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Biomedical subjects

D A Wilson

Publications and source records attributed to D A Wilson.

At least 145 records · Page 8Linked to original sources
PubMed1989

John Caffey award. MR imaging determination of the location of the normal conus medullaris throughout childhood.

This retrospective study was designed to determine the location of the conus medullaris in normal children by reviewing a series of MR images of the lumbar spine. The study group consisted of 184 children ranging in age from newborn to 20 years who had a normal conus level as reported by the radiologist of record. The range of conus levels for the entire group of normal children was T12 to L3. The range for the 0-2-year-old group was T12 to L2-L3 with an average of L1-L2. The range of conus levels for the 19-20-year-old group was L1 to L2 with an average of L1-L2. We conclude that the conus medullaris does not ascend throughout childhood as stated by previous authors but attains the adult level sometime during the first few months of life. A conus level at L2-L3 or above should be considered normal at any age. A conus level at L3 is indeterminate, since it is possible for a normal or a tethered conus to be located at this level.

Child↗
PubMed1989

Norepinephrine and learning-induced plasticity in infant rat olfactory system.

Postnatal olfactory learning produces both a conditioned behavioral response and a modified olfactory bulb neural response to the learned odor. The present report describes the role of norepinephrine (NE) on both of these learned responses in neonatal rat pups. Pups received olfactory classical conditioning training from postnatal days (PN) 1-18. Training consisted of 18 trials with an intertrial interval of 24 hr. For the experimental group, a trial consisted of a pairing of unconditioned stimulus (UCS, stroking/tactile stimulation) and the conditioned stimulus (CS, odor). Control groups received either only the CS (Odor only) or only the UCS (Stroke only). Within each training condition, pups were injected with either the NE beta-receptor agonist isoproterenol (1, 20, or 4 mg/kg), the NE beta-receptor antagonist propranolol (10, 20, 40 mg/kg), or saline 30 min prior to training. On day 20, pups received one of the following tests: (1) behavioral conditioned responding, (2) injection with 14C-2-deoxyglucose (2-DG) and exposed to the CS odor, or (3) tested for olfactory bulb mitral/tufted cell single-unit responses to the CS odor. The results indicated that training with either: (1) Odor-Stroke-Saline, (2) Odor-Stroke-Isoproterenol-Propranolol, or (3) Odor only-Isoproterenol (2 mg/kg) was sufficient to produce a learned behavioral odor preference, enhanced uptake of 14C-2-DG in the odor-specific foci within the bulb, and a modified output signal from the bulb as measured by single-cell recordings of mitral/tufted cells. Moreover, propranolol injected prior to Odor-Stroke training blocked the acquisition of both the learned behavior and olfactory bulb responses. Thus, NE is sufficient and may be necessary for the acquisition of both learned olfactory behavior and olfactory bulb responses.

Animals↗
PubMed1988

Noradrenergic modulation of olfactory bulb excitability in the postnatal rat.

Noradrenergic centrifugal inputs to the rat olfactory bulb mainly terminate on granule cells, which are inhibitory interneurons. In the mature bulb, norepinephrine suppresses granule cell activity, thus increasing the excitability of the primary output neurons of the bulb. However, since the majority of granule cells develop postnatally, the effectiveness of noradrenergic inputs to the bulb during development is unclear. The present report describes the postnatal development of noradrenergic modulation of olfactory bulb function by examining the effects of noradrenergic beta-receptor agonists and antagonists on paired-pulse inhibition at the granule cell/mitral cell reciprocal synapse. The results demonstrate that noradrenergic modulation of olfactory bulb excitability emerges during the first postnatal week in the rat. These results suggest that noradrenergic centrifugal control of olfactory bulb activity appears early during postnatal development, and thus is capable of playing an important role in pup responses to olfactory cues early in life.

Action Potentials↗
PubMed1988

Physical stimulation reduces the brain temperature of infant rats.

