Search PubMed⌕ Search

Biomedical subjects

R F Thompson

Publications and source records attributed to R F Thompson.

At least 199 records · Page 11Linked to original sources
PubMed1978

Neuronal plasticity in the limbic system during classical conditioning of the rabbit nictitating membrane response. II: Septum and mammillary bodies.

Neuronal unit activity was recorded from several limbic system structures during classical conditioning of the rabbit nictiating membrane response to a tone CS. Air puff to cornea was used as a UCS. The present and past investigations of hippocampal activity using this paradigm show a neuronal plasticity which develops early in training, increases rapidly and shifts forward in time as behavioral conditioning develops. Recordings from the lateral septal region demonstrate the same within-trial pattern of unit discharge seen in hippocampus, indicating a projection of hippocampal plasticity over precommissural fornix pathways. Medial septal neurons, on the other hand, respond in an excitatory manner to the onsets of tone and air puff stimulation. While unit discharges seen in hippocampus and lateral septum occur only during the paired (learning) paradigm, medial septal activity is identical under both paired and unpaired (control) conditions. The latter fact lends support for a sensory interpretation of medial septal responses, and is consistent with anatomical evidence of a major septohippocampal projection originating from this region. In contrast to results for lateral septum, recordings from medial and lateral mammillary nuclei indicate only small, diffuse excitation that exhibits no consistent changes over training, and is not related to activity seen in hippocampal or septal regions. The apparent lack of correspondence between learning dependent unit measures obtained from pre- and postcommissural fornix structures is entirely consistent with current modified descriptions of limbic system anatomy.

Action Potentials↗
PubMed1978

Prediction of learning rate from the hippocampal electroencephalogram.

Samples of spontaneous electroencephalographic (EEG) activity from the dorsal hippocampus of rabbits were recorded immediately before classical conditioning of the nictitating membrane response. Computer analysis revealed a significant predictive relationship between EEG frequency characteristics and the subsequent rate of learning.

Animals↗
PubMed1978

Neuronal plasticity in the limbic system during classical conditioning of the rabbit nictitating membrane response. I. The hippocampus.

Hippocampal unit responses were recorded throughout classical conditioning of the rabbit nictitating membrane response to a tone conditioned stimulus (CS) using a corneal air-puff unconditioned stimulus (UCS). Multiple unit analysis revealed that a rapidly developing increase in cell discharges (relative to spontaneous activity) occurs within the first block of paired trials and continues to increment with subsequent training, initially in the UCS period and then in the CS period. The pattern of hippocampal activity within paired trials closely parallels the amplitude-time course of the behavioral response and precedes it temporally. Identical recordsings from animals given unpaired CS-alone and UCS-alone presentations showed no such changes. These control results and additional lines of evidence point to the critical necessity of the learning paradigm for the development of the hippocampal response seen in conditioning animals. A single unit analysis indicates that not all hippocampal neurons exhibit the described conditioned discharge pattern. Hippocampal long-term potentiation is considered as a possible mechanism for mediating this early and rapid neuronal plasticity dependent on specific 'contingent' patterns of stimulation.

Acoustic Stimulation↗
PubMed1978

Identification of pyramidal cells as the critical elements in hippocampal neuronal plasticity during learning.

The activity of single neurons recorded from rabbit hippocampus during classical conditioning of the nictitating membrane reflex was studied. All cells were first categorized according to their responses after fornix stimulation--i.i., antidromic activation, orthodromic activation, or no activation. The majority of cells that were antidromically activated--pyramidal cells--showed a highly positive correlation between the pattern of unit discharge and the topography of the nicititating membrane response within trial periods. Units that were orthodromically driven by fornix stimulation tended to inhibit during the presentation of trial stimuli, whereas most non-activated cells maintained low spontaneous levels of activity at all times. Thus, the major output neurons of the hippocampus appear to be the neuroanatomical substrate for the large and rapidly developing neuronal plasticity induced by this classical conditioning paradigm.

Action Potentials↗
PubMed1978

Descending fibres of the lateral funiculus of the amphibian spinal cord: their course and terminal distribution.

Descending fibres of the lateral funiculus (LF) of the spinal cord have been mapped in the adult bullfrog, Rana catesbeiana. Following large and small lesions of the cervical LF, Nauta preterminal and terminal degeneration staining techniques revealed a large bilateral projection to intermediate regions of the lumbar central grey. Dorsal LF fibres were seen only contralaterally, and ventral fibres mainly ipsilaterally, Medical LF fibre and terminal degeneration occurred bilaterally. Terminal fields of ipsilateral fibres often included the large motoneuron somata situated dorsolaterally in the ventral grey. The smaller contralateral contingent of fibres terminated most often in areas of the central grey dorsal or medial to the motoneuron pool.

Animals↗
PubMed1976

Neuronal substrate of classical conditioning in the hippocampus.

Neuronal activity in dorsal hippocampus was recorded in rabbits-during classical conditioning of nictitating membrane response, with tone as conditioned stimulus and corneal air puff as unconditioned stimulus. Unit activity in hippocampus rapidly forms a temporal neuronal "model" of the behavioral response early in training. This hippocampal response does not develop in control animals given unpaired stimuli.

