Structure and innervation of the pineal gland of the rabbit,Oryctolagus cuniculus (L.)

Summary A light microscopic investigation of the rabbit pineal gland with the aid of silver-stained sections gave the following results. In the gland a medulla and a cortex can be distinguished, the medulla containing so-called light and dark pinealocytes, the cortex only light ones. Autonomic nerve fibres reach the pineal organ by two routes: (1) via the perivascular spaces of pineal blood vessels and (2) via two distinct nerve bundles, the nervi conarii. Bilateral superior cervical ganglionectomy revealed that these pinealo-petal nerve fibres are mainly orthosympathetic postganglionic. Intramural pineal neurones with synaptic-like structures on their cell bodies and dendrites point to the presence of a parasympathetic innervation next to the orthosympathetic one. Direct afferent or efferent neural connections with the brain appeared to be absent. Acknowledgements. The author wishes to thank Professor Dr. J. Ariëns Kappers for encouragement and help, Mr. H. K. Koerten for his technical assistance and Miss A. M. Feddema for typing the manuscipt.     

The burrow structure of the European rabbit (Oryctolagus cuniculus L.)

Samples of rabbit burrows were excavated and measured at four areas around Edinburgh. Of these, 31 burrows over 2 m long were analysed for internal structural relationships and the effect of soil composition and slope of the ground on their form. Seven variables were measured for each burrow—total length, number of entrance holes, number of junctions, number of ends, average length of sections between holes, junctions and ends, average depth and maximum depth. There are three main trends in burrow variation—size, an inverse relationship between relative number of holes and average depth, and an inverse relationship between average section length and relative number of junctions. Burrows in sand have relatively fewer holes and junctions, longer element lengths, a higher average depth and three times the enclosed volume per hole. Burrows dug into slopes have a higher average depth. Areas differed significantly in the relative number of holes and junctions, and average depth. It was concluded that an apparently complex structure could be summarized in terms of relatively few components. The chief of these, size, was largely independent of the soil and site characteristics, whereas the remaining two were dependent on the soil in which the burrow was dug. This may have implications for the ecology and behaviour of rabbits in different areas, and is relevant to the success of some rabbit control procedures such as burrow fumigation and warren ripping.     

Cryptosporidium cuniculus in the rabbit (Oryctolagus cuniculus)

Cryptosporidium cuniculus was identified by light and electron microscopy in two apparently healthy rabbits. Organisms were firmly attached at the brush borders of intestinal epithelial cells. Cellular alterations were minimal, consisting of elongation and shortening of microvilli adjacent to the attachment sites of organisms. Various developmental stages of cryptosporidium were identified by electron microscopy.     

Allelic variation at the VHa locus in natural populations of rabbit (Oryctolagus cuniculus, L.)

The large interallelic distances between the three rabbit Ig V(H)a lineages, a1, a2 and a3, suggest that the persistence time of the V(H)a polymorphism could amount to 50 million years, which is much longer than that of MHC polymorphisms. Rabbit originated in the Iberian Peninsula where two subspecies coexist, one of which is confined to Southwestern Iberia (Oryctolagus cuniculus algirus). We studied the V(H) loci in the original species range to obtain a better understanding of the evolutionary history of this unusual polymorphism. Serological surveys revealed that sera from the subspecies algirus, when tested with V(H)a locus-specific alloantisera, showed either cross-reactivity ("a-positive" variants) or no reaction at all ("a-blank"). Using RT-PCR, we determined 120 sequences of rearranged V(H) genes expressed in seven algirus rabbits that were typed as either a-positive or a-blank. The data show that the V(H) genes transcribed in a-positive rabbits are closely related to the V(H)1 alleles of domestic rabbits. In contrast, a-blank rabbits were found to preferentially use V(H) genes that, although clearly related to the known V(H)a genes, define a new major allotypic lineage, designated a4. The a4 sequences have hallmark rabbit V(H)a residues together with a number of unprecedented amino acid changes in framework region 2 and 3. The net protein distances between the V(H)a4 and the V(H)a1, a2, and a3 lineages were 20, 29, and 21% respectively. We conclude that at least four distantly related lineages of the rabbit V(H)a locus exist, one of which seems to be endemic in the Iberian range.     

The incidence of helminth parasites from the wild rabbit Oryctolagus cuniculus (L.) in eastern Scotland

Samples of wild rabbits were collected each month over the six-year period 1977-82 and their intestines and abdomens examined for helminths. Three species of nematode, four of cestode and one trematode were found. Graphidium strigosum was recorded in 33% of the 786 rabbits, Trichostrongylus retortaeformis in 79%, Passalurus ambiguus in 14.2%, Cittotaenia pectinata in 37%, C. denticulata in 11%, Coenurus pisiformis in 3%, Cysticercus serialis in 0.1% and Fasciola hepatica in 0.1%. G. strigosum and P. ambiguus infections were greatest in the older heavier animals whereas juvenile rabbits had the heaviest T. retortaeformis nematode burdens. Seasonal fluctuations were observed in G. strigosum, T. retortaeformis, P. ambiguus and Cittotaenia denticulata. The sex and reproductive state of the female rabbit did not have any significant effect on either the nematode or cestode worm burdens. Myxomatosis was shown to significantly increase the worm burden of T. retortaeformis and raise that of P. ambiguus. No nematode or cestode from domesticated animals were recovered and it was concluded that since F. hepatica was found only once rabbits did not constitute a serious hazard to the farm animals grazing the area.     

