Glutamate transporters are differentially expressed in the hippocampus during the early stages of one-day spatial learning task.

INTRODUCTION: Uptake of glutamate in the hippocampus by specialized transporters appears to be important for the prevention of glutamate-induced neurotoxicity. However, the role of these transporters in synaptic plasticity and learning is still unclear. We examined the expression pattern of glutamate transporters at different stages of spatial learning using a one-day (three blocks) version of the Morris Water Maze. METHODS: Male rats (Sprague Dawley, 3 months old) were divided into three groups (learner, swim control, or naïve control) and animals were sacrificed after the first, second, or third block of training. The hippocampi were immediately extracted and flash frozen for RNA analysis. Real time polymerase chain reaction was employed to examine the expression of glutamate transporter 1 (Glt-1), Glt1b, glutamate-aspartate transporter (GLAST) and excitatory amino acid carrier-1 (EAAC1) in whole hippocampi. RESULTS: EAAC1 and GLAST RNA were downregulated in the learner and swimmer groups (compared to naïve) after the first two blocks of training during the one-day protocol but EAAC1 returned to control levels by the end of the third block. GLAST levels were upregulated by the third block of training. Glt-1b expression was downregulated during the second block of training but returned to control by the third block. CONCLUSIONS: The observed decreases in glutamate transporter expression may be important during the early stages of spatial learning as a possible mechanism to enhance glutamatergic availability during critical stages of learning. However, similar decreases in glutamate transporter expression in both the learner and swimmer groups indicate that the observed differences may be task-induced. Additional experiments are currently underway to examine this possibility.

Stress During Development of Experimental Endometriosis Influences Nerve Growth and Disease Progression.

PURPOSE: We have previously shown that stress prior to induction worsens clinical presentation and inflammatory parameters in a rat model of endometriosis. This study was designed to examine whether stress during the development of endometriosis can affect the growth of endometriotic implants through nerve growth and immune alterations. METHODS: Endometriosis was surgically induced in female Sprague-Dawley rats by suturing uterine horn implants onto the small intestine mesentery. Two weeks later, one group of rats (endo-stress) was subjected to a 10-day swim stress protocol. Controls had no stress (endo-no stress) or sutures only and stress (sham-stress). On day 60, all rats were killed and examined for the presence of endometriotic vesicles. The size of each vesicle was measured. The uterus and colon were removed and assessed for damage, cell infiltration, and expression of nerve growth factor (NGF), its receptors (p75 and Tropomyosin receptor kinase A (Trk-A)/pTrk-A), and calcitonin gene-related peptide, a sensory fiber marker. A differential analysis of peritoneal fluid white blood cell count was performed. RESULTS: Stress significantly increased endometriotic vesicle size but not colonic damage and increased infiltration of mast cells. Significantly increased expression of NGF and its receptors was found in the uterus of animals with endometriosis receiving stress. CONCLUSIONS: Stress stimulates the development of ectopic endometrial vesicles in an animal model of endometriosis and increases inflammatory cell recruitment to the peritoneum. In addition, stress promotes nerve fiber growth in the uterus.

Gene expression changes in the rodent hippocampus following whole brain irradiation.

Therapeutic cranial irradiation may result in debilitating cognitive impairments. In human patients these deficits are age and radiation dose-dependent and are attributed to a diminished capability to learn and memorize new tasks and information. Because of the known involvement of the hippocampus in memory consolidation, it is important to identify irradiation-induced changes including alterations in gene expression in this structure. Whole brain irradiation doses of 0, 0.3, 3, 10, or 30 Gray (Gy) were administered to 3-month-old rats in a single session. Twenty-four hours following cranial irradiation, hippocampi were processed for oligonucleotide microarrays analysis. Metallothioneins (MT)-I and -II, heat shock protein (Hsp-27), glial fibrillary acidic protein alpha (GFAP), and c-Fos genes were altered significantly across the various doses of irradiation. A pathway analysis shows that these genes were centered around the immediate early gene myc and tumor suppressor gene (TP53). Our results identified important genes and possible pathways that are altered in the hippocampus in the acute phase following cranial irradiation, and implicate gene pathways important for both learning and memory and apoptosis.

Endometriosis Is Associated With a Shift in MU Opioid and NMDA Receptor Expression in the Brain Periaqueductal Gray.

Studies have examined how endometriosis interacts with the nervous system, but little attention has been paid to opioidergic systems, which are relevant to pain signaling. We used the autotransplantation rat model of endometriosis and allowed to progress for 60 days. The brain was collected and examined for changes in endogenous opioid peptides, mu opioid receptors (MORs), and the N-methyl-d-aspartate subunit receptor (NR1) in the periaqueductal gray (PAG), since both of these receptors can regulate PAG activity. No changes in endogenous opioid peptides in met- and leu-enkephalin or ß-endorphin levels were observed within the PAG. However, MOR immunoreactivity was significantly decreased in the ventral PAG in the endometriosis group. Endometriosis reduced by 20% the number of neuronal profiles expressing MOR and reduced by 40% the NR1 profiles. Our results suggest that endometriosis is associated with subtle variations in opioidergic and glutamatergic activity within the PAG, which may have implications for pain processing.

Stress management affects outcomes in the pathophysiology of an endometriosis model.

