Shell Lesions Research Articles

Effects of nucleus accumbens core and shell lesions on autoshaped lever-pressing

Certain Pavlovian conditioned stimuli (CSs) paired with food unconditioned stimuli (USs) come to elicit approach and even consumption-like behaviors in rats (sign-tracking). We investigated the effects of lesions of the nucleus accumbens core (ACbC) or shell (ACbS) on the acquisition of sign-tracking in a discriminative autoshaping procedure in which presentation of one lever CS was followed by delivery of sucrose, and another was not. Although we previously found that bilateral lesions of the whole ACb disrupted the initial acquisition of sign-tracking, neither ACbC or ACbS lesions affected the rate or percentage of trials in which rats pressed the CS+. In addition, detailed video analysis showed no effect of either lesion on the topography of the sign-tracking conditioned response (CR). These and other results from lesion studies of autoshaping contrast with those from previous sign-tracking experiments that used purely visual cues (Parkinson et al., 2000a,b), suggesting that the neural circuitry involved in assigning incentive value depends upon the nature of the CS.

Bacterial communities associated with lesions of two forms of shell disease in the American lobster (Homarus americanus, Milne Edwards) from Atlantic Canada

Shell disease is a major threat to the American lobster (Homarus americanus, Milne Edwards) fishery. Here we describe the composition of microbial communities associated with lesions of 2 forms of shell disease in Atlantic Canada, (i) a trauma shell disease (TSD) characterized by massive lesions and (ii) an enzootic shell disease (EnSD) characterized by irregularly shaped lesions with a distinct orange to yellow color. The microbiology of the lesions was described by polymerase chain reaction and denaturing gradient gel electrophoresis of 16S rDNA amplified from scrapings of the shell lesions and was compared with communities of unaffected carapaces and previously described forms of shell diseases. Both TSD and EnSD lesions were dominated by members of Alphaproteobacteria, Gammaproteobacteria, and Flavobacteria, all commonly detected in other forms of shell disease; however, unique members of Epsilonproteobacteria were also present. Two Vibrio spp. and 2 Pseudoalteromonas spp. were dominant in lesions of TSD and a Tenacibaculum sp. and Tenacibaculum ovolyticum were dominant in lesions of EnSD. The TSD and EnSD in this study contained similar taxa as other shell disease forms; however, their microbiology is mostly different and neither resembles that of epizootic shell disease.

Laser therapy in a soft-shelled turtle ( Pelodiscus sinensis ) for the treatment of skin and shell ulceration

Skin and shell diseases in aquatic turtles are often associated with several underlying causes. The presented case report describes aetiology including differential diagnoses, diagnostic procedures and therapy of a soft-shelled turtle (Pelodiscus sinensis) suffering from a septicaemic ulcerative dermatitis. Central aspect hereby is the positive curing effect of laser therapy on skin and shell lesions.

The Role of Nucleus Accumbens Core/Shell in Sleep-Wake Regulation and their Involvement in Modafinil-Induced Arousal

BackgroundWe have previously shown that modafinil promotes wakefulness via dopamine receptor D1 and D2 receptors; however, the locus where dopamine acts has not been identified. We proposed that the nucleus accumbens (NAc) that receives the ventral tegmental area dopamine inputs play an important role not only in reward and addiction but also in sleep-wake cycle and in mediating modafinil-induced arousal.Methodology/Principal FindingsIn the present study, we further explored the role of NAc in sleep-wake cycle and sleep homeostasis by ablating the NAc core and shell, respectively, and examined arousal response following modafinil administration. We found that discrete NAc core and shell lesions produced 26.5% and 17.4% increase in total wakefulness per day, respectively, with sleep fragmentation and a reduced sleep rebound after a 6-hr sleep deprivation compared to control. Finally, NAc core but not shell lesions eliminated arousal effects of modafinil.Conclusions/SignificanceThese results indicate that the NAc regulates sleep-wake behavior and mediates arousal effects of the midbrain dopamine system and stimulant modafinil.

