Norepinephrine modulates excitatory amino acid-induced responses in developing human and adult rat cerebral cortex

Knockdown of α2C-adrenoceptors in the occipital cortex rescued long-term potentiation in hidden prenatally malnourished rats

Moderate reduction in the protein content of the mother's diet calorically compensated by carbohydrates (the so-called "hidden" prenatal malnutrition) leads to increased neocortical expression of the α(2C)-adrenoceptor subtype, together with decreased cortical release of noradrenaline and impaired long-term potentiation (LTP) and visuospatial memory performance during the rat postnatal life. In order to study whether overexpression of the α(2C)-adrenoceptor subtype is causally related to the decreased indices of neocortical plasticity found in prenatally malnourished rats, we evaluated the effect of intracortical (occipital cortex) administration of an antisense oligodeoxynucleotide (ODN) raised against the α(2C)-adrenoceptor mRNA on the LTP elicited in vivo in the occipital cortex of hidden prenatally malnourished rats. In addition, we compare the effect of the antisense ODN to that produced by systemical administration of the subtype-nonselective α(2)-adrenoceptor antagonist atipamezole. Prenatal protein malnutrition led to impaired occipital cortex LTP together with increased expression of α(2C)-adrenoceptors (about twice Bmax) in the same cortical region. [(3)H]-rauwolscine binding assay showed that a 7-day intracortical antisense ODN treatment in the malnourished rats resulted in 50% knockdown of α(2C)-adrenoceptor expression and, in addition, completely rescued the ability of the occipital cortex to develop and maintain long-term potentiation. Atipamezole (0.3 mg/kg i.p.) also led to full recovery of neocortical LTP in malnourished rats. The present results argue in favor of our original hypothesis that the deleterious effect of prenatal malnutrition on neocortical plasticity in the adult progeny is in part consequence of increased neocortical α(2C)-adrenoceptor expression. This receptor subtype is known to be involved in the presynaptic control of noradrenaline release from central neurons, a neurotransmitter that critically influences LTP and memory formation.

Pre- and postsynaptic beta-adrenergic activation enhances excitatory synaptic transmission in layer V/VI pyramidal neurons of the medial prefrontal cortex of rats

Norepinephrine exerts an important influence on prefrontal cortical functions. The physiological effects of beta-adrenoceptors (beta-ARs) have been examined in other brain regions. However, little is known about beta-AR regulation of synaptic transmission in the prefrontal cortex (PFC). The present study investigated beta-AR modulation of glutamate synaptic transmission in layer V/VI pyramidal cells of the medial PFC (mPFC) of rats. Our results show that 1) isoproterenol (ISO), a selective beta-AR agonist, increased the frequency of spontaneous and miniature excitatory postsynaptic currents (EPSC's); 2) ISO enhancement of miniature EPSC's (mEPSC's) frequency no longer appeared in the presence of the voltage-gated Ca(2+) channel blocker cadmium; 3) ISO enhanced the evoked excitatory postsynaptic currents (eEPSC's) mediated by non-N-methyl-D-aspartic acid receptors (non-NMDA-Rs) and NMDA-Rs. The ISO facilitation of non-NMDA-R eEPSC was blocked by the membrane-permeable cyclic adenosine monophosphate (cAMP) inhibitor Rp-adenosine 3',5'-cyclic monophosphorothioate triethylammonium salt (Rp-cAMPS); 4) ISO enhanced NMDA-induced current, with no effect on glutamate-induced non-NMDA-R current; 5) ISO enhancement of NMDA-R eEPSC and NMDA-induced current was blocked by intracellular application of Rp-cAMPS or the cAMP-dependent protein kinase (PKA) inhibitor PKI(5-24); and 6) ISO suppressed the paired-pulse facilitation of non-NMDA-R and NMDA-R eEPSC's. Taken together, these results provide the first electrophysiological demonstration that beta-AR activation facilitates excitatory synaptic transmission in mPFC pyramidal cells through pre- and postsynaptic mechanisms, probably via cAMP or cAMP/PKA signaling.

