The distribution of substance P (SP), leucine-enkephalin (LENK), serotonin (5HT), dopamine (DA), and tyrosine hydroxylase (TH) was examined in the forebrain of the white sturgeon in order to evaluate several anatomical hypotheses based on cytoarchitectonics, and to gain a better understanding of the evolution of the forebrain in ray-finned fishes. The subpallium of the telencephalon has the highest concentration of the neuropeptides SP and LENK, allowing the pallial-subpallial border to be easily distinguished. The distribution of dopamine is similar to that of serotonin in the subpallium, fibers positive for these transmitters are particularly dense in the dorsal and ventral divisions of the subpallium. In addition, a small population of DA- and 5HT-positive cell bodies – which appear to be unique to sturgeons – was identified at the level of the anterior commissure. The internal granular layer of the olfactory bulbs had large numbers of TH-positive cell bodies and fibers, as did the rostral subpallium. The occurrence of cell bodies positive for LENK in the dorsal nucleus of the rostral subpallium supports the hypothesis that this nucleus is homologous to the striatum in other vertebrates. This is further reinforced by the apparent origin of an ascending dopaminergic pathway from cells in the posterior tubercle that are likely homologous to the ventral tegmental area/substantia nigra in land vertebrates. Finally, the differential distribution of SP and TH in the pallium supports the hypothesis that the pallium, or area dorsalis, can be divided medially into a rostral division (Dm), a caudal division (Dp) that is the main pallial target of secondary olfactory projections, and a narrow lateral division (Dd+Dl) immediately adjacent to the attachment of the tela choroidea along the entire rostrocaudal length of the telencephalic hemisphere.

Histochemical characteristics of the vitellogenic oocytes of the bluefin tuna, Thunnus thynnus L. Características histoquímicas de los ovocitos vitelogénicos del atún rojo, Thunnus thynnus L.

Different antisera directed against mammalian and piscine pituitary hormones, as well as a battery of various conventional histochemical techniques (PAS, Alcian Blue pH 2.5, Bromophenol Blue) and lectins, were used to identify the different hormonal cell types in the pituitary of the Senegalese sole, Solea senegalensis. Prolactin and adrenocorticotrophic cells were located in the rostral pars distalis of the pituitary. Gonadotrophic, thyrotrophic and growth hormone cells were distributed in the proximal pars distalis, but gonadotrophic cells appear also at the border of the pars intermedia. Somatolactin cells, as well as alpha-melanotrophic cells were located in the pars intermedia of the Solea senegalensis pituitary. The PAS reaction was positive in somatolactin cells, which were unreactive with the lead-Haematoxylin technique, whereas melanotrophic cells were positive. Glycoproteins containing mannose and/or glucose, as well as N-acetyl-glucosamine and sialic acid sugar residues, are synthesized and secreted by gonadotrophic, thyrotrophic and somatolactin cells. Adrenocorticotrophic cells and, especially, the amphiphilic somatolactin and acidophilic growth hormone cells were stained with the Bromophenol Blue technique that identifies proteins in general, but adrenocorticotrophic and growth hormone cells were unreactive towards PAS, Alcian Blue pH 2.5 and lectins (Con A and WGA).

The present paper which describes the distribution of zinc in the telencephalon of the rainbow trout, Oncorhynchos myciss, is the first report on the distribution of a heavy metal in the fish brain. Zinc was demonstrated histochemically by silver enhancement using the Neo-Timm method. The staining was mainly confined to the neuropil, but both moderately and intensely stained nerve cell bodies were of common occurrence. Stained fibers were never observed. The staining revealed a specific distribution pattern which could easily be correlated with the telencephalic nuclei defined on the basis of cytoarchitectural features. However, the telencephalon stained much more weakly than the rest of the brain, in striking contrast to the situation in the reptilian, mammalian, and avian brain. In these classes, high staining intensities are observed almost exclusively in the telencephalon. The staining was essentially restricted to the nuclei of the ventral telencephalic area. In the dorsal telencephalic area, only the medial and central zones and medial part of the posterior zone showed comparable staining intensities. The Neo-Timm staining pattern lends support to the view that the pallio-subpallial boundary is between the medial and dorsal zones of the dorsal telencephalic area. The distribution of zinc has been compared with the terminal field of afferent projections, known from experimental mapping, and also with the distribution of substance P and vasoactive intestinal peptide. Finally, the possible functional implications of zinc in synaptic vesicles are considered.

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