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PubMed1990

Origin, course, and endings of abnormal enteric nerve fibres in Hirschsprung's disease defined by whole-mount immunohistochemistry.

Accurate delineation of the intramural pathway of abnormal enteric nerve fibres in Hirschsprung's disease has previously proved impossible because the neural network is invariably transected in conventional histological sections. With the technique of wholemount immunohistochemistry (WI), the bowel segment is converted into a rectangular sheet and the serosa, long muscle (LM), circular muscle (CM), submucosa, and mucosa are separated into layers to allow each nerve plexus to be examined intact and neural pathways traced. The entire resected bowel specimens of nine HD infants and five infants serving as controls were investigated, using neuron-specific enolase and vasoactive intestinal peptide (VIP) for WI. The major new findings are (1) More VIP fibres were observed in aganglionic bowel with WI than with conventional sections; (2) Thick nerve trunks in aganglionic bowel do not descend from intrinsic neurons of oligoganglionic bowel as previously suggested, but have an extrinsic origin, accompanying blood vessels as small nerves initially, expanding subsequently, and ending blindly in submucosa; (3) CM nerve fibres follow muscle fibres concentrically for long distances in aganglionic bowel; and (4) LM nerve fibres meander in spirals in aganglionic bowel instead of running straight. This study shows that (1) WI is highly sensitive; (2) nerve fibres in aganglionic bowel have an extrinsic origin; and (3) innervation abnormalities in Hirschsprung's disease are not only quantitative but qualitative.

Colon↗

PubMed1997

Thinking about networks in the control of male hamster sexual behavior.

Motivated social behaviors such as mating are controlled by a complex network of limbic nuclei. Concepts of network organization derived from computational neuroscience may aid our understanding of the links between the neuroanatomical circuitry and what is represented by the anatomy. Research in my laboratory uses mating behavior in the male Syrian hamster as a model to elucidate how chemosensory and steroid cues are integrated in the brain. An interaction of odors and hormones is required for mating in this species. These two essential stimuli are transmitted through separate parallel pathways in the limbic system. The functional organization of the hamster mating behavior circuit is characterized by distributed representation, divergent and convergent neural pathways, and recurrent feedback. Odors and hormones have different modes of action on this neural network. While chemosensory cues stimulate the input units of the network, steroids facilitate behavior through the hidden units. In this manner, steroids appear to create a permissive environment for subsequent activation by odor cues.

Amygdala↗

PubMed1995

Development of metabolic response in male quail brain during sexual maturation.

Seasonal reproductive activities of Japanese quail Coturnix japonica are induced most obviously by stimulatory effects of long-day photoperiod. This study addressed the metabolic response, as measured by 2-deoxyglucose (2-DG), in brain of male quail during sexual maturation. At 7 weeks of age, reproductively quiescent quail exposed to a short photoperiod of 6L:18D, received 2-DG on day 0 and +3, +6, +9, +12, +15 and +18 days after onset of 16L:8D. Brains were processed for autoradiography; serum testosterone was measured to indicate reproductive response to photoperiod. Circulating testosterone remained low until day 9, then rose sharply, reaching maximum levels at day 18. Heavily labeled nuclei were identified in some discrete neural pathways: both tectofugal and thalamofugal visual pathways, ascending auditory pathway, efferent vocalization pathway, and limbic structures. Metabolic activity of the terminal nucleus (ectostriatum) of the tectofugal pathway increased significantly by day 18, but in the terminal nuclei (the Wulst) of the thalamofugal visual pathway activity did not change significantly. Energy metabolism of some nuclei of the auditory pathway rose significantly by day 3, although in the vocal pathway it did not show augmentation until days 15-18. The metabolic activity of limbic structures also increased. These results suggest that, in Japanese quail, sensory nuclei and some of their integrative areas become sensitive to environmental cues in response to long-day photoperiod. It is possible that the external environmental cues that affect the reproductive activities of quail act through sensory systems.

Animals↗

PubMed1977

Neural control of ACTH release in response to hemorrhage.

