Hippocampal Norepinephrine Research Articles

Effect of neostigmine on the hippocampal noradrenaline release: role of cholinergic receptors.

The effect of the cholinesterase inhibitor neostigmine on hippocampal noradrenaline (NA) release was studied using in vivo microdialysis. Local application of neostigmine significantly increased the release of NA. The effect was potentiated by coperfusion of the nicotinic antagonist mecamylamine but was completely blocked by the muscarinic antagonist atropine. The neostigmine-evoked NA release was not affected by the M2-selective muscarinic antagonist gallamine but was completely blocked by the M1-selective muscarinic antagonist pirenzepine. While muscarinic antagonists had no effect on the resting release of NA, mecamylamine increased it. Our data indicate that acetylcholine can stimulate the hippocampal NA release via M1 muscarinic receptors and that a population of nicotinic receptors mediate inhibitory tone on hippocampal NA release. The fact that neostigmine is able to enhance both cholinergic and noradrenergic neurotransmission may help to understand the beneficial effect of cholinesterase inhibitors in Alzheimer's disease.

Sympathetic sprouting: no evidence for muscarinic modulation of noradrenaline release in hippocampal slices of rats with fimbria-fornix lesions.

Lesions of the septohippocampal pathways elicit sprouting of sympathetic fibers from the superior cervical ganglion, a phenomenon which, within a few months, raises the hippocampal noradrenaline (NA) content above normal. In peripheral sympathetic fibers, the release of NA is modulated via presynaptic muscarinic receptors. Such receptors have not been detected so far on terminals of noradrenergic neurons originating in the locus coeruleus. Whether the release of NA could become sensitive to muscarinic modulation in the hippocampus following sympathetic fiber ingrowth was the major question in this experiment. The contribution of presynaptic nicotinic receptors was also studied. Slices from the ventral hippocampus (only dentate gyrus+CA3 region) of sham-operated (SHAM) and fimbria-fornix lesioned (LES) Long-Evans rats (8-10 months after surgery) were preincubated with [3H]NA and stimulated either once (S1) with 100 microM nicotine or (in parallel experiments) twice electrically (S1, S2), using conditions (six pulses 100 Hz, 2 ms, 28 mA, 4 V/chamber) that precluded autoinhibition. In experiments using electrical stimulation, the superfusion medium contained desipramine (1 microM). In LES rats, the tissue NA content had almost doubled (171% of SHAM levels), but the amount of [3H]NA taken up by the slices was unchanged, and the overflow evoked at S1 by both nicotinic and electrical stimulation was significantly reduced in comparison with SHAM rats. In both groups, the addition of oxotremorine or oxotremorine+atropine (1 microM, each) before S2 failed to affect the electrically evoked overflow of 3H. Nicotine-induced NA release was inhibited by hexamethonium (100 microM) in both groups, although significantly less potently in LES rats. Tissue activity of choline acetyltransferase was reduced in LES rats to 15% of SHAM levels and the 5-hydroxytryptamine content was also strongly diminished (38% of SHAM values). It is concluded that lesion-induced sprouting of sympathetic fibers into the hippocampus is not accompanied by the emergence of a muscarinic modulation of NA release in this tissue, and that the sensitivity of the presynaptic stimulatory effect of nicotine was modified by the lesion.

Hippocampal Neurochemical and Electrophysiological Measures from Freely Moving Rats

This paper describes surgical and recording procedures that have been developed which permit the simultaneous monitoring of levels of select neurochemicals (via microdialysis) and measures of dentate-evoked field potentials within the hippocampal formation of freely moving adult rats. To test and evaluate these procedures, they were employed to examine changes in hippocampal neurochemistry and neuronal excitability associated with the establishment and maintenance of hippocampal long-term potentiation (LTP). Measures of hippocampal norepinephrine (NE) and glutamate levels along with measures of the dentate granule cell population spike amplitude (PSA) were obtained before, during, and after tetanization of the medial perforant path using two separate tetanization paradigms. Results obtained using these new procedures in several animals indicated that changes in NE and glutamate levels were strongly correlated with increases in the dentate granule cell PSA measure obtained following tetanization. The results indicate that this newly developed procedure can be effectively used to directly examine the relationship between neurochemical and neurophysiological changes associated with hippocampal neuroplasticity.

