Neural circuits for triggering saccades in the brainstem
ABSTRACT 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.
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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.Research-grade PCR-based HPV tests continue to be important to ongoing and future epidemiological investigations that will better define HPV incidence at various anatomic sites. Of particular interest will be the elaboration of HPV infections at extragenital sites. In this regard, the potential contribution of HPVs to skin cancer outcomes is likely to become an intensive area of study. The use of HPV assays such as HC2 in large randomized clinical trials has established HPV testing as a viable option in the management of ASCUS Pap smears. Further clinical applications of various types of HPV testing, including applications to routine screening, remain an area of intensive research. In this regard, studies that examine quantities or levels of HPV genomes and specific HPV messages are currently underway. Probably the most exciting clinically relevant development of the past decade has been the implementation of clinical trials for HPV prophylactic vaccines. To date these trials have targeted cervical HPV infections. If prophylactic HPV vaccines can prevent incident HPV infection and CIN, maintenance of long-term vaccine immunity will need to be evaluated and establishment of any potential impact on the incidence of HPV-associated invasive cancers will be determined in one or two decades following widespread implementation.Many individuals and research groups have participated in contributing to understanding the epidemiology of HPV infections. As with the past two decades, future investigations concerning HPV infections will remain an area rich in discovery for all.Perspectives in Medical Virology 01/2002; DOI:10.1016/S0168-7069(02)08014-X
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ABSTRACT: The oculomotor system is the motor system of choice for many neuroscientists studying motor control and learning because of its simplicity, easy control of inputs (e.g., visual stimulation), and precise control and measurement of motor outputs (eye position). This is especially true in primates, which are easily trained to perform oculomotor tasks. Here we provide the first detailed characterization of the oculomotor performance of trained squirrel monkeys, primates used extensively in oculomotor physiology, during saccade and smooth pursuit tasks, and compare it to that of the rhesus macaque. We found that both primates have similar oculomotor behavior but the rhesus shows a larger oculomotor range, better performance for horizontal saccades above 10 degrees, and better horizontal smooth pursuit gain to target velocities above 15 deg/s. These results are important for interspecies comparisons and necessary when selecting the best stimuli to study motor control and motor learning in the oculomotor systems of these primates.Experimental Brain Research 06/2011; 212(3):409-16. DOI:10.1007/s00221-011-2746-4 · 2.17 Impact Factor
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ABSTRACT: The saccade trigger signal was proposed by D.A. Robinson, but neural substrates for triggering saccades by inhibiting omnipause neuron (OPN) activity still remain controversial. We investigated tectal inputs to OPNs by recording intracellular potentials from OPNs and inhibitory burst neurons (IBNs) and searched for interneurons to inhibit OPNs in the brainstem of anesthetized cats. IBNs received monosynaptic excitation from the contralateral caudal superior colliculus (SC) and disynaptic inhibition via contralateral IBNs from the ipsilateral caudal SC, whereas IBNs received disynaptic inhibition from the rostral SC. The latter disynaptic inhibition was mediated by OPNs, since OPNs received monosynaptic excitation from the rostral SC and projected to IBNs. In contrast, OPNs received disynaptic inhibition from the caudal SC. This disynaptic inhibition from the caudal SC was mediated to OPNs by IBNs. These findings suggested possible roles of IBNs for triggering and maintaining saccades by actively inhibiting the tonic activity of OPNs.Annals of the New York Academy of Sciences 09/2011; 1233(1):100-6. DOI:10.1111/j.1749-6632.2011.06171.x · 4.31 Impact Factor