A three dimensional reconstruction of the central neural pathways that appear to mediate release of ACTH in response to hemodynamic change is illustrated in Figure 11. Fibers from receptors in the right atrium and the carotid arteries project to the lateral solitary nucleus and then to the medial and the lateral nucleus intercalatus. A pathway containing projections from these nuclei then converges dominantly in the locus subcoeruleus and locus coeruleus. Multiple pathways then diverge, to travel in part directly to the hypothalamus through dorsal pathways. One pathway inhibits and another facilitates the release of ACTH. Multiple pathways also diverge, to travel in part medially, and then to the hypothalamus through ventral pathways. Again, one pathway inhibits and another facilitates the release of ACTH. The dorsal and ventral inhibitory pathways appear to converge in a region extending from just caudal and ventral to the paraventicular nucleus to the posterior hypothalamic area. Thus, after the coalescences of the various pontine-hypothalamic pathways, three principal pathways remain. These include a posterior inhibitor path, an anterodorsal facilitatory path that terminates in the paraventricular nucleus and that may be mediated through release of vasopressin, and an anteroventral facilitatory path that terminates in the suprachiasmatic and ventromedial nuclei and that is probably mediated through release of corticotropin-releasing hormone. The mode of integration of these pathways has not been defined. The pathways described herein are oligosynaptic: a signal may travel from atrium to hypothalamus over three to seven neurons. The combination of control of input hemodynamic signals and of measurement of ACTH permits quantitation of both sensory and motor events, that inevitably must be embedded in the neuronal pathways described here. The analysis of the input-output relations and their correlation with internal neural events must form the basis of a description of the physiology of the physiology of the system whose central neural anatomy has been defined in part by these studies.

Adrenocorticotropic Hormone↗

PubMed2003

Hormonal-neural integration in the female rat ventromedial hypothalamus: triple labeling for estrogen receptor-alpha, retrograde tract tracing from the periaqueductal gray, and mating-induced Fos expression.

The lordosis reflex, a stereotypic posture adopted by female rats during sexual behavior, requires the convergence of a hormonal signal, estrogen, with a descending neural pathway from the ventromedial hypothalamic nucleus (VMH). The VMH contains at least three lordosis-relevant neural populations: estrogen receptor-alpha immunoreactive (ERalpha-IR) neurons, VMH neurons that project to the periaqueductal gray (PAG), and neurons that are ERalpha-IR and project to the PAG. Expression of Fos, a marker for neuronal activation, is increased in the VMH after mating. However, it is unknown which, if any, of these lordosis-relevant populations is activated. The majority of ERalpha-IR and projection neurons were not colocalized. Of the Fos-positive neurons, 41% neither contained ERalpha nor projected to the PAG, and 35% contained ERalpha but did not project to the PAG. Only 25% of Fos-positive neurons projected to the PAG, including projection neurons that expressed ERalpha. Our results suggest that mating activates several distinct VMH neuron types. However, ERalpha-IR neurons are activated to a greater extent compared with the PAG-projecting neurons.

Animals↗

PubMed2005

Different neuronal pathways support the generation of general and specific mental images.

The aim of this functional magnetic resonance imaging (fMRI) study was to investigate the neural correlates associated with the generation of general (i.e., prototypical) and specific (i.e., exemplar) visual mental images from concrete nouns. The fMRI paradigm included a non-imagery baseline, and two activation conditions requiring the generation of either general or specific images. Image generation times and brain activation were recorded. Analysis of the behavioral results showed that generating general images took less than the specific ones. The comparison of each activation condition with the baseline showed significant increase in brain activation in left frontal areas in both kinds of images, with the additional involvement of the posterior cingulate cortex during the generation of specific images. When the two activation conditions were contrasted with each other and masked for their respective comparison with baseline, significant activation was found in right frontal areas for general mental images, whereas a significant increase in activation in the left superior frontal region and the right thalamus was detected during the generation of specific mental images. These findings suggest that general and specific mental images are generated with the support of two different neural pathways. The generation of general images seems to involve brain areas associated with the formation of global gestalt-like images (areas in the right hemisphere), while the generation of specific mental images appears to require additional support from areas involved in the retrieval of visual details (i.e., the right thalamus).

Adult↗

PubMed2003

Ectopic sympathetic preganglionic neurons maintain proper connectivity in the reeler mutant mouse.

The location of sympathetic preganglionic neurons (SPN) in the spinal cord of the reeler mouse mutant is abnormal. Instead of their normal location in the intermediolateral column, the majority of SPN in the reeler cluster around the central canal. To determine whether ectopically located SPN in the reeler form appropriate synaptic connections with their pre- and postsynaptic partners, we examined 1). whether the axons of descending neural pathways that normally terminate on SPN follow them to their ectopic location, and 2). whether the central autonomic neural circuit that controls sympathetic output to the kidney is organized normally in the reeler. Using antibodies against tyrosine hydroxylase, serotonin, neuropeptide Y, substance P and calcitonin gene-related peptide as markers for adrenergic, serotonergic and peptidergic terminals, we found that axons which normally innervate SPN follow these neurons to their ectopic spinal location in the reeler. Injection of pseudorabies virus into the kidney of wild type and reeler mutant mice revealed similar patterns of renal sympathetic and pre-sympathetic control circuits in the spinal cord, brainstem and forebrain. These results indicate that the presynaptic inputs and postsynaptic targets of SPN in the reeler are normal, despite the ectopic spinal location of their cell bodies.

