Biomedical subjects

T C Foster

Publications and source records attributed to T C Foster.

42 records · Page 3Linked to original sources

PubMed1987

Sequential dependencies regulate sensory evoked responses of single units in the rat hippocampus.

Unit activity from 3 major types of hippocampal cells were recorded from the CA1, CA3 and dentate granule cell layers of the hippocampus in awake freely moving rats. Units were classified as complex spike (ComSp), theta and dentate granule cells (G-cell) based on their spontaneous and stimulus-evoked firing characteristics. Single trial records for each cell type were collected during criterion performance of a two-tone discrimination task. Results showed that: tone-evoked discharges of theta- and G-cells, but not ComSp cells, were influenced by the reward status of the tone presented; the firing tendency of all cell types was significantly influenced by the preceding trial sequence; different types of preceding trial sequences including single and double alternation and runs of positive or negative trials significantly affected the firing tendency of all 3 cell types; the pattern of theta- and G-cell discharges differed with respect to latency to peak discharge and the duration of the discharge following long runs of similar trials. These effects were similar to previously described sequential influence on synaptically identified sensory evoked potentials in the dentate gyrus.

Acoustic Stimulation↗

PubMed1987

Processing of sensory information in the hippocampus.

The functional significance of the mammalian hippocampal formation is considered within the context of specific neural circuits responsible for the processing of sensory information. The anatomic and physiologic features of the major input pathways from the hypothalamus, septum, and entorhinal cortex are reviewed with regard to sensory activation of hippocampal cell fields. A model is presented which interrelates the functional plasticity of hippocampal synaptic processes to reciprocal connections between input and output pathways. The manner in which sensory responsiveness is modulated in the rat dentate gyrus as a function of both cognitive and behavioral factors is described. The hippocampus is discussed with respect to its role as a short-term item-specific store of behaviorally relevant sensory information.

Animals↗

PubMed1986

delta 9-Tetrahydrocannabinol differentially affects sensory-evoked potentials in the rat dentate gyrus.

The effects of low doses of delta 9-tetrahydrocannabinol (THC) on auditory-evoked potentials recorded from the outer molecular layer of the dentate gyrus of the rat hippocampus were assessed during performance of an auditory two-tone discrimination task. Conditioned behavior was disrupted up to 2 hr after i.p. injections of delta 9-THC at 1.0 to 2.0 mg/kg: responses to the rewarded stimulus decreased significantly and latency to respond increased significantly. Concurrent recordings indicated that these same doses of THC did not grossly distort the outer molecular layer averaged evoked potential waveform, but did produce opposing alterations in the amplitudes of the previously studied averaged evoked potential components N1 and N2. The amplitude of the N1 component was decreased significantly 0 to 2 hr after THC injection, whereas the amplitude of the N2 component increased significantly. THC injection at 0.5 mg/kg had no significant effects on performance or on N1 or N2 amplitudes. Recovery from the effects of 1.0 to 2.0 mg/kg of delta 9-THC was essentially complete 2 to 4 hr after injection for both measures of performance and for both N1 and N2 amplitudes. The results demonstrate that low doses of delta 9-THC distort behaviorally relevant sensory information converging on the dentate gyrus and support the hypothesis that the psychoactive effects of marijuana may be mediated by action within the hippocampus.

Animals↗

PubMed1986

Effects of delta 9-tetrahydrocannabinol on sensory-evoked discharges of granule cells in the dentate gyrus of behaving rats.

Extracellular action potentials were recorded from identified cells in the dentate gyrus of the awake freely moving rat during performance of a two-tone discrimination task. The effects of low doses of delta 9-tetrahydrocannabinol (delta 9-THC) were assessed on the firing patterns of granule cells to the tone stimuli. Intraperitoneal injections of delta 9-THC at 1.0 and 2.0 mg/kg, but not 0.5 mg/kg, produced a significant suppression of granule cell activity lasting up to 4 hr. This suppression was present in both the spontaneous (pretone) activity and tone-evoked responses of granule cells. The tone responses of cells recorded from the inferior colliculus were unaffected by THC injection at 1.0 and 2.0 mg/kg, implicating further the hippocampus as a site of specific action of delta 9-THC. In the preceding paper it was demonstrated that such doses produced both impairment of discrimination behavior and modifications of sensory-evoked potentials recorded from the dentate gyrus. However, the influence of delta 9-THC on cell firing in the dentate gyrus was more severe both in magnitude and duration of suppression than were the effects on behavior and on sensory-evoked potentials.

Animals↗

PubMed1985

Sequence-related changes in sensory-evoked potentials in the dentate gyrus: a mechanism for item-specific short-term information storage in the hippocampus.

Sensory-evoked potentials were recorded from the dentate gyrus of the rat hippocampus during performance of a differential auditory discrimination task. The short latency (20 ms) component (N1) of the sensory-evoked potential showed systematic amplitude fluctuations dependent upon the sequence of positive and negative trials preceding the presentation of a given trial and did not depend on the associated reward values of the individual tone stimuli which evoked the potential. The amplitude fluctuations could be accurately depicted by a model which retained the sequence for the five preceding trials in a "buffer" with exponentially decaying influence as a function of time of trial occurrence within the sequence. The results provide evidence that the hippocampus encodes accurate short-lasting representations of sensory events which can provide the basis for storage of information pertaining to past experiences.

Acoustic Stimulation↗

PubMedDate not supplied

Increase in perforant path quantal size in aged F-344 rats.

The data presented here confirm and extend the evidence for fewer, but stronger, perforant path synaptic connections onto the granule cells of the hippocampus in old F-344 rats. The old animals used in the present report were drawn from a population that showed deficits in the retention of a spatial problem in the Morris water task. Using the method of minimal-stimulation of perforant path afferents, unitary granule cell EPSPs were found to be larger in the 25-month than in the 6- and 9-month age groups. Furthermore, applying statistical methods for quantal analysis, data are presented that suggest that the larger synaptic responses of the old rats come about through an increase in quantal size. These experiments therefore suggest that individual synapses become more powerful in the perforant pathway of old rats, and that this strengthening occurs through an increase in quantal size. The implications of these findings for hippocampal information processing are discussed.

Aging↗