INVITED REVIEW Mechanisms of Rectal Gland Secretion

of Beltz et al., in this issue). The present study on Carcinus established that semi-isolated crab brain preparations, perfused at rates as low as 0.45ml/min and at room temperature, remain physiologically active for 6 hours or more. This was confirmed by stimulating the nerve root carrying afferent information from tactile receptors around the eyes to the brain, which results in a reflexive withdrawal of the eyes . Neurons in the proliferation zones of these preparations, perfused with 1mg/ml BrdU in saline for 6 hours, label in the same way as they do in the intact animals. Such labeling is robust and persists in preparations perfused with low Ca or sea water (high Mg), treatments that reversibly block the eye withdrawal reflex. Preparations that were first flushed with saline and then placed in a dish containing BrdU and saline but without continued perfusion, were compared with preparations that were placed in the BrdU saline mixture immediately after dissection, also without continued perfusion. In both cases, reflexive responses were abolished, but cells labeled in the proliferation zones of both brains. A tentative conclusion to be tested is that neurogenesis in the brains of Carcinus is not modulated in the short term by afferent input to the brain, nor is it dependent on the maintenance of sensory-motor reflexive synaptic pathways. In addition, the insensitivity of the Carcinus brain preparation to operational trauma, and the ability to deliver agents directly to active cell proliferation zones, could provide us with a new approach to the study of environmental toxins on neurogenesis in central nervous systems. 1. Beltz, B. S. and D. C. Sandeman. Regulation of life-long neurogenesis in the decapod crustacean brain. Arthropod Structure and Development 32: 39-60 (2003). 2. Goergen, E., L. A. Bagay, K. Rehm, J. L. Benton, and B. S. Beltz. Circadian control of neurogenesis. Journal of Neurobiology 53: 90-95 (2002). 3. Sandeman D.C. (1969) The synaptic link between the sensory and motor axons in the crab eye withdrawal reflex. J