William F. Ganong

Since the discovery of renin 80 years ago, there have been remarkable advances in our understanding of the renin-angiotensin system. The system as it is known today is summarized in Figure 1. Angiotensin III, the active component of the system, has several important physiological actions. The first of these to be identified was its pressor action, and for many years it was felt that the sole function of the renin-angiotensin system was regula­ tion of blood pressure. A new dimension was added in 1960 with the discovery that angiotensin II stimulates the secretion of aldosterone and is therefore in a position to exert important effects on salt and water balance. Several additional actions of angiotensin II were then discovered. It was found that the peptide can increase the secretion of catecholamines from the adrenal and facilitate adrenergic transmission. It also acts directly on the brain to increase blood pressure via sympathetic and parasympathetic path­ ways, to produce thirst, and to stimulate the secretion of vasopressin and ACTH. Through these actions, the renin-angiotensin system plays an im­ portant role in the regulation of blood pressure and of the volume and composition of the extracellular fluid. Major advances have also been made in our understanding of other aspects of the renin-angiotensin system. It has become clear that the hep­ tapeptide metabolite of angiotensin II, [des-Aspl] angiotensin II (angio-

To investigate the interaction in speech perception of auditory information and lexical knowledge (in particular, knowledge of which phonetic sequences are words), acoustic continua varying in voice onset time were constructed so that for each acoustic continuum, one of the two possible phonetic categorizations made a word and the other did not. For example, one continuum ranged between the word dash and the nonword tash; another used the nonword dask and the word task. In two experiments, subjects showed a significant lexical effect--that is, a tendency to make phonetic categorizations that make words. This lexical effect was greater at the phoneme boundary (where auditory information is ambiguous) than at the ends of the condinua. Hence the lexical effect must arise at a stage of processing sensitive to both lexical knowledge and auditory information.

1. The circumventricular organs (CVO) are structures that permit polypeptide hypothalamic hormones to leave the brain without disrupting the blood-brain barrier (BBB) and permit substances that do not cross the BBB to trigger changes in brain function. 2. In mammals, CVO include only the median eminence and adjacent neurohypophysis, organum vasculosum lamina terminalis, subfornical organ and the area postrema. 3. The CVO are characterized by their small size, high permeability and fenestrated capillaries. The subcommissural organ is not highly permeable and does not have fenestrated capillaries, but new evidence indicates that it may be involved in the hypertension produced by aldosterone acting on the brain. 4. Feedback control of corticotropin-releasing hormone (CRH) secretion is exerted by free steroids diffusing into the brain, but substances such as cytokines and angiotensin II act on CVO to produce increases in CRH secretion. Gonadal steroids also diffuse into the brain to regulate gonadotrophin-releasing hormone secretion. Thyrotropin-releasing hormone secretion is regulated by thyroid hormones transported across cerebral capillaries. However, CVO may be involved in the negative feedback control of growth hormone and prolactin secretion.