Departamento de Biologia Experimental

L-Glutamate (L-Glu) is present in most excitatory synapses of the mammalian brain, acting on several receptor subtypes. Height different genes encoding metabotropic glutamate receptors (mGluRs) subtypes have been described (mGluR1-8), having a distinct distribution in the brain. In the present study, the distribution of mGluR1, 3, 4, 5 and 7 mRNAs was determined in 20 thalamic nuclei of adult rats by performing in situ hybridisation with subtype-specific 35S-labelled oligonucleotide probes. High expression of mGluR1 mRNA mainly occurred in midline nuclei such as the centromedial/centrolateral (CM/CL) nuclei, parafascicular and submedius nuclei, and in the ventroposteromedial (VPM) and posterior (Po) nuclei. In contrast, mGluR5 mRNA was more uniformly distributed at weak to moderate levels, except in the reuniens nucleus where a strong signal was detected. The mGluR3 mRNA was highly expressed in the reticular thalamic nucleus and almost not detectable in any other thalamic region. Additionally, mGluR3 mRNA was found not only in neurones but also in putative glial cells. The mGluR4 mRNA was abundant in most thalamic nuclei, with prominent expression in the CM/CL, Po and ventrobasal complex (VPM and ventroposterolateral, VPL). Finally, mGluR7 transcripts were found evenly distributed throughout the thalamus at moderate levels, the highest signal being detected in the paraventricular thalamic nucleus, VPM, VPL and Po. This differential distribution of mGluR subtypes in the rat thalamus may contribute to the heterogeneity of glutamate effects on thalamic neurones. The mGluR1, mGluR4 and mGluR7 receptors may be involved in the processing of somatosensory information because they are expressed in nuclei that receive direct sensory input.

The ventrobasal complex of the thalamus (VB) participates in the transmission and modulation of noxious information. Recent data suggested that GABA(B) receptors in the VB might be involved in the modulation of neuronal activity in response to chronic noxious input. However, in acute inflammatory pain, the role of GABA(B) receptors in the VB remains unknown. The formalin test of nociception was performed in rats stereotaxically injected in the VB contralateral to the formalin-injected paw, with saline (controls), baclofen (0.5 and 0.875 microg), a specific GABA(B) receptor agonist or CGP35348 (25 microg), a GABA(B) receptor antagonist. Control animals exhibited phase 1 (acute pain) and phase 2 (tonic pain) nociception-related activities as previously described. The higher dose of baclofen induced a significant decrease of all pain-related behaviors in both phases of the test and had no observable effects on the animals' motor function, while the lower dose could not reduce the total pain-related activities. Injection of CGP35348 prior to baclofen reduced the antinociceptive effect caused by baclofen during phase 2 in the paw-jerks and in total pain-related activities. CGP35348 alone had antinociceptive effects in both phases, though less pronounced than baclofen 0.875 microg in the total pain-related activities during phase 2. Data demonstrate that both the blockade and the activation of GABA(B) receptors in the VB of rats induce antinociception in acute and tonic pain. An important role for GABA(B) receptors on the thalamic processing of nociceptive input in the VB is suggested.

Reactive gliosis is a prominent morphological feature of mesial temporal lobe epilepsy. Because astrocytes express glutamate receptors, we examined changes in metabotropic glutamate receptor (mGluR) 2/3, mGluR5 and transforming growth factor (TGF)-b in glial cells of the hippocampal regions in an experimental rat model of spontaneous seizures. Rats that exhibited behavioural status epilepticus (SE) directly after 1 h of electrical angular bundle stimulation, displayed chronic spontaneous seizures after a latent period of 1±2 weeks as observed using continuous electrographic monitoring. SE resulted in hypertrophy of astrocytes and microglia activation throughout the hippocampus as revealed by immunolabelling studies. A dramatic, seizure intensity-dependent increase in vimentin immunoreactivity (a marker for reactive astrocytes) was revealed in CA3 and hilar regions where prominent neuronal loss occurs. Increased vimentin labelling was ®rst apparent 24 h after onset of SE and persisted up to 3 months. mGluR2/3 and mGluR5 protein expression increased markedly in glial cells of CA3 and hilus by 1 week after SE, and persisted up to 3 months after SE. Double immunolabelling of brain sections with vimentin con®rmed co-localization with glial ®brillary acidic protein (GFAP), mGluR2/3 and mGluR5 in reactive astrocytes. TGF-b, a cytokine implicated in mGluR3-mediated neuroprotection, was also upregulated during the ®rst 3 weeks after SE throughout the hippocampus. This study demonstrates seizure-induced upregulation of two mGluR subtypes in reactive astrocytes, which ± together with the increased production of TGF-b ± may represent a novel mechanism for modulation of glial function and for changes in glial-neuronal communication in the course of epileptogenesis.

Depression is a neuropsychiatric disorder affecting a huge percentage of the active population especially in developed countries. Research has devoted much of its attention to this problematic and many drugs have been developed and are currently prescribed to treat this pathology. Yet, many patients are refractory to the available therapeutic drugs, which mainly act by increasing the levels of the monoamines serotonin and noradrenaline in the synaptic cleft. Even in the cases antidepressants are effective, it is usually observed a delay of a few weeks between the onset of treatment and remission of the clinical symptoms. Additionally, many of these patients who show remission with antidepressant therapy present a relapse of depression upon treatment cessation. Thus research has focused on other possible molecular targets, besides monoamines, underlying depression. Both basic and clinical evidence indicates that depression is associated with several structural and neurochemical changes where the levels of neurotrophins, particularly of brain-derived neurotrophic factor (BDNF), are altered. Antidepressants, as well as other therapeutic strategies, seem to restore these levels. Neuronal atrophy, mostly detected in limbic structures that regulate mood and cognition, like the hippocampus, is observed in depressed patients and in animal behavioural paradigms for depression. Moreover, chronic antidepressant treatment enhances adult hippocampal neurogenesis, supporting the notion that this event underlies antidepressants effects. Here we review some of the preclinical and clinical studies, aimed at disclosing the role of neurotrophins in the pathophysiological mechanisms of depression and the mode of action of antidepressants, which favour the neurotrophic/neurogenic hypothesis.

Evidence for the involvement of metabotropic glutamate receptors (mGluR) in sensory processing has been emerging. Additionally, the differential distribution of distinct mGluR subtypes mRNA in particular thalamic nuclei of normal rats suggests that they could be ...

The corticotropin-releasing factor (CRF) is a stress-related neuropeptide that modulates Locus Coeruleus (LC) activity. As LC has been involved in pain and stress-related patologies, we tested whether the pain-induced anxiety is a result of the CRF released in the LC. Complete Freund's adjuvant (CFA)-induced monoarthritis (MA) was used as inflammatory chronic pain model. α-helical CRF receptor antagonist was microinjected into the contralateral LC of four weeks MA animals. The nociceptive and anxiety-like behaviors, as well as phosphorylated extracellular signal-regulated kinases 1/2 (pERK1/2) and CRF receptors expression were quantified in the Paraventricular Nucleus (PVN) and in the LC. MA rats manifested anxiety and increased pERK1/2 levels in the LC and PVN, although the expression of CRF receptors was unaltered. α-helical CRF antagonist administration reversed both the anxiogenic-like behavior and the pERK1/2 levels in the LC. pain-induced anxiety is mediated by CRF neurotr...