Mild prenatal protein malnutrition increases α2C-adrenoceptor expression in the rat cerebral cortex during postnatal life

Mild reduction in the protein content in the diet of pregnant rats from 25 to 8% casein, calorically compensated by carbohydrates, does not alter body and brain weights of rat pups at birth, but results in significant changes of the concentration and release of cortical noradrenaline during postnatal life, together with impaired long-term potentiation and memory formation. Since some central noradrenergic receptors are critically involved in neuroplasticity, the present study evaluated, by utilizing immunohistochemical methods, the effect of mild prenatal protein malnutrition on the alpha 2C-adrenoceptor expression in the frontal and occipital cortices of 8- and 60-day-old rats. At day 8 of postnatal age, prenatally malnourished rats exhibited a three-fold increase of alpha 2C-adrenoceptor expression in both the frontal and the occipital cortices, as compared to well-nourished controls. At 60 days of age, prenatally malnourished rats showed normal expression levels scores of alpha 2C-adrenoceptor in the neocortex. Results suggest that overexpression of neocortical alpha 2C-adrenoceptors during early postnatal life, subsequent to mild prenatal protein malnutrition, could in part be responsible for neural and behavioral disturbances showing prenatally malnourished animals during the postnatal life.

Mild prenatal protein malnutrition increases α2C-adrenoceptor density in the cerebral cortex during postnatal life and impairs neocortical long-term potentiation and visuo-spatial performance in rats

Mild reduction in the protein content of the mother's diet from 25 to 8% casein, calorically compensated by carbohydrates, does not alter body and brain weights of rat pups at birth, but leads to significant enhancements in the concentration and release of cortical noradrenaline during early postnatal life. Since central noradrenaline and some of its receptors are critically involved in long-term potentiation (LTP) and memory formation, this study evaluated the effect of mild prenatal protein malnutrition on the alpha2C-adrenoceptor density in the frontal and occipital cortices, induction of LTP in the same cortical regions and the visuo-spatial memory. Pups born from rats fed a 25% casein diet throughout pregnancy served as controls. At day 8 of postnatal age, prenatally malnourished rats showed a threefold increase in neocortical alpha2C-adrenoceptor density. At 60 days-of-age, alpha2C-adrenoceptor density was still elevated in the neocortex, and the animals were unable to maintain neocortical LTP and presented lower visuo-spatial memory performance. Results suggest that overexpression of neocortical alpha2C-adrenoceptors during postnatal life, subsequent to mild prenatal protein malnutrition, could functionally affect the synaptic networks subserving neocortical LTP and visuo-spatial memory formation.

Noradrenaline decreases spike voltage threshold and induces electrographic sharp waves in turtle medial cortex in vitro

The noradrenergic modulation of neuronal properties has been described at different levels of the mammalian brain. Although the anatomical characteristics of the noradrenergic system are well known in reptiles, functional data are scarce. In our study the noradrenergic modulation of cortical electrogenesis in the turtle medial cortex was studied in vitro using a combination of field and intracellular recordings. Turtle EEG consists of a low voltage background interspersed by spontaneous large sharp waves (LSWs). Noradrenaline (NA, 5-40 microM) induced (or enhanced) the generation of LSWs in a dose-dependent manner. Pharmacological experiments suggest the participation of alpha and beta receptors in this effect. In medial cortex neurons NA induced a hyperpolarization of the resting potential and a decrease of input resistance. Both effects were observed also after TTX treatment. Noradrenaline increased the response of the cells to depolarizing pulses, resulting in an upward shift of the frequency/current relation. In most cells the excitability change was mediated by a decrease of the spike voltage threshold resulting in the reduction of the amount of depolarization needed to fire the cell (voltage threshold minus resting potential). As opposed to the mechanisms reported in mammalian neurons, no changes in the frequency adaptation or the post-train afterhyperpolarization were observed. The NA effects at the cellular level were not reproduced by noradrenergic agonists. Age- and species-dependent properties in the pharmacology of adrenergic receptors could be involved in this result. Cellular effects of NA in turtle cortex are similar to those described in mammals, although the increase in cellular excitability seems to be mediated by a different mechanism.

Methylphenidate and intracortical excitability: opposite effects in healthy subjects and attention-deficit hyperactivity disorder

OBJECTIVE

To test the effects of a standard dosage of the psychostimulant methylphenidate (MPH) - which significantly enhances intracortical inhibition but had no effects on intracortical facilitation in children with attention-deficit hyperactivity disorder (ADHD) - on intracortical excitability in healthy subjects.

METHOD

In 12 healthy subjects, aged 20-40 years, intracortical inhibition and facilitation were investigated before and 70 min after the intake of 10 mg MPH using the technique of transcranial magnetic stimulation (TMS) with the paired-stimulus paradigm.

RESULTS

In comparison of the two TMS measurements, a significant enhancement in intracortical facilitation but no effects on intracortical inhibition could be stated under MPH administration.