Previous work indicated that physical stimulation, such as that which mimics the stimulation pups receive from the dam, reduces pup body temperature. The present paper reports that the body and brain temperature of 5-day-old pups covaried under steady-state thermal conditions, cold exposure, and warmth exposure (Expt. 1) suggesting that body thermoregulatory mechanisms may also regulate brain temperature. Indeed, physically stimulating pups decreased brain temperature in the neocortex (Expt. 2) and the olfactory bulb (Expt. 3). The mechanism for this brain temperature decrease appears to be an increase in ventilatory heat exchange, the same mechanism responsible for the decrease in body temperature. Pups increased respiration during stimulation, thereby increasing air flow to the lungs where convective and evaporative heat exchange occurred. Indeed, stimulating pups in a high-humidity environment blocked the decrease in brain temperature (Expt. 4). The ability of physical stimulation to decrease brain temperature appears to be limited to neonatal pups, as 10-, 15-, and 20-day-old pups did not exhibit a brain temperature decrease in response to stimulation (Expt. 5).

Animals↗
PubMed1988

Behavioral and neural correlates of postnatal olfactory conditioning: I. Effect of respiration on conditioned neural responses.

Following olfactory classical conditioning, infant rats exhibit a preference for the conditioned odor and exhibit enhanced uptake of focal 14C 2-deoxyglucose (2-DG) within the olfactory bulb. The present experiments assessed the role of respiration on the expression of the enhanced 2-DG uptake response. Pups were conditioned from postnatal day (PN) 1-18 with an olfactory stimulus paired with a reinforcing tactile stimulus which mimics maternal contact (Odor-Stroke). Control pups received odor only or tactile stimulation only. On PN 19, pups received 1 of 3 tests: 1) a two-odor choice test, 2) an odor/2-DG test with normal respiration allowed, or 3) an odor/2-DG test with respiration experimentally controlled. The results indicated that: 1) Odor-Stroke pups learned the conditioned odor preference, 2) Odor-Stroke, normally respiring pups exhibited enhanced olfactory bulb 2-DG uptake when compared to control pups. No difference in respiration rate was detected between groups in normally respiring pups. 3) Odor Stroke pups whose breathing was experimentally controlled exhibited enhanced olfactory bulb 2-DG uptake when compared to control pups with an identical number of respirations. Together, these results demonstrate that modified respiration during testing is not required for the expression of a modified olfactory bulb response to learned attractive odors. Therefore, the data suggest that the olfactory system itself is modified by early learning.

Animals↗
PubMed1988

Effect of centrally administered encephalinamides on regional cerebral blood flow in the dog.

(D-ala2)-met5-encephalinamide (AM encephalinamide) and (D-ala2)-leu5-encephalinamide (AL encephalinamide) were administered into the cisterna magna in anesthetized dogs to determine whether these opiates effected the neurohypophyseal circulation differently than the circulation of other brain areas. At the beginning of the experimental protocol, animals were given either mock cerebral spinal fluid (CSF) or 5 or 25 mg of AM encephalinamide or 5 mg of AL encephalinamide in equal volumes of mock CSF into the cisterna magna. By 60 min after intracisternal injection, radiolabeled AM encephalinamide distributed throughout the brain with the highest concentration being in the area of the brainstem. Sixty minutes after intracisternal injection, heart rate was decreased 29.0 +/- 5.1%, 41.3 +/- 4.4%, and 36.0 +/- 3.6%, and MABP was decreased 25.2 +/- 8.0%, 26.4 +/- 2.4%, and 32.3 +/- 2.6% in animals treated with AL encephalinamide (5 mg), AM encephalinamide (5 mg), and AM encephalinamide (25 mg), respectively. Neither AL encephalinamide or AM encephalinamide altered CBF or CMRO2 when compared with animals treated with mock CSF, whereas both AL encephalinamide and AM encephalinamide reduced neurohypophyseal blood flow by 30 min (43 +/- 11%, AL encephalinamide; 35 +/- 7%, AM encephalinamide, 5 mg; 46 +/- 8%, AM encephalinamide, 25 mg); the reduction was sustained throughout the 60-min protocol (34 +/- 10%, AL encephalinamide; 37 +/- 3%, AM encephalinamide, 5 mg; 38 +/- 4% AM encephalinamide, 25 mg). Plasma arginine vasopressin was transiently elevated 15 (326 +/- 75%, AL encephalinamide; 323 +/- 109%, AM encephalinamide, 25 mg) and 30 min (271 +/- 68%, AL encephalinamide; 368 +/- 136%, AM encephalinamide, 25 mg) in animals treated with AL encephalinamide or AM encephalinamide (25 mg). Intravenous naloxone administered at the end of the 60-min encephalinamide protocol was associated with a rise toward control values in heart rate and MABP in the AL encephalinamide group and in heart rate, MABP, and neurohypophyseal blood flow in both the AM encephalinamide 5 mg and 25 mg groups. These data suggest that encephalinamides may play a role in the regulation of neurohypophyseal blood flow through their actions on opiate receptors.

