Biomedical subjects

J A Tracy

Publications and source records attributed to J A Tracy.

6 recordsLinked to original sources

PubMed1999

A method for identifying comparison counties: application to a rural telemedicine evaluation project.

The evaluation of telemedicine activity in rural communities is complicated by the fact that most telemedicine sites are chosen because of their existing telecommunications infrastructure and institutional relationships, not by a random selection process. In addition, it is difficult to draw conclusions about the effects of telemedicine without a careful analysis of parallel changes in communities which do not have access to telemedicine services. We have developed a method of identifying comparable counties based on an aggregate measure of health status. A set of 66 variables was collected in a previous project to develop a model to evaluate the relative health status of the population in Missouri. A stepwise regression was used to identify a subset of 15 variables that had the highest predictive value for the health status of a county. Distance measures were then used to identify six counties which were most similar to three telemedicine counties. The method can be used with any study set chosen non-randomly, to identify similar objects that can be used for comparative purposes.

Delivery of Health Care↗

PubMed1998

Purkinje cell responses to pontine stimulation CS during rabbit eyeblink conditioning.

Previous studies have shown that stimuli typically used as CSs in eyeblink conditioning converge with US information in the cerebellum. Extracellular recordings of Purkinje cells have shown learning-related as well as stimulus-related discharge patterns. Stimulation of a portion of the auditory CS pathway, the pontine nucleus, also serves as a highly effective CS. Using a short-latency pontine stimulation CS and air puff US, single Purkinje cell responses were recorded and compared to those elicited with an auditory stimulus in previous work. Purkinje cell recordings in trained and untrained rabbits revealed patterns of responses very similar to those seen in rabbits trained to a tone CS or those given unpaired-tone/air-puff training. Similarities included the proportion of stimulus-related and behavior-related cell responses. However, fewer inhibitory responses were seen than in earlier studies and these differences are considered in light of the differences between an extracellular stimulation CS and a peripherally administered auditory CS.

Acoustic Stimulation↗

PubMed1998

Selective changes in AMPA receptors in rabbit cerebellum following classical conditioning of the eyelid-nictitating membrane response.

alpha-Amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptors are critically involved in several forms of synaptic plasticity proposed to be neural substrates for learning and memory, e.g., long-term potentiation and long-term depression (LTD). The present study was designed to determine changes in cerebellar AMPA receptors following classical conditioning of the eyeblink-nictitating membrane response (NMR) in the rabbit. Quantitative autoradiography was used to assess changes in ligand binding properties of cerebellar AMPA receptors following NMR conditioning elicited by pairing electrical stimulation of the pontine nuclei with an airpuff to the eye. [3H]AMPA and [3H]-6-cyano-7-nitroquinoxaline-2,3-dion (CNQX) binding were determined following preincubation of frozen-thawed brain tissue sections at 0 or 35 degreesC. With 0 degreesC preincubation, no significant differences in [3H]AMPA binding to cerebellar AMPA receptors were seen between any of the experimental groups tested. In contrast, preincubation at 35 degreesC revealed significant decreases in [3H]AMPA binding to the trained side of the cerebellar cortex resulting from paired presentations of the conditioned and the unconditioned stimuli, while unpaired presentations of the stimuli resulted in no significant effect. With 35 degreesC preincubation, there were no significant differences in [3H]CNQX binding between any of the experimental groups and no significant differences in [3H]AMPA binding in the untrained side of the cerebellum. These results indicate that NMR conditioning is associated with a selective modification of AMPA-receptor properties in brain structures involved in the storage of the associative memory. Furthermore, they support the hypothesis that cerebellar LTD, resulting from decreased synaptic efficacy at parallel fiber-Purkinje cell synapses mediated by a change in AMPA-receptor properties, is a form of synaptic plasticity that supports this type of learning.

6-Cyano-7-nitroquinoxaline-2,3-dione↗

PubMed1998

Evidence of plasticity in the pontocerebellar conditioned stimulus pathway during classical conditioning of the eyeblink response in the rabbit.

Electrical stimulation thresholds required to elicit eyeblinks with either pontine or cerebellar interpositus stimulation were measured before and after classical eyeblink conditioning with paired pontine stimulation (conditioned stimulus, CS) and corneal airpuff (unconditioned stimulus, US). Pontine stimulation thresholds dropped dramatically after training and returned to baseline levels following extinction, whereas interpositus thresholds and input-output functions remained stable across training sessions. Learning rate, magnitude of threshold change, and electrode placements were correlated. Pontine projection patterns to the cerebellum were confirmed with retrograde labeling techniques. These results add to the body of literature suggesting that the pons relays CS information to the cerebellum and provide further evidence of synaptic plasticity in the cerebellar network.

Animals↗

PubMed1997

Associative learning.

This chapter reviews evidence demonstrating the essential role of the cerebellum and its associated circuitry in the learning and memory of classical conditioning of discrete behavioral responses (e.g., eyeblink, limb flexion, head turn). It now seems conclusive that the memory traces for this basic category of associative learning are formed and stored in the cerebellum. Lesion, neuronal recording, electrical microstimulation, and anatomical procedures have been used to identify the essential conditioned stimulus (CS) circuit, including the pontine mossy fiber projections to the cerebellum; the essential unconditioned stimulus (US) reinforcing or teaching circuit, including neurons in the inferior olive (dorsal accessory olive) projecting to the cerebellum as climbing fibers; and the essential conditioned response (CR) circuit, including the interpositus nucleus, its projection via the superior cerebellar peduncle to the magnocellular red nucleus, and rubral projections to premotor and motor nuclei. Each major component of the eyeblink CR circuit was reversibly inactivated both in trained animals and over the course of training. In all cases in trained animals, inactivation abolished the CR (and the UR as well when motor nuclei were inactivated). When animals were trained during inactivation (and not exhibiting CRs) and then tested without inactivation, animals with inactivation of the motor nuclei, red nucleus, and superior peduncle had fully learned, whereas animals with inactivation of a very localized region of the cerebellum (anterior interpositus and overlying cortex) had not learned at all. Consequently, the memory traces are formed and stored in the cerebellum. Several alternative possibilities are considered and ruled out. Both the cerebellar cortex and the interpositus nucleus are involved in the memory storage process, suggesting that a phenomenon-like long-term depression (LTD) is involved in the cerebellar cortex and long-term potentiation (LTP) is involved in the interpositus. The experimental findings reviewed in this chapter provide perhaps the first conclusive evidence for the localization of a basic form of memory storage to a particular brain region, namely the cerebellum, and indicate that the cerebellum is indeed a cognitive machine.

Animals↗

PubMed1997

Lifestyle, education, and prevalence of hypertension in populations of African origin. Results from the International Collaborative Study on Hypertension in Blacks.

Lifestyle Incongruity has been shown to be associated with elevated blood pressure in various developing societies. We sought to test this model in an international collaborative study of hypertension in populations of African origin. Data were available for 4770 men and women, aged 25-74, from Africa, the Caribbean, and the United States. The main effects of lifestyle score (LSS) and education on hypertension prevalence were explored, as well as interactions predicted by the Lifestyle Incongruity model. Significant interactions were observed, but only the U.S. men conformed to the pattern predicted. For this group, adjusted ORs for LSS were 4.45 among low-education and 0.71 among high-education subgroups (risk OR = 0.16, 0.03-0.84 95% CI). The Lifestyle Incongruity model therefore received limited support. The model was designed to describe processes in societies experiencing modernization and opportunities for lifestyle differentiation, conditions that may not have been met in some sites.

Adult↗