Modulation of the swallowing reflex by stimulation of the gigantocellular reticular nucleus in the rat

OBJECTIVES

The gigantocellular reticular nucleus (Gi) projects to the nuclues of the solitary tract nucleus (NTS) and the lateral reticular formation (LRF) above the nucleus ambiguus. The swallowing central pattern generator comprises the NTS and the LRF. The present study examined whether stimulation of the Gi affects the swallowing reflex.

METHODS

Experiments were performed on urethane-anesthetized rats. The swallowing reflex was evoked by repetitive electrical stimulation of the superior laryngeal nerve and responses were recorded from the mylohyoid muscle on an electromyogram. The Gi was stimulated electrically. In addition, glutamate was injected into the Gi. The Friedman's test, followed by the Wilcoxon signed-rank test with Bonferroni correction, were used to assess the effects of electrical stimulation of the Gi. The Wilcoxon signed-rank test was used to assess the effects of glutamate injection into the Gi. Differences were considered significant at the P < 0.05 level.

RESULTS

The number of swallows was significantly increased or decreased by electrical stimulation of the Gi or after injection of glutamate into the Gi. In both electrical stimulation of the Gi and injection of glutamate into the Gi, the onset latency of the first swallow was prolonged when the number of swallows was decreased but showed no change when the number of swallows was increased.

CONCLUSIONS

The present results suggest that the Gi is involved in the control of swallowing.

Functional plasticity of glutamatergic neurons of medullary reticular nuclei after spinal cord injury in mice

Spinal cord injury disrupts the descending command from the brain and causes a range of motor deficits. Here, we use optogenetic tools to investigate the functional plasticity of the glutamatergic reticulospinal drive of the medullary reticular formation after a lateral thoracic hemisection in female mice. Sites evoking stronger excitatory descending drive in intact conditions are the most impaired after injury, whereas those associated with a weaker drive are potentiated. After lesion, pro- and anti-locomotor activities (that is, initiation/acceleration versus stop/deceleration) are overall preserved. Activating the descending reticulospinal drive improves stepping ability on a flat surface of chronically impaired injured mice, and its priming enhances recovery of skilled locomotion on a horizontal ladder. This study highlights the resilience and capacity for reorganization of the glutamatergic reticulospinal command after injury, along with its suitability as a therapeutical target to promote functional recovery.

Role of autonomic, nociceptive, and limbic brainstem nuclei in core autism features

Although multiple theories have speculated about the brainstem reticular formation's involvement in autistic behaviors, the in vivo imaging of brainstem nuclei needed to test these theories has proven technologically challenging. Using methods to improve brainstem imaging in children, this study set out to elucidate the role of the autonomic, nociceptive, and limbic brainstem nuclei in the autism features of 145 children (74 autistic children, 6.0-10.9 years). Participants completed an assessment of core autism features and diffusion- and T1-weighted imaging optimized to improve brainstem images. After data reduction via principal component analysis, correlational analyses examined associations among autism features and the microstructural properties of brainstem clusters. Independent replication was performed in 43 adolescents (24 autistic, 13.0-17.9 years). We found specific nuclei, most robustly the parvicellular reticular formation-alpha (PCRtA) and to a lesser degree the lateral parabrachial nucleus (LPB) and ventral tegmental parabrachial pigmented complex (VTA-PBP), to be associated with autism features. The PCRtA and some of the LPB associations were independently found in the replication sample, but the VTA-PBP associations were not. Consistent with theoretical perspectives, the findings suggest that individual differences in pontine reticular formation nuclei contribute to the prominence of autistic features. Specifically, the PCRtA, a nucleus involved in mastication, digestion, and cardio-respiration in animal models, was associated with social communication in children, while the LPB, a pain-network nucleus, was associated with repetitive behaviors. These findings highlight the contributions of key autonomic brainstem nuclei to the expression of core autism features.

