Effects of nicotine on EEG and evoked potentials and their interactions with autonomic drugs

Systemic Nicotine Increases Gain and Narrows Receptive Fields in A1 via Integrated Cortical and Subcortical Actions

Nicotine enhances sensory and cognitive processing via actions at nicotinic acetylcholine receptors (nAChRs), yet the precise circuit- and systems-level mechanisms remain unclear. In sensory cortex, nicotinic modulation of receptive fields (RFs) provides a model to probe mechanisms by which nAChRs regulate cortical circuits. Here, we examine RF modulation in mouse primary auditory cortex (A1) using a novel electrophysiological approach: current-source density (CSD) analysis of responses to tone-in-notched-noise (TINN) acoustic stimuli. TINN stimuli consist of a tone at the characteristic frequency (CF) of the recording site embedded within a white noise stimulus filtered to create a spectral “notch” of variable width centered on CF. Systemic nicotine (2.1 mg/kg) enhanced responses to the CF tone and to narrow-notch stimuli, yet reduced the response to wider-notch stimuli, indicating increased response gain within a narrowed RF. Subsequent manipulations showed that modulation of cortical RFs by systemic nicotine reflected effects at several levels in the auditory pathway: nicotine suppressed responses in the auditory midbrain and thalamus, with suppression increasing with spectral distance from CF so that RFs became narrower, and facilitated responses in the thalamocortical pathway, while nicotinic actions within A1 further contributed to both suppression and facilitation. Thus, multiple effects of systemic nicotine integrate along the ascending auditory pathway. These actions at nAChRs in cortical and subcortical circuits, which mimic effects of auditory attention, likely contribute to nicotinic enhancement of sensory and cognitive processing.

Nicotine impact on the structure of adult male guinea pig auditory cortex

BACKGROUND

A growing body of evidence suggests that chronic cigarette smoking causes detrimental effects on brain morphology.

AIM OF WORK

To study the structural changes in auditory cortex region (Layer V), under the influence of nicotine.

MATERIAL AND METHODS

Three animal groups (10 each) were used; group I (control) and groups IIa and IIb received 3 and 6mg/kg nicotine respectively. The specimens from the auditory cortex were examined using light and electron microscopy and morphometry.

RESULTS

Neurons and blood capillaries of the auditory cortex (layer V), were influenced by chronic nicotine treatment in a dose dependent manner. The neurons and their processes revealed disorganization and dissociation of microtubules. The neuronal cells nucleoli characteristically revealed large fibrillar centers detected by silver stain and ultrastructure. The blood capillaries revealed collapse, irregular lumen, thickened basal lamina, abnormal forms of nuclei and organization of microtubules. Neuroglia revealed marked reactivity. Morphometrically, there was a significant decrease in the thickness of the auditory cortex and the number of light neurons and a significant increase in the number of dark neurons in comparison to the control.

CONCLUSION

Nicotine affects the integrity of the auditory cortex possibly by reducing metabolic and transcription activities.

Nicotinic filtering of sensory processing in auditory cortex

Although it has been known for decades that the drug nicotine can improve cognitive function, the nature of its effects and the underlying mechanisms are not well understood. Nicotine activates nicotinic acetylcholine (ACh) receptors (nAChRs) that normally are activated by endogenous ACh, presumably "hijacking" the cholinergic contribution to multiple cognitive functions, notably attention. Thus, studying nicotine's effects helps to better understand a commonly used drug as well as functions of nAChRs. Moreover, nicotinic agonists are being developed to treat a variety of disorders that involve attention-related or age-related cognitive dysfunction. Studies have shown that nicotine can enhance processing of attended stimuli and/or reduce processing of distracters; that is, nicotine enhances attentional filtering. To examine potential mechanisms within sensory cortex that may contribute to cognitive functions, here we describe nicotinic actions in primary auditory cortex, where well-characterized neural "filters"-frequency receptive fields-can be exploited to examine nicotinic regulation of cortical processing. Using tone-evoked current-source density (CSD) profiles, we show that nicotine produces complex, layer-dependent effects on spectral and temporal processing that, broadly speaking, enhance responses to characteristic frequency (optimal) stimuli while simultaneously suppressing responses to spectrally distant stimuli. That is, nicotine appears to narrow receptive fields and enhances processing within the narrowed receptive field. Since basic cortical circuitry and nAChR distributions are similar across neocortex, these findings may generalize to neural processing in other sensory regions, and to non-sensory regions where afferent inputs are more difficult to manipulate experimentally. Similar effects across sensory and non-sensory cortical circuits could contribute to nicotinic enhancement of cognitive functions.

