Patterns of connections between zona incerta and brainstem in rats

Abstract

To understand better the organisation of zona incerta of the thalamus, this study has examined the patterns of connections that this nucleus has with various nuclei of the brainstem. Injections of biotinylated dextran or cholera toxin subunit B were made into the dorsal raphe, midbrain reticular nucleus, pedunculopontine tegmental nucleus, periaqueductal grey matter, pontine reticular nucleus, substantia nigra, superior colliculus, and ventral tegmental area of Sprague-Dawley rats, and their brains were processed by using standard tracer-detection methods. In general, our results show that zona incerta forms the major zone in the thalamus where these ascending brainstem axons terminate and from which descending axons that travel back to these same brainstem centres originate. These incertal inputs and outputs are limited largely to a distinct sector of zona incerta, the dorsal sector. An exception to this pattern is evident in the incertal projection to the deep layers of the superior colliculus; this projection, unlike all of the others, arises from cells in the ventral sector of zona incerta. Our results also show little evidence for a well-defined topography of projection between the brainstem and the zona incerta. For instance, small injections into each brainstem nucleus result in labelled terminals and in cells spread throughout much of the dorsal sector of zona incerta, with no local zone of concentration within the sector. Again, an exception to this pattern is seen in the incertal projection to the superior colliculus. This projection, unlike the others, shows a clear topographical organisation: A medial-lateral shift in the injection site in the colliculus results in a lateral-medial shift in the position of labelled cells in zona incerta. Curiously, even though the incertal projection to the colliculus appears to be mapped, the collicular projection back to zona incerta is not mapped. In conclusion, then, a number of brainstem nuclei (except for the deep collicular layers) have strong and overlapping connections within the same sector of zona incerta. This convergence of many functionally diverse brainstem afferents within zona incerta places this nucleus in a strategic position to sample the general activity of the brainstem and, perhaps, acts as a relay of this information to higher centres, such as the dorsal thalamic relay nuclei and the cerebral hemispheres.

Nigral Inhibition of GABAergic Neurons in Mouse Superior Colliculus

“…Thus, it is most likely that the evoked IPSCs were the result of SNr stimulation and not of stimulating other structures or passing fibers. However, we cannot exclude the possibility that the IPSCs were partially derived from inputs of the zona incerta, one of the extrinsic GABAergic sources to the SC (Ficalora and Mize, 1989;Appell and Behan, 1990;Kim et al, 1992;May et al, 1997;Kolmac et al, 1998), because the part of zona incerta that projects to SGI is located adjacent to the rostral SNr (May et al, 1997). Therefore, the contribution, if any, of incertotectal inputs to the evoked IPSCs should be much smaller than that of the nigrotectal inputs.…”

“…The stimulating electrodes were placed just ventral to the SC, and repetitive stimulation (20 -50 pulses at 50 Hz) was delivered to elicit the large amount of GABA release that should be necessary for activating GABA B receptors (Isaacson et al, 1993;Mitchell and Silver, 2000;Kaneda and Kita, 2005;Kaneda et al, 2008). Although this stimulation would activate both nigral and other passing GABAergic fibers, including those from the zona incerta and reticular formation (Ficalora and Mize, 1989;Appell and Behan, 1990;Kim et al, 1992;May et al, 1997;Kolmac et al, 1998), the stimulation-evoked IPSCs were not affected by bath application of the selective GABA B receptor antagonist CGP52432 (3 M) in six of six neurons tested (Fig. 3H ).…”

Invited Review Anatomical loops and their electrical dynamics in relation to whisking by rat

“…Importantly, the descending projection from M1 cortex has been shown to directly overlap with neurons in superior colliculus that project to the vibrissa region of the facial nucleus. (Nicolelis et al, 1992;Kolmac et al, 1998). (zona incerta ® trigeminal ganglion ) An inhibitory connection (Nicolelis et al, 1992;Kolmac et al, 1998).…”

“…(Nicolelis et al, 1992;Kolmac et al, 1998). (zona incerta ® trigeminal ganglion ) An inhibitory connection (Nicolelis et al, 1992;Kolmac et al, 1998). (zona incerta ® superior colliculus) An inhibitory connection (Kim et al, 1992;Nicolelis et al, 1992).…”

Distinctive patterns of connectivity between the zona incerta and the red nucleus of rats

“…The rostral sector houses small spindle-shaped cells, many of which are dopaminergic or somatostatinergic (Kolmac and Mitrofanis 1999a). This sector has been described to interconnect heavily with various "limbic" structures including the cingulate cortex, various brainstem nuclei, amygdala, hypothalamus and basal forebrain (Ricardo 1981;Watanabe and Kawana 1982;Shammah-Lagnado et al 1985;Roger and Cadusseau 1985;Romanowski et al 1985;Wagner et al 1995;Kolmac et al 1998;Kolmac and Mitrofanis 1999b;Reardon and Mitrofanis 2000). The dorsal sector has been associated with limbic structures also, together with many arousal centres as well.…”