Role of epinephrine in acute stress

This article presents the likely pathway of stimuli generated by the recognition of high-intensity stressors to ultimately produce a fight-or-flight response. A key element is the recognition that psychological stressors that do not directly alter the internal environment represent the most important etiology of a fight-or-flight response. Adrenomedullary secretion is a critical component of that response; impromptu stimulation of the adrenal medulla can produce plasma epinephrine concentrations greater than 10,000 pg/mL. When these plasma levels reach the hypothalamus to act on the CNS, the result is facilitation of the decision making, and decision execution processes (fight-or-flight), and perhaps further sympathetic stimulation and vasopressin release. Subjects with underlying cardiovascular and/or metabolic pathology may be particularly susceptible to potentially lethal reactions to this neuroendocrine response. Additionally, since this biological reaction may be triggered by sudden changes in the social environment, the coordinated actions of epinephrine, sympathetic stimulation and vasopressin must be directed at not only optimizing the chances for survival, but also at attaining maximal preservation of the individual environmental and social domains.

Projections of the posterodorsal preoptic nucleus and the lateral part of the posterodorsal medial amygdala in male gerbils, with emphasis on cells activated with ejaculation

The posterodorsal preoptic nucleus (PdPN) and the lateral part of the posterodorsal medial amygdala (MeApd) express Fos with ejaculation in male gerbils. Ejaculation-activated cells participate in the PdPN and MeApd projections to each other and to the sexually dimorphic preoptic area (SDA), but those projections involve less than 20% of the activated PdPN cells and less than 50% of the activated MeApd cells. To identify other potential targets of ejaculation-activated cells, we traced PdPN and lateral MeApd outputs using biotinylated dextran amine. The principal part of the bed nucleus of the stria terminalis (BSTpr) and the anteroventral periventricular nucleus (AVPv) were labeled from both sites and were injected with Fluoro-Gold to determine whether PdPN and lateral MeApd cells that express Fos with ejaculation would be retrogradely labeled. Fluoro-Gold was also applied to the dorsomedial hypothalamus (DMH) and retrorubral field (RRF) because such injections label PdPN cells in rats. The PdPN-DMH projection is minimal in gerbils, involving few, if any, ejaculation-related cells. Ejaculation-activated PdPN cells project to the AVPv (43%), dorsal BSTpr (30%), and RRF (12%). Those in the lateral MeApd project to the dorsal BSTpr (43%) and AVPv (18%). When these percentages are combined with those for ejaculation-activated cells involved in the PdPN and lateral MeApd projections to each other and to the medial SDA, the totals reach 100%. Thus, every PdPN and MeApd cell activated with ejaculation may participate in one of these projections. Similar projections may contribute to the similar behavioral effects of the PdPN and MeApd.

[Responses of afferent unit of the caudal nerve of diabetic hyperalgesic rats to sympathetic efferent stimulation]

Responses of afferent unit to sympathetic stimulation (SS), intravenous injection of noradrenaline (NA) and phentolamine in the caudal nerve of diabetic rats were investigated. The results showed that the discharge frequencies of C and Adelta units with spontaneous discharges were increased in diabetic hyperalgesic rats after SS, and these spontaneous discharges were eliminated by adrenergic antagonist. The C (6/21) and Adelta (19/81) units with no spontaneous discharges of diabetic hyperalgesic rat turned from silent state into active state during SS; although SS did not elicit afferent discharges of the C mechanical receptive units (C-M), it elicited afferent discharges of a part of C mechano heat units (C-MH) and C polymodal units (C-Pol); afferent discharges of some of the Adelta mechanical receptive units (Adelta-M) and Adelta mechano heat units (Adelta-MH) were also elicited by SS. The latencies of the C and Adelta units responses upon SS were not equal, but no less than 5 s. SS elicited neither afferent discharges from Abeta mechanical receptive units of diabetic hyperalgesic rat, nor receptive units of all types in the control rat. The C(3/8) and Adelta (4/12) units of diabetic hyperalgesic rat were activated by intravenous injection of NA. The present data suggest that NA released from sympathetic nerve terminals excites C and Adelta units of diabetic hypesthesic rat, which may be a peripheral factor in hyperalgesia and paresthesia of diabetic rats.

