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Biomedical subjects

R F Thompson

Publications and source records attributed to R F Thompson.

At least 163 records · Page 9Linked to original sources
PubMed1984

Effect of bilateral lesions of the dentate and interpositus cerebellar nuclei on conditioning of heart-rate and nictitating membrane/eyelid responses in the rabbit.

It has been shown that unilateral lesions of the medial dentate/lateral interpositus nuclear region of the cerebellum abolish the learned nictitating membrane (NM)/eyelid response of the eye ipsilateral to the lesion. The present study examined the effects of bilateral cerebellar lesions on acquisition of heart-rate conditioning (often viewed as a measure of 'conditioned fear') and both its short-and long-term effects on NM/eyelid learning and relearning. The results demonstrate that cerebellar lesions that completely and permanently abolish acquisition or retention of the somatic response (NM/eyelid) bilaterally have no effect on heart-rate conditioning. The neuronal circuits necessary for learning of the heart-rate response and for learning of the adaptive somatic response are thus in significant part different. Results are tentatively interpreted within the context of a two-process theory of aversive learning: an initial phase indexed by conditioned autonomic and 'non-specific' responses such as heart-rate and a subsequent phase of learning the specific adaptive responses.

Animals↗
PubMed1984

The pattern of monosynaptic Ia-connections to hindlimb motor nuclei in the baboon: a comparison with the cat.

The pattern of Ia-connections to motor nuclei of 17 hindlimb muscles (or groups of muscles) has been investigated in baboons by intracellular recording of Ia-e.ps.p.s evoked in motoneurons from different muscle nerves. The amplitudes are normalized to 70 mV resting potential and compared with similarly normalized Ia-e.ps.p.s in cats. As in the cat, Ia-excitation is drawn from a restricted number of muscles and the homonymous effect is usually dominating. Heteronymous connections to many motor nuclei are different in the two species. For example, hip extensors are generally more Ia-isolated from each other in baboons than in cats, and also knee flexors have fewer Ia-interconnections than in cats. A unidirectional Ia-synergism between some hip extensors and knee flexors in cats has changed to a bidirectional one in baboons, with a tendency to lateralization of the connections. Among ankle extensors, soleus has smaller heteronymous Ia-connections from its synergic ankle extensors than in cats. In baboons, plantaris is heteronymously Ia-excited from gastrocnemius-soleus but not from the intrinsic plantar muscles; whereas in cats there exists a considerable Ia-projection from the intrinsic plantar muscles but not from gastrocnemius-soleus. There is a corresponding difference in the insertion of the plantaris tendon, which shows that this muscle acts as toe extensor in cats but as ankle extensor in baboons. For most of the motor nuclei, the homonymous as well as the total aggregate of Ia-e.ps.p.s is smaller in the baboon than in the cat; but the amplitude range between different motor nuclei is larger in the baboon. Reciprocal Ia-i.ps.p.s are evoked only after spinal transection or when brain function is depressed. It is postulated that baboons, contrary to cats, have descending tonic inhibition of transmission in the reciprocal Ia-inhibitory pathway. The phylogenetic flexibility of Ia-connections is discussed and contrasted with their ontogenetic stability.

Action Potentials↗
PubMed1984

Cerebellum: essential involvement in the classically conditioned eyelid response.

Classical conditioning of the eyelid response in the rabbit was used to investigate the neuronal structures mediating basic associative learning of discrete, adaptive responses. Lesions of the ipsilateral dentate-interpositus nuclei, but not of the cerebellar cortex, abolished the learned eyeblink response. Recordings from these nuclei have revealed neuronal responses related to the learning of the response. Stimulating these recording sites produced the eyelid response. The dentate-interpositus nuclei were concluded to be critically involved in the learning and production of classically conditioned responses.

Acoustic Stimulation↗
PubMed1984

Effects of lesions of cerebellar nuclei on conditioned behavioral and hippocampal neuronal responses.

