重复经颅磁刺激对创伤性颅脑损伤患者脑脊液中兴奋性氨基酸含量的影响

目的：探讨重复经颅磁刺激（rTMS）对急性颅脑损伤患者脑脊液中兴奋性氨基酸（EAA）含量的影响。方法：30例创伤性颅脑损伤（TBI）病人按格拉斯哥昏迷评分分为轻型组（rTMS3）、中型组（rTMS2）、重型组（rTMS1）,每组10例,各组病人分别随机分为rTMS对照亚组（A组）及治疗亚组（B组）,每亚组5例。于TBI后第15天行腰椎穿刺采集脑脊液,采用高效液相色谱法测定脑脊液中谷氨酸（ASP）及门冬氨酸（GLU）含量。结果：脑脊液ASP和GLU水平随着脑损伤程度的加重而升高,各rTMS治疗组与相应各对照组的EAA相比,rTMS治疗组EAA的水平均低于相应对照组。结论：rTMS可通过降低TBI后脑脊液EAA水平发挥脑保护作用。脑脊液EAA的含量变化可作为TBI严重程度的生化指标。     

重复经颅磁刺激对创伤性颅脑损伤患者脑脊液中兴奋性氨基酸 含量的影响

目的:探讨重复经颅磁刺激(rTMS)对急性颅脑损伤患者脑脊液中兴奋性氨基酸(EAA)含量的影响。方法:30例创伤性颅脑损伤(TBI)病人按格拉斯哥昏迷评分分为轻型组(rTMS3)、中型组(rTMS2)、重型组(rTMS1),每组10例,各组病人分别随机分为rTMS对照亚组(A组)及治疗亚组(B组),每亚组5例。于TBI后第15天行腰椎穿刺采集脑脊液,采用高效液相色谱法测定脑脊液中谷氨酸(ASP)及门冬氨酸(GLU)含量。结果:脑脊液ASP和GLU水平随着脑损伤程度的加重而升高,各rTMS治疗组与相应各对照组的EAA相比,rTMS治疗组EAA的水平均低于相应对照组。结论:rTMS可通过降低TBI后脑脊液EAA水平发挥脑保护作用。脑脊液EAA的含量变化可作为TBI严重程度的生化指标。     

The amnesic shellfish poison domoic acid enhances neurotoxicity by excitatory amino acids in cultured neurons

Summary A recent episode of human intoxication by cultured mussels containing a rare excitatory amino acid named domoic acid, received particular attention for its neurological implications. The intoxication produced neurological problems, such as headache, confusion, and loss of memory, particularly severe at times. Neuronal damage was found in the hippocampus and amygdala of four patients. We now report that in neuronal cultures the neurotoxicity of a domoic acid-containing mussel extract is the result of domoic acid potentiation of the excitotoxic effect of glutamic acid and aspartic acid present in high amounts in mussel tissue. Moreover, we show that subtoxic concentrations of domoic acid are sufficient to potentiate glutamic acid and aspartic acid neurotoxicity. We present evidence suggesting that the neurotoxic synergism may be due to a reduction of Mg^{+ +} block at the NMDA receptor-associated channel, following activation of NON-NMDA receptors by domoic acid.     

Direct and indirect presynaptic control of dopamine release by excitatory amino acids

Summary Dopamine (DA) release from nerve terminals of the nigrostriatal DA neurons not only depends on the activity of nigral DA cells but also on presynaptic regulation. Glutamatergie neurons of cortical origin play a prominent role in these presynaptic regulations. The direct glutamatergic presynaptic control of DA release is mediated by N-methyl-D-aspartate (NMDA) and-amino-3-hydroxy-5-methyl-4-isoxazole-4-propionate (AMPA) receptors, located on DA nerve terminals. In addition, by acting on striatal target cells, these glutamatergic neurons contribute also to indirect regulations of DA release involving several transmitters such as GABA, acetylcholine and neuropeptides. Diffusible messengers such as nitric oxide (NO) or arachidonic acid (AA) which are particularly formed under the stimulation of NMDA receptors may also participate to the regulation of DA release. In the present study, it will be shown that the co-application of NMDA and carbachol synergistically increases the release of [³H]-DA and that this effect is reduced by mepacrine or 4-bromophenacylbromide (10⁷M), two inhibitors of PLA2. Therefore endogenously released AA induced by the co-stimulation of NMDA and cholinergic receptors seems to be involved, at least partly, in the release of DA.     

