151
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Knowlton BJ, Thompson RF. Conditioning using a cerebral cortical conditioned stimulus is dependent on the cerebellum and brain stem circuitry. Behav Neurosci 1992. [PMID: 1616617 DOI: 10.1037//0735-7044.106.3.509] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Electrical stimulation of the auditory cortex (AC) was used as a conditioned stimulus (CS) in the rabbit conditioned eyeblink preparation to trace the functional anatomical connections between the AC and the circuitry underlying this conditioned response. Conditioning was shown to be dependent on the cerebellar interpositus nucleus and the pontine nuclei (PN), structures that are essential for conditioning using a peripheral CS. The results suggest that the cerebellum and associated brain stem circuitry are a necessary part of the memory trace circuit for the conditioned eyeblink response, even when the cerebral cortex is artifically engaged as a CS by electrical stimulation. The results also suggest that the PN are a site of convergence between the CS circuit subserving classical conditioning for peripheral stimuli and the AC, and may therefore be a site where the AC can modulate more elaborate forms of conditioning.
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152
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Dugich-Djordjevic MM, Tocco G, Willoughby DA, Najm I, Pasinetti G, Thompson RF, Baudry M, Lapchak PA, Hefti F. BDNF mRNA expression in the developing rat brain following kainic acid-induced seizure activity. Neuron 1992; 8:1127-38. [PMID: 1610567 DOI: 10.1016/0896-6273(92)90133-x] [Citation(s) in RCA: 155] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Brain-derived neurotrophic factor (BDNF) mRNA expression was studied in the hippocampus at various developmental stages in normal rats and following kainic acid (KA)-induced seizure activity. Systemic administration of KA strongly elevated BDNF mRNA levels in all hippocampal subregions after postnatal day 21. In contrast, even though KA induced intense behavioral seizure activity at postnatal day 8, the seizures were not associated with elevations of BDNF mRNA levels, indicating a clear dissociation between behavioral seizures and increases in BDNF mRNA levels and contradicting the view that BDNF mRNA expression is principally regulated by neuronal activity. In the dentate gyrus at postnatal day 13, intense BDNF mRNA expression was limited to a defined area at the border between granule cell and molecular layers, suggesting the possibility that segregation of BDNF mRNA into defined subcellular compartments may play a role in establishing the well-delineated patterns of innervation in the hippocampus.
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153
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Tocco G, Massicotte G, Standley S, Thompson RF, Baudry M. Phospholipase A2-induced changes in AMPA receptor: an autoradiographic study. Neuroreport 1992; 3:515-8. [PMID: 1382660] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
The expression of long-term potentiation and learning of a classical conditioning task increase [3H]-AMPA binding in hippocampus. Phospholipase A2 (PLA2) has been proposed to underly these changes, as PLA2 treatment of membrane preparations increases the affinity of AMPA receptors for agonists. We demonstrate here that preincubation of thin (10 microns) frozen rat brain sections with exogenous PLA2 and calcium at physiological temperature changes the binding properties of AMPA receptors. Quantitative autoradiography reveals that PLA2-treatment produces a differential increase in [3H]-AMPA binding across brain regions. The same treatment also decreases the binding of an antagonist ([3H]-CNQX) throughout the brain. We propose that PLA2 treatment results in a modification of the AMPA receptors which is regionally specific, probably due to different AMPA receptor subunit compositions.
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154
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Abstract
The key interrelated issues in the neurobiology of memory are to identify the neural circuitries essential for memory formation, localize sites of memory storage and analyze mechanisms of memory formation, storage and retrieval. Several circuits have now been identified in vertebrates and researchers are investigating their properties, in particular the role of glutamate receptors and long-term potentiation, in memory formation. Invertebrate preparations continue to be of value and recent studies suggest that changes in gene expression and protein synthesis may be important in long-term sensitization.