Interleukin-2 and -6 induce behavioral-activating effects in mice

Interleukin (IL)-1, IL-2 and IL-6 influence central monoamine activity in a cytokine-specific manner. We demonstrated that whereas IL-2 increased hypothalamic and hippocampal norepinephrine (NE) utilization, and DA turnover in the prefrontal cortex, IL-6 induced profound elevations of serotonin (5-HT) and mesocortical dopamine (DA) activity in the hippocampus and prefrontal cortex [S. Zalcman, J.M. Green-Johnson, L. Murray, D.M. Nance, D.G. Dyck, H. Anisman, A.H. Greenberg, Cytokine-specific central monoamine alterations following IL-1, -2 and -6 administration, Brain Res. 643 (1994) 40–49]. IL-1, in contrast, induced a wide range of central monoamine alterations. We presently report that these cytokines also differentially influence behavior. Profound reductions in non-ambulatory and ambulatory exploration were induced in BALB/c mice following IL-1 administration. In contrast, IL-2-treated mice displayed significant increases in the time spent engaged in non-ambulatory exploration, digging, rearing (particularly the number of free rears), and in the investigation of a novel stimulus (i.e., increased number and duration of stimulus contacts). IL-6-treated mice, moreover, exhibited significant increases in the time spent engaged in ambulatory exploration, digging and rearing (particularly the number of free rears, which tended to be of short duration). Modest increases in locomotion and grooming were also observed in IL-6-treated animals. Plasma corticosterone levels did not vary significantly as a function of IL-6 treatment. Hence, cytokine-specific behavioral-activating effects were induced following administration of IL-2 and IL-6. We suggest that these effects have adaptive significance and relevance to sickness behavior; however, pathological outcomes (e.g., schizophrenia, anxious-like states, anxious depression, motor abnormalities) could develop should these cytokines be overproduced or dysregulated.

α-Conotoxin AuIB Selectively Blocks α3β4 Nicotinic Acetylcholine Receptors and Nicotine-Evoked Norepinephrine Release

Neuronal nicotinic acetylcholine receptors (nAChRs) with putative alpha3 beta4-subunits have been implicated in the mediation of signaling in various systems, including ganglionic transmission peripherally and nicotine-evoked neurotransmitter release centrally. However, progress in the characterization of these receptors has been hampered by a lack of alpha3 beta4-selective ligands. In this report, we describe the purification and characterization of an alpha3 beta4 nAChR antagonist, alpha-conotoxin AuIB, from the venom of the "court cone," Conus aulicus. We also describe the total chemical synthesis of this and two related peptides that were also isolated from the venom. alpha-Conotoxin AuIB blocks alpha3 beta4 nAChRs expressed in Xenopus oocytes with an IC50 of 0.75 microM, a kon of 1.4 x 10(6) min-1 M-1, a koff of 0.48 min-1, and a Kd of 0.5 microM. Furthermore, alpha-conotoxin AuIB blocks the alpha3 beta4 receptor with >100-fold higher potency than other receptor subunit combinations, including alpha2 beta2, alpha2 beta4, alpha3 beta2, alpha4 beta2, alpha4 beta4, and alpha1 beta1 gamma delta. Thus, AuIB is a novel, selective probe for alpha3 beta4 nAChRs. AuIB (1-5 microM) blocks 20-35% of the nicotine-stimulated norepinephrine release from rat hippocampal synaptosomes, whereas nicotine-evoked dopamine release from striatal synaptosomes is not affected. Conversely, the alpha3 beta2-specific alpha-conotoxin MII (100 nM) blocks 33% of striatal dopamine release but not hippocampal norepinephrine release. This suggests that in the respective systems, alpha3 beta4-containing nAChRs mediate norepinephrine release, whereas alpha3 beta2-containing receptors mediate dopamine release.

