PubMed Health⌕ Search

Biomedical subjects

R C Ritter

Publications and source records attributed to R C Ritter.

At least 55 records · Page 3Linked to original sources
PubMed1997

Nuclear Fos immunoreactivity in guinea pig myenteric neurons following activation of motor activity.

To identify enteric neurons activated during intestinal motor activity, we examined myenteric plexus of guinea pig small intestinal segments for expression of the immediate early gene product, Fos. Fos immunoreactivity was detected immunohistochemically following in vitro manipulations, which included distension, electrical stimulation, exposure to forskolin, and peristalsis. All of these manipulations induced neuronal Fos expression, which was prevented by tetrodotoxin, indicating that expression depended on nerve activity. Distension-induced Fos expression was blocked by omega-conotoxin and significantly reduced by hexamethonium, indicating that neurons expressing Fos immunoreactivity were activated synaptically. Blocking smooth muscle contraction with nicardipine reduced expression of neuronal Fos, suggesting that muscle tone influences neuronal activity. Calbindin-immunoreactive putative sensory neurons did not express Fos during distension, peristalsis, or exposure to forskolin and expressed Fos only weakly after strong electrical stimulation. Conversely, calretinin-immunoreactive ascending excitatory interneurons and longitudinal muscle motoneurons exhibited Fos immunoreactivity after all experimental manipulations. These results indicate that Fos expression can, with some caution, be used to identify classes of enteric neurons activated by different stimuli under various experimental conditions.

Animals↗
PubMed1997

Practice analysis survey: revalidation of advanced clinical practice in orthopaedic physical therapy.

The first orthopaedic physical therapy practice analysis survey was completed in 1983. Another practice analysis survey was conducted in 1993 to identify the advance practice of clinicians who practice in orthopaedic physical therapy settings. Since 10 years elapsed, a new practice analysis study was conducted to identify the practice of orthopaedic clinical specialists. The purpose of this report is to describe the results of this survey. Orthopaedic physical therapists, both specialists and nonspecialists, participated in group interviews, subject matter expert meetings, and a national practice survey to delineate important knowledges and responsibilities. The survey was.sent to a stratified convenience sample of 1,000 orthopaedic physical therapists, of which 325 were orthopaedic clinical specialists. The three-part survey contained 180 items. A total of 420 respondents, of which 241 were orthopaedic clinical specialists, rated the importance and application level for the items. The results of this study provide evidence for a core body of knowledge required by clinicians practicing with advanced skills in orthopaedic physical therapy and create the framework for the Orthopaedic Physical Therapy Specialty Exam.

Clinical Competence↗
PubMed1996

Type A CCK receptors mediate satiety effects of intestinal nutrients.

Previous work indicates that endogenous CCK mediates suppression of sham feeding by some intraintestinal nutrients. To test whether the mechanism involved is dependent upon action at type A or type B CCK receptors, we examined the ability of CCKA (devazepide) and CCKB (L-365,260) receptor antagonists to attenuate the suppression of sham feeding by intraintestinal oleic acid, maltotriose, or L-phenylalanine. Suppression by oleic acid or maltotriose was dose dependently attenuated by intraperitoneal administration of the CCKA receptor antagonist, as was suppression by exogenous CCK. The CCKB receptor antagonist failed to attenuate the suppression of sham feeding by these nutrients. Neither receptor antagonist attenuated the suppression of sham feeding induced by intraintestinal L-phenylalanine. These results suggest that suppression of sham feeding by intestinally infused oleic acid and maltotriose is mediated by endogenous CCK acting at CCKA receptors.

Animals↗
PubMed1996

Predictors of caregiver health strain.

Home care nurses work with family caregivers daily. Measuring the strain involved in the role of adult children as caregivers for their elderly family members at home is the basis of this study. Results identify the decline in health reported by caregivers and give the home healthcare nurse guidance in developing interventions for the important population.

Adult↗
PubMed1996

Magnetic neurosurgery.

Because of the complex shape of many brain structures, the ideal brain probe would be highly flexible and give the neurosurgeon the ability to independently and precisely control movement of the probe tip. A magnetic surgery system has been developed that implements this concept. Flexible brain probes with small permanent magnetic tips are placed on the brain surface through a small burr hole and then magnetically manipulated within the brain. Drive forces are produced by an array of six superconducting magnets suspended within a cryostatic helmet. They produce a maximum force of 3 times the threshold needed to move the probe through the parenchymal tissues at its normal speed of 1 mm/s. Computer-controlled magnetic impulses precisely direct the probe movement in any direction desired with movement accuracy of 0.47 mm in phantom gels. Probe position is monitored 3 times per second with orthogonally oriented microchannel plate X-ray systems, X-ray dose from a 3-hour simulated procedure is comparable to that of a chest X-ray. In vivo and in vitro feasibility studies have been carried out in dog and pig brains. Preclinical trials are planned for clinical applications including implantation of flexible brachytherapy threads.

Equipment Design↗
PubMed1995

Review of magnetic neurosurgery research.

