Month: December 2025

Slices from both genotypes were run simultaneously. and enduring synaptic changes, is usually defective in FXS. == Intro == Fragile X mental retardation syndrome arises from an growth of CGG triplet repeats in Rabbit Polyclonal to LAT the X-linkedFMR1gene resulting in promoter methylation and transcriptional silencing. A potentially critical clue for explaining the cognitive component of FXS came with the finding that affected individuals have irregular cortical dendritic spines (Rudelli et al., 1985;Wisniewski et al., 1991;Irwin et al., 2001). Importantly, knocking out fragile X mental retardation protein (FMRP), theFMR1gene product, in mice generates qualitatively similar disturbances to spine morphology (Comery et al., 1997) as well because impairments in long-term potentiation (LTP) (Larson et al., 2005;Zhao et al., 2005;Lauterborn et al., 2007;Hu Benzenesulfonamide et al., 2008). These observations suggest that the fragile-X mutation in some way disturbs cytoskeletal machinery responsible for the anatomy and plasticity of spines, effects that could impact both baseline synaptic tranny and how it is modified by learning. FMRP regulates translation and genetic studies have recognized mRNA focuses on for the protein that are plausibly related to spine cytoskeletal abnormalities (Bardoni and Mandel, 2002;Reeve et al., 2005). TheDrosophilaFMRP homolog is usually linked to Rac1, a small GTPase that regulates effectors (e.g., PAK, WASP) important to Benzenesulfonamide spine morphology in immature neurons (Billuart and Chelly, 2003;Castets et al., 2005). This is of particular interest because a dominant-negative create that reduces PAK activity is usually reported to reverse neocortical spine (along with other) abnormalities in Fmr1-knock-outs (KOs) (Hayashi et al., 2004;Hayashi et al., 2007). FMRP has also been implicated in manifestation of a phosphatase that regulates the activity of cofilin (Castets et al., 2005), a protein that regulates the assembly of actin filaments (Bernstein and Bamburg, 2010) as well as spine development. Despite these points, results from initial attempts to identify problems in actin signaling and dynamics in adult Fmr1-KO hippocampus were bad. Theta burst afferent activation (TBS), a naturalistic activity pattern popular to induce LTP, caused quick cofilin phosphorylation and actin polymerization at synapses to approximately the same degree in slices from Fmr1-KO and wild-type (WT) mice (Lauterborn et al., 2007). It seems, then, that the primary spine cytoskeletal problem in FXS entails aspects of actin management beyond the complex processes leading to filament assembly. Actin filament stabilization is usually one probability. Newly created polymers typically enter a dynamic state (treadmilling) in which they concurrently add and subtract monomers from Benzenesulfonamide Benzenesulfonamide opposing ends of the filament, and remain in this condition until disassembled or stabilized (Carlier, 1998;Pollard and Cooper, 2009). Studies using latrunculin, which disrupts treadmilling by obstructing actin monomer incorporation, suggest that (1) actin filaments in adult spines are dynamic for several minutes following their formation (Krucker et al., 2000;Rex et al., 2009), and (2) the Rac>PAK pathway promotes filament stabilization (Rex et al., 2009). Prompted by these observations, the present studies investigated the possibility that the PAK-related stabilization of TBS-induced spine actin filaments is usually impaired in Fmr1-KOs. The results point to a specific hypothesis regarding the causes of spine and synaptic plasticity abnormalities in FXS. == Materials and Methods == == == == == == Electrophysiology. == Adult (23 weeks) male Fmr1-KO and WT mice (FVB background) were used (Irwin et Benzenesulfonamide al., 2002,;Lauterborn et al., 2007). Hippocampal LTP was performed as previously explained (Lauterborn et al., 2007). Briefly, transverse hippocampal slices (300 m) were prepared in ice-cold artificial CSF (ACSF) (in mm: 124 NaCl, 3 KCl, 1.25 KH2PO4, 3.4 CaCl2, 2.5 MgSO4, 26 NaHCO3, and 10 dextrose, pH 7.35). Slices from both genotypes were run simultaneously. Slices were managed at 31 1C with surface exposed to humidified 95% O2/5% CO2and ACSF perfused at a rate of 6070 ml/h. Field EPSPs (fEPSPs) were recorded from your apical dendrites of CA1b pyramidal cells using a glass electrode (2mNaCl). Bipolar activation was delivered to the apical Schaffer collateralcommissural projections in CA1a and CA1c using alternating pulses at 0.05 Hz having a current that elicited 50% of the maximal fEPSP response. In experimental slices, synaptic potentiation was induced having a train of 10 theta bursts (i.e., 10 bursts of 4 pulses at 100 Hz, with an interburst interval of 200 ms). Yoked control slices from your same mice received low-frequency (3/min) activation. Evoked responses were.

