Combined Lesion Group Research Articles

Behavioral effects of 6-hydroxydopamine-induced damage to nigro-striatal pathway and Locus coeruleus as a rodent model of Parkinson’s disease

Parkinson's disease (PD) is a chronic and progressive neurodegenerative disorder characterized by the loss of dopaminergic neurons in the Substantia nigra pars compacta (SNpc), which leads to motor and non-motor symptoms (NMS). NMS can appear many years before the classical motor symptoms and are associated with the neurodegeneration of several nuclei; in this work, we highlight the neurodegeneration of Locus coeruleus (LC) in PD. The aim was to investigate the effects of depleting SNpc and LC catecholaminergic neurons on behavioral and neurobiological endpoints. Here we used 6-hydroxydopamine (6-OHDA) in order to induced neurotoxic damage in three independent experimental groups: SNpc lesion group, which 6-OHDA was injected into CPu (CPu-6-OHDA), LC lesion group, which 6-OHDA was injected directly on LC to selectively caused a damage on this nucleus (LC-6-OHDA), and the combined SNpc and LC lesion group (CL-6-OHDA). Next, the behavioral studies were performed using the Morris water maze (MWM), open field (OF), and elevated plus maze (EPM). After stereotaxic surgeries, the animals showed a loss of 67% and 77% of Tyrosine hydroxylase (TH) reactive neurons in the SNpc and LC, respectively. The behavioral analysis showed the anxiety-like behavior in CL-6-OHDA group in the EPM test; in the MWM test, the combined lesions (CL-6-OHDA) showed an impairment in memory acquisition and spatial memory; and no changes were observed in locomotor activity in all the tests. Furthermore, our investigation demonstrating the effects of depleting SN and LC catecholaminergic neurons on behavioral and neurobiological parameters. All these data together lead us to believe that a bilateral PD model including a LC bilateral degeneration is potentially a more accurate model to evaluate the NMS in the pathological development of the disease in rodents.

Selective cholinergic depletion of pedunculopontine tegmental nucleus aggravates freezing of gait in parkinsonian rats.

Many patients of advanced Parkinson's disease (PD) suffer from intractable axial symptoms (severe gait and postural impairments), which were recently speculated to be more relevant to cholinergic degeneration in the brainstem than dopaminergic degeneration in the substantia nigra compacta (SNc). To investigate the role of the cholinergic cells of the pedunculopontine tegmental nucleus (PPTg) on motor deficits, especially the axial motor impairments, we measured and analyzed the gait performance of sham lesion rats, SNc dopaminergic lesion rats, PPTg cholinergic lesion rats, and combined lesion rats by using the CatWalk system. Motor performance of PPTg cholinergic lesion rats was also tested on the rotarod. Independent loss of cholinergic neurons in the PPTg did not induce gait disturbance in CatWalk, but PPTg lesion rats showed motor impairments on the rotarod when the demands of the motor task increased. Both SNc lesion rats and combined lesion rats displayed significant changes in many gait parameters, but the terminal dual stance increased much higher in combined lesion group than SNc lesion group. Furthermore, combined lesion rats showed more severe freezing of gait (FOG) than SNc lesion rats during behavioral re-evaluations after lesion. These results suggest that the PPTg cholinergic neurons play a vital role in the occurrence of FOG in PD.

Subthalamic 6-OHDA-induced lesion attenuates levodopa-induced dyskinesias in the rat model of Parkinson's disease

