Mesencephalic Reticular Nucleus Research Articles

Distribution of preprovasopressin mRNA in the rat central nervous system

Vasopressin released in the central nervous system has been shown to be involved both in homeostatic mechanisms (e.g., water balance, thermoregulation, cardiovascular regulation, metabolism, and antinociception) and in higher brain functions (e.g., social recognition and communication, and learning and memory). Many nuclear groups have been proposed to synthesize vasopressin, but available data are conflicting. We have used a sensitive in situ hybridization technique to identify the distribution of the neurons that may be the origin of the vasopressin in the central nervous system of the male Sprague-Dawley rat. Vasopressin mRNA-expressing neurons were most abundant in the hypothalamus (e.g., the paraventricular, supraoptic, and suprachiasmatic nuclei) but were also seen in the medial amygdaloid nucleus, the bed nucleus of stria terminalis, and the nucleus of the horizontal diagonal band. Previously unreported vasopressinergic neurons were seen in the entorhinal and piriform cortices, the ventral lateral portion of the parabrachial nucleus, the pedunculopontine nucleus, and the rostral part of the ventral periaqueductal gray matter and the adjacent portion of the mesencephalic reticular nucleus. Vasopressin mRNA expression suggestive of neuronal labeling was seen in the pyramidal layer of the CA1-3 fields and the dentate gyrus of the hippocampus. In addition, vasopressin mRNA expression, probably representing axonal mRNA, was detected over the hypothalamopituitary tract. No or insignificant preprovasopressin mRNA expression was present in the cerebellum, locus coeruleus, subcoeruleus, or the spinal cord. These findings provide novel information on the distribution of vasopressin neurons that are important for our understanding of how vasopressin acts in the brain.

Origins of the glycinergic inputs to the rat locus coeruleus and dorsal raphe nuclei: a study combining retrograde tracing with glycine immunohistochemistry.

The amino acid glycine is a major inhibitory neurotransmitter in the brainstem and is likely involved in the tonic inhibition of the monoaminergic neurons during all sleep-waking stages. In order to determine the neurons at the origin of the glycinergic innervation of the two principal monoaminergic nuclei, the locus coeruleus and the dorsal raphe of the rat, we applied a double-labelling technique, combining retrograde transport of cholera-toxin B subunit with glycine immunohistochemistry. Using this technique, we found that the locus coeruleus and dorsal raphe nuclei receive a common glycinergic innervation from the ventral and ventrolateral periaqueductal grey, including the adjacent deep mesencephalic reticular nucleus. Small additional glycinergic inputs to these nuclei originated from the lateral paragigantocellular nucleus and the rostral ventromedial medullary reticular formation. The potential role of these glycinergic inputs in the control of the excitability of the monoaminergic neurons of the locus coeruleus and dorsal raphe nuclei is discussed.

Differential effects of the reticulospinal system on locomotion in lamprey.

