Biomedical subjects

R P Gaykema

Publications and source records attributed to R P Gaykema.

At least 19 recordsLinked to original sources

PubMed2001

Intrathecal HIV-1 envelope glycoprotein gp120 induces enhanced pain states mediated by spinal cord proinflammatory cytokines.

Perispinal (intrathecal) injection of the human immunodeficiency virus-1 (HIV-1) envelope glycoprotein gp120 creates exaggerated pain states. Decreases in response thresholds to both heat stimuli (thermal hyperalgesia) and light tactile stimuli (mechanical allodynia) are rapidly induced after gp120 administration. gp120 is the portion of HIV-1 that binds to and activates microglia and astrocytes. These glial cells have been proposed to be key mediators of gp120-induced hyperalgesia and allodynia because these pain changes are blocked by drugs thought to affect glial function preferentially. The aim of the present series of studies was to determine whether gp120-induced pain changes involve proinflammatory cytokines [interleukin-1beta (IL-1) and tumor necrosis factor-alpha (TNF-alpha)], substances released from activated glia. IL-1 and TNF antagonists each prevented gp120-induced pain changes. Intrathecal gp120 produced time-dependent, site-specific increases in TNF and IL-1 protein release into lumbosacral CSF; parallel cytokine increases in lumbar dorsal spinal cord were also observed. Intrathecal administration of fluorocitrate (a glial metabolic inhibitor), TNF antagonist, and IL-1 antagonist each blocked gp120-induced increases in spinal IL-1 protein. These results support the concept that activated glia in dorsal spinal cord can create exaggerated pain states via the release of proinflammatory cytokines.

Animals↗

PubMed2001

Staphylococcal enterotoxin B induces fever, brain c-Fos expression, and serum corticosterone in rats.

The paraventricular nucleus of the hypothalamus (PVH) occupies a pivotal point within the network of brain nuclei coordinating critical host-defense responses. In mice, T cell-dependent immune stimuli, including the bacterial superantigen staphylococcal enterotoxin B (SEB), can activate the PVH. To determine whether T cell-dependent immune stimuli activate the PVH in rats, we assessed plasma corticosterone (Cort) levels, fever responses, and c-Fos expression in the PVH in animals treated with intraperitoneal injections of SEB. In animals with previously implanted abdominal thermisters, intraperitoneal injection of 1 mg/kg SEB resulted in a significant rise in body temperature, with a latency of 3.5-4 h. In separate animals, intraperitoneal injection of 1 mg/kg SEB resulted in a significant elevation of plasma Cort and induced c-Fos expression in parvocellular neurons within the PVH. These results support the idea that T cell-dependent immune stimuli activate brain pathways mediating host-defense responses such as fever and neuroendocrine changes.

Animals↗

PubMed2000

Vagal immune-to-brain communication: a visceral chemosensory pathway.

The immune system operates as a diffuse sensory system, detecting the presence of specific chemical constituents associated with dangerous micro-organisms, and then signalling the brain. In this way, immunosensation constitutes a chemosensory system. Several submodalities of this sensory system function as pathways conveying immune-related information, and can be classified as either primarily brain barrier associated or neural. The vagus nerve provides the major neural pathway identified to date. The initial chemosensory transduction events occur in immune cells, which respond to specific chemical components expressed by dangerous micro-organisms. These immune chemosensory cells release mediators, such as cytokines, to activate neural elements, including primary afferent neurons of the vagal sensory ganglia. Primary afferent activation initiates local reflexes (e.g. cardiovascular and gastrointestinal) that support host defense. In addition, at least three parallel pathways of ascending immune-related information activate specific components of the illness response. In this way, immunosensory systems represent highly organized and coherent pathways for activating host defense against infection.

Animals↗

PubMed2000

Subdiaphragmatic vagotomy blocks interleukin-1beta-induced fever but does not reduce IL-1beta levels in the circulation.