Acute nicotine-induced tachyphylaxis is differentially manifest in the limbic system

Rapid tolerance develops to many of nicotine's behavioral and autonomic effects. A better understanding of the spatiotemporal patterns in neuronal activity as a consequence of acute nicotine tolerance (tachyphylaxis) may help explain its commonly found inverted 'U'-shaped biphasic dose-effect relationship on various behaviors. To this end, we employed high-resolution functional magnetic resonance imaging and relative cerebral blood volume (rCBV) as a marker of neuronal activity, to characterize the regional development of acute tolerance as a function of nicotine dose in naïve, anesthetized rats. A single intravenous nicotine injection at 0.1 and 0.3, but not 0.03 mg/kg, significantly increased neuronal activity in many neocortical areas. In contrast, dose-dependent increases in rCBV were most pronounced in limbic regions, such that responses seen at 0.1 mg/kg nicotine in accumbens, hippocampus, amygdala, and several other limbic areas were not seen following 0.3 mg/kg nicotine. Finally, whereas profound tolerance was observed in many cortical regions after the second of two paired nicotine injections at either 0.1 or 0.3 mg/kg, subcortical limbic structures showed only a weak trend for tolerance. Lack of rCBV changes in animals receiving nicotine methiodide, a quaternary nicotine analog that does not cross the blood-brain barrier, supports a direct neuronal effect of nicotine rather than an action on the vasculature. These data provide pharmacodynamic insight into the regional heterogeneity of nicotine tachyphylaxis development, which may be relevant to behavioral and neurobiological mechanisms associated with repeated tobacco consumption.

The impact of maternal smoking on fast auditory brainstem responses

Deficits in auditory processing have been posited as one of the underlying neurodevelopmental consequences of maternal smoking during pregnancy that leads to later language and reading deficits. Fast auditory brainstem responses were used to assess differences in the sensory processing of auditory stimuli among infants with varying degrees of prenatal cigarette exposure. Maternal report of consumption of cigarettes and blood samples were collected in the hospital to assess exposure levels and participants were then seen at 6-months. To participate in the study, all infants had to pass the newborn hearing exam or a clinically administered ABR and have no known health problems. After controlling for participant age, maternal smoking during pregnancy was negatively related to latency of auditory brainstem responses. Of several potential covariates, only perinatal complications and maternal alcohol use were also related to latency of the ABR responses and maternal smoking level accounted for significant unique variance after controlling for these factors. These results suggest that the relationship between maternal smoking may lead to disruption in the sensory encoding of auditory stimuli.

Nicotinic acetylcholine receptors in sensory cortex

Acetylcholine release in sensory neocortex contributes to higher-order sensory function, in part by activating nicotinic acetylcholine receptors (nAChRs). Molecular studies have revealed a bewildering array of nAChR subtypes and cellular actions; however, there is some consensus emerging about the major nAChR subtypes and their functions in sensory cortex. This review first describes the systems-level effects of activating nAChRs in visual, somatosensory, and auditory cortex, and then describes, as far as possible, the underlying cellular and synaptic mechanisms. A related goal is to examine if sensory cortex can be considered a model system for cortex in general, because the use of sensory stimuli to activate neural circuits physiologically is helpful for understanding mechanisms of systems-level function and plasticity. A final goal is to highlight the emerging role of nAChRs in developing sensory cortex, and the adverse impact of early nicotine exposure on subsequent sensory-cognitive function.

Acute effect of nicotine on non-smokers: I. OAEs and ABRs

This paper is the first in a series of three investigating the role of cholinergic mechanisms in the auditory system by assessing the acute effects of nicotine, an acetylcholinomimetic drug, on aggregate responses within the auditory pathway. In a single-blind procedure, auditory responses were obtained from 20 normal-hearing, non-smokers (10 male) under two conditions (nicotine, placebo). After the drug session, plasma tests revealed a subject's nicotine concentration. The effects of nicotine on early, exogenous responses of the auditory system (otoacoustic emissions and auditory brainstem potentials) are described in this first paper. Results indicated that transdermal administration of nicotine to non-smokers does not significantly affect cochlear activity but does acutely affect the neural transmission of acoustic information. Overall, otoacoustic emissions were unaffected by transdermal nicotine while wave I of the auditory brainstem response was significantly increased in latency and decreased in amplitude.

