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During visual system development, interactions between Eph tyrosine kinase receptors and their ligands, the ephrins, guide retinal ganglion cell (RGC) axons to their topographic targets in the optic tectum. Here we show that Eph/ephrin interactions are also involved in restoring topography during RGC axon regeneration in goldfish. Following optic nerve crush, EphA/ephrin-A interactions were blocked by intracranial injections of recombinant Eph receptor (EphA3-AP) or phospho-inositol phospholipase-C. Topographic errors with multiple inputs to some tectal loci were detected electrophysiologically and increased projections to caudal tectum demonstrated by RT-97 immunohistochemistry. In EphA3-AP-injected fish, ephrin-A2-expressing cells in the retino-recipient tectal layers were reduced in number compared to controls and their distribution was no longer graded. The findings, supported by in vitro studies, implicate EphA/ephrin-A interactions in restoring precise topography and in regulating ephrin-A2 expression during regeneration.

A comprehensive anatomical study was undertaken to examine the rectal salt gland in the Port Jackson shark, Heterodontus portusjacksoni, a shark known to invade estuarine environments. The microstructure and vascular organisation of the rectal salt gland was investigated using histological observation and scanning electron microscopy of vascular corrosion casts. Cellular specialisation was observed in the lining of the central lumen of this gland. This may indicate that there is some modification of the principal product of the gland prior to its secretion. The rectal salt gland has a complex structure related to its function. Contrary to previous reports, the flow in secretory tubules is in the opposite direction to that of the capillaries and thus constitutes a counter-current arrangement. The similarity in the organisation of the counter-current and lobulate arrangement of salt-secreting glands through phylogenetically diverse organisms, such as sharks and birds, suggests that this arrangement is important in achieving efficient salt secretion., (Copyright 2001 S. Karger AG, Basel)

The atypical excitatory effect of acetylcholine on cardiac ventricular muscle was investigated in the horned shark, Heterodontus portusjacksoni. Electrically paced ventricular strips produced a massive 391.45% (+/-26.39%) increase in basal force of contraction in response to exogenously applied acetylcholine. The response was similar in nature to that produced by applied adrenaline, which caused a 382.52% (+/-72.47%) increase. The response to acetylcholine was blocked by the muscarinic cholinoceptor antagonist atropine and the competitive beta-adrenoceptor antagonist propranolol and was reduced by bretylium, an agent known to inhibit the release of catecholamines from adrenergic nerves. These findings strongly suggest that acetylcholine mediates a localised release of a catecholamine via muscarinic cholinoceptors in shark heart. A cholinergically controlled catecholamine store has been proposed (cholinergic-adreno complex), implying that elasmobranchs may be capable of finer control of cardiac output than has previously been suspected. This complex may represent a transitional adrenergic state between humoral and neuronal regulation. The spontaneously beating atrium showed no evidence of such an excitatory response to applied acetylcholine but produced an atropine-sensitive slowing, a response typical of other vertebrates.

The fertility and viability of spermatozoa stored by male and female Gould's wattled bats, Chalinolobus gouldii, was investigated in a captive colony of ten bats (three males and seven females). Bats were housed in outdoor flight cages. Plasma progesterone concentrations, measured using double antibody radioimmunoassay, isolation experiments plus sperm motility and sperm membrane stability tests were used to evaluate the viability and fertility of stored spermatozoa. Mean plasma progesterone concentrations were lowest during midwinter (< 0.5 ng ml-1) with a 20-fold increase recorded in late winter to early spring. During pregnancy, plasma progesterone concentrations increased to about 13 ng ml-1 and returned to basal values soon after parturition. The results of the plasma progesterone assays and the isolation experiments indicate that female C. gouldii can store fertile spermatozoa for at least 33 days. The investigation of spermatozoa stored by male C. gouldii revealed that 6-7 months after peak spermatogenesis about 60% of the stored spermatozoa were motile and more than 60% had stable membranes, indicating that the spermatozoa stored by males were viable and likely to be fertile. The results of this study clearly indicate that both male and female C. gouldii are capable of storing fertile spermatozoa for prolonged periods.

The adrenergic innervation of the heart of the bat (Miniopterus schreibersii) was studied with a fluorescence histochemical technique. The appearance and distribution pattern of the terminal adrenergic nerve fibers demonstrated in the atria, sinoatrial and atrioventricular nodes, and ventricles is typically mammalian. Fine varicose adrenergic fibers run in and parallel to the ventricular muscle where they are common and uniformly distributed. Indian ink perfusion of the coronary vasculature demonstrates the high density of vessels in the ventricles, but obscures the terminal innervation of the ventricular muscle. This alone, or in combination with the apparent seasonal change in the terminal innervation of the ventricles, may explain the inability of previous workers to identify an adrenergic ventricular innervation in the bat Nyctalus noctula. The adrenergic ventricular innervation might be involved in the large increases in cardiac output associated with the commencement of flight and in the massive sympathetic activation that mediates arousal from torpor.

The innervation of the pulmonary vasculature of the semi-arboreal rat snake, Elaphe obsoleta, was examined with glyoxylic acid-induced catecholamine histochemistry, peptide immunohistochemistry, and in vitro perfusion of the pulmonary vasculature. An adrenergic innervation was present on the pulmonary artery, the smaller pulmonary arteries, the veins draining the lung, and the main pulmonary vein. Vasoactive intestinal polypeptide-like immunoreactive axons were observed on the pulmonary artery and vein, small arteries, and occasionally small veins within the lung parenchyma. A dense plexus of substance P-like immunoreactive (SP-LI) axons was observed on the distal extrinsic pulmonary artery. SP-LI axons were found on the more distal arteries within the lung parenchyma, but not on the veins. The distribution of calcitonin gene-related peptide- and SP-LI axons was similar suggesting that the axons are sensory nerves. In the perfused pulmonary vasculature, vagal stimulation caused a predominant vasoconstriction which was abolished by atropine indicating it was cholinergic in nature. A post-stimulus vasodilatation was abolished by bretylium and propranolol indicating it was adrenergic in nature. The responses to nerve stimulation were located in both the extrinsic and intrinsic pulmonary vasculature. No evidence for non-adrenergic, non-cholinergic transmission to the vascular smooth muscle was found. The extensive, functional innervation of the main pulmonary artery, as well as the more distal vasculature within the lung, may reflect adaptation to cardiovascular problems imposed by an elongated body and arboreal habits.

In contrast to other mammals, muscarinic receptors in the bat ventricle can mediate significant decrease in basal contractile force (greater than 50%), not only at 37 degrees C but also at hibernation temperature (12 degrees C). At frequencies of contraction that approximate in vivo values for 37-12 degrees C, no significant shift in receptor affinity or maximum response to applied acetylcholine was found for either ventricular or atrial muscle. Low temperature does not appear to compromise receptor function in hibernators. The atypical cholinergic innervation of the ventricle may maintain a regulative role during hibernation.