CONCLUSION

This study provides first evidence for opposite effects of MPH on intracortical excitability in healthy adult subjects showing enhanced intracortical facilitation in contrast to ADHD children in whom enhanced intracortical inhibition has recently been shown.

Amino acid and monoamine alterations in the cerebral cortex and hippocampus of mice submitted to ricinine-induced seizures

The alkaloid ricinine isolated from the plant Ricinus communis, when administered to mice at high doses, induces clonic seizures accompanied by electroencephalographic alterations in the cerebral cortex and hippocampus. The lethal nature of ricinine-induced seizures is considered to be a good model for the study of the events that cause death during clonic seizures, particularly those related to respiratory spasms. The initial signs (pre-seizure period) were marked by exophthalmus and decreased locomotor behavior. Animals killed during the preseizure period presented an increased utilization rate (HVA/DA) of dopamine (DA), an increased concentration of noradrenaline (NA), and a decreased concentration of glutamate (Glu), glutamine (Gln), taurine (Tau), and serotonin (5-HT) in the cerebral cortex. The seizure period is characterized by the occurrence of hind limb myoclonus and respiratory spasms, which are followed by death. Alterations in the cerebral cortex concentration of these neurotransmitters persisted during the seizure period. These alterations are only partially observed in the hippocampus, mainly during the seizure period. The present results suggest that an increased release of Glu in the cerebral cortex can be implicated in the genesis of the ricinine-induced seizure and that it triggers many anticonvulsive mechanisms, like the release of Tau, DA, 5-HT, and NA.

Modulation of beta-adrenergic receptor subtype activities in perioperative medicine: mechanisms and sites of action

This review focuses on the mechanisms and sites of action underlying beta-adrenergic antagonism in perioperative medicine. A large body of knowledge has recently emerged from basic and clinical research concerning the mechanisms of the life-saving effects of beta-adrenergic antagonists (beta-AAs) in high-risk cardiac patients. This article re-emphasizes the mechanisms underlying beta-adrenergic antagonism and also illuminates novel rationales behind the use of perioperative beta-AAs from a biological point of view. Particularly, it delineates new concepts of beta-adrenergic signal transduction emerging from transgenic animal models. The role of the different characteristics of various beta-AAs is discussed, and evidence will be presented for the selection of one specific agent over another on the basis of individual drug profiles in defined clinical situations. The salutary effects of beta-AAs on the cardiovascular system will be described at the cellular and molecular levels. Beta-AAs exhibit many effects beyond a reduction in heart rate, which are less known by perioperative physicians but equally desirable in the perioperative care of high-risk cardiac patients. These include effects on core components of an anaesthetic regimen, such as analgesia, hypnosis, and memory function. Despite overwhelming evidence of benefit, beta-AAs are currently under-utilized in the perioperative period because of concerns of potential adverse effects and toxicity. The effects of acute administration of beta-AAs on cardiac function in the compromised patient and strategies to counteract potential adverse effects will be discussed in detail. This may help to overcome barriers to the initiation of perioperative treatment with beta-AAs in a larger number of high-risk cardiac patients undergoing surgery.

Biogenic amines in the human neocortex in patients with neocortical and mesial temporal lobe epilepsy: identification with in situ microvoltammetry

Biogenic amines in well defined subtypes of human temporal lobe epilepsy (TLE) have not been well characterized. Specimens from five patients with neocortical TLE (NTLE) and nine with mesial TLE (MTLE) were immediately placed in Ringer's lactate; stearate indicator microelectrodes were placed in temporal gray matter, Ag/AgCl reference microelectrodes and auxiliary microelectrodes were placed 3-7 mm contralaterally to the indicator microelectrode. Dopamine (DA), ascorbic acid (AA), norepinephrine (NE) and serotonin (5-HT) were identified by their characteristic oxidative potentials in vitro. Four of five patients with NTLE had NE depletion in temporal neocortex while eight of nine patients with MTLE had high concentrations of NE (chi-square P<0.01). Significant concentrations of DA were present in the temporal lobes of three of five NTLE patients but in only one of the nine MTLE patients (chi-square P<0.05). 5-HT was present in the neocortex of both NTLE and MTLE patients in similar concentrations. AA was found in the neocortex of one NTLE patient. These data support an association between NE depletion and NTLE. The relative NE deficiency along with the consistent presence of DA in NTLE patients suggest an impairment in the catecholamine pathway. The presence of AA, a co-factor in NE synthesis, in the neocortex of one NTLE patient may also be related since AA is a cofactor in NE synthesis.

