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Biomedical subjects

L Kruger

Publications and source records attributed to L Kruger.

At least 19 recordsLinked to original sources
PubMed2006

Characterization of [125I]ZM 241385 binding to adenosine A2A receptors in the pineal of sheep brain.

Adenosine is a ubiquitous neuromodulator and homeostatic regulator that exerts its physiologic actions through activation of A(1), A(2A), A(2B) and A(3) adenosine receptor subtypes. In the central nervous system, adenosine's action in neurons is manifested in its modulation of tonic inhibitory control. Adenosine released in the brain during hypoxia has critical depressant effects on breathing in fetal and newborn mammals, an action suggested to be mediated by A(2A) receptors in the posteromedial thalamus. In an effort to more accurately define the spatial distribution of adenosine A(2A) receptors in fetal sheep diencephalon, we have used a receptor autoradiographic technique utilizing an iodinated radioligand [(125)I]ZM 241385, which has greater sensitivity and resolution than the tritiated compound. The distribution of ligand binding sites in the fetal sheep diencephalon indicated that the highest levels of binding were in select thalamic nuclei, including those implicated in hypoxic depression of fetal breathing, and the pineal. Given the high density of labeled A(2A) receptors in the pineal, these sites were characterized more fully in homogenate radioligand binding assays. These data indicate that [(125)I]ZM 241385 binding sites display a pharmacological signature consistent with that of adenosine A(2A) receptors and are expressed at similar levels in fetal, lamb and adult ovine brain. The adenosine A(2A) receptor pharmacologic signature of the [(125)I]ZM 241385 binding site in pineal cell membranes generalized to the site characterized in membranes derived from other portions of the lamb thalamus, including the sector involved in hypoxic inhibition of fetal breathing. These results have important implications for the functional roles of adenosine A(2A) receptors in the thalamus and pineal of sheep brain.

Adenosine↗
PubMed2000

Inflammation-induced changes in primary afferent-evoked release of substance P within trigeminal ganglia in vivo.

Substance P (SP) is synthesized in a subset of nociceptive sensory neurons and is released from their peripheral and central terminals. Here we demonstrate with the use of in vivo microdialysis and radioimmunoassay techniques that SP is also released within trigeminal ganglia following intraganglionic application of KCl, veratridine or capsaicin, and after electrical stimulation of peripheral afferent fibers. Both the basal and KCl-evoked release of SP are shown to be dependent on extracellular calcium. Using the turpentine-induced model of unilateral orofacial inflammation we also show that both the basal and KCl-evoked release of SP within trigeminal ganglia are greatly increased on the inflamed side 48 h after induction of inflammation. Coupled with previous demonstrations of excitatory effects of SP on sensory neurons, these results suggest that SP fulfils the role of a non-synaptically released diffusible chemical messenger that may modulate the somatic excitability of neurons within sensory ganglia in inflammatory pain states.

Animals↗
PubMed2000

Thalamic lesions dissociate breathing inhibition by hypoxia and adenosine in fetal sheep.

The effects of diencephalic lesions on respiratory responses to intra-arterially infused adenosine (ADO) were determined in chronically catheterized fetal sheep (>0.8 term). These studies were designed to test the hypothesis that the inhibitory effects of ADO on fetal breathing, like those of hypoxia, are mediated by the parafascicular nuclear complex (Pf) of the posteromedial thalamus. ADO inhibited breathing [control (C): 26 +/- 2.6, ADO: 4 +/- 1 min/h] in normal fetuses and in a fetus with a lesion that virtually destroyed the thalamus but left intact most of Pf. Neuronal lesions in the diencephalon, produced by injecting ibotenic acid, abolished the inhibitory effects of ADO on breathing (C: 31 +/- 5.1, ADO: 30 +/- 4.5 min/h) when the lesions encompassed Pf or the sector immediately rostral to Pf that retained the capacity to regulate hypoxic inhibition. Smaller lesions created by the insertion of needles also eliminated the depressant effects of ADO when disruptions were within Pf or a rostral component of the thalamic cortical activating system. It is concluded that 1) a medial thalamic sector is critically involved in ADO-induced apnea and 2) ADO-dependent and ADO-independent mechanisms mediate hypoxic inhibition.

Adenosine↗
PubMed1999

Foreign body in the medial pterygoid space.