We have previously shown detrimental effects of stress in an animal model of endometriosis. We now investigated whether the ability to control stress can affect disease parameters. Endometriosis was surgically induced in female Sprague-Dawley rats before exposing animals to a controllable (submerged platform) or uncontrollable (no platform) swim stress protocol. Corticosterone levels and fecal pellet numbers were measured as an indicator of stress. Uncontrollable stress increased the number and size of the endometriotic cysts. Rats receiving uncontrollable stress had higher anxiety than those exposed to controllable stress or no stress and higher corticosterone levels. Uncontrollable stressed rats had more colonic damage and uterine cell infiltration compared to no stress, while controllable stress rats showed less of an effect. Uncontrollable stress also increased both colonic and uterine motility. In summary, the level of stress controllability appears to modulate the behavior and pathophysiology of endometriosis and offers evidence for evaluating therapeutic interventions.

Ceftriaxone, a GLT-1 transporter activator, disrupts hippocampal learning in rats.

Glutamate transporters (GluTs) are important for maintaining optimal glutamate concentrations at the synapse. This allows proper synaptic response, plasticity and prevents neurotoxicity. It has been shown that the ß-lactam antibiotic ceftriaxone (Rocephin) induces an up-regulation of the glutamate transporter GLT-1. This GLT-1 up-regulation blocks the metabotropic glutamate receptor (mGluR) dependent long-term depression (LTD) at the mossy fiber (MF)-CA3 hippocampal synapse. It also has negative effects on long-term potentiation (LTP). However, the effects of GLT-1 up-regulation on hippocampal learning in rats are not known. In this study, we examine the role of chronic administration of ceftriaxone on novel object recognition, which is a hippocampal-dependent spatial learning task. Male Sprague Dawley rats (2-3 months old) were administered ceftriaxone (via i.p. injections, 200 mg/kg) for 8 consecutive days prior to training and testing on a standard novel object recognition task. We found that rats administered with ceftriaxone display memory impairments in novel object recognition, when compared to control rats (p<0.05). Our findings show that a potential up-regulation of GLT-1 via ceftriaxone administration has detrimental effects on spatial learning and memory in rats. Our results further support the notion that glutamate transporters provide an essential regulatory role in hippocampal learning and memory.

Stress exacerbates endometriosis manifestations and inflammatory parameters in an animal model.

Women with endometriosis have significant emotional distress; however, the contribution of stress to the pathophysiology of this disease is unclear. We used a rat model of endometriosis to examine the effects of stress on the development of this condition and its influence on inflammatory parameters. Female Sprague-Dawley rats were subjected to swim stress for 10 consecutive days prior to the surgical induction of endometriosis by suturing uterine horn implants next to the intestinal mesentery (endo-stress). Sham-stress animals had sutures only, and an endo-no stress group was not subjected to the stress protocol. At the time of sacrifice on day 60, endometriotic vesicles were measured and colons assessed for macroscopic and microscopic damage. Colonic tissue and peritoneal fluid were collected for inflammatory cell analysis. Endometriosis, regardless of stress, produced a decrease in central corticotropin-releasing factor immunoreactivity, specifically in the CA3 subregion of the hippocampus. Prior exposure to stress increased both the number and severity of vesicles found in animals with endometriosis. Stress also increased colonic inflammation, motility, myeloperoxidase levels, and numbers of mast cells. In summary, prior stress may contribute to the development and severity of endometriosis in this animal model through mechanisms involving cell recruitment (eg, mast cells), release of inflammatory mediators, and deregulation of hypothalamic-pituitary axis responses in the hippocampus.

Metabotropic glutamate receptor antagonist AIDA blocks induction of mossy fiber-CA3 LTP in vivo.

Metabotropic glutamate receptors (mGluR) are implicated in long-term memory storage. mGluR-I and mGluR-II antagonists impede various forms of learning and long-term potentiation (LTP) in animals. Despite the evidence linking mGluR to learning mechanisms, their role in mossy fiber-CA3 long-term potentiation (LTP) is not yet clear. To explain the involvement of mGluR-I in memory mechanisms, we examined the function of the mGluR-I antagonist 1-aminoindan-1, 5-dicarboxylic acid (AIDA) on the induction of mossy fiber-CA3 LTP in vivo in male Sprague Dawley and Fischer 344 (F344) rats. Acute extracellular mossy fiber (MF) responses were evoked by stimulation of the MF bundle and recorded in the stratum lucidum of CA3. The excitatory postsynaptic potential (EPSP) magnitude was measured by using the initial slope of the field EPSP slope measured 2-3 ms after response onset. After collection of baseline MF-CA3 responses at 0.05 Hz, animals received either ((+/-))-3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (N-methyl-D-aspartate-R antagonist, 10 mg/kg ip), naloxone (opioid-R antagonist, 10 mg/kg ip), or AIDA (mGluR antagonist, 1 mg/kg ip or 37.5 nmol ic). LTP was induced by two 100-Hz trains at the intensity sufficient to evoke 50% of the maximal response. Responses were collected for an additional 1 h. AIDA blocked induction of LTP in the mossy fiber pathway (P < 0.05) in both strains of rats after systemic and in Sprague Dawley rats after intrahippocampal injection.