The Journal of Neuroscience, February 1, 2002, 22(3):1098-1107
Effects of Activation of the Histaminergic Tuberomammillary
Nucleus on Visual Responses of Neurons in the Dorsal Lateral Geniculate
Nucleus
Daniel J.
Uhlrich,
Karen A.
Manning, and
Jin-Tang
Xue
Department of Anatomy, University of Wisconsin Medical School,
Madison, Wisconsin 53706
We investigated the effects of the central histaminergic system on
afferent sensory signals in the retinogeniculocortical pathway in the
intact brain. Extracellular physiological recordings in
vivo were obtained from neurons in the cat dorsal lateral
geniculate nucleus (LGN) in conjunction with electrical activation of
the histamine-containing cells in the tuberomammillary nucleus of the
hypothalamus. Tuberomammillary activation resulted in a rapid and
significant increase in the amplitude of baseline activity and visual
responses in LGN neurons. Geniculate X- and Y-cells were affected
similarly. LGN cells that exhibited a burst pattern of activity in the
control condition switched to a tonic firing pattern during
tuberomammillary activation. Effects on visual response properties were
assessed using drifting sinusoidal gratings of varied spatial
frequency. The resultant spatial tuning curves were elevated by
tuberomammillary activation, but there was no change in tuning curve
shape. Rather, the effect was proportionate to the control response,
with the greatest tuberomammillary effects at spatial frequencies
already optimal for the cell. Tuberomammillary activation caused a
small phase lag in the visual response that was similar at all spatial
frequencies, consistent with the induced shift from burst to tonic
firing mode. These results indicate a significant histaminergic effect
on LGN thalamocortical cells, with no clear effect on thalamic
inhibitory neurons. The histaminergic system appears to strengthen
central transmission of afferent information, intensifying but not
transforming the retinally derived signals. Promoting sensory input may
be one way in which the histaminergic system plays a role in arousal.
Key words:
histamine; lateral geniculate nucleus; tuberomammillary
nucleus; visual receptive field; hypothalamus; burst and tonic modes; arousal; spatial tuning
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