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PubMed1988

Preoptic-hypothalamic pathways controlling nocturnal prolactin surges, pseudopregnancy, and estrous cyclicity in the rat.

Frontal, dorsal, or sham deafferentations were placed at various locations within the hypothalamus in order to study the neural pathways involved in pseudopregnancy (PSP), estrous cyclicity, and prolactin (PRL) secretion in the rat. Dorsal or sham transections did not interfere with PSP or estrous cyclicity. Frontal cuts placed on day 3-4 of PSP between the posterior border of the optic chiasm and the anterior tip of the mediobasal hypothalamus (MBH) led to interruption of diestrus within 3-5 days. With frontal cuts placed more caudally in the MBH, and with frontal cuts placed rostrally at the anterochiasmatic area, the duration of PSP was within normal range. Irrespective of their effects on PSP, anterochiasmatic and retrochiasmatic cuts were associated with onset of persistent estrus, and MBH transections resulted in either persistent estrus in some rats or regular estrous cycles in the others. In deafferentated rats that showed persistent estrus, the basal plasma concentrations of PRL measured 3-4 weeks after ovariectomy were 2- to 3-fold higher than in deafferentated and sham-deafferentated animals that were cyclic before ovariectomy. Electrical vaginocervical stimulation induced secretion of nocturnal PRL surges in long-term ovariectomized rats with dorsal or sham transections, but not in those bearing frontal cuts, regardless of the neuroanatomical location of the frontal cut. These results suggest that (1) impulses generated at the uterine cervix must reach the medial preoptic area, a putative 'anti-surge center', and proceed from there to the MBH, in order to allow initiation of nocturnal PRL release.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1986

Synthesis of a growth-associated protein by embryonic rat cerebrocortical neurons in vitro.

Proteins synthesized by embryonic rat cortical cultures were studied under conditions that were either permissive or nonpermissive to neurite outgrowth. Freshly dissected cortex from embryonic day 17 rat pups was mechanically dissociated and plated on poly(L-lysine) substrate in the presence of (1) serum-free media, which allowed neuronal survival but no outgrowth; (2) serum, which allowed survival of both neurons and glia as well as neurite outgrowth; or (3) a hormone-supplemented defined media, which allowed preferential survival and outgrowth of neurons. In addition, postnatal tissue was cultured as a source of glia. Cultures were pulse-labeled with 35S-methionine 48 hr after plating and the protein synthesis patterns examined by 2-dimensional gel electrophoresis followed by fluorography. The expression of an acidic 50 kDa protein, associated with the particulate fraction of cells, was found to be a prominent correlate of neurite outgrowth. This protein was synthesized in serum- or hormone-treated embryonic cultures showing neurite outgrowth but was undetectable in embryonic cultures without outgrowth or in postnatal glial cultures. By virtue of its migration position on 2-dimensional gels, its presence in a light membrane fraction, and its cleavage products after Staphylococcus aureus protease treatment, the 50 kDa protein appears to be identical to an acidic 43-49 kDa protein that has been identified in several developing and regenerating neural pathways, as well as to the B-50 phosphoprotein. These findings lend support for a critical role of this protein in neural development and demonstrate the feasibility of using primary CNS cell cultures to study its biosynthesis and function.

Animals↗

PubMed2005

Recognition of objects in non-canonical views: a functional MRI study.

BACKGROUND: The neural correlate of object recognition in non-canonical views is uncertain, but there is evidence for involvement of neural pathways, possibly separate from those used for object recognition in canonical views. METHODS: Boxcar functional MRI (fMRI) techniques were used to detect neural activity while eight normal subjects were instructed to identify digital photographs of objects in non-canonical and canonical orientations. RESULTS: The right angular gyrus, the left inferior temporal gyrus, and the right cerebellum showed significant fMRI activity during non-canonical as opposed to canonical viewing. CONCLUSIONS: Subjects recognizing objects in non-canonical orientations engage in a process separate from, or in addition to, the process used in recognizing objects in canonical orientations.

Adult↗

PubMed1991

Neural induction.

