Brainstem cholinergic modulation of the limbic learning circuit
Kubota, Yasuo
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Permalink
https://hdl.handle.net/2142/20310
Description
Title
Brainstem cholinergic modulation of the limbic learning circuit
Author(s)
Kubota, Yasuo
Issue Date
1996
Doctoral Committee Chair(s)
Gabriel, Michael
Department of Study
Psychology
Discipline
Psychology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Neuroscience
Psychology, Psychobiology
Psychology, Physiological
Language
eng
Abstract
Training-induced neuronal activity (TIA) develops in the limbic (anterior and medial dorsal) thalamic nuclei and cingulate cortex as rabbits learned to locomote after a foot-shock predictive tone (CS+) and to ignore another tone (CS$-$) not predictive of shock (Gabriel et al., Behav. Brain Res., 1991, 46, 175-185). This study examined a role of cholinergic afferents to the anterior ventral (AV) thalamic nucleus in generation of excitatory (increase in CS-elicited neuronal activity during learning relative to before training) and discriminative (development of greater discharges in response to the CS+ than to the CS$-$) TIA. In Experiment 1, local injections of a cholinergic muscarinic receptor blocker, scopolamine, in the AV nucleus reduced avoidance responding and the amplitude of cingulate cortical excitatory TIA in rabbits trained to asymptotic performance. In Experiment 2, bilateral lesions in the brainstem laterodorsal tegmental (LDT) and pedunculopontine tegmental (PPT) nuclei, a primary source of AV thalamic cholinergic afferents, retarded acquisition of the avoidance response and attenuated excitatory TIA in the AV nucleus and posterior cingulate cortex during late stages of training. Experiment 3 demonstrated late-developing excitatory TIA in the LDT and PPT nuclei, as well as in the lateral mamillary and supramamillary nuclei. However, TIA in these areas could not account for all properties of excitatory TIA in the anterior thalamus.
These experiments demonstrated that the brainstem cholinergic system participates in the acquisition and performance of the avoidance response. These results and a previous finding that the transection of mamillothalamic tract (MTT) blocked AV thalamic excitatory TIA (Gabriel et al., J. Neurosci., 1995, 15, 1437-1445) supported a hypothetical model of AV thalamic excitatory TIA, describing cholinergic modulation of the mamillothalamic input through muscarinic M$\sb2$ receptors. Ineffectiveness of cholinergic disturbance on discriminative TIA (Experiments 1 and 2), a loss of AV thalamic discriminative TIA in rabbits with MTT transections (Gabriel et al., 1995), and development of discriminative TIA in the mamillary nuclei analogous to that in the anterior thalamic nuclei (Experiment 3) suggested that discriminative TIA is projected to the AV nucleus via the MTT and does not require interactions with cholinergic projections.
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