Role of excitatory amino acids in the regulation of dopamine synthesis and release in the neostriatum

Summary We have explored the role of excitatory amino acids in the increased dopamine (DA) release that occurs in the neostriatum during stress-induced behavioral activation. Studies were performed in awake, freely moving rats, usingin vivo microdialysis. Extracellular DA was used as a measure of DA release; extracellular 3,4-dihydroxyphenylalanine (DOPA) after inhibition of DOPA decarboxylase provided a measure of apparent DA synthesis. Mild stress increased the synthesis and release of DA in striatum. DA synthesis and release also were enhanced by the intra-striatal infusion of N-methyl-D-aspartate (NMDA), an agonist at NMDA receptors, and kainic acid, an agonist at the DL-a-amino-3-hydroxy-5-methyl-4-isoxazole-4-propionate (AMPA)/kainate site. Stress-induced increase in DAsynthesis was attenuated by co-infusion of 2-amino-5-phosphonovalerate (APV) or 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), antagonists of NMDA and AMPA/kainate receptors, respectively. In contrast, intrastriatal APV, CNQX, or kynurenic acid (a non-selective ionotropic glutamate receptor antagonist) did not block the stress-induced increase in DArelease. Stress-induced increase in DA release was, however, blocked by administration of tetrodotoxin along the nigrostriatal DA projection. It also was attenuated when APV was infused into substantia nigra. Thus, glutamate may act via ionotropic receptors within striatum to regulate DA synthesis, whereas glutamate may influence DA release via an action on receptors in substantia nigra. However, our method for monitoring DA synthesis lowers extracellular DA and this may permit the appearance of an intra-striatal glutamatergic influence by reducing a local inhibitory influence of DA. If so, under conditions of low extracellular DA glutamate may influence DA release, as well as DA synthesis, by an intrastriatal action. Such conditions might occur during prolonged severe stress and/or DA neuron degeneration. These results may have implications for the impact of glutamate antagonists on the ability of patients with Parkinson's disease to tolerate stress.     

Effects of excitatory amino acids on inositol phosphate accumulation in slices of the cerebral cortex of young and aged rats

The effects of glutamate, NMDA and quisqualate on carbachol-and norepinephrine-elicited formation of inositol phosphate (IP) were evaluated in slices prepared from the cerebral cortex of 3-and 24-month Sprague-Dawley rats. Glutamate, NMDA, and quisqualate antagonized the IP response to carbachol in a concentration-dependent fashion. This antagonism was more pronounced in aged than in young rats, both for glutamate (IC5O 0.114 and 0.210 mM) and NMDA (IC5O 0.0029 and 0.127 mM), but not for quisqualate. Glutamate (but not NMDA) also antagonized in a concentration-dependent fashion the IP response to norepinephrine, IC50s were 0.061 and 0.126 mM for aged and young rats, respectively; quisqualate had an inhibitory effect only at 1 mM concentration in the two age-groups, while in aged rats some stimulatory effect was present at 0.1 mM concentration. Glutamate, NMDA and quisqualate (1 mM) did not affect basal IP accumulation in either young or aged rats; quisqualate, however, at 0.1 mM concentration had some stimulatory effect, more pronounced in aged rats. This effect was probably responsible for the biphasic effect of quisqualate in this age-group. The most important finding consists of the demonstration of an age-related increase in the inhibitory effects of NMDA on carbachol-induced IP accumulation. This implies an altered modulation of cholinergic post-receptor mechanisms by glutamatergic mechanisms.     