Specific effects of stimulating different parts of the reticulospinal (RS) system on the spinal locomotor pattern are described in lamprey. In the in vitro brain stem and spinal cord preparation, microstimulation in different areas of the reticular formation was performed by ejecting a small amount of -glutamate from a micropipette. These areas were distributed over the four reticular nuclei of the brain stem: the mesencephalic reticular nucleus (MRN) and the anterior, middle and posterior rhombencephalic reticular nuclei (ARRN, MRRN, and PRRN, respectively). To prevent synaptic spread of excitation within the brain stem, the synaptic transmission was blocked by using a low Ca2+, high Mn2+ physiological saline in the brain stem pool. "Fictive" locomotion was evoked by applying N-methyl--aspartate (NMDA) to the spinal cord. Rhythmical discharges of motoneurons were recorded bilaterally in the midbody area, from the ventral roots that had been subdivided in dorsal and ventral branches, supplying the dorsal and ventral part of the myotome, respectively. Two major effects of brain stem stimulation were elicited: a change in the frequency of the locomotory rhythm and an induction of asymmetry (left/right, dorsal/ventral) in the segmental motor output. Approximately 50% of the stimulated sites evoked a change in locomotor frequency. In the PRRN almost all effective sites evoked an increase in frequency (10-50%). In the other nuclei, increase and decrease (10-30%) were observed equally frequently. Most of the stimulated sites (50-80%) in any reticular nucleus evoked asymmetry in the segmental motor output. Distortion of the segmental output symmetry was classified into eight categories by comparing the intensity of locomotor bursts in the dorsal and ventral branches of the two ventral roots, ipsilateral and contralateral to the stimulated side. These categories differed in the direction of the body flexion, which would be evoked during normal swimming: ipsilateral (I), contralateral (C), dorsal (D), ventral (V), ipsilateral and dorsal (ID), ipsilateral and ventral (IV), contralateral and dorsal (CD), and contralateral and ventral (CV). The different categories were not equally represented in each nucleus and across the nuclei. The most pronounced categories for each nucleus were as follow. In MRN: I (33%); ARRN: C (44%); MRRN: rostral part, I (36%) and caudal part, CV (42%); and PRRN: rostral part, I (40%) and caudal part, IV (35%). Other categories were also present but less common in each nucleus. To examine if the effects of brain stem stimulation were uniform along the spinal cord, recordings were performed from distal parts of the cord. Stimulation of a given point in the brain stem produced similar pattern of effects in 59% of cases and different patterns in 41% of cases. The main conclusion of the present study is that the proportion of RS neurons with different influences on the spinal locomotor network differs significantly among different parts of the reticular formation of the lamprey. The specificity of RS influences may represent a basis for modifications of the segmental locomotor output necessary for the control of equilibrium and steering during locomotion.

Basal ganglia organization in amphibians: afferent connections to the striatum and the nucleus accumbens.

As part of a research program to determine if the organization of basal ganglia (BG) of amphibians is homologous to that of amniotes, the afferent connections of the BG in the anurans Xenopus laevis and Rana perezi and the urodele Pleurodeles waltl were investigated with sensitive tract-tracing techniques. Hodological evidence is presented that supports a division of the amphibian BG into a nucleus accumbens and a striatum. Both structures have inputs in common from the olfactory bulb, medial pallium, striatopallial transition area, preoptic area, ventral thalamus, ventral hypothalamic nucleus, posterior tubercle, several mesencephalic and rhombencephalic reticular nuclei, locus coeruleus, raphe, and the nucleus of the solitary tract. Several nuclei that project to both subdivisions of the BG, however, show a clear preference for either the striatum (lateral amygdala, parabrachial nucleus) or the nucleus accumbens (medial amygdala, ventral midbrain tegmentum). In addition, the anterior entopeduncular nucleus, central thalamic nucleus, anterior and posteroventral divisions of the lateral thalamic nucleus, and torus semicircularis project exclusively to the striatum, whereas the anterior thalamic nucleus, anteroventral, and anterodorsal tegmental nuclei provide inputs solely to the nucleus accumbens. Apart from this subdivision of the basal forebrain, the results of the present study have revealed more elaborate patterns of afferent projections to the BG of amphibians than previously thought. Moreover, regional differences within the striatum and the nucleus accumbens were demonstrated, suggesting the existence of functional subdivisions. The present study has revealed that the organization of the afferent connections to the BG in amphibians is basically similar to that of amniotes. According to their afferent connections, the striatum and the nucleus accumbens of amphibians may play a key role in processing olfactory, visual, auditory, lateral line, and visceral information. However, contrary to the situation in amniotes, only a minor involvement of pallial structures on the BG functions is present in amphibians.

Spinohypothalamic tract neurons in the cervical enlargement of rats: locations of antidromically identified ascending axons and their collateral branches in the contralateral brain.

