Thalamic afferents from the brain stem. An experimental study using retrograde single and double labelling with HRP and iron-dextran in the rat. II. Nucleus laterodorsalis and subnucleus compactus nuclei pedunculo-pontini.

The reticulo-thalamic projection arising from the ncl. latero-dorsalis and from the subncl. compactus nuclei pedunculo-pontini was studied in single and double experiments using 51 injections of HRP and/or iron-dextran. The ncl. latero-dorsalis projects to the midline nuclei, to the ncl. mediodorsalis and to the ncl. ventralis lateralis, and, together with the subncl. compactus, also to the anterior, intralaminar nuclei, to the ncl. ventralis basalis and ncll. posteriores. Part of the substantia grisea centralis pontis adjoining the oral pole of the ncl. latero-dorsalis sends out fibres throughout the region of the above listed nuclei while projecting only scantily to the anterior nuclei and to the ventrobasal complex. The projection from the ncl. laterodorsalis has a major contralateral component (about one third of the labelled cells) whereas the contralateral component arising from the subncl. compactus is very scanty. We found no topographic arrangement in the projection (though there were signs of a crude mediolateral organization). The projection, mainly from the ncl. latero-dorsalis, shows relatively dense collateralization (double-labelled cells): ipsi- as well as contralaterally to the intralaminar nuclei, or collaterals to the ipsilateral intralaminary nuclei and, at the same time, to the contralateral ncl. mediodorsalis. A similar, albeit smaller collateralization, was also seen in the ncl. pedunculo-pontinus, its subncl. compactus: ipsilateral collateralization between the anterior and intralaminar nuclei or between the anterior and posterior intralaminar nuclei of the ipsilateral side.