Retained intra-oral foreign bodies have been reported rarely in the literature. A case of a foreign body retained for an extended period of time in the medial pterygoid space is reported here.

Adult↗
PubMed1998

Thalamic locus mediates hypoxic inhibition of breathing in fetal sheep.

The effects of lesions rostral to the brain stem on breathing responses to hypoxia were determined in chronically catheterized fetal sheep (>0.8 term). These studies were designed to test the hypothesis that the diencephalon is involved in hypoxic inhibition of fetal breathing. As in normal fetuses, hypoxia inhibited breathing with transection rostral to the thalamus or transection resulting in virtual destruction of the thalamus but sparing most of the parafascicular nuclear complex. Neuronal lesions were produced in the fetal diencephalon by injecting ibotenic acid through cannulas implanted in the brain. Hypoxic inhibition of breathing was abolished when the lesions encompassed the parafascicular nuclear complex but was retained when the lesions spared the parafascicular nuclear region or when the vehicle alone was injected. A new locus has been identified immediately rostral to the midbrain, which is crucial to hypoxic inhibition of fetal breathing. This thalamic sector involves the parafascicular nuclear complex and may link central O2-sensing cells to motoneurons that inhibit breathing.

Animals↗
PubMed1997

Source of extracellular brain adenosine during hypoxia in fetal sheep.

Microdialysis was performed to determine whether hypoxia increases fetal brain adenosine (ADO) concentration through dephosphorylation of extracellular 5'-adenosine monophosphate (5-AMP). Hypoxia (fetal PaO2 approximately 14 Torr) increased fetal brain ADO levels approximately two-fold when the probes were perfused with synthetic cerebrospinal fluid (CSF) containing inhibitors of the nucleoside transporter but not with this solution plus a blocker of ecto-5'-nucleotidase (AOPCP). The hypoxia-induced rise in fetal brain ADO concentrations depends critically upon the hydrolysis of extracellular 5'-AMP.

Adenosine Diphosphate↗
PubMed1997

GAP-43 mRNA and calcitonin gene-related peptide mRNA expression in sensory neurons are increased following sympathectomy.

Sympathectomy has been shown to result in an increased density of fibers immunoreactive for sensory peptides in peripheral targets innervated by both sensory and sympathetic neurons, providing evidence for functional interactions between sympathetic and sensory systems. These findings provided the background for examining the hypothesis that axonal outgrowth is induced from sensory neurons following sympathectomy. We examined the expression of GAP-43 mRNA, a specific marker for axonal outgrowth, in cervical (C3, C7, C8) and thoracic (T1, T2) dorsal root ganglia (DRG) of the rat following bilateral removal of the superior cervical ganglion, to assess whether the described increases in peptidergic afferent fibers reflected axonal outgrowth. In situ hybridization was used with 35S labeled riboprobes complementary to GAP-43 mRNA, and to calcitonin gene-related peptide (CGRP) mRNA, a marker for a major subset of thin-fiber sensory neurons. The density of GAP-43 mRNA nearly doubled by 18 h following sympathectomy and reached a threefold increase by 3 days. By 45 days following surgery, the GAP-43 mRNA level was still nearly twice that of normal animals, CGRP immunoreactivity was also examined: the density of fibers in the iris and cornea of sympathectomized animals was considerably greater from two weeks to 45 days following surgery, than in sham-operated controls. Concomitantly, there was a slight but significant increase in CGRP mRNA expression in T1 and C3 DRG 14 days postsympathectomy. Quantitative computerized image analysis demonstrated that GAP 43 mRNA expression in sympathectomized animals was 1.5 times greater in medium-sized DRG neurons and almost fourfold greater in small DRG neurons than in control rats. These results indicate that sympathetic denervation elicits axonal outgrowth in the population of sensory neurons that give rise to the small unmyelinated and thinly myelinated axons of peripheral nerves.

Animals↗
PubMed1997

Warm-sensitive afferent splanchnic C-fiber units in vitro.

