The effects of a 5-HT2 receptor antagonist (ICI 169,369) on changes in waking EEG, pupillary responses and state of arousal in human volunteers

Functional Organization of the Sympathetic Pathways Controlling the Pupil: Light-Inhibited and Light-Stimulated Pathways

Pupil dilation is mediated by a sympathetic output acting in opposition to parasympathetically mediated pupil constriction. While light stimulates the parasympathetic output, giving rise to the light reflex, it can both inhibit and stimulate the sympathetic output. Light-inhibited sympathetic pathways originate in retina-receptive neurones of the pretectum and the suprachiasmatic nucleus (SCN): by attenuating sympathetic activity, they allow unimpeded operation of the light reflex. Light stimulates the noradrenergic and serotonergic pathways. The hub of the noradrenergic pathway is the locus coeruleus (LC) containing both excitatory sympathetic premotor neurones (SympPN) projecting to preganglionic neurones in the spinal cord, and inhibitory parasympathetic premotor neurones (ParaPN) projecting to preganglionic neurones in the Edinger-Westphal nucleus (EWN). SympPN receive inputs from the SCN via the dorsomedial hypothalamus, orexinergic neurones of the latero-posterior hypothalamus, wake- and sleep-promoting neurones of the hypothalamus and brain stem, nociceptive collaterals of the spinothalamic tract, whereas ParaPN receive inputs from the amygdala, sleep/arousal network, nociceptive spinothalamic collaterals. The activity of LC neurones is regulated by inhibitory α₂-adrenoceptors. There is a species difference in the function of the preautonomic LC. In diurnal animals, the α₂-adrenoceptor agonist clonidine stimulates mainly autoreceptors on SymPN, causing miosis, whereas in nocturnal animals it stimulates postsynaptic α₂-arenoceptors in the EWN, causing mydriasis. Noxious stimulation activates SympPN in diurnal animals and ParaPN in nocturnal animals, leading to pupil dilation via sympathoexcitation and parasympathetic inhibition, respectively. These differences may be attributed to increased activity of excitatory LC neurones due to stimulation by light in diurnal animals. This may also underlie the wake-promoting effect of light in diurnal animals, in contrast to its sleep-promoting effect in nocturnal species. The hub of the serotonergic pathway is the dorsal raphe nucleus that is light-sensitive, both directly and indirectly (via an orexinergic input). The light-stimulated pathways mediate a latent mydriatic effect of light on the pupil that can be unmasked by drugs that either inhibit or stimulate SympPN in these pathways. The noradrenergic pathway has widespread connections to neural networks controlling a variety of functions, such as sleep/arousal, pain, and fear/anxiety. Many physiological and psychological variables modulate pupil function via this pathway.

Juvenile myoclonic epilepsy: Clinical characteristics, standard and quantitative electroencephalography analyses

OBJECTIVES

Most studies comparing inter-ictal background quantitative electroencephalography (EEG) measures in generalized epilepsies with normal controls do not specifically determine patients with juvenile myoclonic epilepsy (JME) as a separate group. The study aims at comparing absolute spectral power and global field coherence in various frequency bands between patients diagnosed exclusively with JME and 10 healthy controls, and correlating significantly different quantitative EEG measures with various clinical characteristics and standard EEG abnormalities.

MATERIALS AND METHODS

Clinical and EEG data were collected from 10 patients with JME and 10 healthy controls. Spectral power and global field spectral coherence were calculated using Welch's averaged periodogram method. The data was analyzed using descriptive statistics, Fisher's exact test and t-test.

RESULTS

Statistically significant (or trend level) higher power (global α and θ, frontal α and θ, left temporal θ, right occipital α, δ and γ1, and central δ, θ, α, β, and γ2) and coherence (global α and γ1) was found in JME patients when compared to controls. Significant correlation of left frontal and central θ-power with presence of absence seizures (negative), central δ-, and θ-power with the presence of psychiatric comorbidity and central θ-power with frequency of myoclonic seizures was found.

CONCLUSION

Findings on global-frontal and temporal-occipital power support mild diffuse epileptogenic state and θ-activity as an endophenotype concepts in JME patients, respectively; findings suggest future studies on JME to include psychiatric comorbidity while selecting the sample; some spectral measures (e.g., central θ-power) do relate to progression of JME while some do not.

Comparison of ketanserin, buspirone and propranolol on arousal, pupil size and autonomic function in healthy volunteers

RATIONALE

The human pupil may be a suitable physiological test system for the assessment of excessive daytime sleepiness (EDS), but pupillometric assessment could be confounded by medication for comorbid hypertension and mood disorders.

OBJECTIVES

We examined the profile of the 5HT-2/alpha1/H1 antagonist ketanserin, the 5HT1a agonist buspirone and the beta adrenoceptor antagonist propranolol on pupillary and other measures of arousal.