Action Potentials↗
PubMed1976

Mechanisms of efferent neuronal control of the reflex nicitating membrane response in rabbit (Oryctolagus cuniculus)

Efferent mechanisms controlling the nicitating membrane (NM) reflex response to air puff in the albino rabbit were analyzed using stimulation, lesions, and recording techniques. In brief, stimulation of the sixth nerve (abducens) yields short-latency NM extension. Stimulation of the fourth and seventh nerves and the superior cervical ganglion has essentially no effect on the NM. Stimulation of the third nerve causes short-latency retraction of the NM. Lesions and recording data are consistent with this result - the sole efferent neuronal control of NM extension is the sixth cranial nerve and of NM retraction is the third cranial nerve. The NM extension response appears to be mediated by mechanical actions via retraction of the eyeball by the retractor bulbi muscle, and NM retraction appears to result from direct activation of muscle fibers in the NM by the third nerve. The superior cervical ganglion appears to play no role in reflex NM retraction in the rabbit, in contrast to its action in the cat.

Abducens Nerve↗
PubMed1976

Tone-induced changes in excitability of abducens motoneurons and of the reflex path of nictitating membrane response in rabbit (Oryctolagus cuniculus).

Excitability of the reflex nicitating membrane (NM) response to air puff and of the abducens motoneurons (final common path) to direct electrical stimulation (measured as amplitude of the evoked NM response) in rabbit was tested at various times after onset and offset of a 350-msec tone. Excitability to air puff showed a substantial increase during tone on a gradual decrease following tone off, in agreement with Ison and Leonard. Excitability of motoneurons showed a similar marked increase during tone on a transient decrease immediately following tone off, and then a gradual decrease. It is suggested that these excitability changes, which parallel closely the interstimulus-interval conditionability function reported by Gormezano for the same preparation, may provide an independent measure of the "molar stimulus trace". Excitability of abducens motoneurons tested in the intertrial intervals during subsequent tone-air puff conditioning showed no consistent changes. Surprisingly, animals given tone-abducens nucleus shock testing developed conditioned responses. In subsequent conditioning, using standard tone-air puff training, they showed 85% savings in acquisition relative to nonstimulated controls.

Abducens Nerve↗
PubMed1976

Habituation of a monosynaptic response in frog spinal cord: evidence for a presynaptic mechanism.

1. Using the isolated spinal cord of bullfrogs (Rana catesbeiana), intracellular correlates of habituation-like depression of the monosynaptic response elicited in motoneurons by lateral column (LC) stimulation were investigated. The following properties of the motoneuron were compared before and after response depression produced by stimulation of the LC at 0.5/s: resting membrane potential, membrane conductance, critical firing level, and rheobasic current. No alteration was found in any of these parameters. 2. To determine whether transmitter release mechanisms were changing over trials, the LC was stimulated with pairs of stimuli separated by 6 ms presented at 0.5/s. While the amplitude of the first EPSP declined (74% of initial value), the amplitude of the second EPSP increased (111% of initial value). Facilitation ratios thus increased. 3. The following conclusions can thus be drawn: 1) habituation involves a process intrinsic to the LC-motoneuron synapse; 2) habituation is not totally mediated by receptor desensitization; 3) habituation is not mediated by a mechanism extrinsic to the LC-motoneuron synapse that depolarizes terminal endings, e.g., presynaptic inhibition or accumulation of extracellular potassium; 4) habituation is not produced by transmitter depletion. Any of these possibilities has as a necessary consequence that facilitiation ratios remain unchanged. 4. Possible mechanisms that could mediate habituation are: 1) alterations in mobilization and/or release of transmitter; 2) decreased probability of invasion of terminal branches of the presynaptic fiber by the action potential.

Animals↗
PubMed1975

Unit activity in posterior association cortex of cat.

1. "Association" neurons in the posterior middle suprasylvian gyrus of cat were found to be predominantly polysensory, with 82% of the units in the chloralose-anesthetized preparation responding to auditory, visual, and somatic stimuli. There was no evidence of response differentiation associated with cortical depth distribution. Most units responded with a short-latency response (median 35-60 ms) to all stimulus modalities, with the response to visual stimulation occurring at the shortest latency. Among polysensory cells, almost half responded with equal probability to auditory, visual, and somatic stimulation. The visual stimulus was the most potent for those cells responding with a higher probability to a single modality. Varying degrees of response complexity were noted in some cells in terms of changes in responsivity over time, discharge to stimulus offset, and inhibition of spontaneous activity. The unitary discharge was seen to occur on the negative peak and slope of the locally recorded evoked potential. When only the larger amplitude spikes were analyzed, most of the unitary activity occurred on the negative peak of the evoked potential. Almost half of trimodally responsive cells displayed similar phase relationships between unitary activity and evoked potentials for all three modalities. The absolute refractory period for most cells was from 200 to 300 ms, with relative refractory periods extending up to 30 s...

Anesthesia, General↗