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PubMed2006

A study on eggshell pigmentation: biliverdin in blue-shelled chickens.

Biliverdin is an important pigment in the eggshell of chickens and other avian species. Determination of the biosynthesis site for biliverdin is essential for understanding the biochemical process and genetic basis of eggshell pigmentation. Either blood or the shell gland could be the biosynthesis site of eggshell biliverdin. A segregation population with full-sib sisters genotyped Oo and oo, which laid blue-shelled eggs and light brown eggs, respectively, was constructed in a native Chinese chicken breed. Ultraviolet spectrophotometry and HPLC were used to determine the biliverdin concentration in eggshells, blood, bile, excreta, and shell gland of both groups of chickens. Biliverdin content was significantly different between egg shells of blue-shelled and brown-shelled chickens (P < 0.01). Blood and bile were tested 3 to 4 h before oviposition, and excreta was tested randomly. Results showed no significant difference in biliverdin concentration in blood, bile, and excreta between the 2 groups. In the shell gland, the biliverdin contents for the blue-shelled and brown-shelled chickens were 8.25 +/- 2.55 and 1.29 +/- 0.12 nmol/g, respectively, which showed a significant difference (P < 0.01). Our results demonstrated that blood is not the biosynthesis site of the shell biliverdin. Biliverdin is most likely synthesized in the shell gland and then deposited onto the eggshell of chickens.

Animals↗

PubMed1986

Effect of short-term feed deprivation on shell quality in laying hens.

Hens with feed withheld for 24 hr had poorer shell quality for the next 3 days. Hens with feed withheld for the first 8 hr (0400 to 1200 hr) of the 16-hr light cycle showed no decline in shell quality, but those with feed withheld the last 8 hr (1200 to 2000 hr) had poorer shell quality on the following day. When the period from 1200 to 2000 hr was divided into 2 periods (1200 to 1600 hr and 1600 to 2000 hr), feed restriction during the 1600 to 2000-hr period caused a decline in shell quality on the next day, but removal during the 1200 to 1600-hr period had no effect on shell quality. Shell quality was related to the feed intake of the hens, because about 34% of their feed intake was during the period 1600 to 2000 hr. Hens fed a low Ca diet (.7%) from 1200 to 2000 hr had poorer shell quality but not as poor as those with feed withheld. Feeding a high Ca diet (7.6%) from 0400 to 1200 hr prior to feed restriction from 1200 to 2000 hr, or giving oyster shell during the period of feed removal, improved shell quality, but not to the level of the full-fed birds. Daily feed restriction from 1200 to 2000 hr caused a reduction in shell quality for the first 4 days after which shell quality returned, but a slight decline in egg production was noted. These hens were able to consume approximately 70% of the feed consumed by the full-fed birds.

Animals↗

PubMed1998

Less choosy or different preference? Impact of hypoxia on hermit crab shell assessment and selection.

Hermit crabs that rely on gastropod shells for protection have to assess a number of shell features, each of which can bring different, and sometimes conflicting, advantages to their bearer. We examined how environmentally induced stress, in the form of hypoxia, can alter the relative benefits of different shell features and result in the selection of different shells by the hermit crab Pagurus bernhardus. Hermit crabs under hypoxic conditions spent significantly less time investigating shells before entering them. Despite this apparently superficial assessment, they chose shells that were well suited to hypoxic conditions. After 24 h, they were found in shells that were significantly lighter than those chosen by hermit crabs under normal oxygen. This shift in preference was achieved at the expense of the internal spaciousness of the shell, which may have deleterious implications for predation and reproduction. This cost was more evident for larger hermit crabs since there was no relationship between hermit crab size and shell characteristics for hermit crabs in hypoxia. Under oxygen stress, hermit crabs therefore alter their shell preference in favour of lighter, and thus smaller, shells, probably reflecting a greater concern for energy minimization than protection from predation or reproduction. Copyright 1998 The Association for the Study of Animal Behaviour.

Journal Article↗

PubMed2004

Nassarius kraussianus shell beads from Blombos Cave: evidence for symbolic behaviour in the Middle Stone Age.