Intracerebroventricular infusion of CRF increases extracellular concentrations of norepinephrine in the hippocampus and cortex as determined by in vivo voltammetry

Previous studies have indicated that intracerebroventricular (i.c.v.) infusions of corticotropin-releasing factor (CRF) activate locus coeruleus (LC) noradrenergic neurons and increase the metabolism and extracellular concentrations of norepinephrine (NE) in several brain regions, suggesting increased release. To examine the temporal aspects and mechanism of the presumed release of NE, CRF was infused i.c.v. and the oxidation current was recorded using carbon fiber voltammetric electrodes placed in rat hippocampus or cortex. The CRF (1 μg, i.c.v.) caused a significant increase of oxidation current with a delay of approximately 5 min, and a peak at approximately 35 min. Similar responses were observed in the medial prefrontal cortex. The hippocampal response was markedly attenuated when CRF was infused into rats pretreated with DSP-4 to deplete NE, suggesting that the observed changes in current resulted from oxidation of NE. The increase of NE-like current did not occur when 25 μg alpha-helical CRF 9–41 (ahCRF) was injected immediately before 1 μg CRF, suggesting that the response was mediated by cerebral CRF-receptors. Subcutaneous pretreatment with the ganglionic blocker, chlorisondamine, at a dose of 3 mg/kg had no effect on the voltammetric response to CRF, but a 6 mg/kg dose completely prevented the response. The β-adrenoceptor antagonists, S-propranolol (5 mg/kg), nadolol (5 and 10 mg/kg), and timolol (5 mg/kg) attenuated the NE response to i.c.v. CRF to varying degrees. When chlorisondamine (3 μg) or nadolol (5 μg) were given i.c.v. before the CRF, the hippocampal responses were not blocked. These results suggest peripheral actions of ganglionic and β-adrenergic blockers. We conclude that peripheral autonomic mechanisms, and probably both central and peripheral β-adrenoceptors, contribute to the increased secretion of hippocampal NE in response to i.c.v. CRF.

Brain neurotransmission during peripheral inflammation.

It is now well established that an inflammatory challenge as evoked by bacterial endotoxin (LPS) induces autonomic, endocrine, and behavioral responses that are controlled by the brain. However, detailed information on the neuronal pathways and neurotransmitters involved is scarce. We used in vivo microdialysis and biotelemetry in rats to monitor hippocampal and preoptic serotonergic and noradrenergic neurotransmission, body temperature, and heart rate after an i.p. LPS injection. Moreover, free corticosterone levels were measured in the dialysates, and behavioral activity was scored by visual observation. Apart from a biphasic fever response, tachycardia, elevated free corticosterone levels, and sickness behavior, peripheral injection of LPS caused a dramatic increase in preoptic extracellular concentrations of noradrenaline, but no effect on serotonin in this structure. The increase in preoptic noradrenaline levels appears to underlie the first fever phase and may participate in hypothalamic-pituitary-adrenocorticul axis activation. In contrast, whereas LPS had only a moderate effect on hippocampal noradrenaline, a marked increase in hippocampal extracellular serotonin levels was found. Use of the interleukin (IL)-1 receptor antagonist and the cyclooxygenase inhibitor indomethacine learned that IL-1 and prostaglandins are mediators in this response. Our data show that an endotoxin challenge results in highly differentiated changes in brain neurotransmission, probably subserving the coordinate processing of immune information in circuits involved in autonomic, neuroendocrine, and behavioral regulation.

Mechanism of triazolo-benzodiazepine and benzodiazepine action in anxiety and depression: Behavioral studies with concomitant in vivo CA 1 hippocampal norepinephrine and serotonin release detection in the behaving animal

