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Biomedical subjects

B M Davis

Publications and source records attributed to B M Davis.

At least 91 records · Page 5Linked to original sources
PubMed1988

Modulation of EPSP amplitude during high frequency stimulation depends on the correlation between potentiation, depression and facilitation.

High frequency bursts were delivered every 2 s to single group Ia fibers in anesthetized cats. The modulation of EPSP amplitude in target motoneurons was determined. Changes in EPSP amplitude during the high frequency stimulation (facilitation or depression) were correlated with those occurring 2 s after the burst (potentiation). Connections displaying high levels of potentiation exhibited more depression resulting in a net negative modulation. Negative amplitude modulation was greatest at connections on low rheobase ('small') motoneurons that develop large EPSPs. Positive modulation occurred at a subset of connections on high rheobase ('large') motoneurons that exhibit small EPSPs. We suggest that these synaptic properties permit the appropriate amount of depolarization to be delivered to the heterogeneous elements of the motoneuron pool during high frequency Ia fiber activity characteristic of the step cycle.

Action Potentials↗
PubMed1988

Intraspinal substance P-containing projections to the sympathetic preganglionic neuropil in pigeon, Columba livia: high-performance liquid chromatography, radioimmunoassay and electron microscopic evidence.

The present study uses quantitative and electron microscopic methods to investigate the hypothesis that intraspinal substance P-sympathetic preganglionic neuron circuitry exists in vertebrates. Radioimmunoassay and high-performance liquid chromatography were used to: (1) characterize the chemical nature of the substance P-like immunoreactivity in the sympathetic preganglionic neuropil; and (2) quantify the relative contributions of brain stem, primary sensory and intraspinal neurons to the substance P content within the sympathetic preganglionic neuropil. Electron microscopic observations on the localization of substance P-like immunoreactivity within the preganglionic neuropil caudal to complete thoracic spinal cord transections are also reported. High-performance liquid chromatographic analyses demonstrate that pigeon substance P-like immunoreactivity co-migrates with synthetic substance P, suggesting that the substance P-like material is authentic substance P content within the sympathetic preganglionic neuropil. Electron microscopic observations on the localization of substance P-like immunoreactivity within the preganglionic neuropil caudal to complete preganglionic cell column (inclusive of intermediate spinal laminae V and VII as well as preganglionic neurons located within nucleus intercalatus spinalis); (2) cutting the dorsal rootlets entering the last cervical (C14) and first two thoracic (T1, T2) spinal segments resulted in massive depletion of substance P content in dorsal horn of T1, but no detectable losses within the preganglionic cell column or ventral horn of T1; and (3) total mid-thoracic (T3-4) spinal cord transection significantly depleted the substance P content in the preganglionic cell column (T3-4) as well as in the dorsal (T1-4) and ventral horns (T2-4). Ultrastructural examination of the sympathetic preganglionic neuropil caudal to spinal transections (survival times of 3-14 days) revealed the presence of numerous, intact, normal appearing substance P-like immunoreactive terminals. Immunolabeled terminals formed asymmetric contacts on medium-sized and small caliber dendrites. Extensive degeneration was evident in this material as well. The ultrastructural features of degenerating processes were distinctive and quite dissimilar in appearance from those exhibiting substance P-like immunoreactive staining. No evidence for damage-induced sequestration of substance P-like material into glial elements was found. The above observations are consistent with earlier findings in rat and pigeon, and provide new quantitative and qualitative evidence to support the hypothesis that intraspinal substance P-containing interneurons contribute t

Animals↗
PubMed1988

Endocrine changes in Alzheimer's disease.

In conclusion, at present, no consistent endocrine abnormalities can be detected in patients suffering from Alzheimer's disease. However, assessment of neuroendocrine function might help identify subpopulations of patients with particular neurotransmission abnormalities who are likely to benefit from a specific pharmacologic strategy. For example, patients in whom cholinomimetic drugs produce the greatest elevation in plasma cortisol concentration appear to derive the most symptomatic benefit from these drugs.

Alzheimer Disease↗
PubMed1988

Endocrine changes in Alzheimer's disease.

