ネコの視床後腹側核の視床内結合に関する実験解剖学的研究

The present study was undertaken to elucidate the intrathalamic fiber connections of the posterior ventral nuclei of the thalamus. Localized stereotaxic lesions were placed in various parts of these nuclei in 13 cats, and the ensuing terminal degeneration in the dorsal thalamic nuclei were studied by the Nauta and Gygax method.<br>Within the posterior ventral nuclei, the posteromedial and posterolateral ventral nuclei are diffferentiated. The posteromedial ventral nucleus is further divided into the medial parvocellular and the lateral main parts. The posterior ventral nuclei have intrathalamic connections to the surrounding thalamic nuclei, in addition to cortical projections. Regarding the intrathalamic connections from different parts of the posterior ventral nuclei some differences in termination are noted. The medial part of the posteromedial ventral nucleus, regarded as a thalamic relay station in the gustatory paths, sends fibers profusely to the intralaminar nuclei in a wide sense, including the centre médian and parafascicular nuclei, and are connected across the midline with the paracentral and lateral central nuclei and the medial part of the posteromedial ventral nucleus on the opposite side. It should be mentioned that the rhomboid and medial ventral nuclei are not only pierced by decussating fibers, but also receive terminal fiders from the medial part of the posteromedial ventral nucleus. This part sends a limited number of fibers to the lateral part of the posteromedial ventral nucleus and the other ventral nuclei, including the submedial nucleus, as well as to the dorsal medial, posterior lateral and suprageniculate nuclei, but gives off no fibers to the medial and lateral geniculate bodies or the medial and inferior pulvinar nuclei.<br>The lateral main part of the posteromedial ventral nucleus and the posterolateral ventral nucleus are considered to be thalamic relay centers for somatic sensibility. The former sends fibers to the other ventral nuclei, viz. the posterolateral ventral, lateral ventral, medial ventral and submedial nuclei. It also gives off fibers to the intralaminar nuclei in a wide sense, the lateral part of the dorsal medial nucleus and the posterior lateral, suprageniculate and medial pulvinar nuclei, but send scarcely any fibers to the medial and lateral geniculate bodies. It sends no decussating fibers to the contralateral dorsal thalamus.<br>The dorsolateral part of the posterolateral ventral nucleus sends fibers to the posterior lateral, inferior pulvinar, suprageniculate nuclei and the lateral geniculate body, particularly its ventral nucleus. It also gives off fibers to the lateral part of the posteromedial ventral nucleus and the lateral ventral nucleus, but sends no fibers to the medial part of the posteromedial ventral nucleus or the dorsal medial, medial pulvinar, submedial and medial ventral nuclei. In addition, it gives rise to neither decussating fibers to the contralateral side nor terminal fibers to the midline nuclei. The dorsolateral part sends only few fibers to the intralaminar nuclei in a wide sense.<br>The ventromedial part of the posterolateral ventral nucleus sends more abundant fibers to the intralaminar nuclei in a wide sense and the posteromedial ventral, medial ventral and submedial nuclei than does the dorsolateral part, but gives off a lesser amount of fibers to the lateral geniculate body and the inferior pulvinar and lateral ventral nuclei. It sends fibers to the posterior lateral and suprageniculate nuclei, and only few fibers to the medial geniculate and dorsal medial nuclei which receive no fibers from the dorsolateral part.