Lesion Groups (lesion + groups)

Distribution by Scientific Domains


Selected Abstracts


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

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 2 2008
E. R. Murphy
Abstract 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. [source]


Time-sensitive enhancement of motor learning with the less-affected forelimb after unilateral sensorimotor cortex lesions in rats

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 8 2005
J. Edward Hsu
Abstract Unilateral damage to the forelimb region of the sensorimotor cortex (FLsmc) results in time-dependent changes in neuronal activity, structure and connectivity in the contralateral motor cortex of adult rats. These changes have been linked to facilitation of motor skill learning in the less-affected/ipsilesional forelimb, which is likely to promote its use in the development of behavioral compensation. The goal of this study was to determine whether an early post-lesion-sensitive time period exists for this enhanced learning and whether it is linked to synaptogenesis in the contralesional motor cortex. Rats were trained for 21 days on a skilled reaching task with the ipsilesional forelimb beginning 4 or 25 days after unilateral ischemic (endothelin-1-induced) FLsmc lesions or sham operations. As found previously, reaching performance was significantly enhanced in rats trained early post-lesion compared with sham-operates. In rats trained later post-lesion, performance was neither significantly different from time-matched sham-operates nor strikingly different from animals trained earlier post-lesion. In layer V of the contralesional motor cortex, stereological methods for light and electron microscopy revealed significantly more total, multisynaptic bouton and perforated synapses per neuron compared with sham-operates, but there were no significant differences between early- and late-trained lesion groups. Thus, there appears to be a sensitive time window for the maximal expression of the enhanced learning capacity of the less-affected forelimb but this window is broadly, rather than sharply, defined. These results indicate that relatively long-lasting lesion-induced neuronal changes are likely to underlie the facilitation of learning with the less-affected forelimb. [source]


Different behavioral effects of neurotoxic dorsal hippocampal lesions placed under either isoflurane or propofol anesthesia

HIPPOCAMPUS, Issue 3 2008
Mark G. Baxter
Abstract Anesthetic protocols for behavioral neuroscience experiments are evolving as new anesthetics are developed and surgical procedures are refined to improve animal welfare. We tested whether neurotoxic dorsal hippocampal lesions produced under two different anesthetic protocols would have different behavioral and/or histo-pathological effects. Rats were anesthetized with either propofol, an intravenous anesthetic, or isoflurane, a gaseous anesthetic, and multiple injections of an excitotoxin (N -methyl- D -aspartate) were stereotaxically placed in the dorsal hippocampus bilaterally. Intraoperative physiological parameters were similar in the two surgical groups, as were the volumes of the lesions, although the profile of postoperative impairment in a spatial learning task differed between the lesion groups depending on the anesthetic regimen used. These results show that the choice of anesthetic protocol is a critical variable in designing behavioral neuroscience experiments using neurosurgical procedures. This factor should be considered carefully in experimental design and in cross-study comparisons of lesion effects on behavior. © 2007 Wiley-Liss, Inc. [source]


Learning associations between places and visual cues without learning to navigate: Neither fornix nor entorhinal cortex is required

HIPPOCAMPUS, Issue 4 2003
E.A. Gaffan
Abstract Rats with fornix transection, or with cytotoxic retrohippocampal lesions that removed entorhinal cortex plus ventral subiculum, performed a task that permits incidental learning about either allocentric (Allo) or egocentric (Ego) spatial cues without the need to navigate by them. Rats learned eight visual discriminations among computer-displayed scenes in a Y-maze, using the constant-negative paradigm. Every discrimination problem included two familiar scenes (constants) and many less familiar scenes (variables). On each trial, the rats chose between a constant and a variable scene, with the choice of the variable rewarded. In six problems, the two constant scenes had correlated spatial properties, either Allo (each constant appeared always in the same maze arm) or Ego (each constant always appeared in a fixed direction from the start arm) or both (Allo + Ego). In two No-Cue (NC) problems, the two constants appeared in randomly determined arms and directions. Intact rats learn problems with an added Allo or Ego cue faster than NC problems; this facilitation provides indirect evidence that they learn the associations between scenes and spatial cues, even though that is not required for problem solution. Fornix and retrohippocampal-lesioned groups learned NC problems at a similar rate to sham-operated controls and showed as much facilitation of learning by added spatial cues as did the controls; therefore, both lesion groups must have encoded the spatial cues and have incidentally learned their associations with particular constant scenes. Similar facilitation was seen in subgroups that had short or long prior experience with the apparatus and task. Therefore, neither major hippocampal input,output system is crucial for learning about allocentric or egocentric cues in this paradigm, which does not require rats to control their choices or navigation directly by spatial cues. Hippocampus 2003;13:445,460. © 2003 Wiley-Liss, Inc. [source]


Real-world bare metal stenting: Identification of patients at low or very low risk of 9-month coronary revascularization

CATHETERIZATION AND CARDIOVASCULAR INTERVENTIONS, Issue 2 2004
Stephen G. Ellis MD
Abstract The high cost of drug-eluting stents (DESs) has made identification of patients who are at low risk for subsequent revascularization after treatment with bare metal stents (BMSs) highly desirable. Previous reports from randomized trials suffer from biases induced by restricted entry criteria and protocol-mandated angiographic follow-up. Between 1994 and 2001, 5,239 consecutive BMS patients, excluding those with coil stents, technical failure, brachytherapy, staged procedure, or stent thrombosis within 30 days, were prospectively identified from a large single-center tertiary-referral-center prospective registry for long-term follow-up. We sought to identify characteristics of patients with very low (, 4%) or low (4,10%) likelihood of coronary revascularization 9 months after BMS. Nine-month clinical follow-up was obtained in 98.2% of patients. Coronary revascularization was required in 13.4% and did not differ significantly by stent type. On the basis of multivariate analysis identifying 11 independent correlates and previous reports, 20 potential low-risk patient and lesion groups (228 ± 356 patients/groups) were identified (e.g, patients with all of the following: native vessel, de novo, reference diameter , 3.5 mm, lesion length < 5 mm, no diabetes, not ostial in location). Actual and model-based outcomes were analyzed. No group had both predicted and observed 9-month revascularization , 4% (very low risk). Conversely, 19 of 20 groups had a predicted and observed revascularization rate of 4,10% (low risk). In the real-world setting, the need for intermediate-term revascularization after BMS may be lower than expected, but it may be very difficult to identify patients at very low risk. Conversely, if the benefits of DESs are attenuated in routine practice, many groups of patients treated with BMSs may have nearly comparable results. Catheter Cardiovasc Interv 2004;63:135,140. © 2004 Wiley-Liss, Inc. [source]