The social behaviour of free-ranging domestic rabbits (Oryctolagus cuniculus L.)

A colony of 8 free-ranging domestic rabbits (3 males and 5 females) was observed during 3 successive periods in order to determine the social organization of this domestic species (Oryctologus cuniculus L.). The study is based on the spatial distribution of the rabbits and on the social contacts observed in the colony. Each male has his own territory, but the female is not territorial and shares a home-range with several other females. A dominance hierarchy exists between the males and another between the females.     

The occurrence and abundance of helminth parasites of the mountain hare Lepus timidus (L.) and the wild rabbit Oryctolagus cuniculus (L.) in Aberdeenshire, Scotland

Mountain hares were collected each month between April 1984 and March 1985 and their intestines examined for helminths. 26 rabbits were also collected between July and December 1984 and examined for gastro-intestinal helminths. Three nematode and two cestode species were found in the hares while only two nematode and one cestode species were found in the rabbits. Trichostrongylus retortaeformis was recorded from 88% of the 193 hares and 92% of the rabbits while comparable figures for Passalurus ambiguus were 0.5% and 54% and for Mosgovoyia pectinata 14% and 81%. Seasonal fluctuations were observed in the T. retortaeformis populations in the hare; numbers tended to be low during the winter months and high throughout the summer. Paranoplocephala wimerosa was reported for the first time from the British Isles and Trichostrongylus axei was recorded for the first time in the mountain hare.     

Bait shyness and its prevention in the rabbit Oryctolagus cuniculus L.

Abstract

Caged New Zealand white rabbits were examined for the development, and prevention, of a learned aversion to toxic feed. Two familiar feeds were offered. One feed, a paste, contained sublethal amounts of sodium monofluoroacetate (1080); the other feed, cereal‐based pellets, was unpoisoned. On initial poisoning, consumption of both feeds decreased, but more markedly for the 1080‐dosed pastes. Suppressed feed consumption was observed for several days and may have been illness induced. A second poisoning elicited a significant depression of consumption of pastes but not pellets. The addition of a mixture of certain drugs (neurotransmitter antagonists) to the poisoned paste appeared to prevent the characteristic depression of this paste intake. We speculate that the drugs disrupted the associative process linking 1080 to recognisable attributes of the toxin or bait itself.

The implications of these results on aversion formation in rabbits and pest control are discussed.     

The Himalayan rabbit (Oryctolagus cuniculus L.): spontaneous incidences of endpoints from prenatal developmental toxicity studies

The historical database represents the spontaneous, i.e. normal changes of characters, in laboratory animals, and is a must for the assessment of toxic effects of compounds. For the Himalayan rabbit (CHBB:HM, SPF) background data were collected from the control groups of regulatory studies between 1968-1999 in the Biberach laboratory of Boehringer Ingelheim (Germany). In the present study these data were compared with the background data from the years 1974-1984, with those from the Ingelheim laboratory, Germany (1977-1984) and those from the breeding colony at Kawanishi, Japan (1971-1991, 1972-1984). Fertility in the Biberach laboratory was relatively constant through the years, due to the strict breeding system. Litter parameters (corpora lutea, implantations and viable fetuses), including fetal sex distribution and fetal weight, were constant in the Biberach laboratory through the years and compared well with the data from Ingelheim and Kawanishi. From these three laboratories the results of spontaneous changes in fetal morphology above 0.1% incidence suggest a pattern of deviations from the Bauplan (fundamental body plan). These comprise synosteosis of sternebrae, lumbar (additional) ribs, hypoplasia of 12th rib, status of ossification, aplasia of gall bladder, hypoplasia of gall bladder, incompletely subdivided lung, dilated ventricle of heart, deviations at the A. carotis and at the aortic arch and flexure of paw. The absence of a time-dependent statistical trend indicates that the spontaneous change of endpoints remained constant through the time axis. Comparison with the spontaneously changed fetal morphology of the other strains (NZW, JW, SF rabbits) does not provide support for their being a totally strain-specific pattern, and this pattern may be closer to the species than specific to a single strain. The firm patterns of deviations in fetal morphology provide suitable and valuable markers for assessing toxic effects on ontogenesis. According to our experience these morphological endpoints react very sensitively to teratogenic compounds, which is demonstrated by increased incidences. Our knowledge of evolution of organisms and of mechanisms leading to morphological deviations points to a strict selection of phenotypes. For laboratory animals the decisive selection factors are defined by man. These are nutritive factors, environmental conditions, the mating system, handling and treatment, and experimental design. All these factors have to be held constant through the years, which is an absolute pre-condition for the application of valid historical data. The Himalayan rabbit is highly suitable for use in developmental toxicity studies due to the stability of reproductive data within the same laboratory over a period of more than 30 years, due to the similarity of reproductive data among three different laboratories, and due to an absence of relevant differences to the reproductive data of other rabbit strains.     