Peripheral interleukin-1beta has been implicated in the initiation of fever responses, yet the pathways by which it influences brain function are still unclear. Sectioning the abdominal vagus has been reported to inhibit fever after intraperitoneal administration of interleukin-1beta, suggesting that vagal afferents participate in signaling the brain to mount a fever response to interleukin-1beta. However, the inhibitory effect of subdiaphragmatic vagotomy could be due to alterations in pharmacokinetics such that the intraperitoneally injected cytokine does not reach the general circulation in sufficient quantities to activate the brain via blood-borne signaling. We measured both fever and plasma levels of interleukin-1beta in vagotomized and sham-operated rats after intraperitoneal administration of 1 microg/kg human recombinant interleukin-1beta to determine whether vagotomy reduces fever and levels of circulating interleukin-1beta after intraperitoneal injection. Plasma levels of human recombinant and endogenous rat interleukin-1beta were measured in separate enzyme-linked immunosorbent assays. While intraperitoneal administration of human recombinant interleukin-1beta elevated plasma levels of this cytokine similarly in vagotomized and sham-operated animals, only sham-operated rats responded with fever. Plasma levels of endogenous rat interleukin-1beta were unchanged by any treatment. These results demonstrate that the blockade of intraperitoneal interleukin-1beta-induced fever after subdiaphragmatic vagotomy cannot be accounted for by alterations of interleukin-1beta levels in the general circulation.

Animals↗

PubMed2000

Subdiaphragmatic vagotomy does not block intraperitoneal lipopolysaccharide-induced fever.

Several recent findings, including the inability of subdiaphragmatic vagotomy to block lipopolysaccharide (LPS)-induced interleukin-1beta (IL-1beta) protein in brain, have made it necessary to reexamine the role of the subdiaphragmatic vagal afferents in immune-to-brain communication. In this study, we examined the effects of intraperitoneal (i.p.) injections of LPS on core body temperature in control and subdiaphragmatically vagotomized rats. Vagotomized and sham-operated male Sprague-Dawley rats were injected i.p. with vehicle (pyrogen-free saline) on the control day and LPS (1, 10 or 50 microg/kg) on the experimental day, and core body temperature was monitored by telemetry for 6 h after the injection. At this time, rats were sacrificed, and serum, liver, and pituitary samples were collected. The i.p. injection of LPS increased core body temperature in both sham-operated and vagotomized rats compared to the saline injection. In addition, LPS significantly increased IL-1beta levels in serum, liver, and pituitary compared to saline-injected controls. There were no significant differences in the magnitude of the fever or in the levels of IL-1beta in serum, liver, or pituitary between sham-operated and vagotomized rats. Thus, the current data indicate that, at the doses tested, subdiaphragmatic vagal afferents are not crucial for i.p. LPS-induced fever. Because several effects of vagotomy have been shown to be dependent on dose, we are currently investigating whether vagal afferents are involved in lower-dose i.p. LPS-induced fever.

Animals↗

PubMed2000

Effects of vagotomy on lipopolysaccharide-induced brain interleukin-1beta protein in rats.

The production of interleukin-1beta (IL-1beta) in brain is thought to be a critical step in the induction of central manifestations of the acute phase response, and the vagus nerve has been implicated in immune-to-brain communication. Thus, this study examined the effects of intraperitoneal (i.p.) injections of lipopolysaccharide (LPS) on brain IL-1beta protein levels in control and subdiaphragmatically vagotomized rats. In the first experiment, vagotomized and sham-operated male Sprague-Dawley rats were injected i.p. with one of three doses (10, 50, 100 microg/kg) of LPS or vehicle (sterile, pyrogen-free saline) and sacrificed 2 h after the injection. In the second experiment, vagotomized and sham-operated rats were injected i.p. with 100 microg/kg LPS or vehicle and sacrificed 1 h after the injection. The i.p. injection of LPS dose-dependently increased IL-1beta protein levels in the hypothalamus, hippocampus, dorsal vagal complex, cerebellum, posterior cortex, and pituitary 2 h after the injection. Brain and pituitary IL-1beta levels were also significantly increased 1 h after the injection of 100 microg/kg LPS. There were no significant differences in brain IL-1beta levels between sham-operated and vagotomized rats at either the 2 h or 1 h time points. The current data are consistent with previous studies showing increases in brain IL-1beta after peripheral injections of LPS, and support the notion that brain IL-1beta is a mediator in the illness-induction pathway. Furthermore, these data indicate that, at the doses and times tested, subdiaphragmatic vagal afferents are not crucial for LPS-induced brain IL-1beta protein.

