Effects of Brainstem Parabrachail Activation on Receptive Field Properties of Cells in the Cat's Lateral Geniculate Nucleus. Uhlrich, D.J., N. Tamamaki, P.C. Murphy, and S. M. Sherman. Department of Neurobiology, State University of New York, Stony Brook, New York 11794-5230; and Department of Anatomy, University of Wisconsin, Madison, Wisconsin 53706
APStracts 2:0007N, 1995.
SUMMARY AND CONCLUSIONS
1. The lateral geniculate nucleus is the primary thalamic relay for the transfer of retinal signals to the visual cortex. Geniculate cells are heavily innervated from nonretinal sources, and these modify retinogeniculate transmission. A major ascending projection to the lateral geniculate nucleus arises from cholinergic cells in the parabrachial region of the brainstem. This is an important pathway in the ascending control of arousal. In an in vivo preparation, we used extracellular recordings to study the effects of electrical activation of the parabrachial region on the spontaneous activity and visual responses of X and Y cells in the lateral geniculate nucleus of the cat. 2. We studied the effects of two patterns of parabrachial activation on the spontaneous activity of geniculate cells. Burst stimulation consisted of a short pulse at high frequency (16 msec at 250 Hz). Train stimulation was of longer duration at lower frequency (e.g., 1 sec at 50 Hz). The firing rate of almost all geniculate cells was enhanced by either pattern of stimulation. However, the burst pattern of stimulation elicited a short, modulated response, with excitatory and inhibitory epochs. We found that the different epochs could differentially modulate the visual responses to drifting gratings. Thus, the temporal alignment of the brainstem and visual stimuli was critical with burst stimulation, and varied alignments could dramatically confound the results. In comparison, the train pattern of stimulation consistently produced a relatively flat plateau of increased firing, after a short initial period of more variable effects. We used the less confounding pattern of train stimuli to study the effects of parabrachial activation on visual responses. 3. Our main emphasis was to examine the parabrachial effects on the visual responses of geniculate cells. For most visual stimuli, we used drifting sinewave gratings that varied in spatial frequency; these evoked modulated responses from the geniculate cells. Parabrachial activation enhanced the visual responses of almost all geniculate cells, and this enhancement included both increased depth of modulation as well as greater response rates. 4. Our results were incorporated quantitatively into a Difference of Gaussians model of visual receptive fields to study the parabrachial effects on the spatial structure of the receptive field. This model fit our data well and provided measures of the response amplitude and radius of the receptive field center and surround. Parabrachial activation produced a fairly consistent elevation of the response amplitude of the receptive field center (Kc), and the center radius (Rc) was little affected, leading to an increase in the strength of the receptive field center (proportional to Kc Rc2). The effects on the response amplitude (Ks) and radius (Rs) of the receptive field surround were more variable. Despite this variability, increases in surround amplitude more than offset decreases in surround radius (and vice versa) such that parabrachial activation also consistently increased the strength of the receptive field surround (proportional to Ks Rs2). In some cells, surround and center strength increased proportionally, resulting in a proportionate increase at all spatial frequencies. In other cases, surround strength increased more than center strength, causing the cells to behave more like high pass filters. The reverse was found for other cells. 5. By most measures, geniculate X and Y cells were similarly affected by parabrachial activation. One notable exception is that the response amplitude of the receptive field center of X cells was increased significantly more than that of Y cells. We suggest that this may relate to a morphological difference in retinogeniculate circuitry between cell types. Most retinal inputs to X cells are strongly affected by interneuron terminals with which they form triadic contacts; retinal inputs to Y cells tend to be simpler and nontriadic. There is considerable parabrachial input to triads, affording the parabrachial region with a potentially powerful means of gating retinogeniculate transmission for X cells. 6. We confirm that parabrachial activation enhances the transmission of ascending visual information through the lateral geniculate nucleus. For almost all cells, the increase was observed at all spatial frequencies. The enhanced transmission of higher frequency stimuli will better convey information about the details of a visual scene. In addition, the increase in the strength of the receptive field surround will maintain the lateral inhibitory mechanisms that are crucial for the enhancement of visual contrast edges. These combined effects will result in the transmission of a sharper visual image. This is what one would expect under conditions of increased alertness, and it is consistent with the idea that the parabrachial region is involved in arousal. 

Received 29 November 1994; accepted in final form 3 February 1995.
APS Manuscript Number J605-3.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on  3 April 1995.