The adhesion molecule TAG-1 mediates the migration of cortical interneurons from the ganglionic eminence along the corticofugal fiber system

Cortical nonpyramidal cells, the GABA-containing interneurons, originate mostly in the medial ganglionic eminence of the ventral telencephalon and follow tangential migratory routes to reach the dorsal telencephalon. Although several genes that play a role in this migration have been identified, the underlying cellular and molecular cues are not fully understood. We provide evidence that the neural cell adhesion molecule TAG-1 mediates the migration of cortical interneurons. We show that the migration of these neurons occurs along the TAG-1-expressing axons of the developing corticofugal system. The spatial and temporal pattern of expression of TAG-1 on corticofugal fibers coincides with the order of appearance of GABAergic cells in the developing cortex. Blocking the function of TAG-1, but not of L1, another adhesion molecule and binding partner of TAG-1, results in a marked reduction of GABAergic neurons in the cortex. These observations reveal a mechanism by which the adhesion molecule TAG-1, known to be involved in axonal pathfinding, also takes part in neuronal migration.

Distribution of efferent neurones innervating the oviduct in the pig

This study was aimed, by means of the retrograde tracing technique, at disclosing the distribution of efferent neurones innervating the porcine oviduct. The fluorescent retrograde tracer Fast Blue was injected into the wall of the right oviduct in six juvenile pigs during laparotomy performed under anaesthesia. After a recovery period of 3 weeks the animals were reanaesthetised, perfused with 4% buffered paraformaldehyde (pH 7.4) and different ganglia, thought to be potent sources of the efferent innervation, were collected. The occurrence and distribution of Fast Blue-positive neurones were studied in the sympathetic chain and prevertebral ganglia, including the coeliac-superior mesenteric ganglion complex, adrenal ganglion, aorticorenal ganglion, ovarian ganglion and inferior mesenteric ganglion. The labelled neurones were found only in the right, ipsilateral ganglia. The largest number of Fast Blue-positive neurones was found in the inferior mesenteric ganglion, ovarian ganglion and in the coeliac-superior mesenteric ganglion complex. In the inferior mesenteric ganglion, the Fast Blue-positive neurones showed a tendency to gather in the dorso-cranial and the dorso-caudal region of the ganglion, forming two discrete "oviductal centres". The aortico-renal and adrenal ganglion contained a smaller population of Fast Blue-positive nerve cell bodies. The smallest number of Fast Blue-positive neurones was found in the sympathetic chain ganglia (T14-L5). The localisation of Fast Blue-positive neurones in the sympathetic chain ganglia and prevertebral ganglia suggests that these nerve structures play a fundamental role in the efferent innervation of the porcine oviduct.

Projection of the magnocellular red nucleus to the region of the accessory abducens nucleus in the rabbit

The projection of the magnocellular red nucleus (RNm) to the region of the accessory abducens nucleus (AABD) was traced in rabbit using the bidirectional tracer wheat germ agglutinin-horseradish peroxidase (WGA-HRP). In one set of animals, recordings of antidromic responses from RNm neurons elicited by electrical stimulation of the rubrospinal tract were used to localize injections of WGA-HRP for orthograde labeling of RNm terminals. In a different set of animals, horseradish peroxidase was injected into the retractor bulbi muscle to retrogradely label motoneurons of the AABD. The positions of RNm fibers and terminals were examined and compared to the locations and distribution of AABD cell bodies and labeled dendrites. Analyses revealed that along the entire rostrocaudal extent of the AABD, RNm efferents terminate primarily lateral to, or in the lateral aspects of, labeled motoneurons. For the rostral AABD, RNm efferents terminate only lateral to the nucleus. Although the terminals are not positioned to contact cell bodies of the AABD, they could overlap with dendrites that extend in the lateral direction. RNm efferents terminate more extensively within the posterior AABD, overlapping within both dendritic and cell body regions of the nucleus. Even in this posterior region, however, RNm efferents were distributed primarily over the lateral half of the nucleus. These data show that RNm can monosynaptically influence the AABD, through primarily its lateral and posterior aspects. Our findings also show that a major target of RNm efferents is the reticular cell population located lateral to the AABD, suggesting that the RNm also may affect AABD motoneuronal output indirectly through its projection to reticular cells.

Neuroanatomy of magnetoreception: the superior colliculus involved in magnetic orientation in a mammal

The neural substrate subserving magnetic orientation is largely unknown in vertebrates and unstudied in mammals. We combined a behavioral test for magnetic compass orientation in mole rats and immunocytochemical visualization of the transcription factor c-Fos as a marker of neuronal activity. We found that the superior colliculus of the Zambian mole rat (Cryptomys anselli) contains neurons that are responsive to magnetic stimuli. These neurons are directionally selective and organized within a discrete sublayer. Our results constitute evidence for the involvement of a specific mammalian brain structure in magnetoreception.