The study of neural induction in Xenopus can be approached from two broad perspectives. One can study the competence of the ectoderm to respond to neural induction signals and any potential prepattern within the ectoderm. The second area of study involves the neural induction signals, in terms of the chemical nature of the signals, their sources, and their method of delivery. The neural competence of ectoderm has been studied by either grafting the ectoderm into areas which normally form neural tissue or by grafting tissues which normally induce neural structures onto the ectoderm to be tested. In general, it appears that ectoderm loses neural competence by midgastrula. However, there is some experimental evidence from various amphibian studies that the loss of neural competence in ectoderm does not occur simultaneously throughout all regions. It is not yet known if this phenomenon is also true in Xenopus. There appear to be several signaling events involved in the process of neural induction. Molecular probes have made it possible to study early steps in the neural induction and patterning processes which were not possible to study using only the development of neural morphology as a marker for neural induction. Antibodies directed against early epidermal versus neural epithelium indicate that the dorsal animal blastomeres are biased toward a neural pathway during early cleavage. Another signaling event occurs at early gastrula and the resulting dorsal ectoderm now responds more readily to some neural induction events than does the ventral ectoderm. The source of the early gastrula signals has been studied by a variety of methods, including exogastrula embryos, Keller sandwiches, and grafting a blastopore lip to the edge of competent ectoderm. The blastopore lip can send signals through the plane of the ectoderm capable of inducing competent ectoderm to become neural tissue. There are several issues relative to the process of neural induction which are not yet resolved. The major issue involves the mechanism of establishing pattern within the neural plate. Ectoderm appears to lose neural competence prior to the time when involuted dorsal mesoderm comes to underlie the anterior neural plate region. Several investigators have shown that information for expression of spatially restricted neural-specific molecules can travel through the ectoderm, independent of underlying dorsal mesoderm.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1988

The distribution of fibronectin and tenascin along migratory pathways of the neural crest in the trunk of amphibian embryos.

It is generally assumed that in amphibian embryos neural crest cells migrate dorsally, where they form the mesenchyme of the dorsal fin, laterally (between somites and epidermis), where they give rise to pigment cells, and ventromedially (between somites and neural tube), where they form the elements of the peripheral nervous system. While there is agreement about the crest migratory routes in the axolotl (Ambystoma mexicanum), different opinions exist about the lateral pathway in Xenopus. We investigated neural crest cell migration in Xenopus (stages 23, 32, 35/36 and 41) using the X. laevis-X. borealis nuclear marker system and could not find evidence for cells migrating laterally. We have also used immunohistochemistry to study the distribution of the extracellular matrix (ECM) glycoproteins fibronectin (FN) and tenascin (TN), which have been implicated in directing neural crest cells during their migrations in avian and mammalian embryos, in the neural crest migratory pathways of Xenopus and the axolotl. In premigratory stages of the crest, both in Xenopus (stage 22) and the axolotl (stage 25), FN was found subepidermally and in extracellular spaces around the neural tube, notochord and somites. The staining was particularly intense in the dorsal part of the embryo, but it was also present along the visceral and parietal layers of the lateral plate mesoderm. TN, in contrast, was found only in the anterior trunk mesoderm in Xenopus; in the axolotl, it was absent. During neural crest cell migration in Xenopus (stages 25-33) and the axolotl (stages 28-35), anti-FN stained the ECM throughout the embryo, whereas anti-TN staining was limited to dorsal regions. There it was particularly intense medially, i.e. in the dorsal fin, around the neural tube, notochord, dorsal aorta and at the medial surface of the somites (stage 35 in both species). During postmigratory stages in Xenopus (stage 40), anti-FN staining was less intense than anti-TN staining. In culture, axolotl neural crest cells spread differently on FN- and TN-coated substrata. On TN, the onset of cellular outgrowth was delayed for about 1 day, but after 3 days the extent of outgrowth was indistinguishable from cultures grown on FN. However, neural crest cells in 3-day-old cultures were much more flattened on FN than on TN. We conclude that both FN and TN are present in the ECM that lines the neural crest migratory pathways of amphibian embryos at the time when the neural crest cells are actively migrating. FN is present in the embryonic ECM before the onset of neural crest migration.(ABSTRACT TRUNCATED AT 400 WORDS)

Ambystoma↗

PubMed1988

Asymmetries in ON and OFF visual pathways of humans revealed using contrast-evoked cortical potentials.

Positive- and negative-contrast stimuli yield the perceptions of brightness and darkness, respectively, and are processed separately by ON and OFF neural pathways. The properties of these morphologically and pharmacologically distinct subsystems were measured in humans by recording visual evoked potentials (VEPs). These electrical responses from the visual cortex were elicited by novel positive- and negative-contrast stimuli, designed to emphasize, selectively, contributions from ON and OFF pathways. Results revealed differential processing of the two types of contrast information, suggesting asymmetries in ON and OFF subsystems; OFF subsystems have finer spatial tuning and greater contrast gain than ON subsystems. These VEPs may be useful in diagnosing neurological disorders that involve primarily one subsystem.

