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The lungs of cetaceans undergo anatomical and physiological adaptations that facilitate extended breath-holding during dives. Here, we present new insights on the ontogeny of the microscopic anatomy of the terminal portion of the airways of the lungs in five cetacean species: the fin whale (Balaenoptera physalus); the sperm whale (Physeter macrocephalus), the Cuvier's beaked whale (Ziphius cavirostris); the bottlenose dolphin (Tursiops truncatus); and the striped dolphin (Stenella coeruleoalba). We (a) studied the histology of the terminal portion of the airways; (b) used immunohistochemistry (IHC) to characterize the muscle fibers with antibodies against smooth muscle (sm-) actin, sm-myosin, and desmin; (c) the innervation of myoelastic sphincters (MESs) with an antibody against neurofilament protein; and (d) defined the diameter of the terminal bronchioles, the diameter and length of the alveoli, the thickness of the septa, the major and minor axis, perimeter and section area of the cartilaginous rings by quantitative morphometric analyses in partially inflated lung tissue. As already reported in the literature, in bottlenose and striped dolphins, a system of MESs was observed in the terminal bronchioles. Immunohistochemistry confirmed the presence of smooth muscle in the terminal bronchioles, alveolar ducts, and alveolar septa in all the examined species. Some neurofilaments were observed close to the MESs in both bottlenose and striped dolphins. In fin, sperm, and Cuvier's beaked whales, we noted a layer of longitudinal smooth muscle going from the terminal bronchioles to the alveolar sacs. The morphometric analysis allowed to quantify the structural differences among cetacean species by ranking them into groups according to the adjusted mean values of the morphometric parameters measured. Our results contribute to the current understanding of the anatomy of the terminal airways of the cetacean lung and the role of the smooth muscle in the alveolar collapse reflex, crucial for prolonged breath-holding diving., (© 2020 Wiley Periodicals LLC.)

Male Syrian hamsters that were exposed for 8 weeks to short photoperiod (LD 10:14) or treated with melatonin in the late afternoon under long photoperiod conditions (LD 14:10) had a significantly higher content of androgen receptors in the Lipidex-purified soluble fractions isolated from the Harderian glands as compared to the long photoperiod (LD 14:10) exposed controls. Simultaneous computer-assisted analyses of all series of saturation and competition experiments revealed that the numerical value of the apparent Kd, as determined by using the synthetic androgen R-1881 (methyltrienolone), was not different between the experimental groups, and ranged from 0.050 to 0.067 nM. Of the principal natural androgens, testosterone (T) was most potent in inhibiting methyltrienolone binding to the receptor (Ki values from 0.33 to 0.55 nM), and 5 alpha-dihydrotestosterone (DHT) and delta 4-androstenedione (AD) were less effective (Ki values between 1 and 1.9 nM). In the hypothalami and pituitaries of the same animals, used in parallel control assays, DHT was twice as potent as T. Short-term castration (24 hr post-orchidectomy) did not result in significant changes in the receptor binding characteristics. Following 8 weeks exposure to a long photoperiod (LD 14:10) the Bmax values demonstrated a four-fold increase in castrated animals (179 fmoles/mg protein vs. 47 fmoles/mg protein) over intact controls. The relative binding affinity of the major androgens under these conditions remained unchanged, with the exception of AD, where a five-fold increase in the numerical Ki values (decrease in the binding affinity) was recorded (Ki = 9.6 nM).(ABSTRACT TRUNCATED AT 250 WORDS)

The present study describes the patterns of melatonin production in the mule (Equus asinus x Equus caballus). Blood was sampled hourly for 24 h from eight mule mares in spring and fall. The data obtained show the presence of a circadian rhythm of production of melatonin, with highest values during the dark phase both in spring and fall. In fall the nightly rise of melatonin production begins earlier in the dark phase and reaches higher quantitative levels than in spring. The morning decline of melatonin production is similar in the two seasons. Maximal levels of nightly melatonin production in the mule are about 10 x higher than those described in the horse. The results reported here indicate the persistence of brain structures able to receive and transduce environmental signals in the mule, a genetically sterile mammalian hybrid.

Vasoactive intestinal peptide (VIP)-like immunoreactive nerve fibers were demonstrated by peroxidase antiperoxidase (PAP) immunohistochemistry to be distributed throughout the entire pineal gland of the sheep. VIP-containing fibers were observed along the blood vessels, penetrating into the gland from the pial capsule and also in the capsule itself. Some fibers left the perivascular position and entered the pineal parenchyma, where they were located among pinealocytes. This suggested that the VIPergic fibers might influence both pinealocytes and blood vessels of the gland. The location of VIP-containing fibers in the capsule of the pineal gland indicates that the fibers originate from perikarya located in a peripheral ganglion.

It has recently been shown that a 1.5-ml subcutaneous saline injection into the dorsal aspect of the hind limb induces a dramatic and rapid fall in N-acetyltransferase activity and melatonin content of the rat pineal gland at night. Since many studies have shown the opposite response to stress during the day, the first experiment was undertaken to test whether the timing of the saline injection at night influences the response of the pineal gland. In the present studies, rats were kept under light:dark (LD) cycles of 14:10 with lights out daily at 2000 h. Groups of rats were then given a saline injection at one of the following times: 2315, 0015, 0115, 0215, or 0315. Early in the dark phase (2315 and 0015) the saline injection depressed both the N-acetyltransferase (NAT) activity and the melatonin content of the pineal. As the animals were treated later in the dark period, the response became more blunted and, finally, disappeared. In the second experiment, animals that were kept in light during the usual dark period showed no pineal response when subjected to a hind leg injection of saline at either 2315 or 0315. Additionally, no response was seen in the two pineal parameters when rats had darkness onset delayed by 4 h (to 2400) and were then treated with saline at 0410. The results of these studies indicate that the pineal response to saline injection is time dependent. Also, if the nighttime rise in melatonin is suppressed by light exposure, a saline injection has no further inhibitory effect on pineal NAT activity or melatonin levels.

Blood was collected from the cerebral sinuses and from the jugular vein of 5 ewes during both the day and night. Cerebral sinus samples were collected by means of a permanently indwelling cannula (roughly every 5 min) while jugular vein samples were collected by venipuncture (roughly every 10 min). In each of the 5 animals mean nighttime melatonin concentrations were greater at night than during the day. In 2 animals, cerebral sinus plasma melatonin concentrations were greater than in the jugular vein; in 2 animals the sinus and jugular plasma had similar melatonin levels; in 1 ewe jugular vein blood melatonin levels exceeded those in the cerebral sinus plasma. These differences among animals are presumably due to slight positional differences in the cerebral venous cannula placement. In several animals episodic release of melatonin was apparent. Whereas the episodes were most obvious in the cerebral venous blood at night, they were also apparent in 1 case in the jugular vein plasma and in 1 animal during the day. When episodes appeared they occurred about every 15-20 min.