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155
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Thompson RF. Memory. Curr Biol 1992. [DOI: 10.1016/0960-9822(92)90526-g] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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156
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Weiss C, Thompson RF. Delayed acquisition of eyeblink conditioning in aged F1 hybrid (Fischer-344 x Brown Norway) rats. Neurobiol Aging 1992; 13:319-23. [PMID: 1522946 DOI: 10.1016/0197-4580(92)90045-y] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
We previously reported that the freely moving male Fischer-344 rat provides a useful model to demonstrate the progressive impairment of eyeblink conditioning associated with aging. However, because the youngest F-344 rats only performed at 60% of maximum, we ran the same experiment with hybrid rats and discovered most (i.e., those age 9-24 months) learned rapidly and exhibited conditioned responses on greater than 80% of trials by the end of two training sessions. In contrast, the aged rats (36 months) exhibited significantly fewer CRs on all four training days. However, unlike all ages of F-344 rats (3-30 months) which were run in our last study, these aged hybrid rats exhibited considerable improvement with extra training. These data indicate clear differences in the rate of learning between the two strains and suggest that even young F-344 rats may have deficits in the neural circuits which mediate eyeblink conditioning. Other anecdotal findings on differences between the two strains are noted.
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157
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Tocco G, Maren S, Shors TJ, Baudry M, Thompson RF. Long-term potentiation is associated with increased [3H]AMPA binding in rat hippocampus. Brain Res 1992; 573:228-34. [PMID: 1380390 DOI: 10.1016/0006-8993(92)90767-4] [Citation(s) in RCA: 89] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
The location and nature of the changes underlying long-term potentiation (LTP) remain controversial issues. In this study, we tested the possibility that changes in binding properties of the alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionate (AMPA/quisqualate and N-methyl-D-aspartate (NMDA) subtype of glutamate receptors are associated with LTP. LTP was elicited in vivo by stimulation of the perforant pathway in anesthetized rats. One hour following stimulation the animals were sacrificed. We performed quantitative ligand binding autoradiography on frozen brain sections using [3H]AMPA and [3H]N-(1-(2-thienyl)cyclohexyl)-3,4-piperidine ([3H]TCP) to label the AMPA/quisqualate and the NMDA receptors, respectively. No changes in [3H]TCP binding were detected in any of the treatment groups. However, increases in [3H]AMPA binding were observed only in animals that exhibited LTP. These increases were bilateral and present in several subfields of the hippocampus and cortical areas. Administration of the NMDA receptor antagonist, ketamine, prior to tetanic stimulation prevented both the increase in binding and the induction of LTP. These results suggest that changes in the characteristics of AMPA/quisqualate receptors are a biochemical correlate of LTP.
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158
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Knowlton BJ, Thompson RF. Conditioning using a cerebral cortical conditioned stimulus is dependent on the cerebellum and brain stem circuitry. Behav Neurosci 1992; 106:509-17. [PMID: 1616617 DOI: 10.1037/0735-7044.106.3.509] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Electrical stimulation of the auditory cortex (AC) was used as a conditioned stimulus (CS) in the rabbit conditioned eyeblink preparation to trace the functional anatomical connections between the AC and the circuitry underlying this conditioned response. Conditioning was shown to be dependent on the cerebellar interpositus nucleus and the pontine nuclei (PN), structures that are essential for conditioning using a peripheral CS. The results suggest that the cerebellum and associated brain stem circuitry are a necessary part of the memory trace circuit for the conditioned eyeblink response, even when the cerebral cortex is artifically engaged as a CS by electrical stimulation. The results also suggest that the PN are a site of convergence between the CS circuit subserving classical conditioning for peripheral stimuli and the AC, and may therefore be a site where the AC can modulate more elaborate forms of conditioning.
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159
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Swain RA, Shinkman PG, Nordholm AF, Thompson RF. Cerebellar stimulation as an unconditioned stimulus in classical conditioning. Behav Neurosci 1992; 106:739-50. [PMID: 1445654 DOI: 10.1037/0735-7044.106.5.739] [Citation(s) in RCA: 55] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Rabbits were implanted with chronic stimulating electrodes in white matter underlying lobule HVI of the cerebellar cortex. Stimulation elicited movements of the face or neck and, when paired with a tone conditioned stimulus (CS), produced learning comparable to that seen with peripheral unconditioned stimuli (USs). CS-alone trials produced extinction. Reinstatement of paired trials produced reacquisition with savings. Additional groups received either explicitly or randomly unpaired CS-US trials before paired conditioning. Low-frequency responding during these sessions indicated that the paired training results were associative and not due to pseudoconditioning or sensitization. Explicitly unpaired sessions retarded learning on subsequent paired trials compared with groups that received either randomly unpaired or no CS-US preexposure. These results are interpreted in terms of the role of the cerebellum and associated pathways in classical conditioning of motor responses.