[Structural and functional changes in sympathetic ganglia following endotoxin and alpha1-antitrypsin exposure]

Structural and functional organisation of sympathetic ganglia under conditions of endotoxemia was studied in white rats, cats, and dogs. Submicroscopic characteristics of the changes occurring in the rat prevertebral sympathetic ganglia after endotoxin administration or application of endogenous proteinase inhibitor alpha 1-antitrypsin, were assessed as well as ultrastructural bases of the febrile rat ganglionic responses to antipyretic drug administration. Effects of endotoxin on synaptic transmission in inferior mesenteric plexus' ganglia of cats and on electrical activity in inferior mesenteric plexus' ganglia of dogs, were electrophysiologically demonstrated.

[Structure and function of the cerebellum]

INTRODUCTION

The cerebellum is a neural structure, of a crystalline like organization, present in all vertebrates. Its progressive growth from fishes to mammals, and particularly in primates, takes place following the repetition of a primitive cellular plan and connectivity.

DEVELOPMENT

The cerebellum is organized in folia located one behind the other in the rostrocaudal axis, and placed transversally on the brain stem. The cerebellar cortex has five types of neuron: Purkinje, stellate, basket, Golgi and granule cells. Apart from granule cells, the other cell types are inhibitory in nature. Afferent fibers to the cerebellar cortex are of two types (mossy and climbing) and carry information from somatosensory, vestibular, acoustic and visual origins, as well as from the cerebral cortex and other brain stem and spinal motor centers. The only neural output from the cerebellar cortex is represented by Purkinje axons that synapse on the underlying deep nuclei. Cerebellar nuclei send their axons towards many brain stem centers and, by thalamic relay nuclei, act on different cortical areas. Functionally, the cerebellum seems to be organized in small modules, similar in structure, but different in the origin and end of their afferent and efferent fibers. The cerebellum is involved in the coordination or integration of motor and cognitive processes.

CONCLUSION

Although cerebellar lesion does not produce severe motor paralysis, loss of sensory inputs or definite deficits in cognitive functions, its certainly affects motor performance and specific perceptive and cognitive phenomena.

The neuroendocrinology of childhood obesity

The regulation of energy balance is enormously complex, with numerous genetic, hormonal, neural and behavioral, and societal influences. Although the current epidemic of obesity clearly has its underpinnings in the changes in culture during the past half-century (see other articles in this issue), the role of the neuroendocrine system in the genesis of obesity, as described in this article, is physiologically and therapeutically unavoidable. An understanding of this system has suggested organic causes (and therapies) for some rare and not-so-rare forms of obesity. With so many inputs, it is not far-fetched to assume that dysfunction of other parts of this feedback system will be found to explain other forms of obesity in the future. What does this mean for obese children entering the pediatrician's office? Fortunately or unfortunately, diet and exercise are the mainstays of obesity therapy for children and adults. Most diet-exercise programs result in an acute 11-kg weight loss in adults; the question is whether it can be sustained without significant long-term behavioral modification. For instance, the European Sibutramine Trial of Obesity Reduction and Maintenance trial showed that 42% of treated subjects drop out; of those remaining, 77% of subjects lost more than 5% of initial body weight, but only 43% of those maintained more than 80% of this over 2 years. Could there be an organic component in those who do not respond? Of course, obesity pharmacotherapies sometimes have beneficial acute effects, but these drugs work for only as long as they are consumed; discontinuation tends to result in a "rebound" weight gain, suggesting that the cause of the obesity is still present. Furthermore, in 2001, there are no obesity drugs approved for children. A useful guiding principle is that children deserve at the minimum an initial medical evaluation, including birth weight, medical history, family history, dietary evaluation, and exercise assessment. Perhaps the most important feature that can distinguish "organic" from "behavioral" weight gain in childhood is the age of the "adiposity rebound." The Centers for Disease Control and Prevention now supplies BMI charts for boys and girls at www.cdc.gov/growthcharts. Plotting of the BMI versus age allows pediatricians to determine the age at which the BMI starts to increase (mean, 5.5 years). The earlier the adiposity rebound, the more likely the child will be obese as an adult, and the more likely that an organic cause can be determined. In such patients, thyroid levels and fasting insulin and leptin levels should be measured. An initial attempt at diet and exercise is essential; patients who do not respond with BMI stabilization should be investigated for a more ominous cause of their obesity. As the nosology of obesity improves, pediatricians will be able to increase the diagnostic efficiency and therapeutic success of this unfortunate, debilitating, and expensive epidemic.

