Neurotensin: revealing a novel neuromodulator circuit in the nucleus accumbens-parabrachial nucleus projection of the domestic chick.

Abstract

Lower brainstem projections from nucleus accumbens (Ac) subregions to the parabrachial complex (PB), the nucleus of the solitary tract and the vagal motor nuclei have been described previously in the domestic chick by our group. Such projections, particulary those from the core and rostral pole regions of Ac have not been found in mammals or pigeons. Here we report on the presence of neurotensin (NT) in the neurons projecting from different Ac subnuclei, and also from the bed nucleus of stria terminalis, to the PB in the domestic chicken. The study is based upon correlated retrograde tracing (using Fast Blue) and NT immunohistochemistry, supplemented with regional charting and quantitative analysis of double-labeled neurons. The number of retrogradely labeled cells in Ac subdivisions reflects the size of FB tracer deposit, and the degree to which it extends to the medial PB. Of all Ac subregions, the core contained the largest amount of double-labeled cells. The findings demonstrate that the anatomical pathway through which the Ac can directly modulate taste-responsive neurons of the PB employs mainly neurotensin as a neuromodulator. The observed anatomical difference between mammals and birds is either a general taxonomic feature or it reflects feeding strategies specific for the domestic chick. The results are also relevant to a better understanding of the role of NT in food intake and reward-related behaviors in birds.