Joint modulation of neocortical electrical activity by nicotinic and muscarinic receptors

Roles of the mitochondrial genetics in cancer metastasis: not to be ignored any longer

Mitochondrial DNA (mtDNA) encodes for only a fraction of the proteins that are encoded within the nucleus, and therefore has typically been regarded as a lesser player in cancer biology and metastasis. Accumulating evidence, however, supports an increased role for mtDNA impacting tumor progression and metastatic susceptibility. Unfortunately, due to this delay, there is a dearth of data defining the relative contributions of specific mtDNA polymorphisms (SNP), which leads to an inability to effectively use these polymorphisms to guide and enhance therapeutic strategies and diagnosis. In addition, evidence also suggests that differences in mtDNA impact not only the cancer cells but also the cells within the surrounding tumor microenvironment, suggesting a broad encompassing role for mtDNA polymorphisms in regulating the disease progression. mtDNA may have profound implications in the regulation of cancer biology and metastasis. However, there are still great lengths to go to understand fully its contributions. Thus, herein, we discuss the recent advances in our understanding of mtDNA in cancer and metastasis, providing a framework for future functional validation and discovery.

Potential Role of Synaptic Activity to Inhibit LTD Induction in Rat Visual Cortex

Long-term depression (LTD), a widely studied form of activity-dependent synaptic plasticity, is typically induced by prolonged low-frequency stimulation (LFS). Interestingly, LFS is highly effective in eliciting LTD in vitro, but much less so under in vivo conditions; the reasons for the resistance of the intact brain to express LTD are not well understood. We examined if levels of background electrocorticographic (ECoG) activity influence LTD induction in the thalamocortical visual system of rats under very deep urethane anesthesia, inducing a brain state of reduced spontaneous cortical activity. Under these conditions, LFS applied to the lateral geniculate nucleus resulted in LTD of field postsynaptic potentials (fPSPs) recorded in the primary visual cortex (V1). Pairing LFS with stimulation of the brainstem (pedunculopontine) reticular formation resulted in the appearance of faster, more complex activity in V1 and prevented LTD induction, an effect that did not require muscarinic or nicotinic receptors. Reticular stimulation alone (without LFS) had no effect on cortical fPSPs. These results show that excitation of the brainstem activating system blocks the induction of LTD in V1. Thus, higher levels of neural activity may inhibit depression at cortical synapses, a hypothesis that could explain discrepancies regarding LTD induction in previous in vivo and in vitro work.

Effects of haloperidol pretreatment on the smoking-induced EEG/mood activation response profile

This study examined the role of dopamine in modulating the CNS response to cigarette smoking. In a randomized, double-blind, repeated-measures design, quantitative electroencephalographic (EEG) changes and self-reports induced by the smoking of a single cigarette were assessed in 16 smokers following pretreatment with placebo and a dopamine antagonist, haloperidol (2 mg). Following placebo pretreatment, absolute (muV) and relative (%) amplitudes in slow-frequency bands (delta, theta, alpha1) were reduced and absolute and relative amplitudes in fast-frequency bands (alpha2, beta) were increased following cigarette smoking as compared to sham smoking. Haloperidol pretreatment inhibited the smoking-induced increase in absolute beta frequency. Self-ratings indicated that cigarette smoking induced increases in alertness, contentedness and calmness but not euphoria, and reduced cigarette cravings as compared to the sham smoking conditions. Smoking-induced, alpha2 increments were associated with increases in alertness and decreases in euphoria while beta increments were associated with increased calmness. Smoking-related self-ratings of mood and cigarette acceptability were not altered by haloperidol, but subjects were less content overall in the haloperidol condition as compared to placebo. Discussion of these results focuses on transmitter systems and their relationship to neuro-electric and behavioural activities associated with the smoking habit.

Eptastigmine restores the aged rat's normal cortical spectral power pattern

We studied the ability of eptastigmine, a second-generation acetylcholinesterase inhibitor (AChEI), to reverse the age-related increase of electroencephalogram (EEG) mean cortical spectral power in slow-wave delta activity and decrease in fast-wave alpha and beta activity. The relative basal spectral power profile evaluated for 50 min of the old (27-30 months) in comparison to young (4-6 months) awake rats was consistently different, showing a significant increase in delta(0.2-4.0 Hz) frequency and a significant decrease of alpha(8.2-13.0 Hz) and beta(13.2-25.0) bands. When 0.5, 1, 2, 4 mg kg(-1)of eptastigmine were administered orally as single increasing doses for old and young rats 2 h prior to the EEG recordings, lasting 2 h, the relative mean spectral power difference (Delta%) showed a linear log dose-related decrease in delta activity and a progressive increase in alpha and beta activity in old rats. Compared to vehicle, in young rats, the eptastigmine dose of 0.5 mg kg(-1)produced a significant decrease in delta activity and an increase in beta activity. The spontaneous motor activity, evaluated through cumulative horizontal and vertical counts for 30 min in old rats was significantly decreased when compared to young rats. Single oral treatment with eptastigmine (0.5 mg kg(-1)for young and 2 mg kg(-1)for old rats) given 2 h before the test did not significantly change motor activity in comparison to vehicle group of the same age. These results suggest a possible strategy to alleviate the severe slowing of neocortical EEG accompanying the cognitive decline.

