenine dinucleotide phosphate diaphorase reactive neurons were found in several regions of human brainstem. Three major groups were located in the medulla: a dorsomedial group in the central gray and floor of the fourth ventricle, a ventromedial group in the vicinity of the medullary raphe, and a lateral group in the lateral reticular nucleus. In the upper pons a large cluster of reactive neurons was centered in the nucleus centralis oralis extending into the locus coeruleus and dorsal tegmental region. A second cluster in the lateral parabrachial nucleus merged with this group more rostrally and continued into the midbrain tegmentum (paracoeruleus-cuneiform group). Nicotinamide adenine dinucleotide phosphate diaphorase neurons in this region often contained acetylcholinesterase activity. A second midbrain group was seen in the nucleus paranigralis. Aside from these discrete neuronal collections, scattered reactive neurons were found in the medullary reticular formation, periaqueductal gray, inferior colliculus and superior colliculus. Nicotinamide adenine dinucleotide phosphate diaphorase neurons were classified into three groups based on somal size. Parvocellular neurons (10–20 μm) were primarily found in the ventromedial medulla and lateral parabrachial nucleus. Intermediate neurons (20–25 μm) were located in the paranigralis nucleus and dorsomedial medulla. Magnocellular neurons (25–35 μm) were characteristically found in the lateral reticular nucleus and paracoeruleus-cuneiform region. Nicotinamide adenine dinucleotide phosphate diaphorase reactive neurons are present in substantial numbers in human brainstem and their distribution is complex. They represent the caudal end of a widespread network of nicotinamide adenine dinucleotide phosphate diaphorase-enriched neurons that extend rostrally from the brainstem reticular formation into the basal forebrain, striatum, and cerebral cortex.

Central distribution of efferent and afferent components of the pudendal nerve in rat.

Central distribution of efferent and afferent components of the pudendal nerve was examined in the rat by the horseradish peroxidase (HRP) method after HRP application to the central cut end of the pudendal nerve. The pudendal motoneurons were located in the dorsolateral, dorsomedial and lateral groups at L5 and L6. Each of the dorsolateral and dorsomedial groups constituted a slender longitudinal cell column. Pudendal motoneurons in the lateral group were scattered at L5, rostrodorsally to the dorsolateral group. The neurons in the dorsolateral and lateral groups were labelled with HRP applied to the nerve branch innervating the ischiocavernosus and sphincter urethrae muscles. The neurons in the dorsomedial group were labelled with HRP applied to the branch supplying the sphincter ani externus and bulbospongiosus muscles. Some dendrites of pudendal motoneurons in the dorsomedial group extended to the contralateral dorsomedial group. These crossing dendrites were observed not only in male rats but also in female. The average number of the pudendal motoneurons in the dorsolateral and dorsomedial groups were larger in male rats than in female. A few neurons of the intermediolateral nucleus at upper L6 were also labelled with HRP applied to the dorsalis penis (clitoridis) nerve. Axon terminals of the pudendal nerve were distributed, bilaterally with an ipsilateral predominance, to the gracile nucleus, as well as to the dorsal horn and dorsal commissural gray from L4 to S2. A few labelled axons were seen in the intermediolateral nucleus at L6 and S1. Axon terminals from the dorsalis penis nerve were distributed more medially in the dorsal horn than those from the perinealis nerve.

Cobaltic lysine study of the morphology and distribution of the cranial nerve efferent neurons (motoneurons and preganglionic parasympathetic neurons) and rostral spinal motoneurons in the Japanese toad.

The morphology and distribution of the cranial nerve motoneurons (except III, IV, and VI) and rostral spinal motoneurons were systematically studied in the Japanese toad (Bufo japonicus) by retrograde labelling with cobaltic lysine complex. The cobaltic lysine clearly labelled whole neurons, i.e., cell bodies, proximal and distal dendrites, and axons. The branchial motoneurons (V, VII, IX, and X) had similar morphological characteristics and formed a more-or-less continuous cell column through the brainstem. The dendrites could be grouped mainly into the dorsomedial and the ventrolateral dendritic arrays. The dorsomedial dendrites formed a dendritic plexus in the subependymal gray matter, which extended as far peripherally as beneath the ependymal layer. The ventrolateral dendrites formed a broom-like dendritic plexus in the lateral to ventrolateral white matter. They usually extended as far peripherally as the pial surface. The rostrocaudal extent of the dendritic field was also wide and usually exceeded the motor nuclear boundaries. The hypoglossal motoneurons were grouped into the dorsomedial and ventrolateral cell groups, and the latter was considered to be part of the rostral spinal motoneuron column, from their morphology and distribution. The former had well-differentiated dendrites and occupied a more medial position than the branchial motoneurons. Besides the equivalent of the dorsomedial and ventrolateral dendritic arrays of the branchial motoneurons, they had dorsal and commissural dendrites. The accessory motoneurons had morphological characteristics and a distribution pattern similar to those of the rostral spinal motoneurons rather than the branchial motoneurons. The rostral spinal motoneurons had morphological characteristics somewhat different from the branchial motoneurons and the hypoglossal motoneurons (dorsomedial group). Functional implications of the motoneuron morphology are discussed, mainly based on the present results and earlier anatomical and physiological studies of the spinal motoneurons. The present study also revealed the anatomical features of the preganglionic parasympathetic neurons supplying some cranial nerves. These neurons had small somata with less elaborate dendrites and formed an almost continuous cell column that occupied a more dorsal position than the motoneurons of the corresponding nerve. They are thought to be homologous to the salivatory nucleus and the dorsal motor nucleus of the vagus. The basic anatomical organization of the general visceral efferent column seems to be similar throughout vertebrates.