Animals↗

PubMed2001

[Fridtjof Nansen as a neurobiologist].

Fridtjof Nansen (1861-1930) started his four-year research carrier in neurobiology at the Museum in Bergen in 1882. His PhD thesis from 1886 describes the structure of the nervous system in selected groups of invertebrates and in Amphioxus and the hagfish. For his time, he was a firm antireticularist and is still recognised as a forerunner of the emerging neurone doctrine of contiguity and no continuity between neurons in neural pathways.

Animals↗

PubMedDate not supplied

The theory of chronic deafferentation dysesthesias.

The chronic dysesthesias are abnormal disturbing somatic sensations, which are painful or non-painful. Their abnormality is revealed by their null or distorted psychophysical relationships; they occur spontaneously or can be peripherally induced by innocuous or noxious stimuli. Among nonverbal or mentally incompetent humans and also subhumans, these dysesthesias are expressed by patterns of escape or avoidance behaviors. There is no contemporaneous and necessary relationship with peripheral nociception. The basic mechanisms of these abnormalities have been obscure, and conventional modes of therapy have been unsuccessful. The origin of these chronic abnormalities is known to arise from lesions of peripheral or central components of the neural pathway for normal pain and temperature sensibility. The cause of these abnormalities is thought to reside in pathophysiological foci of excitability among deafferented central nocireceptive neurons. The spontaneous dysesthesias can occur after partial or total deafferentation. The peripherally induced dysesthesias occur after partial deafferentations, which include loss of small caliber myelinated afferents in cases of peripheral origin; and they are mediated via remaining afferent pathways. Little is known about the deafferented neurons in the brain, or the pertinent remaining central afferent pathways. More is now known about the pathophysiological effects of deafferentation on nonspecific nocireceptive neurons in the dorsal horn. These include morphological alterations, reduced inhibition, supersensitivity, hyperexcitability, and novel afferent excitation. Additional studies of chronic deafferentation in subhumans are necessary to provide further information and to test hypotheses concerning the chronic deafferentation dysesthesias.

Afferent Pathways↗

PubMed2000

Angiotensin peptides and baroreflex control of sympathetic outflow: pathways and mechanisms of the medulla oblongata.

The baroreceptor reflex is a relatively high gain control system that maintains arterial pressure within normal limits. To a large extent, this is accomplished through central neural pathways responsible for autonomic outflow residing in the medulla oblongata. The circulating renin-angiotensin system also contributes to the regulation of blood pressure, predominantly through its effects on the control of hydromineral balance and fluid volume. All the components of the renin-angiotensin system are also found in the brain. One of the principal products of the renin-angiotensin system cascade (brain or blood), angiotensin II, modulates the baroreceptor reflex by diminishing the sensitivity of the reflex and shifting the operating point for regulation of sympathetic outflow to higher blood pressures. This paper reviews our current knowledge about the neuronal pathways in the medulla oblongata through which angiotensin peptides alter the baroreceptor reflex control of sympathetic nerve activity. Emphasis is placed on the probable components and neural mechanisms of the medullary baroreflex arc that account for the ability of angiotensin peptides to change the sensitivity of the baroreceptor reflex and to shift the baroreceptor reflex control of sympathetic outflow to higher blood pressures in a pressure-independent manner.

Angiotensins↗

PubMed2006

Thalamic-prefrontal cortical-ventral striatal circuitry mediates dissociable components of strategy set shifting.

The mediodorsal nuclei of thalamus (MD), prefrontal cortex (PFC), and nucleus accumbens core (NAc) form an interconnected network that may work together to subserve certain forms of behavioral flexibility. The present study investigated the functional interactions between these regions during performance of a cross-maze-based strategy set-shifting task. In Experiment 1, reversible bilateral inactivation of the MD via infusions of bupivacaine did not impair simple discrimination learning, but did disrupt shifting from response to visual cue discrimination strategy, and vice versa. This impairment was due to an increase in perseverative errors. In Experiment 2, asymmetrical disconnection inactivations of the MD on one side of the brain and PFC on the other also caused a perseverative deficit when rats were required to shift from a response to a visual cue discrimination strategy, as did disconnections between the PFC and the NAc. However, inactivation of the MD on one side of the brain and the NAc contralaterally resulted in a selective increase in never-reinforced errors, suggesting this pathway is important for eliminating inappropriate strategies during set shifting. These data indicate that set shifting is mediated by a distributed neural circuit, with separate neural pathways contributing dissociable components to this type of behavioral flexibility.