Role of excitatory amino acids in the direct and indirect presynaptic regulation of dopamine release from nerve terminals of nigrostriatal dopaminergic neurons

Summary In vivo experiments carried out in halothane-anaesthetized cats implanted with push-pull cannulae demonstrated that glutamate (GLU) released from corticostriatal fibers triggers the release of dopamine (DA), even in the absence of activity in nigral DA cells. As shown in vitro, using rat striatal slices or synaptosomes or in vivo in the cat, both NMDA and AMPA receptors subtypes are involved in the GLU-induced release of DA. Beside this direct regulation, GLU also exert several indirect facilitatory and inhibitory controls on DA release, particularly through cholinergic and GABAergic striatal neurons. Indeed, as shown by numerous authors, the GLU-evoked release of DA is markedly reduced in the presence of tetrodotoxin, bicuculline or atropine or by previous kainate- or ibotenate-induced lesion of striatum. Differences in the presynaptic regulation of DA release in striosomal and matrix compartments have also been found with NMDA and acetylcholine. The effect of acetylcholine was of shorter duration in the matrix than in the striosomal-enriched areas. Two opposite indirect regulations of DA release could be demonstrated: one is facilitatory and involves nicotinic receptors, the other is inhibitory, involves muscarinic receptors and mediated, at least in the matrix by dynorphin containing neurons. The NMDA-evoked responses are of larger amplitude and more sensitive to tetrodotoxin in the matrix than in the striosomes. In conclusion, GLU released from corticostriatal fibers, is able to control the release of DA from terminals of nigrostriatal neurons through direct facilitatory mechanisms (NMDA and AMPA receptors), but also through indirect facilitatory and inhibitory local circuits involving cholinergic and GABAergic neurons.     

Release of endogenous excitatory amino acids in the neostriatum of the rat under physiological and pharmacologically-induced conditions

Summary There is immunohistochemical evidence suggesting that glutamate (Glu) is released from nerve terminals and acts, via several receptor subtypes, as a major excitatory neurotransmitter in the cortico-striatal pathway of the rat. Aspartate (Asp) is also present in cortico-striatal neurons, but its role as a neurotransmitter has been questioned, since, in contrast to Glu, it has not been demonstrated in presynaptic vesicles. Glu and Asp can be found at subM concentrations in the extracellular compartment of most areas of the basal ganglia. Their concentrations are largely regulated by transport mechanisms, but also by a synaptotagmin-dependent exocytotic release, and are sufficiently high to occupy junctional and extrajunctional receptors.We have investigated whether Glu and Asp release in the neostriatum can be selectively modulated by different neuronal systems. Dopamine (DA) and cholecystokinin (CCK) selectively stimulate Asp release, via D₁ and CCK_B receptor subtypes, respectively. Also opioid -agonists increase Asp release. We propose that the selective modulation of Asp release by D_1–, CCK_B- and agonists involves striatal neurons containing Asp, but not Glu. In contrast, local perfusion with the ,-opioid antagonist D-Phe-Cys-Tyr-D-Trp-Orn-ThrPen-Thr-NH₂ (CTOP) increases both Glu and Asp release. This effect is probably exerted on cortico-striatal terminals, via presynaptic inhibitory -receptors. Thus, these results demonstrate that extracellular levels of Glu and Asp are modulated differentially by different neuronal systems, and suggest that in the neostriatum of the rat there are neuronal populations using Glu and/or Asp as messenger(s).     

Corticofugal regulation of auditory sensitivity in the bat inferior colliculus

Under free-field stimulation conditions, corticofugal regulation of auditory sensitivity of neurons in the central nucleus of the inferior colliculus of the big brown bat, Eptesicus fuscus, was studied by blocking activities of auditory cortical neurons with Lidocaine or by electrical stimulation in auditory cortical neuron recording sites. The corticocollicular pathway regulated the number of impulses, the auditory spatial response areas and the frequency-tuning curves of inferior colliculus neurons through facilitation or inhibition. Corticofugal regulation was most effective at low sound intensity and was dependent upon the time interval between acoustic and electrical stimuli. At optimal interstimulus intervals, inferior colliculus neurons had the smallest number of impulses and the longest response latency during corticofugal inhibition. The opposite effects were observed during corticofugal facilitation. Corticofugal inhibitory latency was longer than corticofugal facilitatory latency. Iontophoretic application of γ-aminobutyric acid and bicuculline to inferior colliculus recording sites produced effects similar to what were observed during corticofugal inhibition and facilitation. We suggest that corticofugal regulation of central auditory sensitivity can provide an animal with a mechanism to regulate acoustic signal processing in the ascending auditory pathway. Accepted: 15 July 1998     

Sound direction modifies the inhibitory as well as the excitatory frequency tuning characteristics of single neurons in the frog torus semicircularis (inferior colliculus)