Organization of the motoneurons innervating the pelvic muscles of the male rat

The cytoarchitecture of the motoneuron pool of the male rat was studied at the lumbo-sacral transition area, particularly in L6. In the latter segment a dorso-medial (DM), ventral (V), dorso-lateral (DL), and retrodorso-lateral group (RDL) could be defined. The DL group was associated with a prominent longitudinal dendrite bundle and the CM group with smaller transverse bundles. Moreover, close soma-somatic apposition was found between neurons in these columns. Because L6 gives rise to n. pudendus and contributes to n. ischiadicus, horseradish peroxidase (HRP) was applied to the cut n. ischiadicus and in other experiments injected into the pelvic muscles. Neurons in RDL were labeled following exposure of n. ischiadicus to HRP. Injections in m. levator ani resulted in labeled neurons in the V group, mainly below L6. Injections in m. sphincter urethrae resulted in labeled neurons in the DL group as well as neurons immediately cranial to this column. Musculus ischiocavernosus injections resulted in transport of HRP to neurons in the DL group, primarily in its medial part, and to more cranially located neurons. In addition, some neurons in the V group in L6 were labeled. Following injections in m. bulbocavernosus and m. sphincter ani, labeled neurons were found primarily in the DM group, and to a lesser extent in the V group. Histochemical investigations with staining methods for the localization of acetyl cholinesterase (AChE) and heavy metals (the Timm method) demonstrated that part of the neuropil of DL and of DM were different from the rest of the motoneuron neuropil. In the DL group the area with the diverging staining patterns corresponded to the region of the dendrite bundle. The experimental data indicated and the ultrastructural studies demonstrated that the histochemical differences could be correlated with differences in the composition of the populations of boutons. The comparison of the cytoarchitectural and histochemical data with the results obtained by the aid of the retrograde HRP tracing technique established that mm. sphincter urethrae, ischiocavernosus, bulbocavernosus, and sphincter ani were each innervated by two populations of neurons that were situated in separate areas which had different histochemical properties, and which thus probably have different compositions of their afferent inputs. The duality in the motoneuron pool that innervates the pelvic mucscle might be a reflection of the dual influence on these muscles. As all other striated muscles the pelvic muscles are under voluntary control. However, they are also tightly linked to the function of the pelvic viscera and thus under influence of the autonomic nervous system.

A topographic map of sensory cell terminal arborizations in the cricket CNS; correlation with birthday and position in a sensory array.

The development of a group of club-shaped sensilla called clavate hairs, located on the cerci of the cricket (Acheta domesticus), was examined morphologically. The clavate hairs are located on the base of the cercus and are thought to inform the animal of its orientation with respect to gravity. There are two groups of clavate hairs distinguished from one another by the orientation of their sockets: a dorso-medial group whose sockets are oriented perpendicular to the long axis of the cercus and a ventro-medial group inclined 45-60 degrees away from the perpendicular. The ventro-medial group consists of a series of rows of sensilla running parallel to the long axis of the cercus. By examining a cast-off exoskeleton in the scanning electron microscope and comparing it with newly developed cuticle of the subsequent instar (Fig. 3), we showed how receptors were added to the ventro-medial array of clavate hairs. The first ventral hair (#10,Fig.1) appeared in the second instar. Three more hairs were added in the third instar: two (#11 and #12) proximal to hair 10 forming the first row and one (#20) medial to 11 and initiating the second row. After the third instar on hair was usually added proximal to each row each time the specimen molted. Because of the regular positioning of hairs and their orderly addition to the array, it is possible to identify uniquely all of the hairs in the three largest rows of ventral hairs (Fig. 4). We developed a simple method for staining the neuron associated with each hair. A hair was injured by cutting off its tipe. A bubble of cobaltous acetate was then placed on the hair for 18-20 hours and only the neuron associated with the injured hair took up the stain. The synaptic terminal aborizations of identified neurons examined in this manner were unique and reproducible from specimen to specimen (Fig.6). Furthermore, there is a topographic order to the terminal aborizations. Within one row the oldest neurons project furthest into the nervous system and arborize over the greatest area, whereas younger neurons aborize in more restricted areas nwer the entrance of the cercal nerve. Thus it was concluded that birthday was correlated with the morphology of the synaptic aborization. By staining neurons that were the same age but located in different rows, we determined that birthday was not the only variable influencing the morphology of the terminal arbors. The terminal arbors of neurons 11 and 20, both of which first appear in the third instar, were very different from one another. Thus another variable, presumably position on the body surface, was also correlated with the morphology of a neuron's terminal arborization. We concluded from these results that position on the cercus as well as birthday is encoded in the devlopmental program of these neurons and that the morphology of their terminal arborizations is a joint junction of these two variables.