Receptive fields of 41 slowly conducting sensory fibers were located using a thermal (warm) search stimulus in an in vitro splanchnic nerve-mesentery preparation. Warm-sensitive receptive fields were punctate and were densest in the region surrounding the prevertebral ganglia, an area with prominent deposits of brown adipose tissue, where the abdominal aorta branches into the major trunks supplying the abdominal viscera. Impulse activity was recorded while applying a warm stimulus to identified receptive fields (RFs). The warm stimulus consisted of a warming ramp (10-15 degrees C in 1-2 s to a 42-49 degrees C peak temperature) followed by a 10- to 30-s period during which the RF was maintained at this peak temperature (plateau phase). Eighty percent (33/41) of warm-sensitive units responded to warming with discharge comprising both a phasic and a tonic component (slowly adapting warm-sensitive, or SA-W, units). The remainder (8/41) responded with only phasic discharge (rapidly adapting warm-sensitive, or RA-W, units). Units' adaptation characteristics were consistent from trial to trial and when applying stimuli from different positions. Fifty percent of SA-W units (8/16) and 17% of RA-W units (1/6) were activated by transient exposure to 9-90 nM bradykinin (BK). Twenty-seven percent (9/33) of SA-W units and 12% (1/8) of RA-W units were activated by probing their RF with von Frey hairs with bending forces < 10 mN (approximately 1 g equivalent mass). An additional five SA-W units tested were activated by strong mechanical stimuli (compression with a metal probe or firm stretching). No BK-responsive warm-sensitive units were activated by von Frey probing < 10 mN, but two (both SA-W) responded to strong mechanical stimuli. In six SA-W units and one RA-W unit, the number of impulses evoked by warming approximately 5 min after exposure to BK was > 2 SD greater than the mean pre-BK response, indicating sensitization. This sensitization was transient, the response to warming returning to within one standard deviation of the pretrial mean or less over the course of the next 5-10 min. Changes in background activity, mechanical sensitivity, BK sensitivity, and BK-induced sensitization were noted in various splanchnic units over the course of prolonged observations, suggesting that these indices may not reliably distinguish unit type, but instead may indicate the functional state of the sense organ. Splanchnic neurons responsive to the intense warming used in the present in vitro experiments may participate in the cardiovascular responses observed in vivo in heat-stressed rats. The dense distribution of warm-receptive fields in the vicinity of the celiac-superior mesenteric ganglionic complex is consistent with the localization of splanchnic thermosensitive units previously noted in vivo in the rabbit.

Adipose Tissue, Brown↗
PubMed1996

H2O2 sensitivity of afferent splanchnic C fiber units in vitro.

1. Single-unit impulse activity evoked by transient, focal application of hydrogen peroxide (H2O2) to identified visceral receptive fields has been characterized in an in vitro rat splanchnic nerve-mesentery preparation. In addition to H2O2 responsiveness, units were characterized in terms of sensitivity to mechanical stimuli, warming, and bradykinin. 2. Mesenteric receptive fields of single splanchnic afferent C fibers in vitro were located with the use of warm (approximately 45 degrees C saline) or mechanical search stimuli. After delimitation of the warm-sensitive and/or mechanosensitive receptive field, units were tested for responsiveness to transient, focal application of H2O2. Microliter volumes (usually 1 microliter) of H2O2 (88-880 mM) evoked responses in 25 of 42 (60%) units with identified warm-sensitive and/or mechanosensitive receptive fields, and in an additional 10 units for which H2O2 was the only effective stimulus. 3. Tachyphylaxis to repeated H2O2 stimulation was observed with interstimulus intervals <30 min, but did not indicate irreversible inactivation of the terminal, because 1) during this period warm and mechanical stimuli elicited responses equal to or greater than those before H2O2 treatment, and 2) H2O2 sensitivity was restored after units were allowed to recover. 4. Eight units unresponsive to an initial dose of H2O2 responded vigorously to a repeated application at the same site, suggesting a potentiating effect of prior H2O2 exposure. 5. Sixty-two percent (8 of 13) of H2O2-responsive units, but no (0 of 6) H2O2-unresponsive units responded to transient, focal bradykinin (9-90 nM) application. 6. An indirect mode of H2O2-evoked afferent excitation in some units was suggested by several observations, including the prolonged (up to 8 min) duration of the response of some units to transient H2O2 application, and the occasionally long (>2 min) response latencies to focal application of H2O2 to defined receptive fields. 7. Excitation of splanchnic neurons by H2O2 may be relevant to the modulation of reactive oxygen species production by immunocompetent cells, because sensory neuropeptides contained in these afferent fibers are known to influence the respiratory burst of macrophages and neutrophils.

