Effects of Cycloleucine in the Nucleus Accumbens Septi on the Elevated plus Maze Test in Rats.

INTRODUCTION: In recent years, an important number of studies have emphasized the psychopharmacological actions of cycloleucine (1-aminocyclopentanecarboxylic acid) acting on the NR1 subunit (glycine allosteric site) of NMDA (N-methyl-D-aspartic acid) receptor. We studied the effects of its injection in an anxiety test. METHODS: The elevated plus maze test was used. Male rats bilaterally cannulated into the nucleus accumbens septi (NAS) were employed. Rats were divided into 5 groups that received either 1 µL injections of saline or cycloleucine (0.5, 1, 2, or 4 µg) 15 min before testing. RESULTS: Time spent in the open arm was significantly increased by cycloleucine treatment with all doses (1 and 2 µg, p < 0.05; 0.5 and 4 µg, p < 0.01), like number of extreme arrivals (0.5 and 1 µg, p < 0.05; 2 µg, p < 0.01; and 4 µg, p < 0.001). Open arm entries were increased by the highest dose only (4 µg, p < 0.01). DISCUSSION/CONCLUSION: Present results show no difference between all doses in the time spent in the open arm, suggesting an indirect, noncompetitive action of the drug. The increase in extreme arrivals and open arm entries suggests a dose influence in these parameters. We conclude that cycloleucine influence on the NMDA receptors within NAS leads to anxiolytic-like effects and behavioral disinhibition, which once more confirms the involvement of NAS in anxiety processing.

Preclinical analyses of intravesical chemotherapy for prevention of bladder cancer progression.

There is a critical need to identify treatment options for patients at high risk for developing muscle invasive bladder cancer that avoid surgical removal of the bladder (cystectomy). In the current study, we have performed preclinical studies to investigate the efficacy of intravesical delivery of chemotherapy for preventing progression of bladder cancer. We evaluated three chemotherapy agents, namely cisplatin, gemcitabine, and docetaxel, which are currently in use clinically for systemic treatment of muscle invasive bladder cancer and/or have been evaluated for intravesical therapy. These preclinical studies were done using a genetically-engineered mouse (GEM) model that progresses from carcinoma in situ (CIS) to invasive, metastatic bladder cancer. We performed intravesical treatment in this GEM model using cisplatin, gemcitabine, and/or docetaxel, alone or by combining two agents, and evaluated whether such treatments inhibited progression to invasive, metastatic bladder cancer. Of the three single agents tested, gemcitabine was most effective for preventing progression to invasive disease, as assessed by several relevant endpoints. However, the combinations of two agents, and particularly those including gemcitabine, were more effective for reducing both tumor and metastatic burden. Our findings suggest combination intravesical chemotherapy may provide a viable bladder-sparing treatment alternative for patients at high risk for developing invasive bladder cancer, which can be evaluated in appropriate clinical trials.

Adjuvant intra-arterial chemotherapy and radiotherapy versus surgery alone in resectable pancreatic and periampullary cancer: a prospective randomized controlled trial.

BACKGROUND: Success of surgical treatment for pancreatic and periampullary cancer is often limited due to locoregional recurrence and/or the development of distant metastases. OBJECTIVE: The survival benefit of celiac axis infusion (CAI) and radiotherapy (RT) versus observation after resection of pancreatic or periampullary cancer was investigated. METHODS: In a randomized controlled trial, 120 consecutive patients with histopathologically proven pancreatic or periampullary cancer received either adjuvant treatment consisting of intra-arterial mitoxantrone, 5-FU, leucovorin, and cisplatinum in combination with 30 x 1.8 Gy radiotherapy (group A) or no adjuvant treatment (group B). Groups were stratified for tumor type (pancreatic vs. periampullary tumors). RESULTS: After surgery, 120 patients were randomized (59 patients in the treatment group, 61 in the observation group). The median follow-up was 17 months. No significant overall survival benefit was seen (median, 19 vs. 18 months resp.). Progressive disease was seen in 86 patients: in 37 patients in the CAI/RT group, and in 49 patients in the observation group (log-rank P < 0.02). Subgroup analysis showed significantly less liver metastases after adjuvant treatment in periampullary tumors (log-rank P < 0.03) without effect on local recurrence. Nonetheless, there was no significant effect on overall survival in these patients (log-rank P = 0.15). In patients with pancreatic cancer, CAI/RT had no significant effect on local recurrence (log-rank P = 0.12) neither on the development of liver metastases (log-rank P = 0.76) and consequently, no effect on overall survival. CONCLUSION: This adjuvant treatment schedule results in a prolonged time to progression. For periampullary tumors, CAI/RT induced a significant reduction in the development of liver metastases, with a possible effect on overall survival. Especially in these tumors, CAI/RT might prove beneficial in larger groups and further research is warranted.