Single-unit recordings were made from the frog inferior colliculus to determine whether or not the direction-dependent sharpening of a unit's free-field excitatory frequency-threshold curve (FTC_e) was accompanied by a broadening of its inhibitory frequency-threshold curve (FTC_i). To determine the FTC_i, a two-tone-suppression paradigm was employed. The unit's FTC_is and FTC_es were collected at three azimuths: contralateral to the recording site, ipsilateral to the recording site, and frontal midline. The result showed that: (1) most inferior colliculus neurons (95%) displayed two-tone suppression, (2) the majority (54%) of neurons displayed stronger two-tone-suppression leading to broader FTC_is when the sound was presented from the ipsilateral side than from the contralateral side, (3) for some neurons, the borders of the FTC_es and FTC_is were closely aligned, and this juxtaposition persisted at all sound azimuths (namely, when a change in sound direction produced a narrowing of a unit's FTC_e, its FTC_i was broadened concomitantly). For the remaining neurons, however, direction-dependent sharpening of the FTC_e was not accompanied by an increase in two-tone-suppression. The neural mechanisms that underlie the direction-dependent changes in the FTC_es and FTC_is are discussed. Accepted: 19 November 1997     

Neural correlates of behavioral gap detection in the inferior colliculus of the young CBA mouse

The gap detection paradigm is frequently used in psychoacoustics to characterize the temporal acuity of the auditory system. Neural responses to silent gaps embedded in white-noise carriers, were obtained from mouse inferior colliculus (IC) neurons and the results compared to behavioral estimates of gap detection. Neural correlates of gap detection were obtained from 78 single neurons located in the central nucleus of the IC. Minimal gap thresholds (MGTs) were computed from single-unit gap functions and were found to be comparable, 1–2 ms, to the behavioral gap threshold (2 ms). There was no difference in MGTs for units in which both carrier intensities were collected. Single unit responses were classified based on temporal discharge patterns to steady-state noise bursts. Onset and primary-like units had the shortest mean MGTs (2.0 ms), followed by sustained units (4.0 ms) and phasic-off units (4.2 ms). The longest MGTs were obtained for inhibitory neurons (xˉ = 14 ms). Finally, the time-course of behavioral and neurophysiological gap functions were found to be in good agreement. The results of the present study indicate the neural code necessary for behavioral gap detection is present in the temporal discharge patterns of the majority of IC neurons. Accepted: 6 February 1997     

Neurons with different temporal firing patterns in the inferior colliculus of the little brown bat differentially process sinusoidal amplitude-modulated signals

We examined how well single neurons in the inferior colliculus (IC) of an FM bat (Myotis lucifugus) processed simple tone bursts of different duration and sinusoidal amplitude-modulated (SAM) signals that approximated passively heard natural sounds. Units' responses to SAM tones, measured in terms of average spike count and firing synchrony to the modulation envelope, were plotted as a function of the modulation frequency to construct their modulation transfer functions. These functions were classified according to their shape (e.g., band-, low-, high-, and all-pass). IC neurons having different temporal firing patterns to simple tone bursts (tonic, chopper, onset-late, and onset-immediate) exhibited different selectivities for SAM signals. All tonic and 83% of chopper neurons responded robustly to SAM signals and displayed a variety of spike count-based response functions. These neurons showed a decreased level of time-locking as the modulation frequency was increased, and thereby gave low-pass synchronization-based response functions. In contrast, 64% of onset-immediate, 37% of onset-late and 17% of chopper units failed to respond to SAM signals at any modulation frequency tested (5–800 Hz). Those onset neurons that did respond to SAM showed poor time-locking (i.e., non-significant levels of synchronization). We obtained evidence that the poor SAM response of some onset and chopper neurons was due to a preference for short-duration signals. These data suggest that tonic and most chopper neurons are better-suited for the processing of long-duration SAM signals related to passive hearing, whereas onset neurons are better-suited for the processing of short, pulsatile signals such as those used in echolocation.Abbreviations C chopper - FM frequency-modulated - IC inferior colliculus - MTF modulation transfer function - O₁ onset-immediate - O_L onset-late - PAM pulsatile amplitude-modulation - PSTH peri-stimulus time histogram - SAM sinusoidal amplitude-modulation - SC synchronization coefficient - T tonic     

