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P F Chapman

Publications and source records attributed to P F Chapman.

26 records · Page 2Linked to original sources
PubMed1990

Effects of lidocaine injection in the interpositus nucleus and red nucleus on conditioned behavioral and neuronal responses.

The role of the cerebellum and the red nucleus in the conditioned eyeblink response was assessed, using a combination of reversible lesions and multiple-unit extracellular recording in the awake, behaving rabbit. Lesion, recording, and stimulation experiments have indicated that both of these structures are involved in the performance of learned skeletal muscle responses. The present study sought to distinguish the relative contributions of the interpositus nucleus and the red nucleus to the expression of the learned response by recording behavior-related multiple unit activity in one structure while reversibly inactivating the other via injections of local anesthetic. Results indicate that inactivating either the interpositus or the red nucleus temporarily abolishes the learned eyeblink response. Injection of lidocaine into the interpositus also abolishes the neuronal unit model of the conditioned response in the red nucleus, while injection into the red nucleus does not affect the model in the interpositus. These results are consistent with the hypothesis that the red nucleus acts as a relay for motor commands from the cerebellum, and that the plasticity that generates conditioned responses occurs in the cerebellum or an afferent structure.

Animals↗
PubMed1990

Long-term synaptic potentiation in the amygdala.

The manner in which the circuitry of the amygdala computes its suspected mnemonic functions has been a mystery, partly because the cytoarchitectual complexity of this nuclear group has impeded the necessary cellular analysis. Here we report in vitro methods and results that may help elucidate cellular learning mechanisms in amygdala neurons. The amygdala brain slice preparation was combined with the single-electrode clamp (SEC) technique for intracellular analysis of membrane properties and synaptic responses. With respect to the active and passive membrane properties, we found considerable diversity among the population of cells that were sampled in the lateral and basolateral nuclei (n = 85). Synaptic inputs to these neurons were studied by stimulating the external capsule (EC), which was shown to produce a complex response that typically consisted of an excitatory followed by an inhibitory component. Based on several criteria, the excitatory component appeared to reflect a monosynaptic connection from the EC. One immediate goal was to discover whether the excitatory component displays the phenomenon of long-term potentiation (LTP)--a persistent increase in synaptic strength that can be induced by brief periods of the appropriate synaptic stimulation. Indeed, we found that high-frequency (100 Hz) stimulation of the EC induced LTP in 80% of the cells from which suitable recordings were obtained (n = 20). This finding of LTP in the amygdala is significant in regard to current efforts to explore linkages between this use-dependent form of synaptic plasticity and rapid kinds of associative learning.

Amygdala↗
PubMed1988

Long-term synaptic potentiation.

Long-term synaptic potentiation (LTP) is a leading candidate for a synaptic mechanism of rapid learning in mammals. LTP is a persistent increase in synaptic efficacy that can be quickly induced. The biophysical process that controls one type of LTP is formally similar to a synaptic memory mechanism postulated decades ago by the psychologist Donald Hebb. A key aspect of the modification process involves the N-methyl-D-aspartate (NMDA) receptor-ionophore complex. This ionophore allows calcium influx only if the endogenous ligand glutamate binds to the NMDA receptor and if the voltage across the associated channel is also sufficiently depolarized to relieve a magnesium block. According to one popular hypothesis, the resulting increase in the intracellular calcium concentration activates protein kinases that enhance the postsynaptic conductance. Further biophysical and molecular understanding of the modification process should facilitate detailed explorations of the mnemonic functions of LTP.

Animals↗
PubMed1988

Classical conditioning does not occur when direct stimulation of the red nucleus or cerebellar nuclei is the unconditioned stimulus.

