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 degrees) 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.