Anatomical experiments were performed in 12 cats in order to ascertain whether the periaqueductal gray matter (PAG) projects to several thalamic nuclei by divergent axons collaterals originating from the same population of cells. By means of the double labeling technique based on the retrograde axonal transport of fluorescent tracers, PAG neurones were searched that contribute bifurcating axons to the following couples of thalamic nuclei: i) to the nuclei ventrales posteromediales (VPM) of the two sides; it) to the nucleus parafascicularis (Pf) and ventralis posterolateralis (VPL) of the same side; iii) to the nucleus Pf and VPM of the same side. Fast Blue (FB), Evans Blue (EB) and Nuclear Yellow (NY) were used as fluorescent tracers. In other two groups, each consisting of 4 cats, FB injections into Pf were associated with either EB or NY injections within VPL or VPM. Double labeled neurones could be found within the PAG only in animals of the first group. It is concluded that PAG sends bifurcating axons originating from the same neurons to VPM of both sides and that the set of PAG neurones projecting to VPL or VPM are separate from the set projecting to Pf.
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Con il contributo del Ministero per i Beni e le Attività Culturali