Image guided surgical techniques are often used to provide useful localizing information during the course of otherwise "standard" surgical procedures. In this review, a magnetic surgery system (MSS) is described that couples image guidance methods with a novel magnetic treatment delivery system. The MSS was designed with the unique capacity to manipulate an implant remotely, to follow complex curvilinear paths, and to implement serial movements over time without reoperation. Magnetically tipped intracerebral implants are placed on the brain surface and then directed along a target trajectory by means of externally generated magnetic gradients. The location of the implant is calculated by comparing preoperative magnetic resonance imaging (MRI) imaging data with intraoperative biplanar fluoroscopic images. A command computer presents the surgeon with relevant MRI-derived images and implements movement commands by sending currents of various strength to the six superconducting magnets suspended about the subject's head. The results of multidisciplinary preclinical research and development work are reviewed.

Brain↗
PubMed1995

Peptide cholesystokinin receptor antagonist increases food intake in rats.

An analogue of the C-terminal heptapeptide of cholecystokinin (CCK) t-Boc-Tyr(SO3-)-Nle-Gly-D-Trp-Nle-Asp-a-2-phenylethylester is a potent, specific CCK receptor antagonist. Intraperitoneal injection of the antagonist abolished suppression of real feeding and sham feeding by exogenous CCK-8 (1.8 nmol/kg), and significantly increased real feeding. Assuming an antagonist distribution like that of exogenous CCK-8, our results suggest that exogenous CCK-8 and endogenous CCK reduce food intake by acting at a site(s) accessible to peripherally administered peptides.

Amino Acid Sequence↗
PubMed1995

Functional design features and initial performance characteristics of a magnetic-implant guidance system for stereotactic neurosurgery.

A helmet with a roughly cubic array of six super-conducting coils is used to apply force on a small permanent magnet pellet in brain or in brain phantom material. This apparatus, called the Magnetic Stereotaxis System, will be used to deliver drugs and other therapies directly into deep brain tissues, under control of a computer and fluoroscopic imaging system. This paper considers only the force application aspects of the instrument. The primary design features of the helmet and power supply controls are presented, along with field plot data and single-axis motion results. The field plot data show that agreement with the finite-element iron-free field calculations is sufficiently high (> 1%) for the instrument. These preliminary motion data indicate accuracy better than 2 mm for the impulsive pellet motion, even though the visual position observations had significantly greater error than the completed imaging system will have. The companion paper will take up analysis of the control aspects of the motion, and our recent solutions to difficulties found in the experimental work described here.

Brain↗
PubMed1995

Characteristics of an improved magnetic-implant guidance system.

The previous companion paper described the motivation, design, and early experiments of a Magnetic Stereotaxis System. The part of the system considered in these papers is a helmet with a roughly cubic array of six superconducting coils used to apply force on small permanent magnet pellets in brain and in brain phantom material. This apparatus will be used to deliver drugs and other therapies directly into deep brain tissues, under control of a computer and fluoroscopic imaging system. Here, we analyze the general stability problems of controlling the currents in the coils for impulsive stepwise motion of the pellet, subject to quench avoidance in the superconducting coils, and in the face of Earnshaw's theorem governing stability in static magnetic fields. We also describe solutions that have been found to the primary difficulties limiting controlled pellet motion in the studies presented in the companion paper.

Brain↗
PubMed1994

Intestinal capsaicin transiently attenuates suppression of sham feeding by oleate.

Intraintestinal infusion of oleic acid reduces food intake in rats and other mammals. The neural mechanisms that mediate this behavioral response to intestinal stimulation are incompletely appreciated. We have found that intraintestinal infusion of capsaicin reduces sham feeding. In addition, 24 h after a single intestinal capsaicin infusion, reduction of sham feeding by intestinal oleate infusion was attenuated. However, by 48 h post-capsaicin, suppression of sham feeding by oleate had returned to pre-capsaicin levels. Repeated intestinal administration of capsaicin produced less attenuation of oleate-induced suppression of sham feeding, suggesting the development of tolerance to capsaicin. Unlike systemic capsaicin, intestinal capsaicin does not impair cholecystokinin-induced reduction of feeding or the corneal chemosensory reflex. Furthermore, there are no histochemical signs of vagal sensory degeneration in the hindbrain after intraintestinal capsaicin. Our results suggest that a capsaicin-sensitive substrate in or near the intestine is responsible for mediating the reduction of sham feeding by intestinal oleate infusion.

Animals↗
PubMed1993

Suppression of sham feeding by intraintestinal nutrients is not correlated with plasma cholecystokinin elevation.