A decrease in S-adenosyl-L-methionine potentiates arachidonic acid cytotoxicity in primary rat hepatocytes enriched in CYP2E1.

Previous studies show that treatment with a polyunsaturated fatty acid, arachidonic acid (AA), or high concentrations of cycloleucine, an inhibitor of methionine adenosyltransferase (MAT), which lowers levels of S-adenosyl-L-methionine (SAM), increased toxicity in hepatocytes from pyrazole-treated rats which expressed high levels of cytochrome P450 2E1 (CYP2E1). In this study, I used concentrations of cycloleucine or AA, which by themselves do not produce any toxicity, to evaluate whether a decrease in SAM sensitizes hepatocytes to AA toxicity, especially in hepatocytes enriched in CYP2E1. Levels of SAM were lower by 50% in hepatocytes from pyrazole- compared to saline-treated rats. Cycloleucine treatment caused a 50% decline in SAM levels with both hepatocyte preparations and SAM levels were lowest in the pyrazole-treated hepatocytes. The combination of cycloleucine plus AA produced some toxicity and apoptosis in hepatocytes from saline-treated rats but increased toxicity and apoptosis was found in the hepatocytes from pyrazole-treated rats. Cytotoxicity could be prevented by incubation with SAM, the antioxidant trolox, and the mitochondrial permeability transition inhibitor trifluoperazine. The enhanced cytotoxicity could also be protected by treating rats with chlormethiazole, a specific inhibitor of CYP2E1, thus validating the role of CYP2E1. Cycloleucine plus AA treatment elevated production of reactive oxygen species (ROS) and lipid peroxidation to greater extents with the hepatocytes from pyrazole-treated rats than that from the saline-treated rats. I hypothesize that increased production of ROS by hepatocytes enriched in CYP2E1 potentiates AA-induced lipid peroxidation and toxicity when hepatoprotective levels of SAM are lowered. Such interactions, e.g. induction of CYP2E1, decline in SAM and polyunsaturated fatty acid-induced lipid peroxidation, may contribute to alcohol-induced liver injury.

Involvement of hippocampal metabotropic glutamate receptors in radial maze performance.

We investigated the role of hippocampal metabotropic glutamate receptors in spatial learning and memory, using an eight-arm radial maze task. (S)-4-Carboxyphenylglycine, a group I metabotropic glutamate receptor antagonist, or trans-(+/-)-1-amino-(1S,3R)-cyclopentanedicarboxylic acid, a broad-spectrum metabotropic glutamate receptor agonist, was administered into the dorsal hippocampus after rats had acquired the task. Both of these agents significantly impaired radial maze performance, suggesting a functional importance of hippocampal metabotropic glutamate receptors in spatial working memory.

NMDA receptor antagonism blocks the cardiovascular responses to microinjection of trans-ACPD into the NTS of awake rats.

The possible interaction of glutamatergic metabotropic agonists and N-methyl-d-aspartate (NMDA) receptors was investigated in the nucleus tractus solitarii (NTS) of awake rats. The cardiovascular responses to unilateral microinjection of trans-1-amino-1,3-cyclopentanediocarboxylic acid (trans-ACPD; 250 pmol/50 nL) into the NTS (n= 8) produced hypotension (-64 +/- 4 mmHg) and bradycardic (-206 +/- 11 bpm) responses, which were blocked by previous microinjection of 2-amino-5-phosphonovaleric acid (AP-5; 10 nmol/50 nL), a selective antagonist of NMDA ionotropic receptors, into the same site. Intravenous injection of methyl-atropine blocked both the bradycardic and hypotensive responses to microinjection of trans-ACPD into the NTS, indicating that the hypotension was secondary to the intense bradycardic response. The data also showed that the bradycardic and hypotensive responses to microinjection of an NMDA agonist (10 pmol/50 nL) into the NTS were not affected by previous microinjection of alpha-methyl-4-carboxyphenylglycine (MCPG; 5 nmol/50 nL), a non-selective antagonist of metabotropic receptors. The results showing that the cardiovascular responses to microinjection of trans-ACPD into the NTS were blocked by AP-5 indicate that the responses to metabotropic agonists in the NTS involves NMDA receptors.