Since 1991, excavations at Blombos Cave have yielded a well-preserved sample of faunal and cultural material in Middle Stone Age (MSA) levels. The uppermost MSA phase, M1, is dated to c. 75 ka by optically stimulated luminescence (OSL) and thermoluminescence, and the middle M2 phase to a provisional c. 78 ka. Artefacts unusual in a MSA context from these phases include bifacial points, bone tools, engraved ochre and engraved bone. In this paper, we describe forty-one marine tick shell beads recovered from these MSA phases and tick shell beads from Later Stone Age (LSA) levels at Blombos Cave and the Die Kelders site. Thirty-nine shell beads come from the upper M1 phase and two from M2. Morphometric, taphonomic and microscopic analysis of modern assemblages of living and dead tick shell demonstrate that the presence of perforated Nassarius kraussianus shells in the Blombos MSA levels cannot be due to natural processes or accidental transport by humans. The types of perforation seen on the MSA shells are absent on modern accumulations of dead shells and not attributable to post-depositional damage. Their location, size, and microscopic features are similar to those obtained experimentally by piercing the shell wall, through the aperture, with a sharp bone point. Use-wear, recorded on the perforation edge, the outer lip, and the parietal wall of the aperture indicates the shells having being strung and worn. MSA shell beads differ significantly in size, perforation type, wear pattern and shade compared to LSA beads and this eliminates the possibility of mixing across respective levels. Thirty-one beads were found in four groups of five to twelve beads, each group being recovered in a single square or in two adjacent sub-squares during a single excavation day. Within a group, shells display a similar shade, use-wear pattern and perforation size suggesting their provenance from the same beadwork item, lost or disposed during a single event. The likely symbolic significance of these finds suggests levels of cognitively modern behaviour not previously associated with MSA people.

Animals↗

PubMed2005

Acetylcholine receptor effects on accumbal shell dopamine-mediated turning behaviour in rats.

The nature of acetylcholine receptor effects on dopaminergic functions within the nucleus accumbens shell was studied in rats, using turning behaviour as read-out parameter. Unilateral injections of the acetylcholine receptor agonist, carbachol (1.0-5.0 microg), into the nucleus accumbens shell dose-dependently elicited contraversive circling. Unilateral injections of the combination of a fixed dose of the dopamine D(2) receptor agonist, quinpirole (10.0 microg), with increasing doses of the dopamine D(1) receptor agonist, SKF 38393 (1.0-5.0 microg), into the nucleus accumbens shell dose-dependently elicited contraversive pivoting. The same held for the combination of a fixed dose of SKF 38393 (5.0 microg) with increasing doses of quinpirole (5.0 and 10.0 microg), which was injected into the nucleus accumbens shell. The nicotinic acetylcholine receptor antagonist, mecamylamine (5.0 and 10.0 microg), injected into the nucleus accumbens shell, which alone did not elicit any turning behaviour, significantly suppressed both the contraversive circling induced by carbachol (5.0 microg) and the contraversive pivoting induced by the mixture of SKF 38393 (5.0 microg) and quinpirole (10.0 microg). The muscarinic acetylcholine receptor antagonist, methylscopolamine (1.0 and 2.5 microg), injected into the nucleus accumbens shell, which alone did not elicit any turning behaviour, significantly suppressed the contraversive circling induced by carbachol (5.0 microg), whereas it significantly increased the contraversive pivoting induced by both the mixture of SKF 38393 (1.0 microg) and quinpirole (10.0 microg) and the mixture of SKF 38393 (5.0 microg) and quinpirole (5.0 microg). Neither SKF 38393 (5.0 microg) nor quinpirole (10.0 microg) injected into the nucleus accumbens shell affected the contraversive circling induced by carbachol (5.0 microg). Carbachol (1.0 microg) injected into the nucleus accumbens shell caused a slight initial potentiation followed by an inhibition of the contraversive pivoting induced by the mixture of SKF 38393 (5.0 microg) and quinpirole (10.0 microg). These results confirm that stimulation of both nicotinic and muscarinic acetylcholine receptors in the nucleus accumbens shell is required for the accumbens-dependent, acetylcholine-mediated circling. The study provides the original evidence that stimulation of nicotinic acetylcholine receptors in the nucleus accumbens shell is required for the accumbens-dependent, dopamine-mediated pivoting. Finally, the present study shows that muscarinic acetylcholine receptors in the nucleus accumbens shell play an inhibitory role in the production of the accumbens-dependent, dopamine-mediated pivoting.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗

PubMed2001

Patterns of shell penetration by Chorus giganteus juveniles (Gastropoda: Muricidae) on the mussel Semimytilus algosus.

Patterns are described for shell penetration by the sublittoral muricid snail Chorus giganteus during predatory attacks on the mussel Semimytilus algosus. Location, form and size of shell penetrations were observed in relation to the size of the predator. The results suggested that positions of the perforations on the mussel shells were related to size of the attacking snail. Smaller snails perforated areas near the shell ligament and in the central zone of the shell, while larger snails more frequently attacked shell borders, principally on the ventral side. These observations may be related to: (a) changes in the process of manipulation of the prey during development of the foot and the shell tooth of the predator, (b) changes in internal structure of the snails related to the shell perforation mechanism, or (c) learned behavior acquired experientially by the snails during early growth. Although in other studies of muricid penetration patterns larger boreholes made in shells of the prey were positively correlated with increasing predator size, this relation did not appear to hold with C. giganteus, as larger specimens often made relatively small shell perforations. Areas of boreholes made in the mussel shells by this snail varied from 0.01 to 1.1 mm(2), and were unusually variable in size and shape, especially when compared with literature results on bores characteristic of other muricid species.

Journal Article↗

PubMed1999

Behavioral neurochemistry reveals a new functional dichotomy in the shell subregion of the nucleus accumbens.

1. The behavioral and neurochemical effects produced by the direct infusion of amphetamine by reverse microdialysis into either the core or shell of the nucleus accumbens were studied across the anteroposterior axis of this nucleus. 2. Amphetamine (0.05; 0.10; 0.50; 1.00 microM) produced a dose-dependent increase in locomotor activity after microinfusion into either the rostral shell, caudal shell or core of the nucleus accumbens. However, the amphetamine-induced locomotor activating effect, was significantly higher in the rostral shell of the nucleus accumbens compared with both the caudal shell and core. 3. The lowest concentrations of amphetamine produced an equipotent decrease in dialysate dopamine in either the rostral shell, caudal shell, or core. At 1.0 microM, however, amphetamine selectively increased dopamine in the rostral shell. In contrast, the highest dose of amphetamine significantly increased dialysate serotonin levels over baseline only in the caudal shell of the nucleus accumbens. 4. These results demonstrate the preferential effect of amphetamine on dopamine in the rostral shell and serotonin in the caudal shell subterritory of the nucleus accumbens.

Amphetamine↗

PubMed2002

Silicone gel breast implant failure: evaluation of properties of shells and gels for explanted prostheses and meta-analysis of literature rupture data.

After 30 years of clinical use, the 1992 Food and Drug Administration moratorium on silicone gel breast implants (SGBIs) resulted from a paucity of scientific data concerning their safety. The frequency of rupture and reoperative procedures was not known, nor were reliable data available for changes in the physical properties of shells and the composition of gels that might lead to SGBI failure. For this reason the authors conducted large-cohort meta-analyses of failure data for SGBIs based on numerous literature reports and also investigated systematically shell and gel properties from explanted SGBIs. They report their failure analysis data for more than 9,770 SGBIs (an update of an earlier study of more than 8,000 implants) as well an examination of the properties of shells and gels for 74 explanted SGBIs that ranged in age from 2 to 19 years (mean implanted age, 9.9 years). The explants tested were from several different manufacturers. For the modest-size explant cohort that was tested, 31 of 74 implants (42%) were found to be ruptured (some extensively). Even many intact shells were so weakened that only 51 shells had sufficient strength to enable preparation of samples for testing of mechanical properties and for analysis of composition by solvent extraction. Shells were found to contain 15 to 25% of extractable silicone. Exhaustive extraction of gels showed that they actually contained very little crosslinked silicone--85 to 95% being extractable soluble silicone fluid. Tensile and tear strengths of explanted silicone elastomer shells were lower than unimplanted prostheses and were generally well below reported manufacturers' values. This updated large-cohort failure analysis continues to show that shell rupture is related directly to implant duration (e.g., from analysis of variance statistics, 26% failure at 3.9 years, 47% at 10.3 years, 69% at 17.8 years; < or = 0.001). However, for the relatively small series of explants for which physical property data are reported, no significant correlation was observed between implant duration and the degradation of implant strength. It therefore appears most reasonable to conclude that after early weakening of shells as a result of swelling of the shell elastomer by diffusion of silicone oil from the gel, SGBI failure can occur in a time-dependent manner as a result of continuing implant motion and cyclic stresses that are exacerbated by stress concentration at thin areas, defects, and folds in the shells.