Animals↗
PubMed1994

Evidence for uptake of vital dye by activated rat peritoneal mast cells: an in vitro imaging study.

Uptake of material from surrounding medium by activated rat peritoneal mast cells (PMCs) was studied using in vitro peritoneal eluate cells, the vital fluorescent dye sulforhodamine B (SFRM-B), secretagogue compound 48/80, and an imaging technique. PMCs, which undergo different states of degranulation, are shown to possess the ability to take up (by endocytosis) SFRM-B in an activity-dependent manner. The endocytosed dye is incorporated in the granules and can be discharged into the medium when the cells are reactivated. Both the uptake and the discharge processes are calcium-dependent. The reactivity of mast cells to secretagogue is not altered by the application of the dye. SFRM-B, a negatively charged, nonspecific protein stain, displays greater photostability and less leakage than the positively charged acridine orange, and its fluorescence persists for hours, whereas acridine orange fluorescence fades within 1 min when exposed to ultraviolet illumination. The fluorescent image of the dye-loaded mast cells can be preserved overnight in a container at room temperature. SFRM-B elicits no detectable damaging influence on the activated afferent discharge of splanchnic afferent nerve fibers with mesenteric terminals. This enables the use of SFRM-B for studying the interactions between mesenteric afferent terminals and their surrounding mast cells.

Afferent Pathways↗
PubMed1994

Some sensory neurons express neuropeptide Y receptors: potential paracrine inhibition of primary afferent nociceptors following peripheral nerve injury.

Neuropeptide Y (NPY) has been suggested to exert antinociceptive actions by inhibiting the release of neurotransmitters from trigeminal and dorsal root ganglia (DRG) neurons, but the site of direct NPY action in vivo and the NPY receptor subtype mediating these effects are unknown. 125I-peptide YY (PYY) was used to localize and characterize NPY receptor binding sites in trigeminal ganglia, DRG, and spinal cord of the rat, rabbit, and monkey. In the rat, rabbit, and monkey, 5-20% of trigeminal ganglia and DRG neurons express NPY binding sites. Unilateral cuff-induced neuropathy or transection of the rat sciatic nerve did not significantly alter the density or number of DRG neurons expressing NPY receptors. A unimodal size distribution for L4 and L5 DRG neurons expressing NPY binding sites in the rat was determined, with a mean cross-sectional area of 947 microns 2. In the spinal cord the highest concentration of NPY receptors is found in laminae I, II, V, X, and Onuf's nucleus. Pharmacological experiments using selective Y1 and Y2 receptor antagonists suggest that Y2 is the prominent NPY receptor subtype expressed in trigeminal ganglia neurons, DRG neurons, and spinal cord. Previous studies have demonstrated that a population of large-diameter, presumably myelinated primary afferents express NPY after peripheral nerve injury. NPY released from these injured large-diameter DRG neurons may act in a paracrine fashion to block the transmission of nociceptive information from the small- and medium-diameter DRG neurons that constitutively express NPY receptors. NPY receptors are therefore uniquely positioned to inhibit primary afferent nociceptors directly, especially after peripheral nerve injury.

Animals↗
PubMed1993

Distribution of GAP-43 mRNA in the adult rat brain.

Regional distribution of gene expression of the axonal growth-associated protein, GAP-43, was studied in adult rat brains by in situ hybridization autoradiography to determine the features of mature neuronal populations that synthesize GAP-43 protein. Such synthesis appears to correlate with axonal growth during maturation and regrowth after axotomy. In most adult neurons, the sharp decline in GAP-43 gene expression implies a reduced capacity for axonal growth. Neurons capable of extending axonal knobs in the absence of injury may indicate a "plasticity" underlying dynamic processes of interaction between neurons and their synaptic targets. Antisense and sense (control) riboprobes were used on serial sections in the three principal axes, and the magnitude of hybridization signal was examined to determine regional patterns. GAP-43 mRNA levels are pronounced in diverse neuronal groups including the locus coeruleus, raphé nn., dopaminergic nigral and ventral tegmental nn., mitral cells, hippocampal CA3, inferior olivary n., vagal motor n. and other parasympathetic preganglionic neurons, select thalamic midline and intralaminar nn., several specific nn. of the hypothalamus and basal forebrain, the granular layer of cerebellar cortex, the infragranular neocortex, and the granular olfactory paleocortex; there is a substantial range in the magnitude of expression. Regions revealing minimal signal include most thalamic sensory relay nuclei, the granule neurons of the olfactory bulb and dentate gyrus, and the caudate and putamen. Possible concomitants of GAP-43 expression include regulation of ion flux and neurotransmitter release. Those neurons with long, extensively dispersed and numerous synaptic connections display the strongest signals and may possess the greatest propensity for continuous growth and turnover of their axon terminals, in contrast to short-axon and specific projection neurons exhibiting minimal levels. These data may enable inferring which populations display normal or experimentally induced axonal growth.