Perioperative bradycardia and asystole: relationship to vasovagal syncope and the Bezold-Jarisch reflex

Reflex cardiovascular depression with vasodilation and bradycardia has been variously termed vasovagal syncope, the Bezold-Jarisch reflex and neurocardiogenic syncope. The circulatory response changes from the normal maintenance of arterial pressure, to parasympathetic activation and sympathetic inhibition, causing hypotension. This change is triggered by reduced cardiac venous return as well as through affective mechanisms such as pain or fear. It is probably mediated in part via afferent nerves from the heart, but also by various non-cardiac baroreceptors which may become paradoxically active. This response may occur during regional anaesthesia, haemorrhage or supine inferior vena cava compression in pregnancy; these factors are additive when combined. In these circumstances hypotension may be more severe than that caused by bradycardia alone, because of unappreciated vasodilation. Treatment includes the restoration of venous return and correction of absolute blood volume deficits. Ephedrine is the most logical choice of single drug to correct the changes because of its combined action on the heart and peripheral blood vessels. Epinephrine must be used early in established cardiac arrest, especially after high regional anaesthesia.

[Activation of sanogenesis mechanisms in central nervous system disorders]

Brain dysfunctions develop in brain injuries. Drug therapy is aimed at restitution processes which are often insufficient for recovery of impaired functions. Activation of the compensatory mechanisms of damaged and intact hemispheres will modify the time and qualitative characteristics of the restitution period. With this aim in view, transcranial electromagnetic stimulation in physiological range of efferent pathways and audiovisual stimulation of afferent pathways are recommended.

Distribution of reticulospinal neurons in the chicken by retrograde transport of WGA-HRP

To determine the distribution of reticulospinal (RS) neurons in the chicken, WGA-HRP was injected into the cervical or lumbosacral enlargement either unilaterally or bilaterally. The brainstem reticular nuclei sent largely descending fibers to both the spinal enlargements. The mesencephalon (medial and lateral mesencephalic reticular formation) and the rostral pons (nucleus reticularis [n.r.] pontis oralis) project mainly to the cervical enlargement. RS neurons were mainly distributed from the pontomedullary junction to the rostral medulla including n. r. pontis caudalis and pars gigantocellularis, n. r. gigantocellularis, n. r. parvocellularis, n. r. paragigantocellularis, and n. r. subtrigeminalis. It is suggested that the majority of these neurons send axons at least as far as the lumbosacral enlargement. In the lower medulla, RS neurons were distributed in the dorsal and ventral parts of the central nucleus of the medulla.

Unilateral hearing losses alter loud sound-induced temporary threshold shifts and efferent effects in the normal-hearing ear

In animals with bilaterally normal hearing, olivocochlear pathways can protect the cochlea from the temporary shifts in hearing sensitivity (temporary threshold shifts; TTSs) caused by short-duration intense loud sounds. The crossed olivocochlear pathway provides protection during binaural loud sound, and uncrossed pathways protect when monaural or binaural loud sounds occur in noise backgrounds. Here I demonstrate that when there is a chronic unilateral hearing loss, effects of loud sounds, and efferent effects on loud sound, in the normal-hearing ear differ markedly from normal. Three categories of test animals with unilateral hearing loss were tested for effects at the normal-hearing ear. In all categories a monaural loud tone to the normal-hearing ear produced lower-than-normal TTSs, apparently because of a tonic re-setting of that ear's susceptibility to loud sound. Second, in the two test categories in which the hearing-loss ear was only partly damaged, binaural loud sound exacerbated TTSs in the normal-hearing ear because it caused threshold shifts that were a combination of "pure" TTSs and uncrossed efferent suppression of cochlear sensitivity. (In normal cats, this binaural tone results in crossed olivocochlear protection that reduces TTS.) Binaural loud sound did not produce such uncrossed efferent effects in the test category in which the nontest ear had suffered total hearing loss, suggesting that this uncrossed efferent effect required binaural input to the CNS. It is noteworthy that, in the absence of this uncrossed efferent suppression, the pure loud sound-alone induced TTSs after binaural exposure were low. Thus in the absence of any efferent effect, the normal-hearing cochlea had a reduced susceptibility to loud tone-induced damage. Finally, the results suggest that, with respect to cochlear actions at high sound levels, uncrossed and crossed efferent pathways may exert different effects at the one type of receptor cell.

