GALANIN IMMUNOREACTIVITY WITHIN THE PRIMATE BASAL FOREBRAIN - EVOLUTIONARY CHANGE BETWEEN MONKEYS AND APES

Galanin immunoreactivity (GAL-ir) is differentially expressed within t he basal forebrain of monkeys and humans. Most monkey magnocellular ba sal forebrain neurons colocalize GAL-ir. In contrast, virtually no hum an magnocellular basal forebrain neurons express GAL-ir. Rather, an ex trinsic galaninergic fiber plexus innervates these neurons in humans. The present study examined the expression of GAL-ir within the basal f orebrain of apes to establish the phylogenetic level at which this tra nsformation occurs. The staining patterns of GAL-ir within the basal f orebrain of both lesser (gibbons) and great (chimpanzee and gorilla) a pes were compared to that previously observed within monkeys and human s. All apes displayed a pattern of basal forebrain GAL-ir indistinguis hable from humans. GAL-ir was not expressed within ape basal forebrain magnocellular neurons as seen in monkeys. Rather like humans, a dense collection of GAL-ir fibers was seen in close apposition to magnocell ular perikarya. In addition, a few GAL-ir parvicellular neurons were s cattered within the ape basal forebrain. These data indicate that the evolutionary change in the expression of GAL-ir within the primate bas al forebrain occurs at the branch point of monkeys and apes. (C) 1993 Wiley-Liss, Inc.