beta-Adrenoceptor and nNOS-derived NO interactions modulate hypoglycemic pial arteriolar dilation in rats

We examined the relative contributions from nitric oxide (NO) and catecholaminergic pathways in promoting cerebral arteriolar dilation during hypoglycemia (plasma glucose congruent with 1.4 mM). To that end, we monitored the effects of beta-adrenoceptor (beta-AR) blockade with propranolol (Pro, 1.5 mg/kg iv), neuronal nitric oxide synthase (nNOS) inhibition with 7-nitroindazole (7-NI, 40 mg/kg ip) or ARR-17477 (300 microM, via topical application), or combined intravenous Pro + 7-NI or ARR-17477 on pial arteriolar diameter changes in anesthetized rats subjected to insulin-induced hypoglycemia. Additional experiments, employing topically applied TTX (1 microM), addressed the possibility that the pial arteriolar response to hypoglycemia required neuronal transmission. Separately, Pro and 7-NI elicited modest but statistically insignificant 10-20% reductions in the normal ~40% increase in arteriolar diameter accompanying hypoglycemia. However, combined Pro-7-NI was accompanied by a >80% reduction in the hypoglycemia-induced dilation. On the other hand, the combination of intravenous Pro and topical ARR-17477 did not affect the hypoglycemia response. In the presence of TTX, the pial arteriolar response to hypoglycemia was lost completely. These results suggest that 1) beta-ARs and nNOS-derived NO interact in contributing to hypoglycemia-induced pial arteriolar dilation; 2) the interaction does not occur in the vicinity of the arteriole; and 3) the vasodilating signal is transmitted via a neuronal pathway.

Synaptic control of motoneuron excitability in rodents: from months to milliseconds

1. Motoneurons (MN) shape motor patterns by transforming inputs into action potential output. This transformation, excitability, is determined by an interaction between synaptic inputs and intrinsic membrane properties. Excitability is not static, but changes over multiple time scales. The purpose of the present paper is to review our recent data on synaptic factors important in the dynamic control of MN excitability over time scales ranging from weeks to milliseconds. 2. Developmental changes in modulation of MN excitability are well established. Noradrenergic potentiation of hypoglossal (XII) MN inspiratory activity in rhythmically active medullary slice preparations from rodents increases during the first two postnatal weeks. This is due to increasing alpha 1- and beta-adrenoceptor excitatory mechanisms and to a decreasing inhibitory mechanism mediated by alpha 2-adrenoceptors. Over a similar period, ATP potentiation of XII inspiratory activity does not change. 3. Motoneuron excitability may also change on a faster time scale, such as between different behaviours or different phases of a behaviour. Examination of this has been confounded by the fact that excitatory synaptic drives underlying behaviour can obscure smaller concurrent changes in excitability. Using the rhythmically active neonatal rat brain-stem-spinal cord preparation, we blocked excitatory inspiratory drive to phrenic MN (PMN) to reveal a reduction in PMN excitability specific to the inspiratory phase that: (i) arises from an inhibitory GABAergic input; (ii) is not mediated by recurrent pathways; and (iii) is proportional to and synchronous with the excitatory inspiratory input. We propose that the proportionality of the concurrent inhibitory and excitatory drives provides a means for phase-specific modulation of PMN gain. 4. Modulation across such diverse time scales emphasizes the active role that synaptic factors play in controlling MN excitability and shaping behaviour.

Welfare during stunning and slaughter of poultry

This paper describes research on the electrical stunning of poultry and the problems of achieving an effective humane stun with water bath stunners. The welfare and meat quality advantages of using gas mixtures to stun and kill birds are then described. The evidence strongly suggests that chickens and turkeys can be killed very humanely using either 90% argon in air or a mixture of 30% carbon dioxide and 60% argon in air.

