Neuroscience
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Auditory thalamus (medial geniculate body [MGB]) receives ascending inhibitory GABAergic inputs from inferior colliculus (IC) and descending GABAergic projections from the thalamic reticular nucleus (TRN) with both inputs postulated to play a role in shaping temporal responses. Previous studies suggested that enhanced processing of temporally rich stimuli occurs at the level of MGB, with our recent study demonstrating enhanced GABA sensitivity in MGB compared to IC. The present study used sinusoidal amplitude-modulated (SAM) stimuli to generate modulation transfer functions (MTFs), to examine the role of GABAergic inhibition in shaping the response properties of MGB single units in anesthetized rats. ⋯ The ability of GABA circuits to shape responses at higher modulation frequencies is an emergent property of MGB units, not observed at lower levels of the auditory pathway and may reflect activation of MGB NMDA receptors (Rabang and Bartlett, 2011; Rabang et al., 2012). Together, GABAARs exert selective rate control over selected fms, generally without changing the units' response type. These results showed that coding of modulated stimuli at the level of auditory thalamus is at least, in part, strongly controlled by GABA neurotransmission, in delicate balance with glutamatergic neurotransmission.
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Using fear-conditioning model, we have used a 3-s auditory conditioned stimulus (CS) as a stressor and observed fear and stress responses during a specific experimental period regardless of the presence or absence of the CS. Because the CS was extremely short compared with the experimental period, we observed responses primarily in the absence of the CS. In contrast, most studies in the literature have analyzed responses in the presence of the CS. ⋯ Finally, the 3-s CS produced more intense freezing and corticosterone secretion than the 20-s CS. On the basis of these characteristics, we conclude that the 3-s auditory CS is a more effective stressor than the 20-s auditory CS. Our findings also suggest that foot shock intensity is an additional determinant in the type of fear response induced by the CS.
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Despite ample evidence of N-methyl-D-aspartate (NMDA) receptor dysfunction in schizophrenia, no study has addressed the effects of enriched environment (EE) on sensorimotor gating deficits induced by postnatal NMDA receptor blockade. We evaluated the effect of EE on sensorimotor gating (measured by prepulse inhibition, PPI), or on sensorimotor gating deficit induced by the NMDA receptor antagonist (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate (MK-801) in both sexes of Wistar rats. Rats were injected with MK-801 (1 mg/kg) on postnatal days (P) 6-10. ⋯ An extended period of EE did not influence PPI deficit in female rats. Our results indicate that postnatal exposure to MK-801 may exert long-lasting effects on neuronal circuits underlying sensorimotor gating. Sex-specific modulation of such effects by EE suggests sexually dimorphic mechanisms are involved.
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Maternal immune activation can result in different behavioral abnormalities and brain dysfunction, depending on the nature of the inflammogen and the timing of the challenge. Few studies report the possible link between prenatal exposure to inflammation and mood disorders. Here we aimed to evaluate the effects of a single low lipopolysaccharide (LPS) injection to the dam at gestational day 9 on the offspring behavior and hippocampal function. ⋯ In addition, LPS mice had reduced serotonin and noradrenaline levels in the hippocampus and diminished Reelin immunoreactivity in the dentate gyrus, while their adult hippocampal neurogenesis was not affected. Results presented here support specific long-term effects of the response to a bacterial immunogen early in pregnancy, as opposed to different effects previously reported of viral immunogens and/or responses in late pregnancy. Our work adds to recent reports and stresses the relevance of considering prenatal exposure to a maternal immune response as a risk factor for mood disorders.
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Group I metabotropic glutamate receptors (mGluR1 and mGluR5) are functionally linked to estrogen receptors and play a key role in the plasticity of central neurons. Estrogen status strongly influences sensory input from the temporomandibular joint (TMJ) to neurons at the spinomedullary (Vc/C1-2) region. This study tested the hypothesis that TMJ input to trigeminal subnucleus caudalis/upper cervical cord (Vc/C1-2) neurons involved group I mGluR activation and depended on estrogen status. ⋯ Neither mGluR1 nor mGluR5 antagonism altered the spontaneous activity of TMJ units in HE or LE rats. High-dose MPEP caused a small reduction in the size of the convergent cutaneous receptive field in HE rats, while CPCCOEt had no effect. These data suggest that group I mGluRs play a key role in sensory integration of TMJ nociceptive input to the Vc/C1-2 region and are largely independent of estrogen status.