Adult↗

PubMed1979

Effects of psychotropic drugs on pressor and behavioral responses to brain stimulation in unrestrained, unanesthetized rats.

Electrical stimulation of the posterior hypothalamus (PH) and the mesencephalic reticular formation (MRF) in unanesthetized, unrestrained rats with chronic electrode implants and an arterial cannula elicited a rise in blood pressure accompanied by behavioral changes such as exploration, flight or escape responses. Pentobarbital inhibited both the pressor and behavioral responses to PH and MRF stimulation. Chlorpormazine, diazepam and imipramine depressed the pressor response to PH stimulation rather than that to MRF stimulation with affecting the behavioral responses. It is concluded from these results that chlorpromazine, diazepam and imipramine exert their action on the neural pathway involved in the pressor response rather than on that inducing behavioral responses, whereas pentobarbital affects more extended brain areas related to these neural systems.

Animals↗

PubMed2005

Introduction: neurobiological impact of environmental estrogens.

This paper provides an introduction to a special issue dedicated to the action of environmental estrogens on neural circuits and behavior. The problem of endocrine disrupting chemicals (EDCs), i.e. chemicals that have the capacity to interfere with the endocrine system, has gained increasing attention as it has become clear that these environmental contaminants may be active in humans, as well as in wildlife and domestic animal species. The majority of the early investigations were aimed at the discovery of the toxicological effects of the EDCs, but biomedical observations were among some of the first indications that estrogenic compounds may exert deleterious effects, even some time after exposure. The data derived from women exposed prenatally to diethylstilbesterol provided powerful evidence for long-term effects and endocrine disruption associated with selected compounds. The examination of wild animal populations exposed to industrial chemicals showed that the chemical exposure, though nonlethal, left the individual impaired or even incapable of reproducing. Among the multiple targets of the action of EDCs, several researches performed in recent years have investigated subtle modifications of the animal behaviors (reproductive, aggressive) that are likely to be related to alterations of specific neural pathways. We have, therefore, focused here on the behavioral studies as one of the more powerful tools to investigate EDCs effects on specific neural circuits.

Animals↗

PubMed2001

Neural mechanisms of cardiovascular regulation during exercise.

This brief review addresses current hypotheses concerning the reflex control of circulation during exercise in humans. In particular, the specific objective of this review is to describe how time and frequency domain analysis of blood pressure and heart rate variability signals permitted to gain new insights onto reflex mechanisms of cardiovascular regulation during exercise, without the need of perturbing the cardiovascular system from the outside, utilizing fully noninvasive approaches and avoiding artificially isolating the influence of the different neural pathways involved in the control of the cardiovascular system. Throughout the article, particular emphasis is given to the complexity and plasticity of the neural control of the circulation during exercise, by presenting data that show how the reflex mechanisms involved in cardiovascular regulation, namely, the arterial baroreflex and the muscle metaboreflex, may be differently modulated in relation to the muscular activity being performed, such as the type of exercise, the intensity of exercise and the size of active muscle masses.

Autonomic Nervous System↗

PubMed2000

Evoked potential monitoring in anaesthesia and analgesia.

Electrophysiological monitoring of selected neural pathways of the brain, brainstem, spinal cord and peripheral nervous system has become mandatory in some surgery of the nervous system where preventable neural injury can occur. Evoked potentials are relatively simple methods of testing the integrity of various aspects of the nervous system. This review covers the variety of evoked potentials that can be monitored and outlines the principles of their measurement. Their use in specific situations and how factors such as anaesthesia might affect them is presented.

Analgesics↗

PubMed2001

Sensorimotor adaptation to violations of temporal contiguity.

Most events are processed by a number of neural pathways. These pathways often differ considerably in processing speed. Thus, coherent perception requires some form of synchronization mechanism. Moreover, this mechanism must be flexible, because neural processing speed changes over the life of an organism. Here we provide behavioral evidence that humans can adapt to a new intersensory temporal relationship (which was artificially produced by delaying visual feedback). The conflict between these results and previous work that failed to find such improvements can be explained by considering the present results as a form of sensorimotor adaptation.

Adult↗

PubMed1982

Herpes simplex virus infection of isolated autonomic neurons in culture: viral replication and spread in a neuronal network.