Antidromic activation was used to determine the locations of ascending spinohypothalamic tract (SHT) axons and their collateral projections within C1, medulla, pons, midbrain, and caudal thalamus. Sixty-four neurons in the cervical enlargement were antidromically activated initially by stimulation within the contralateral hypothalamus. All but one of the examined SHT neurons responded either preferentially or specifically to noxious mechanical stimuli. A total of 239 low-threshold points was classified as originating from 64 ascending (or parent) SHT axons. Within C1, 38 ascending SHT axons were antidromically activated. These were located primarily in the dorsal half of the lateral funiculus. Within the medulla, the 29 examined ascending SHT axons were located ventrolaterally, within or adjacent to the lateral reticular nucleus or nucleus ambiguus. Within the pons, the 25 examined ascending SHT axons were located primarily surrounding the facial nucleus and the superior olivary complex. Within the caudal midbrain, the 23 examined SHT ascending axons coursed dorsally in a position adjacent to the lateral lemniscus. Within the anterior midbrain, SHT axons traveled rostrally near the brachium of the inferior colliculus. Within the posterior thalamus, all 17 examined SHT axons coursed rostrally through the posterior nucleus of thalamus. A total of 114 low-threshold points was classified as collateral branch points. Sixteen collateral branches were seen in C1; these were located primarily int he deep dorsal horn. Forty-five collateral branches were located in the medulla. These were primarily in or near the medullary reticular nucleus, nucleus ambiguus, lateral reticular nucleus, parvocellular reticular nucleus, gigantocellular reticular nucleus, cuneate nucleus, and the nucleus of the solitary tract. Twentysix collateral branches from SHT axons were located in the pons. These were in the pontine reticular nucleus caudalis, gigantocellular reticular nucleus, parvocellular reticular nucleus, and superior olivary complex. Twenty-three collateral branches were located in the midbrain. These were in or near the mesencephalic reticular nucleus, brachium of the inferior colliculus, cuneiform nucleus, superior colliculus, central gray, and substantia nigra. Int he caudal thalamus, two branches were in the posterior thalamic nucleus and two were in the medial geniculate. These results indicate that SHT axons ascend toward the hypothalamus in a clearly circumscribed projection in the lateral brain stem and posterior thalamus. In addition, large numbers of collaterals from SHT axons appears to project to a variety of targets in C1, the medulla, pons, midbrain, and caudal thalamus. Through its widespread collateral projections, the SHT appears to be capable of providing nociceptive input to many areas that are involved in the production of multifaceted responses to noxious stimuli.

The projections to the spinal cord of the rat during development: a timetable of descent.

In order to establish a timetable for the developmental descent of supraspinal descending projections in the rat, a retrograde neuronal tracer was injected into the spinal cord of rat fetuses and neonates both at different gestational ages and at different levels of the spinal cord. From the results of these experiments a position interval could be deduced for the leading descending fibers of each spinal-projecting nucleus at each age studied. The chronological series of position intervals of each supraspinal descending projection (the descent pattern) depicts the descent of its fiber front during development and allows for easy comparison between the various projections. According to these descent patterns the descent sequences of the various spinal-projecting nuclei were established. At E17 fibers from the lateral vestibular nucleus, the raphe magnus nucleus and the gigantocellular reticular nucleus were present in the lumbosacral spinal cord; their descent along the spinal cord thus occurs before this stage. At E18 fibers from the parafascicular prerubral nucleus, the interstitial nucleus of Cajal, the mesencephalic reticular nucleus, the caudal pontine reticular nucleus, the laterodorsal tegmental nucleus, the subcoerulean nucleus, the spinal vestibular nucleus, the interpolar spinal trigeminal nucleus, the raphe obscurus nucleus and the ventral medullary reticular nucleus arrived in the lumbosacral cord. At the same stage fibers from the oral and caudal spinal trigeminal nucleus reached their caudalmost extent in the spinal cord, respectively, the lower and upper thoracic cord. At E19 fibers from the oral pontine reticular nucleus, the parvocellular reticular nucleus, the ventral gigantocellular reticular nucleus and the ambiguous nucleus first appeared in the lumbosacral cord. At E20 fibers from Darkschewitsch's nucleus, the paralemniscal and parabrachial nuclei, cell group A5, the locus coeruleus, the gigantocellular reticular nucleus-alpha, the raphe pallidus nucleus, the paramedian reticular nucleus, and from the dorsal medullary reticular nucleus arrived in the lumbosacral cord. Last to arrive in the lumbar cord during the prenatal period, at E21, were fibers from the posterior commissural nucleus, the red nucleus, the Edinger-Westphal nucleus, the paragigantocellular reticular nucleus, the medial vestibular nucleus, Roller's nucleus, and the solitary nucleus. Fibers from the paraventricular hypothalamic nucleus and from the lateral hypothalamic area only arrived in the lumbosacral cord at P1, followed by fibers from the incertal nucleus at P4. A transient spinal projection from an unknown group of neurons located immediately lateral to and partly intermingled with the mesencephalic trigeminal nucleus arrived in the lumbosacral spinal cord at E18 and had disappeared at P1. This cell group, called Gr?, closely resembled the mesencephalic trigeminal nucleus (Me5). Both were teardrop shaped; an oblong mass of neurons at the caudal end with a long and thin trailing edge. The trailing edge of Gr?, however, curved dorsad towards the dorsal midline raphe of the caudal mesencephalon, while the trailing edge of Me5 curved rostrad, parallel to the sulcus limitans of the sylvian aquaduct. The neurons of Gr? are mainly round, but in the caudal part of the nucleus some horizontally oriented fusiform neurons were observed. All neurons of Gr? were tiny. These results confirm that the generation sequence of the source nuclei is not a prime determinant of descent sequence along the spinal cord. The distance between the source nucleus and the entrance to the target seems of influence only in the most extreme cases (diencephalic source nuclei and the cerebral cortex). Descent velocity of the fiber fronts is not equal between different sources, nor is the descent velocity of specific fiber fronts constant over time. (ABSTRACT TRUNCATED)