The subthalamic nucleus (STN) receives direct dopaminergic innervation from the substantia nigra pars compacta that degenerates in Parkinson's disease. The present study aimed to investigate the role of dopaminergic denervation of STN in the origin of levodopa-induced dyskinesias. Rats were distributed in four groups which were concomitantly lesioned with 6-OHDA or vehicle (sham) in the STN and in the medial forebrain bundle (MFB) as follows: a) MFB-sham plus STN-sham, b) MFB-sham plus STN-lesion, c) MFB-lesion plus STN-sham, and d) MFB-lesion plus STN-lesion. Four weeks after lesions, animals were treated with levodopa (6mg/kg with 15mg/kg benserazide i.p.) twice daily for 22 consecutive days. Abnormal involuntary movements were measured. In situ hybridization was performed measuring the expression of striatal preproenkephalin, preprodynorphin, STN cytochrome oxidase (CO) and nigral GAD67 mRNAs. STN 6-OHDA denervation did not induce dyskinesias in levodopa-treated MFB-sham animals but attenuated axial (p<0.05), limb (p<0.05) and orolingual (p<0.01) dyskinesias in rats with a concomitant lesion of the nigrostriatal pathway. The attenuation of dyskinesias was associated with a decrease in the ipsilateral STN CO mRNA levels (p<0.05). No significant differences between MFB-lesion plus STN-sham and MFB-lesion plus STN-lesion groups in the extent of STN dopaminergic denervation were observed. Moreover, intrasubthalamic microinfusion of dopamine in the MFB-lesion plus STN-lesion group triggered orolingual (p<0.01), but not axial or limb, dyskinesias. These results suggest that dopaminergic STN innervation influences the expression of levodopa-induced dyskinesias but also the existence of non dopaminergic-mediated mechanisms. STN noradrenergic depletion induced by 6-OHDA in the STN needs to be taken in account as a possible mechanism explaining the attenuation of dyskinesias in the combined lesion group.

Characterization of Japanese-American men with a single neocortical AD lesion type

Neocortical neuritic plaques (NP) and neurofibrillary tangles (NFT) are hallmarks of Alzheimer's disease (AD) and usually, both are present. The Honolulu-Asia Aging Study autopsy series includes a significant number of individuals with only one neocortical AD lesion type. These could represent an early phase of the AD process. If so, such individuals would be expected to share other clinical and pathological features of AD. We compared frequency of apolipoprotein epsilon E4 (APOE4) allele, average Braak stage, and burden of cerebral amyloid angiopathy (CAA) among the two single lesion type groups, a group without AD lesions, and groups with high and low frequencies of both AD lesions. Single AD lesion groups shared only the characteristics associated with their unique lesion type with the combined AD lesion group and did not have higher prevalence of dementia than the no AD lesion group. Only the NP + NFT group showed a “dose–response” relationship with greater probability of dementia with higher neocortical frequencies of either AD lesion. The single neocortical AD lesion groups do not appear to represent early AD.

P.1.c.045 The effects of risperidone, olanzapine and haloperidol on enzyme activities in erythrocytes and plasma of rats

The subthalamic nucleus (STN) receives direct dopaminergic innervation from the substantia nigra pars compacta that degenerates in Parkinson's disease. The present study aimed to investigate the role of dopaminergic denervation of STN in the origin of levodopa-induced dyskinesias. Rats were distributed in four groups which were concomitantly lesioned with 6-OHDA or vehicle (sham) in the STN and in the medial forebrain bundle (MFB) as follows: a) MFB-sham plus STN-sham, b) MFB-sham plus STN-lesion, c) MFB-lesion plus STN-sham, and d) MFB-lesion plus STN-lesion. Four weeks after lesions, animals were treated with levodopa (6 mg/kg with 15 mg/kg benserazide i.p.) twice daily for 22 consecutive days. Abnormal involuntary movements were measured. In situ hybridization was performed measuring the expression of striatal preproenkephalin, preprodynorphin, STN cytochrome oxidase (CO) and nigral GAD67 mRNAs. STN 6-OHDA denervation did not induce dyskinesias in levodopa-treated MFB-sham animals but attenuated axial (p < 0.05), limb (p < 0.05) and orolingual (p < 0.01) dyskinesias in rats with a concomitant lesion of the nigrostriatal pathway. The attenuation of dyskinesias was associated with a decrease in the ipsilateral STN CO mRNA levels (p < 0.05). No significant differences between MFB-lesion plus STN-sham and MFB-lesion plus STN-lesion groups in the extent of STN dopaminergic denervation were observed. Moreover, intrasubthalamic microinfusion of dopamine in the MFB-lesion plus STN-lesion group triggered orolingual (p < 0.01), but not axial or limb, dyskinesias. These results suggest that dopaminergic STN innervation influences the expression of levodopa-induced dyskinesias but also the existence of non dopaminergic-mediated mechanisms. STN noradrenergic depletion induced by 6-OHDA in the STN needs to be taken in account as a possible mechanism explaining the attenuation of dyskinesias in the combined lesion group.