Morphology of pulmonary rapidly adapting receptor relay neurons in the rat

The term rapidly adapting pulmonary stretch receptor (RAR) refers to one of the major pulmonary sensory receptors that responds to inflation and deflation of the lungs as well as to irritant stimuli with rapidly adapting irregular discharges. The functional role and central pathways are largely unknown. The aim of this study was to elucidate morphological characteristics of second-order neurons (RAR cells) activated by vagal afferent fibers originating from RARs. A mixture of horseradish peroxidase (HRP) and Neurobiotin was injected intracellularly into physiologically identified RAR cells in Nembutal-anesthetized, immobilized, and artificially ventilated Wister rats. Direct visualization of individual RAR cells (n = 12), including their somata, dendritic arborizations, and fine axonal branches with terminal boutons, was possible for the first time. Their somata were located in the commissural or medial subdivision of the nucleus of the solitary tract, caudal to the level of the area postrema. The RAR cells had, in addition to dendrites extending into the NTS area, one or two long dendrites extending laterally and/or ventrolaterally into the medullary reticular formation. The stem axons issuing from the RAR cells first coursed ventrolaterally toward the reticular formation in the vicinity of the ambiguus nucleus and then bifurcated into ascending and descending axons: three RAR cells possessed only ascending axons. Some of the ascending axons could be traced as far as the level of the facial nucleus and some of the descending axons beyond the spinomedullary junction. These ascending and/or descending axons gave off extensive axon collaterals distributing boutons within and in the vicinity of the ambiguus nucleus. These results, showing an anatomical substrate for the network implicated in RAR-evoked reflexes, provide useful clues for study of the RAR system.

Efferent projections of infralimbic and prelimbic areas of the medial prefrontal cortex in the Japanese monkey, Macaca fuscata

The infralimbic area (IL) and prelimbic area (PL) have been postulated as an autonomic motor region in the medial prefrontal cortex. The present study was conducted to reveal the projection sites of IL and PL of the monkey, Macaca fuscata, using biotinylated dextran amine as an anterograde tracer. IL and PL projected densely to the ventromedial caudate nucleus, the core and shell of the nucleus accumbens (Acb), parvicellular lateral basal and magnocellular accessory basal nuclei of the amygdala, lateral preoptic area, ventromedial hypothalamic nucleus, tubero-mammillary nucleus (TM), medial part of the magnocellular and dorsal part of the parvicellular (MDpc) dorsomedial thalamic nuclei, reunience and medial part of the medial pulvinar nucleus, and dorso-lateral part of the periaqueductal gray (PAGdl) in the mesencephalon. Moderately to weakly projected areas were the intermediate and lateral parts of the agranular insular cortex, orbital part of area 12, agranular and dysgranular part of the temporal pole cortex (TPa-g), auditory temporal cortex, lateral and medial (MS) septal nuclei, bed nucleus of the stria terminalis, diagonal band of Broca, substantia innominata, and medial preoptic area, dorsomedial, lateral, and posterior hypothalamic nuclei, magnocellular lateral basal and lateral amygdaloid nuclei, paratenial, paraventricular (PV), inter-antero-medial (IAM), reticular, central medial (CeM), parafascicular (PF) and limitans nuclei of the thalamus, lateral habenular nucleus, pedunculo-pontine nucleus, dorsal part of the lateral lemniscal nucleus, ventral tegmental area (VTA), dorsal raphe, superior central nucleus, medial and lateral parabrachial nuclei (PBl) and nucleus locus coeruleus (LC). A few scattered terminals were observed in the perifornical nucleus of the hypothalamus and substantia nigra pars compacta. PL and area 24 were characterized by projections to the entorhinal (Ent) and piriform (Pir) cortex as well as to the magnocellular part of the ventral anterior thalamic nucleus (VAmc). The morphology of the terminal arborization in each nuclei was different in appearance, perhaps reflecting the synaptic interaction between the nerve terminals and postsynaptic dendrites. PL projected uniquely to Ent, Pir and VAmc and IL projected uniquely to TPa-g, MS, IAM, CeM, MDpc, PF, PBl and LC. IL projected more strongly than PL to the shell of Acb, amygdaloid nuclei, PV, TM, VTA and PAGdl. The present results support the hypothesis that IL is a major cortical autonomic motor area and PL integrates limbic and autonomic inputs in the primate.

