In order to study the collateral projections from the parabrachial nucleus to the spinal cord and the nucleus of solitary tract in the rat

the fluorescent double labeling method was used in the present study.After PI and Bb were injected into the caudal part of the nucleus of solitary tract and the ipsilateral dorsal horn of the spinal cord respectively

PI labeled

Bb labeled and PI/Bb double labeled neurons were observed in the Kolliker Fuse nucleus(K F)which is a subnucleus of the parabrachial nucleus. The percentages of PI labeled

Bb labeled and PI/Bb double labeled neurons to all labeled neurons in the K F were 43.62%

40.08%and 16.28% respectively.Most of the double labeled neurons were multipolar and trangular.The diameters of the double labeled neuronal cell bodies were between 10 to 18 μm. The projections from the parabrachial nucleus to the spinal cord might transmit the somatosensory information

while the projections from the parabrachial nucleus to nucleus of solitary tract might transmit the visceral information. Those PI/Bb double labeled neurons in the K F that project directly to both the nucleus of the solitary tract and the spinal cord may simultaneously transmit somatosensory information and visceral information to exert modulatory influences upon neurons in the solitary tract and the spinal cord.