Visual wulst influences on flash evoked responses in the ectostriatum of the zebra finch

Abstract

Anatomical data suggest that visual information from the thalamofugal pathway contributes to visual processing in the tectofugal pathway. We addressed the question of the functionality of anatomically described connections to the visual system of a laterally eyed bird, the zebra finch. The study shows the contribution of visual wulst efferents to visual processing in the ectostriatum by recordings of visually evoked slow field potentials. Suppression of visual wulst activity resulted in a selective reduction of distinct potential components in contralaterally evoked slow field potentials. A clear reduction was observed in the maximum amplitude of short latency components in the negative wave. Long latency components of the negative wave and the entire positive wave of the contralaterally flash evoked potentials were almost abolished. Ipsilateral visual evoked potentials (VEPs) were not significantly affected. Cooling and spreading depression of the optic tectum resulted in a uniform amplitude reduction of the negative wave. The positive wave was almost abolished. Ipsilateral VEPs disappeared completely during suppression of optic tectum activity. The results showed that the visual wulst has a significant, most likely facilitatory, influence on the processing of contralateral visual information in the ectostriatum. Ipsilateral stimulus processing was partly independent from visual wulst activity. A model for thalamo-and tectofugal connectivity in the ectostriatum is suggested.

Enhanced fos expression in the zebra finch (Taeniopygia guttata) brain following first courtship

“…The sensory modalities of these groups of neurons and their c‐fos activity pattern would also indicate a similar response to certain behavioral situations. This connection has been found in zebra finches, in which the ectostriatum integrates information from the thalamofugal pathway (Engelage and Bischof, 1994; Bischof and Watanabe, 1997). The LNH does receive a moderate projection from the HAD (Sadananda and Bischof, 1997), which other studies (Shimizu and Karten, 1995) also support, an indicator that the visual wulst modulates tectofugal processing.…”

Visual System Alterations in White Zebra Finches

“…Figure 3 shows representative recordings from central parts of the investigated structures. Complete recording tracks are not provided here, as these have been depicted in previ ous publications [Engelage and Bischof, 1988;Engelage and Bischof, 1989;Bredenkotter and Bischof, 1990a] trials, ipsilateral VEPs are substantially enhanced in white birds, reaching the amplitudes of the contralateral response in some cases ( fig. 3B).…”

“…In previous experiments we showed that ipsilateral stimulus processing is especially subject to severe inhibition [Engelage and Bischof, 1988;Brcdenkotter and Bischof, 1990a]. All recordings from white zebra finches show increased amplitudes of ipsilateral VEPs and therefore indicate a reduced inhibition of ipsilateral stimulus processing.…”

“…As mentioned above, the amplitude of ipsilateral VEPs within the ectostriatum of wild type birds is rather low. However, if we enucleated one eye [Engelage and Bischof, 1988] or masked it by injection of tetrodotoxin [Bredenkotter and Bischof, 1990a], the response to ipsilateral applied flashes increased to a level comparable to the amplitude of the contralateral response. This result can be interpreted to show that the activity of the contralateral eye, under normal conditions, influences the processing of ipsilateral visual stimuli.…”

“…Our morpho logical investigations should clarify whether white zebra finches show features of an albino, such as reduced pig mentation of the eyes or morphological alterations of the retinofugal pathway. Previous studies have shown that wild type zebra finches, although lacking ipsilaterally projecting retinal ganglion cells like all investigated avian species, exhibit substantial visually evoked potentials (VEPs) to ipsilateral stimulation within the ectostriatum [Engelage and Bischof, 1988]. If the physiological effects of low pig mentation in white zebra finches are similar to those ob served in albino mammals, the ipsilateral potentials should be reduced or eliminated.…”