Egocentric spatial orientation in a water maze by rats subjected to transection of the fimbria-fornix and/or ablation of the prefrontal cortex

The acquisition of a water maze based task requiring egocentric spatial orientation in the absence of distal cues was studied in four groups of rats: animals in which the fimbria-fornix had been transected, rats that received bilateral ablations of the anteromedial prefrontal cortex, animals in which both of these structures had been lesioned, and a sham-operated control group. Isolated lesions of both the anteromedial prefrontal cortex and the hippocampus were associated with a significantly impaired task acquisition. Both of these individually lesioned groups did, however, eventually demonstrate full functional recovery by reaching the task proficiency of the sham-operated control group. In contrast, the group in which both of these structures had been lesioned failed to demonstrate full functional recovery and was severely and long-lastingly impaired when compared to all other groups. Behavioural challenges in the form of a no-platform session and two reversals of platform position demonstrated that while the sham-operated control group and the group subjected to fimbria-fornix transections in isolation utilized rather pure egocentric orientation strategies, the two prefrontally lesioned groups (and especially the combined lesion group) employed a different set of solution strategies which at least partly relied on a “circling” method. Even in the behaviour of the prefrontally lesioned groups, however, indications of a certain level of cognitive representations of the platform positions were seen. It is concluded that both the prefrontal cortex and the hippocampus contribute to the mediation of egocentric spatial orientation. Furthermore, the hippocampus is a significant and potentially irreplaceable part of the neural substrate of functional recovery of the presently studied task after prefrontal lesions—while the prefrontal cortex may play a similar role with respect to hippocampal lesions.

Place learning and object recognition by rats subjected to transection of the fimbria-fornix and/or ablation of the prefrontal cortex

The acquisition of a water maze-based allocentric place learning task and an exploration based object recognition task were studied in four groups of rats: animals in which the fimbria-fornix had been transected, rats who had received bilateral ablations of the anteromedial prefrontal cortex, animals in which both of these structures had been lesioned, and a sham operated control group. None of the groups showed impairments of object recognition. Ablations of the prefrontal cortex caused a mild impairment in the acquisition of the place learning task. The two fimbria-fornix transected groups exhibited a severe impairment during the acquisition of this task. All groups reached criterion level task performance eventually. All groups were subjected to a number of behavioural and pharmacological challenges in order to elucidate the neural and cognitive mechanisms of this behavioural recovery. During a no-platform session both the fimbria-fornix transected group and the prefrontally ablated group demonstrated a normal preference for the former platform position. The combined lesion group, however, failed to show a similar preference for this position. The outcome of the pharmacological challenges demonstrated that while the task performance of all four groups relied equally on catecholaminergic mediation, only the task solution of the fimbria-fornix transected group was significantly impaired by disturbance of the catecholaminergic systems. The data indicated a high likelihood that prefrontal cortical mechanisms contribute to the recovery of allocentric place learning after fimbria-fornix transections.

Medullary serotonergic neurones and adjacent neurones that express neurokinin‐1 receptors are both involved in chemoreception in vivo

Neurokinin-1 receptor (NK1R)-expressing neurones that are involved in chemoreception at the retrotrapezoid nucleus (Nattie & Li, 2002b) are also prominent at locations that contain medullary serotonergic neurones, which are chemosensitive in vitro. In medullary regions containing both types, we evaluated their role in central chemoreception by specific cell killing. We injected (2 x 100 nl) (a) substance P-saporin (SP-SAP; 1 microm) to kill NK1R-expressing neurones, (b) a novel conjugate of a monoclonal antibody to the serotonin transporter (SERT) and saporin (anti-SERT-SAP; 1 microm) to kill serotonergic neurones, or (c) SP-SAP and anti-SERT-SAP together to kill both types. Controls received IgG-SAP injections (1 microm). There was no double-labelling of NK1R-immunoreactive (ir) and tryptophan-hydroxylase (TPOH)-ir neurones. Cell (somatic profile) counts showed that NK1R-ir neurones in the SP-SAP group were reduced by 31%; TPOH-ir neurones in the anti-SERT-SAP group by 28%; and NK1R-ir and TPOH-ir neurones, respectively, in the combined lesion group by 55% and 31% (P < 0.001; two-way ANOVA; P < 0.05, Tukey's post hoc test). The treatments had no significant effect on sleep/wake time, body temperature, or oxygen consumption but all three reduced the ventilatory response to 7% inspired CO(2) in wakefulness and sleep by a similar amount. SP-SAP treatment decreased the averaged CO(2) responses (3, 7 and 14 days after lesions) in wakefulness and sleep by 21% and 16%, anti-SERT-SAP decreased the responses by 15% and 18%, and the combined treatment decreased the responses by 12% and 12% (P < 0.001; two-way ANOVA; P < 0.05, Tukey's post hoc test). We conclude that separate populations of serotonergic and adjacent NK1R-expressing neurones in the medulla are both involved in central chemoreception in vivo.