1. 1. Real time, in vivo microvoltammetric studies were performed, using miniature carbon-based sensors, to concurrently detect norepinephrine (NE) release and serotonin (5-HT) release, in 2 separate electrochemical signals, within CA 1 region of hippocampus in the freely moving and behaving, male, Sprague Dawley laboratory rat. 2. 2. Concurrently, four parameters of open-field Behavior I.E. Ambulations, Rearing, Fine Movements and Central Ambulatory behavior (a measure of anxiety reduction behavior), were assayed by infrared photobeam detection. 3. 3. Time course studies showed that the mechanism of action of the triazolobenzodiazepine (TBZD), adinazolam, (Deracyn®) is dramatically different from that of the classical benzodiazepine (BZD), diazepam (Valium®) i.e., adinazolam increased, whereas diazepam decreased, 5-HT release within CA 1 region of hippocampus in the freely moving and behaving rat. 4. 4. Adinazolam initially increased NE release and then decreased NE release in CA 1 region of hippocampus in the freely moving and behaving rat whereas diazepam only decreased the electrochemical signal for NE; the decrease in NE produced by adinazolam was greater than the decrease in NE release produced by diazepam. 5. 5. The Behavioral Activity Patterns, derived from same animal controls, simultaneously with detection of in vivo microvoltammetric signals for NE release and 5-HT release, showed that the BZD, diazepam, exhibited more potent sedative properties than did the TBZD adinazolam. 6. 6. Hippocampal 5-HT and NE release effects of the TBZD, adinazolam, concomitant with behavioral effects lends explanation to the dual anxiolytic/antidepressant properties of the TBZDs.

Nicotine induces long-lasting potentiation in the dentate gyrus of nicotine-primed rats

A challenge dose of nicotine (0.4 mg kg-1 s.c.) produced a long-lasting potentiation (LLP) of field EPSPs evoked in the dentate gyrus by stimulation of the medial perforant path of urethane-anaesthetized rats primed four weeks previously with seven daily injections of nicotine (0.8 mg kg-1 s.c.). The same dose of nicotine did not alter EPSPs evoked in rats primed with saline vehicle. Systemic injection of either mecamylamine or propranolol, 30 min before nicotine challenge, prevented induction of LLP without affecting baseline EPSPs but neither drug affected LLP when given after it was established. Since the nicotine-priming regime is known to increase tyrosine hydroxylase activity and hippocampal noradrenaline release in response to nicotine challenge, the results suggest that systemic injection of nicotine released sufficient noradrenaline in nicotine-primed rats to induce a beta-adrenoceptor-mediated LLP.

Neuropharmacological Effects of Low and High Doses of Repeated Oral Dexfenfluramine in Rats: A Comparison with Fluoxetine

CACCIA S., S. CONFALONIERI, A. BERGAMI, C. FRACASSO, M. ANELLI AND S. GARATTINI. Neuropharmacological effects of low and high doses of repeated oral dexfenfluramine in rats. A comparison with fluoxetine. PHARMACOL BIOCHEM BEHAV 57 [4] 851–856, 1997.—The neuropharmacological effects of repeated oral doses of dexfenfluramine (DF; 1.25–10 mg/kg, twice daily for 21 days) were examined in rats and related to the drug brain levels. Results were compared with fluoxetine (FL) given at similar doses relative to its anorectic ED 50. Both drugs dose-dependently slowed body weight gain and reduced brain serotonin (5-HT). However, at 1.25 mg/kg DF caused only a slight and transient decrease in cortical 5-HT. Comparable doses of FL (6.25–12.5 mg/kg) lowered 5-HT more than DF, besides slightly reducing striatal dopamine. At higher doses DF markedly reduced 5-HT in all regions, and to a lesser extent noradrenaline in hippocampus. There was a negative relationship between 5-HT and log total active drug levels and the indole was approximately halved at drug levels about 50 times lower with DF than FL. However, the ratio between drug levels causing marked 5-HT reductions and those considered anorectic was similar for DF and FL because brain levels at the anorectic ED 50 were higher with FL than DF. Long-lasting reductions of 5-HT were also observed but recovery was only consistently slow beginning from 5 mg/kg DF. Comparable doses of FL could not be used because its general toxicity leads to the death of rats after only 2–4 multiples of its anorectic ED 50.

