Effect of vagal autotransplantation and bifemelane hydrochloride on cholinergic markers and event-related potentials in rats with lesions of the nucleus basalis magnocellularis

Age-related cognitive decline in the menopause: effects of hormone replacement therapy on cognitive event-related potentials

OBJECTIVE

Although epidemiological and clinical studies suggest that hormone replacement therapy (HRT) may protect against cognitive disorders and neurodegenerative diseases, the relation between estrogen and cognition in postmenopausal women remains controversial.

METHODS

In a double-blind placebo-controlled, parallel group design study the effects of HRT with the estrogen-progestogen combination Presomen 1.25 compositum((R)) (1.25mg equine conjugated estrogens administered for 21 days plus the progestogen 5mg medrogeston given for 11 days) on event-related potentials (ERPs) in postmenopausal patients with age-related cognitive decline (DSM-IV code 780.9, ICD-10 code R 41.8) were investigated. After a pre-drug comparison with age-matched normal postmenopausal controls, 48 psychotropic drug-free patients aged 60 +/- 6 years were randomized to receive either placebo or verum for 4 months. ERPs were recorded before as well as on the 91-92 days of the study, which thus fell into the estrogen phase of the treatment during the fourth cycle.

RESULTS

At baseline, patients showed a lengthening of P300 latency and an attenuation of P300 amplitudes as compared with normal controls. After HRT with Presomen, a significant shortening of P300 latency as compared with placebo was observed.

CONCLUSIONS

The baseline P300 differences suggest that in the patient group the aging process was advanced, while after HRT with Presomen a significant improvement and normalization of information processing as indexed by P300 was observed.

Blockade of epinephrine priming of the cerebral auditory evoked response by cortical cholinergic deafferentation

The present study tested hypotheses derived from a neurobehavioral model of anxiety that posits an important role of the basal forebrain cholinergic system in the cortical processing of anxiety-associated stimuli and contexts. We hypothesized that visceral afferent activity induced by systemic administration of epinephrine would enhance the processing of auditory stimuli as evidenced by the cerebral auditory evoked response. We further predicted that selective lesions of the basal forebrain cortical cholinergic projection system would disrupt this processing, and would further block the effects of epinephrine. Results confirmed these hypotheses. Epinephrine was found to enhance the amplitude of the P70 component of the auditory evoked response in rats. Selective lesions of the basal forebrain corticopetal cholinergic projection, by intrabasalis infusions of 192 IgG saporin, delayed and reduced the amplitude of the P70 component, and blocked the potentiating effects of epinephrine on the auditory evoked response. The present results are consistent with the view that visceral afferent input may modulate cortical processing of sensory signals via the basal forebrain cholinergic system. These considerations emphasize the potential importance of ascending, bottom-up modulation of processing by telencephalic circuits that may impact on a wide range of behavioral functions.

Effects of hormone replacement therapy on perceptual and cognitive event-related potentials in menopausal insomnia

The influence of a combined estrogen-progestin regimen (Climodien, Lafamme) on auditory event-related potentials (ERPs) was investigated in a double-blind, placebo-controlled, comparative, randomized 3-arm trial phase (Climodien 2/3=estradiol valerate 2 mg+the progestin dienogest 3 mg, EV=estradiol valerate 2 mg, and placebo), followed by an open-label phase in which all patients received Climodien 2/2 (estradiol valerate 2 mg+dienogest 2 mg). Both the double-blind and the open-label phase lasted 2 months. ERPs were recorded from 19 EEG leads in a two-tone odd-ball paradigm in 49 patients aged between 46 and 67 yr with the diagnosis of insomnia (G 47.0) related to postmenopausal syndrome (N 95.1). Climodien reduced standard N1 and target P300 latencies as compared to placebo, while EV did not affect N1 latency but similarly reduced P300 latency. Climodien increased N1, P2 and P300 amplitudes dose-dependently, predominantly at frontal leads. Estrogen alone had only minor effects on ERP amplitudes. The shortening of standard N1 latency and enhancement of N1 and P2 amplitudes indicates a positive effect of Climodien on perceptual processing, most likely due to vigilance improvements also observed in EEG mapping. Concerning target P300, it seems that estradiol is responsible for the improvement in stimulus evaluation time, as reflected by the shortening of the peak latency, while dienogest seems to account for the improvement in cognitive information processing capacity, whereby 3 mg induced a more pronounced augmentation of P300 amplitudes than 2 mg. Based on the spatial distribution of this increase, it can be speculated that Climodien mainly affects the more frontally distributed P3a subcomponent, which is associated with attention and orientation. Furthermore, the observed changes in ERP-components are consistent with recent studies showing significant positive effects of hormone replacement therapy on cholinergic functions. Thus, Climodien seems to be of interest in preventing cognitive decline and treating cognitive disorders in postmenopausal women. Indeed, there is increasing evidence of beneficial effects of estrogen in dementia. Our present findings suggest that the estrogen effects may be augmented by dienogest.