Acute effect of nicotine on non-smokers: II. MLRs and 40-Hz responses

This paper is the second in a series of three investigating the role of cholinergic mechanisms in the auditory system by assessing the acute effects of nicotine, an acetylcholinomimetic drug, on aggregate responses within the auditory pathway. In a single-blind procedure, auditory responses were obtained from 20 normal-hearing, non-smokers (10 male) under two conditions (nicotine, placebo). The effects of nicotine on central, mesogenous responses of the auditory system (middle latency and 40-Hz responses) are described in this second paper. Results indicated that transdermal administration of nicotine to non-smokers does significantly affect the central, neural transmission of acoustic information. Na-Pa amplitude and Nb latency of the middle latency response and latency measures of the 40-Hz response were acutely altered by the presence of nicotine.

Acute effect of nicotine on non-smokers: III. LLRs and EEGs

This paper is the last in a series of three investigating the role of cholinergic mechanisms in the auditory system by assessing the acute effects of nicotine, an acetylcholinomimetic drug, on aggregate responses within the auditory pathway. In a single-blind procedure, auditory responses were obtained from 20 normal-hearing, non-smokers (10 male) under two conditions (nicotine, placebo). The effects of nicotine on long-latency responses of the auditory system and on electroencephalograms are described in this paper. Results indicated that transdermal administration of nicotine to non-smokers significantly affects the afferent and efferent transmission of acoustic information, as well as enhancing cortical activation. Long-latency response amplitudes and electroencephalogram activity (dominant power and frequencies) were altered by acute doses of transdermal nicotine.

Human flash-VEP and quantitative EEG are independently affected by acute scopolamine

Scopolamine in acute intramuscular doses of 0.25-0.75 mg reduced the P2-N3 flash-VEP amplitude and, in the quantitative EEG, the 8.5-12.0 Hz power and total power in 8 healthy young male volunteers. The effects on flash-VEP and EEG total power were dose dependent and were evident 30 min and 90 min respectively after drug administration, regardless of dose. The reduction in 8.5-12.0 Hz power was limited to the 0.50 and 0.75 mg doses. No systematic effects on the pattern-VEP were observed. Possible interferences with flash- or pattern-VEP amplitude of the scopolamine-induced EEG changes were identified and removed by regression analysis and computation of VEP residuals from the regression function. The P2-N3 flash-VEP residuals proved EEG independent and showed relationships with dose and time after drug administration that were superimposable on those of the original data, with comparable significance levels at the drug/placebo and pre/postdrug statistical comparisons. The results indicate that VEP estimates of drug effects which are independent from EEG changes can be identified in human studies and allow some inference on the cholinergic specificity of the systems affecting late flash-VEP components. The statistical approach used in this study is suitable for application in VEP studies when effects of interacting factors are to be expected.

Effects of smoking/nicotine on anxiety, heart rate, and lateralization of EEG during a stressful movie

The effects of smoking cigarettes with differing FTC nicotine deliveries on anxiety and EEG activity were evaluated in 40 smokers who were compared with 40 non-smokers, matched for age and gender. Following smoking (sham-smoking in the case of the non-smokers), the participants viewed a stress-inducing movie. Smoking higher-nicotine delivery cigarettes during the movie, as compared to smoking low-nicotine control cigarettes, was associated with reductions in anxiety and right hemisphere activation, increased heart rate, and enhancement of the ratio of left-hemisphere parietal EEG activation to right-hemisphere activation. These results are interpreted as indicating that the anxiolytic effects of nicotine may be mediated by the right hemisphere. The EEG activity and emotional responses of non-smokers were more like those of smokers who smoked the lower-nicotine cigarettes than those of smokers of the higher-nicotine cigarettes.

Dimethylphenylpiperazinium-induced vomiting: nicotinic mediation in area postrema

In unanesthetized cats the emetic action of dimethylphenylpiperazinium (DMPP) was investigated, after it was injected into the cerebral ventricles through chronically implanted cannulae. DMPP injected in 0.2-2.0 mg doses into the cerebral ventricle produced dose-dependent vomiting, which was abolished after ablation of area postrema. However, copper sulfate given intragastrically evoked vomiting in cats with an ablated area postrema. Further, the emetic response to ICV DMPP and to intragastric copper sulfate was depressed or abolished in cats pretreated with ICV reserpine. The emetic response to ICV DMPP, but not that caused by intragastric copper sulfate, was potentiated in cats pretreated with ICV 5,6-dihydroxytryptamine. Ganglionic blocking agents, mecamylamine and hexamethonium, injected ICV prevented the vomiting elicited by ICV DMPP. On the other hand, selected anti-muscarinic drugs, alpha and beta adrenergic antagonists, dopamine antagonists, antihistamines and a 5-hydroxytryptamine (5-HT) antagonist all injected into the cerebral ventricles had virtually no effect on the vomiting induced by DMPP. It is postulated that DMPP evokes vomiting by its action on nicotinic receptors of nerve cells within the area postrema but not on catecholaminergic, serotonergic, or cholinergic receptors. Finally, 5-HT and acetylcholine could also be involved in the inhibition of the complex mechanisms underlying the central regulation of vomiting.