Animals↗

PubMed2000

Vagotomy does not inhibit high dose lipopolysaccharide-induced interleukin-1beta immunoreactivity in rat brain and pituitary gland.

In the present study, we examined whether the vagus nerve is involved in mediating lipopolysaccharide (LPS)-induced appearance of IL-1beta immunoreactive cells in the brain and pituitary gland. Rats were either sham-operated or subjected to subdiaphragmatic vagotomy. Four weeks later, pyrogen free saline or 400 microg/kg LPS was administered to the rats intraperitoneally. Four and 8 h later, the animals were intracardially perfused with 4% paraformaldehyde and tissues were prepared for IL-1beta immunocytochemistry. IL-1beta positive cells were observed at both time-intervals after LPS administration in the choroid plexus, meninges, circumventricular organs and pituitary gland of both sham-operated and vagotomized rats. We conclude that under the conditions studied, the vagus nerve does not mediate LPS-induced appearance of IL-1beta in the rat brain and pituitary gland.

Animals↗

PubMed2000

Effects of vagotomy on serum endotoxin, cytokines, and corticosterone after intraperitoneal lipopolysaccharide.

The vagus nerve appears to play a role in communicating cytokine signals to the central nervous system, but the exact extent of its involvement in cytokine-to-brain communication remains controversial. Recently, subdiaphragmatic vagotomy was shown to increase bacterial translocation across the gut barrier and thus may cause endotoxin tolerance. The current experiment tested whether or not vagotomized animals have similar systemic responses to endotoxin challenge as do sham-operated animals. Subdiaphragmatically vagotomized and sham-operated animals were injected intraperitoneally with one of three doses (10, 50, 100 microg/kg) of lipopolysaccharide (LPS) or vehicle, and blood samples were taken at 15, 30, 60, 90, and 120 min after the injection. The intraperitoneal injection of LPS increased circulating LPS levels at all time points examined. In addition, all three doses of LPS significantly increased serum interleukin (IL)-1beta, IL-6, and corticosterone in both control and vagotomized rats. In conclusion, vagotomy itself has no marked effect on circulating endotoxin levels or the production of IL-1beta, IL-6, or corticosterone in blood after an intraperitoneal injection of LPS.

Animals↗

PubMed1999

Interleukin-1beta in immune cells of the abdominal vagus nerve: a link between the immune and nervous systems?

Intraperitoneal administration of the cytokine interleukin-1beta (IL-1beta) induces brain-mediated sickness symptoms that can be blocked by subdiaphragmatic vagotomy. Intraperitoneal IL-1beta also induces expression of the activation marker c-fos in vagal primary afferent neurons, suggesting that IL-1beta is a key component of vagally mediated immune-to-brain communication. The cellular sources of IL-1beta activating the vagus are unknown, but may reside in either blood or in the vagus nerve itself. We assayed IL-1beta protein after intraperitoneal endotoxin [lipopolysaccharide (LPS)] injection in abdominal vagus nerve, using both an ELISA and immunohistochemistry, and in blood plasma using ELISA. IL-1beta levels in abdominal vagus nerve increased by 45 min after LPS administration and were robust by 60 min. Plasma IL-1beta levels increased by 60 min, whereas little IL-1beta was detected in cervical vagus or sciatic nerve. IL-1beta-immunoreactivity (IR) was expressed in dendritic cells and macrophages within connective tissues associated with the abdominal vagus by 45 min after intraperitoneal LPS injection. By 60 min, some immune cells located within the nerve and vagal paraganglia also expressed IL-1beta-IR. Thus, intraperitoneal LPS induced IL-1beta protein within the vagus in a time-frame consistent with signaling of immune activation. These results suggest a novel mechanism by which IL-1beta may serve as a molecular link between the immune system and vagus nerve, and thus the CNS.

Abdomen↗

PubMed1998

Interleukin-1 induces c-Fos immunoreactivity in primary afferent neurons of the vagus nerve.

Peripheral administration of bacterial endotoxin, an immune stimulant, induces evidence of activation in vagal primary afferent neurons. To determine whether interleukin-1beta (IL-1beta) is part of the molecular pathway leading to this activation, we assessed the expression of the neuronal activation marker c-Fos in vagal primary afferent neurons after intraperitoneal injections of IL-1beta (2 microg/kg). IL-1beta, but not vehicle, induced c-Fos expression, demonstrating that IL-1beta is likely an important signal from the immune system to the vagus nerve, and thus the brain.