NMDA receptors in nucleus tractus solitarii are linked to soluble guanylate cyclase.

We sought to test the hypothesis that cardiovascular responses to activation of ionotropic, but not metabotropic, glutamate receptors in the nucleus tractus solitarii (NTS) depend on soluble guanylate cyclase (sGC) and that inhibition of sGC would attenuate baroreflex responses to changes in arterial pressure. In adult male Sprague-Dawley rats anesthetized with chloralose, the ionotropic receptor agonists N-methyl-d-aspartate (NMDA) and dl-alpha-amino-3-hydroxy-5-methylisoxazole-propionic acid (AMPA) and the metabotropic receptor agonist trans-dl-amino-1,3-cyclopentane-dicarboxylic acid (ACPD) were microinjected into the NTS before and after microinjection of sGC inhibitors at the same site. Inhibition of sGC produced significant dose-dependent attenuation of cardiovascular responses to NMDA but did not alter responses produced by injection of AMPA or ACPD. Bilateral inhibition of sGC did not alter arterial pressure, nor did it attenuate baroreflex responses to pharmacologically induced changes in arterial pressure. This study links sGC with NMDA, but not AMPA or metabotropic, receptors in cardiovascular signal transduction through NTS.

Expression of angiogenic factors in hepatocellular carcinoma after transcatheter arterial chemoembolization.

In order to investigate the changes of vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) expression in residual hepatocellular carcinoma (HCC) after transcatheter arterial chemoembolization (TACE), the expression levels of VEGF and bFGF expression in specimens surgically removed from 48 HCC patients were detected by immunohistochemical methods, and staining intensity of VEGF and bFGF was assessed by a computer-assisted image-analyzer. Among the 48 patients, 25 underwent partial hepatectomy alone (single operating group), and 23 were subjected to second stage surgical resection after TACE (TACE group). The results showed that the average absorbance value (A) of VEGF was higher in TACE group than that in single operating group (0.152 +/- 0.021 vs 0.131 +/- 0.012, P < 0.01). The Average A of bF-GF in TACE group was 0.127 +/- 0.023, higher than in single operating group (0.111 +/- 0.016, P < 0.05). These results suggested that TACE of HCC can up-regulate the expression of VEGF and bFGF in HCC tissues possibly due to anoxia and ischemia.

Glutamate induces different neuronal conditioned responses than ACPD when used as a locally ionophoresed unconditioned stimulus in the cat motor cortex.

Single unit recordings were made from the motor cortex of conscious cats with glass micropipettes that allowed ionophoretic application of 0.5 M glutamate in 2 M NaCl or 0.5 M ACPD (1S,3R-1-amino-cyclopentane-1,3-dicarboxylic acid, a mGluR agonist) in 2 M NaCl. Activity in response to a 70 dB click (1 ms rectangular pulse to loudspeaker) was studied before, during, and immediately after applying each agent locally as a paired US (90 nA current 570 ms after click for 300 ms in combination with glabella tap). A 70 dB hiss sound was presented 4.4 sec after the click as a discriminative stimulus (DS). CS and DS were presented 10 times initially (adaptation); then CS, US plus tap, and DS (approximately 10 times as conditioning); and then CS and DS (2-10 times to test post-conditioning). Glutamate potentiated the mean, early, 8-16 ms response to the click after conditioning (t=18.2, p<0.0001), but not the baseline activity which decreased from a mean of 17 spk/sec to 7 spk/sec (t=3.71, p<0.001). Baseline activity increased to 31 spk/sec when glutamate was applied during conditioning (t=3.30, p<0.005). ACPD reduced the intermediate, 64-72 ms response to the click after conditioning (t=8.18, p<0.0001), and potentiated the late 104-112 ms response (t=15.4, p<0.0001). Baseline activity was slightly increased after conditioning with ACPD. Saline did not potentiate the response to click. The results indicate that glutamate agonists that differ in their receptor affinities can induce different CRs when used as locally applied USs to condition neuronal responses to a click CS in the motor cortex of cats.