Cultures of isolated neurons, derived from the superior cervical ganglion (SCG) of the newborn rat and maintained in the absence of nonneuronal cells, were infected with herpes simplex virus (HSV) type 1. By phase-contrast microscopy, including time-lapse cinematography, cytopathologic changes appeared first in neuronal cell bodies and only approximately 24 hours later were axonal abnormalities detectable. Despite low yields of viral progeny, infection spread readily within the two-dimensional network of neurons and their processes. Immunoperoxidase staining for viral antigens confirmed the replication and spread of virus and revealed that antigen extended along axons during infection. Antiviral antibody added to the overlay medium slowed but did not prevent the spread of infection, indicating that virus passed from neuron to neuron over axonal pathways. Despite alteration of neuronal macromolecular synthesis early in infection, axonal transport is apparently preserved long enough to allow propagation of virus over interconnecting neural pathways.

Animals↗

PubMedDate not supplied

Cardiopulmonary and sinoaortic baroreceptors and volume expansion in the monkey.

Experiments were performed to determine the effect of combined cardiopulmonary and and sinoaortic baroreceptor denervation on the renal responses of the anesthetized nonhuman primate to acute intravascular volume expansion. Adult male Macaca fascicularis monkeys underwent chronic bilateral thoracic sympathectomy (middle cervical ganglion--T6) or sham surgery performed in two stages. After a 1-3 week recovery period, each animal was anesthetized with sodium pentobarbital and subjected to cervical vagotomy--sinoaortic denervation or further sham denervation. Estimated blood volume was then acutely expanded 20% with 6% dextran in isotonic saline. Control renal excretory function did not differ between the two groups, and both groups had similar increases in urine flow, sodium excretion, osmolar clearance, free water clearance and renal plasma flow after volume expansion. The patterns of the responses showed some group differences in that the increases in renal excretion after volume-loading had an earlier onset in the denervated animals. These results demonstrate that combined ablation of thoracic sympathetic, vagal and sinoaortic neural pathways does not compromise the ability of the nonhuman primate to increase salt and water excretion when blood volume is acutely expanded. Therefore, these neural mechanisms are not necessary for eliciting the renal responses to this hypervolemic stimulus in this species during the anesthetized state.

Animals↗

PubMed2002

Anatomical and functional evidence for a neural hypothalamic-testicular pathway that is independent of the pituitary.

Testosterone (T) secretion is classically considered to be under the primary control of pituitary LH, itself regulated by the hypothalamic peptide LH-releasing hormone. Secretagogues present in the general circulation and/or manufactured in the testis can also alter Leydig cell activity independently of the pituitary. Finally, spanchnic innervation regulates testicular LH receptors and blood flow. In the present work, we provide evidence that, in addition, there may be a neural brain-testicular circuit that regulates T release function independently of LH release. We had recently reported that the intracerebroventricular injection of IL-1beta, corticotropin-releasing factor, or beta-adrenergic agonists significantly interfered with the T response to human chorionic gonadotropin through mechanisms that did not involve LH. Here, we show that the injection of the transganglionic retrograde tracer pseudorabies virus into the testes caused viral staining in the spinal cord, the brain stem, and the hypothalamus. This observation indicates the presence of a neural pathway between the central nervous system and the testis. We then demonstrated that spinal cord injury significantly interfered with this staining, thus supporting the hypothesis that the proposed circuit travels through the cord. Finally, we showed that spinal cord injury completely abolished the ability of intracerebroventricularly injected IL-1beta or corticotropin-releasing factor to blunt the T response to human chorionic gonadotropin, which suggests that these two secretagogues act within the brain to stimulate a neural pathway that interferes with Leydig cell function independently of the pituitary. The hitherto unsuspected brain-testicular circuit that these experiments have uncovered may play a role in pathologies, so far unexplained, that are characterized by decreased T levels despite normal LH production.

Animals↗

PubMed2000

Mechanisms of central pain.

Central pain is common in patients with stroke, multiple sclerosis, syringomyelia, and spinal cord injury. It frequently develops after a delay of weeks or months, is associated with sensory change involving the spinothalamic pathways, and has a poor prognosis for spontaneous remission. Hypotheses to explain the varied clinical manifestations can be divided in two categories: those stressing aberrant neural activity in the deafferented circuits and those focusing on the postlesion imbalance between facilitatory and inhibitory neural pathways. All models inherently assume a degree of specialization of cerebral structures in pain processing, which has not been proved conclusively.

Central Nervous System Diseases↗

PubMed2006

The role of the muscarinic system in regulating estradiol secretion varies during the estrous cycle: the hemiovariectomized rat model.

