Efferent projections from temperature sensitive recording loci within the marginal zone of the nucleus caudalis of the spinal trigeminal complex in the cat

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Abstract
The efferent projections from nucleus caudalis of the spinal trigeminal complex in cats were studied with retrograde and anterograde axonal transport techniques combined with localization of recording sites in the thalamus and marginal zone of nucleus caudalis to innocuous skin cooling. Results showed brainstem projections from nucleus caudalis to rostral levels of the spinal trigeminal complex, to the ventral division of the principal trigeminal nucleus, the parabrachial nucleus, cranial motor nuclei 7 and 12, solitary complex, contralateral dorsal inferior olivary nucleus, portions of the lateral reticular formation, upper cervical spinal dorsal horn and, lateral cervical nucleus. Projections to the thalamus included: a dorsomedial region of VPM (bilaterally) and to the main part of VPM and PO contralaterally. Neuronal activity was recorded in the dorsomedial region of VPM to cooling the ipsilateral tongue. HRP injections in this thalamic region retrogradely labeled marginal neurons in nucleus caudalis. These results show that marginal neurons of nucleus caudalis provide a trigeminal equivalent of spinothalamic projections to the ventroposterior nucleus in cats.