Vagosympathetic interactions in ischemia-induced myocardial norepinephrine and acetylcholine release

To elucidate the pathophysiological roles of vagosympathetic interactions in ischemia-induced myocardial norepinephrine (NE) and acetylcholine (ACh) release, we measured myocardial interstitial NE and ACh levels in response to a left anterior descending coronary occlusion in the following groups of anesthetized cats: intact autonomic innervation (INT, n = 7); vagotomy (VX, n = 6); local administration of atropine (Atro, n = 6); transection of the stellate ganglia (TSG, n = 5); local administration of phentolamine (Phen, n = 6); and combined vagotomy and transection of the stellate ganglia (VX+TSG, n = 5). The maximum NE release was enhanced in the VX group (141 +/- 30 nmol/l, means +/- SE, P < 0.05) compared with the INT group (61 +/- 12 nmol/l). Neither the Atro (50 +/- 24 nmol/l) nor VX+TSG groups (84 +/- 25 nmol/l) showed enhanced NE release. The maximum ACh release was unaltered in the TSG and Phen groups compared with the INT group (19 +/- 4, 18 +/- 4, and 13 +/- 3 nmol/l, respectively). These findings indicate that the cardiac vagal afferent but not efferent activity reduced the ischemia-induced myocardial NE release. In contrast, the cardiac sympathetic afferent and efferent activities played little role in the ischemia-induced myocardial ACh release.

Laminar organization of the pyramidal cell layer of the subiculum in the rat

The distribution of neurons in the subiculum of the rat that give rise to subcortical connections was studied using retrograde labeling with horseradish peroxidase conjugated to wheat germ agglutinin. Injections were made into the anteroventral thalamic nucleus, the medial mammillary nucleus, the nucleus accumbens, and the lateral septal nucleus. To facilitate the analysis, the hippocampal formation with adjacent cortices were "flattened," which allowed the cutting of sections perpendicular to the full septotemporal axis. Cells projecting to the anteroventral thalamic nucleus (AV cells), the medial mammillary body (MMB cells), and the nucleus accumbens (ACC cells) were observed consistently throughout the entire septotemporal (dorsoventral) and transverse extent of the subiculum (from field CA1 of the hippocampus to the presubiculum). In the transverse plane, the three kinds of projection cells were arranged in a laminar fashion: The AV cells were observed in the deepest portion of the subicular pyramidal cell layer, the ACC cells were observed in the most superficial portion of the layer, and the MMB cells were observed in the middle portion of the layer. Although this laminar arrangement was observed at all septotemporal levels of the subiculum, it was most apparent at the septal level. At more temporal levels, the "laminae" shifted such that the superficially located ACC cells were more prominent in the proximal half of the subiculum, whereas the AV cells were shifted toward the distal half of the subiculum. The average size of somata of the AV cells was 72.3 microm(2), that of the ACC cells was 105.2 microm(2), and that of the MMB cells was 121.8 microm(2). The connectional and cytoarchitectonic data indicate that there is a distinct sublamination of the subicular pyramidal cell layer, suggesting that the subiculum may be analogous to the infragranular layer (layers V and VI) of the isocortex.

Connectivity of the tectal zones coding for upward and downward oblique eye movements in goldfish

Deep layers of the goldfish tectum code movements in a topographically ordered motor map. This work studies the relationship between tectal sites (coding eye movements with different vertical directions) and the distributions of boutons (left by their projections), within rostral mesencephalic structures and rhombencephalic reticular formations. These regions have been involved in the generation of the vertical and horizontal components of eye movement, respectively, as suggested by the Cartesian hypothesis of de-codification of tectal signal. With this aim, discrete injections of biotinylated dextran amine (BDA) and Fluoro-Ruby (FR) were made into functionally identified tectal sites, coding oblique eye movements with similar amplitude of the horizontal component but opposite upward and downward vertical directions, and the distribution of synaptic endings was determined. The main findings of the present work were as follows: 1) within the tectal descending tract, axons were organized according to the location of injected sites within the tectum; 2) BDA and FR boutons were distributed in separate clusters within the medial longitudinal fasciculus and oculomotor nuclei, as well as in the nearby mesencephalic reticular formation; and 3) the regions containing both types of bouton overlapped moderately within the mesencephalic reticular formation at the isthmus level. Overlapping was more extended at the different levels of the rhombencephalic reticular formation, although a shift in the distribution of both types of bouton was always observed. These results suggest that, within the vertical generator, the endings were separated to contact the different neuronal population that codes the upward and downward components of movements. In contrast, in the horizontal generator, tectal endings more likely converge on the same neuronal population to code the horizontal component of movements, irrespective of whether the oblique movements were directed upward or downward.