Descending facilitatory modulation of a behavioral nociceptive response by stimulation in the adult rat anterior cingulate cortex.

It is well documented that the descending endogenous analgesia system, including the periaqueductal gray (PAG) and the rostral ventral medulla (RVM), play an important role in modulation of nociceptive transmission and morphine- and cannabinoid-produced analgesia. Neurons in the PAG receive inputs from different nuclei of higher structures, including the anterior cingulate cortex (ACC). However, it is unclear if stimulation of neurons in the ACC modulates spinal nociceptive transmission. The present study has examined the effects of electrical stimulation and chemical activation of metabotropic glutamate receptors (mGluRs) in the ACC on a spinal nociceptive tail-flick (TF) reflex induced by noxious heating. Activation of the ACC at high intensities (up to 500 microA) of electrical stimulation did not produce any antinociceptive effect. Instead, at most sites within the ACC (n = 36 of 41 sites), electrical stimulation produced significant facilitation of the TF reflex (i.e. decreases in TF latency). Chemical activation of mGluRs within the ACC also produced a facilitatory effect. Descending facilitation from the ACC apparently relays at the RVM. Electrical stimulation in the RVM produces a biphasic modulatory effect, showing facilitation at low intensities and inhibition at higher intensities. The present study provides evidence that activation of mGluRs within the ACC can facilitate spinal nociception.

Behavioural evidence supporting a differential role for group I and II metabotropic glutamate receptors in spinal nociceptive transmission.

Metabotropic glutamate receptors (mGluRs) have been shown to contribute to nociceptive processing in spinal cord. This study examined the effects of intrathecal treatment with group I and II mGluR compounds on withdrawal thresholds to noxious mechanical stimuli, in the absence of tissue damage or inflammation, in adult female sheep. Both the group I/II mGluR agonist (+/-)-1-aminocyclopentane-trans-1,3-dicarboxylic acid (trans-ACPD; 5.2-520 nmol) and the group II agonist (2S,1S, 2S)-2-(carboxycyclopropyl)glycine (L-CCG-I; 620 nmol) significantly increased mechanical withdrawal thresholds between 5-15 min post-injection. These anti-nociceptive effects were blocked by co-administration of the mGluR antagonist (2S)-alpha-ethylglutamate (EGLU; 570 nmol; group II), but not (RS)-1-aminoindan-1,5-dicarboxylic acid (AIDA; 450 nmol; group I). Intrathecal administration of the group I-specific agonist (S)-3,5-dihydroxyphenylglycine ((S)-3,5-DHPG; 50 nmol) produced a significant reduction in mechanical thresholds, which was blocked by co-administration of the group I antagonist AIDA. In contrast, the highest dose of (S)-3,5-DHPG tested, 5 micromol, significantly elevated response thresholds. These results demonstrate that both group I and II mGluRs play crucial, but contrasting roles in mediating acute mechanical nociceptive events in spinal cord.

Group II metabotropic glutamate receptors are a common target of N-anisoyl-GABA and 1S,3R-ACPD in enhancing ACh release in the prefrontal cortex of freely moving SHRSP.

Aniracetam is a therapeutically useful cognition enhancer for treating various neuropsychiatric symptoms occurring after cerebral infarction. We recently reported that local perfusion of its major metabolites N-anisoyl-GABA and p-anisic acid, but not aniracetam itself, enhanced acetylcholine (ACh) release with a delayed onset in cerebral regions of stroke-prone spontaneously hypertensive rats (SHRSP). In this study, we examined the possible involvement of metabotropic and ionotropic glutamate (mGlu and AMPA) receptors in the N-anisoyl-GABA-induced ACh release using brain in vivo microdialysis. Basal ACh release in SHRSP was commonly lower in the nucleus reticularis thalami, dorsal hippocampus and prefrontal cortex than that in age-matched Wistar Kyoto rats. The delayed ACh release in the prefrontal cortex of SHRSP was completely blocked by MCPG, a group I and II mGlu receptor antagonist, and MCCG, a group II-selective mGlu receptor antagonist. In contrast, it was largely unaffected by AIDA, a group I-selective mGlu receptor antagonist, or by YM90K, an AMPA receptor antagonist. 1S,3R-ACPD, a preferential group II mGlu receptor agonist, enhanced ACh release with a similar latency and the effect was antagonized by MCCG, whereas AMPA induced a prompt ACh release. These results indicate that N-anisoyl-GABA and 1S,3R-ACPD share a common mechanism mediated by group II mGlu receptors in enhancing ACh release. The findings suggest a possible mechanism for aniracetam's clinical efficacy in stroke patients with cholinergic deficits.

