Cardiovascular changes during and after arousal from hibernation in golden hamsters

This thesis examines the plasticity of cardiovascular control of golden hamsters {Mesocricetus auratus) in four physiological conditions, normal controls at euthermy, cold controls (cold-exposed animals that did not undergo hibernation), hibernating animals and animals aroused from hibernation for 2 h. There were two main areas of study 1) the endothelium and perivascular innervation of mesenteric and renal arteries using electron-immunocytochemical techniques and 2) gap junctions in the left ventricle and aorta using immunohistochemistry combined with laser confocal microscopy. During hibernation, the percentages of both nitric oxide synthase (NOS)- positive and endothelin (ET)-positive endothelial cells in the superior mesenteric artery and renal artery were markedly lower than in the controls. In the mesenteric artery, the percentage of NOS and ET positive endothelial cells fell from 22% and 17%, respectively, in the normal controls to 1% and 6%, respectively, during hibernation. In the renal artery 23% and 43% of endothelial cells contained NOS and ET, respectively in the normal controls but only 5% contained NOS and ET in the hibernating group. On arousal, the percentages of NOS and ET immunopositive endothelial cells were similar to the normal control values (18% and 13%, respectively, in the mesenteric artery and 21% and 30%, respectively, in the renal artery). In perivascular nerves, there was an increase in the percentage of axon profiles positive for sympathetic nerve markers, tyrosine hydroxylase (from 17% to 57% during hibernation in the mesenteric artery and from 20% to 76% during hibernation in the renal artery) and neuropeptide Y (from 30% to 65% during hibernation in the mesenteric artery and from 25% to 77% in the renal artery). There was also a hibernation-associated decrease in the percentage of axon profiles containing a parasympathetic nerve marker, vasoactive intestinal polypeptide (from 14% to 4% during hibernation) in the mesenteric artery. These changes are consistent with increased peripheral vascular resistance during hibernation. The endothelial and neural changes reported may reflect a predominantly sympathetic vasoconstrictor control during hibernation concomitant with a reduced endothelial contribution to the maintenance of vascular tone. The density of immunoreactive connexin (Cx) 43 gap junctions was significantly increased in left ventricular cardiomyocytes in hibernating hamsters (area and numerical density were 9.73±1.4 and 16.11 ±1.6 µm2/1000 µm2, respectively, in hibernation compared to 4.03±0.93 and 10.68±1.7 µm2/1000 µm2 in normal control, hibernation compared to 4.03±0.93 and 10.68±1.7 µm2/1000 in normal control, P<0.05). Cx43 plaque size was larger in cold controls and hibernating animals (0.52+0.04 and 0.58±0.03 µm2, respectively, compared to normal controls, P<0.05). Cx40 immunoexpression at the endothelium lining coronary arterioles of the ventricle was increased in the cold control group only: Cx40 area density was 38.99±4.19 µm2/1000 µm2 in cold controls compared to 25.26±3.2 µm2/1000 µm2 in normal controls and was significantly greater than during hibernation (23.04±3.1 µm2/1000 µm2, P<0.05). There were no changes in Cx40 levels in the aortic endothelium or in levels of Cx43 in smooth muscle of the aorta. The increase in cardiomyocyte gap junction proteins in the cold controls may represent a compensatory response to prepare the animal for hibernation avoiding ventricular fibrillation, while during hibernation, increased connexin expression may facilitate intercellular transfer of selected signals in readiness for arousal. The elevation of gap junction channels in coronary arteriolar endothelium corresponds with the requirement of increased intercellular communications during the prolonged circulatory changes required to maintain core temperature. In summary, cardiovascular changes during hibernation operate at several different levels, neural, endothelial and at the level of cell to cell communication via gap junctions. These changes emphasise the active rather than passive nature of the process of hibernation and arousal

Egg-laying-hormone immunoreactivity in the neural ganglia and ovary of Haliotis asinina Linnaeus

Immunoreactivity against the abalone egg-laying hormone (aELH) was detected in the fine granules of type 1 and 2 neurosecretory (NS) cells, neurites in the neuropil, and blood sinuses in the connective tissue sheath of the cerebral, pleuropedal, and visceral ganglia of the tropical abalone, Haliotis asinina Linnaeus. The number of positive NS cells, and the intensity of staining in the ganglia, varied and might be related to the stage of ovarian cycle. At any stage, positive cells were most numerous in the pleuropedal, and least numerous in the visceral ganglion. In addition, several cells of the statocyst and associated nerves also exhibited the immunoreactivity. In the ovary, the most intense reactivity was detected in the follicular and granular cells adjacent to mature oocytes, in the trabeculae and the ovarian capsule. The cytoplasm of mature oocytes was also moderately stained. The results indicate that the cerebral, pleuropedal, and visceral ganglia are the main sites of aELH-producing cells. The ovary may also produce aELH locally.<br /

Is cold acclimation of benefit to hibernating rodents?