Pattern of long-distance projections from fetal hippocampal field CA3 and CA1 cell grafts in lesioned CA3 of adult hippocampus follows intrinsic character of respective donor cells

Fetal hippocampal grafts transplanted to the lesioned CA3 of adult hippocampus can extend axonal projections to many regions of the host brain. However, the identity of grafted cells that project to specific host regions is unknown. We hypothesize that the pattern of long-distance axonal projections from distinct fetal hippocampal cells grafted to lesioned CA3 is specified by the intrinsic nature of respective donor cells rather than characteristics of the host graft region. We grafted fetal hippocampal CA3 or CA1 cells into kainic acid lesioned CA3 of adult hippocampus at four days post-lesion. Neurons projecting to either the contralateral hippocampus or the ipsilateral septum were then measured in these grafts at four months post-grafting using Fluoro-Gold and DiI tract tracing. CA3 grafts located close to the degenerated CA3 cell layer showed a high propensity for establishing projections into the contralateral hippocampus (commissural projections) compared to similarly located CA1 grafts, which exhibited negligible commissural projections. Similar distinction was observed between the two graft types even when they were located only partially in the lesioned CA3. Among CA3 grafts, those placed near the degenerated CA3 cell layer established significantly greater commissural projections than those placed only partially in the CA3 region. Septal projections, in contrast, were robust from both CA3 and CA1 grafts. This differential projection pattern between CA3 and CA1 grafts resembles projections of CA3 and CA1 cells in intact hippocampus.These results demonstrate that the intrinsic character of grafted fetal cells determines the type of efferent projections from fetal grafts into different targets in the lesioned adult host brain. However, the extent of efferent projections from specific grafts is also influenced by the location of grafted cells within the host region. Thus, graft-mediated appropriate reconstruction of damaged circuitry in the lesioned brain may require grafting of homotopic donor cells. Further, the robust and specific projections observed from CA3 grafts is likely beneficial for functional recovery of hippocampus following CA3 injury and hence of significance towards developing a graft-mediated therapy for human temporal lobe epilepsy.

Vagal neurotransmission to the ferret lower oesophageal sphincter: inhibition via GABA(B) receptors

GABA(B) receptors modulate the function of the lower oesophageal sphincter (LOS) in vivo by inhibiting neurotransmitter release in the vagal pathway controlling LOS relaxation. We aimed to determine whether this effect was mediated peripherally on vagal motor outflow to the ferret LOS in vitro. The LOS, with intact vagal innervation, was prepared from adult ferrets and LOS tension measured. Vagal stimulation (0.5 - 10 Hz, 30 V) evoked a tetrodotoxin-sensitive, frequency-dependent relaxation. Both GABA (3x10(-4) M) and (+/-)baclofen (2x10(-4) M) inhibited vagally-stimulated LOS relaxation. The potent GABA(B) receptor-selective agonist 3-APPA dose-dependently inhibited vagally-stimulated LOS relaxation, with an EC(50) value of 0.7 microM Decreased responses following vagal stimulation in the presence of (+/-)baclofen or 3-APPA were reversed with the potent GABA(B) receptor antagonist CGP 62349. Neither CGP 62349 nor muscimol (GABA(A) receptor agonist) alone affected LOS responses following vagal stimulation. Agonists of other G protein-coupled receptors (clonidine (alpha(2)-adrenoceptor) (5x10(-6) M), U50488 (kappa opioid) (10(-5) M), neuropeptide Y (10(-6) M)) did not affect vagally-mediated LOS relaxation. The present study supports a discrete presynaptic inhibitory role for GABA(B) receptors on vagal preganglionic fibres serving inhibitory motorneurones in the ferret LOS.