Nicotinic acetylcholine receptor antagonist effect of fluoxetine in rat hippocampal slices

We compared the effect of mecamylamine and fluoxetine on the hippocampal noradrenaline (NA) release evoked by nicotine in vitro. Nicotine (100 μM) increased the basal release of [ 3H]NA from rat hippocampal slices. This effect was blocked by the potent nicotinic antagonist mecamylamine in a dose-dependent manner (IC 50=0.19 μM). The selective serotonin reuptake inhibitor (SSRI) fluoxetine also antagonised the response to nicotine in a dose-dependent manner with a similar strength (IC 50=0.57 μM). Our data indicate that fluoxetine has nicotinic acetylcholine receptor antagonist effect in the central nervous system. The possible clinical significance of this finding is discussed.

Noradrenergic DSP-4 Lesions Aggravate Impairment of Working Memory Produced by Hippocampal Muscarinic Blockade in Rats

To clarify the interactions between hippocampal cholinergic and adrenergic systems in working memory function of rats, the effects of hippocampal muscarinic receptor blockade combined with noradrenaline depletion on this behavior were examined with a three-panel runway task. Intrahippocampal administration of the muscarinic receptor antagonist scopolamine at a dose of 3.2 μg/side significantly increased the number of errors (attempts to pass through two incorrect panels of the three panel-gates at four choice points) in the working memory task, whereas the 0.32 μg/side dose of scopolamine did not affect working memory errors. Administration of the noradrenergic neurotoxin N-(2-chloroethyl)- N-ethyl-2-bromobenzylamine (DSP-4) at 50 mg/kg IP caused a marked reduction in hippocampal noradrenaline concentration, but it had no effect on working memory errors. Intrahippocampal administration of 0.32 μg/side scopolamine, the behaviorally ineffective dose in intact rats, significantly increased the number of working memory errors in the noradrenaline-depleted animals. These results suggest that hippocampal muscarinic/noradrenergic interactions are involved in neural processes mediating working memory function of rats.

Opiate modulation of striatal dopamine and hippocampal norepinephrine release following morphine withdrawal.

When opiates are abruptly withdrawn after chronic treatment, increases in hippocampal noradrenergic function are observed which are accompanied by decreases in striatal dopamine release. The latter effects have to shown to persist for several weeks following the onset of opiate withdrawal. We examined the long-term effects of opiate withdrawal on 4-aminopyridine and potassium stimulated release of striatal dopamine and hippocampal norepinephrine. Tissue samples were obtained either from rats that had been exposed to opiate withdrawal following a seven day morphine infusion or sham treated control subjects. At 48 hours after the onset of withdrawal (cessation of morphine infusions), slices were loaded with [3H] neurotransmitter, washed extensively, and exposed to different drug treatments. 4-aminopyridine induced concentration related increases in striatal dopamine release, which was 36% calcium independent. Similar values for fractional release of striatal dopamine were obtained in morphine withdrawn and control subjects, for both potassium and 4-aminopyridine induced release. In addition, thresholds for 4-aminopyridine or potassium induced release of striatal dopamine did not differ between control and morphine withdrawn subjects. Treatment with 1.0 microM morphine sulfate potentiated potassium evoked release of norepinephrine to an equal extent in both morphine withdrawn and sham treated hippocampal tissue. Exposure to a threshold concentration of potassium (8.0 mM), stimulated increased release of hippocampal norepinephrine in a significantly greater fraction of tissue samples obtained from morphine withdrawn animals. Although these results do not support changes in striatal dopamine release following opiate withdrawal, opiate mechanisms appear to be important determinants of in vitro hippocampal norepinephrine release.

Dual effect of DMPP on the resting release of noradrenaline from rat hippocampal slices.