Development of cytotoxic cerebral edema in rats following intracaudatum injection of tACPD, an agonist of metabotropic glutamate receptors.

OBJECTIVE: To explore the involvement of metabotropic glutamate receptors (mGluRs) in the formation of cerebral edema. METHODS: Male Wistar rats weighing from 250 g to 300 g were used. Trans-1-aminocyclopentane-1, 3-diacarboxylic acid (tACPD), an agonist of mGluRs, was microinjected into the right caudatum. Brain water content was determined by a wet weight/dry weight technique and Na+, K+ and Ca2+ contents were measured by inductive Couple Plasma-9000 at 6 h, 24 h and 48 h post-injection. Extravasation of Evan's blue (EB) into the brain was determined as an indicator of disturbance in the blood-brain barrier (BBB) and endothelial cells. Histologic studies were performed under a Leitz microscope and a Philips EM208s electron microscope. RESULTS: Dose-dependent and time-related increase of brain water was induced after tACPD (10, 50, 500 and 1000 nmol) injection. A significant increase in Na+ and K+ content but not in Ca2+ content was observed. EB extravasation showed no blue stain, indicating no increase in BBB permeability induced by tACPD-injection. Electron microscope study confirmed this finding and revealed remarkable swelling of astrocytes especially endfoot processes of astrocytes around capillaries at 6 h after tACPD-injection. In addition, all changes mentioned above occurred in both caudatum. CONCLUSION: These results indicate that activation of mGluRs by tACPD injected into the caudatum induced cytotoxic brain edema and interfered with astrocyte K+ buffering. This may provide new clues for therapeutic intervention.

Roles of metabotropic glutamate receptor subtypes in modulation of pentylenetetrazole-induced seizure activity in mice.

The anticonvulsant or proconvulsant properties of ligands at metabotropic glutamate receptors (mGluRs) were examined in a chemoconvulsant model using pentylenetetrazole (PTZ). Mice received mGluR ligands by intracerebroventricular (i.c.v.) infusion prior to a subcutaneous injection of PTZ and the latency to onset of tonic convulsions was recorded. The group I mGluR antagonist 1-aminoindan-1,5-dicarboxylic acid (AIDA) dose-dependently antagonised PTZ-induced seizures with a mean ED50 value of 465 nmol. In contrast, the selective group I mGluR agonist, (S)-3,5-dihydroxyphenylglycine [(S)-DHPG], was proconvulsive and decreased the PTZ-induced seizure latency (ED50=60 nmol i.c.v.). A selective agonist of group II mGluRs, (1S,3S)-1-aminocyclopentane dicarboxylic acid [(1S,3S)-ACPD], was proconvulsive but did not affect PTZ-induced seizure latency. Moreover, the proconvulsant effect of (IS,3S)-ACPD was not blocked by the mGluR2 antagonist, alpha-methylserine-O-phosphate monophenyl ester but was blocked by AIDA suggesting the involvement of group I mGluRs. (2S,1'S,2'S,3'R)-2-(2'-carboxy-3'-phenylcyclopropyl)glycine (PCCG-IV), which is a potent mGluR2 antagonist and a group III mGluR agonist at higher doses, increased the PTZ-induced seizure latency (ED50=51 nmol) and this effect was fully reversed by the group III mGluR antagonist, (S)-2-amino-2-methyl-4-phosphonobutanoic acid (MAP4). Similarly, the group III mGluR agonist 1-amino-3-(phosphonomethylene)cyclobutanecarboxylate (cyclobutylene-AP5) increased the PTZ-induced seizure latency (ED50=12 nmol) in a MAP4-sensitive manner. Collectively, these data suggest that mGluR ligands modulate PTZ-induced seizure activity in mice by either antagonizing group I mGluRs or activating group III mGluRs.

Characterisation of mGluRs which modulate nociception in the PAG of the mouse.