Selective potentiating effect of RS14203 on a serotoninergic pathway in anesthetized rats

The usefulness of selective inhibitors of type 4 phosphodiesterase (PDE4) in the treatment of inflammation and pulmonary diseases is limited by their side effects: nausea and vomiting. We studied the effect of three structurally diverse PDE4 inhibitors on the vagal nerve afferent and efferent fibers in anesthetized rats. The effects of RS14203, (R)-rolipram, and CT-2450 were evaluated on the von Bezold-Jarisch reflex (vagal afferent fibers) and in a model of vagal electrical stimulation (vagal efferent fibers). All three PDE4 inhibitors were administered at 1, 10, or 100 microg/kg (iv) 15 min prior to the induction of bradycardia by an iv injection of 2-methyl-5-HT (von Bezold-Jarisch reflex) or by vagal electrical stimulation. At 100 microg/kg, RS14203 significantly potentiated the 2-methyl-5-HT response. No statistically significant effects were observed with (R)-rolipram or CT-2450 at the doses studied. RS14203, (R)-rolipram, or CT-2450 (1-100 microg/kg iv) did not affect the bradycardia induced by vagal electrical stimulation. Consequently, our results show that RS14203 selectively facilitates serotoninergic neurotransmission in vagal afferent fibers. The emetic action of RS14203 may be mediated by this mechanism.

Aberrant trajectory of entorhino-dentate axons in the mutant Shaking Rat Kawasaki: a Dil-labelling study

The Shaking Rat Kawasaki (SRK) is a neurological mutant that exhibits abnormalities of cell migration and lamination, with many similarities to the mouse reeler mutant. We recently used lamina-specific antibody staining to show that despite severe aberrations in the laminar organization of the SRK dentate gyrus, the entorhinal terminal field in the outer dentate molecular layer appeared relatively normal (Woodhams & Terashima, 1999, J. Comp. Neurol. 409 p57). However, neurofilament immunostaining suggested that entorhino-dentate afferents take an abnormal trajectory in reaching their appropriate targets, the granule cells dendrites. In the present study, anterograde tracing with the carbocyanine dye 1, 1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI) has been used to delineate directly the path that entorhinal axons take to the dentate gyrus, confirming that in SRK entorhinal axons do indeed reach their appropriate terminal fields in the molecular layer, with laminar segregation between projections from the lateral and medial entorhinal cortices. However, these fibres fail to cross the hippocampal fissure between the subiculum and the dentate gyrus, coursing instead parallel to it until they curve round the deepest point of the fissure in field CA3. Similar findings were seen in the murine reeler mutant. Insertion of DiI crystals into the entorhinal cortex of neonatal rats also retrogradely labelled the developmentally transient Cajal-Retzius cells at the hippocampal fissure; these survive for longer in SRK than in normal littermates. The presence of a marked astrogliosis at the SRK hippocampal fissure may play a part in determining the abnormal trajectory taken by entorhino-dentate afferents in this mutant.

Signalling in body-weight homeostasis: neuroendocrine efferent signals

Whilst a number of neuroendocrine afferent signals are implicated in body-weight homeostasis, the major efferent pathway is the sympathetic nervous system (SNS), which affects both energy expenditure and substrate utilization. Thyroid hormones and their interactions with the SNS may also have a role to play. Some of the variability in resting energy expenditure can be explained by differences in SNS activity, and beta-blockade can reduce energy expenditure and diet-induced thermogenesis in Caucasians. Excess energy intake leads to SNS activation and increased diet-induced thermogenesis. A relationship has also been demonstrated between spontaneous physical activity and SNS activity. In many animal models the SNS activates brown adipose tissue thermogenesis, hence increasing diet-induced thermogenesis and dissipating excess energy as heat. This effect is mediated via beta3-adrenoceptors and activation of an uncoupling protein unique to brown adipose tissue. Homologous proteins have been identified in human tissues and may play a role in human energy expenditure. How the SNS is implicated in this process is unclear at present. beta3-Adrenoceptor polymorphism has been associated both with lower resting energy expenditure in some populations and with reduced autonomic nervous system activity. SNS effects on substrate cycling may also play a role. In the development of obesity the effects of the SNS in promoting lipolysis and fat oxidation are likely to be at least as important as its effects on thermogenesis. beta-Blockade has relatively small effects on energy expenditure, but more pronounced effects on reducing lipid oxidation, so tending to favour fat storage and weight gain. Low lipid oxidation is a risk factor for weight gain, and there is some evidence that low basal sympathetic nerve activity in muscle is associated with this process. Overall, the relationship between SNS activity and obesity is complex, with evidence of low SNS activity occurring in some, but not all, studies.