Alterations in Rat Striatal Glutamate Synapses Following a Lesion of the Cortico- and/or Nigrostriatal Pathway

Ultrastructural changes within the ipsilateral dorsolateral striatum were investigated 1 month following a unilateral ablation of the rat frontal cortex (CTX), removing corticostriatal input, or injection of the neurotoxin, 6-hydroxydopamine (6-OHDA), into the substantia nigra pars compacta, removing nigrostriatal input. In addition, a combined ipsilateral cortical and 6-OHDA lesion (CTX/6-OHDA) was carried out. We find that following a CTX, 6-OHDA, or CTX/6-OHDA lesion, there was a significant decrease in the density of striatal nerve terminal glutamate immunoreactivity compared to the control group. There was also a significant increase in all three lesion groups in the mean percentage of asymmetrical synapses associated with a perforated postsynaptic density. There was a large increase within the CTX/6-OHDA-lesioned group and a smaller but still significant increase in the CTX-lesioned group in the percentage of terminals or boutons with multiple synaptic contacts (i.e., multiple synaptic boutons, MSBs), compared to either the 6-OHDA or the control group. There was no change in any of these measurements within the contralateral striatum. There was a significant decrease in the number of apomorphine-induced contralateral rotations in the CTX/6-OHDA versus the 6-OHDA-lesioned group. Animals receiving just the single CTX or 6-OHDA lesion recovered in motor function compared to the control group as measured by the Rotorod test, while the CTX/6-ODA-lesioned group recovered to less than 50% of the control level. The data suggest that following a CTX and/or 6-OHDA lesion, there is an increase in striatal glutamatergic function. The large increase in the percentage of MSBs in the combined lesion group suggests that dopamine or other factors released by the dopamine terminals assist in regulating synapse formation.

The effects of separate and combined perirhinal and prefrontal cortex lesions on spatial memory tasks in the rat

In order to compare the relative involvement of prefrontal and temporal regions in spatial memory, rats with bilateral electrolytic lesions of perirhinal cortex, prefrontal cortex, or both regions were tested in the water and radial-arm maze. Perirhinal and prefrontal lesions produced similar performance deficits during water-maze acquisition and in the radial-maze procedure. Perirhinal cortex lesions also disrupted performance in a water-maze probe trial conducted 5 min after four training trials, whereas prefrontal lesions did not. Surprisingly, the combined-lesion group was not impaired during water-maze acquisition and performed significantly better than the perirhinal-lesioned group in the probe trial. This finding is interpreted in terms of the executive function of prefrontal cortex and its possible role in switching behavior between different search strategies, only some of which may be dependent on perirhinal cortex.

6-OHDA Lesions of the Nucleus Accumbens Accentuate Memory Deficits in Animals with Lesions to the Forebrain Cholinergic Projection System: Effects of Nicotine Administration on Learning and Memory in the Water Maze