Organization of projections from the ventromedial nucleus of the hypothalamus: a Phaseolus vulgaris-leucoagglutinin study in the rat.

The organization of projections from the four parts of the ventromedial nucleus (VMH) and a ventrolaterally adjacent region tentatively identified as the tuberal nucleus (TU) have been analyzed with small injections of the anterograde axonal tracer Phaseolus vulgaris-leucoagglutinin (PHA-L). Extrinsic and intranuclear projections of each part of the VMH display clear quantitative differences, whereas the overall patterns of outputs are qualitatively similar. Overall, the VMH establishes massive intrahypothalamic terminal fields in other parts of the medial zone, tending to avoid the periventricular and lateral zones. The ventrolateral VMH is more closely related to other parts of the hypothalamus that also express gonadal steroid hormone receptors, including the medial preoptic, tuberal, and ventral premammillary nuclei, whereas other parts of the VMH are more closely related to the anterior hypothalamic and dorsal premammillary nuclei. All parts of the VMH project to the zona incerta (including the A13 region) and parts of the midline thalamus, including the paraventricular and parataenial nuclei and nucleus reuniens. The densest inputs to the septum are to the bed nuclei of the stria terminalis, where the ventrolateral and central VMH innervate the anteroventral and anterodorsal areas and transverse and interfascicular nuclei, whereas the anterior and dorsomedial VMH innervate the latter two. The central, lateral, and medial amygdalar nuclei receive substantial inputs from various parts of the VMH. Other regions of the telencephalon, including the nucleus accumbens and the piriform-amygdaloid, infralimbic, prelimbic, anterior cingulate, agranular insular, piriform, perirhinal, entorhinal, and postpiriform transition areas, also receive sparse inputs. All parts of the VMH send a massive, topographically organized projection to the periaqueductal gray. Other brainstem terminal fields include the superior colliculus, peripeduncular area, locus coeruleus, Barrington's nucleus, parabrachial nucleus, nucleus of the solitary tract, and the mesencephalic, pontine, gigantocellular, paragigantocellular, and parvicellular reticular nuclei. The projections of the TU are similar to, and a subset of, those from the VMH and are thus not nearly as widespread as those from adjacent parts of the lateral hypothalamic area. Because of these similarities, the TU may eventually come to be viewed most appropriately as the lateral component of the VMH itself. The functional implications of the present findings are discussed in view of evidence that the VMH plays a role in the expression of ingestive, affective, and copulatory behaviors.