Breast Implants↗

PubMed2001

Effects of dietary 1,4-diaminobutane (putrescine) on eggshell quality and laying performance of hens laying thin-shelled eggs.

Experiments were conducted to evaluate the potential for dietary 1,4-diaminobutane (putrescine) to influence eggshell quality and overall laying performance in hens. Forty-eight, 60-wk-old White Leghorn hens laying thin-shelled eggs were fed a corn and soybean meal-based diet supplemented with 0.00 (control), 0.05, 0.10, or 0.15% putrescine for 4 wk. Twelve hens that laid thick-shelled eggs were also fed the control diet. The feeding of supplemental putrescine decreased feed consumption; however, egg weight decreased only at higher levels of supplementation. Increasing dietary levels of putrescine responded quadratically in eggshell deformation, eggshell weight, and eggshell weight as a percentage of egg weight (P < 0.05). There were no significant differences in shell deformation, shell thickness, or shell weight when comparing hens laying thick-shelled eggs and those laying thin-shelled eggs that were fed 0.05% supplemental putrescine. Calcium intake, calcium retention, and calcium balance decreased linearly (P < 0.05) with increasing levels of dietary putrescine. Pancreatic putrescine concentrations were significantly higher (P < 0.05) in hens laying thick-shelled eggs compared with hens laying thin-shelled eggs. It appeared that pancreatic cells synthesized more polyamines in hens laying thick-shelled eggs. This increase in polyamines might have caused improved eggshell quality by increasing calcium transport. It was concluded that 0.05% supplemental putrescine improved eggshell quality; however, higher levels proved to be toxic.

Animals↗

PubMed1990

Plasma calcitriol in chickens producing strong and weak egg shells and the response of hens to exogenous calcitriol.

Calcitriol (CAL) regulates intestinal calcium transport by inducing an increase in membrane phosphatidylcholine (PC) and calbindin. A positive correlation has been reported between shell gland PC and egg shell strength. Three experiments were conducted to test the hypothesis that the improvement in egg shell strength associated with increased PC is mediated via changes in the concentration of CAL. Sera from aged laying hens, identified as either strong (SES) or weak (WES) egg shell producers, were obtained from blood samples collected at 16 h after oviposition and assayed for CAL. Laying hens were injected (i/m) with 1.0 or 0.4 micrograms CAL/d for 28 d. Serum CAL in the WES hens was 70% of that in the SES hens (P less than .05). Hens producing extremely weak shells did not respond to 0.4 micrograms CAL/d for 10 d. Administration of CAL did not improve egg shell strength nor was serum CAL increased when WES hens were molted and shell gland PC increased. The results show that serum CAL is lower in aged hens producing weak egg shells but shell strength is not responsive to exogenous CAL and increased shell gland PC in WES hens after molting is not associated with higher serum CAL.

Animal Nutritional Physiological Phenomena↗

PubMedDate not supplied

Cytodifferentiation of trophoblast in the anchoring villi and trophoblastic shell in the first half of gestation in the macaque.

