Mesotocin Research Articles

Immunocytochemical identification of the mesotocin- and vasotocin-producing systems in the brain of temperate and desert lizard species and their modifications by cold exposure

Using immunofluorescent techniques, mesotocin (MT) and vasotocin (VT) neurosecretory systems were identified in the brain of different lizards: one temperate species living in southern France and three desert species coming from southern Algeria. In the four species, MT and VT were shown to be synthesized in specific neurons located in the anterior preoptic area (POA), the supraoptic (SON), paraventricular (PVN), and ventromedial (VMN) nuclei. The neurosecretory axons of the POA neurons terminated in the vicinity of the lamina terminalis; in the three desert species, several additional VT fibers extended more rostrally, going into the olfactory bulb. The axons originating in SON, PVN, and VMN ended either in the external zone of the rostral median eminence (ME) near the adenohypophyseal portal vessels, or in the neural lobe of the hypophysis. A short exposure to cold (4°) in some specimens of Lacerta muralis induced a differential response in the dorsal and ventral parts of the PVN. Whereas the dorsal part remained unchanged, the ventral part instead appeared to be essentially composed of small neurons void of secretory granules. Cold exposure also led to a marked accumulation of both MT and VT in the internal zone of the ME, but of only VT in the external ME zone. On the other hand, a conspicuous amount of MT appeared in adenohypophyseal cells.

The presence of vasotocin-and mesotocin in serum and the hypothalamo—neurohypophyseal axis of chick embryos before hatching and in posthatch chicks

Decreasing hematocrit values were observed in chick embryos, from Day 17 to 1 day posthatching. Arginine vasotocin (AVT) and mesotocin (MT) were determined radioimmunologically in serum, neural lobe, and hypothalamic tissue. Serum levels of AVT and MT were significantly increased on Day 18 of incubation compared to Day 17. Thereafter AVT levels decreased, reaching at hatching levels even below Day 17. Serum MT remained elevated on Day 19, but decreased thereafter to the concentration values of Day 17. The amount of AVT in the preoptic hypothalamus and infundibulum was maximal on Day 19, whereas in the neural lobe the maximum was attained on Day 20. The MT content of the -infundibulum and neural lobe reached a maximum plateau on Day 18. These results suggest that a stimulation of the hypothaaamo-neurohypophyseal axis in the chick embryo occurs at the end of incubation. A possible causal relation with the observed decreasing hematocrit values is discussed.

The topography of mesotocin and vasotocin systems in the brain of the domestic mallard and Japanese quail: immunocytochemical identification.

The neurosecretory systems producing mesotocin (MT) and vasotocin (VT) (the avian homologues of oxytocin and vasopressin, respectively) were characterized in the brains of the domestic mallard and Japanese quail by means of indirect immunofluorescence techniques using specific antisera. In the anterior preoptic region, including the organum vasculosum of the lamina terminalis, and at different levels of the supraoptic and paraventricular nuclei, separate mesotocin- and vasotocin-producing neurons were identified. Mesotocinergic and vasotocinergic neurons were also located in the tuberomammillary area, among the ectomammillary tract fibers. The supraoptico-neurohypophysial tract, formed by vasotocin- and mesotocin-containing axons, enters the internal zone of the median eminence and ends in the posterior lobe of the pituitary. The external zone of the rostral median eminence appears to contain vasotocin and mesotocin fibers, which terminate in close contact with the capillaries of the hypophysial portal system.

Renal and vascular responses of the bullfrog (Rana catesbeiana) to mesotocin

Although mesotocin (MT) has long been known to occur in the amphibian neurohypophysis, there have been few reports on its action among amphibians. In the present investigation, renal responses of intact bullfrogs (Rana catesbeiana) and perfused bullfrog kidneys to MT were studied. The blood pressure responses of this amphibian to MT were also analyzed. We found that MT is diuretic at low doses and that the response is dose related. At high doses the diuretic response decreases progressively and, at times, antidiuresis is observed. The changes in urine flow are proportional to the changes in glomerular filtration rate. In addition, there is a dose-related depressor effect. Data from perfused kidney studies suggest that MT may dilate the afferent glomerular vessels. The possible action of MT as a physiologically important diuretic agent is discussed.