Animals↗
PubMed1988

Sonography of brain abscesses complicating Citrobacter neonatal meningitis.

The incidence of cerebral complications from citrobacter meningitis is high, and these problems are often difficult to diagnose clinically. Cranial sonography provides the ideal imaging modality to detect the early complications of meningitis and the problems that may occur during or after treatment. Early and serial use of cranial sonography should help to preserve brain tissue and minimize the long-term neurologic deficits that arise from this disease.

Brain↗
PubMed1988

Peripheral chemoreceptor control of neurohypophysial blood flow.

Neurohypophysial blood flow responses to hypoxic hypoxia were studied under conditions of vagotomy, carotid sinus denervation, and combined vagotomy and carotid sinus denervation. Arterial O2 tension was lowered from 128 +/- 3 to 31 +/- 1 Torr, whereas pH and arterial CO2 tension remained constant. Denervation of either carotid sinus or aortic arch chemoreceptors alone does not attenuate the dilation of neurohypophysial vessels that accompanies hypoxic hypoxia. Combined denervation, however, completely blocks this response for the neurohypophysis but not for any other brain region studied. Hypoxic hypoxia resulted in an increase in plasma vasopressin (AVP) from approximately 8 to approximately 40 pg/ml. This increase occurred in the intact, vagotomy, and carotid sinus-denervation conditions. This neurosecretory response was also completely inhibited by combined denervation. For most brain regions peripheral chemoreceptors are not involved in the blood flow response; however, the response of the neurohypophysis appears to be mediated via these chemoreceptors, presumably by altering the neuroeffector activity to this region. In addition our data suggest a temporal relationship between neurohypophysial vasodilation and neurosecretion of AVP.

Animals↗
PubMed1988

Spatial patterns of olfactory bulb single-unit responses to learned olfactory cues in young rats.

1. Neonatal rat pups were classically conditioned to an odor stimulus from postnatal day 1 (PN1) to PN18. Tactile stimulation (stroking) was used as the unconditioned stimulus. On PN19, mitral/tufted cell single-unit responses to the conditioned odor were examined in both conditioned and control pups. Recordings were made from mitral/tufted cells in two regions of the olfactory bulb: 1) an area typically associated with focal [14C]2-deoxyglucose (2-DG) uptake in response to the conditioned odor and 2) an area distant from focal 2-DG uptake to the conditioned odor. Animals were anesthetized with urethane and were naturally respiring during the single-unit recording procedure. 2. Changes in mitral/tufted cell firing rate in response to odors in both bulbar regions and all training groups were classified as either excitatory, suppressive, or no response. This response classification was used to compare response patterns to the conditioned odor between bulbar regions and training groups. 3. Classical conditioning selectively modified the response patterns of mitral/tufted cells to the conditioned odor when those cells were associated with regions of focal 2-DG uptake for that odor. Mitral/tufted cells demonstrated significantly more suppressive and fewer excitatory responses to the conditioned odor than cells in control pups. Response patterns to a novel odor were not similarly modified. 4. Response patterns of mitral/tufted cells distant from the focal region of 2-DG uptake to the conditioned odor were not modified by conditioning compared with control pups. 5. The difference in response pattern between cells in the 2-DG focus and cells distant to the 2-DG focus was apparent within 500 ms of the stimulus onset. Given the respiratory rate of these pups (2 Hz), these data suggest that the modified response pattern occurred on the first inhalation of the learned odor. 6. These data demonstrate that both spatial and temporal patterns of olfactory bulb output neuron activity are used in the coding of olfactory information in the bulb. Furthermore, these spatial/temporal response patterns can be modified by early learning.