The involvement of the cerebellum and the red nucleus in the classically conditioned nictitating membrane/eyeblink response in the rabbit is investigated using direct stimulation of the interpositus or the red nucleus as the unconditioned stimulus. Stimulation of either of these structures produced eye closure in naive animals, and this eye closure was paired with a tone in the standard Pavlovian conditioning paradigm. The results indicate that eyelid closure due to stimulation of either the red nucleus or the interpositus nucleus is not sufficient for the development of conditioned responses to the tone. Animals which had received interpositus stimulation as the unconditioned stimulus acquired the conditioned response to tone significantly faster following the substitution of air puff for stimulation than did those animals that had received red nucleus stimulation, or controls that did not receive any stimulation. However, animals that had been trained to tone-air puff could not retain the conditioned response after being switched to tone-interpositus stimulation. Lesions of the interpositus and the red nucleus through the stimulating electrodes were effective in impairing or abolishing conditioned responses. The results are interpreted to indicate that the red nucleus and interpositus are elements of the circuit that carries out the expression of the conditioned response. In addition the interpositus, but not the red nucleus, may be critical in the formation of the memory trace for the conditioned stimulus-unconditioned stimulus association, by virtue of the greatly accelerated learning that results from its stimulation.

Animals↗
PubMed1988

Videomicroscopy of acute brain slices from amygdala and hippocampus.

Video-enhanced contrast, differential-interference contrast microscopy (VEC-DICM) was used to visualize the cytoarchitecture and subcellular neuronal structure of acute brain slices from rat hippocampus and amygdala. Even at low-power magnification, the VEC-DICM system vastly improved our ability to visualize and examine the gross organization of the tissue. With medium-power magnification, the neuronal somata and proximal dendrites were clearly visible. With high-power magnification, some of the subcellular details could be clearly discerned--including cell nuclei, cell nucleoli, fine dendritic processes, and varicosities that may be synaptic expansions. We conclude that improved optical techniques should be valuable to cellular neurobiologists interested in structure-function relationships in brain slices.

Aging↗
PubMed1986

Classical conditioning of the rabbit eyelid response with a mossy-fiber stimulation CS: I. Pontine nuclei and middle cerebellar peduncle stimulation.

The nictitating membrane/eyelid responses of 18 rabbits were classically conditioned using cerebellar mossy-fiber stimulation as a conditioned stimulus (CS) and air puff as an unconditioned stimulus (US). The dorsolateral, lateral, and medial pontine nuclei and the middle cerebellar peduncle were effective stimulation-CS sites for training. In one group of rabbits, robust conditioned eyelid responses were produced with paired trials and subsequently extinguished with CS-alone and explicitly unpaired presentation of the CS and US. In a second group of rabbits, no conditioned responses were evident for 4 days of unpaired CS and US presentations. Conditioned responses did develop, however, after paired training was begun. Lesions of the interpositus nucleus of the cerebellum completely abolished the conditioned responses of a third group of rabbits overtrained with the mossy-fiber CS and air-puff US. These results support previous studies which have demonstrated that the cerebellum is critically involved in acquisition and retention of simple learned responses. In addition, the present results support previous theories of cerebellar function which have proposed that mossy fibers supply critical "learning" input to the cerebellum for acquisition and retention of motor skills.

Animals↗
PubMedDate not supplied

Long-term potentiation in vivo in layers II/III of rat barrel cortex.

Long-term potentiation was studied in vivo in the rat barrel cortex. It was found that LTP lasting several hours could be induced in layer II/III by tetanic stimuli applied in layer IV. The probability of inducing LTP at a given site was high (86%) provided that the electrodes were not displaced too far horizontally. LTP was not observed if the stimulating electrode was located on the far side of the neighbouring barrel-column from the recording electrode. The strongest LTP was induced by stimulating layer IV septal locations or the edge of the barrel and recording in the near half of the neighbouring barrel. However, examples were found of LTP from layer IV to II/III within the same barrel, within the same septum and from barrel to adjacent septum. The probability of inducing LTP on a particular occasion was greatly increased by iontophoresis of bicuculline at the recording site during the tetanus (from 20 to 55% judged by a change in peak amplitude). The average increase in the peak amplitude was 29 +/- 3.2% for protocol 1 (urethane anesthesia, monopolar stimulation) and 23 +/- 7% for protocol 2 (barbiturate anesthesia, bipolar stimulation). The probability of inducing LTP was greater if the first tetanus was accompanied by BMI application (67%) than for any subsequent attempts (39%). These results suggest it should be possible to study the effect of LTP on sensory processing in defined positions within the barrel field.

Animals↗