Animals↗

PubMed1997

Subdiaphragmatic vagotomy does not prevent fever following intracerebroventricular prostaglandin E2: further evidence for the importance of vagal afferents in immune-to-brain communication.

Brain-mediated sickness responses can be blocked by subdiaphragmatic vagotomy, suggesting that vagal afferents signal peripheral inflammation or infection. This study tested whether subdiaphragmatic vagotomy disrupts sickness responses by interrupting effector pathways. If this explanation is correct, intracerebroventricular prostaglandin E2-induced fever should be blocked by this procedure. Fever was unaffected by subdiaphragmatic vagotomy, thus these data provide support for the conclusion that vagal afferents signal the brain during immune activation.

Animals↗

PubMed1997

Parvalbumin-containing neurons in the basal forebrain receive direct input from the substantia nigra-ventral tegmental area.

By means of anterograde tracing of Phaseolus vulgaris-leucoagglutinin (PHA-L) it was determined if parvalbumin-immunoreactive neurons in the basal forebrain receive a direct synaptic input from the A9-A10 dopaminergic nuclei of the substantia nigra and ventral tegmental area. Forebrain sections were processed for immunocytochemical detection of PHA-L and parvalbumin (PV) at light and electron microscopic levels. At the ultrastructural level, PHA-L-labeled terminals were found to establish synaptic contacts with PV-immunoreactive neuronal somata in the ventromedial globus pallidus, the ventral pallidum, the internal capsule, and the substantia innominata. PV-containing neurons in pallidal and adjacent basal forebrain territories are thus directly targeted by presumably A9-A10 dopaminergic neurons and represent a novel aspect of midbrain dopaminergic control of basal forebrain neuronal activity.

Animals↗

PubMed1997

Cortical input to the basal forebrain.

The arborization pattern and postsynaptic targets of corticofugal axons in basal forebrain areas have been studied by the combination of anatomical tract-tracing and pre- and postembedding immunocytochemistry. The anterograde neuronal tracer Phaseolus vulgaris leucoagglutinin was iontophoretically delivered into different neocortical (frontal, parietal, occipital), allocortical (piriform) and mesocortical (insular, prefrontal) areas in rats. To identify the transmitter phenotype in pre- or postsynaptic elements, the tracer staining was combined with immunolabeling for either glutamate or GABA, or with immunolabeling for choline acetyltransferase or parvalbumin. Tracer injections into medial and ventral prefrontal areas gave rise to dense terminal arborizations in extended basal forebrain areas, particularly in the horizontal limb of the diagonal band and the region ventral to it. Terminals were also found to a lesser extent in the ventral part of the substantia innominata and in ventral pallidal areas adjoining ventral striatal territories. Similarly, labeled fibers from the piriform and insular cortices were found to reach lateral and ventral parts of the substantia innominata, where terminal varicosities were evident. In contrast, descending fibers from neocortical areas were smooth, devoid of terminal varicosities, and restricted to the myelinated fascicles of the internal capsule en route to more caudal targets. Ultrastructural studies obtained indicated that corticofugal axon terminals in the basal forebrain areas form synaptic contact primarily with dendritic spines or small dendritic branches (89%); the remaining axon terminals established synapses with dendritic shafts. All tracer labeled axon terminals were immunonegative for GABA, and in the cases investigated, were found to contain glutamate immunoreactivity. In material stained for the anterograde tracer and choline acetyltransferase, a total of 63 Phaseolus vulgaris leucoagglutinin varicosities closely associated with cholinergic profiles were selected for electron microscopic analysis. From this material, 37 varicosities were identified as establishing asymmetric synaptic contacts with neurons that were immunonegative for choline acetyltransferase, including spines and small dendrites (87%) or dendritic shafts (13%). Unequivocal evidence for synaptic interactions between tracer labeled terminals and cholinergic profiles could not be obtained in the remaining cases. From material stained for the anterograde tracer and parvalbumin, 40% of the labeled terminals investigated were found to establish synapses with parvalbumin-positive elements; these contacts were on dendritic shafts and were of the asymmetrical type. The present data suggest that corticofugal axons innervate forebrain neurons that are primarily inhibitory and non-cholinergic; local forebrain axonal arborizations of these cells may represent a mechanism by which prefrontal cortical areas control basal forebrain cholinergic neurons outside the traditional boundaries of pallidal areas.