Animals↗
PubMed1988

Parainflammatory leukoencephalomyelitis: clinical and magnetic resonance imaging findings.

Parainflammatory leukoencephalomyelitis is a broad term used to include the spectrum of disorders that affect the central nervous system following infection, immunization, or other noxious stimuli. There is a wide range of clinical and pathologic severity, ranging from acute cerebellar ataxia to acute hemorrhagic leukoencephalopathy. With the improved survival of these patients, magnetic resonance imaging provides a window to the pathologic process, which can aid in the long-term management of these patients. Although lesions of the brainstem and spinal cord correlate well to clinical symptoms, multiple cortical lesions may be present without specific localizing signs. The distribution of magnetic resonance lesions is different from that commonly seen in multiple sclerosis. In some cases, prolonged immunosuppression may be required to prevent recrudescence of the inflammatory response.

Cerebellum↗
PubMed1987

Caudal cruciate ligament function and injury in the horse.

The caudal cruciate ligament assists the medial femorotibial ligament in supporting the medial aspect of the femorotibial joint. It also limits the outward rotation of the tibia during weight bearing. In two lame horses tearing of the caudal portion of the femoral attachment of the caudal cruciate ligament was recorded together with cracking and tearing of the medial meniscus. In one case, synovitis and restrictive fibrous periarthritis were the sequelae of secondary stifle sepsis.

Animals↗
PubMed1987

Evidence of lateral synaptic interactions in olfactory bulb output cell responses to odors.

Lateral inhibitory circuits are found throughout the nervous system. While the neuroanatomical basis for lateral inhibitory interactions exists in the olfactory bulb of Norway rats, there has been no direct demonstration of lateral inhibition in the responses of olfactory bulb output neurons to odor stimulation. In this report we recorded the extracellular activity of a large number of sequentially recorded mitral/tufted cells in response to odor stimuli at two different concentrations, as well as the inter-cell distance between these cells. The probability of recording two cells with excitatory responses to the same odor was then determined for inter-cell distances up to 500 microns. For cells stimulated with high concentration odors, the probability of two cells 100-200 microns apart both being excited by the same odor was significantly lower than that predicted if all cells responded independently. Cells separated by greater or shorter inter-cell distances did not differ from the predicted value. Responses to the low odor concentration were not dependent on inter-cell distance. These results demonstrate that lateral synaptic interactions within the olfactory bulb influence output cell responses to odor stimulation.

Animals↗
PubMed1987

Abrupt decrease in synaptic inhibition in the postnatal rat olfactory bulb.

Olfactory bulb responses to paired-pulse stimulation of the lateral olfactory tract were examined in urethane-anesthetized rats, aged 5 days to adult. Brief inter-pulse intervals resulted in a depression of test responses at all ages. The magnitude of this depression decreased dramatically between postnatal days 19 and 20 to approach adult levels. Longer inter-pulse intervals resulted in a facilitation of test response amplitude in adult animals. This facilitation was evident at adult levels by postnatal day 10. These results suggest that both inhibitory and facilitatory synaptic mechanisms appear early in the course of rat olfactory bulb development. Furthermore, presumed granule cell-mediated inhibition is present at unusually high levels in the developing bulb, decreasing sharply between days 19 and 20.

Aging↗
PubMed1987

Serial sonograms to detect pancreatitis in children receiving L-asparaginase.

The clinical, laboratory, and ultrasonographic findings in children receiving L-asparaginase therapy were retrospectively reviewed and correlated to determine the diagnostic reliability and clinical usefulness of serial pancreatic sonograms in detecting L-asparaginase-induced pancreatitis. A total of 217 sonograms were obtained in 92 patients. Six of the 92 (6.5%) had L-asparaginase-induced pancreatitis. The diagnosis of pancreatitis was based solely on clinical symptoms in three patients, on clinical and laboratory findings in two, and on sonographic and laboratory findings in one. No confirmed cases of pancreatitis were detected solely by ultrasonography before clinical or laboratory evidence was obtained. Sonograms were useful only in confirming clinical and/or laboratory evidence of pancreatitis, but were of no value in making the early or preclinical diagnosis of drug-induced pancreatitis. We have discontinued the practice of obtaining routine serial pancreatic sonograms in children receiving L-asparaginase at our institution.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1987

Sonographic spectrum of placental abruption.

