Transient SB203580 nmr pupil
dilation in humans was elicited after presentation of a visual stimulus in the periphery. The evoked pupil responses were modulated systematically by stimulus contrast, with faster and larger pupil responses triggered by higher contrast stimuli. The pupil response onset latencies for high contrast stimuli were similar to those produced by the light reflex and significantly faster than the darkness reflex, suggesting that the initial component of pupil dilation is probably mediated by inhibition of the parasympathetic pathway. The contrast modulation was pronounced under different levels of baseline pupil size. Together, our results demonstrate visual contrast modulation on the orienting pupil response in humans. “
“The acoustic startle reflex is strongly inhibited by a moderate-intensity acoustic stimulus that precedes the startling stimulus by roughly selleck chemical 10–1000 ms (prepulse inhibition, PPI). At long interstimulus intervals (ISIs) of 100–1000 ms, PPI in rats is reduced by the muscarinic receptor antagonist scopolamine. Here, we studied the
role of GABA receptors in PPI at full ISI ranges in both mice and rats. In B6 mice, PPI begins and ends at shorter ISIs (4 and 1000 ms, respectively) than in Wistar rats (8 and 5000 ms). The GABAA antagonist bicuculline (1 mg/kg i.p.) reduced PPI at ISIs near the peak of PPI in both rats and mice. The GABAB antagonist phaclofen (10 or 30 mg/kg i.p. in rats or mice, respectively) reduced PPI only at long ISIs, similar to the effects of the muscarinic antagonist scopolamine (1 mg/kg i.p.). The effects of phaclofen and scopolamine were additive in rats, suggesting independent effects of GABAB and muscarinic receptors. Patch-clamp recordings of startle-mediating PnC (nucleus reticularis pontis caudalis) giant Succinyl-CoA neurons in rat slices show that EPSCs evoked by either trigeminal or auditory fiber stimulation were inhibited by
the GABAA/C agonist muscimol or the GABAB agonist baclofen via postsynaptic mechanisms. Hyperpolarization of PnC neurons by muscimol was reversed with bicuculline, indicating that postsynaptic GABAA receptors strongly inhibit PnC giant neurons needed for startle. Therefore, GABA receptors on PnC giant neurons mediate a substantial part of PPI, with GABAA receptors contributing at the peak of PPI, and GABAB receptors adding to muscarinic effects on PPI at long ISIs. “
“The oral part of the pontine reticular formation (PnO) contributes to the regulation of sleep, anesthesia and pain. The role of PnO γ-aminobutyric acid (GABA) in modulating these states remains incompletely understood. The present study used time to loss and time to resumption of righting response (LoRR and RoRR) as surrogate measures of loss and resumption of consciousness.