MATERIALS AND METHODS

Ketanserin (20 mg), buspirone (10 mg) and propranolol (40 mg) were administered in three independent experiments according to a crossover, placebo-controlled, double-blind design. Resting pupil diameter (RPD) was sampled over 5-min in darkness with infrared pupillometry. Tests also included critical flicker fusion frequency (CFFF), visual analogue scales (VAS), the pupillary light reflex and heart rate/blood pressure.

RESULTS

Ketanserin reduced RPD, CFFF, VAS-rated arousal and blood pressure and increased the light reflex amplitude. Buspirone reduced RPD and blood pressure. Propranolol reduced heart rate but had no effects on pupillary functions or any arousal measure.

CONCLUSIONS

Ketanserin but not propranolol had a fully sedative profile and may confound pupillometric assessment of EDS. Beta adrenergic receptors do not appear to participate in arousal and pupillary functions, while 5HT1a receptors reduce pupil size without affecting arousal. Pupil size may not be used unequivocally as an index of the level of alertness in the case of drug-induced changes, when drugs interfere with the central pupil control mechanism in ways that are unrelated to their effects on arousal.

The role of oscillations and synchrony in cortical networks and their putative relevance for the pathophysiology of schizophrenia

Neural oscillations and their synchronization may represent a versatile signal to realize flexible communication within and between cortical areas. By now, there is extensive evidence to suggest that cognitive functions depending on coordination of distributed neural responses, such as perceptual grouping, attention-dependent stimulus selection, subsystem integration, working memory, and consciousness, are associated with synchronized oscillatory activity in the theta-, alpha-, beta-, and gamma-band, suggesting a functional mechanism of neural oscillations in cortical networks. In addition to their role in normal brain functioning, there is increasing evidence that altered oscillatory activity may be associated with certain neuropsychiatric disorders, such as schizophrenia, that involve dysfunctional cognition and behavior. In the following article, we aim to summarize the evidence on the role of neural oscillations during normal brain functioning and their relationship to cognitive processes. In the second part, we review research that has examined oscillatory activity during cognitive and behavioral tasks in schizophrenia. These studies suggest that schizophrenia involves abnormal oscillations and synchrony that are related to cognitive dysfunctions and some of the symptoms of the disorder. Perspectives for future research will be discussed in relationship to methodological issues, the utility of neural oscillations as a biomarker, and the neurodevelopmental hypothesis of schizophrenia.

Corticotropin-releasing factor modulates cardiovascular and pupillary autonomic reflexes in man: is there a link to inflammation-induced autonomic nervous hyperreflexia?

In two recent studies, we found autonomic nervous hyperreflexia in subjects with chronic inflammatory diseases, particularly, in those subjects with higher degrees of systemic inflammation. Since corticotropin-releasing factor (CRF) is induced by inflammatory stimuli and acts within the brain to change neuroendocrine and autonomic activity, we investigated CRF modulation of standard autonomic nervous reflexes. Fifteen healthy subjects were administered 100 microg CRF i.v., which led to a short-term increase of heart rate (p < 0.001) and a decrease in systolic and diastolic blood pressure (p < 0.050). These changes were accompanied by a reduction in heart rate variation at rest (p = 0.010) and during the respiratory sinus arrhythmia test (p = 0.019), and a reduction of pupillary latency time (p = 0.038). In further 21 normal subjects we studied the effect of prednisolone treatment on autonomic nervous function (100 mg/d during three days --> CRF reduction), which resulted in an increase of heart rate (p < 0.001), increase of heart rate variation during the respiratory sinus arrhythmia test (p < 0.001), increase in pupillary latency time (p = 0.012), a increase in maximal pupillary area (p = 0.002), and a decrease in diastolic blood pressure (p = 0.002). In conclusion, induction of a low central CRF content by prednisolone leads to a marked hyperreflexia in respiratory sinus arrhythmia and hyporeflexia in the latency time test. It is obvious that CRF can regulate autonomic reflexes. Possibly, central CRF status may also influence autonomic reflexes during chronic inflammation due to chronically changed central CRF concentration.

Topographic analysis of EEG photic driving in patients with schizophrenia following clozapine treatment

Reduced EEG photic driving has been found to be diagnostically sensitive and specific for schizophrenia. Thirty-one patients with schizophrenia were tested in this study to identify the typical and atypical neuroleptic effects on the photic driving. Compared with the placebo, clozapine significantly enhanced the photically driven EEG in theta and low alpha frequency band, while haloperidol did not have the same effect. These changes with clozapine appeared to be symmetrical and located primarily in the frontal, central and mid-parietal areas but not in the lateral parietal, temporal and occipital regions. Results were consistent with previous findings and suggested that the atypical EEG profile of clozapine might be associated with 5-HT2 antagonistic property.

