Neurosecretory cells in the optic lobes of the brain and activity rhythms in Lycosa tarentula (Araneae: Lycosidae)

Several paired groups of neurosecretory cells (NS) were identified in the dorsal cortical neurons of the optic lobes of the brain of Lycosa tarentula (Araneae). Two large bottle-shaped cells (NS A1, A2) and a cluster of ca. 20 smaller cells (NS B) were found between the lamina and medulla of the anterior median eyes (AM). The forward oriented bundles of NS B axons run alongside large fibres linked to the synaptic zones of the indirect eyes. In front of the arcuate body, an islet of about 10 fusiform cells (NS C1) sends short axons close to the internal cortical border. Other large cells (NS C2, C3) are found from the medulla of the AM to the anterior border of the central body. Their long axons end deeply in the brain neuropil. NS B and C1 function synchronously. The secretory cycles of NS A1 and A2 seem to be in opposition. The activity of these three types of NS depends on the phase of the day. Anatomical relationships of NS A, B and C1 with visual afferent/efferent fibres via synaptic buttons indicate a role of these cells in the modulation of circadian rhythms of visual and locomotor activity. On the other hand, NS C2 and C3, the functioning of which is not synchronous, might be involved in the modulation or control of the elementary movements of L. tarentula when active or at rest.