Cholinergic systems in the rat brain: III. Projections from the pontomesencephalic tegmentum to the thalamus, tectum, basal ganglia, and basal forebrain.
ABSTRACT The ascending cholinergic projections of the pedunculopontine and dorsolateral tegmental nuclei, referred to collectively as the pontomesencephalotegmental (PMT) cholinergic complex, were investigated by use of fluorescent tracer histology in combination with choline-O-acetyltransferase (ChAT) immunohistochemistry and acetylcholinesterase (AChE) pharmacohistochemistry. Propidium iodide, true blue, or Evans blue was infused into the anterior, reticular, mediodorsal, central medial, and posterior nuclear areas of the thalamus; the habenula; lateral geniculate; superior colliculus; pretectal/parafascicular area; subthalamic nucleus; caudate-putamen complex; globus pallidus; entopeduncular nucleus; substantia nigra; medial septal nucleus/vertical limb of the diagonal band area; magnocellular preoptic/ventral pallidal area; and lateral hypothalamus. In some animals, separate injections of propidium iodide and true blue were made into two different regions in the same rat brain, usually a dorsal and a ventral target, in order to assess collateralization patterns. Retrogradely transported fluorescent labels and ChAT and/or AChE were analyzed microscopically on the same brain section. All of the above-delimited targets were found to receive cholinergic input from the PMT cholinergic complex, but some regions were preferentially innervated by either the pedunculopontine or dorsolateral tegmental nucleus. The former subdivision of the PMT cholinergic complex projected selectively to extrapyramidal structures and the superior colliculus, whereas the dorsolateral tegmental nucleus was observed to provide cholinergic input preferentially to anterior thalamic regions and rostral portions of the basal forebrain. The PMT cholinergic neurons showed a tendency to collateralize extensively.
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ABSTRACT: Neurobiological oscillations are regarded as essential to normal information processing, including coordination and timing of cells and assemblies within structures as well as in long feedback loops of distributed neural systems. The hippocampal theta rhythm is a 3-12 Hz oscillatory potential observed during cognitive processes ranging from spatial navigation to associative learning. The lower range, 3-7 Hz, can occur during immobility and depends upon the integrity of cholinergic forebrain systems. Several studies have shown that the amount of pre-training theta in the rabbit strongly predicts the acquisition rate of classical eyeblink conditioning and that impairment of this system substantially slows the rate of learning. Our lab has used a brain-computer interface that delivers eyeblink conditioning trials contingent upon the explicit presence or absence of hippocampal theta. A behavioral benefit of theta-contingent training has been demonstrated in both delay and trace forms of the paradigm with a two- to four-fold increase in learning speed. This behavioral effect is accompanied by enhanced amplitude and synchrony of hippocampal local field potentials, multiple-unit excitation, and single-unit response patterns that depend on theta state. Additionally, training in the presence of hippocampal theta has led to increases in the salience of tone-induced unit firing patterns in the medial prefrontal cortex, followed by persistent multi-unit activity during the trace interval. In cerebellum, rhythmicity and precise synchrony of stimulus time-locked local field potentials with those of hippocampus occur preferentially under the theta condition. Here we review these findings, integrate them into current models of hippocampal-dependent learning and suggest how improvement in our understanding of neurobiological oscillations is critical for theories of medial temporal lobe processes underlying intact and pathological learning.Frontiers in Systems Neuroscience 04/2015; DOI:10.3389/fnsys.2015.00050
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ABSTRACT: The external globus pallidus (GPe) is central for basal ganglia processing. It expresses muscarinic cholinergic receptors and receives cholinergic afferents from the pedunculopontine nuclei (PPN) and other regions. The role of these receptors and afferents is unknown. Muscarinic M1-type receptors are expressed by synapses from striatal projection neurons (SPNs). Because axons from SPNs project to the GPe, one hypothesis is that striatopallidal GABAergic terminals may be modulated by M1 receptors. Alternatively, some M1 receptors may be postsynaptic in some pallidal neurons. Evidence of muscarinic modulation in any of these elements would suggest that cholinergic afferents from the PPN, or other sources, could modulate the function of the GPe. Here, we show this evidence using striatopallidal slice preparations: after field stimulation in the striatum, the cholinergic muscarinic receptor agonist, muscarine, significantly reduced the amplitude of inhibitory postsynaptic currents (IPSCs) from synapses that exhibited short-term synaptic facilitation. This inhibition was associated with significant increases in paired pulse facilitation and quantal content (CV(-2)) was proportional to IPSC amplitude. These actions were blocked by atropine, pirenzepine and mamba toxin-7; suggesting that receptors involved were M1. In addition, we found that some pallidal neurons have functional post-synaptic M1-receptors. Moreover, some evoked IPSCs exhibited short-term depression and exhibited a different kind of modulation: they were indirectly modulated by muscarine via the activation of presynaptic cannabinoid-1 receptors (CB1). Thus, pallidal synapses presenting distinct forms of short-term plasticity were modulated differently.Journal of Neurophysiology 11/2014; 113(3):jn.00385.2014. DOI:10.1152/jn.00385.2014 · 3.04 Impact Factor
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ABSTRACT: Stimulation of dopamine (DA) D1 receptors in the ventral tegmental area (VTA) is involved in primary rewards. In the current study we investigated whether VTA D1 receptor stimulation likewise plays a role in mediating the rewarding effects of cocaine-associated stimuli, using the cocaine conditioned place preference (CPP) paradigm. Rats were prepared with cannulae so as to allow microinjections in the VTA and later conditioned to a cocaine-associated environment using the CPP paradigm. Prior to each conditioning session rats were injected with either saline or cocaine (10mg/kg, intraperitoneally) and then placed in one of the two sides of the CPP apparatus. Sessions lasted thirty minutes a day over a period of eight days, such that rats alternated daily between consistently experiencing cocaine in one side and saline in the other. On the test day, which was conducted one day after conditioning, rats were given bilateral microinjections of one of four doses of the D1 antagonist, SCH 23390, (0, 2, 4 or 8μg/0.5μl) directly into the VTA and allowed free access to both sides of the apparatus. Preference for either side was measured as time spent in each side and compared to the same measures taken before conditioning. The D1 antagonist produced a dose-related, significant reduction in the preference for the cocaine-paired side compared to vehicle. These data suggest that the expression of cocaine conditioned place preference requires stimulation of VTA D1 receptors and, as such, are the first to suggest a role for VTA dendritically released DA in cocaine-, or other reward-, related learning.Behavioural Brain Research 07/2014; 272. DOI:10.1016/j.bbr.2014.07.008 · 3.39 Impact Factor