The localization of oxytocin (OT)-binding sites in the developing rat kidney and their pharmacological characterization were investigated by means of autoradiographic techniques. The cellular localization was studied by application of the histoautoradiographic technique to (1) frozen sections and semithin sections from kidney slices incubated in vitro in the presence of a 125I-labelled OT antagonist and (2) frozen and semithin sections from kidneys after in vivo systemic infusion of the radioligand. Pharmacological characteristics were determined in competition experiments by using quantitative film autoradiography. Specific OT-binding sites were first detected at embryonic day 17 (E17) in the cortex. At early stages up to postnatal days (PN30), the cortical OT-binding sites were highly concentrated on the juxta- and paraglomerular portion of the distal tubule; in the adult they were restricted to the macula densa. In the medulla, OT-binding sites were first detected at E19 when this region is forming; they were localized on the thin limb of Henle's loop. These data obtained by in vivo binding were confirmed by in vivo binding at PN30 which showed, in addition, the presence in one rat of OT-binding sites in the inner stripe of the outer medulla. At all stages examined (PN15 to PN90), cortical OT-binding sites had a higher selectivity for OT versus vasopressin (IC50 = 0.78 +/- 0.04 nM and 8 +/- 0.5 nM respectively at PN90) than medullary sites (IC50 = 1.9 +/- 0.27 nM and 2 +/- 1.13 nM respectively at PN90). These data suggest that the OT-binding sites of the macula densa and thin Henle's loop, detected in the rat kidney, represent two subtypes of OT receptors which could mediate distinct effects of OT on kidney function.

The localization and pharmacological characteristics of vasopressin (VP) binding sites of the V_1a subtype in developing and adult rat kidney were investigated by radioautography on kidney sections incubated in the presence of a radioiodinated selective V_1a antagonist. Their localization after in vivo systemic infusion of the radioligand was also investigated. V_1a binding sites first appear at embryonic day 16 on vascular elements. In the adult, they were localized in the cortex (vascular and tubular structures, juxtaglomerular apparatus), the outer medulla outer stripe (vasa recta) and inner stripe (thin descending limbs of short looped nephrons) and the inner medulla (collecting ducts). Data obtained in vitro were confirmed by in vivo binding at postnatal day 30 (PN30). Whatever their localizations, the V_1a binding sites exhibited full V_1a pharmacological profile in postnatal stages rats and in adult rats: a high affinity (nM range) for VP and for the V_1a agonist, a lower affinity (µM range) for oxytocin and no affinity for the oxytocin agonist. The presence of V_1a binding sites in these different structures raises the question of the putative roles of VP in modulating renal functions. A striking finding is the presence of V_1a binding sites in the outer medullary thin descending limbs of short looped nephrons suggesting their colocalization with urea transporters.

The long homer proteins 1b/c, 2a/b, and 3a/b play an important role in postsynaptic neurons by clustering glutamate receptors and by coupling the receptors with various intracellular effectors. Using immunohistochemistry and Western-blot analysis, this study shows that the expression of the long homer isoforms 1b/c and 3a/b was induced in rat cerebellum in response to cocaine administration. Acute treatment produced a very robust induction of both constitutive isoforms, whereas repeated treatment for 10 days induced a large expression of homer 1b/c and a more modest increase in the expression of the 3a/b isoform. The heat shock protein hsp 27 was also considerably induced in the cerebellum of cocaine-treated rats, suggesting that it participates in assisting the correct folding of proteins, and by counteracting oxidative stress mechanisms triggered by the psychostimulant. In addition of being expressed in Purkinje neurons, homer 3a/b and hsp 27, but not homer 1b/c, were localized within Bergmann glial cells and in their extensions, which surround Purkinje cells, as assessed by coimmunoreactivity with glial fibrillary acidic protein. Cocaine was also found to induce both proteins in the Bergmann glial cells. Since we found that homer 3a/b colocalized with the mGluR1 receptor in Purkinje cells, the data suggest that the long homer isoforms are involved in the cocaine-induced neuroplasticity that takes place in the cerebellum, by reshaping postsynaptic densities in Purkinje cell dendrites.

The localization of oxytocin (OT) binding sites and vasopressin (VP) binding sites of the V1a subtype was investigated by radioautography in kidneys of rabbits, mice and meriones during postnatal development and in the adult, and in the human kidney. Kidney sections were incubated in the presence of selective radioiodinated OT and V1a antagonists, respectively. The localizations were compared with those previously described in the rat. The main finding of the study was the almost constant presence in the cortex of V1a binding sites in the connecting tubule, the cortical collecting duct and in the juxtaglomerular apparatus (on the intra- and extraglomerular mesangium and the afferent arteriole). This distribution suggests an interaction of VP via V1a receptors and the kallikrein-kinin system in the kidney. OT binding sites, in comparison with V1a binding sites, were fewer and less constantly detectable in the kidney of the different species. In the mouse, their presence on the limbs of Henle’s loop in the medulla points to the possibility of their involvement in the medullary concentrating process. In the kidneys of the various species, OT and V1a binding sites occurred always in differential structures. In contrast, in the human kidney cortex, a colocalization of OT and V1a binding sites was almost constantly observed. This raises the question as to the specificity of the neurohypophysial hormone receptors in the human kidney.