Animals↗

PubMed1998

Physiological basis and pharmacology of motion sickness: an update.

Motion sickness can occur when sensory inputs regarding body position in space are contradictory or are different from those predicted from experience. Signals from the vestibular system are essential for triggering motion sickness. The evolutionary significance of this malady is unclear, although it may simply represent the aberrant activation of vestibuloautonomic pathways that typically subserve homeostasis. The neural pathways that produce nausea and vomiting during motion sickness are presumed to be similar to those that generate illness after ingestion of toxins. The neural substrate of nausea is unknown but may include neurons in the hypothalamus and inferior frontal gyrus of the cerebral cortex. The principal motor act of vomiting is accomplished through the simultaneous contractions of inspiratory and expiratory respiratory muscles and is mediated by neurons in the lateral medullary reticular formation and perhaps by cells near the medullary midline. Cocontraction of the diaphragm and abdominal muscles increases pressure on the stomach, which causes gastric contents to be ejected through the mouth. Effective drugs for combating motion sickness include antihistamines, antimuscarinics, 5-HT1A (serotonergic) receptor agonists and neurokinin type 1 receptor antagonists. However, considerable information concerning the physiological basis and pharmacology of motion sickness is unknown; future research using animal models will be required to understand this condition.

Antiemetics↗

PubMed1961

A mechanism of light adaptation.

In the isolated retina of the bullfrog (Rana catesbiana) illumination of one part of a ganglion cell's receptive field increased the light threshold (for response by that cell) not only in the illuminated part but also in the unilluminated parts of the field. Scattered light is insufficient to account for the effect. Apparently it depends on changes in the efficiency of excitation transmission along the neural pathways from photoreceptors to ganglion cell.

Acclimatization↗

PubMed2001

Estrogen attenuates the drinking response induced by activation of angiotensinergic pathways from the lateral hypothalamic area to the subfornical organ in female rats.

The present study was carried out to investigate whether estrogen modulates the drinking response induced by activation of angiotensinergic neural pathways from the lateral hypothalamic area (LHA) to the subfornical organ (SFO) in the female rats. Microinjection of ANG II (10(-10) M, 0.2 microl) into the LHA caused drinking in 17 out of 26 ovariectomized (OVX) female rats that were treated with propylene glycol (PG) vehicle and in 18 out of 28 OVX female rats that were treated with estrogen benzoate (EB). In both groups, previous injections of the ANG II antagonist saralasin (Sar, 10(-10) M, 0.2 microl) into the SFO significantly attenuated the water intake caused by the ANG II injection, suggesting that the ANG II-induced drinking response may be mediated by the angiotensinergic LHA projections to the SFO. Injections of ANG II (10(-10) M, 0.2 microl) into the SFO elicited drinking in all the animals that demonstrated the drinking response to ANG II injected into the LHA. The amount of water intake caused by either the injection of ANG II into the LHA or the SFO was significantly greater in the PG-treated than in the EB-treated animals. These results suggest that the circulating estrogen may act to attenuate the dipsogenic response induced by activation of the angiotensinergic pathways from the LHA to the SFO.

Angiotensin II↗

PubMed2003

In vivo tracing of major rat brain pathways using manganese-enhanced magnetic resonance imaging and three-dimensional digital atlasing.

The magnetic resonance imaging (MRI)-detectable T1 contrast agent manganese (Mn2+) has recently been introduced as a neural tracer in rodents, birds, and monkeys. We have tested to what extent this in vivo method is useful for three-dimensional (3-D) survey of connectivity patterns in the rat somatosensory system. A commonly available 3 T human clinical MRI scanner was used to trace neural pathways following focal injection of manganese chloride (MnCl2) in the somatosensory cortex. Six to 10 h after MnCl2 injection, we found significant signal enhancement in major projection systems, including corticocortical, corticostriatal, corticothalamic, corticotectal, corticopontine, and corticospinal pathways. To facilitate the assignment of anatomic localization to the observed Mn2+ signal enhancement, we registered the MRI data with a 3-D digital reconstruction of a stereotaxic rat brain atlas. Across-animal comparison using the digital model allowed demonstration of a corticothalamic 3-D topographic organization in agreement with previously published two-dimensional topographic schemes based on classical neural tracing data. We conclude that anterograde MnCl2/MRI tracing allows rapid analysis of topographic organization across multiple brain regions. The method allows a higher data throughput for 3-D studies of large-scale brain connectivity than conventional methods based on tissue sectioning.