Involvement of A13 dopaminergic neurons in prehensile movements but not reward in the rat

Tyrosine hydroxylase (TH)-containing neurons of the dopamine (DA) cell group A13 are well positioned to impact known DA-related functions as their descending projections innervate target regions that regulate vigilance, sensory integration, and motor execution. Despite this connectivity, little is known regarding the functionality of A13-DA circuits. Using TH-specific loss-of-function methodology and techniques to monitor population activity in transgenic rats in vivo, we investigated the contribution of A13-DA neurons in reward and movement-related actions. Our work demonstrates a role for A13-DA neurons in grasping and handling of objects but not reward. A13-DA neurons responded strongly when animals grab and manipulate food items, whereas their inactivation or degeneration prevented animals from successfully doing so-a deficit partially attributed to a reduction in grip strength. By contrast, there was no relation between A13-DA activity and food-seeking behavior when animals were tested on a reward-based task that did not include a reaching/grasping response. Motivation for food was unaffected, as goal-directed behavior for food items was in general intact following A13 neuronal inactivation/degeneration. An anatomical investigation confirmed that A13-DA neurons project to the superior colliculus (SC) and also demonstrated a novel A13-DA projection to the reticular formation (RF). These results establish a functional role for A13-DA neurons in prehensile actions that are uncoupled from the motivational factors that contribute to the initiation of forelimb movements and help position A13-DA circuits into the functional framework regarding centrally located DA populations and their ability to coordinate movement.

Effect of Motor Task on Cortex Brainstem Modulation: Preliminary Results

Reticulospinal Tracts (RSTs) have divergent connections to multiple spinal segments that innervate many upper extremity muscles. Therefore, increased RST engagement can often lead to muscle coactivation across multiple limb joints. The RST originates from the reticular formation (RF) and receives projections from the cortex. This provides the anatomical basis for cortex-brainstem modulation. Currently, we know little about how cortex modulates the RF to control RST engagement during motor preparation for various motor tasks, such as tasks involving proximal and distal upper limb joint coordination vs. a purely distal task. We hypothesize that since a simultaneous arm lifting and hand opening task (LIFTOPEN) requires more selective muscle recruitment than a hand opening task (OPEN), the cortex will suppress the RF to reduce the RST engagement at distal muscles during LIFTOPEN. To test this hypothesis, we investigated the startReact response in thirteen able-bodied participants performing the OPEN and LIFTOPEN tasks in response to a startling and non-startling acoustic stimulation. Our results showed that activation of distal muscles was significantly decreased, and the startle response was delayed in LIFTOPEN compared to OPEN. Both results suggest that the cortex suppressed RF and reduced the RST engagement in LIFTOPEN compared to OPEN.Clinical Relevance- Our results provide foundational knowledge of the task-specific nature of cortex-brainstem modulation. This scientific finding provides a base to compare how a unilateral brain injury may affect this cortex-brainstem modulation.

Pattern of Driver-Like Input onto Neurons of the Mouse Ventral Lateral Geniculate Nucleus

The ventral lateral geniculate nucleus (vLGN) is a retinorecipient region of thalamus that contributes to a number of complex visual behaviors. Retinal axons that target vLGN terminate exclusively in the external subdivision (vLGNe), which is also transcriptionally and cytoarchitectonically distinct from the internal subdivision (vLGNi). While recent studies shed light on the cell types and efferent projections of vLGNe and vLGNi, we have a crude understanding of the source and nature of the excitatory inputs driving postsynaptic activity in these regions. Here, we address this by conducting in vitro whole-cell recordings in acutely prepared thalamic slices and using electrical and optical stimulation techniques to examine the postsynaptic excitatory activity evoked by the activation of retinal or cortical layer V input onto neurons in vLGNe and vLGNi. Activation of retinal afferents by electrical stimulation of optic tract or optical stimulation of retinal terminals resulted in robust driver-like excitatory activity in vLGNe. Optical activation of corticothalamic terminals from layer V resulted in similar driver-like activity in both vLGNe and vLGNi. Using a dual-color optogenetic approach, we found that many vLGNe neurons received convergent input from these two sources. Both individual pathways displayed similar driver-like properties, with corticothalamic stimulation leading to a stronger form of synaptic depression than retinogeniculate stimulation. We found no evidence of convergence in vLGNi, with neurons only responding to corticothalamic stimulation. These data provide insight into the influence of excitatory inputs to vLGN and reveal that only neurons in vLGNe receive convergent input from both sources.