The structure of cytotrophoblast cells in cell columns of the anchoring villi and trophoblastic shell were studied by light and transmission electron microscopy during days 19-70 of pregnancy in the macaque. Additional placentas were prepared for 3H-thymidine autoradiography to demonstrate DNA synthesis. The cell columns of the anchoring villi consist of proximal, mid, and distal regions, and similarly the trophoblastic shell has a region forming the base of the intervillous space, a central zone, and a junctional zone. The proximal region of the cell column is composed of closely apposed, largely undifferentiated cytotrophoblast cells lacking intercellular space. In the mid region, the cells, which contain segregated glycogen areas, are separated into branching strands by extensive extracellular matrix. The distal zone abuts the trophoblastic shell and has fewer mostly peripheral cytotrophoblast cells and abundant matrix. Where cytotrophoblast of the shell is exposed to intervillous space or underlies syncytial trophoblast bordering the intervillous space, pads of cuboidal cells are seen. The central zone of the shell is arranged in strands of contiguous cells. Near the maternal junctional zone, the cells have fewer junctional regions and contain lipid rather than glycogen. Results of thymidine incorporation studies are consistent with observations of others using Ki67 distribution, indicating that cell replication occurs in the proximal region of the cell column, with subsequent migration of cells into the trophoblastic shell. Changes with age include an increase in extracellular matrix in the proximal region, a more linear organization in the expanded central zone of the shell, and a decrease in necrosis at the junction of the shell with endometrium, resulting in close association of shell cytotrophoblast cells, maternal decidual cells, large granular lymphocytes, and macrophages. It is concluded that the cytotrophoblast of the cell columns and trophoblastic shell is a pleomorphic cell type responding to adjacent constituents including the matrix it forms.

Animals↗

PubMed1993

Ultrastructure of serotonin-immunoreactive terminals in the core and shell of the rat nucleus accumbens: cellular substrates for interactions with catecholamine afferents.

The nucleus accumbens is composed of a core region involved in motor functions and a shell region implicated in emotional and motivational processes. Both of these regions receive serotonin- and dopamine-containing afferents. We examined whether the serotonin innervation or relation to catecholamine (mainly dopamine) axons in the nucleus accumbens shows common features or specializations corresponding to the noted functional differences in core and shell subregions. To address this question, we examined the ultrastructure of serotonin-containing axons and their relation to catecholamine-containing afferents in either the core or shell of the nucleus accumbens. Single coronal sections through the rat forebrain were processed for immunoperoxidase labeling of serotonin and immunogold silver labeling of tyrosine hydroxylase, the catecholamine-synthesizing enzyme. Varicose processes showing peroxidase product for serotonin by light microscopy were confirmed to be axons and terminals by electron microscopy. In a quantitative analysis of serotonin-immunoreactive terminals forming one or more contacts in single sections, some common features were observed. For the core (n = 120) and the shell (n = 82), 41% formed synaptic junctions with unlabeled dendrites, 75% were in apposition with unlabeled terminals, which often formed asymmetric junctions, and 20% were in apposition with axons or terminals containing tyrosine hydroxylase. Thus, in both the core and shell of the nucleus accumbens, serotonin terminals synapse on postsynaptic neurons and are likely to modulate or be modulated by presynaptic interactions with excitatory axons forming asymmetric junctions and by catecholaminergic afferents. Marked differences in the morphology of serotonin axons were also seen in the core versus shell of the nucleus accumbens. By light microscopy, serotonin-immunoreactive axons were thicker and more varicose than those found in the core. Ultrastructural analysis confirmed that, in contrast to the core, serotonin-immunoreactive axons and terminals in the shell were larger in cross-sectional diameter size (0.7 micron vs. 0.3 micron). Additionally, serotonin axon terminals in the shell contained more numerous immunoreactive large dense core vesicles and more frequently formed symmetric as opposed to asymmetric contacts with dendrites. The larger size and more numerous dense core vesicles in serotonin-immunoreactive terminals in the shell support the concept that serotonin or co-existing neurotransmitter may be more tonically released in the shell versus core of the nucleus accumbens.