Animals↗

PubMed1996

Direct catecholaminergic-cholinergic interactions in the basal forebrain. II. Substantia nigra-ventral tegmental area projections to cholinergic neurons.

Previous observations indicate that the basal forebrain receives dopaminergic input from the ventral midbrain. The present study aimed at determining the topographic organization of these projections in the rat, and whether this input directly terminates on cholinergic neurons. Injections of the anterograde tracer Phaseolus vulgaris-leucoagglutinin (PHA-L) into discrete parts of the ventral tegmental area (VTA) and the substantia nigra pars compacta (SNC) labeled axons and terminals in distinct parts of the basal forebrain, including medial and lateral septum, diagnoal band nuclei, ventral pallidum, globus pallidus, substantia innominata, globus pallidus, and internal capsule, where PHA-L-labeled terminals abutted cholinergic (choline acetyltransferase = ChAT-containing) profiles. Three-dimensional (3-D) computerized reconstruction of immunostained sections clearly revealed distinct, albeit overlapping, subpopulations of ChAT-immunoreactive neurons apposed by PHA-L-labeled input from medial VTA (mainly in vertical and horizontal diagonal band nuclei), lateral VTA and medial SNC (ventral pallidum and anterior half of substantia innominata), and lateral SNC (caudal half of the substantia innominata and globus pallidus). At the ultrastructural level, about 40% of the selected PHA-L-labeled presynaptic terminals in the ventral pallidum and substantia innominata were found to establish synaptic specializations with ChAT-containing profiles, most of which on the cell body and proximal dendritic shafts. Convergent synaptic input of unlabeled terminals that formed asymmetric synapses with the ChAT-immunoreactive profiles were often found in close proximity to the PHA-L-labeled terminals. These observations show that the cholinergic neurons in the basal forebrain are targets of presumably dopaminergic SNC/VTA neurons, and suggest a direct modulatory role of dopamine in acetylcholine release in the cerebral cortical mantle.

Animals↗

PubMed1995

Subdiaphragmatic vagotomy suppresses endotoxin-induced activation of hypothalamic corticotropin-releasing hormone neurons and ACTH secretion.

In order to assess the possibility that endotoxin-induced activation of the hypothalamus-pituitary-adrenal (HPA) axis is mediated by vagal afferents, we studied the effects of transection of the vagal nerves on endotoxin-induced Fos expression in hypothalamic corticotropin-releasing hormone (CRH) neurons and plasma ACTH and corticosterone responses. Groups of rats were subjected to sham surgery, complete subdiaphragmatic vagotomy (SVGX), or selective transection of the hepatic branch (HVGX). Two weeks after surgery, endotoxin or saline was injected i.p. and rats were sacrificed by decapitation two hours later. SVGX blocked or attenuated the ACTH response to 20 and 250 micrograms/kg endotoxin, respectively. HVGX did not suppress the ACTH response to either endotoxin dose. In addition, corticosterone responses were not affected by SVGX or HVGX. The endotoxin-induced Fos expression in CRH neurons was suppressed in SVGX, but not in HVGX animals. These observations lead us to postulate that the CRH and ACTH responses to a low dose of endotoxin are mediated by vagal afferents. The responses to a high dose of endotoxin involve additional neuronal or humoral pathways.

Adrenocorticotropic Hormone↗

PubMed1991

Prefrontal cortical projections to the cholinergic neurons in the basal forebrain.