Buspirone, but not sumatriptan, induces miosis in humans: relevance for a serotoninergic pupil control

BACKGROUND AND OBJECTIVE

Drugs that act on the serotoninergic system have been shown to influence the pupil size. However, the 5-hydroxytryptamine (5-HT) receptor type or subtype that affects pupil diameter has not been defined in humans. With a placebo-controlled, double-blind randomized design, we investigated in healthy volunteers the effect on pupil size of buspirone and sumatriptan, which mainly act on 5-HT1A- and the 5-HT1-like receptors, respectively.

METHODS

The pupil area was measured by means of a videopupillometer before and after a single oral administration of placebo or of three different doses of active drugs. Heart rate and arterial blood pressure were recorded after pupil area measurement.

RESULTS

Buspirone (5, 10, and 20 mg) caused a dose-dependent miosis. Sumatriptan (50, 100, and 200 mg) did not affect the pupil size. Twenty milligrams of buspirone reduced the mydriasis induced by pretreatment with homatropine eyedrops. A 20 mg dose of buspirone reduced blood pressure without change in heart rate, whereas buspirone, at doses lower than 20 mg, and sumatriptan did not affect heart rate and blood pressure.

CONCLUSIONS

This study suggests that buspirone, but not sumatriptan, the selective agonist of 5-HT1-like receptors, causes miosis in humans by activation of 5-HT1A receptors, possibly located in the central nervous system where they inhibit iris sympathetic pathways. Measurement of pupil size seems to provide a valuable and sensitive index of 5-HT1A receptor function in humans.

Acute and subchronic effects of nefazodone and imipramine on highway driving, cognitive functions, and daytime sleepiness in healthy adult and elderly subjects

The acute and subchronic effects of two dosages of a new serotonergic antidepressant, nefazodone, and those of the tricyclic imipramine were examined in a double-blind, crossover, placebo-controlled study. Twenty-four healthy subjects from two age groups (12 adults and 12 elderly from both sexes) received the four treatments (nefazodone, 100 and 200 mg twice daily; imipramine, 50 mg twice daily; and placebo) for 7 days with a 7-day washout period. Measurements were performed after the morning doses on day 1 and day 7. These included a standard over-the-road highway driving test, a psychomotor test battery, and sleep latency tests. Blood samples were taken on both days and analyzed to determine concentrations of parent drugs and their major metabolites. The main results showed that the reference drug, imipramine, had a detrimental effect after a single dose on lateral position control in the driving test, primarily in the adult group, that diminished after repeated dosing. Minor impairment on psychomotor test performance was found with both days. On the other hand, a single administration of both doses of nefazodone did not impair highway driving performance (even showed some improvement) and had no or only minor effects on psychomotor performance. After repeated dosing, nefazodone 200 mg twice daily (but not the 100-mg dose) produced slight impairment of lateral position control; dose-related impairment of cognitive and memory functions was found. The effects of nefazodone were generally in the same direction in both age groups. Significant correlations were found between steady-state concentrations of nefazodone in plasma (200-mg, twice-daily condition) as well as imipramine, and reaction time changes in a memory scanning task. Neither drug appeared to induce daytime sleepiness as measured by the sleep latency tests.

The effects of a selective 5-HT2 receptor antagonist (ICI 170,809) on platelet aggregation and pupillary responses in healthy volunteers

1. ICI 170,809 (2-(2-dimethylamino-2-methylpropylthio)-3-phenylquinoline hydrochloride) is a potent 5-hydroxytryptamine (5-HT) type 2 postsynaptic receptor antagonist. 2. Effects of ICI 170,809 as single oral doses (3, 7, 15 and 30 mg) or placebo were studied on the duration of antagonism for the ex vivo platelet aggregatory response to 5-HT and to the pupillary light constrictor response in eight healthy male volunteers. 3. Pupillary dark adapted responses to a 0.5 s light stimulus were measured using a portable infrared pupillometer, for up to 24 h after dosing. 4. The in vitro platelet 5-HT aggregation response was reduced by ICI 170,809, with depression of the dose-response curve to 5-HT at all concentrations of 5-HT and with no evidence for a parallel shift. 5. The ex vivo platelet 5-HT response demonstrated a dose related significant (P less than 0.02) decrease in aggregation reaching a maximum at 2 h after dosing with the effect persisting for at least 8 h after dosing with the 7 and 15 mg doses. 6. Resting pupil diameter (RPD), and light induced pupillary responses in the dark adapted pupil, showed a significant (P less than 0.01) dose related reduction with significant (P less than 0.05) effects still present with the 15 and 30 mg doses at 8 h after dosing. 7. We conclude that, changes in both ex vivo platelet aggregation to 5-HT and dark adapted pupil size, are significantly correlated (P less than 0.0001) with log plasma concentrations (ng ml-1) of ICI 170,809, enabling the assessment of 5-HT2-receptor antagonism in man.