Kinetics of drug action in disease states XI: effect of nicotine on the pharmacodynamics and pharmacokinetics of phenobarbital and ethanol in rats

The purpose of this investigation was to determine if the reported prolongation of barbiturate- and ethanol-induced sleeping times by nicotine in rodents are pharmacodynamic or pharmacokinetic interactions. Adult female rats were pretreated with nicotine, either 0.5 or 1.5 mg/kg ip acutely or 0.5 mg/kg ip daily for 6 d, whereas control animals received saline solution. Phenobarbital or ethanol was infused intravenously at a slow rate until the rats lost their righting reflex. Acute pretreatment with nicotine reduced significantly the serum, brain, and cerebrospinal fluid (CSF) concentrations of phenobarbital and ethanol, respectively, at the onset of the loss of the righting reflex. Chronic pretreatment with nicotine had no such potentiating effects, indicative of rapid development of tolerance to nicotine. Neither acute nor chronic pretreatment with nicotine had any apparent effect on the elimination kinetics of phenobarbital or ethanol, on biochemical indices of hepatic integrity and renal function, or on the permeability of the blood-CSF barrier to protein. Nicotine, unlike morphine, did not increase the nociceptive threshold (tail squeeze) of rats under the experimental conditions. It is concluded that acute, but not chronic, pretreatment with nicotine increases the sensitivity of rats to the hypnotic effects of phenobarbital and ethanol, respectively. These interactions are entirely pharmacodynamic and have no apparent pharmacokinetic component.

Central nicotinic receptors: vomiting, ear twitching and panting

Vomiting, ear twitching and panting produced by either nicotine or dimethylphenylpiperazinium (DMPP) administered intracerebroventricularly (ICV) to the unanesthetized cat were studied and compared. On a molar basis, nicotine evoked stronger effects overall in terms of the three responses studied, but the DMPP-induced vomiting and ear twitching responses, while weaker, were of longer duration. No significant differences were found in the duration of panting evoked by these nicotinic agonists. The nicotinic blocker hexamethonium injected ICV abolished the vomiting and ear twitching caused by either ICV nicotine or ICV DMPP, but vomiting and ear twitching persisted following the ICV administration of the muscarinic blocker, atropine. Both hexamethonium and atropine depressed or abolished the panting response evoked by either ICV nicotine or ICV DMPP. In cats with ablations of the area postrema, nicotine and DMPP injected ICV did not produce the vomiting response, but ear twitching and panting still occurred. It is concluded that the ICV injection of nicotine or DMPP evoked vomiting and ear twitching in the cat by way of an action on the central nicotinic receptors. However, panting produced by these nicotine agonists is mediated by the mimicking action of acetylcholine on central receptors having mixed nicotinic and muscarinic properties.

Effects of nicotine on the visual evoked response

The effects of smoking cigarettes differing in nicotine content (0.14 vs 1.34 mg/cigarette) on the peak-to-peak amplitude and peak latency of the human averaged visual evoked response (AVER) were measured in 10 male smokers after a 2-hr smoking deprivation period. The AVER was obtained under five different flash intensities. Eight different peaks were involved in the amplitude and latency measurements. The nicotine dosage and flash intensity factors both had significant effects on peak-to-peak amplitudes while only the flash intensity factor affected peak latencies. The general enhancement of peak-to-peak amplitudes by the 1.34 mg cigarette, relative to the 0.14 mg cigarette, indicates that the effects of cigarette smoking on the AVER are predominantly due to nicotine's psychopharmacologic action, as opposed to other elements in tobacco smoke or as opposed to nonpharmacologic mechanisms involving learning processes. Past research, on an electrophysiological and behavioral level, indicating that nicotine, as administered via cigarette smoking, may have enhancing and/or restorative effects on visual attentional processes in the quiescent smoker was supported.