The separate and combined effects of lesions to the forebrain cholinergic projection systen (FCPS) and to dopamine (DA) terminals in the nucleus accumbens (n.acc) were assessed in two water maze tasks: (1) standard acquisition using two trials/day with a 10 min intertrial interval (ITI) for 15 days with the platform in the same position and (2) a working memory task requiring matching to a platform position located by chance on Trial 1, with four trials/day separated by a 30-s ITI and a different platform position on each of 4 days. Effects of nicotine (0.1 mg/kg) were also examined in animals with FCPS, n.acc, and combined lesions in order to determine whether facilatory effects of nicotine in FCPS lesioned animals are mediated by dopamine release in the n.acc. The FCPS and combined lesion groups were impaired in both tasks, but the combined lesion group was substantially worse than animals with FCPS lesions alone. The n.acc lesion group did not differ from controls. Nicotine did not affect acquisition in either the FCPS or combined lesion group, but impaired learning in animals with n.acc lesions. In the working memory task nicotine exerted a nonspecific facilatory effect in the FCPS and combined lesion groups, by reducing latency to find the platform both on the first trial and on the subsequent matching to position trials. Choline acetyltransferase (ChAT) activity was reduced in hippocampus and cortex in the FCPS lesion group, whereas DA levels in n.acc were increased. Conversely, in the n.acc lesion group accumbal DA levels were reduced, while cortical and hippocampal ChAT activity was increased, suggesting that reciprocal changes were induced by the separate lesions. However the combined lesion group showed mixed and more widespread effects; ChAT activity was unaltered in cortex and substantially reduced in hippocampus, and DA levels were reduced in both n.acc and caudate. The results indicate that combined FCPS and n.acc lesions impair spatial learning and working memory far more severley than FCPS lesions alone, although this does not reflect simple additive reductions in DA and ChAT activity. Nicotine improved spatial search strategy, an effect detected in the working memory task with daily changes in platform position, rather than in the standard acquisition task, but did not appear specifically to improve working memory. Since the facilitatory effect of nicotine was seen in both FCPS and combined lesion groups, the findings suggest that nicotine-induced improvements do not depend on accumbal DA release.

Spatial Location Learning in Mice with Ibotenate Lesions of Entorhinal Cortex or Subiculum

This study examined the effects of ibotenate lesions of either the entorhinal cortex (EC) or the subiculum (SUB) on the ability of mice to memorize a single spatial location (initial discrimination), and on their capacity to switch to a new location (transfer) following the initial learning in an eight-arm radial maze. Results indicated that mice with ibotenate lesions of the EC or SUB were impaired in postoperative acquisition of the spatial discrimination task, making more reference, but not working memory, errors and displaying fewer first correct response trials than sham-operated control mice. Furthermore, additional damage to the ventral hippocampus exacerbated the impairment of performance induced by lesions of the SUB alone. In addition, all mice, except for the combined lesion group, exhibited similar performance levels when they were trained to choose another arm of the maze that had not previously been baited (transfer). These findings suggest that both the EC and the SUB play important roles in spatial information processing in mice.

Animal models of human amnesia and dementia: Hippocampal and amygdala ablation compared with serotonergic and cholinergic blockade in the rat

The behavioral effects of combined bilateral hippocampal and amygdala ablation (previously proposed as a model of human global amnesia) were compared to those seen with central blockade of the ascending cholinergic and serotonergic projections (a possible model of human global dementia) in male hooded rats. Rats were prepared with: (a) bilateral surgical lesions of the hippocampus and amygdala; (b) pharmacological blockade of central cholinergic and serotonergic function by systemic injections of scopolamine and p-chlorophenylalanine; and (c) neurotoxic lesions of the rostrally projecting serotonergic nuclei in the brainstem using intracerebral injections of 5,7-dihydroxytryptamine, later combined with scopolamine. The behavioral tests used were: an open field test, a swim-to-platform test, and a Lashley III maze. In all 3 tests, rats with either the neurotoxin lesions plus scopolamine or p-chlorophenylalanine plus scopolamine treatment showed greater impairments in comparison with controls than did the combined lesion group. These results indicate that simultaneous blockade of central serotonergic and cholinergic transmission has a greater effect on some aspects of the organization of behavior than large surgical lesions of the hippocampus and amygdala.

Intracranial hypertension and brain oedema in albino rabbits. Part I: Experimental models.