Whole-brain monosynaptic inputs and outputs of glutamatergic neurons of the vestibular nuclei complex in mice

Vestibular nuclei complex (VN) glutamatergic neurons play a critical role in the multisensory and multimodal processing. The dysfunction of VN leads to a series of vestibular concurrent symptoms, such as disequilibrium, spatial disorientation, autonomic disorders and even emotion disorders. However, the reciprocal neural connectivity in the whole brain of VN glutamatergic neurons was incompletely understood. Here, we employed a cell-type-specific, cre-dependent, modified virus vector to retrogradely and anterogradely trace VN glutamatergic neurons in the VGLUT2-IRES-Cre mouse line. We identified and analyzed statistically the afferents and efferents of VN glutamatergic neurons in the whole brain, and also reconstructed monosynaptic inputs distribution of VN glutamatergic neurons at the three-dimensional level with the combination of a fluorescence micro-optical sectioning tomography system (fMOST). We found that VN glutamatergic neurons primarily received afferents from 57 nuclei and send efferents to 59 nuclei in the whole brain, intensively located in the brainstem and cerebellum. Projections from nuclei in the cerebellum targeting VN glutamatergic neurons mainly performed the balance control - the principal function of the vestibular system. In addition, VN glutamatergic neurons sent projections to oculomotor nucleus, trochlear nucleus and abducens nucleus dominating the eye movement. Except for the maintenance of balance, VN glutamatergic neurons were also directly connected with other functional regions, such as sleep-wake state (locus coeruleus, dorsal raphe nucleus, and laterodorsal tegmental nucleus, gigantocellular reticular nucleus, lateral paragigantocellular nucleus, periaqueductal gray, subcoeruleus nucleus, parvicellular reticular nucleus, paramedian raphe nucleus), and emotional regulation (locus coeruleus and dorsal raphe nucleus). Hence, this study revealed a comprehensive whole-brain neural connectivity of VN glutamatergic neurons and provided with a neuroanatomic foundation to further study on central vestibular circuits.

Brainstem BOLD response to visual and acoustic stimuli

Understanding the fundamental roles of brainstem function resulting in proper motor control is critical to motor-rehabilitation after brain injuries. In particular, vestibular and reticular formation nuclei are thought to be associated with spasticity in chronic stroke patients. We used two kinds of stimuli in 10 healthy subjects to activate these nuclei while collecting high-resolution (1.5-mm) fMRI across the majority of brainstem. Optokinetic stimuli evoked illusory self-motion to activate the vestibular nuclei. Acoustic-startle stimuli were sets of loud tones designed to activate of the reticular formation. We summarized the response represented in a form of activation volume, mean percent signal change, and the phase delay (time lag) following the stimulus. We observed patterns of significant activations in the brainstem but did not find significant differences between the stimulus. We conclude that more sensitive measurement techniques are needed to reliably detect vestibular and reticular formation nuclei responses.

The White Paper: Wilder Penfield, the Stream of Consciousness, and the Physiology of Mind

Wilder Penfield is justly famous for his contributions to our understanding of epilepsy and of the structure-function relationship of the brain. His theory on the relationship of the brain and mind is less well known. Based on the effects of the electrical stimulation of the cortex in conscious patients, Penfield believed that consciousness and mind are functions of what he referred to as the centrencephalic integrating system. This functional system comprised bidirectional pathways between the upper brainstem, the thalami, and the cerebral cortex of both hemispheres, and was the physical substrate from which memory, perception, initiative, will, and judgment arose. It was the source of the stream of consciousness and the physical basis of mind. This paper reviews how Penfield arrived at this conception of the mind-brain relationship. Although Penfield ultimately felt that he had failed in his attempt to unify brain and mind, his work shed new light on the relationship of memory to the mesial temporal structures and to the temporal cortex; and his association of consciousness and the brainstem preceded the conceptualization of the reticular activating system by a generation. In these, as in so many aspects of neurobiology, Penfield was prescient.