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160
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Uenishi N, Shors TJ, Finch CE, Nichols NR, Thompson RF. Increased synthesis of two polypeptides in area CA1 of the hippocampus in response to repetitive electrical stimulation. Brain Res 1991; 567:248-52. [PMID: 1687806 DOI: 10.1016/0006-8993(91)90802-3] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Changes in the pattern of newly synthesized polypeptides were investigated in the in vitro hippocampal slice following exposure to repetitive stimulation with and without the induction of long-term potentiation. Using [35S]methionine labeling of polypeptides and two-dimensional gel electrophoresis, we detected an increase in the rate of synthesis of two polypeptides (48 kDa and 89 kDa) in CA1 in response to repetitive stimulation of the Schaffer collaterals. The synthesis of the 48 kDa polypeptide (pI approximately 6.6) increased 240% in response to high-frequency stimulation (100 Hz) relative to the same protein from unstimulated slices (n = 14), and increased 220% in response to low-frequency stimulation (1 Hz) (n = 5). Blockade of the N-methyl-D-aspartate (NMDA) receptor induced the protein 180%, with no further increase following tetanic stimulation. An 89 kDa doublet (pI approximately 6.8) increased 150% following high-frequency and 140% following low-frequency stimulation. Blockade of the NMDA receptor increased this protein as well (180% of the unstimulated control) and no further increase was observed following high-frequency stimulation. Based on physicochemical and electrophysiological properties, these proteins are not identifiable as any of those previously associated with long-term potentiation or repetitive electrical stimulation.
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161
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Tocco G, Devgan KK, Hauge SA, Weiss C, Baudry M, Thompson RF. Classical conditioning selectively increases AMPA receptor binding in rabbit hippocampus. Brain Res 1991; 559:331-6. [PMID: 1665385 DOI: 10.1016/0006-8993(91)90020-v] [Citation(s) in RCA: 57] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The NMDA and AMPA receptors have been shown to play critical roles in various forms of synaptic plasticity (learning and memory, long-term potentiation). The present study investigated the involvement of these two receptors in a well-characterized classical conditioning paradigm. Following classical conditioning of the rabbit nictitating membrane the binding properties of these two subclasses of excitatory amino acid transmitter receptors were analyzed in dorsal hippocampi by quantitative autoradiography. [3H] TCP and [3H] AMPA were used to identify the NMDA and AMPA receptors, respectively. The binding of [3H]TCP to the NMDA receptor remained unchanged in all the experimental groups tested. Paired presentations of the conditioned and unconditioned stimuli resulted in increased [3H] AMPA binding to the AMPA receptor in several subfields of the hippocampus, while unpaired presentations had no significant effects. The increase in binding was due to an increased affinity of the low-affinity component of the AMPA receptor. The results support the hypothesis that changes in glutamate receptors participate in the synaptic plasticity involved in certain forms of learning.
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162
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Tocco G, Shors TJ, Baudry M, Thompson RF. Selective increase of AMPA binding to the AMPA/quisqualate receptor in the hippocampus in response to acute stress. Brain Res 1991; 559:168-71. [PMID: 1664274 DOI: 10.1016/0006-8993(91)90302-c] [Citation(s) in RCA: 52] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The binding properties of ligands specific for two subclasses of glutamate receptors were studied by quantitative autoradiography after one hour of acute immobilization/shock stress. [3H]N-(1-(2-thienyl)cyclohexyl)-3,4-piperidine (TCP) and [3H]alpha-amino-3-methylisoxazole-4-propionic acid (AMPA) were used to visualize the N-methyl-D-aspartate receptor and the AMPA/quisqualate receptor types, respectively. While no change was observed in the binding properties of the [3H]TCP, [3H]AMPA binding was significantly increased in several areas of the hippocampus of acutely stressed rats relative to naive controls.
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163
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Schreiber SS, Maren S, Tocco G, Shors TJ, Thompson RF. A negative correlation between the induction of long-term potentiation and activation of immediate early genes. BRAIN RESEARCH. MOLECULAR BRAIN RESEARCH 1991; 11:89-91. [PMID: 1662748 DOI: 10.1016/0169-328x(91)90025-s] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
In the present study we examined the relationship between the induction of long-term potentiation (LTP) in the dentate gyrus of anesthetized rats and activation of immediate early genes (IEGs; c-fos and zif/268) using several different high-frequency stimulation paradigms. Stimulation parameters that effectively induced LTP were not associated with IEG activation. Conversely, stimulation parameters that failed to induce LTP consistently resulted in IEG activation. These results suggest that there is a negative correlation between IEG activation and LTP, and that activation of IEGs is neither necessary nor sufficient for the induction of LTP.
