EARLY FORMATION OF SEXUALLY DIMORPHIC GLOMERULI IN THE DEVELOPING OLFACTORY LOBE OF THE BRAIN OF THE MOTH MANDUCA-SEXTA

The antennal lobes (ALs), the primary olfactory centers, of the moth M anduca sexta are sexually dimorphic. Only ALs of males possess the mac roglomerular complex (MGC), the site of primary processing of informat ion about the female's sex pheromone. To understand the development of identified, odor-specific olfactory glomeruli, we investigated the ce llular events involved in the morphogenesis of the MGC by means of var ious fluorescence staining techniques and laser-scanning confocal micr oscopy. The MGC lies near the entrance of the antennal nerve into the AL of the adult male and comprises three glomeruli, the globular cumul us and two toroidal structures. The MGC forms during early stages of m etamorphic adult development through a stereotyped sequence of coordin ated changes in MGC-specific receptor axons, glial cells, and early-in growing projection neurons of the medial group of AL neurons. The MGC divisions are the earliest glomeruli to form in the male AL, and their basic organization is established within about 3 days after ingrowth of the first sensory axons. Despite their special anatomical features, the MGC glomeruli develop in a manner similar to that of the ordinary glomeruli. Comparison of the ALs of males and females reveals that tw o relatively large and early-developing glomeruli that are situated do rsolaterally in the female AL appear to be female-specific. Developmen t of the sexually dimorphic glomeruli diverges immediately after the i ngrowth of the first olfactory receptor axons, resulting in the format ion of these large glomeruli in females and the MGC in males. (C) 1998 Wiley-Liss, Inc.