Protein kinase C inhibitor chelerythrine attenuates the morphine-induced excitatory amino acid release and reduction of the antinociceptive effect of morphine in rats injected intrathecally with pertussis toxin

Neuropathic pain syndromes respond poorly to opioid treatment. In our previous studies, we found that intrathecal (i.t.) injection of pertussis toxin (PTX) produces thermal hyperalgesia, which is poorly responsive to morphine and is accompanied by an increase in cerebrospinal fluid (CSF) levels of excitatory amino acids (EAAs) and protein kinase C (PKC) activation. In the present study, rats were implanted with an i.t. catheter for drug injection and a microdialysis probe for CSF dialysate collection. On the fourth day after injection of PTX (2 microg, i.t.), there was a significant reduction in the antinociceptive effect of morphine (10 microg, i.t.) which was accompanied by an increase in levels of EAAs. Pretreatment with the PKC inhibitor, chelerythrine (25 microg, i.t.) one hour before morphine injection markedly inhibited both effects. These results suggest that, in PTX-treated rats, PKC plays an important role in inhibiting the morphine-induced spinal EAA release, which might be related to the reduced antinociceptive effect of morphine.     

Frequency tuning, latencies, and responses to frequency-modulated sweeps in the inferior colliculus of the echolocating bat, Eptesicus fuscus

Neurons in the inferior colliculus (IC) of the awake big brown bat, Eptesicus fuscus, were examined for joint frequency and latency response properties which could register the timing of the bat's frequency-modulated (FM) biosonar echoes. Best frequencies (BFs) range from 10 kHz to 100 kHz with 50% tuning widths mostly from 1 kHz to 8 kHz. Neurons respond with one discharge per 2-ms tone burst or FM stimulus at a characteristic latency in the range of 3–45 ms, with latency variability (SD) of 50 μs to 4–6 ms or more. BF distribution is related to biosonar signal structure. As observed previously, on a linear frequency scale BFs appear biased to lower frequencies, with 20–40 kHz overrepresented. However, on a hyperbolic frequency (linear period) scale BFs appear more uniformly distributed, with little overrepresentation. The cumulative proportion of BFs in FM₁ and FM₂ bands reconstructs a scaled version of the spectrogram of FM broadcasts. Correcting FM latencies for absolute BF latencies and BF time-in-sweep reveals a subset of IC cells which respond dynamically to the timing of their BFs in FM sweeps. Behaviorally, Eptesicus perceives echo delay and phase with microsecond or even submicrosecond accuracy and resolution, but even with use of phase-locked FM and tone-burst stimuli the cell-by-cell precision of IC time-frequency registration seems inadequate by itself to account for the temporal acuity exhibited by the bat. Accepted: 21 June 1997     

Modulation of phosphoinositide metabolism in rat brain slices by excitatory amino acids,arachidonic acid,and GABA