The thermal challenge associated with cold acclimation (CA) and hibernation requires effective cardio-respiratory function over a large range of temperatures. We examined the impact of acute cooling in a cold-naïve hibernator to quantify the presumed improvement in cardio-respiratory dysfunction triggered by CA, and estimate the role of the autonomic nervous system in optimising cardiac and respiratory function. Golden hamsters (Mesocricetus auratus) were held at a 12 h:12 h light:dark photoperiod and room temperature (21°C euthermic control) or exposed to simulated onset of winter in an environmental chamber, by progression to 1 h:23 h light:dark and 4°C over 4 weeks. In vivo acute cooling (core temperature Tb=25°C) in euthermic controls led to a hypotension and bradycardia, but preserved cardiac output. CA induced a hypertension at normothermia (Tb=37°C) but on cooling led to decreases in diastolic pressure below euthermic controls and a decrease in cardiac output, despite an increase in left ventricular conductance. Power spectral analysis of heart rate variability suggested a decline in vagal tone on cooling euthermic hamsters (Tb=25°C). Following CA, vagal tone was increased at Tb=37°C, but declined more quickly on cooling (Tb=25°C) to preserve vagal tone at levels similar to euthermic controls at Tb=37°C. For the isolated heart, CA led to concentric hypertrophy with decreased end-diastolic volume, but with no change in intrinsic heart rate at either 37 or 25°C. Mechanical impairment was noted at 37°C following CA, with peak developed pressure decreased by 50% and peak rate-pressure product decreased by 65%; this difference was preserved at 25°C. For euthermic hearts, coronary flow showed thermal sensitivity, decreasing by 65% on cooling (T=25°C). By contrast, CA hearts had low coronary flow compared with euthermic controls, but with a loss of thermal sensitivity. Together, these observations suggest that CA induced a functional impairment in the myocardium that limits performance of the cardiovascular system at euthermia, despite increased autonomic input to preserve cardiac function. On acute cooling this autonomic control was lost and cardiac performance declined further than for cold-naïve hamsters, suggesting that CA may compromise elements of cardiovascular function to facilitate preservation of those more critical for subsequent rewarming

The structural characteristics of the heart ventricle of the African lungfish Protopterus dolloi: freshwater and aestivation

This paper reports on the structure and ultrastructure of the ventricular myocardium of the African lungfish Protopterus dolloi in freshwater (FW), in aestivation (AE), and after the AE period. The myocardium shows a conventional myofibrillar structure. All the myocytes contain large intracytoplasmic spaces occupied by a pale material that could contain glycosaminoglycans and/or glycogen, which may be used as food and water reservoirs. In FW, the myocytes in the trabeculae associated with the free ventricular wall show structural signs of low transcriptional and metabolic activity (heterochromatin, mitochondria of the dense type). These signs are partially reversed during the AE period (euchromatin, mitochondria with a light matrix), with a return to the FW appearance after arousal. The myocytes in the septum show, in FW conditions, nuclear polymorphism (heterochromatin, euchromatin), and two types (colliquative and coagulative) of necrosis. In AE, all the septal myocytes show euchromatin, and the number of necrotic cells increases greatly. Cell necrosis appears to be related to the septal architecture. After arousal, the septal myocytes exhibit a heterochromatin pattern, the number of necrotic cells decreases, cell debris accumulates under the endocardium, and phagocytosis takes place. Despite being a morphologic continuum, the trabeculae associated with the free ventricular wall appear to constitute a different compartment from that formed by the trabeculae in the ventricular septum. Paradoxically, AE appears to trigger an increase in transcriptional and synthetic myocardial activities, especially at the level of the ventricular septum. This activity may be involved in mechanisms of autocrine/paracrine regulation. Aestivation cannot be regarded as the result of a general depression of all cellular and organic activities. Rather, it is a much more complex state in which the interplay between upregulation and downregulation of diverse cell activities appears to play a fundamental role

Identification of a putative egg-laying hormone in neural and ovarian tissues of the black tiger shrimp, Penaeus monodon, using immunocytochemistry

The existence of an egg-laying hormone (ELH) was identified for the first time in the black tiger shrimp, Penaeus monodon, by means of immunoenzyme and immunofluorescence techniques. This was achieved using a polyclonal antibody produced against expressed recombinant ELH of the female Australian blacklip abalone, Haliotis rubra. The shrimp ELH reactive material was found to be localised within female neurosecretory tissues and the secretory tissue of the antennal gland, but was not identified in the X-organ sinus gland within the eyestalk. It was also present in the ovary, where the amount of ELH present was observed to be greatest in the period prior to spawning. These findings implied that the induction of P. monodon spawning might be involved with humoral regulation relating to ELH expression.<br /