Corticosterone suppresses vasotocin-enhanced clasping behavior in male rough-skinned newts by novel mechanisms interfering with V1a receptor availability and receptor-mediated endocytosis

In rough-skinned newts, Taricha granulosa, exposure to an acute stressor results in the rapid release of corticosterone (CORT), which suppresses the ability of vasotocin (VT) to enhance clasping behavior. CORT also suppresses VT-induced spontaneous activity and sensory responsiveness of clasp-controlling neurons in the rostromedial reticular formation (Rf). The cellular mechanisms underlying this interaction remain unclear. We hypothesized that CORT blocks VT-enhanced clasping by interfering with V1a receptor availability and/or VT-induced endocytosis. We administered a physiologically active fluorescent VT conjugated to Oregon Green (VT-OG) to the fourth ventricle 9 min after an intraperitoneal injection of CORT (0, 10, 40 μg/0.1mL amphibian Ringers). The brains were collected 30 min post-VT-OG, fixed, and imaged with confocal microscopy. CORT diminished the number of endocytosed vesicles, percent area containing VT-OG, sum intensity of VT-OG, and the amount of VT-V1a within each vesicle; indicating that CORT was interfering with V1a receptor availability and VT-V1a receptor-mediated endocytosis. CORT actions were brain location-specific and season-dependent in a manner that is consistent with the natural and context-dependent expression of clasping behavior. Furthermore, the sensitivity of the Rf to CORT was much higher in animals during the breeding season, arguing for ethologically appropriate seasonal variation in CORT's ability to prevent VT-induced endocytosis. Our data are consistent with the time course and interaction effects of CORT and VT on clasping behavior and neurophysiology. CORT interference with VT-induced endocytosis may be a common mechanism employed by hormones across taxa for mediating rapid context- and season-specific behavioral responses.

Crypto-rhombomeres of the mouse medulla oblongata, defined by molecular and morphological features

The medulla oblongata is the caudal portion of the vertebrate hindbrain. It contains major ascending and descending fiber tracts as well as several motor and interneuron populations, including neural centers that regulate the visceral functions and the maintenance of bodily homeostasis. In the avian embryo, it has been proposed that the primordium of this region is subdivided into five segments or crypto-rhombomeres (r7-r11), which were defined according to either their parameric position relative to intersomitic boundaries (Cambronero and Puelles, in J Comp Neurol 427:522-545, 2000) or a stepped expression of Hox genes (Marín et al., in Dev Biol 323:230-247, 2008). In the present work, we examine the implied similar segmental organization of the mouse medulla oblongata. To this end, we analyze the expression pattern of Hox genes from groups 3 to 8, comparing them to the expression of given cytoarchitectonic and molecular markers, from mid-gestational to perinatal stages. As a result of this approach, we conclude that the mouse medulla oblongata is segmentally organized, similarly as in avian embryos. Longitudinal structures such as the nucleus of the solitary tract, the dorsal vagal motor nucleus, the hypoglossal motor nucleus, the descending trigeminal and vestibular columns, or the reticular formation appear subdivided into discrete segmental units. Additionally, our analysis identified an internal molecular organization of the migrated pontine nuclei that reflects a differential segmental origin of their neurons as assessed by Hox gene expression.

An old hypothesis and new tools: Alfred Fessard's approach to the problem of consciousness

In 1954, a symposium was held in Canada on "Brain Mechanisms and Consciousness." It was a time for the promotion of international and interdisciplinary scientific cooperation, of new technological expectation, and of speculating about complex human behavior. Alfred Fessard's lecture on "Mechanisms of Nervous Integration and Conscious Experience" was one of the outstanding presentations, rich in critical analysis of the then available experimental data and in working hypothesis proposals. Reading the concept expressed by Fessard, it was found that several of his ideas had anticipated data obtained in modern research with new technologies.

Carbachol injections into the ventral pontine reticular formation activate locus coeruleus cells in urethane-anesthetized rats

STUDY OBJECTIVES

Two pontine reticular regions are implicated in cholinergic triggering of rapid eye movement (REM) sleep: the dorsomedial tegmental region and the ventral nucleus pontis oralis. We previously determined that, in urethane-anesthetized rats, microinjections of a cholinergic agonist, carbachol, into the dorsal region produce REM sleep-like effects comprising cortical activation, hippocampal theta rhythm, suppression of hypoglossal (XII) nerve activity, and silencing of pontine noradrenergic neurons. Our goal was to determine whether carbachol injections into the ventral nucleus pontis oralis elicits comparable effects.