We present that nicotine self-administration augmented footshock-induced PVN glutamate release, but decreased GABA release further. handles after intra-PVN saclofen (GABA-B receptor antagonist). As a result, the exaggerated decrease in GABA discharge by footshock during nicotine self-administration disinhibits CRF neurons. This disinhibition coupled with improved glutamate input offers a brand-new system for HPA sensitization to tension by chronic nicotine self-administration. This system, which will not protect homeostatic plasticity, supports the concept that smoking functions as a chronic stressor that sensitizes the HPA to stress. Keywords:nicotine self-administration, adrenocorticotropic hormone, corticosterone, footshock stress, homeostatic plasticity, rat == Introduction == Nicotine, the principal psychoactive component Rabbit polyclonal to AMDHD1 of tobacco, acutely stimulates secretion of the stress-responsive hypothalamo-pituitary-adrenal (HPA) axis hormones, adrenocorticotropic hormone (ACTH) and corticosterone (Mattaet al. 1987). In addition, chronic nicotine self-administration (Chenet al. 2008) and other stressors (Aguilera 1994) augment ACTH and corticosterone responses to a novel stressor, such as mild footshock stress. However, the neuroplastic changes underlying this effect of chronic nicotine exposure on the stress response are only partially understood. In the hypothalamic paraventricular nucleus (PVN), the critical output nucleus controlling the HPA axis, corticotropin-releasing factor (CRF) neurons in the parvocellular division (pcPVN), integrate the HPA responsiveness to diverse stressors and stimulate plasma ACTH secretion (Hermanet al. 2005). We have shown that acutely injected nicotine and chronically self-administered nicotine are stressors that activate CRF neurons and elevate plasma ACTH levels (Valentineet al. 1996,Yuet al. 2008,Chen et al. 2008). Chronic nicotine self-administration also alters the phenotype of pcPVN CRF neurons by inducing the co-expression of arginine vasopressin (AVP). Stressor stimulation of these CRF+/AVP+neurons would potentiate CRF-dependent ACTH secretion by co-releasing AVP, another modulator of pituitary corticotrophs (Rivier and Vale 1983,Yu et al. 2008). We have reported that PVN responsiveness to norepinephrine, a primary regulator of CRF neurons, is selectively enhanced in rats self-administering nicotine, but only during stress (Yu and Sharp 2010). Neuroplasticity in the phenotype of CRF neurons and their responsiveness to norepinephrine during stress would both contribute to CADD522 the enhanced secretion of ACTH and corticosterone during mild footshock stress. However, the contribution of other neurotransmitters to this interaction between nicotine self-administration and a stressor is unknown. From a neuroanatomical perspective, pcPVN CRF neurons receive both glutamatergic and GABAergic afferents (van den Polet al. 1990,Decavel and Van CADD522 den Pol 1990), with CRF neurons juxtaposed to glutamatergic or GABAergic terminals (Ziegler and Herman 2000,Miklos and Kovacs 2002). Additionally, ionotropic glutamate receptor and GABA receptor subunits are highly expressed on pcPVN CRF neurons (Cullinan 2000,Hermanet al. 2000). Pharmacological CADD522 studies have shown that an intra-PVN injection of either glutamate or a GABA receptor antagonist elicited ACTH and corticosterone release (Feldman and Weidenfeld 1997,Cole and Sawchenko 2002). Blockade of PVN glutamate receptors inhibited the corticosterone response to restraint stress (Ziegler and Herman 2000), whereas GABA receptor blockade enhanced restraint stress-induced corticosterone release (Cullinanet al. 2008). Therefore, both glutamate and GABA inputs to PVN CRF neurons modulate basal activity and stress responsiveness, and could potentially affect responsiveness to norepinephrine during stress. We have proposed that nicotine self-administration is a chronic stressor, sensitizing the HPA to novel stressors (Chen et al. 2008,Yu et al. 2008). We have shown that increased c-Fos expression in CRF+/AVP+neurons after stress is a distal component of the HPA sensitization induced by chronic nicotine self-administration. However, apart from norepinephrine (Yu and Sharp 2010), the effect of nicotine self-administration on neurotransmitters modulating these critical neurons is unknown. We hypothesized that nicotine self-administration would alter the balance of glutamatergic stimulation and GABAergic inhibition during mlid footshock stress, thereby augmenting the response of CRF neurons to the stressor. We determined the effects of nicotine self-administration on footshock-induced release of (1) PVN glutamate and GABA, and (2) plasma ACTH and corticosterone after blockade of glutamate or GABA receptors.