Bacterial Communities Associated with Lesions of Shell Disease in the American Lobster,Homarus americanusMilne-Edwards

Shell disease in Crustacea is a widely recognized syndrome having a polymicrobial etiology, and manifesting itself as lesions of the shell with a variable structure and shell location. We characterized major members of bacterial communities in epizootic shell disease lesions of the American lobster (Homarus americanus, Milne Edwards) and compared these communities with the ones found in study cases of impoundment and enzootic shell disease. Bacteria belonging to several Flavobacteriaceae genera (Aquimarina, Tenacibaculum, Polaribacter, Maribacter, Cellulophaga) within the phylum Bacteroidetes appear to have particular attraction to lobster lesions. The most prominent Bacteroidetes in lobster lesions were representatives of the genus Aquimarina sp., but only Aquimarina ‘homaria’ was detected in all analyzed lesions of epizootic, impoundment, and enzootic shell disease. It was found on 45% of surfaces unaffected by shell disease, but in smaller numbers compared with lesions. Alphaproteobacteria represent the most diverse class of proteobacteria found in both lesions and on unaffected surfaces. Three bacteria of this class appear to be ubiquitous in shell disease lesions, but only one specific alphaproteobacterium tentatively assigned to the genus Thalassobius (herein designated as ‘Thalassobius’ sp.) was present in all analyzed lesions of epizootic, impoundment, and enzootic shell disease. A ubiquitous gammaproteobacterium called ‘Candidatus Homarophilus dermatus’ was also prevalent in lesions, but just as commonly it was associated with surfaces unaffected by shell disease. The bacteria A. ‘homaria’ and ‘Thalassobius’ sp. are dominant and appear obligatory in lobster shell lesions, and are only occasionally detected on unaffected surfaces, which serve as intermediate reservoirs for the two potential pathogens. Therefore, these two bacteria stand out as potential shell-disease pathogens.

Differential effects of accumbens core vs. shell lesions in a rat concurrent conditioned place preference paradigm for cocaine vs. social interaction.

BackgroundA main challenge in the therapy of drug dependent individuals is to help them reactivate interest in non-drug-associated activities. Among these activities, social interaction is doubly important because treatment adherence itself depends on it. We previously developed a rat experimental model based on the conditioned place preference (CPP) paradigm in which only four 15-min episodes of social interaction with a gender- and weight-matched male conspecific (i) reversed CPP from cocaine to social interaction despite continuing cocaine training and (ii) prevented the reinstatement of cocaine CPP. In the present study, we investigated if the two subregions of the nucleus accumbens (Acb), i.e., the core (AcbC) and the shell (AcbSh), would differentially affect CPP for cocaine vs social interaction.Methodology/Principal FindingsAnimals were concurrently trained for CPP pairing cocaine with one compartment and social interaction with the other (i.e., mutually exclusive stimulus presentation during training). Excitotoxic lesioning of the AcbC or the BLA shifted CPP toward social interaction, whereas AcbSh inactivation shifted CPP toward cocaine.ConclusionsOverall, our findings suggest that inactivation of the AcbC or the BLA is sufficient to shift CPP away from a drug of abuse toward social interaction. Lesioning the AcbSh produced the opposite effect.

The general and outcome-specific forms of Pavlovian-instrumental transfer are differentially mediated by the nucleus accumbens core and shell.

Tests of Pavlovian-instrumental transfer (PIT) demonstrate that reward-predictive stimuli can exert a powerful motivational influence on the performance of instrumental actions. Recent evidence suggests that predictive stimuli produce this effect through either the general arousal (general PIT) or the specific predictions (outcome-specific PIT) produced by their association with reward. In two experiments, we examined the effects of pretraining lesions (Experiment 1) or muscimol-induced inactivation (Experiment 2) of either the core or shell regions of the nucleus accumbens (NAC) on these forms of PIT. Rats received Pavlovian training in which three auditory stimuli each predicted the delivery of a distinct food outcome. Separately, the rats were trained to perform two instrumental actions, each of which earned one of the outcomes used in Pavlovian conditioning. Finally, the effects of the three stimuli on performance of the two actions were assessed in extinction. Here we report evidence of a double dissociation between general and outcome-specific PIT at the level of the accumbens. Shell lesions eliminated outcome-specific PIT but spared general PIT, whereas lesions of the core abolished general PIT but spared outcome-specific PIT. Importantly, the infusion of muscimol into core or shell made immediately before the PIT tests produced a similar pattern of results. These results suggest that whereas the NAC core mediates the general excitatory effects of reward-related cues, the NAC shell mediates the effect of outcome-specific reward predictions on instrumental performance, and thereby serve to clarify reported discrepancies regarding the role of the NAC core and shell in PIT.