Rabbits were overtrained using classical conditioning of the rabbit nictitating membrane (NM)/eyelid response. Unilateral electrolytic lesions were then made through electrodes previously implanted in dentate and interpositus cerebellar nuclei ipsilateral to the trained (left) eye. Lesions caused a complete or near-complete abolition of conditioned behavioral responses on the ipsilateral side, but had no effect on unconditioned responses to corneal airpuff. When training was switched to the contralateral (right) side, animals learned within the first few trials, but did not relearn when training was returned to the left (lesioned) side. Control animals in which lesions spared the deep nuclei showed no such learning deficits. Lesions of cerebellar nuclei also abolished conditioned increases in hippocampal CAl neural activity evoked by the tone conditioned stimulus in this paradigm. As with the behavior, training on the right (non-lesioned) side reinstated the conditioned neuronal response within the first few trials of training, even though behavioral responding on lesioned side showed little or no improvement. These results indicate that the cerebellum is an essential structure for the behavioral expression of learning, and plays an important role in the generation of conditioned hippocampal responses observed in this paradigm.

Animals↗
PubMed1984

Amygdaloid unit activity during classical conditioning of the nictitating membrane response in rabbit.

Single and multiple unit activity was recorded from the amygdaloid nuclei in awake unanesthestized rabbits during classical conditioning of the nictitating membrane (NM) response. Over half o the unit recordings from the amygdaloid complex demonstrated changes in firing rate following the presentation of the tone conditioned stimulus (CS) or corneal air-puff unconditioned stimulus (US). Of the unit records that were responsive to the training stimuli, 58% showed responses to the CS and 73% showed responses to the US. Amygdaloid responses to either the CS or the US tended to be a long latency (greater than 70 msec), long duration (greater than 250 msec), modest increase (less than 2 fold) in unit firing. There were no statistically significant differences between the spontaneous firing rates, response latencies, response magnitudes, or response type distributions seen during unpaired (control) and paired stimulus presentations. However, four of 18 single and multiple unit groups that were tested during both unpaired and paired training developed new or enhanced responses following the onset of paired training. All four of these records were from the basolateral or lateral amygdaloid nuclei. Although these few records did develop response alterations after CS-US pairing, the majority of the records indicated that essentially the same amygdaloid response patterns occur during unpaired training as during paired training. it is therefore unlikely that the critical neuronal changes that underlying NM conditioning occur within the amygdaloid complex. Other possible roles for the amygdaloid complex during conditioning are considered.

Acoustic Stimulation↗
PubMed1984

Increased responsivity of dentate granule cells during nictitating membrane response conditioning in rabbit.

We examined the responsivity of dentate gyrus granule cells to perforant path stimulation during classical conditioning of the rabbit nictitating membrane response. Dentate field potentials elicited by perforant path stimulation were recorded during training to test for changes in granule cell responsivity. Results showed above-baseline increases in dentate population spike amplitudes over the course of training in paired but not unpaired animals. In addition, population spike amplitudes were smaller when elicited during tone presentations in both paired and unpaired animals than between trials when no conditioning stimuli were present. While alternative interpretations remain, these results provide preliminary evidence that processes similar to long-term potentiation may occur in the hippocampus during behavioral conditioning.

Action Potentials↗
PubMed1984

Classical conditioning of the rabbit eyelid response increases glutamate receptor binding in hippocampal synaptic membranes.

Hippocampal pyramidal neurons exhibit a rapid within-trial increase in firing frequency during classical conditioning of the rabbit eyelid response. It has been proposed that the cellular mechanisms responsible for hippocampal long-term potentiation (LTP) may also mediate this learning-dependent increase in neuronal activity. The induction of LTP in rat hippocampal slices results in an increase in the number of [3H]glutamate-binding sites in the potentiated region. The present study investigates the kinetics of [3H]glutamate binding to hippocampal synaptic membranes after eyelid conditioning in the rabbit. We report that the regional distribution of [3H]glutamate binding across the layers of rabbit hippocampus is compatible with a dendritic localization. The pharmacological and ionic properties of the binding suggest that it is associated with an excitatory amino acid receptor. After eyelid conditioning, the maximal number of hippocampal [3H]glutamate-binding sites is increased in animals receiving paired presentations of the tone conditioned stimulus and corneal air-puff unconditioned stimulus relative to that found in naive or unpaired control animals. These results strengthen the hypothesis that an LTP-like mechanism underlies the increase in hippocampal firing frequency during rabbit eyelid conditioning.