Effect of vagal autotransplantation on quantitative [3H]-vesamicol binding image in rats with unilateral lesions of nucleus baslis magnocellularis

It is considered that nodosal ganglion grafting improves learning and memory disorder in nucleus basalis magnocellularis lesioned rats, and that [3H]-vesamicol is one of the mapping agents for presynaptic cholinergic neurons. Quantitative autoradiography was performed using high sensitive imaging plate system to evaluate the effect of neurotransplantation on [3H]-vesamicol binding. The affected-side to unaffected-side ratio of [3H]-vesamicol in the nucleus basalis magnocellularis lesioned group was significantly lower than that in the sham-operated group at 1, 2 and 4weeks (P<0.01). In the transplanted group, the ratio was significantly higher than that in the untreated group at 4weeks (P<0.05). [3H]-vesamicol binding is one of the most sensitive indicators of nucleus basalis magnocellularis lesions and the effect of the nodosal ganglion grafting.

Acetylcholine in mind: a neurotransmitter correlate of consciousness?

The cholinergic system is one of the most important modulatory neurotransmitter systems in the brain and controls activities that depend on selective attention, which are an essential component of conscious awareness. Psychopharmacological and pathological evidence supports the concept of a 'cholinergic component' of conscious awareness. Drugs that antagonize muscarinic receptors induce hallucinations and reduce the level of consciousness, while the nicotinic receptor is implicated as being involved in the mechanism of action of general (inhalational) anaesthetics. In degenerative diseases of the brain, alterations in consciousness are associated with regional deficits in the cholinergic system. In Alzheimer's disease (AD), there is a loss of explicit (more than implicit) memory and hypoactivity of cholinergic projections to the hippocampus and cortex, while the visual hallucinations experienced by subjects with Dementia with Lewy bodies (DLB) are associated with reductions in neocortical ACh-related activity. In Parkinson's disease, the additional loss of pedunculopontine cholinergic neurones, which control REM (rapid eye movement) sleep or dreaming, is likely to contribute to REM abnormalities, which also occur in DLB. Widespread basal-forebrain and rostral brainstem cholinergic pathways, which include converging projections to the thalamus, appear to be located strategically for generating and integrating conscious awareness. Alleviation of a range of cognitive and non-cognitive symptoms by drugs that modulate the cholinergic system, which are being developed for the treatment of AD and related disorders, could be caused by changes in consciousness.

Long latency event-related potentials in rats: response of amygdala, nucleus accumbens, dorsal hippocampus and frontal cortex to changes in reward characteristics of conditioned stimuli

Circuits involving major afferents to the ventral striatum from the frontal cortex, amygdala and hippocampus have been implicated in the selective processing of conditioned stimuli predictive of 'important events' or reward-related processes. We utilized an animal model of event-related potentials (ERPs) to explore the relationship between these brain areas during the performance of a conditioning/extinction task. Significant reductions in the N1 component in cortex and P2 component in amygdala of the rat ERP were found as a consequence of removal of the food reward previously associated with the stimuli. Lesions of the nucleus basalis magnocellularis were without effect on the pattern of ERP morphology changes associated with the removal of the reward. Since the N1 component of the ERP has been linked to attentional processes, these studies suggest that elimination of reward characteristics of conditioning stimuli can lead to a specific reductions in 'attention' and or 'sensory reaction' in frontal cortex and amygdala but not to general habituation to these stimuli or in other areas of the CNS.

A possible role for cholinergic neurons of the basal forebrain and pontomesencephalon in consciousness

Excitation at widely dispersed loci in the cerebral cortex may represent a neural correlate of consciousness. Accordingly, each unique combination of excited neurons would determine the content of a conscious moment. This conceptualization would be strengthened if we could identify what orchestrates the various combinations of excited neurons. In the present paper, cholinergic afferents to the cerebral cortex are hypothesized to enhance activity at specific cortical circuits and determine the content of a conscious moment by activating certain combinations of postsynaptic sites in select cortical modules. It is proposed that these selections are enabled by learning-related restructuring that simultaneously adjusts the cytoskeletal matrix at specific constellations of postsynaptic sites giving all a similar geometry. The underlying mechanism of conscious awareness hypothetically involves cholinergic mediation of linkages between microtubules and microtubule-associated protein-2 (MAP-2). The first reason for proposing this mechanism is that previous studies indicate cognitive-related changes in MAP-2 occur in cholinoceptive cells within discrete cortical modules. These cortical modules are found throughout the cerebral cortex, measure 1-2 mm2, and contain approximately 10(3)-10(4) cholinoceptive cells that are enriched with MAP-2. The subsectors of the hippocampus may function similarly to cortical modules. The second reason for proposing the current mechanism is that the MAP-2 rich cells throughout the cerebral cortex correspond almost exactly with the cortical cells containing muscarinic receptors. Many of these cholinoceptive, MAP-2 rich cells are large pyramidal cell types, but some are also small pyramidal cells and nonpyramidal types. The third reason for proposing the current mechanism is that cholinergic afferents are module-specific; cholinergic axons terminate wholly within individual cortical modules. The cholinergic afferents may be unique in this regard. Finally, the tapering apical dendrites of pyramidal cells are proposed as primary sites for cholinergic mediation of linkages between MAP-2 and microtubules because especially high amounts of MAP-2 are found here. Also, the possibility is raised that muscarinic actions on MAP-2 could modulate microtubular coherence and self-collapse, phenomena that have been suggested to underlie consciousness.