There is evidence that one gonad has functional predominance. The present study analyzed the acute effects of unilateral ovariectomy (ULO) and blocking the cholinergic system, by injecting atropine sulfate (ATR), on estradiol (E2) serum concentrations during the estrous cycle. The results indicate that ULO effects on E2 concentrations are asymmetric, vary during the estrous cycle, and partially depend on the cholinergic innervation. Perforation of the left peritoneum resulted in lower E2 serum concentrations in the three stages of the estrous cycle. At proestrus, unilateral or bilateral perforation of the peritoneum resulted in lower E2 serum concentrations.ULO of the right ovary (left ovary in situ) resulted in significantly higher E2 concentrations than animals with ULO of the left ovary (right ovary in situ). ATR treatment to ULO rats on D1 resulted in a significant drop of E2 serum concentrations. ULO rats treated with ATR on D2 or P, resulted in an asymmetrical E2 secretion response; when the right ovary remained in situ an increase in E2 was observed, and a decrease when the left ovary remained in situ. The results obtained in the present study suggest that each ovary's ability to compensate the secretion of E2 from the missing ovary is different and varies during the estrous cycle. The results also suggest that the cholinergic system participates in regulating ovarian E2 secretion. Such participation varies according to the ovary remaining in situ and the stage of the estrous cycle of the animal. The results agree with previously stated hypothesis of a neural pathway arising from the peritoneum that participates in regulating E2 secretion, and also supports the idea of cross-talk between the ovaries, via a neural communication, that modulates E2 secretion.

Anesthesia↗

PubMed2000

The role of nigral and thalamic output pathways in the expression of oral stereotypies induced by amphetamine injections into the striatum.

Microinjections of amphetamine into the ventrolateral striatum (VLS) elicit a striking behavioral syndrome characterized by compulsive oral and forelimb motor stereotypies. The neural pathways that mediate these behavioral responses downstream from the striatum have not yet been identified. In a series of experiments, we investigated the involvement of the substantia nigra pars reticulata (SNr) and the ventromedial nucleus of the thalamus (VMT) in the mediation of this behavioral syndrome. We demonstrated that lidocaine-induced reversible inactivation of the SNr reduced amphetamine-induced stereotyped biting and gnawing behaviors, suggesting that the nigral output pathway plays a significant role in the expression of these behavioral responses. In turn, injections of lidocaine into the VMT only transiently reduced amphetamine-stimulated biting and increased stereotyped gnawing and paw nibbling, suggesting that the expression of oral stereotypies induced by amphetamine injections into the VLS is not dependent on thalamocortical feedback.

Amphetamine↗

PubMed2003

Reductions in N-acetylaspartylglutamate and the 67 kDa form of glutamic acid decarboxylase immunoreactivities in the visual system of albino and pigmented rats after optic nerve transections.

This study compares the immunohistochemical distributions of N-acetylaspartylglutamate (NAAG) and the large isoform of the gamma-aminobutyric acid (GABA)-synthesizing enzyme glutamic acid decarboxylase (GAD(67)) in the visual system of albino and pigmented rats. Most retinal ganglion cells and their axons were strongly immunoreactive for NAAG, whereas GAD(67) immunoreactivity was very sparse in these cells and projections. In retinorecipient zones, NAAG and GAD(67) immunoreactivities occurred in distinct populations of neurons and in dense networks of strongly immunoreactive fibers and synapses. Dual-labeling immunohistochemistry indicated that principal neurons were stained for NAAG, whereas local interneurons were stained for GAD(67). In contrast to the distribution observed in retinorecipient zones, most or all neurons were doubly stained for NAAG and GAD(67) in the thalamic reticular nucleus. Ten days after unilateral optic nerve transection, NAAG-immunoreactive fibers and synapses were substantially reduced in all contralateral retinal terminal zones. The posttransection pattern of NAAG-immunoreactive synaptic loss demarcated the contralateral and ipsilateral divisions of the retinal projections. In addition, an apparent transynaptic reduction in GAD(67) immunoreactivity was observed in some deafferented areas, such as the lateral geniculate. These findings suggest a complicated picture in which NAAG and GABA are segregated in distinct neuronal populations in primary visual targets, yet they are colocalized in neurons of the thalamic reticular nucleus. This is consistent with NAAG acting as a neurotransmitter release modulator that is coreleased with a variety of classical transmitters in specific neural pathways.

Animals↗