Developmental modulation of mouse hypoglossal nerve inspiratory output in vitro by noradrenergic receptor agonists

The ontogeny of the noradrenergic receptor subtypes modulating hypoglossal (XII) nerve inspiratory output was characterized. Noradrenergic agents were locally applied over the XII nucleus of rhythmically active medullary slice preparations isolated from mice between zero and 13 days of age (P0-P13) and the effects on XII inspiratory burst amplitude quantified. The alpha1 receptor agonist phenylephrine (PE, 0.1-10 microM) produced a dose-dependent, prazosin-sensitive (0.1-10 microM) increase in XII nerve inspiratory burst amplitude. The magnitude of this potentiation increased steadily from a maximum of 15+/-8% in P0 mice to 134+/-4% in P12-P13 mice. The beta receptor agonist isoproterenol (0.01-1.0 mM) produced a prazosin-insensitive, propranolol-sensitive potentiation of XII nerve burst amplitude. The isoproterenol-mediated potentiation increased with development from 27+/-5% in P0-P1 slices, to 37+/-3% in P3 slices and 45+/-4% in P9-P10 slices. The alpha2 receptor agonist clonidine (1 mM) reduced XII nerve inspiratory burst amplitude in P0-P3 slices by 29+/-5%, but had no effect on output from P12-P13 slices. An alpha2 receptor-mediated inhibition of inspiratory activity in neonates (P0-P3) was further supported by a 19+/-3% reduction in XII nerve burst amplitude when norepinephrine (NE, 100 microM) was applied in the presence of prazosin (10 microM) and propranolol (100 microM). Results indicate that developmental increases in potentiating alpha1 and, to a lesser extent, beta receptor mechanisms combine with a developmentally decreasing inhibitory mechanism, most likely mediated by alpha2 receptors, to determine the ontogenetic time course by which NE modulates XII MN inspiratory activity.

Alpha 1-adrenoceptor blockade increases behavioral deficits in traumatic brain injury

Experimental enhancement of noradrenergic activity following traumatic brain injury (TBI) accelerates behavioral recovery if performed at a time when brain norepinephrine (NE) turnover is decreased. But, since NE turnover is markedely increased immediately after TBI, the present study was undertaken to evaluate the effect of modulating these early changes in NE metabolism on recovery of function. Rats were pretrained on a modified beam walking task. Thirty minutes prior to unilateral somatosensory cortex contusion they were treated with a NE reuptake blocker [desmethy-limipramine (DMI); 10 mg/kg, ip, n = 6] or an alpha 1-adrenoreceptor antagonist [prazosin (PRZ); 3 mg/kg, ip, n = 6]. PRZ pretreatment markedly worsened beam walking performance throughout the 3 weeks following injury, whilst DMI pretreatment did not affect performance compared to injured controls (n = 4). Despite the marked behavioral deficits, PRZ-treated animals showed no apparent worsening of histological damage (n = 11 per group) and lesion size was the same in all groups. In separate experiments (n = 4 per group), PRZ lowered basal blood pressure and prevented the rise in pressure immediately following TBI. However, blood pressures in the three groups came to the same level within 20 sec following TBI. This suggest that the action of PRZ was not simply due to hypotension-induced ischemia. It is possible that blockade of alpha 1-adrenoreceptors in the immediate posttrauma period leads to enhancement of excitatory neurotransmission, which exacerbates behavioral deficits.

Synergistic interactions between noradrenaline and glutamate in cytosolic calcium influx in cultured visual cortical neurons

In primary neuronal cultures derived from the visual cortex of embryonic day 16-18 rats, intracellular free calcium concentration, [Ca2+]i, was increased by bath application of glutamate in a dose-dependent manner. Noradrenaline applied alone had relatively small effects. However, when glutamate concentrations eliciting modest increases in [Ca2+]i were applied together with 1 microM noradrenaline, the increase in [Ca2+]i could be enhanced by a factor of up to eight. The synergistic effect was seen in 147 neurons out of a total of 215 cells observed in 54 experiments. The observed enhancement was much more obvious at low doses of glutamate than with higher doses, augmenting all submaximal calcium responses to similar asymptotic levels. 2-Amino-5-phosphonovalerate (APV), the NMDA receptor antagonist, completely blocked the adrenergic enhancing effect (29/29 cells in 8 experiments). Among the antagonists specific to alpha 1, alpha 2 and beta subtypes of adrenoceptors, the beta antagonist propranolol most completely blocked the enhancing effect (13/14 cells in 4 experiments, reducing the effect by an amplitude of 90%). The involvement of the beta receptor pathway was further supported by the ability of a cAMP analog to mimic the enhancing effect of noradrenaline. On the other hand, an alpha 1 blocker showed no effect and an alpha 2 blocker showed only a relatively small effect. These results suggest that receptors for noradrenaline and glutamate colocalize on postsynaptic cortical cells and that adrenergic modulation of glutamate induced calcium influx most likely operate through the beta receptor pathway. It is further postulated that cortical ocular dominance plasticity may be at least partially implemented via a calcium dependent cascade.