Behavioural brain research
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The pyramidal tract and red nucleus send prominent projections to the spinal cord and are thought to co-operate in producing skilled movements. In the present study, skilled reaching for food located on a shelf and spontaneous grasping, handling and eating pieces of pasta were video-recorded and analyzed in control rats, rats with unilateral ibotenic acid lesions of the red nucleus (RN), unilateral pyramidal tract lesions (PT) and combined lesions. The behavioral results suggest that skilled movements are organized as action patterns, easily recognizable and distinctive for each task. ⋯ Nevertheless, even after combined lesions, the rats were able to advance the limb, grasp food and withdraw the limb. The sparing following combined lesions suggests that other neural systems as well as compensatory adjustments assist the impaired limb. The results are discussed in relation to the possible distinctive contributions of the rubrospinal and corticospinal tract to the action patterns that comprise skilled movements in rats.
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The present study investigated whether spatial performance in the Morris water maze (MWM) recovers after bilateral transection of the fimbria/fornix (FF) in rats, whether such recovery results from restored or residual spatial cognitive capacity, and what contribution, if any, pre-operative training makes to such recovery. Following surgery, rats were administered extensive training to a constant submerged platform location with frequent probe tests to assess performance strategies. Following the attainment of asymptotic performance levels, rats were tested for acquisition of a second platform location. ⋯ The deficit shown in acquisition of the second platform location argues against recovery of spatial cognition and suggests that the basis of recovered performance is residual spatial cognitive capacity. Several limitations of this residual capacity are apparent: (i) rate of acquisition of spatial information is reduced; (ii) utilization of spatial information stored pre-operatively is restricted; and (iii) translation of spatial information into navigational behaviour is less efficient. The neural bases of this residual system are speculated to include spared intra-hippocampal storage mechanisms and/or mechanisms involved in extra-hippocampal long-term memory consolidation while the neural bases of the FF's contribution to spatial information storage in the intact brain are speculated to involve theta synchronization of hippocampal activity and the induction and expression of hippocampal long-term potentiation.
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Review
The acoustic startle response in rats--circuits mediating evocation, inhibition and potentiation.
This review describes the neuronal mechanisms underlying the mediation and modulation of the acoustic startle response (ASR) in rats. The combination of anatomical, physiological and behavioral methods has identified pathways which mediate and modulate the ASR. The ASR is mediated by a relatively simple, oligosynaptic pathway located in the lower brainstem which activates spinal and cranial motor neurons. ⋯ Interestingly, this nucleus is also the target of input from various brain nuclei which are involved in the modulation (e.g. fear-potentiation, sensitization, habituation, prepulse inhibition and pleasure-attenuation) of the ASR. Hence, the PnC can be described as a sensorimotor interface, where the transition of sensory input into the motor output can be directly influenced by excitatory or inhibitory afferents. On the basis of these facts we conclude that the ASR may be a valuable model for the study of general principles of sensorimotor-motivational information processing at the behavioral and neurophysiological level in mammals.
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The involvement of different sub-types of dopamine receptors in the electrical self-stimulation behaviour was investigated using DA receptor subtype specific agonists viz R(+) SKF 38393 and LY 171555 (quinipirole). Rats were chronically implanted with bipolar electrodes in lateral hypothalamus-medial forebrain bundles (LH-MFB) and ventral tegmental area-substantia nigra (VTA-SN) or guide cannula in nucleus accumbens (nACB) or medial prefrontal cortex (mPFRCx) or cannula-cum-electrode in VTA-SN. Combining these, it was possible to inject a given receptor ligand in either nACB or mPFRCx or VTA-SN and assess the changes in intracranial self-stimulation (ICSS) of LH-MFB or VTA-SN. ⋯ The coactivation of D1 and D2 receptors in VTA-SN leads to the suppression of ICSS of both VTA-SN and LH-MFB. Similar injections of these receptor ligands into mPFRCx did not alter the ICSS of either LH-MFB or VTA-SN. The pre- or post-synaptic DA receptors of mPFRCx do not appear to influence the ICSS of either VTA-SN or LH-MFB in any significant manner.
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This study characterizes physiological, histological and behavioral effects of traumatic brain injury (TBI) produced by a controlled pneumatic impactor striking the entire right sensorimotor cortex of the anesthetized rat. Damage to both the fore- and hindlimb sensorimotor areas resulted in a hemiparetic animal which allowed us to use four sensitive behavioral/neurological tests to track the recovery sequelae after injury. Initial experiments measured cardiovascular and respiratory effects after cortical impact which depressed the dura to varying depths. ⋯ Significant axonal degeneration occurred bilaterally around the deep cerebellar nuclei. Degenerating fibers extended into the folia and terminated in the cerebellar granule cell layer. Thus the entire sensorimotor control system appeared to have been affected by a cortical injury.