Transferrin (Tf) polymorphism in wild rabbit, Oryctolagus cuniculus

Evidence for two new alleles (TfC and TfD) at the transferrin locus (Tf) in wild rabbit, Oryctolagus cuniculus, is presented. Blood samples were collected in Continental Portugal (178 individuals), and in the Azores Islands of Terceira (52) and S. Miguel (59). The frequency of TfA, which is the only allele detected up to now in domestic rabbits, varied from 0.20 +/- 0.13 to 0.95 +/- 0.05 in the populations sampled in Continental Portugal. In the island populations sampled the frequency of TfA was greater than 0.8.     

Coccidiosis of the wild rabbit (Oryctolagus cuniculus) in France

In 1998-1999 a survey of coccidiosis in wild rabbits was carried out in six different localities in France. About five individuals were caught monthly in each locality and a total of 254 wild rabbits was examined. Ten species of Coccidio were identified: Eimeria perforans, E. flavescens, E. piriformis, E. exigua, E. media, E. magna, E. coecicola, E. stiedai, E. roobroucki, E. intestinalis. Intensity of infection in young individuals was higher than in adults. Intensity was highest in winter but, as there are no young rabbits in winter, in young individuals it was higher in spring and autumn than in summer. Intensities were higher in the northern rather than in southern localities. Ranking of prevalence was remarkably stable, in contrast to the variability of the parasitic load. The equilibrium between congeneric species of rabbit coccidia (stable prevalence rank, variable parasitic load) is thought to be probably the consequence of the opportunistic feeding habits of rabbits.     

Helminths of the wild rabbit (Oryctolagus cuniculus) in Macaronesia

Two hundred and four rabbits from 8 Macaronesian islands (Pico, San Jorge, San Miguel, Terceira, and Flores from Azores Archipelago; Tenerife and Alegranza from Canary Islands; and Madeira from Madeira Archipelago) were examined for helminth parasites between 1995 and 2000. Three species of cestodes, Taenia pisiformis (larvae), Andrya cuniculi, and Mosgovoyia ctenoides, and 5 species of nematodes, Trichuris leporis, Graphidium strigosum, Trichostrongylus retortaeformis, Passalurus ambiguus, and Dermatoxys hispaniensis, were identified. Only 3 species (M. ctenoides, T. retortaeformis, and P. ambiguus) were regularly distributed over the 3 archipelagos. Taenia pisiformis was not collected in Madeira, nor was A. cuniculi in the Azores and G. strigosum in the Canary Islands. Trichuris leporis and D. hispaniensis were only found in Madeira. Significant differences in the general prevalence of the nematodes G. strigosum and T. retortaeformis were detected between Azores and Madeira. The prevalence of T. retortaeformis differs significantly between the Azores and the Canaries and that of P. ambiguus was higher in Madeira than in Azores and Canaries. The helminth richness found in the wild rabbit in these Macaronesian archipelagos was very low compared with the Palearctic helminth fauna of this host. The wild rabbit was introduced from the Iberian Peninsula into different Macaronesian islands. Helminths introduced with Oryctolagus cuniculus into these islands also are commonly found in Iberian wild rabbits, which are excellent colonizers, as demonstrated in this study.     

Videofluorographic analysis of tongue movement in the rabbit (Oryctolagus cuniculus)

The movement of the entire tongue and intermolar eminence during mastication is described in the domestic rabbit (Oryctolagus cuniculus). Tongue movement and jaw position were analyzed videofluorographically from separate lateral and dorso-ventral views in six rabbits. Metallic markers were inserted into the tongue so that its movement was visible on the fluorographic image. Frame-by-frame analysis of the videofluorographic tape recordings demonstrates that tongue movement in all animals was identical in direction during each part of the chewing cycle. In the lateral view the forepart of the tongue moves down and forward during the opening stroke, whereas the intermolar eminence moves up and forward to appose the palate. During the closing stroke, as the tip of the tongue moves up and back, the intermolar eminence lowers from the palate and retracts. During the power stroke the forepart of the tongue is at its most elevated and retruded position, while the intermolar eminence is its lowest and most retruded. The dorso-ventral view showed that lateral movement of the tongue and mandible are highly synchronous. The intermolar eminence decreases in width during the power stroke, possibly twisting to place or keep food on the teeth. An anterior to posterior undulating movement of the entire tongue occurs throughout the chewing cycle. As the intermolar eminence elevates to appose the palate during the opening stroke, it may replace the bolus on the teeth on the chewing side. The intermolar eminence also appears to be twisting during the closing and power strokes to place or maintain food on the teeth.