In conclusion, at present, no consistent endocrine abnormalities can be detected in patients suffering from Alzheimer's disease. However, assessment of neuroendocrine function might help identify subpopulations of patients with particular neurotransmission abnormalities who are likely to benefit from a specific pharmacologic strategy. For example, patients in whom cholinomimetic drugs produce the greatest elevation in plasma cortisol concentration appear to derive the most symptomatic benefit from these drugs.

Alzheimer Disease↗
PubMed1987

Distribution of potentiation following short high frequency bursts to motoneurons of different rheobase.

Potentiation of composite EPSPs has been studied at group Ia fiber/alpha motoneuron connections using a short burst of conditioning stimuli [32 shocks with 6 ms interstimulus interval (ISI)]. Potentiation reached its peak (range 1.2-2.0 X control value) 100-150 ms following the burst. Potentiation decayed slowly and was still present 2 s after the burst. High frequency burst stimulation of a nerve to a synergist muscle did not potentiate the response to stimulation of the homonymous nerve. Three independent sets of measurements suggest that the time course of decline of potentiation depends on the amount of transmission during the potentiated state. First, connections on high rheobase motoneurons exhibited more peak potentiation than those on low rheobase motoneurons but potentiation decayed more rapidly in the former than in the latter. Second, increasing the frequency of the conditioning burst enhanced peak potentiation but the rate of decay of this potentiation also increased. Third, potentiated EPSPs exhibited more low frequency depression than unpotentiated ones at the same connection suggesting that low frequency stimulation during the potentiated state could elevate the rate of decay of potentiation. The short burst paradigm could cause peak potentiation similar in magnitude to that evoked by long, high frequency trains (studied here at the same connection) but with much less of an increase in latency and rise time of the potentiated EPSP. The magnitude of potentiation was unrelated to changes in EPSP latency and rise time. These findings indicate that potentiation can act to modulate EPSP amplitude under conditions of normal motor behaviour when spindle afferents fire in patterns similar in duration and frequency to those used in the present experiments.

Animals↗
PubMed1987

RS 86 in the treatment of Alzheimer's disease: cognitive and biological effects.

Twelve patients who met Research Diagnostic Criteria for Alzheimer's disease (AD) completed a double-blind crossover study comparing oral RS 86, a long-acting and specific muscarinic agonist, with placebo. Cognitive and noncognitive effects were assessed with the Alzheimer's Disease Assessment Scale (ADAS). RS 86 was found to improve ADAS test scores consistently (both cognitive and noncognitive subscales) in seven patients, with a clinically obvious improvement in only two patients. RS 86 produced a significant increase in peak nocturnal cortisol levels, and this increase correlated with improvement on ADAS testing. Similarly, there was a 38% increase in amplitude of the P300 evoked potential with RS 86. The biological findings suggest that RS 86 was effective only to the extent that it enhanced central cholinergic activity.

Aged↗
PubMed1987

Effects of debrisoquin and haloperidol on plasma homovanillic acid concentration in schizophrenic patients.

Plasma levels of the dopamine metabolite homovanillic acid (pHVA) may potentially reflect upon central dopamine activity. This study examines the effects of debrisoquin, haloperidol, and the two drugs combined on pHVA concentrations of schizophrenic patients. Debrisoquin is a drug that suppresses the peripheral formation of homovanillic acid without affecting the central formation. Acute haloperidol administration consistently increased pHVA concentrations in patients pretreated or not pretreated with debrisoquin, suggesting that this increment reflects haloperidol's central and not peripheral effects.

Adult↗
PubMed1987

Hyperbiliverdinemia in the bronze baby syndrome.

The bronze baby syndrome is an unusual complication of phototherapy for hyperbilirubinemia in the neonate. The pigment or pigments responsible for the discoloration in this syndrome have not yet been identified. Suspected pigments include photodegradation products of bilirubin and copper-porphyrins. We present here the case of a neonate with bronze baby syndrome whose serum had increased spectral absorbance in the region of maximum absorbance for biliverdin. We suggest that biliverdin pigments may also contribute to the "bronze" color associated with this syndrome.

Adult↗
PubMed1987

Relationship between circulating anti-Ro/SS-A antibody levels and skin disease activity in subacute cutaneous lupus erythematosus.