Axonal pathways in the brain-retrocerebral neuroendocrine complex of Manduca sexta (L.) (Lepidoptera: Sphingidae)

Axonal pathways of the various neurosecretory cell groups in the brain of larvae and pupae of Manduca sexta were studied, using a cobalt diffusion and precipitation technique. Five groups of cells were found to send axons to each retrocerebral complex. Axons from the fused nervi corporis cardiaci I and II arise from 2 ipsilateral dorsomedial groups, a controlateral anteromedial group, and a controlateral dorsolateral group. Axons from the NCC III arise from a group of ipsilateral tritocerebral neurosecretory cells. All of the cell groups sending axons through the NCC I+II innervate the corpus allatum. By contrast, only a few of the axons making up the NCC I+II appear to terminate in the corpora cardiaca (CC). The tritocerebral cells send axons to the CC only. Extensive migration of neurosecretory cells takes place during metamorphosis. The dorsomedial cells of the larva migrate laterad to become the lateral neurosecretory cells of the pupa and adult. The anteromedial cells of the larva migrate dorsad to become the medial neurosecretory cells of the pupa and adult.

Habituation to electrical stimulation of the thalamus in unanaesthetized cats

Electrical high frequency stimulation of widely separate thalamic areas yielded orienting responses in unanaesthetized, freely moving cats. Although these responses looked identical at the first presentation of the stimulus, marked differences appeared when it was repeated. The animals soon habituated to stimulation of a lateral group of nuclei, consisting mainly of the sensory relay nuclei. On the other hand, orienting responses elicited from the intralaminar nuclei were highly resistant to such habituation, whereas a dorso-medial group took an intermediate position. The observed differences may be explained in the following ways: (1) Stimulation of the lateral nuclear group produces some kind of sensory experience of no signal value, and the animal therefore soon ceases to respond. (2) Stimulation of the intralaminar group either directly activates neurones involved in an arousal or orienting mechanism, or it is negatively or positively reinforcing. (3) The prolonged habituation observed in the dorso-medial group may be explained by the negatively reinforcing properties of such stimulation.

The organization of motivation at the thalamic level of the cat

Abstract Three different behavioral tests in combination with recording of the electrical activities of different parts of the brain have been used to study the motivational effects elicited from different parts of the nonspecific thalamic system by electrical stimulation. Stimulation of the anterior region (anterior and dorsomedial group of nuclei) produced different forms of arrest reactions sometimes mixed with phasic movements and exerted a suppressing effect on conditional reflexes. In the case of low frequency stimulation a strict correlation was found between the suppressing effect and a late surface negative wave in the neocortical leads. In the case of high frequency stimulation a correlation between the hemispherical localization of high amplitude slow wave spindles and the direction of movements was obtained. In striking contrast to the anterior thalamus stimulation of the posterior thalamic (including the pretectal) region produced marked activating effects in a conditional environment. Self-stimulation could only be obtained from the anterior region. The effects are interpreted as the result of interactions of an internal negative feed-back and reciprocal inhibitory mechanisms showing increasing complexities as one ascends in a caudo-anterior direction through the thalamic nonspecific system.

The nucleus of the facial nerve; the relation between cellular groups and peripheral branches of the nerve

Summary The morphology of the facial nucleus in the cat has been studied in serial sections in the three conventional planes. Four groups are recognized: the dorsomedial, the ventromedial, the intermediate and the lateral groups. With the method of Gudden as modified by Brodal—a method of retrograde chromatolysis in which newborn animals are used—peripheral branches of the facial nerve have been demonstrated to originate from one or another of these groups. The dorsomedial group is related to the rami auriculares posteriores, the ventromedial group to the branch innervating the platysma, the intermediate group to the rami temporalis and zygomatico-orbitalis and the lateral group to ramus buccolabialis superior and ramus buccolabialis inferior. The dorsomedial group related to auricular muscles is the most prominent in cats. This is possibly related to the relative importance of the auricular musculature in that animal.