Three models of experimental cerebral oedema in rabbits are described, one producing vasogenic oedema with a cold lesion, the other producing a cytotoxic cerebral oedema with a metabolic inhibitor, 6-aminonicotinamide (6-ANA), and finally a model employing in the same animal both vasogenic and cytotoxic injuries. The following parameters were assessed: behaviour, EEG, intracranial pressure (ICP), cerebral elastance (Em), blood brain barrier integrity, brain water, electrolyte content, and volume change. Behaviour was normal in the cold lesion group, was abnormal following the administration of 6-ANA, and pronouncedly abnormal in animals with a combined lesion. Mean ICP (PaCO2 37 +/- 42 torr) in the control group was 2.7 +/- 2 torr, in the cold lesion group 8.4 +/-6, in the 6-ANA group it was 8.7 +/- 4, and in the combined lesion group 15.8 +/- 8 torr. Em for the control group was 2.6 +/- 1.3 torr, in the cold lesion group it was 5.6 +/- 4 torr, in the 6-ANA group it was 8.8 +/- 5 torr, and in the combined lesion group it was 8.0 +/- 4 torr. The 6-ANA group manifested oedema that involved primarily the grey matter. In the control animals grey matter water content was 79.99 +/- 0.8%, and in the 6-ANA group it was 81.73 +/- 0.9% (P less than 0.001). A group had both grey and white matter content measurements under the area of a sham lesion, and this was 79.2 +/- 1.3% for the left hemisphere and 79.1 +/- 1.3% for the right. Following a cold lesion of the left hemisphere, the water content was 81.85 +/- 1% (P less than 0.005), and 80.25 +/- 1% (P less than 0.01) in the unlesioned right hemisphere. In those animals with combined cold lesion and 6-ANA administration, the water content of the left hemisphere increased to 82.8 +/- 1% (P less than 0.05 from vasogenic oedema alone), and in the right hemisphere to 81.1 +/- 1% (P less than 0.5 from vasogenic oedema alone).

Acute dimethyl sulfoxide therapy in experimental brain edema: Part I. Effects on intracranial pressure, blood pressure, central venous pressure, and brain water and electrolyte content.

Albino rabbits with experimental brain edema produced by a cryogenic lesion or by a cryogenic lesion combined with a metabolic blocker, 6-aminonicotinamide, were given 1 g of a 10% solution of dimethyl sulfoxide (DMSO) per kg by intravenous bolus. Simultaneous recording of intracranial pressure (ICP), systemic arterial pressure (SAP), and central venous pressure and electroencephalography were performed while the animals were mechanically ventilated at a constant PaCO2 (PaCO2, 38 to 42 torr). One hour after the administration of DMSO, the rabbits were killed by air embolus, and the brain was removed promptly for the determination of wet and dry weights and electrolyte content. The ICP at 15, 30, and 60 minutes after DMSO was lower in both groups; ICP was significantly lower at 30 minutes (p less than 0.5) in the cold lesion group and at 15 minutes in the combined group (p less than 0.05). These was no significant change in SAP after DMSO in either group. There was s significant reduction of brain water content after DMSO in the combined lesion group (p less than 0.005 for the left hemisphere and p less than 0.025 for the right); there was no significant reduction of water content in the group with a cold lesion only.

Behavioral effects of selective midbrain raphe lesions in the rat

Lesions were produced in the median (n= 8), dorsal (n= 7) or both (n= 7) midbrain raphe nuclei and their effects on behavior (days 16–54 postoperatively) compared to that of controls (n= 9). In addition, forebrain 5-hydroxytryptamine (5-HT) concentrations were determined. Only the median and combined lesion groups showed increased running wheel and open field activity, as well as enhanced reactivity to novel stimuli and environmental change. None of the lesion groups, however, showed changes in home cage activity on postoperative day 21. Although all lesion groups were deficients in the acquisition and retention of one-way avoidance, the deficits were of a greater magnitude in the median and combined lesion groups. The latter two groups, furthermore, were impaired in forced extinction of the one-way avoidance response, but only the combined lesion group evidenced facilitation of the two-way avoidance acquisition. Thus, in contrast to the effects of median or combined raphe lesions, lesions in the dorsal raphe nucleus affected few of the behavioral parameters studied. These results suggest that the dorsal raphe nucleus plays a different behavioral role than the median raphe nucleus. The median nucleus appears to be involved in the regulation of activity level, the reaction to novelty and environmental change, and the response to aversive stimuli. Possible mechanisms for the observed behavioral changes are discussed, as well as their apparent similarity to the effects of other mesencephalic and limbic lesions. Lastly, the median, dorsal and combined raphe lesions lowered forebrain 5-HT by 26, 65, and 77%, respectively, versus controls. These reductions differed significantly from each other, and with previously reported data indicate that the dorsal raphe nucleus is the principal origin of forebrain 5-HT. It is suggested, furthermore, that the behavioral effects of midbrain raphe lesions are not due primarily to their associated reductions in forebrain 5-HT.