Neuroscience
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Selective immunotoxic cholinergic lesions in the nucleus basalis magnocellularis (NBM) impair visuospatial attention performance in a 5-choice serial reaction time task (5-CSRT task). The features of the reported deficits, however, do not perfectly match among studies, in which some lesions may have been too weak while others largely encroached onto the septal region. Using the 5-CSRT task, we therefore re-assessed the effects of NBM lesions that produced minimal septal damage. ⋯ Furthermore, overall performance levels decreased when the stimulus duration was shortened (i.e. 0.5-0.2 s) or its intensity attenuated, and rats with cholinergic lesions remained consistently impaired vs. controls. These results show that disruption of sustained visual attention functions by damage to the NBM cholinergic neurons can be evidenced despite weak or no effects on variables accounting for motivational, locomotion- or impulsivity-related biases. Discrepancies with previously reported results are discussed in terms of differences in lesion extent/specificity and training levels.
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In a previous study, it was shown that populations of climbing fibers, derived from the inferior olivary complex (IOC) contain the peptide corticotropin releasing factor (CRF) and that the expression of this peptide in climbing fibers could be modulated by the level of activity in olivary afferents. The intent of this study was to determine if there was comparable plasticity in the distribution of the type 1 CRF receptor (CRF-R1) in the cerebellum of the rat. Our results indicate that CRF-R1 was localized primarily to Purkinje cell somata and their primary dendrites and granule cells. ⋯ Further, interneurons responded with a decrease in receptor expression following more intense levels of stimulation suggesting the possibility of internalization of the receptor. In contrast, Bergmann glial cells showed an increased expression in receptor expression. These data suggest that CRF released from climbing fibers may modulate the physiological properties of basket and stellate cells as well as having a heretofore unidentified and potentially unique effect on Bergmann glia.
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The dorsal striatum (DS) is involved in various forms of learning and memory such as procedural learning, habit learning, reward-association and emotional learning. We have previously reported that bilateral DS lesions disrupt tone fear conditioning (TFC), but not contextual fear conditioning (CFC) [Ferreira TL, Moreira KM, Ikeda DC, Bueno OFA, Oliveira MGM (2003) Effects of dorsal striatum lesions in tone fear conditioning and contextual fear conditioning. Brain Res 987:17-24]. ⋯ Overall, the present results underscore that other routes, aside from the well-established CeA projections to the periaqueductal gray, may contribute to the acquisition/consolidation of the freezing response associated to a TFC task. It is suggested that CeA may presumably influence DS processing via a synaptic relay on dopaminergic neurons of the substantia nigra compacta and retrorubral nucleus. The present observations are also in line with other studies showing that TFC and CFC responses are mediated by different anatomical networks.
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The ventral tegmental area (VTA) is a nodal link in reward circuitry. Based on its striatal output, it has been subdivided in a caudomedial part which targets the ventromedial striatum, and a lateral part which targets the ventrolateral striatum [Ikemoto S (2007) Dopamine reward circuitry: two projection systems from the ventral midbrain to the nucleus accumbens-olfactory tubercle complex. Brain Res Rev 56:27-78]. ⋯ In general, these projections, like the spiralated striato-nigro-striatal loops, display a medial-to-lateral organization. This anatomical arrangement conceivably permits the ventromedial striatum to influence the activity of the lateral striatum. The caudal pole of the VTA appears to be a critical site for a global recruitment of the mesotelencephalic system.
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This study was designed to determine the organization of nociceptive inputs with different behavioral significance into spinal-brainstem circuits in the rat. Induction of Fos protein was used to localize spinal dorsal horn and hypothalamic neurons activated by noxious heating of the hind paw dorsum at rates known to preferentially activate C- or A-heat nociceptors. This was combined with retrograde transport of cholera toxin subunit B from the dorsolateral/lateral- (DL/L-) or the ventrolateral- (VL-) periaqueductal gray (PAG) in order to map the organization of A- and C-fiber input to spinal-brainstem circuits. ⋯ A-fiber-activated neurons were found throughout the rostral hypothalamus but those projecting to the PAG were focused in the lateral area of the anterior hypothalamus (LAAH), from where approximately 20% projected to the VL-PAG, which was significantly more than to the DL/L PAG (P<0.05). We hypothesize that the organization of A- versus C-fiber inputs to the PAG enables the coordination of coping strategies appropriate to meet the demands imposed by these different noxious stimuli. Hypothalamic-PAG projections activated by A-fiber inputs did not reflect this level of organization and we suggest that this may relate to their role in thermoregulation as opposed to autonomic responses to particular nociceptive inputs.