DESIGN

Recording of cortical electroencephalogram, hippocampal activity, XII nerve activity, and discharge of noradrenergic cells of the locus coeruleus.

SETTING

Basic neurophysiologic research laboratory.

PARTICIPANTS AND INTERVENTIONS

Urethane-anesthetized, paralyzed, and artificially ventilated or nonparalyzed and spontaneously breathing rats with microinjections of carbachol (10 nL, 10 mM) into the ventral nucleus pontis oralis.

MEASUREMENTS AND RESULTS

In artificially ventilated rats, carbachol injections repeatedly elicited cortical activation and hippocampal theta rhythm. Concomitantly, the activity of locus coeruleus neurons increased from 2.0 per second +/- 0.4 (SE) to 2.6 per second +/- 0.4 (P < .05, n = 8), as did XII nerve activity (by 42.5% +/- 8.8%; P < .01). In spontaneously breathing animals, carbachol similarly activated the cortical electroencephalogram and hippocampal activity, whereas XII nerve activity was reduced by 6.7% +/- 2.5% (P < .05) together with increased ventilation, as indicated by reduced end-expiratory CO2.

CONCLUSION

Carbachol injections into the ventral nucleus pontis oralis activate, rather than silence, noradrenergic locus coeruleus neurons. This is not compatible with the state of REM sleep.

REM sleep enhancement induced by different procedures improves memory retention in rats

Growing evidence supports the idea that sleep following learning is critically involved in memory formation. Recent studies suggest that information acquired during waking is reactivated and possibly consolidated during subsequent sleep, especially during rapid-eye movement (REM) or paradoxical sleep (PS). Critical reviews, however, have questioned PS and memory relationships, particularly because of shortcomings of the PS deprivation paradigm applied in many studies. Therefore, in the present study we used an opposite strategy, i.e. we investigated the effects of PS enhancement on memory retention. In three experiments, we found that selective PS enhancement, induced by different procedures after discrimination training in rats, results in increased retention tested 24 h later. Moreover, calculated in all animals (n = 61), there was a highly significant correlation between post-training PS values and retention scores. Our results suggest that an experimentally induced increase of PS after learning facilitates memory consolidation.

Differential effects of the 5-HT1A receptor agonist flesinoxan given locally or systemically on REM sleep in the rat

The effects of flesinoxan, a selective 5-HT1A receptor agonist on spontaneous sleep, were studied in adult rats implanted for chronic sleep recordings. Flesinoxan was administered systemically or infused directly into the dorsal raphe nucleus, the left laterodorsal tegmental nucleus or the medial pontine reticular formation. Systemic administration of flesinoxan (0.03 and/or 0.06 micromol/kg) significantly increased wakefulness and sleep latencies, and reduced rapid eye movement (REM) sleep and the number of REM periods, during the first and/or second 2-h period after treatment. Direct infusion of the 5-HT1A receptor agonist (0.06 and/or 0.12 nmol) into the dorsal raphe nucleus induced a significant increment of REM sleep and augmented the number of REM periods during the second and/or third 2-h period of recording. Microinjection of flesinoxan (0.03, 0.06 and/or 0.12 nmol) into the laterodorsal tegmental nucleus reduced REM sleep and the number of REM periods, and augmented REM sleep latency during the first, second and/or third 2-h recording period. Finally, direct infusion of flesinoxan (0.48 nmol) into the medial pontine reticular formation decreased REM sleep and the number of REM periods, and increased REM sleep latency during the first and second 2 h of recording. Our results indicate that the 5-HT1A receptor is involved in the inhibitory effect of serotonin on brainstem structures that act to promote and to induce REM sleep.