Dopamine in nucleus accumbens: salience modulation in latent inhibition and overshadowing

Latent inhibition (LI) is demonstrated when non-reinforced pre-exposure to a to-be-conditioned stimulus retards later learning. Learning is similarly retarded in overshadowing, in this case using the relative intensity of competing cues to manipulate associability. Electrolytic/excitotoxic lesions to shell accumbens (NAc) and systemic amphetamine both reliably abolish LI. Here a conditioned emotional response procedure was used to demonstrate LI and overshadowing and to examine the role of dopamine (DA) within NAc. Experiment 1 showed that LI but not overshadowing was abolished by systemic amphetamine (1.0 mg/kg i.p.). In Experiment 2, 6-hydroxydopamine (6-OHDA) was used to lesion DA terminals within NAc: both shell- and core- (plus shell-)lesioned rats showed normal LI and overshadowing. Experiment 3 compared the effects of amphetamine microinjected at shell and core coordinates prior to conditioning: LI, but not overshadowing, was abolished by 10.0 but not 5.0 µg/side amphetamine injected in core but not shell NAc. These results suggest that the abolition of LI produced by NAc shell lesions is not readily reproduced by regionally restricted DA depletion within NAc; core rather than shell NAc mediates amphetamine-induced abolition of LI; overshadowing is modulated by different neural substrates.

Selective lesions of the dorsomedial striatum impair serial spatial reversal learning in rats

Impairments in reversal learning have been attributed to orbitofrontal cortex (OFC) dysfunction in many species. However, the role of subcortical areas interconnected with the OFC such as the striatum remains poorly understood. This study directly evaluated the contribution of core and shell sub-regions of the nucleus accumbens (NAc), dorsomedial (DMS) and dorsolateral (DLS) striatum to reversal learning of an instrumental two-lever spatial discrimination task in rats. Selective NAc core, DMS and DLS lesions were achieved with microinjections of quinolinic acid and NAc shell lesions with ibotenic acid. Damage to NAc core or shell did not affect retention of a previously acquired instrumental spatial discrimination. In contrast, DLS and DMS lesions produced changes in aspects of discrimination performance such as the latency to collect earned food pellets. Neither NAc core or shell lesions nor DLS lesions affected the main indices of reversal performance. Conversely, DMS lesion rats showed a significant impairment in reversal learning. DMS damage increased the number of errors to reach criteria that were perseverative in nature. The deficit in reversal learning in DMS lesion rats was not associated with an impairment to extinguish instrumental responding. There were no effects on spontaneous locomotor activity. Our data are in agreement with recent work showing that lesions of the medial striatum in marmoset monkeys produce perseverative impairments during a serial visual discrimination reversal task and support the hypothesis that dorsomedial striatal dysfunction contributes to pathological perseveration, which is a common feature of many psychiatric disorders.

Phaeohyphomycosis of the Carapace in an Aldabra Tortoise (Geochelone gigantea)

An adult male Aldabra tortoise (Geochelone gigantea) presented with a deep flaking area of the carapace, and histologic examination of biopsies from this area revealed phaeohyphomycosis of the superficial keratinized layers. The disease progressed rapidly and spread to numerous sites on the carapace. After several weeks of regular debridement, deep bone involvement was evident and was confirmed through histologic examination. Fungal culture was attempted but was unsuccessful at isolating the infectious agent. Polymerase chain reaction analysis of extracted DNA from the fixed tissue block identified the fungus as Exophiala oligosperma. Initial treatment included weekly debridement and oral and topical antifungal agents. A nuclear scintigraphy bone scan was performed to determine the extent and status of the infection. Multiple foci of uptake of the radiopharmaceutical marker were present within the carapace, indicating active lesions. The tortoise was maintained on oral antifungal treatment, and lesions resolved over several months. A repeat bone scan performed 1 yr after initial presentation showed reduction in marker uptake, indicating a response to treatment in the deeper lesions. Phaeohyphomycosis should be considered as a differential diagnosis for cases of shell lesions in chelonians.