To test the possibility that blood-borne cholecystokinin (CCK) participates in suppression of sham feeding by intestinal nutrients in rats, we examined the ability of oleate, maltose, L-phenylalanine (L-Phe), and casein to suppress sham ingestion of 15% sucrose solution. Plasma CCK concentrations were measured in parallel experiments in which the same intestinal nutrients were infused in rats that were not feeding. Intraintestinal oleate suppressed sham feeding and elevated plasma CCK concentrations. Casein infusion produced plasma CCK concentrations similar to those produced by oleate but did not suppress sham feeding. Both maltose and L-Phe suppressed sham feeding but failed to significantly elevate plasma CCK. Previously we demonstrated that CCK receptor antagonists attenuate suppression of sham feeding by intestinal infusion of either oleate or maltose, suggesting that endogenous CCK participates in suppression of sham feeding by some intestinal nutrients. The results of the study reported here suggest that plasma CCK levels after nutrient infusion are not correlated with suppression of sham feeding. Therefore, the mechanism of CCK's participation in nutrient-induced suppression of sham feeding may not depend on stimulus-induced elevation of plasma CCK.

Animal Nutritional Physiological Phenomena↗
PubMed1993

Caudal hindbrain participation in the suppression of feeding by central and peripheral bombesin.

We have previously demonstrated that bombesin (BBS) infused into the fourth cerebral ventricle in rats suppressed feeding at doses 10-1,000 times less than those required after lateral ventricular administration. These results suggest that centrally administered BBS acts in the caudal hindbrain to suppress food intake. To investigate the participation of caudal hindbrain structures in fourth-ventricular BBS-induced suppression of feeding, we made lesions that destroyed the following: 1) area postrema (AP) and 2) and medial nucleus of the solitary tract (NST). Additionally, we examined the role of the AP/NST in the suppression of food intake after peripheral BBS administration. Our experiments revealed that lesions of the AP/NST abolished the suppression of food intake by fourth-ventricular BBS and attenuated the suppression of food intake by peripheral BBS. Lesions restricted to the AP attenuated the suppression of food intake by fourth-ventricular BBS but had no effect on suppression of intake by peripherally administered BBS. These results suggest that the NST may be a common neural substrate for the inhibition of food intake by both centrally and peripherally administered BBS.

Animals↗
PubMed1992

CCK-receptor antagonists attenuate suppression of sham feeding by intestinal nutrients.

To test the possibility that endogenous cholecystokinin (CCK) participates in suppression of sham feeding by intraintestinal nutrient infusions, we examined the effect of CCK-receptor antagonists on the suppression of sham feeding by intraintestinally infused oleic acid, maltose or L-phenylalanine (L-Phe). In addition, we monitored amylase activity in the intestinal lumen during some sham feeding experiments and measured plasma CCK in parallel experiments using intestinally infused animals that were not feeding. Suppression of sham feeding by oleic acid or maltose was attenuated by CCK-receptor antagonists, while suppression of sham feeding by L-Phe was not. Oleate infusion increased plasma CCK concentration and luminal amylase activity. Oleate-induced increase in luminal amylase activity was attenuated by a CCK-receptor antagonist. Intraintestinal maltose or L-Phe did not increase plasma CCK concentration or luminal amylase activity, suggesting that they did not release endocrine CCK. These results suggest 1) that endogenous CCK mediates suppression of sham feeding by oleate and maltose but not by L-Phe and 2) that CCK participating in suppression of feeding by intestinal stimuli might not be of endocrine origin.

Amylases↗
PubMed1991

Goniometric motion controller for the superconducting coil in a magnetic stereotaxis system.

For the purpose of positioning the 80 kg, 2 T superconducting coil/cryostat used in the developmental version of a magnetic stereotaxis system, a four degree-of-freedom goniometer has been designed, built, and tested. Computer-controlled, stepping motor actuators enable movement of the coil via either joystick, keyboard, or translator-module keypad commands. An integral arrangement of counterweights and counterbalances minimizes the overall weight and size of the goniometer, while maintaining static and dynamic stability during operation. As much of the structure as possible has been made of nonmagnetic materials (mostly aluminum) to minimize distortion of the superconducting coil's field. In this paper, we present the design principles for the goniometer, describe the essential features of its construction, and discuss its performance characteristics and limitations. We also discuss a strategy for performing precision magnetic stereotaxis procedures with an arrangement of static superconducting coils.

Brain Neoplasms↗
PubMed1991

Capsaicin attenuates bombesin-induced suppression of food intake.

This study was conducted to evaluate the extent to which bombesin (BBS)-induced suppression of food intake relies on small, unmyelinated sensory neurons. Rats were pretreated intraperitoneally with capsaicin, a neurotoxin that destroys a subpopulation of small-diameter sensory neurons, and tested for suppression of food intake after intraperitoneal administration of 2, 4, 8, 16, and 32 micrograms/kg BBS. Capsaicin pretreatment attenuated suppression of food intake by BBS over a wide range of doses. The site of capsaicin action was not determined in this study. However, work by others indicates that vagal and nonvagal neural substrates participate in suppression of food intake by BBS. Afferents of both of these substrates are predominantly small and unmyelinated. Therefore, the deficits in BBS-induced suppression of food intake that we observed may reflect damage to both vagal and/or nonvagal neurons that participate in BBS-induced suppression of food intake.

Animals↗