Reticular theory versus neuron theory in the work of Camillo Golgi

In 1873 Golgi invented a revolutionary method for microscopic research of the nervous system, based on a particular technique for staining nerve cells, which came to be known as "black reaction". Thanks to this method, he was able to provide a thorough and precise description of nerve cells in various regions of the cerebro-spinal axis, clearly distinguishing the axon from the dendrites. He drew up a new classification of cells on the basis of the structure of their nervous prolongation, and he criticized Gerlach's theory of the "protoplasmic network". Golgi claimed to observe in the gray matter an extremely dense and intricate network, composed of a web of intertwined branches of axons coming from different cell layers ("diffuse nervous network"). This structure, which emerges from the axons and is therefore essentially different from that hypothesized by Gerlach, appeared in his view to be the main organ of the nervous system, the organ that connected different cerebral areas both anatomically and functionally by means of the transmission of an electric nervous impulse. Golgi's reticular theory, along with the other reticular theories of the nervous system prevalent at the end of the nineteenth century, had in a certain sense overturned the 'atomistic-reductionist' principle that lay behind the cell theory. These theories were in fact based on a holistic model, according to which the cerebro-spinal axis was considered to be a continuous structure, and its functions the result of a collective action. At the end of the 1880's, Ramon y Cajal began to elaborate the neuron theory, using Golgi's microscopic technique. Golgi, however, did not accept this theory, and a controversy arose between the two scientists that was not put to rest even after the rivals were both awarded the Nobel Prize in 1906. If we look at the reasons for which Golgi opposed the neuron theory, we can see that they derived not so much from disagreement over the actual data observed, as from a different way of conceiving the anatomo-physiological architecture of the nervous system: Golgi appeared to support a holistic conception of the nervous system, the same that lay behind the theories of the opponents to cerebral localization, whereas Cajal and the 'neuronists' embraced an 'atomistic-reductionist' assumption, according to which the nervous system is made up of the sum of just so many neurons, each of which is an anatomical, functional, and embryological individuality, and not merely a <<transit station>> in a network of nervous filaments.

The antinociceptive and sedative effects of carbachol and oxycodone administered into brainstem pontine reticular formation and spinal subarachnoid space in rats

To clarify the supraspinal and spinal actions of a cholinergic agonist, carbachol, and an opioid, oxycodone, we studied their antinociceptive and behavioral effects when administered into brainstem medial pontine reticular formation (mPRF) or spinal subarachnoid space with or without pretreatment of muscarinic receptor subtype antagonist. Sprague-Dawley rats were implanted with a 24-gauge stainless steel guide cannula into the mPRF and chronically implanted with a lumbar intrathecal catheter. Antinociception was tested using tail flick latency, motor coordination was evaluated by the rotarod test, and overt sedation was assessed using a behavioral checklist. Carbachol (0.5-4.0 microg) administered into the mPRF produced significant dose- and time-dependent antinociception, sedation, and motor dysfunction. These were completely blocked by pretreatment with atropine and the M(2) muscarinic antagonist, methoctramine, and partially blocked by pretreatment with M(1) pirenzepine but not with M(3) p-fHHSID: Oxycodone administered into the mPRF did not produce such effects. Spinal carbachol and oxycodone produced antinociception without any behavioral effects; their antinociceptive effects were completely blocked by pretreatment with atropine and M(2) antagonist. These results suggest that the antinociceptive action of carbachol is mediated by muscarinic cholinergic receptor activation, especially by M(2) receptor subtype in mPRF and spinal cord, and that although oxycodone seems unlikely to affect the cholinergic transmission of mPRF, spinal oxycodone-induced analgesia is at least partly mediated via the activation of M(2) receptor subtype at the spinal cord.

IMPLICATIONS

Carbachol-induced antinociception and sedation is mediated with the activation of M(2) muscarinic receptors. Oxycodone administered into brainstem medial pontine reticular formation did not cause any antinociceptive or behavioral effects, but its spinal administration produced a significant antinociception via M(2) muscarinic receptor activation

Location of reticular premotor areas of a motor center innervating craniocervical muscles in the mallard (Anas platyrhynchos L.)

