Neuroscience
-
The somatotopic map of the first nociceptive component in the primary somatosensory cortex (S1) is still unclear. In this study, a CO(2) laser was applied to the tail of the rat to induce nociception without the interference from large myelinated (A(beta)) fibers. Thus, only noxious fibers could be activated. ⋯ We found that whether light touch or laser-induced nociception was applied to the tail of the rat, the responsive topography in S1 was consistent. Discrimination of these two modalities was achieved vertically in the same column; the deeper layer represented the nociceptive response while the superficial layer encoded the response to light touch. This is quite different from that of a primate brain.
-
Experiential therapies, such as enriched environment (EE), have been shown to influence the neurodegenerative processes that underlie Parkinson's disease. We have previously demonstrated that EE promotes functional improvement in dopamine-depleted rats. Here we compare the influence of exposure to EE prior to versus after dopamine depletion in the 6-hydroxydopamine rat model of Parkinson's disease. ⋯ Exposure to pre-lesion EE in particular promoted structural plasticity as indicated by increased expression of the main cytoskeletal component microtubule associated protein-2 in the lesion dorsal striatum. Continuous EE showed absence of rotational bias suggesting attenuated dopamine loss. These data indicate that enriched lifestyle before the onset of motor symptoms and rehabilitation programs after diagnosis might be beneficial in patients with Parkinson's disease.
-
Penetrating limb injuries are common and usually heal without long-lasting effects, even when nerves are cut. However, rare nerve-injury patients develop prolonged and disabling chronic pain (neuralgia). When pain severity is disproportionate to severity of the inciting injury, physicians and insurers may suspect exaggeration and limit care or benefits, although the nature of the relationship between lesion-size and the development and persistence of neuralgia remains largely unknown. ⋯ Numbers of GFAP-immunoreactive astrocytes increased independently of lesion size and pain status. Small nerve injuries can thus have magnified and disproportionate effects on dorsal-horn neurons and glia, perhaps providing a biological correlate for the disproportionate pain of post-traumatic neuralgias (including complex regional pain syndrome-I) that follow seemingly minor nerve injuries. However, the presence of similar dorsal-horn changes in rats without pain behaviors suggests that not all transcellular responses to axotomy are pain-specific.
-
One way of investigating affective learning is the use of aversive pictures as unconditioned stimuli (UCS) in conditioning paradigms. In the last decades, there has been a heated debate on the influence of contingency awareness on conditioned responses (CRs). Only a few studies found CRs in contingency unaware subjects whereas other studies only reported conditioned reactions in contingency aware participants. ⋯ Investigation of SCRs and valence ratings revealed that only aware participants showed conditioned reactions. Our results point toward dissociations between response levels (e.g. brain activity) not affected by contingency awareness and more cognitive response levels (e.g. subjective ratings and SCRs) which are affected by contingency awareness. As a unique finding in human aversive conditioning, we discuss the role of the nucleus accumbens as well as practical implications for affective learning models.
-
Comparative Study
The distribution of gamma-hydroxybutyrate-induced Fos expression in rat brain: comparison with baclofen.
gamma-Hydroxybutyrate (GHB) is a euphoric, prosocial and sleep inducing drug that binds with high affinity to its own GHB receptor site and also more weakly to GABA(B) receptors. GHB is efficacious in the treatment of narcolepsy and alcoholism, but heavy use can lead to dependence and withdrawal. Many effects of GHB (sedation, hypothermia, catalepsy) are mimicked by GABA(B) receptor agonists (e.g. baclofen). ⋯ Surprisingly, Fos immunoreactivity was not observed with either GHB or baclofen in reward-relevant regions such as the nucleus accumbens, striatum and ventral tegmental area. Overall these results indicate a distinctive signature of brain activation with GHB that may be only partly due to GABA(B) receptor effects. This confirms a unique neuropharmacological profile for GHB and indicates key neural substrates that may underlie its characteristic influence on sleep, body temperature, sociability and endocrine function.