MORPHOLOGY AND DENDRITIC DOMAINS OF NEURONS IN THE LATERAL PARABRACHIAL NUCLEUS OF THE RAT

The present study provides a description of the dendritic morphology a nd the dendritic domains of neurons in the lateral parabrachial nucleu s (PB) of the rat. The cells were intracellularly stained in vitro wit h Lucifer yellow. A subpopulation of these cells was characterized bef orehand as neurons projecting to the amygdaloid complex by retrograde transport with rhodamine beads. With respect to their dendritic arbori zation, different types of ''spatially'' organized PB neurons were dis criminated. One major cell type in the external lateral PB (PBel) is c haracterized by long, elongated dendritic trees that are preferentiall y oriented parallel to the superior cerebellar peduncle. The majority of their dendrites appears to respect subnuclear boundaries, yet their distal dendrites often exceed the limits of the PBel to encroach upon adjacent subnuclei located dorsally and ventrolaterally to the PBel. Another prominent cell type in the PBel has fairly small and locally r estricted dendritic trees that are also elongated, running with their main axis from ventrolateral to dorsomedial. The dendrites of the majo rity of these neurons apparently stay within the confines of the PBel. A distinct group of neurons is found in the ventral portion of the PB el. The majority of their dendrites is mediolaterally oriented and not confined to the PBel subnucleus. In addition, we found a smaller numb er of neurons scattered within the lateral PB whose dendrites do not s how a preferential orientation but travel across subnuclear boundaries into several different PB subnuclei. Our data show that the dendrites of a large proportion of neurons in the lateral PB either stay within the confines of a particular subnucleus or slightly extend across sub nuclear limits. In any case, they appear to match with terminal territ ories of afferent axons and, thus, maintain the functional specificity of inputs by their relay through the PB. In contrast, PB neurons that extend their dendrites across subnuclear boundaries or known terminal territories are likely to receive inputs of different qualities from a variety of sources and therefore transmit a more general, integrated signal to the forebrain. (C) 1995 Wiley-Liss, Inc.