In rat brain slices the synthesis of [³H]phosphoinositides and the production of [³H]inositol monophosphate (IP₁) induced by norepinephrine (NE) were inhibited by glutamate. Calcium concentrations were varied to test if these inhibitory effects of glutamate were mediated by a calcium-dependent process. Although reducing calcium or addition of the calcium antagonist verpamil reduced the inhibitory effects of glutamate, these results were equivocal because reduced calcium directly decreased agonist-induced [³H]phosphoinositide synthesis. The inhibitory effects of glutamate were mimicked by quisqualate in a dose-dependent manner, but none of a variety of excitatory amino acid receptor antagonists modified the inhibition caused by quisqualate. It is suggested that glutamate activates a quisqualate-sensitive receptor (for which an antagonist is not available) and causes inhibition of phosphoinositide hydrolysis mediated in part by a direct or indirect inhibitory effect of calcium on phosphoinositide synthesis. Modulatory effects of arachidonic acid were examined because glutamate and calcium can activate phospholipase A₂. Arachidonic acid caused a rapid and dose-dependent inhibition of [³H]phosphoinositide synthesis and of NE-stimulated [³H]IP₁ production. A similar inhibition of the response to carbachol also occurred. The inhibition caused by arachidonic acid was unchanged by addition of inhibitors of cyclooxygenase or lipoxygenase. Activation of phospholipase A₂ with melittin caused inhibitory effects similar to those of arachidonic acid. Inhibitors of phospholipase A₂ were found to impair phosphoinositide metabolism, likely due to their lack of specificity for phospholipase A₂. Further studies were carried out in slices that were prelabelled with [³H]inositol in an attempt to separate modulatory effects on [³H]phosphoinositide synthesis and agonist-stimulated [³H]IP₁ production. Several excitatory amino acid agonists inhibited NE-stimulated [³H]IP₁ production. This inhibitory inter-action could be due to impaired synthesis of [³H]phosphoinositides because, even though the slices were prelabeled, addition of unlabelled inositol reduced NE-stimulated [³H]IP₁ production, indicating that continuous regeneration of [³H]phosphoinositides is required. In contrast to the inhibitory effects of the excitatory amino acids, gamma-aminobutyric acid (GABA) enhanced the response to NE in cortical and hippocampal slices. GABA also enhanced the response to carbachol in hippocampal and striatal slices and to ibotenic acid in hippocampal slices. Baclofen potentiated the response to NE similarly to the effect of GABA and baclofen partially blocked the inhibitory effect of arachidonic acid but did not alter that of quisqualate.Abbreviations AMPA -amino-3-hydroxy-5-methyl-4-isoxazolepropionic - acid AP₄ dl-2-amino-4-phosphonobutyric acid - BPB bromphenacyl bromide - BSA bovine serum albumin - CNQX 6-cyano-7-nitroquinoxaline-2,3-dione - DFMO -difluoromethylornithine - DIDS diisothiocyanotostilbene-2,2-disulfonic acid - EGTA ethyleneglycol-bis-N - N, N N-tetraacetic acid - GABA -aminobutyric acid - GDEE glutamate diethyl ether - -GG -glutamylglycine - IP₁ inositol monophosphate - IP₂ inositol bisphosphate - IP₃ inositol trisphosphate - NDGA nordihydroguaiaretic acid - NE norepinephrine - NMDA N-methyl-d-aspartate     

Changes with aging in the levels of amino acids in rat CNS structural elements II. Taurine and small neutral amino acids

Taurine (Tau) and the small neutral amino acids glycine (Gly), serine (Ser), threonine (Thr), and alanine (Ala) were measured in 53 brain areas of 3- and 29-month-old male Fisher 344 rats. The ratio of highest to lowest level was 34 for Tau, 9.1 for Thr, 7.6 for Gly and Ser, and 6.5 for Ala. The heterogeneity was found in numerous areas; for example, Tau levels were more than 90 nmol/mg protein in 6 areas, and less than 20 nmol/mg protein in 10 areas. Similar heterogeneity was found with the other amino acids. The relative distribution of the small neutral amino acids showed several similarities; Tau distribution was different. With age, four amino acids decreased in 10–18 areas, and increased in only 1–3, while Thr increased in more areas than it decreased. The five amino acids of this paper, and the four of the previous paper, are among the amino acids at highest level in the brain; the sequence in their levels shows considerable regional heterogeneity.     

Effect of excitatory amino acid neurotransmitters on acid secretion in the rat stomach

Excitatory amino acids (EAAs), in particular,L-aspartate (L-Asp) neurons and their processes, were localized in the rat stomach using a immunohistochemical method with specific antibodies against eitherL-Asp or its synthesizing enzyme, aspartate aminotransferase (AAT). Myenteric ganglia and nerve bundles in the circular muscle and in the longitudinal muscle were found to be AAT-orL-Asp-positive. In addition, AAT- orL-Asp-positive cells were also found in the muscle layer and the deep mucosal layer. The distribution of AAT- orL-Asp-positive cells in both the mucosal and muscle layers was heterogeneous in the stomach. In addition,L-Asp at 10^–6 M negligibly influenced acid secretion in an everted preparation of isolated rat stomach. However, according to our results,L-Asp markedly inhibited the histamine-stimulated acid secretion, but not the oxotremorine- or the pentagastrin-stimulated acid secretion. Furthermore,L-Asp also inhibited histamine-induced elevation of cAMP.L-Asp itself did not affect the cAMP level although it elevated the cGMP level in the stomach. Moreover, either (+)2-amino-5-phosphonovaleric acid or (±)3-(2-carboxy-piperazin-4-yl)prophyl-1-phosphonic acid, i.e. two specific antagonists for N-methyl-D-aspartic acid (NMDA) receptors, blocked the inhibitory effect ofL-Asp on histamine-stimulated acid secretion or histamine-induced elevation of cAMP. Since cAMP has been strongly implicated as the second messenger involved in histamine-induced acid secretion, we believe thatL-Asp regulates acid secretion in the stomach by inhibiting histamine release through the NMDA receptors, subsequently lowering the level of cAMP and ultimately reducing acid secretion.     