Functional Interaction between the Hippocampus and Nucleus Accumbens Shell Is Necessary for the Acquisition of Appetitive Spatial Context Conditioning

The nucleus accumbens (NAc) has been implicated in a variety of associative processes that are dependent on the integrity of the amygdala and hippocampus (HPC). However, the extent to which the two subregions of the NAc, the core and shell, form differentiated circuits within the amygdala- and hippocampal-ventral striatal circuitry remains unclear. The present study investigated the effects of selective excitotoxic lesions of the nucleus accumbens shell or core subregion on appetitive elemental cue and context conditioning, shown previously to be dependent on the basolateral amygdala and hippocampus, respectively. Rats were trained sequentially to acquire discrete conditioned stimulus-sucrose conditioning, followed by spatial context-sucrose conditioning in a place preference apparatus characterized by three topographically identical chambers, the chambers being discriminable only on the basis of path integration. NAc shell lesions selectively impaired the acquisition of conditioned place preference and the use of spatial information to retrieve information about a discrete cue, whereas, as expected, NAc core lesions attenuated the acquisition of cue conditioning compared with sham rats. In a subsequent experiment, disconnection of the HPC from the NAc shell using unilateral asymmetric lesions of each structure resulted in a pattern of impairment in place conditioning and context-dependent cue retrieval similar to that produced by NAc shell lesions. These data not only suggest that the NAc core and shell subregions subserve distinct associative processes but also that the NAc shell and HPC are important functional components of a limbic corticostriatal network involved in spatial context conditioning.

Contrasting effects of selective lesions of nucleus accumbens core or shell on inhibitory control and amphetamine‐induced impulsive behaviour

The core and shell subregions of the nucleus accumbens receive differential projections from areas of the medial prefrontal cortex that have dissociable effects on impulsive and perseverative responding. The contributions of these subregions to simple instrumental behaviour, inhibitory control and behavioural flexibility were investigated using a ‘forced choice’ task, various parameter manipulations and an omission schedule version of the task. Post-training, selective core lesions were achieved with microinjections of quinolinic acid and shell lesions with ibotenic acid. After a series of behavioural task manipulations, rats were re-stabilized on the standard version of the task and challenged with increasing doses of d-amphetamine (vehicle, 0.5 or 1.0 mg/kg i.p. 30 min prior to test). Neither core- nor shell-lesioned rats exhibited persistent deficits in simple instrumental behaviour or challenges to behavioural flexibility or inhibitory control. Significant differences between lesion groups were unmasked by d-amphetamine challenge in the standard version of the forced task. Core lesions potentiated and shell lesions attenuated the dose-dependent effect of d-amphetamine on increasing anticipatory responses seen in sham rats. These data imply that the accumbens core and shell subregions do not play major roles in highly-trained task performance or in challenges to behavioural control, but may have opposed effects following d-amphetamine treatment. Specifically, they suggest the shell subregion to be necessary for dopaminergic activation driving amphetamine-induced impulsive behaviour and the core subregion for the normal control of this behaviour via conditioned influences.

The Nucleus Accumbens Core has a More Important Role in Resisting Reactivation of Extinguished Conditioned Place Preference in Morphine-addicted Rats

We investigated the roles of the core and shell subfields of the nucleus accumbens (NAc) in drug- or foot-shock-induced reactivation of extinguished conditioned place preference (CPP) in morphine-addicted rats. Rats were given electrolytic lesions to either the core or shell after CPP was established. After surgery, a reduction of CPP scores to morphine was observed in all groups. During the reacquisition of morphine-seeking behaviour, rats in the shell and sham lesion groups regained their CPP, while the CPP in core lesion rats remained severely impaired. Similarly, foot-shock-induced reactivation of CPP in the core lesion group was significantly lower than that of the shell and sham lesion groups, and there was no significant difference between these latter groups. Our results demonstrate that NAc core and shell lesions elicited dissociable effects on reactivation of extinguished CPP in rats, suggesting that the NAc core might play a more important role in resisting reactivation of extinguished CPP in morphine-addicted rats.