Differential effects of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid and N-methyl-D-aspartate receptor antagonists applied to the basal forebrain on cortical acetylcholine release and electroencephalogram desynchronization

It is known that glutamatergic tracts activated from the pedunculopontine tegmentum represent a major input to the nucleus basalis magnocellularis. To establish the role of different ionotropic glutamate receptors in synaptic transmission in the basal forebrain, the pedunculopontine tegmentum was stimulated in urethane-anesthetized rats and the resulting increases in cortical acetylcholine release and desynchronization of the electroencephalogram were monitored. R(-)-3-(2-carboxypiperazine-4-yl)-propyl-I-phosphonic acid (CPP), an antagonist at N-methyl-D-aspartate-type glutamate receptors, and 6, 7-dinitroquinoxaline-2, 3-dione (DNQX), an antagonist at alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA)-type glutamate receptors, were delivered through a microdialysis probe placed in the basal forebrain. The N-methyl-D-aspartate antagonist preferentially inhibited cortical acetylcholine release, while the AMPA antagonist was more powerful in reducing desynchronization. A combination of both N-methyl-D-aspartate and AMPA antagonists abolished the increase in cortical acetylcholine release without reducing desynchronization. The dissociation between increased cortical acetylcholine release and electroencephalogram desynchronization suggests that the activity of corticopetal basal forebrain cholinergic neurons is neither necessary nor sufficient to produce electroencephalogram desynchronization. Rather, the nucleus basalis can probably affect the electroencephalogram by its projections to the thalamus. The reversal of the inhibitory effect of DNQX on the electroencephalogram by CPP may be due to the blockade of N-methyl-D-aspartate receptors on the GABAergic projection from the basal forebrain to the thalamus.

Modification of neocortical acetylcholine release and electroencephalogram desynchronization due to brainstem stimulation by drugs applied to the basal forebrain

Acetylcholine released from the cerebral cortex was collected using microdialysis while stimulating the region of the pedunculopontine tegmentum in urethane-anesthetized rats. Electrical stimulation in the form of short trains of pulses delivered once per minute produced a 350% increase in acetylcholine release and a desynchronization of the electroencephalogram, as measured by relative power in the 20-45 Hz range (low-voltage fast activity). Perfusion of the region of cholinergic neurons believed to be responsible for the cortical release of acetylcholine, the nucleus basalis magnocellularis, was carried out using a second microdialysis probe. Exposure of the nucleus basalis magnocellularis to blockers of neural activity (tetrodotoxin or procaine) or to blockers of synaptic transmission (calcium-free solution plus magnesium or cobalt) produced a substantial decrease in the release of acetylcholine and desynchronization evoked by brainstem stimulation. Exposure of the nucleus basalis magnocellularis to the glutamate antagonist, kynurenate, resulted in a decrease in evoked acetylcholine release and electroencephalogram desynchronization similar in magnitude to that produced by nonspecific blockers, whereas application of muscarinic or nicotinic cholinergic blockers to the nucleus basalis magnocellularis did not reduce acetylcholine release or electroencephalogram desynchronization. Application of tetrodotoxin to the collection site in the cortex abolished the stimulation-evoked acetylcholine release, but not the low baseline release indicating that cholinergic nucleus basalis magnocellularis neurons have a low spontaneous firing rate in urethane-anesthetized animals. The results of this study suggest that the major excitatory input to the cholinergic neurons of the nucleus basalis magnocellularis from the pedunculopontine tegmentum is via glutamatergic and not cholinergic synapses.

Visualization of cholinoceptive neurons in the rat neocortex: colocalization of muscarinic and nicotinic acetylcholine receptors

The present investigation analyzes the cellular distribution of muscarinic and nicotinic acetylcholine receptors in rat neocortex, by use of monoclonal antibodies raised against purified receptor proteins. The degree of colocalization of both types of receptors was determined by way of immunofluorescent double-labeling techniques. For both classes of receptors, pyramidal and nonpyramidal cells were found immunostained and an identical laminar distribution pattern of immunopositive neurons in the rat neocortex became apparent. A striking similarity in distribution of the two cholinergic receptor types was found in the frontal/motor and parietal cortex. Accordingly, we observed a high degree of colocalization of muscarinic and nicotinic acetylcholine receptors within immunopositive cortical neurons. Approximately 90% of the cholinoceptive neurons expressed both types of receptors. The current data demonstrate that (i) the distribution of muscarinic and nicotinic cholinoceptive neurons in the neocortex is present in identical laminar patterns and represent the same type of cells, (ii) both classes of cholinergic receptors are highly colocalized within cholinoceptive neurons, which points at individual neurons as a likely site of interaction between muscarinic and nicotinic acetylcholine receptor-mediated processes.