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164
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Nordholm AF, Lavond DG, Thompson RF. Are eyeblink responses to tone in the decerebrate, decerebellate rabbit conditioned responses? Behav Brain Res 1991; 44:27-34. [PMID: 1910568 DOI: 10.1016/s0166-4328(05)80236-0] [Citation(s) in RCA: 30] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Bloedel and associates recently claimed to have established conditioned eyeblink responses in the acute decerebrate, decerebellate rabbit. Their training procedure was extreme massed practice (mean intertrial interval of 9 s) and they used an idiosyncratic definition of the conditioned response (10% or more of the unconditioned response amplitude). They did not measure or control the excitability of their preparations and did not run any separate control groups for alpha responses, alpha conditioning or pseudoconditioning. Using normal animals we compared their training procedure with procedures standard in the field and analyzed the consequences of their scoring procedure. Our group trained at a 30-s intertrial interval (ITI) showed clear learning in the training session. In marked contrast, 3 groups trained at a 9-s ITI developed no conditioned responses. We also found that the method of scoring used by Bloedel and associates counts many spontaneous responses as conditioned responses (CRs) if unconditioned response (UR) amplitudes are low, excludes genuine CRs if UR amplitudes are high and does not control for the occurrence of spontaneous responses. It must therefore be concluded that the eyeblink responses to tone reported by Bloedel and associates to occur in the decerebrate, decerebellate rabbit are not associative CRs as they develop in the normal animal.
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165
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Maren S, Baudry M, Thompson RF. Differential effects of ketamine and MK-801 on the induction of long-term potentiation. Neuroreport 1991; 2:239-42. [PMID: 1832985 DOI: 10.1097/00001756-199105000-00006] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Ketamine and MK-801 are phencyclidine (PCP)-like noncompetitive antagonists of the N-methyl-D-aspartate (NMDA) receptor that produce a use-dependent blockade of the NMDA receptor-coupled channel. Recent studies have suggested that the binding properties of these drugs to the NMDA receptor in-vitro are different. In the present study, the effects of ketamine and MK-801 on the induction of long-term potentiation (LTP) were compared at perforant path--granule cell synapses in anaesthetized rats. LTP was observed in animals treated with either saline or MK-801, but not in those treated with ketamine. These results reveal that ketamine and MK-801 differentially modulate the induction of LTP, and we propose that this differential modulation may be related to the different binding properties of the drugs.
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166
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Weiss C, Thompson RF. The effects of age on eyeblink conditioning in the freely moving Fischer-344 rat. Neurobiol Aging 1991; 12:249-54. [PMID: 1876231 DOI: 10.1016/0197-4580(91)90105-s] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
The effects of age were assessed on the ability of male Fischer-344 rats to acquire a classically conditioned eyeblink using the "delay" paradigm. Using a 350 ms white noise conditioning stimulus and a 100 ms coterminating periorbital shock (2 mA, 60 Hz, AC) we have demonstrated that these rats exhibit deficits as early as middle age. Middle-aged and senescent rats (18 and 30 months) exhibited significantly fewer conditioned responses than young rats (3 and 12 months). Since all of the rats responded to a test noise, and there were no differences in threshold to evoke a blink, this result is likely to be due to an associative deficit. Thus, our results indicate that eyeblink conditioning in the freely moving rat is a useful model system for behavioral and neurobiological analyses of the effects of age on associative learning and memory.
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167
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Bartha GT, Thompson RF, Gluck MA. Sensorimotor Learning and the Cerebellum. RESEARCH NOTES IN NEURAL COMPUTING 1991. [DOI: 10.1007/978-3-642-84545-1_25] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
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168
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Abstract
Evidence supports the view that "memory traces" are formed in the hippocampus and in the cerebellum in classical conditioning of discrete behavioral responses (e.g. eyeblink conditioning). In the hippocampus, learning results in long-lasting increases in excitability of pyramidal neurons that appear to be localized to these neurons (i.e. changes in membrane properties and receptor function). However, these learning-altered pyramidal neurons are distributed widely throughout CA3 and CA1. Although it plays a key role in certain aspects of classical conditioning, the hippocampus is not necessary for learning and memory of the basic conditioned responses. The cerebellum and its associated brain stem circuitry, on the other hand, does appear to be essential (necessary and sufficient) for learning and memory of the conditioned response. Evidence to date is most consistent with a localized trace in the interpositus nucleus and multiple localized traces in cerebellar cortex, each involving relatively large ensembles of neurons. Perhaps "procedural" memory traces are relatively localized and "declarative" traces more widely distributed.
