A detailed description is given of the distribution of vasopressin-immunoreactive structures in the brain of intact adult male rats. By application of a modified immunocytochemical procedure, vasopressin-immunoreactive fibers were detected in many new areas. In adult male rats which were castrated 15 weeks before death, vasopressin-immunoreactive cell bodies had disappeared from the bed nucleus of the stria terminalis and the medial amygdaloid nucleus. No obvious changes were found in vasopressin-immunoreactive cell bodies in other areas. Furthermore, a very strong reduction was seen in the density of vasopressin-immunoreactive fibers in the olfactory tubercle, nucleus of the diagonal band and its immediate surroundings, ventral pallidum, basal nucleus of Meynert, lateral septum, septofimbrial nucleus, ventral hippocampal formation, amygdaloid area, pre- and supramammillary nucleus, supramammillary decussation, (inter)dorsomedial, parafascicular, and ventral aspect of paraventricular thalamic nuclei, zona incerta, lateral habenular nucleus, ventral tegmental area, substantia nigra, periventricular gray, dorsal and median raphe nucleus, and locus coeruleus. No changes were observed in other areas containing vasopressin-immunoreactive fibers. These changes following gonadectomy were not observed in castrated rats which had been treated with testosterone. The results suggest that vasopressin projections from the bed nucleus of the stria terminalis and possibly from the medial amygdaloid nucleus require the presence of gonadal hormones for their normal appearance. This is in contrast to pathways arising from the hypothalamic vasopressin-producing nuclei, which fail to show obvious changes following castration.

We have found two immunologically distinguishable cone types in the retina of the mouse, each localized to two opposite halves of the eye. One cone type was labelled by the monoclonal antibody COS-1 specific to the middle-to-long wave sensitive visual pigment of the mammals, while the other type was stained by the shortwave-specific monoclonal antibody (OS-2). These results were confirmed with other antibodies directed against specific sequences of the visual pigments. As a result of the uneven distribution of the two cone types the mouse retina is divided into two fields separated by an oblique meridional line. The middlewave sensitive cones were present exclusively in the dorsal half of the mouse retina (M-field). The overwhelming majority of the shortwave sensitive cones occupied the ventral half (S-field), and only a small number was scattered among the middlewave sensitive cones in the dorsal retina. The ratio of the two cone types in the M-field corresponds to what has been found in the retina of other mammals, including rodents such as the gerbil and the rat. The S-field represents an entirely unique area with the unusually great number of shortwave sensitive cones and with the complete lack of the middlewave sensitive ones. The present study provides the structural basis for dichromacy in a rodent species considered for a long time to be monochromat. In addition, it shows that the ventral retina, containing exclusively S-cones in a relatively high density, is a unique retinal field not present in other mammalian species studied so far.

The rat brain contains a large number of vasopressin (VP) immunoreactive fibers, the sites of origin of which have not yet been established completely. For instance, the sources of VP fiber systems in the amygdala, ventral hippocampus (VH), mediodorsal thalamic nucleus, ventral tegmental area, and dorsal raphe yet remain obscure. These VP fibers may originate in any of the recently described extrahypothalamic VP cell groups, viz., medial amygdaloid nucleus (AME), dorsomedial hypothalamic nucleus, or locus coeruleus, since VP efferents from these cells still remain to be demonstrated. In search of AME VP efferents three approaches were followed: (1) the Phaseolus vulgaris anterograde tracing method, (2) immunocytochemistry after AME lesioning, and (3) retrograde transport of a fluorescent dye in combination with immunofluorescence. The results demonstrate that VP cells in the AME project to (1) the lateral septum (LS) by the ventral amygdalofugal pathway and (2) the VH via the amygdalohippocampal transition zone. In addition, the VP projection from the bed nucleus of the stria terminalis (BST) to the LS was confirmed. There was no indication that VP cells in the AME project through the amygdalotegmental pathway to the medulla oblongata and spinal cord. The results support the possibility that the BST and AME are an anatomical entity that may be part of the central loci controlling sexual processes in the rat.

No abstract

The retina of mammals contains various amounts of cone photoreceptors that are relatively evenly distributed and display a radially or horizontally oriented area of peak density. In most mammalian species two spectrally different classes of cone can be distinguished with various histochemical and physiological methods. These cone classes occur in a relatively constant ratio, middle‐to‐longwave sensitive cones being predominant over short‐wave cones. Recent observations do not support the idea that each cone subpopulation is uniformly distributed across the retina. With appropriate type‐specific markers, unexpected patterns of colour cone topography have been revealed in certain species. In the mouse and the rabbit, the “standard” uniform pattern was found to be confined exclusively to the dorsal retina. In a ventral zone of variable width all cones express short‐wave pigment, a phenomenon whose biological significance is not known yet. Dorso‐ventral asymmetries have been described in lower vertebrates, matching the spectral distribution of light reaching the retina from various sectors of the visual field. It is not clear, however, whether the retinal cone fields in mammals carry out a function similar to that of their counterparts in fish and amphibians. Since in a number of mammalian species short‐wave cones are the first to differentiate, and the expression of the short‐wave pigment seems to be the default pathway of cone differentiation, we suggest that the short‐wave sensitive cone fields are rudimentary areas conserving an ancestral stage of the photopigment evolution. © 1996 Wiley‐Liss, Inc.