Auditory projections from the cochlear nucleus to pontine and mesencephalic reticular nuclei in the rat

We investigated projections from the cochlear nucleus in the rat using the anterograde tracer Phaseolus vulgaris-leucoagglutinin. We focused on nuclei in the brainstem which are not considered to be part of the classical auditory pathway. In addition to labeling in auditory nuclei, we found presumed terminal fibers in 4 pontine and mesencephalic areas: (1) the pontine nucleus (PN), which receives bilateral projections from the antero- and posteroventral cochlear nuclei; (2) the ventrolateral tegmental nucleus (VLTg), which receives a contralateral projection from the rostral portion of the anteroventral cochlear nucleus; (3) the caudal pontine reticular nucleus (PnC), which receives bilateral input originating predominantly in the dorsal cochlear nucleus; and (4) the lateral paragigantocellular nucleus (LPGi), which receives projections from all subdivisions of the cochlear nuclei. In the VLTg and PnC, anterogradely labeled varicose axons were often found in close apposition to the primary dendrites and somata of large reticular neurons. Injections of the retrograde fluorescent tracer Fluoro-Gold into the VLTg demonstrated that the neurons of origin are mainly located contralaterally in the rostral anteroventral cochlear nucleus and in the cochlear root nucleus. The relevance of these auditory projections for short-latency audio-motor behaviors and acoustically elicited autonomic responses is discussed.

Distribution of histaminergic neurons in the brain of the lamprey lampetra fluviatilis as revealed by histamine‐immunohistochemistry

An antiserum against conjugated histamine was used to study the distribution of histaminergic neurons in the CNS of the lamprey Lampetra fluviatilis. Numerous histamine-immunoreactive cell bodies were detected in the dorsal and ventral hypothalamic nuclei and in the adjacent postinfundibular commissural nucleus. Histamine-immunoreactive fibers of high density were present in the ventral hypothalamus, and fibers could also be traced dorsally from the hypothalamus to the corpus striatum and septal nucleus where they appeared to terminate in dense plexuses. Another, smaller group of histamine-immunoreactive perikarya was observed in the border area between mesencephalon and rhombencephalon, near the caudal pole of the mesencephalic reticular nucleus. Sparsely distributed histamine-immunoreactive fibers were present in the ventral mesencephalon. The distribution of histaminergic neurons in cyclostomes, which diverged very early from the main vertebrate line, shows similarities with the corresponding systems in the CNS of amphibians and mammals, which suggests that histaminergic neuronal systems are phylogenetically old and have been conserved during evolution.

A Reticulo-Frontal Disconnection Syndrome

Persistent executive deficit, usually seen following prefrontal damage, is reported in a patient recovering from head trauma. Repeated neuroradidological examinations failed to reveal a lesion within the frontal lobes, but a circumscribed lesion in the ventral mesencephalic tegmentum was found. It is proposed that the observed syndrome was caused by damage to mesencephalic reticular nuclei and their projections into prefrontal cortex. The concept of a "reticulo-frontal disconnection syndrome" is introduced and its possible role in head truma and schizophrenia discussed.

Further evidence for excitatory amino acid transmission in lamprey reticulospinal neurons: Selective retrograde labeling with (3H)D‐aspartate

The distribution of radiolabeled neurons in the brain stem of Lampetra fluviatilis was studied following unilateral injections of (3H)D-aspartate in the rostral spinal cord. After survival periods of 1-3 days, labeled perikarya were present within and nearby the posterior, middle, and anterior rhombencephalic reticular nuclei and in the mesencephalic reticular nucleus. The highest number of (3H)D-aspartate labeled cell bodies were present in the posterior rhombencephalic reticular nucleus. The labeled reticulospinal neurons were distributed mainly ipsilateral to the injection site and included the giant Müller cells as well as medium-sized and small neurons. Contralateral labeling occurred in cell bodies scattered along the lateral margin of the rhombencephalic reticular formation, the most rostral of these contralaterally projecting neurons being the Mauthner cell. The (3H)D-aspartate labeling correlates with previous electrophysiological studies showing that lamprey reticulospinal neurons utilize excitatory amino acid transmission.

Distribution of immunoreactive α-neo-endorphin in the rat brain

The distribution of immunoreactive α-neo-endorphin (α-Neo) in the rat brain was demonstrated by means of highly specific radioimmunoassay (RIA). The highest concentrations of immunoreactive (ir) α-Neo (100 pmol/g tissue) were found in the substantia nigra, the hypothalamic supraoptic nucleus (86 pmol/g) and the preoptic area (63 pmol/g); medium levels were found in the basal ganglia, mesencephalic reticular formation, nucleus accumbens and hippocampus. Other structures contained less α-Neo-ir. The possible anatomical interaction between α-Neo and monoaminergic nerve terminals or cell bodies in some structures is discussed.