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169
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Abstract
We used in-situ hybridization to study the effect of acute stress on induction of the immediate early genes (IEGs), c-fos and zif/268, in the rat brain. After one hour of restraint plus intermittent tail shock, messenger RNA (mRNA) levels for both genes were significantly increased bilaterally in the neocortex, particularly in layers IV, V and VI, and in the CA1 region of the hippocampus. This regionally-specific response suggests that IEGs may have a role in the mediation of acute stress responses in the central nervous system.
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170
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Chapman PF, Steinmetz JE, Sears LL, Thompson RF. Effects of lidocaine injection in the interpositus nucleus and red nucleus on conditioned behavioral and neuronal responses. Brain Res 1990; 537:149-56. [PMID: 2085770 DOI: 10.1016/0006-8993(90)90351-b] [Citation(s) in RCA: 66] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
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.
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171
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Woodruff-Pak DS, Logan CG, Thompson RF. Neurobiological substrates of classical conditioning across the life span. Ann N Y Acad Sci 1990; 608:150-73; discussion 174-8. [PMID: 2075952 DOI: 10.1111/j.1749-6632.1990.tb48896.x] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
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172
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173
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Austrom MG, Thompson RF, Hendrie HC, Norton J, Farlow MR, Edwards MK, Dean R. Foci of increased T2 signal intensity in MR images of healthy elderly subjects. A follow-up study. J Am Geriatr Soc 1990; 38:1133-8. [PMID: 2229868 DOI: 10.1111/j.1532-5415.1990.tb01377.x] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
An 18-month follow-up study was conducted on 26 healthy elderly subjects with and without foci of increased T2 signal intensity on MR imaging. The subjects did not differ with respect to health status or cognitive performance as measured by the Cognitive Subscale of the Cambridge Mental Disorders of the Elderly Examination and the Mini Mental State Examination at follow-up. There was a significant decline in performance on the Digit Symbol Substitution Test in subjects who had evidence of T2 foci compared to the performance of subjects without T2 foci. This may indicate that the presence of T2 foci is correlated with subtle difficulties in learning and memory.
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174
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Thompson RF. Neural mechanisms of classical conditioning in mammals. Philos Trans R Soc Lond B Biol Sci 1990; 329:161-70. [PMID: 1978361 DOI: 10.1098/rstb.1990.0161] [Citation(s) in RCA: 170] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Evidence supports the view that 'memory traces' are formed in the hippocampus and in the cerebellum in classical conditioning of discrete behavioural responses. In the hippocampus learning results in long-lasting increases in excitability of pyramidal neurons that resemble the phenomenon of long-term potentiation. Although it plays a role in certain aspects of conditioning, the hippocampus is not necessary for learning and memory of the basic conditioned responses. The cerebellum and its associated brain-stem circuitry, on the other hand, does appear to be essential (necessary and sufficient) for learning and memory of the conditioned response. Evidence to date supports the view that mossy fibre convey conditioned stimulus information and that climbing fibres conveys the critical 'reinforcement' information to the cerebellum and that 'memory traces' appear to be formed in cerebellar cortex and interpositus nucleus.
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175
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Shors TJ, Foy MR, Levine S, Thompson RF. Unpredictable and uncontrollable stress impairs neuronal plasticity in the rat hippocampus. Brain Res Bull 1990; 24:663-7. [PMID: 2192774 DOI: 10.1016/0361-9230(90)90005-k] [Citation(s) in RCA: 81] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Almost by definition, learning and the effect of stress on learning represent modifications of existing neuronal circuitry. Under some circumstances, this modification can be measured electrophysiologically. One such measure of plasticity is long-term potentiation (LTP), a long-lasting increase in synaptic efficacy following brief exposure to tetanic stimulation. In 1987, Foy et al. reported that hippocampal LTP was impaired by exposure to inescapable shock. We have recent evidence that the impairment in LTP can be prevented by allowing the animal to learn to escape the shock (Shors et al., 1989), indicating that the stress effect is to some extent mediated by "psychological" variables. Regardless of LTP's putative role in learning and memory processes, such a stress-induced decrease in neuronal plasticity is likely to have profound effects on the behaving organism.
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