The prefrontal cortex (PFC) projections to the basal forebrain cholinergic cell groups in the medial septum (MS), vertical and horizontal limbs of the diagonal band of Broca (VDB and HDB), and the magnocellular basal nucleus (MBN) in the rat were investigated by anterograde transport of Phaseolus vulgaris leuco-agglutinin (PHA-L) combined with acetylcholinesterase (AChE) histochemistry or choline acetyltransferase (ChAT) immunocytochemistry. The experiments revealed rich PHA-L-labeled projections to discrete parts of the basal forebrain cholinergic system (BFChS) essentially originating from all prefrontal areas investigated. The PFC afferents to the BFChS display a topographic organization, such that medial prefrontal areas project to the MS, VDB, and the medial part of the HDB, whereas the orbital and agranular insular areas predominantly innervate the HDB and MBN, respectively. Since the recurrent BFChS projection to the prefrontal cortex is arranged according to a similar topography, the relationship between the BFChS and the prefrontal cortex is characterized by reciprocal connections. Furthermore, tracer injections in the PFC resulted in anterograde labeling of numerous "en passant" and terminal boutons apposing perikarya and proximal dendrites of neurons in the basal forebrain, which were stained for the cholinergic marker enzymes. These results indicate that prefrontal cortical afferents make direct synaptic contacts upon the cholinergic neurons in the basal forebrain, although further analysis at the electron microscopic level will be needed to provide conclusive evidence.

Acetylcholine↗

PubMed1991

Patterns of direct projections from the hippocampus to the medial septum-diagonal band complex: anterograde tracing with Phaseolus vulgaris leucoagglutinin combined with immunohistochemistry of choline acetyltransferase.

The projections from the Ammon's horn to the cholinergic cell groups in the medial septal and diagonal band nuclei were investigated with anterograde tracing of Phaseolus vulgaris leucoagglutinin combined with immunocytochemical detection of choline acetyltransferase, in the rat. Tracer injections were placed into various fields of the septal and temporal parts of the Ammon's horn (CA1-3). These injections revealed differential distributions of Phaseolus vulgaris leucoagglutinin-labeled projections in both the lateral septal area and the medial septum-diagonal band complex. In addition to the labeling of dense axonal networks in the lateral septal area, significant numbers of arborizing fibers were labeled in the medial septal and diagonal band nuclei, in particular after tracer injections into the fields CA2-3. The distributions of the projections to the medial septum-diagonal band complex arising from the septal portion of fields CA1 and CA2-3 are similar. In contrast, the septal part and temporal portion of field CA3 project in a topographically differentiated manner to the medial septum and nuclei of the diagonal band. The septal pole of the Ammon's horn innervates the dorsal and medial parts of the medial septal nucleus and the anterior and dorsal parts of the vertical limb of the diagonal band. Axons of the temporal pole of the hippocampus reach the lateral and ventral parts of the medial septum and the intermediate, caudal and ventral parts of the vertical limb of the diagonal band. These results demonstrate direct feedback projections of the Ammon's horn to the medial septum-diagonal band complex, which show a topographic organization mainly as a function of the septotemporal level of the hippocampus. Within the medial septal and diagonal band nuclei, the labeled varicosities are formed in close proximity to the cell bodies and dendrites of the cholinergic neurons.

Animals↗

PubMed1991

The basal forebrain cholinergic system: efferent and afferent connectivity and long-term effects of lesions.

The first part of this article deals with several aspects of efferents and afferents of the rat basal forebrain cholinergic system (BFChS) studied with anterograde transport of Phaseolus vulgaris leucoagglutinin (PHA-L). PHA-L tracing of the BFChS efferents revealed topographically differentiated axonal trajectories and patterns of presynaptic endings to the neocortex, mesocortex, olfactory nuclei and hippocampus. Combining this method with second immunolabeling, we identified the muscarinic cholinoceptive neurons in the neocortex and the somatostatinergic neurons in the hippocampus as being directly innervated by the magnocellular basal nucleus and the medial septum, respectively. The prefrontal cortex was identified as a source of afferent input to the basal forebrain cholinergic neurons. This projection also exhibits a topographic organization, which shows a reciprocal relationship with the BFChS efferents to the cortex. The second part of this article describes the anatomical changes of cortical cholinergic and some other neurotransmitter systems after long-term cholinergic denervation in the aged rat cortex. The spared cholinergic projection in the largely denervated areas shows abundant malformations, which are similar in appearance to the anatomical alterations of the surviving cholinergic fibers in dementia of the Alzheimer type (AD). Hypertrophic changes also occur in the serotonergic system. The neuropeptide-Y- and somatostatin-containing cortical systems respond with an increment of their axonal densities, in contrast to the decline of these peptides in AD. Although transsynaptic effects are mediated by long-term cholinergic lesions, they do not support the hypothesis that the cholinergic deficiency is a primary event in the pathophysiology of AD.

Afferent Pathways↗