Animals↗
PubMed1992

Fine structural organization of the ependymal region of the paraventricular nucleus of the rat thalamus and its relation with projection neurons.

The ependymal lining of the diencephalic third ventricle is known to exhibit significant variation in zonal architecture and the relations of neurites to the ventricular surface in different regions remains obscure. The present study explores the fine structural organization of the ependymal region of the thalamic paraventricular nucleus. Methodology was developed for tracing neurites of cells retrogradely labelled with horseradish peroxidase based on our recent observation that paraventricular neurons projecting to the amygdaloid complex cluster near the ventricle and emit numerous dendrites extending toward the ependymal surface. A relatively uniform population of cuboidal 'pale' ependymocytes dominates the ventricular lining of the thalamic paraventricular nucleus, although a few 'dark' ependymocytes are interspersed. The subependymal region displays a variety of glial elements. Dendrites of thalamic paraventricular projection neurons terminate in proximity to the ependymal layer from which they are generally separated by thin cytoplasmic processes of putative astrocytes, and few indent the basal portion of ependymal cells. Thin 'terminal' (i.e., serially traced) horseradish peroxidase-labelled dendrites filled with lipid and lysosome-like dense bodies were often enveloped by astrocyte membrane whorls. This feature may constitute a reactive glial response in horseradish peroxidase-labelled dendritic terminals. A distinctive arrangement of tortuous astrocyte leaflets was insinuated between the basal portion of ependymocytes in a zone exhibiting numerous caveolae, apparently isolating neurites from direct contact with the cerebrospinal fluid. These findings indicate that the ependymal region of the thalamic paraventricular nucleus is not characterized by those features of the basal third ventricle suspected to confer neuroendocrine interaction between neurons and cerebrospinal fluid. The structural arrangement between ependymocytes and thalamic paraventricular projection cells indicate a specialized relation of these neurons with the ependymal interface, but apparently not directly with the overlying cerebrospinal fluid.

Animals↗
PubMed1992

Sources of anterior gastric vagal efferent discharge in rats: an electrophysiological study.

The source of vagal efferent discharge (VED) in the anterior branch of the gastric vagus was investigated in urethane-chloralose anesthetized rats using successive and selective vagal cuts. After cutting the right cervical vagus, the basal VEDs were increased in 15 out of 21 cases by 4-53% (median 18%). After both cervical vagi were cut, VEDs were reduced by 10-95% (median 90%) in 14 of 17 experiments and a subcervical basal VED was observed in all rats. Additional cut of the distal end of the anterior gastric branch did not induce a consistent effect. A small segment of subdiaphragmatic anterior gastric vagus (4-5 mm) was further isolated by a fourth cut at the proximal end of the anterior gastric vagus; abolition of the subcervical VED occurred in only 4 of 14 successful cuts whereas in the other 10 experiments, the VED was reduced by 38-94% (median 87%). Histological examination revealed the presence of neurons in a paraganglion lying within the isolated nerve segment. These findings indicate that the stomach not only receives VED descending directly from medullary vagal motor neurons (about 90%), but also (approximately 10%) from neural elements located between subcervical to upper abdomen levels (the 'subcervical VED') and/or between the bifurcation of the accessory celiac branch to the gastro-esophageal junction (the 'residual VED'). In rats there is little crossed gastric vagal innervation, in agreement with anatomical observations, although there is a robust inhibitory influence from contralateral vagal afferents on medullary vagal motor neurons.

Animals↗