Afferent Pathways↗

PubMed1993

The patterns of afferent innervation of the core and shell in the "accumbens" part of the rat ventral striatum: immunohistochemical detection of retrogradely transported fluoro-gold.

Recent data have emphasized the neurochemically distinct nature of subterritories in the accumbens part of the rat ventral striatum termed the core, shell, and rostral pole. In order to gain a more comprehensive understanding of how afferents are distributed relative to these subterritories, immunohistochemical detection of retrogradely transported Fluoro-Gold was carried out following iontophoretic injections intended to involve selectively one of the subterritories. The data revealed that a number of cortical afferents of the medial shell and core originate in separate areas, i.e., the dorsal peduncular, infralimbic, and posterior piriform cortices (to medial shell) and the dorsal prelimbic, anterior agranular insular, anterior cingulate, and perirhinal cortices (to core). The lateral shell and rostral pole are innervated by cortical structures that also project either to the medial shell or core. The orbital, posterior agranular insular, and entorhinal cortices, hippocampus, and basal amygdala were observed to innervate the accumbens in a topographic manner. Following core injections, strong bilateral cortical labeling was observed. Few labeled cortical cells were observed contralaterally following injections in the medial shell. Intermediate numbers of labeled neurons were observed in contralateral cortices following lateral shell injections. Robust subcortical labeling in a variety of structures in the ventral forebrain, lateral hypothalamus, deep temporal lobe, and brainstem was observed after shell injections, particularly those that involved the caudal dorsomedial extremity of the shell, i.e., its "septal pole." Selective ipsilateral labeling of subcortical structures in the basal ganglia circuitry was observed following injections in the core and, to a lesser extent, lateral shell. It was concluded that a number of afferent systems exhibit varying degrees of segregation with respect to the accumbal subterritories.

Afferent Pathways↗

PubMed2006

Distribution of butyltin and derivatives in oyster shells and trapped sediments of two estuaries in Cantabria (Northern Spain).

Distribution of butyltin compounds (BTs) and derivatives (monobutyltin, MBT; dibutyltin, DBT and tributyltin, TBT) was analysed in Crassostrea gigas oyster shells and the sediments trapped in the shell chambers, from two different estuaries in Cantabria (Northern Spain), with very different environmental conditions, where previous data have not been reported. Inorganic tin analysis in oyster shells was performed in order to study the degradation of BTs. Shell thickening and losses in biological growth are related with the presence of TBT, and were determined using three morphological indexes. Total BTs concentrations, expressed as Sn, ranged from 18.0 ng g(-1) to 176.7 ng g(-1) in sediments, and from 2.4 ng g(-1) to 11.1 ng g(-1) in oyster shells. Total inorganic tin concentrations ranged from 1775.0 ng g(-1) to 4781.3 ng g(-1) in oyster shells. The amount of BTs in oyster shells has been associated with the concentrations in the sediments trapped in the shell chambers. Partition coefficients between oyster sediments and oyster shells show the affinity of BTs by the sediments and the higher inorganic tin in oyster shells does not seem to be related to the BTs pollution.

Animals↗

PubMed2001

gamma-Aminobutyric acid receptor subtype antagonists differentially alter opioid-induced feeding in the shell region of the nucleus accumbens in rats.

