The most prominent function of the central nervous system is the control of motor functions by rapidly transmitted impulses through efferent cranial and spinal peripheral nerves. Besides electrically transmitted neural impulses, humoral mechanisms with more sustained actions are exercised by the brain and spinal cord to regulate body homeostasis. Thus, the brain may be regarded as an "endocrine gland" discharging neurohormones (peptides) either into the general circulation (neurohypophyseal hormones) or into the hypothalamo-adenohypophyseal portal circulation (releasing and inhibiting hormones). The brain, therefore, which is protected by the blood-brain barrier from disturbing and potentially noxious exogenous and endogenous agents circulating in the blood, has to have certain neurohemal regions beyond this barrier, such as the neural lobe and the median eminence (infundibulum), where neurohor mones have free access to the blood stream. To regulate somatic and autonomic functions in the best possible way, the central nervous system is highly dependent on feedback signals conveyed through somatic and visceral afferent nerves as well as on peripheral humoral signals such as peripheral hormones and other circulating substances that are under homeostatic regulation, e. g., peptides, arnines, electrolytes, and other biologically active agents. In this chapter, the role of the blood-brain barrier in the regulation of these sub stances will be discussed with special emphasis on the access through the blood-brain barrier to cardiovascular centers. 2 The Blood-Brain Barrier 2."

Latest issue in the CURRENT TOPICS IN NEUROENDOCRINOLOGY se- ries which has been gaining a great deal of reputation as a primary source for reviews in neuroendocrinology and related areas in the past few years.

I think the reader will agree that we have attained a good balance in Volume 6 between human-or animal-host and plant-host-related topics from outstanding research scientists. In Chapter 1, Frank Collins, Susan Paskewitz, and Victoria Finnerty explore the potential of recombinant DNA technology to distinguish indi vidual species and to establish phylogenetic relationships among member species in the Anopheles gambiae species complex, which includes the principal malaria vectors. Currently, relatively little is known about these morphologically identical species that are sympatric over most of their range but are not always equally involved in malaria transmission. With respect to individual species identification, the researchers have thus far described two DNA fragments, derived from the ribosomal DNA interge nic spacer region, that reliably distinguish five species in the complex by means of an RFLP visualized on a Southern blot. They have also described other species-specific fragments derived from a ribosomal DNA intron that could form the basis for a rapid dot blot assay. With respect to the phylogenetic relationships among member species in the complex, Collins, Paskewitz, and Finnerty focus on a comparison at the level of restriction site mapping and Southern analysis of the rDNA intergenic spacer regions. As expected, the two spacer regions near the coding region junctions are well conserved among the species, whereas the central regions tend to be highly variable among member species in the complex."