Animals↗
PubMed1984

Neuronal responses of the rabbit cerebellum during acquisition and performance of a classically conditioned nictitating membrane-eyelid response.

Neuronal activity was recorded from regions of the cerebellar cortex and dentate-interpositus nuclei during learning and/or performance of a classically conditioned nictitating membrane (NM-a third eyelid)/eyeblink response in the rabbit. It was found that neurons located within restricted portions of the ansiform lobule and anterior lobe cortical regions and of the dentate-interpositus nuclei respond in relation to the performance of the learned eyeblink response. Furthermore, chronic recordings from the dentate-interpositus nuclei revealed that these responses develop in close relation to the learning of the conditioned eyeblink response. Stimulation of the dentate-interpositus nuclei through the recording electrodes in some cases yielded eyelid closure and NM extension in both trained and untrained animals. Lesion of the axons of the dentate-interpositus nuclei (superior cerebellar peduncle), a manipulation which is known to abolish the learned eyeblink response, abolished the stimulation effect. We have previously reported that lesions of the dentate-interpositus nuclei cause abolition of the learned eyeblink response. In the present study, we report that lesions of the regions of cerebellar cortex projecting to the dentate-interpositus nuclei do not permanently abolish the conditioned response, although the amplitude-time course of the learned response could be affected. These results, together with results of other studies, demonstrate that the medial dentate and/or lateral interpositus nuclei are active during learning and performance of the conditioned eyeblink response, are capable of producing this learned response, and are essential for the learning and retention of the conditioned eyeblink response. Therefore, the medial dentate and/or lateral interpositus nuclei are a part of the essential neuronal circuit involved in the learning and production of the classically conditioned eyeblink response in the rabbit.

Acoustic Stimulation↗
PubMed1983

Neuronal responses of the rabbit brainstem during performance of the classically conditioned nictitating membrane (NM)/eyelid response.

Through the use of a chronic microdrive recording system, neuronal unit activity was recorded throughout the brainstem of the rabbit during performance of the classically conditioned nictitating membrane (NM) extension/eyeblink response using an acoustical conditioned stimulus (CS) and a corneal airpuff unconditioned stimulus (UCS). Regions which exhibited neuronal responses near the onset of the learned response were found to be relatively localized to: the abducens, accessory abducens, and facial nuclei (the motoneurons known to innervate the muscles responsible for expression of the conditioned response); the sensory nuclei of the fifth (probably representing somatosensory or proprioceptive feedback from the conditioned response); the superior colliculus; the periaqueductal gray; various reticular regions and the brainstem nuclei directly connected with the cerebellum (pontine nuclei, tegmental reticular nucleus (Bechterew), red nucleus, and perhaps the inferior olive). Stimulus (tone-airpuff) evoked responses were found within all classical auditory nuclei of the brainstem; the superior colliculus; the periaqueductal gray; pontine nuclei; fifth sensory nuclei, and various reticular regions. Recent lesion studies have shown the ipsilateral cerebellum to be essential for the learning and retention of this response. Collectively these results indicate that the cerebellum and its related brainstem nuclei are critically involved in the control and production of the classically conditioned NM/eyeblink response and may contain essential long term neuronal changes--the 'memory trace'--which serves to encode this learned response.

Acoustic Stimulation↗
PubMed1983

Abolition of conditioned heart-rate responses in rabbits following central administration of [N-MePhe3, D-Pro4] morphiceptin.

Rabbits were initially habituated to a tone and then give 15-20 paired trials where the tone was followed by periorbital shock resulting in conditioned heart-rate decelerations to tone onset and an acceleration of heart-rate following shock offset. The animals were matched for learning performance and divided into two groups. Each animal received a microinfusion into the region of the fourth ventricle of either the opiate [N-MePhe3,D-Pro4] morphiceptin, a highly selective mu receptor agonist, or a mixture of the morphiceptin analogue and the opiate antagonist naltrexone. Administration of the morphiceptin analogue eliminated the conditioned bradycardia to the tone but not the acceleration to the shock. Rabbits given the mixture continued to show conditioned heart-rate decelerations. Previous studies have shown that opiates abolish a recently learned conditioned nictitating membrane response. These effects are consistent with the hypothesis that the opiate effect on conditioning is due to an attenuation of conditioned fear.