Vacuum-assisted closure for treatment of a deep shell abscess and osteomyelitis in a tortoise

A female Aldabra tortoise (Geochelone gigantea) was evaluated because of focal necrosis of the carapace. Debridement revealed a 14.5 x 11.5-cm area of shell necrosis, deep abscess formation, and osteomyelitis involving bacterial (Klebsiella pneumoniae, Staphylococcus aureus, and Pseudomonas spp) and fungal pathogens. Following extensive debridement, vacuum-assisted closure incorporating silver-impregnated bandaging materials was used. The wound was considered healed after 55 days, at which time a layer of epidermal tissue with progressing keratinization was present, with smooth underlying ossification. Keratinization with normal pigmentation continued over the next 67 days. Findings suggested that vacuum-assisted closure with silver-impregnated bandaging materials may provide advantages over traditional methods in the treatment of shell lesions in chelonians, including faster wound healing, improved cosmetic appearance of the healed wound, superior control of microbial contamination, and lower overall treatment costs.

Lesions of the nucleus accumbens shell can reduce activity in the elevated plus-maze

Across different behavioural tasks, nucleus accumbens (n.acc) lesions have generated conflicting effects on locomotor activity and in particular, the relative roles of the n.acc shell and core subfields in this have been controversial. To date there is only one study examining effects of lesions to the medial n.acc on elevated plus-maze (EPM) behaviour; these lesions were shown to increase both locomotor and exploratory activity. Given the well-documented distinction between shell and core, the present study sought to extend previous research by testing lesions selective to each n.acc subfield in the EPM. Results showed no statistical differences between core lesioned and sham-operated animals on any measure. In contrast, shell lesions consistently reduced locomotion and exploratory activity. This direction of effects is opposite to that previously observed after medial n.acc. lesions. In conclusion, locomotion and exploratory activity were clearly reduced by shell but not core lesions, consistent with other evidence for the functional heterogeneity of n.acc shell and core.

Evidence for Multiple Sites within Rat Ventral Striatum Mediating Cocaine-Conditioned Place Preference and Locomotor Activation

Considerable evidence suggests that psychostimulants can exert rewarding and locomotor-stimulating effects via increased dopamine transmission in the ventral striatum. However, the relative contributions of ventral striatal subregions to each of these effects have been little investigated. In the present study, we examined the contribution of different ventral striatal sites to the rewarding and locomotor-activating effects of cocaine. Initially, the effects of bilateral 6-hydroxydopamine lesions of the nucleus accumbens core or medial shell on cocaine-induced locomotor stimulation (0.5-1.5 mg/kg i.v. or 5-20 mg/kg i.p.) and conditioned place preference (0.5 mg/kg i.v. or 10 mg/kg i.p.) were examined. In a subsequent study, we investigated the effects of olfactory tubercle versus medial shell lesions on cocaine-conditioned place preference and locomotor activity (0.5 mg/kg i.v.). Dopaminergic lesion extent was quantified by radioligand binding to the dopamine transporter. Multiple linear regression was used to identify associations between behavioral effects and residual dopamine innervation in ventral striatal subregions. On this basis, the accumbens core was associated with the locomotor stimulant effects of i.v. and i.p. cocaine. In contrast, the medial shell was associated with the rewarding effect of i.v. cocaine, but not of i.p. cocaine. Finally, the olfactory tubercle was identified as an additional site contributing to conditioned place preference produced by i.v. cocaine. Overall, these findings provide additional evidence that the locomotor stimulant and rewarding effects of systemically administered psychomotor stimulant drugs are segregated within the ventral striatum.

Facilitated extinction of appetitive instrumental conditioning following excitotoxic lesions of the core or the medial shell subregion of the nucleus accumbens in rats

The nucleus accumbens has been implicated in the control of goal-directed behaviour, including instrumental conditioning. Here, we evaluated the effect of N-methyl-D: -aspartate (NMDA)-induced excitotoxic lesions restricted to either the core or the medial shell subregions of the nucleus accumbens (NAC) on extinction in rats using a trial discrete fixed ratio-5 (FR-5) appetitive operant procedure. Neither core nor shell lesions of the NAC affected the acquisition of instrumental responding. Both lesions facilitated the cessation of responding when the instrumental act no longer yielded reinforcement. Our results suggest that both the NAC core and medial shell contribute to the control of extinction learning of appetitively motivated instrumental behaviour.