Fifty-seven cases of placental abruption detected by sonography were retrospectively reviewed. The location of hemorrhage was subchorionic in 46 cases (81%), retroplacental in nine cases (16%), and preplacental in two cases (4%). Subchorionic hematomas were more frequently shown in the 33 patients presenting before 20 menstrual weeks (91%) than in the 24 patients presenting after 20 weeks (67%). The echogenicity of hemorrhage depended on the time the sonogram was performed relative to the onset of symptoms: Acute hemorrhage was hyperechoic to isoechoic compared with the placenta, while resolving hematomas became hypoechoic within 1 week and sonolucent within 2 weeks. Acute hemorrhage was occasionally difficult to distinguish from the adjacent placenta. This occurred in five retroplacental hematomas that showed only an abnormally thick and heterogeneous placenta. Nine cases of placental abruption were initially confused with other mass lesions. Placental abruption causes a wide spectrum of sonographic findings that may be overlooked or misdiagnosed.

Abruptio Placentae↗
PubMed1987

Influence of chemoreceptors on neurohypophyseal blood flow during hypoxic hypoxia.

Neurohypophyseal blood flow was studied using radiolabelled microspheres in 13 dogs. Hypoxic hypoxia and carbon monoxide hypoxia with similar arterial oxygen contents (CaO2, approximately 8 vol %) were produced. Under conditions of hypoxic hypoxia, 100-200% increases in blood flow in caudate nucleus, white matter, neurohypophysis, and all other brain regions occurred. Similar blood flow responses were observed with carbon monoxide hypoxia in all brain regions except the neurohypophysis. The role of carotid and aortic chemoreceptors in mediating this blood flow response was studied in 6 additional dogs. Similar degrees of hypoxic hypoxia were produced in chemoreceptor-intact and completely denervated animals (CaO2 approximately 8 vol %, PaO2 approximately 33 mm Hg). Hypoxic hypoxia produced a 250% increase in neurohypophyseal blood flow and a concurrent rise in plasma arginine vasopressin from 8 +/- 3 to 52 +/- 8 pg/ml. Chemoreceptor denervation completely inhibited the increase in neurohypophyseal blood flow associated with hypoxic hypoxia. Arginine vasopressin was not increased by hypoxic hypoxia under conditions of complete denervation. A unique role for peripheral chemoreceptors in regulating neurohypophyseal blood flow is postulated.

Animals↗
PubMed1987

Single-unit analysis of postnatal olfactory learning: modified olfactory bulb output response patterns to learned attractive odors.

Neonatal rats learn to approach odors associated with stimulation normally provided by their mother. The present report describes changes in olfactory bulb single-unit activity following olfactory learning in young rats. Rat pups were exposed from postnatal day 1 to 18 to either (1) peppermint-scented air while receiving tactile stimulation (Pepp-Stroked), (2) peppermint-scented air with no tactile stimulation (Pepp-Only), (3) clean air and tactile stimulation (Stroked-Only), or (4) clean air and no tactile stimulation (Naive). On day 19, single-unit activity was recorded from mitral/tufted cells in urethane-anesthetized, freely breathing pups in response to either peppermint or a novel orange odor. Mitral/tufted cell response patterns to peppermint were significantly altered in Pepp-Stroked animals compared to control pups. Peppermint exposure alone, not associated with tactile stimulation (Pepp-Only), did not affect subsequent single-cell response patterns to that odor. In addition, the modification of response patterns was specific to peppermint and was not associated with a change in respiration rate. Furthermore, Pepp-Stroked pups had a relative behavioral preference for peppermint on day 19 compared to control pups. These results demonstrate that postnatal olfactory learning selectively modifies the subsequent response patterns of olfactory bulb output cells to the attractive odor. Furthermore, these results indicate that the initial coding of an odor's attractive value occurs within the olfactory bulb.

Animals↗