Different effects of cholinergic agents on responses recorded from the cat visual cortex and lateral geniculate nucleus dorsalis

The effect of the cold pressor test on a visually evoked cerebral blood flow velocity response

We investigated the hypothesis that during tonic pain stimulus, neurovascular coupling (NVC) decreases, measuring visually evoked cerebral blood flow velocity response (VEFR) during cold pressor test (CPT) in healthy human subjects as a test. VEFR was calculated as a relative increase in blood flow velocity in the posterior cerebral artery from average values during the last 5 s of the stimulus-OFF period to average values during the last 10 s of the stimulus-ON period. Three consecutive experimental phases were compared: basal, CPT and recovery. During CPT, end-diastolic and mean VEFR increased from 20.2 to 23.6% (p < 0.05) and from 17.5 to 20.0% (p < 0.05), respectively. In recovery phase, end-diastolic and mean VEFR decreased to 17.7% and 15.5%, respectively. Both values were statistically significantly different from CPT phase (p < 0.05). Compared with the basal phase, only end-diastolic VEFR was statistically significantly different in the recovery phase (p < 0.05). Our results are consistent with the assumption that there is a change in the activity of NVC during CPT because of the modulatory influence of subcortical structures activated during tonic pain. Contrary to our expectations, the combined effect of such influences increases rather than decreases NVC.

Studies of human visual pathophysiology with visual evoked potentials

Visual evoked potentials (VEPs) offer reproducible and quantitative data on the function of the visual pathways and the visual cortex. Pattern reversal VEPs to full-field stimulation are best suited to evaluate anterior visual pathways while hemi-field stimulation is most effective in the assessment of post-chiasmal function. However, visual information is processed simultaneously via multiple parallel channels and each channel constitutes a set of sequential processes. We outline the major parallel pathways of the visual system from the retina to the primary visual cortex and higher visual areas via lateral geniculate nucleus that receive visual input. There is no best method of stimulus selection, rather visual stimuli and VEPs' recording should be tailored to answer specific clinical and/or research questions. Newly developed techniques that can assess the functions of extrastriate as well as striate cortices are discussed. Finally, an algorithm of sequential steps to evaluate the various levels of visual processing is proposed and its clinical use revisited.

The effects of certain H(1)-antagonists on visual evoked potential in rats

The present study was undertaken to clarify the effects of certain H(1)-antagonists on visual evoked potential (VEP) in rats. Pyrilamine (5 and 10 mg/kg), diphenhydramine (5 and 10 mg/kg) and chlorpheniramine (10 and 20 mg/kg) caused a significant reduction in the amplitude of late VEP components (P(3)-N(3), N(3)-P(4)), although these drugs showed no significant changes in early VEP components (P(1)-N(1), N(1)-P(2)). Cyproheptadine caused a slight enhancement of late components of VEP at a dose of 20 mg/kg. On the other hand, epinastine caused no significant effect on late VEP components even at a dose of 20 mg/kg. The reduction in the late VEP components induced by pyrilamine and diphenhydramine was significantly antagonised by pre-treatment of histidine (200 and 500 mg/kg), but not by physostigmine even at a dose of 0.01 mg/kg. The effect induced by cyproheptadine was significantly potentiated by histidine (500 mg/kg), and significantly reduced by DOI (2 mg/kg). These results indicate that an inhibition of the late VEP components induced by H(1)-antagonist pyrilamine, diphenhydramine and chlorpheniramine may be due to an inhibition of specific sensory system relating the histaminergic mechanisms. In addition, slight enhancement of these components induced by cyproheptadine may be attributable to its anti-serotonergic effects.