Neuronal activity in primate visual cortex assessed by immunostaining for the transcription factor Zif268.

It is now well established that environmental signals mediated via neurotransmitters and hormones can induce responses in cells which involve a cascade of receptors, G proteins, and second messengers. These in turn can induce transcription factors which regulate long-term changes in gene expression. It has been proposed that the stimulus-transcription coupling properties of these DNA-binding proteins can be exploited to visualize activated neurons by way of immunostaining. We have used standard immunohistochemical techniques to detect the expression of one specific transcription factor, Zif268, in the visual cortex (area 17, V1) of vervet monkeys (Cercopithecus aethiops). Immunopositive neurons were present in large numbers throughout the visual cortex of the normal animal, being concentrated in layers 2/3 and 6 and at moderate levels in 4C beta and 5. To determine if Zif268 expression was affected by visual stimulation in the monkey, we restricted light input to one eye with the aim of revealing ocular-dominance columns in striate cortex. We found that short-term monocular deprivation induced either by enucleation, intravitreal TTX injection, or eyelid suturing resulted in dramatic changes in Zif268 levels, revealing vertically oriented columns of reduced Zif268 staining interdigitated with columns of normal expression. Furthermore, these columns were discernible after just 2 h of monocular blockade. A comparison of the ocular-dominance pattern obtained with Zif268 immunostaining and cytochrome oxidase histochemistry in long-term monocularly deprived animals showed a coincident reduction of both markers along columns that were precisely aligned in adjacent sections, indicating that Zif268 expression is restricted to cortical regions of high metabolic activity. Simultaneous immunostaining for Zif268 and the calcium-binding proteins calbindin and parvalbumin showed a negative correlation, suggesting that the Zif268 protein may be expressed selectively within excitatory neurons. A similar approach with immunostaining for neurofilament and microtubule-associated proteins (SMI-32 and MAP2) revealed pyramidal neurons which were regularly found to contain a Zif268-positive nucleus. Furthermore, confocal images of lucifer yellow filled neurons possessing Zif268-positive nuclei all showed pyramidal morphology. Taken together, these results point to activity-dependent expression of Zif268 within a subset of excitatory neurons.