The contribution of metabotropic glutamate receptors (mGluRs) to the modulation of nociception by the periaqueductal gray (PAG) matter was investigated in mice. Intra-PAG microinjection of (IS,3R)-ACPD, an agonist of groups I and II mGluRs, as well as (S)-3,5-DHPG, a selective agonist of group I mGluRs, increased the latency of the nociceptive reaction (NR) in the hot plate test. (RS)-AIDA, an antagonist of group I mGluRs, antagonized the effect of (S)-3,5-DHPG, but changed the effect induced by (1S,3R)-ACPD in that a decrease in the latency for the NR could now be observed. L-CCG-I and L-SOP, which are agonists of groups II and III mGluRs respectively, decreased the latency of the NR. (2S)-alpha-EGlu and (RS)-alpha-MSOP, which are antagonists of groups II and III mGluRs, respectively, antagonized the effect of L-CCG-I and L-SOP. (RS)-AIDA and (RS)-alpha-MSOP alone decreased and increased, respectively, the latency of the NR with the highest doses used. (2S)-alpha-EGlu alone did not change significantly the latency of the NR. Intra-PAG microinjection of LH, an agonist of ionotropic glutamate receptors, induced a dose-dependent analgesia which was blocked by pretreatment with DL-AP5, a selective antagonist of NMDA receptors. No mGluRs antagonists were able to prevent LH-induced analgesia. These results emphasize the possible involvement of mGluRs in the modulation of nociception. It seems that activation of group I mGluRs potentiates, while groups II and III mGluRs decrease, the activity of the PAG for the modulation of nociception.

Behavioral activity of 1S,3R-ACPD, an agonist of metabotropic glutamate receptors.

The influence of intracerebroventricular (i.c.v.) injections of 1-aminocyclopentane-1,3-dicarboxylic acid (1S,3R-ACPD), an agonist of metabotropic glutamate receptors, on the activity of the central nervous system was examined in rats. 1S,3R-ACPD at the i.c.v. doses of 100 and 200 nmole significantly decreased apomorphine-induced stereotypy, and at a dose 200 nmole significantly diminished catalepsy caused by haloperidol, two behavioral symptoms controlled mainly by central dopaminergic system. The tested compound had no influence on the locomotor and exploratory activity of rats estimated in open field. 1S,3R-ACPD significantly improved acquisition at the i.c.v. dose of 100 nmole, and consolidation of information at the i.c.v. doses of 100 and 200 nmole. The tested compound had no influence on retention processes in passive avoidance situation. This compound also did not improve recognition memory tested in the object recognition test. These results indicated that 1S,3R-ACPD improved memory motivated affectively but had no influence on recognition memory and the diminished dopaminergic transmission.

Microinfusion of the metabotropic glutamate receptor agonist 1S,3R-1-aminocyclopentane-1,3-dicarboxylic acid into the nucleus accumbens induces dopamine-dependent locomotor activation in the rat.

Although the striatum has one of the highest densities of metabotropic glutamate receptor (mGluR) binding sites in the brain, little is known about their physiological role. In this study we characterized the contribution of mGluRs located in the ventral part of the striatum (the nucleus accumbens) to the control of extrapyramidal motor function. Activation of mGluRs by local infusion of the selective agonist 1S,3R-1-aminocyclopentane-1,3-dicarboxylic acid (1S,3R-ACPD; 25, 50 and 100 nmol/0.5 microl) into the nucleus accumbens induced a dose-dependent increase in locomotor activity in rats. Intra-accumbens infusion of a selective antagonist of mGluRs, alpha-methyl-4-carboxyphenylglycine (MCPG) did not modify spontaneous locomotion but decreased the locomotor response to 1S,3R-ACPD. This effect appeared to be mediated by dopamine, since blockade of dopamine receptors with haloperidol (0.05 and 0.1 mg/kg i.p.) dose-dependently reduced 1S,3R-ACPD-induced locomotor activation. Furthermore, D-amphetamine (0.5 mg/kg, i.p.) combined with intra-accumbens infusion of 1S,3R-ACPD (100 nmol) potentiated the locomotor hyperactivity response to a higher level than that seen with a single treatment with either drug. In contrast, D-amphetamine-induced hypermotility was abolished by infusion of MCPG (100 nmol) into the nucleus accumbens. These results demonstrate that glutamate may control extrapyramidal motor function through metabotropic receptors. Furthermore, activation of metabotropic glutamate receptors appears to act in synergy with the dopamine system at the level of the nucleus accumbens to produce a motor stimulant response.