The supraspinal nucleus (SSp) in the mallard, which lies in the rostral spinal cord and caudal brainstem, is a motor nucleus that forms the rostral continuation of the ventral horn. It contains part of the motoneurons innervating the craniocervical muscles. Injections with horseradish peroxidase (HRP) and wheat germ agglutinin conjugated to HRP (WGA) in the SSp were used to localize the craniocervical premotor neurons in the medullary reticular formation. A mixture of WGA and HRP (WGA/HRP) or biotinylated dextran amine (BDA) were injected in the different reticular areas to test the results. Small numbers of craniocervical premotor neurons were found bilaterally in the ventromedial part of the parvocellular reticular formation (RPcvm) and in the caudal extension of RPcvm, the nucleus centralis dorsalis of the medulla oblongata, and the gigantocellular reticular formation (RGc). In a second series of experiments, WGA/HRP and BDA injections in these reticular areas were used to visualize afferent fibers and terminals in the SSp. The combination of the two types of experiments shows that RPcvm and RGc contain modest numbers of craniocervical premotor neurons. Because the reticular formation also contains jaw and tongue premotor neurons and receives a variety of sensory projections, the present results suggest that the medullary reticular formation plays a role in the coordination of complex movements (e.g., feeding). The pattern of afferent and efferent connections of the reticular formation is used to redefine its subdivisions in the myelencephalon of the mallard.

Midbrain reticular influences upon single neurons in lateral geniculate nucleus

The effect of electrical stimulation of the midbrain reticular formation upon patterns of discharge of single lateral geniculate neurons was studied. Data were processed by means of a 256-channel scaler analyzer. The rate of spontaneous discharge of geniculate neurons was raised by electrical stimulation of the reticular formation and their ability to respond to intermittent light was enhanced.

A comparative study of the effects of drugs on the arousal system of the brain

The effects of twelve drugs, eleven of which are reported to be tranquillizers, have been studied in relation to thresholds for arousal produced both by direct stimulation of the brain stem reticular formation and also by afferent nerve stimulation. The drugs can be grouped according to whether (a) like chlorpromazine they produce a slight rise in thresholds for brain stem stimulation and block sensory-induced arousal, (b) cause dissociation between behaviour and electrical activity of the brain, (c) have no effects on thresholds for brain stem stimulation and only slight effects on afferent nerve-induced arousal or (d) have no effect on arousal responses at all.

The development of nuchal atonia associated with active (REM) sleep in fetal sheep: presence of recurrent fractal organization

The behavioral state of active or rapid eye movement sleep (REMS) is dominant during fetal life and may play an important role in brain development. One marker of this state in fetal sheep is neck nuchal muscle atonia (NA). We observed burst within burst NA patterns suggestive of recurrent fractal organization in continuous 13 day in utero recordings of NA during the third trimester. Consistent with fractal renewal processes, the cumulative mean and standard deviation (SD) diverged over this time and the tail of NA distributions fit a stable Lévy law with exponents that remained invariant over the periods of development examined. The Hurst exponent, a measure of self-affine fractals, indicated that long-range correlations among NA intervals were present throughout development. A conserved complex fractal structure is apparent in NA which may help elucidate ambiguities in defining fetal states as well as some unique properties of fetal REMS.

Tooth pulp neurons in the caudal medulla oblongata of the cat

The medulla oblongata caudal to the obex was explored for neurons responsive to tooth pulp (TP) stimulation in cats. Four different subclasses of TP neurons were found. The latter included TP specific (TPS) neurons, trigeminal wide dynamic range (trigeminal WDR) neurons with TP input, trigeminal subnucleus reticularis ventralis (trigeminal SRV) neurons with TP input and convergent reticular formation (convergent RF) neurons with TP input. TPS neurons were located in the dorsal marginal rim of the trigeminal subnucleus caudalis, i.e., in the marginal layer or the outer zone of substantia gelatinosa. WDR neurons with TP input were found in the neck region of medullary dorsal horn which corresponds to the lateral part of subnucleus reticularis dorsalis (SRD). Trigeminal SRV neurons with TP input were located in the lateral part of SRV. Convergent RF neurons with TP input were found in the middle third of the caudal bulbar RF consisting of SRD and SRV. Both TPS neurons and WDR neurons with TP input included trigeminothalamic neurons as evidenced by the antidromic activation from the nucleus ventralis posteromedialis of the contralateral thalamus. A significant proportion of both trigeminal SRV and convergent RF neurons with TP input were antidromically activated by stimulation of the nucleus centralis lateralis of the contralateral thalamus. The former two subclasses may subserve the sensory-discriminative aspect of toothache, while the latter two subclasses, the emotional-motivational aspect.

