Neural circuits for triggering saccades in the brainstem
Department of Systems Neurophysiology, Graduate School of Medicine, Tokyo Medical and Dental University, Yushima, Bunkyo-ku, Tokyo 113-8519, Japan.Progress in brain research (Impact Factor: 2.83). 02/2008; 171:79-85. DOI: 10.1016/S0079-6123(08)00611-0
Here we review the functional anatomy of brainstem circuits important for triggering saccades. Whereas the rostral part of the superior colliculus (SC) is considered to be involved in visual fixation, the caudal part of the SC plays an important role in generation of saccades. We determined the neural connections from the rostral and caudal parts of the SC to inhibitory burst neurons (IBNs) and omnipause neurons (OPNs) in the nucleus raphe interpositus. To reveal the neural mechanisms of triggering saccadic eye movements, we analysed the effects of stimulation of the SC on intracellular potentials recorded from IBNs and OPNs in anaesthetized cats. Our studies show that IBNs receive monosynaptic excitation from the contralateral caudal SC, and disynaptic inhibition from the ipsilateral caudal SC, via contralateral IBNs. Further, IBNs receive disynaptic inhibition from the rostral part of the SC, on either side, via OPNs. Intracellular recording revealed that OPNs receive excitation from the rostral parts of the bilateral SCs, and disynaptic inhibition from the caudal SC mainly via IBNs. The neural connections determined in this study are consistent with the notion that the "fixation zone" is localized in the rostral SC, and suggest that IBNs, which receive monosynaptic excitation from the caudal "saccade zone," may inhibit tonic activity of OPNs and thereby trigger saccades.
- [Show abstract] [Hide abstract]
ABSTRACT: Over the past 15 years we have watched the unfolding of an enormous volume of information regarding HPV infections. Elaboration of the incredible genetic diversity of these viruses has been important to the development of laboratory tools for epidemiological investigations and will facilitate the future direction of studies targeting specific molecular mechanisms of disease. Through the use of these laboratory tools, HPV has been determined to be a necessary but not sufficient etiologic agent in the development of cervical cancer and other cancers of the anogenital tract. The duration of incident genital HPV infections has been partially established and this information demonstrates that most detectable HPV infections are transient. Recent observations of a second peak of cervical HPV prevalence in older women suggests the possibility that at least in some women, HPV infections may lay dormant at undetectable levels and subsequently become reactivated. The potential that older women may experience a reactivation of latent HPV infections, which may be accompanied by disease, requires further investigation. Current dogma concerning the long-term natural history of HPV infections awaits clarification by future studies. Furthermore, these future investigations remain important to appropriately characterize molecular processes within the host cell that are critical to the study of specific host immune responses to these infections.
- [Show abstract] [Hide abstract]
ABSTRACT: The superior colliculus (SC) plays an important role in controlling eye and head movements. The neural organization of the pathways from the SC to motoneurons in the horizontal oculomotor system has been well analyzed, but the neural mechanisms in the vertical saccade have not yet been analyzed in detail. This article reviews the current state of knowledge of the neural mechanisms of the horizontal and vertical saccadic eye movement system, and shows that they have common features: both systems contain excitatory and inhibitory burst neurons which receive inputs from the SC and directly project to motoneurons. Our recent study showed the presence of commissural inhibition between the upper and lower fields of motor map of the bilateral SCs. This reciprocal inhibition between the medial upward saccade area in one SC and the lateral downward saccade area in the other SC is very similar to that in the vestibular system. This similarity of the patterns of reciprocal inhibition in the SC system and the semicircular canal system implies that the SC output system may use the coordinate system based on the semicircular canals.
Data provided are for informational purposes only. Although carefully collected, accuracy cannot be guaranteed. The impact factor represents a rough estimation of the journal's impact factor and does not reflect the actual current impact factor. Publisher conditions are provided by RoMEO. Differing provisions from the publisher's actual policy or licence agreement may be applicable.