Pressor and sympathetic responses to excitatory amino acids are not augmented in the ventrolateral medulla of Dahl salt-sensitive rats.

We assessed the pressor and sympathetic responses to microinjection of excitatory amino acids (EAA) into the rostral ventrolateral medulla (RVLM) to see whether the response would be augmented in salt-induced hypertension. Seven-week-old Dahl-Iwai salt-sensitive rats were fed either a high- (8%, n = 10) or a low- (0.3%, n = 12) salt diet for 3 weeks. Then, L-glutamate (2 nmol), N-methyl-D-aspartate (NMDA; ionotropic EAA receptor agonist, 20 pmol) or (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid [(1S,3R)-ACPD; metabotropic EAA receptor agonist, 1 nmol] was microinjected into the RVLM of urethane-anesthetized, artifically ventilated rats. The rats fed a high-salt diet showed a significantly (P < 0.001) higher mean arterial pressure (123 +/- 3 mmHg) than those fed a low-salt diet (99 +/- 2 mmHg). We found similar increases in mean arterial pressure and splanchnic sympathetic nerve activity elicited by microinjection of L-glutamate into the RVLM in the high- (33 +/- 2 mmHg and 52 +/- 10%) and low- (35 +/- 3 mmHg and 46 +/- 8%) salt groups. Similarly, pressor and sympathoexcitatory responses to either NMDA or (1S,3R)-ACPD did not differ between the groups. Microinjections of the lower doses of L-glutamate, NMDA and (1S,3R)-ACPD also showed comparable pressor responses between the groups. These results indicate that salt-induced hypertension in Dahl salt-sensitive rats is not associated with enhanced responsiveness of the RVLM to EAA. This is in contrast with our previous findings that pressor and sympathetic responses to EAA are enhanced in spontaneously hypertensive rats.

HFS-induced long-term potentiation and LFS-induced depotentiation in area CA1 of the hippocampus are not good models for learning.

Spatial learning in rats has been shown to be dependent on the intact hippocampus and lesioning this region impairs learning performance. Long-term potentiation (LTP) and depotentiation (DP) of synaptic transmission have been suggested to model memory formation at the neuronal level. Recently it was shown that LTP in the dentate gyrus or area CA3 of the hippocampus is not essential for the ability to learn a spatial water maze task. Here we show that the metabotropic glutamate receptor agonist (1S,3S)-1-aminocyclopentane-1,3-dicarboxylic acid (1S,3S-ACPD), which acts predominantly at presynaptic sites, only marginally impaired spatial learning in a water maze or radial arm maze (three out of eight arms baited) when injected ICV (5 microliters of a 20 mM solution). There also were small impairments in non-spatial and visual discrimination tasks, indicating that the small learning impairments were due to nonselective effects of the drug. The same dose depressed field EPSPs and completely blocked LTP induced by high-frequency stimulation (HFS, 200 Hz) in the CA1 region of the rat hippocampus in vivo. A lower (5 microliters of a 10 mM solution) dose did not depress baseline but still blocked LTP. Injecting the same dose after induction of LTP blocked DP induced by low-frequency stimulation (LFS, 10 Hz). These results indicate that neither HFS-induced LTP nor LFS-induced DP in area CA1 are good models for the induction of synaptic changes that might underlie spatial learning in the rat.

Activation of metabotropic glutamate receptors increases neuropeptide Y expression in the rat hippocampus. Immunohistochemical studies.

Neuropeptide Y (NPY), a 36-amino acid peptide, is present in some hippocampal interneurons and nerve terminals and seems to modulate glutamatergic transmission in this structure. Earlier studies of some other authors showed an increase in NPY expression in the hippocampus during seizures and activation of ionotropic glutamate receptors. In the present study the effect of metabotropic glutamate receptor (mGluR) stimulation was investigated in rat hippocampus by immunohistochemical methods. It was found that (1S,3R)1-aminocyclopentane-1,3-dicarboxylic acid (1S,3R-ACPD), a selective agonist of mGluRs injected into the rat lateral ventricle (1 mumol/10 microliters) or hippocampus (0.1 mumol/1 microliter), 24 h before taking the brains for immunohistochemical studies, induced a significant increase in NPY-immunoreactivity in the hippocampus, especially in the hilar region. The obtained results indicate that mGluRs positively modulate the NPY content in the hippocampal neurons.