Presence of a substance P-like immunoreactive neurone system from the parabrachial area to the central amygdaloid nucleus of the rat with reference to coexistence with calcitonin gene-related peptide.

An ascending neurone system containing substance P-like immunoreactivity (SPI) from the lateral parabrachial nucleus (PBL) to the central amygdaloid nucleus (AC) was detected. Destruction of the external subdivision of the PBL resulted in a marked ipsilateral reduction of SPI fibres in the AC, which suggests that SPI neurones project mainly ipsilaterally to the AC. This was supported by the findings that injection of biotin-wheatgerm agglutinin into the AC labelled many neurones in the ipsilateral external subdivision of the PBL. Simultaneous staining with antiserum showed that some of these neurones contain SP. Immunohistochemical double-staining revealed that almost all of the SPI neurones in the external subdivision of the PBL contained calcitonin gene-related peptide.