Afferents to the zona incerta in the rat: a combined retrograde and anterograde study.

In a first set of experiments, the retrograde transport of horseradish peroxidase (HRP) was utilized to investigate the afferent projections to the zona incerta (ZI) in the hooded rat. HRP was introduced in its crystalline form into various sectors of the ZI of seven subjects. The largest contingent of afferents arises from the following centers: the cingulate and somatosensory cortices, central amygdaloid nucleus, ventromedial hypothalamic nucleus, posterior thalamic nucleus, anterior pretectal nucleus, peripeduncular area, deep and intermediate layers of the superior colliculus, dorsal and ventral parabrachial nuclei, principal and interpolar trigeminal subnuclei, and cuneate nucleus. Other centers less systematically or more sparsely labeled were the lateral hypothalamic area, ventrobasal complex, lateral geniculate nucleus pars ventralis, medial geniculate nucleus, interstitial nucleus of Cajal, Darkschewitsch nucleus, perirubral fields, cuneiform, tegmental pedunculopontine, and deep mesencephalic reticular nuclei, pontine reticular nucleus pars oralis, lateral and interpositus cerebellar nuclei, and gracile nucleus. In a second set of experiments, an anterograde tracer (WGA-HRP) was injected in several centers projecting to the ZI in order to localize their terminal fields within this structure. It has been thus possible to distinguish a ventral zone (ventral sector of pars caudalis and pars ventralis) in which the somesthetic (somatosensory cortex, trigeminal complex, and dorsal column nuclei (DCN), collicular, and cerebellar projections terminate, from a dorsal zone (pars dorsalis) to which a limbic input (cingulate cortex and ventromedial hypothalamic nucleus) is directed. In most cases, the labeled terminal fields consisted of well-delimited, narrow bands disposed obliquely, parallel to the cerebral peduncle or the internal capsule. The contingent of somatosensory afferents is relatively large and there is a high degree of overlapping between the different somatosensory terminal fields within the ventral ZI. This suggests a participation of this structure in the treatment of somesthetic information and/or in the transmission of noxious stimuli.

Projection systems and terminal localization of dorsal column afferents: An autoradiographic and horseradish peroxidase study in the rat

Projection systems from the gracile nucleus and the cuneate nuclear complex to their terminal sites in the mesencephalon, diencephalon, and cerebellum were examined by means of anterograde autoradiography and retrograde horseradish peroxidase methods. Three projection systems emerge from the dorsal column nuclei, decussate via internal arcuate fibers, and form the contralateral medial lemniscus (ML). At the obex, some fibers split off the ML and course dorsolaterally, forming an ascending lateral system which fits the "lemniscal adjunct channel" (LAC) concept of Graybiel ('72). The ML continues rostrally as the "main lemniscal line channel" (MLLC). At the inferior colliculus, some LAC fibers terminate in the pontine nuclei, parabrachial, dorsal reticular nuclei, and the external and ventral medial part of the central nucleus of the inferior colliculus. More rostrally at the level of the superior colliculus, terminal fields are found in the medial nucleus of the medial geniculate body, the suprageniculate, pretectal, and mesencephalic reticular nuclei, marking the end of the LAC. In the diencephalon, gracile fibers leave the MLLC and form a crescentlike terminal field along the extreme lateral border of the ventral posterior lateral nucleus (VPL) of the thalamus. Cuneate MLLC fibers terminate in a bandlike formation in the VPL medial to the gracile termination. The third fiber system, the cuneocerebellar projection, emerges from the cuneate, the external cuneate nuclei, and the "cellular bridge" and immediately enters the ipsilateral inferior cerebellar peduncle. Upon entering the cerebellum, the major fiber component remains ipsilateral and terminates as vertical bands in vermal and paravermal lobules, and lobules I through IVa. The posterior cerebellar lobe contains terminal bands in lobules VII-IX, the copula pyramidis, and the paramedian lobule. It is concluded that the dorsolateral fiber system conforms to Graybiel's LAC. It is more divergent and probably less modality specific, whereas the medial lemniscal system conforms to the MLLC, which is said to be modality specific, less divergent, and locked to specific sensory-motor response characteristics. The topography of cerebellar terminal bands indicates that there is sensory-motor representation from all parts of the body to all parts of the cerebellum, at least in the rat.