Food intake is significantly increased by administration of mu-selective opioid agonists into the nucleus accumbens, particularly its shell region. Pretreatment with either opioid (mu, delta(1), delta(2) or kappa(1)) or dopaminergic (D(1)) receptor antagonists in the nucleus accumbens shell reduce mu opioid agonist-induced feeding. Selective GABA(A) (muscimol) and GABA(B) (baclofen) agonists administered into the nucleus accumbens shell each stimulate feeding which is respectively and selectively blocked by GABA(A) (bicuculline) and GABA(B) (saclofen) antagonists. The present study investigated whether feeding elicited by the mu-selective opioid agonist, [D-Ala(2),NMe(4),Gly-ol(5)]-enkephalin in the nucleus accumbens shell was decreased by intra-accumbens pretreatment with an equimolar dose range of either GABA(A) or GABA(B) antagonists, and further, whether general opioid or selective GABA antagonists decreased feeding elicited by GABA(A) or GABA(B) agonists in the nucleus accumbens shell. Feeding elicited by the mu-selective opioid agonist was dose-dependently increased following intra-accumbens pretreatment with GABA(A) (bicuculline) antagonism; this enhancement was significantly blocked by pretreatment with general or mu-selective opioid antagonists. In contrast, mu opioid agonist-induced feeding elicited from the nucleus accumbens shell was dose-dependently decreased by GABA(B) (saclofen) antagonism. Neither bicuculline nor saclofen in the nucleus accumbens shell altered baseline food intake. Whereas muscimol-induced feeding elicited from the nucleus accumbens shell was reduced by bicuculline and naltrexone, but not saclofen pretreatment, baclofen-induced feeding elicited from the nucleus accumbens shell was reduced by saclofen, but not by bicuculline or naltrexone. These data indicate that GABA(A) and GABA(B) receptor subtype antagonists differentially affect feeding elicited by mu opioid receptor agonists within the nucleus accumbens shell in rats.

Animals↗

PubMed2002

Shelled opisthobranchs.

In his contributions to the monographic series "Manual of Conchology", Henry Pilsbry reviewed the subgroup Tectibranchiata, comprising those opisthobranch snails that (at least primitively) still possess a shell (Pilsbry, 1894-1896). Exemplified by the Cephalaspidea (bubble shells), others included in this group at Pilsbry's time and since were Anaspidea (sea hares) and the shelled members of Notaspidea (side-gilled slugs) and Sacoglossa (leaf slugs). Pilsbry (and others since his time) considered tectibranchs to be the "root stock" from which more advanced gastropods such as Nudibranchia and Pulmonata were derived. Tectibranch systematics is firmly based on conchology and most species were originally described from empty shells. However, soft-anatomical characters were acknowledged quite early on as equally important in tectibranchs, due to the reduction of their shells and their evolutionary proximity to unshelled gastropods. Today, Tectibranchiata is not recognized as a natural taxon although the word "tectibranch" (like "prosobranch" and "mesogastropod") continues in vernacular use. Shelled opisthobranchs have been redistributed among various taxa, including several new ones--the unresolved basal opisthobranchs (Architectibranchia) and the "lower Heterobranchia", an enigmatic and currently much-studied group of families considered basal to all of Euthyneura (Opisthobranchia and landsnails (Pulmonata)). Despite their polyphyletic status, shelled opisthobranchs remain important subjects in evolutionary studies of gastropods--as the most basal members of nearly every opisthobranch clade and as organisms with mosaic combinations of primitive and derived features within evolutionary "trends" (e.g., loss of the shell, detorsion, concentration of the nervous system, ecological specialization, etc.). Although they play a pivotal role, the shelled opisthobranchs have received minimal attention in more comprehensive gastropod studies, often relegated to token representatives at the derived end of prosobranchs or at the basal end of nudibranchs. The choice of this representative in a larger study is critical if its morphology and/or molecules are to adequately exemplify a larger group. This review explores the shelled opisthobranchs, including their history, current status and presumed synapomorphies, and emphasizes the importance of anatomical data to our current understanding of these "transitional" forms. A synthetic phylogenetic analysis, based on a combination of characters used in four published phylogenies involving tectibranchs, shows the current state of our knowledge and emphasizes areas for future study. The results indicate that Opisthobranchia, Cephalaspidea and Sacoglossa are monophyletic taxa, and that Acteon, the traditional basal opisthobranch, is convincingly a lower heterobranch. In most of the resulting cladograms, Anaspidea formed a monophyletic group with Cephalaspidea, as did pleurobranchoidean Notaspidea with Nudibranchia (the latter recently named as Nudipleura Wägele and Willan, 2000).

Animals↗

PubMed1998

The role of accumbens dopamine in lever pressing and response allocation: effects of 6-OHDA injected into core and dorsomedial shell.