Changes with aging in the levels of amino acids in rat CNS structural elements I. Glutamate and related amino acids

Glutamate and related amino acids were determined in 53 discrete brain areas of 3-and 29-month-old male Fischer 344 rats microdissected with the punch technique. The levels of amino acids showed high regional variation-the ratio of the highest to lowest level was 9 for aspartate, 5 for glutamate, 6 for glutamine, and 21 for GABA. Several areas were found to have all four amino acids at very high or at very low level, but also some areas had some amino acids at high, others at low level. With age, in more than half of the areas, significant changes could be observed, decrease occurred 5 times more frequently than increase. Changes occurred more often in levels of aspartate and GABA than in those of glutamate or glutamine. The regional levels of glutamate and its related amino acids show severalfold variations, with the levels tending to decrease in the aged brain.     

Regulation of vesicular acetylcholine transporter by the activation of excitatory amino acid receptors in the avian retina

1. Previous studies have shown that phorbol esters induce protein kinase C (PKC) mediated phosphorylation of the vesicular acetylcholine transporter (VAChT) and change its interaction with vesamicol. However, it is not clear whether physiological activation of receptors coupled to PKC activation can alter VAChT behavior.2. Here we tested whether activation of kaianate (KA) receptors alters VAChT. Several studies suggest that the cholinergic amacrine cells display KA/AMPA receptors that mediate excitatory input to these neurons. In addition, KA in the chicken retina can generate intracellular messengers with the potential to regulate cellular functions.3. In cultured chicken retina (E8C11) KA reduced vesamicol binding to VAChT by 53%. This effect was potentiated by okadaic acid, a protein phosphatase inhibitor, and was totally prevented by BIM, a PKC inhibitor.4. Phorbol myristate acetate (PMA), but not -PMA, reduced in more than 85% the number of L-[³H]-vesamicol-specific binding sites in chicken retina, confirming that activation of PKC can influence vesamicol binding to chicken VAChT.5. The data show that activation of glutamatergic receptors reduces [³H]-vesamicol binding sites (VAChT) likely by activating PKC and increasing the phosphorylation of the ACh carrier.     

Increasing dispensable amino acids in diets of kittens fed essential amino acids at or below their requirement increases the requirement for arginine

Summary Kittens fed diets containing 0.75 × the NRC (1986) essential amino acid requirement (EAArq) and 210 to 560g crude protein(CP)/kg diet exhibited, with increasing CP: 1) decreasing weight gain, 2) decreasing plasma arginine concentrations, 3) increasing urinary orotic acid excretion, 4) increasing plasma glutamic acid concentrations, and 5) plasma isoleucine concentrations at levels that suggest a marginal isoleucine deficiency. Kittens fed a control diet (CD) containing 1.5 × EAArq and 350 g CP/kg diet had maximal weight gains and no orotic aciduria. It was concluded that the decreased weight gain and adverse metabolic effects were caused by arginine deficiency and possibly glutamic acid toxicity induced by high dietary dispensable amino acids. Kittens fed the diets containing 1.0 × EAArq and 350 and 560 g CP/kg diet had depressed plasma arginine and elevated glutamic acid concentrations and orotic aciduria. These results indicate that 10 g arg/kg diet is not adequate at CP concentrations above 280 g/kg and the calculated requirement of arginine is (0.02 g arginine/g CP) × (Y g CP/kg diet) + (4.0 g arginine/kg diet) where Y is the dietary CP level.Abbreviations CD control diet - CP crude protein (g CP/kg diet = g nitrogen/kg diet × 6.25) - DAA dispensable amino acids - EAA essential amino acids - EAArq essential amino acid requirement