Temporal patterns of unit activity of mesencephalic reticular nuclei during sleep and waking

Temporal patterns of unit activity in the mesencephalic reticular nuclei (n. cuneiformis, n. parabrachialis) were studied in unrestrained rats during the sleep-waking cycle; activity was derived by means of movable metallic microelectrodes. Analysis of the data showed that most neurons of these mesencephalic reticular nuclei (76 and 66% respectively) generate activity with the highest frequency during active waking and the emotional stage of paradoxical sleep; they discharge with lower frequency during passive wakefulness and the nonemotional stage of paradoxical sleep, and they exhibit least activity during slow-wave sleep. Comparatively few neurons (24 and 15%) demonstrate the opposite kind of temporal pattern of activity: They discharge more intensively during slow-wave sleep and more slowly during active wakefulness and the emotional stage of paradoxical sleep. Activity of these neurons during quiet wakefulness and the nonemotional stage of paradoxical sleep reaches the level of activity observed during slow-wave sleep. Neurons discharging intensively during active wakefulness were found in n. parabrachialis; their discharge frequency during passive wakefulness and slow-wave sleep and its frequency was least during paradoxical sleep. The similarity and differences of the neurophysiological mechanisms of regulation of the phases and stages of the sleepwaking cycle are discussed.

Efferent projections of the cat oculomotor reticular omnipause neuron region: an autoradiographic study.

Omnipause neurons (OPNs) are midline pontine neurons that are thought to be instrumental in the generation of saccadic eye movements. Inhibition of the tonically active OPNs is postulated to disinhibit the burst neurons that cause the saccadic discharge in motoneurons, leading to a saccade. To test whether the anatomical connections of OPNs are consistent with this scheme, we studied the efferent projections of the OPN region by using the technique of anterograde transport of tritiated amino acids. Injections into the OPN region yield a distinct pattern of labeled tracts and terminal fields that is different from the patterns following control injections in the surrounding reticular formation. Caudally, there are terminal fields over the paramedian reticular formation, the caudal part of the medial accessory nucleus of the inferior olivary complex, the nucleus prepositus hypoglossi, and the nucleus reticularis paragigantocellularis dorsalis caudal and ventromedial to the abducens nuclei. Rostrally, terminal label is distributed over parts of the nuclei reticularis pontis caudalis and oralis, the nucleus raphe pontis, the nucleus reticularis tegmenti pontis, the mesencephalic reticular nucleus, the central gray, and the nucleus of the H-field. Thus, there are direct projections from the OPN region to all areas known to contain burst neurons. In addition, OPNs also apparently have indirect access to the spinal cord and cerebellum. Many of the latter connections parallel the efferent projections of the superior colliculus.

Dose effects of morphine on the spontaneous unit activity recorded from the thalamus, hypothalamus, septum, hippocampus, reticular formation, central gray, and caudate nucleus.

Spontaneous activity was recorded from 652 units in 8 subcortical structures of unanesthetized rats. Recordings were obtained in central gray, mesencephalic reticular formation, parafasciculus thalami, caudate nucleus, anterior and ventromedial hypothalamus, lateral septum, and dorsal hippocampus. Eighty recordings were obtained from untreated animals and 80 from saline-injected controls, none of which showed any significant changes of unit activity during the 4- 5-hr observation period. The effect of morphine, given in 5 incremental doses from 0.5 to 30.0 mg/kg ip, was followed in 492 units. Morphine enhanced or depressed spontaneous discharge rates, or caused biphasic effects, ie enhancement alternating with depression and vice versa. Naloxone induced increase in firing after either effect of morphine, or reduced spontaneous activity after morphine-induced increases. However, when morphine reduced neuronal discharges, naloxone never caused further depression. In 86 units, morphine at any dosage failed to alter neuronal activity, but in 54 of these units naloxone nevertheless induced alterations in firing rates. The pattern of responses to morphine differed between all 8 brain regions examined and was characteristic for each individual structure. This is the first systematic study describing the dose-response characteristics of morphine in 8 brain sites recorded simultaneously. Furthermore, it utilized freely behaving animals without the interference of anesthetics, which are themselves known to interact with opiates. The variety of response patterns seen supports the neuropharmacological evidence for multiple opiate receptors or multiple sites of opiate action.