Latent inhibition of conditioned taste aversion is not disrupted, but can be enhanced, by selective nucleus accumbens shell lesions in rats

Latent inhibition is a form of negative priming in which repeated non-reinforced pre-exposures to a stimulus retard subsequent learning about the predictive significance of that stimulus. The nucleus accumbens shell and the anatomical projection it receives from the hippocampal formation have been attributed a pivotal role in the control or regulation of latent inhibition expression. A number of studies in rats have demonstrated the efficacy of selective shell lesions to disrupt latent inhibition in different associative learning paradigms, including conditioned active avoidance and conditioned emotional response. Here, we extended the test to the conditioned taste aversion paradigm, in which the effect of direct hippocampal damage on latent inhibition remains controversial. We demonstrated the expected effect of selective shell lesions on latent inhibition of conditioned emotional response and of conditioned active avoidance, before evaluating in a separate cohort of rats the effect of comparable selective lesions on latent inhibition of conditioned taste aversion: a null effect of the lesions was first obtained using parameters known to be sensitive to amphetamine treatment, then an enhancement of latent inhibition was revealed with a modified conditioned taste aversion procedure. Our results show that depending on the associative learning paradigm chosen, shell lesions can disrupt or enhance the expression of latent inhibition; and the pattern is reminiscent of that seen following hippocampal damage.

Tumor-like formations on the shells of Japanese scallops Patinopecten yessoensis (Jay)

Three types of tumor-like formations on the shell of commercial Japanese scallop Patinopecten(= Mizuhopecten) yessoensis were identified. The first type of tumor-like formation (Type I) is a brown prominent knob on the inner shell surface. This is the result of penetration of aggregations of the polychaete worms of genus Polydora into the scallop cavity usually through the upper valve of scallop and subsequent covering of their boreholes by shell calcite carbonate. The second type (Type II) is tumor-like lamination of the shell with the inclusion of organic matter between calcite layers on the inner surface of the upper and lower valves. These laminations have no outlet to the outer shell surface. The third type of scallop shell tumor-like lesion (Type III) mainly built up on the inner surface of the lower valve. It is a cone-shaped lump, which seemed to consist of aggregated coarse-grained sand. It has no outlet to the outer shell surface. Tumors of the different types are not equally distributed. Type I tumors are the most common, followed by Type II and Type III. Other kinds of tumor-like lesions on the inner shell surface are not found in the species studied. On the outer surface of scallop shell tumor-like formations were not found. The shell tumor-like lesions occurred significantly more frequently on scallops that are inhabiting muddy bottom sediments than sand. A positive relationship was found between scallop age and occurrence of shell lesions. The tumor-like formations of all types adversely influence scallops. The shell height and total, soft tissue and adductor muscle weights were lower for scallops with tumor-like formations on the shell than for healthy individuals.

Double dissociation of the effects of selective nucleus accumbens core and shell lesions on impulsive‐choice behaviour and salience learning in rats

The nucleus accumbens can be subdivided into at least two anatomically distinct subregions: a dorsolateral 'core' and a ventromedial 'shell', and this distinction may extend to a functional dissociation. Here, we contrasted the effects of selective excitotoxic core and medial shell lesions on impulsive-choice behaviour using a delayed reward choice paradigm and a differential reward for low rates of responding (DRL) test, against a form of salience learning known as latent inhibition (LI). Core lesions led to enhanced impulsive choices as evidenced by a more pronounced shift from choosing a continuously reinforced lever to a partially reinforced lever, when a delay between lever press and reward delivery was imposed selectively on the former. The core lesions also impaired performance on a DRL task that required withholding the response for a fixed period of time in order to earn a reward. Medial shell lesions had no effect on these two tasks, but abolished the LI effect, as revealed by the failure of stimulus pre-exposure to retard subsequent conditioning to that stimulus in an active avoidance procedure in the lesioned animals. As expected, selective core lesions spared LI. The double dissociations demonstrated here support a functional segregation between nucleus accumbens core and shell, and add weight to the hypothesis that the core, but not the shell, subregion of the nucleus accumbens is preferentially involved in the control of choice behaviour under delayed reinforcement conditions and in the inhibitory control of goal-directed behaviour.