Three experiments investigated the behavioral effects of injections of the neurotoxic agent 6-hydroxydopamine (6-OHDA) into the core or shell of the nucleus accumbens. In the first experiment, it was observed that injections of 6-OHDA into either core or shell had no significant effect on variable interval 30-s responding. In Experiment 2, responding on a fixed ratio 5 (FR5) schedule was impaired by 6-OHDA injections in the core, but not the shell. Rats with core injections of 6-OHDA showed significant alterations in the relative distribution of interresponse times, which were indicative of reductions in the maximal rate of responding and increases in the number of pauses. In the third experiment, rats were tested using a lever-pressing/chow-feeding procedure, in which a preferred food (Bioserve pellets) was available by pressing a lever on a FR5 schedule, but a less preferred food (lab chow) was also available concurrently in the test chamber. Untreated rats usually pressed the lever at high rates to obtain the food pellets and ate little of the lab chow. After training, dopamine depletions were produced by injections of 6-OHDA directly into the core or dorsomedial shell subregions. Injections of 6-OHDA into the core significantly decreased lever pressing for food pellets, increased lab chow consumption, and decreased the relative amount of food obtained by lever pressing. Dorsomedial shell injections of 6-OHDA had no significant effects on either lever pressing or lab chow consumption. Neurochemical results indicate that injections of 6-OHDA in the shell produced substantial depletions in the shell that were somewhat selective; however, injections of 6-OHDA into the core tended to deplete both core and shell. Correlational analyses revealed that decreases in FR5 lever pressing were associated with dopamine levels in the core, but not the shell. The present results indicate that substantial depletions of dopamine in the dorsomedial shell are not sufficient for suppressing reinforced lever pressing, and indicate that dopamine depletions must include the core area to impair performance on these tasks. The lack of effect of accumbens dopamine depletions on VI30 responding are consistent with the notion that accumbens dopamine depletions affect responding on schedules that generate a high rate of responding (FR5), but not those that generate a moderate rate of responding (e.g., VI30 s). The results of the concurrent FR5/chow-feeding experiment indicate that rats with accumbens dopamine depletions remain directed towards the acquisition and consumption of food. These results suggest that dopamine in the core region of accumbens sets constraints upon the selection of food-related behaviors, and that core dopamine depletions alter the relative allocation of food-related responses.

Animals↗

PubMed2003

The arrangement of first- and second-shell water molecules in trivalent aluminum complexes: results from density functional theory and structural crystallography.

The structural and energetic features of a variety of gas-phase aluminum ion hydrates containing up to 18 water molecules have been studied computationally using density functional theory. Comparisons are made with experimental data from neutron diffraction studies of aluminum-containing crystal structures listed in the Cambridge Structural Database. Computational studies indicate that the hexahydrated structure Al[H(2)O](6)(3+) (with symmetry T(h)()), in which all six water molecules are located in the innermost coordination shell, is lower in energy than that of Al[H(2)O](5)(3+).[H(2)O], where only five water molecules are in the inner shell and one water molecule is in the second shell. The analogous complex with four water molecules in the inner shell and two in the outer shell undergoes spontaneous proton transfer during the optimization to give [Al[H(2)O](2)[OH](2)](+).[H(3)O(+)](2), which is lower in energy than Al[H(2)O](6)(3+); this finding of H(3)O(+) is consistent with the acidity of concentrated Al(3+) solutions. Since, however, Al[H(2)O](6)(3+) is detected in solutions of Al(3+), additional water molecules are presumed to stabilize the hexa-aquo Al(3+) cation. Three models of a trivalent aluminum ion complex surrounded by a total of 18 water molecules arranged in a first shell containing 6 water molecules and a second shell of 12 water molecules are discussed. We find that a model with S(6) symmetry for which the Al[H(2)O](6)(3+) unit remains essentially octahedral and participates in an integrated hydrogen bonded network with the 12 outer-shell water molecules is lowest in energy. Interactions between the 12 second-shell water molecules and the trivalent aluminum ion in Al[H(2)O](6)(3+) do not appear to be sufficiently strong to orient the dipole moments of these second-shell water molecules toward the Al(3+) ion.

Aluminum Compounds↗