Subcortical projections to the lateral geniculate body in the rat.

The subcortical projections to the lateral geniculate body (LGB) in the rat were studied by means of discrete HRP iontophoretic deposits in the dorsal or the ventral LGB; the labelling was compared to that resulting from HRP deposits in neighboring nuclei. After injecting HRP in the dorsal LGB, labelled cells appeared bilaterally in the ventral LGB, pretectum, superior colliculus, lateral groups of the dorsal raphe nucleus and locus coeruleus. Ipsilaterally, labelled cells were found in the lateral posterior thalamus, nucleus of the posterior commissure and deep mesencephalic reticular nucleus. After injecting HRP into the ventral LGB, labelled cells were observed bilaterally in the pretectum, superior colliculus and dorsal raphe nucleus (lateral groups). Contralateral labelling appeared in the ventral LGB and parabigeminal nucleus. Ipsilateral labelling was found in the zona incerta, lateral posterior thalamus, lateral and medial mesencephalic reticular formation, vestibular and dorsal tegmental nuclei. These findings provide evidence of subcortical projections to the LGB arising in visually-related areas as well as extravisual areas, which might be related to the LGB boutons that survive complete cortical and retinal ablations.

Afferent and efferent connections of the optic tectum in the carp ( Cyprinus carpio L.)

The afferent and efferent connections of the tectum opticum in the carp (Cyprinus carpio L.) were studied with the HRP method. Following iontophoretic peroxidase injections in several parts of the tectum anterograde transport of the enzyme revealed tectal projections to the lateral geniculate nucleus, dorsal tegmentum, pretectal nuclei, nucleus rotundus, torus longitudinalis, torus semicircularis, nucleus isthmi, contralateral tectum and to the mesencephalic and bulbar reticular formations. Tectal afferents were demonstrated by retrograde HRP transport in the area dorsalis pars centralis of the telencephalon, torus longitudinalis, torus semicircularis, nucleus isthmi, nucleus profundus mesencephali, several pretectal nuclei, dorsomedial and dorsolateral thalamic nuclei, nucleus of the posterior commissure, mesencephalic and bulbar reticular nuclei and nucleus ruber. Visuo-cerebellar circuitry was investigated by means of peroxidase injections in the various parts of the cerebellum. These experiments revealed indirect retino- and tecto-cerebellar pathways via the pretectal nuclei and the nucleus isthmi.

Ascending connections to the forebrain in the Tegu lizard.

The ascending connections to the striatum and the cortex of the Tegu lizard, Tupinambis nigropunctatus, were studied by means of anterograde fiber degeneration and retrograde axonal transport. The striatum receives projections by way of the dorsal peduncle of the lateral forebrain bundle from four dorsal thalamic nuclei: nucleus rotundus, nucleus reuniens, the posterior part of the dorsal lateral geniculate nucleus and nucleus dorsomedialis. The former three nuclei project to circumscribed areas of the dorsal striatum, whereas nucleus dorsomedialis has a distribution to the whole dorsal striatum. Other sources of origin to the striatum are the mesencephalic reticular formation, substantia nigra and nucleus cerebelli lateralis. With the exception of the latter afferentation all these projections are ipsilateral. The ascending connections to the pallium originate for the major part from nucleus dorsolateralis anterior of the dorsal thalamus. The fibers course in both the medial forebrain bundle and the dorsal peduncle of the lateral forebrain bundle and terminate ipsilaterally in the middle of the molecular layer of the small-celled part of the mediodorsal cortex and bilaterally above the intermediate region of the dorsal cortex. The latter area is reached also by fibers from the septal area. The large-celled part of the mediodorsal cortex receives projections from nucleus raphes superior and the corpus mammillare.