Anti-Ro/SS-A antibody levels in 80 serum specimens from 12 patients with subacute cutaneous lupus erythematosus (SCLE) were determined by immunodiffusion and enzyme-linked immunosorbent assay in order to examine the changes in this autoantibody response with time and to study the relationship between levels of this antibody and SCLE skin disease activity. Anti-Ro/SS-A antibody levels were found to vary considerably over time in a given patient when measured by both assays. Several patients who did not have detectable levels of this antibody at the time of their initial examination were found to be antibody positive at follow-up examinations. However, no significant relationship was found between antibody levels in either assay and SCLE skin disease activity. While not ruling out a pathogenetic role for this antibody in the elicitation of SCLE skin lesions, these results would suggest that other factors are likely to be involved.

Adult↗
PubMed1987

Induction of depression with oxotremorine in patients with Alzheimer's disease.

Cholinergic neurotransmission has long been implicated in the development of depression. In this study seven patients with Alzheimer's disease were given oral oxotremorine, a long-acting cholinergic agonist, to assess the drug's effects on cognitive function. There were unexpected depressive reactions in five of the seven patients; three patients dropped out of the study because of the side effects. Cardiovascular effects of the drug were negligible, but its effect on memory and cognition remains unknown because of the small number of subjects who completed the study.

Aged↗
PubMed1987

Influence of age and relative weight on cortisol suppression in normal subjects.

The authors examined the effects of certain nonpsychiatric variables on dexamethasone suppression test (DST) results. Sixty physically healthy, nondepressed, nondemented adults participated in a standard outpatient 1-mg DST. Postdexamethasone plasma cortisol concentrations were higher in older subjects and were lower in more obese subjects. The authors conclude that age and relative weight influence cortisol suppression in healthy subjects.

Adult↗
PubMed1986

Cortisol and Alzheimer's disease, I: Basal studies.

Patients with Alzheimer's disease and nondemented elderly control subjects participated in studies of cortisol secretion during sleep and at 9:00 a.m. and were given dexamethasone suppression tests (DSTs) and lumbar punctures. Nocturnal and 9:00 a.m. cortisol concentrations were significantly higher in the demented patients. CSF MHPG negatively correlated with mean nocturnal cortisol. The most severely demented patients had the highest 9:00 a.m. and mean nocturnal cortisol concentrations. DST results did not distinguish samples with substantially different nocturnal cortisol concentrations. These results suggest that measurements of basal plasma cortisol concentrations and dexamethasone suppression provide different information but support the notion of somewhat higher than normal cortisol concentrations in Alzheimer's disease patients.

Aged↗
PubMed1986

Correlates of lateral ventricular size in chronic schizophrenia, II: biological measures.

CSF homovanillic acid levels showed a significant negative correlation with ventricle-brain ratios (VBRs) in a group of drug-free chronic schizophrenic male veterans, while CSF 5-hydroxyindoleacetic acid levels showed a similar, nearly significant trend. The response of plasma human growth hormone to 0.75 mg of apomorphine also demonstrated a significant negative correlation with VBR in this group, but other measures of central neurotransmitter activity were unrelated to ventricular size.

Adult↗
PubMed1986

Amplitude modulation of EPSPs in motoneurons in response to a frequency-modulated train in single la afferent fibers.

In anesthetized cats, single group Ia fibers were activated with a train of 52 stimuli whose interspike intervals were obtained from the discharge of a group Ia fiber in a walking cat (courtesy of Dr. G. E. Loeb, NIH). The EPSPs recorded in motoneurons to which the afferents projected were averaged in register (EPSP1, EPSP2, ..., EPSP52) in response to multiple presentations of the train at a rate (0.77 Hz) similar to the stepping rate of the cat. Amplitudes of these averaged EPSPs were found to be highly variable, depending both on afferent discharge rate and history of activation. The initial EPSP was generally potentiated, and EPSPs in the high-frequency (greater than 200 Hz) middle portion of the train were generally reduced in amplitude. Connections at which the first EPSP was most potentiated tended to be those which showed the most depression of EPSP amplitude during the high-frequency portion of the train. Thus, at some connections, modulation of EPSP amplitude during the frequency-modulated train was much greater than at other connections. In general, the extent of modulation was greater on low-rheobase motoneurons than on high-rheobase motoneurons. We suggest that these differences in transmission permit type S (i.e., low-rheobase) motoneurons, which on average generate the largest EPSPs, to reach threshold at low levels of input (size principle) but prevent excessive depolarization due to temporal summation during high-frequency stimulation.

Afferent Pathways↗