The effect of the nicotinic receptor agonist dimethylphenylpiperazinium iodide (DMPP) on the resting release of [3H]noradrenaline from superfused hippocampal slices was studied in rat. Continuous administration of DMPP at a concentration range of 1-100 microM increased the [3H]noradrenaline release in a dose-dependent manner. The response to DMPP was characterized by an immediate steep increase (peak response) followed by a sudden decline to a lower level that was constant with time (tall response) and still was significantly higher than the spontaneous release. Further analysis revealed that the release of noradrenaline in response to DMPP consists of two components. While nicotinic receptor antagonists (mecamylamine 10 microM, pancuronium 10 microM, pipecuronium 10 microM), the nonselective Ca-antagonist Cd2+ (125 microM) and tetrodotoxin (TTX, 1 microM) completely abolished the peak response (phase I), they had no effect on the tall response (phase II). Ca(2+)-free medium containing 1 mM EGTA also blocked phase I but in contrast with other drugs enhanced phase II. The release during phase I is subject to presynaptic feedback modulation, since the alpha 2-adrenoceptor agonist xylazine (3 microM) inhibited the DMPP-evoked stimulation of [3H]noradrenaline release, that inhibition was antagonized by a selective alpha 2-adrenoceptor antagonist, (+/-)-[7,8-(methylenedioxy)-14-alpha-hydroxyalloberbane hydrochloride [(+/-)-CH-38083] (2 microM). (+/-)-CH-38083 (2 microM) alone significantly enhanced the DMPP-evoked increase of [3H]noradrenaline release. Phase II was not effected by alpha 2-adrenergic drugs. Whereas the noradrenaline uptake blockers despramine (DMI, 1-10 microM), nisoxetine (1-10 microM), and nomifensine (10 microM) inhibited both phases, nomifensine at a concentration of 1 microM selectively blocked only phase II. Our data indicate that DMPP has a dual effect on the hippocampal noradrenaline release: phase I is a transient, nicotinic receptor-mediated exocytotic release, and phase II is a maintained, carrier-mediated process.

Modulation of hippocampal norepinephrine release by cholinergic agonists is altered by AF64A lesion.

The effect of lesioning hippocampal cholinergic neurons with the neurotoxin AF64A on the ability of cholinergic agonists to modulate stimulation-induced release of 3H-norepinephrine (NE) from rat hippocampal slices was studied. Rats received intracerebroventricular injections of either AF64A (ethylcholine mustard aziridinium, 2 nmol) or vehicle (sham operated). Six weeks after treatment, release of 3H-NE evoked by electrical stimulation (2 Hz, 2 min) in the presence or absence of cholinergic agonists and/or antagonists was measured. Activation of M2 receptors with oxotremorine (in the presence of the M1 antagonist pirenzepine) caused a small inhibition of NE release, which was abolished in hippocampi from AF64A-treated rats. The Kd for high-affinity binding of the selective M2 ligand [3H] AF-DX 384 was increased 10-fold in lesioned tissues. The M1 selective agonist McN-A-343 produced a significant enhancement of NE release, which was unchanged by AF64A lesion. Binding studies with [3H] pirenzepine showed no change in the affinity or number of M1 receptors. Nicotine also caused a significant enhancement of evoked NE release, but this effect was markedly reduced in tissues from AF64A-treated rats. AF64A treatment caused a twofold decrease in the number of [3H] nicotine binding sites. This study suggests that long-term lesion of hippocampal cholinergic neurons with AF64A alters the function of postsynaptic muscarinic M2 and nicotinic cholinergic receptors that modulate the release of NE in the hippocampus.

192 IgG-saporin lesion of basal forebrain cholinergic neurons in neonatal rats

Seven day old rats received bilateral intraventricular injections (200 ng) of the immunotoxin 192 IgG-saporin. When assayed in adulthood, these rats showed an 84% loss of hippocampal and a 52% loss of cortical choline acetyltransferase (ChAT) activity. ChAT was unaffected in the caudate. Cholinergic neurons immunoreactive (IR) for the low affinity neurotrophin receptor (P75NTR) were severely reduced throughout the basal forebrain nuclei. Cortical and hippocampal norepinephrine were increased and these areas showed ingrowth of ectopic, P75NTR and dopamine β-hydroxylase IR varicosities. These were probably sympathetic axons. No obvious forebrain dysmorphogenesis was observed and cortical thickness was unaffected. These rats showed no evidence of impaired spatial learning/memory as assessed by the Morris water maze and delayed spatial alternation. However, they were less active on the elevated plus apparatus and spent less time on the open arms, suggestive of increased timidity. 192 IgG-saporin appears to be a powerful tool to selectively lesion basal forebrain cholinergic neurons in the neonatal rat. Surprisingly, the neuromorphological and behavioral sequelae seem minimal. It may be necessary to achieve near-total neonatal destruction of forebrain cholinergic neurons before severe, lasting mnemonic effects are evident.