Pontine microinjection of carbachol does not reliably enhance paradoxical sleep in rats

It has been repeatedly shown in cats that acute administration of carbachol into the pontine reticular formation (PRF) readily evokes a state that closely mimics natural paradoxical sleep (PS). Surprisingly, there are few corresponding studies in rats. In order to further characterize the effects of pontine carbachol in rats, 151 injections of different doses (from 3 micrograms to 0.005 microgram in 0.1 microliter saline) of carbachol were made at different sites within the PRF of 70 rats. Sleep-waking states obtained in the 4 hours following carbachol administration were compared to control values, obtained both under baseline condition (no injection) and following pontine injection of 0.1 microliter saline. On the one hand, from the whole set of carbachol injections, it appeared that: 1) most injections (112/151) did not significantly alter the sleep-wake states; 2) when carbachol was effective, it induced either increased PS (20 injections) or increased waking (19 injections); and 3) effective injection sites were intermingled with noneffective sites. Dose- or site-dependency effects can account in part, but not totally, for these discordant results. On the other hand, in accordance with previous rat studies, we found that: 1) the PRF medial and ventral to the motor trigeminal nucleus was the most effective region for carbachol to increase PS; 2) carbachol-induced PS enhancement was of moderate magnitude (+60% above control saline level over the 4-hour recording time); 3) latency to onset of the first PS episode was not shortened; and 4) only the number of PS episodes was increased, their duration was not prolonged. These characteristics of carbachol-induced PS enhancement strongly differ, both in terms of magnitude and timing, from those described in cats. We suggest that the less reliable and weaker effects of pontine carbachol injection in rats compared to cats can be due to methodological problems inherent in the intracerebral microinjection technique and also to species-related differences in the mechanisms controlling the PS state.

MRI findings in narcolepsy

The neuropathology of narcolepsy is unknown. Recently, Plazzi et al. (1) reported magnetic resonance imaging (MRI) abnormalities in the pontine tegmentum of three patients with long-standing idiopathic narcolepsy. Considering the localization of the neuroradiological findings in the pontine reticular formation, where rapid eye movement (REM) sleep is generated, the authors suggested a causal relationship between narcolepsy and MRI abnormalities. Frey and Heiserman, however, found pontine MRI abnormalities in only two of 12 patients with narcolepsy both of whom had long-standing hypertension (2). Pullicino et al. noted similar pontine MRI abnormalities in patients with subcortical arteriosclerotic encephalopathy-like ischemic rarefaction of the pons (3). Thus, the changes noted by Plazzi et al. may have been caused by small-vessel disease rather than narcolepsy. To assess whether altered pontine MRI signals are a regular feature of idiopathic narcolepsy, we selected randomly from our database seven patients with narcolepsy with cataplexy. Of these seven, three agreed to have brain MRIs; their cases are described below. None had pontine MRI abnormalities.

[Control and development of breathing, pathophysiological aspects]

The respiratory control system guarantees acid-base-homeostasis as well as the rhythmic activities of the respiratory motor system in accordance with exercise and behavioural programmes of the human being. Cortical patterns and synchronized respiratory patterns with tracheal flow and pressure variations in the fetus indicate the common network of respiration and sleep-wake mechanisms in an early stage already. During fetal life acid-base-homeostasis is dependent on progesterone controlled mechanisms. CO2 partial pressure of the uterine artery reduces to 32 mmHg. The O2 Partial pressure of the umbilical vein is 25-30 mmHg only. The raise of PCO2 during delivery is accompanied by a shower of sensory input to the reticular formation causing arousal and the opening of the lungs. The continuation of postnatal breathing is the consequence of the integration of the central chemosensitive mechanism and the reticular activating system at an adequate threshold. Perinatal defense reflexes, functional patterns and strategies in early life may outline later pathophysiological mechanisms for sleep apnea, apparently life threatening event (ALTE), sudden infant death, and congenital central hypoventilation syndrome.