Animals↗

PubMed2004

Visual and tactile interhemispheric transfer compared with the method of Poffenberger.

In a simple manual reaction time task, reaction times are longer if the responding hand and visual field of the stimulus are contralateral than when the hand and field are ipsilateral. This small crossed vs. uncrossed difference (CUD) has often been attributed to the interhemispheric transmission time incurred when the hemisphere receiving the sensory input is not the one initiating the motor response. We assessed the generality of the visual CUD by comparing it to the CUD for tactile stimuli. Visual and tactile CUDs did not differ significantly in magnitude, and in both modalities the CUD showed a strong asymmetry, with a positive CUD occurring only for the left hand. This outcome indicates that the properties of the visual CUD are not determined by neural pathways, or hemispheric asymmetries, that are specific to the visual system.

Adult↗

PubMed2006

Ascending spinal pathways from sexual organs: effects of chronic spinal lesions.

A recent survey of paraplegics indicates that regaining sexual function is of the highest priority for both males and females (Anderson, K.D. (2004) Targeting recovery: priorities of the spinal cord-injured population J. Newrotrauma, 21: 1371-1383). Our understanding of the neural pathways and mechanisms underlying sexual behavior and function is limited at the present time. More studies are obviously needed to direct experiments geared toward developing effective therapeutic interventions. In this chapter, a review of studies on the processing of sensory inputs from the male and female reproductive organs is presented with a review of what is known about the location of ascending spinal pathways conveying this information. The effect of spinal cord injury on sexual function and the problems that ensue are discussed.

Afferent Pathways↗

PubMed1994

Transmitter mechanisms in vagal afferent-induced reduction of lower oesophageal sphincter (LOS) pressure in the rat.

The extrinsic neural pathways and transmitter mechanisms involved in neural influences controlling lower oesophageal sphincter (LOS) pressure have been evaluated in three groups of experiments in urethane anaesthetized rats. A miniature perfused sleeve/sidehole catheter measured gastric, LOS and oesophageal pressures. Group 1: Vago-vagal and vago-spinal reflex pathways were activated simultaneously via the central nervous system by stimulation of the central cut end of the left vagus. This caused a prolonged drop in LOS pressure with a rapid onset and a slow return to baseline. Subsequent right (bilateral) vagotomy in these animals increased basal LOSP (P < 0.001). Central vagal stimulation-induced reduction of LOSP was not significantly changed in amplitude but was shorter in duration (P < 0.01) than before bilateral vagotomy. IV administration of the 5-HT3 receptor antagonist granisetron (50 micrograms/kg), after bilateral vagotomy had no effect on the response to central vagal stimulation. The nitric oxide (NO) synthase inhibitor L-nitroarginine methyl ester (L-NAME) (100 mg/kg) reduced the depth of relaxation (P < 0.01) and temporarily increased basal LOSP. Propranolol (1.5 mg/kg, i.v.) subsequently increased basal LOSP (P < 0.01), but had no further effect on the vagal stimulation-induced reduction in LOSP. Alpha adrenergic blockade with phentolamine (1 mg/kg, i.v.) decreased basal LOSP (P < 0.01), and nearly abolished the response to vagal stimulation (P < 0.01). Group 2: Both alpha 1- and alpha 2-adrenoceptors were shown to be involved by the combined use of the more selective antagonists yohimbine (1 mg/kg, i.v.) and prazosin (200 micrograms/kg) in place of phentolamine. Group 3: To observe neurotransmitter mechanisms in the vago-vagal pathway, central left vagal stimulation was performed after left vagotomy, and subsequently after blockade of sympathetic motor pathways with guanethidine (5 mg/kg), leaving intact efferent pathways in the right vagus. Guanethidine increased basal LOSP (P < 0.01), and reduced the duration of vagal-induced LOS relaxation (P < 0.05). Depth of relaxation was unchanged. Subsequently, granisetron and L-NAME had no significant effects. Finally, additional right vagotomy abolished the remaining response. Our data indicate the existence of vago-spinal and vago-vagal inhibitory reflex pathways to the rat LOS. The inhibitory vago-spinal pathway is mainly alpha-adrenergic, and has a minor NO-mediated component, but no 5-HT3 receptor-mediated mechanism. In the vago-vagal pathway, no significant involvement of NO-mediated or 5-HT3 receptor-mediated effects was observed. Other non-adrenergic inhibitory mechanisms were, however, apparent.(ABSTRACT TRUNCATED AT 400 WORDS)

Adrenergic alpha-Antagonists↗