192 IgG-saporin lesion of basal forebrain cholinergic neurons in neonatal rats

Seven day old rats received bilateral intraventricular injections (200 ng) of the immunotoxin 192 IgG-saporin. When assayed in adulthood, these rats showed an 84% loss of hippocampal and a 52% loss of cortical choline acetyltransferase (ChAT) activity. ChAT was unaffected in the caudate. Cholinergic neurons immunoreactive (IR) for the low affinity neurotrophin receptor (P75 NTR) were severely reduced throughout the basal forebrain nuclei. Cortical and hippocampal norepinephrine were increased and these areas showed ingrowth of ectopic, P75 NTR and dopamine β-hydroxylase IR varicosities. These were probably sympathetic axons. No obvious forebrain dysmorphogenesis was observed and cortical thickness was unaffected. These rats showed no evidence of impaired spatial learning/memory as assessed by the Morris water maze and delayed spatial alternation. However, they were less active on the elevated plus apparatus and spent less time on the open arms, suggestive of increased timidity. 192 IgG-saporin appears to be a powerful tool to selectively lesion basal forebrain cholinergic neurons in the neonatal rat. Surprisingly, the neuromorphological and behavioral sequelae seem minimal. It may be necessary to achieve near-total neonatal destruction of forebrain cholinergic neurons before severe, lasting mnemonic effects are evident.

8-OH-DPAT-induced release of hippocampal noradrenaline in vivo: evidence for a role of both 5-HT 1A and dopamine D 1 receptors

Here we investigate the effects of the novel selective 5-HT 1A receptor antagonist, N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]methyl]- N-(2-pyridinyl cyclo-hexanecarboxamide (WAY 100635), and the dopamine D 1 receptor antagonist, R-(+)-8-chloro-2,3,4,5-tetrahydro-3-methyl-5-phenyl-1 H-3-benzazepin-7-ol (SCH 23390), on the increase in extracellular noradrenaline in rat hippocampus induced by the 5-HT 1A receptor agonist, 8-hydroxy-2-(di- N-propylamino)tetralin (8-OH-DPAT). 8-OH-DPAT (0.1 and 1 mg/kg s.c.) caused a dose-related increase in extracellular noradrenaline. WAY 100635 (0.3 and 1 mg/kg s.c.) did not block the release of noradrenaline induced by the higher dose of 8-OH-DPAT (1 mg/kg s.c.) but abolished the response to the lower dose (0.1 mg/kg s.c.). When administered alone, WAY 100635 (0.3 and 1 mg/kg s.c.) had no effect on extracellular noradrenaline. The postsynaptically mediated 5-HT behavioural syndrome induced by the higher dose of 8-OH-DPAT, in contrast to the increase in noradrenaline, was completely blocked by WAY 100635 (0.3 mg/kg s.c.). Finally, the noradrenaline response to 8-OH-DPAT (0.1 mg/kg s.c.) was blocked by SCH 23390 (0.5 mg/kg s.c.). Our data confirm that noradrenaline can be released by activation of 5-HT 1A receptors but show that these receptors are not tonically activated, and may be more sensitive to stimulation than classical postsynaptic 5-HT 1A receptors. A role for the dopamine D 1 receptor in the noradrenaline response to 8-OH-DPAT is also suggested.

Effects of alcohol exposure and artificial rearing during development on septal and hippocampal neurotransmitters in adult rats.