Acoustic Stimulation↗
PubMed1983

Acute ethanol treatment modifies response properties and habituation of the DR-VR reflex in the isolated frog spinal cord.

Ethanol modification of habituation, a fundamental form of behavioral plasticity, was examined in the isolated frog spinal cord preparation. The polysynaptic dorsal root to ventral root (DR-VR) reflex response was assessed in normal Ringer's and at one of four ethanol concentrations. The reflex itself was facilitated at lower levels (0.025%) and depressed at higher levels (0.05-0.5%) of ethanol. Habituation, decrement of the polysynaptic ventral root response to repeated dorsal root stimulation, was reduced at all ethanol concentrations. Understanding the mechanisms of ethanol action involved in the disruption of simple forms of plasticity will help us to explain its actions on more complex forms of associational processes.

Animals↗
PubMed1983

Single-unit analysis of different hippocampal cell types during classical conditioning of rabbit nictitating membrane response.

Extracellular single-unit recordings from neurons in the CA1 and CA3 regions of the dorsal hippocampus were monitored during classical conditioning of the rabbit nictitating membrane response. Neurons were classified as different cell types using response to fornix stimulation (i.e., antidromic or orthodromic activation) and spontaneous firing characteristics as criteria. Results showed that hippocampal pyramidal neurons exhibit learning-related neural plasticity that develops gradually over the course of classical conditioning. The learning-dependent pyramidal cell response is characterized by an increase in frequency of firing within conditioning trials and a within-trial pattern of discharge that correlates strongly with amplitude-time course of the behavioral response. In contrast, pyramidal cell activity recorded from control animals given unpaired presentations of the conditioned and unconditioned stimulus (CS and UCS) does not show enhanced discharge rates with repeated stimulation. Previous studies of hippocampal cellular electrophysiology have described what has been termed a theta-cell (19-21, 45), the activity of which correlates with slow-wave theta rhythm generated in the hippocampus. Neurons classified as theta-cells in the present study exhibit responses during conditioning that are distinctly different than pyramidal cells. theta-Cells respond during paired conditioning trials with a rhythmic bursting; the between-burst interval occurs at or near 8 Hz. In addition, two different types of theta-cells were distinguishable. One type of theta-cell increases firing frequency above pretrial levels while displaying the theta bursting pattern. The other type decreases firing frequency below pretrial rates while showing a theta-locked discharge. In addition to pyramidal and theta-neurons, several other cell types recorded in or near the pyramidal cell layer could be distinguished. One cell type was distinctive in that it could be activated with a short, invariant latency following fornix stimulation, but spontaneous action potentials of such neurons could not be collided with fornix shock-induced action potentials. These neurons exhibit a different profile of spontaneous firing characteristics than those of antidromically identified pyramidal cells. Nevertheless, neurons in this noncollidable category display the same learning-dependent response as pyramidal cells. It is suggested that the noncollidable neurons represent a subpopulation of pyramidal cells that do not project an axon via the fornix but project, instead, to other limbic cortical regions.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1982

Locus coeruleus lesions and resistance to extinction of a classically conditioned response: involvement of the neocortex and hippocampus.

Bilateral electrolytic lesions of the locus coeruleus were made in rabbits prior to classical conditioning of the nictitating membrane (NM) response. After recovery, the animals received one session of unpaired training followed by 3 days of paired acquisition training and 4 days of unpaired training (extinction). At the end of extinction norepinephrine (NE) and dopamine (DA) levels were measured in several brain regions. Each lesioned animal was placed into one of two groups according to whether or not the animal exhibited a significant depletion of cortical/hippocampal NE. A third group was formed by non-lesioned controls. There were no significant differences between the 3 groups during acquisition; however, during days 3 and 4 of unpaired extinction the group with cortical/hippocampal NE depletion showed significantly larger NM responses on the conditioned stimulus-alone trials than either of the two control groups. This extinction deficit appeared mainly in the unconditioned stimulus-period component of the tone-alone conditioned responses. The magnitude of the extinction deficit was highly correlated with the depletion of NE in both cortical and hippocampal samples but not with the depletion of NE in the hypothalamus/mid-thalamus, or cerebellum.

Animals↗