The effect of alcohol exposure during the early postnatal period in the rat on the hippocampus and septal region was investigated. The alcohol group was given 5 g/kg/day of ethanol from postnatal days 4 to 10 via an artificial rearing procedure. Control groups consisted of a gastrostomy control group that was treated in the same manner as the alcohol group, but not exposed to alcohol and a suckle control group that was reared normally by dams. Between 90 and 100 days of age, the hippocampus and septal region were assayed under nonstressed or stressed conditions using HPLC with electrochemical detection. Alcohol-exposed female rats exhibited increased hippocampal noradrenaline concentrations under stressed conditions, increased septal serotonin, and 5-hydroxyindoleacetic acid (5-HIAA) concentrations under nonstressed conditions, and decreased septal dopamine concentrations under stressed conditions. Artificially reared male rats (regardless of alcohol exposure) exhibited an increase in hippocampal noradrenaline concentrations under stressed conditions; a decrease in hippocampal 5-HIAA concentrations under nonstressed conditions; and a decrease in septal noradrenaline, serotonin, 5-HIAA, and dopamine concentrations under nonstressed conditions. The results suggest that female rats may be more susceptible to alcohol exposure during the postnatal period than male rats and that male rats may be more susceptible to the effects of artificial rearing than female rats.

Release of [3H]-noradrenaline from rat hippocampal synaptosomes by nicotine: mediation by different nicotinic receptor subtypes from striatal [3H]-dopamine release.

1. The aim of the present experiment was to characterize nicotine-evoked [3H]-noradrenaline ([3H]-NA) release from rat superfused hippocampal synaptosomes, using striatal [3H]-dopamine release for comparison. 2. (-)-Nicotine, cytisine, DMPP and acetylcholine (ACh) (with esterase inhibitor and muscarinic receptor blocker) increased NA release in a concentration-dependent manner (EC50 6.5 microM, 8.2 microM, 9.3 microM, and 27 microM, respectively) with similar efficacy. 3. Nicotine released striatal dopamine more potently than hippocampal NA (EC50 0.16 microM vs. 6.5 microM). (+)-Anatoxin-a also increased dopamine more potently than NA (EC50 0.05 microM vs. 0.39 microM), and maximal effects were similar to those of nicotine. Isoarecolone (10-320 microM) released dopamine more effectively than NA but a maximal effect was not reached. (-)-Lobeline (10-320 microM) evoked dopamine release, but the effect was large and delayed with respect to nicotine; NA release was not increased but rather depressed at high concentrations of lobeline. High K+ (10 mM) released and NA to similar extents. 4. Addition of the 5-hydroxytryptamine (5-HT) reuptake blocker, citalopram (1 microM) to hippocampal synaptosomes affected neither basal NA release nor nicotine-evoked release. 5. The nicotinic antagonist, mecamylamine (10 microM), virtually abolished NA and dopamine release evoked by high concentrations of nicotine, ACh, cytisine, isoarecolone, and anatoxin-a. Although NA release evoked by DMPP (100 microM) was entirely mecamylamine-sensitive, DMPP-evoked dopamine release was only partially blocked. Dopamine release evoked by lobeline (320 microM) was completely mecamylamine-insensitive. 6. The nicotinic antagonists dihydro-beta-erythroidine and methyllycaconitine inhibited nicotine-evoked dopamine release approximately 30 fold more potently than NA release. In contrast, the antagonist chlorisondamine, displayed a reverse sensitivity, whereas trimetaphan and mecamylamine did not preferentially block either response. None of these antagonists, given at a high concentration, significantly altered release evoked by high K+. 7. Blockade of nicotine-evoked transmitter release by methyllycaconitine and dihydro-beta-erythroidine was surmounted by a high concentration of nicotine (100 microM), but blockade by mecamylamine, chlorisondamine, and trimetaphan was insurmountable. 8. Nicotine-evoked NA release was unaffected by tetrodotoxin, whereas veratridine-evoked NA release was virtually abolished. 9. We conclude that presynaptic nicotinic receptors associated with striatal dopamine and hippocampal NA terminals differ pharmacologically. In situ hybridization studies suggest that nigrostriatal dopaminergic neurones express mainly alpha 4, alpha 5, and beta 2 nicotinic cholinoceptor subunits, whereas hippocampal-projecting noradrenaline (NA) neurones express alpha 3, beta 2 and beta 4 subunits. Pharmacological comparisons of recombinant receptors suggest that release of hippocampal NA may be modulated by receptors containing alpha 3 and beta 4 subunits.