Electrically evoked noradrenaline release in the rat hypothalamic paraventricular nucleus studied by in vivo electrochemistry: autoregulation by alpha-2 receptors

α1 and α2-adrenoceptors in the medial amygdaloid nucleus modulate differently the cardiovascular responses to restraint stress in rats

Medial amygdaloid nucleus (MeA) neurotransmission has an inhibitory influence on cardiovascular responses in rats submitted to restraint, which are characterized by both elevated blood pressure (BP) and intense heart rate (HR) increase. In the present study, we investigated the involvement of MeA adrenoceptors in the modulation of cardiovascular responses that are observed during an acute restraint. Male Wistar rats received bilateral microinjections of the selective α1-adrenoceptor antagonist WB4101 (10, 15, and 20 nmol/100 nL) or the selective α2-adrenoceptor antagonist RX821002 (10, 15, and 20 nmol/nL) into the MeA, before the exposure to acute restraint. The injection of WB4101 reduced the restraint-evoked tachycardia. In contrast, the injection of RX821002 increased the tachycardia. Both drugs had no influence on BP increases observed during the acute restraint. Our findings indicate that α1 and α2-adrenoceptors in the MeA play different roles in the modulation of the HR increase evoked by restraint stress in rats. Results suggest that α1-adrenoceptors and α2-adrenoceptors mediate the MeA-related facilitatory and inhibitory influences on restraint-related HR responses, respectively.

Meal pattern analysis of macronutrient intake after PVN norepinephrine and peripheral clonidine administration

Norepinephrine (NE) injected into the paraventricular nucleus (PVN) of the hypothalamus of rats is a potent stimulant of food intake, more specifically ingestion of the carbohydrate nutrient. In 2 experiments of the present study, this effect was found to be dose-dependent, and the effectiveness of NE in potentiating total food consumption was greatly reduced when the carbohydrate diet was removed. In addition, experiments using a computer-automated data acquisition apparatus were performed to characterize, in detail, the impact of PVN injection of NE and peripheral administration of the alpha2-noradrenergic agonist clonidine (CLON) on the macrostructure of feeding behavior in animals given 3 pure macronutrient diets. These 2 compounds, injected at the onset of the nocturnal feeding cycle, had very similar effects on meal patterns, with both affecting nutrient intake by increasing meal size and duration rather than by increasing meal frequency. They both affected primarily the first meal of the dark cycle, selectively enhancing carbohydrate ingestion by increasing Kcal intake, percent composition in the total diet and feeding time, and also by decreasing the satiating impact of this macronutrient. These stimulatory effects of NE and CLON on carbohydrate ingestion during the first meal were followed by complete recovery over the next 1 to 2 hours after injection. In addition to these predominant effects on carbohydrate intake, PVN NE at the highest doses tested (10 and 20 nmoles) produced a small increase in fat intake, whereas peripheral CLON actually decreased intake of fat and protein over the 12-hour cycle. The similarities in the impact of NE and CLON on carbohydrate feeding patterns support the hypothesis that both agonists may be acting via the same PVN alpha2-noradrenergic system controlling ingestion of the carbohydrate-rich meals which predominate at dark onset.

Noradrenaline overflow in mouse dentate gyrus following locus coeruleus and natural stimulation: real-time monitoring by in vivo voltammetry

The pattern of catecholaminergic innervation of the dentate gyrus (DG) of the hippocampus, particularly the relatively dense and selective noradrenergic input, creates favourable conditions for real-time monitoring of noradrenaline (NA) release following stimulation of the locus coeruleus (LC) by in vivo voltammetry. Two electrochemically active species with different temporal characteristics were registered in the DG following electrical stimulation of the LC. Several approaches, including testing of anatomical and pharmacological specificity, coating of microelectrodes with Nafion and use of fast cyclic voltammetry, were used to verify the characteristics of electrochemical responses. The first sharp peak that appeared immediately during stimulation was definitely associated with NA overflow. The second late peak was possibly attributable to ascorbic acid. We examined the characteristics of alpha-2 adrenoceptor regulation of NA release in the DG, and showed for the first time that noradrenergic terminals resemble dopaminergic terminals in their mechanisms of increasing the refilling rate of the readily releasable pool following stimulation repeated at short intervals. Amperometric registration of NA in the DG was complicated by interference with electrical activity of hippocampus. This interference could be used, after appropriate filtration, for simultaneous recording from the same microelectrode of NA release and electrical activity of the hippocampus.

Enhanced tail pinch-induced activation of catecholamine metabolism in the pericerulean area of RU 24722-treated rats

Our study was devoted to determine in freely moving rats whether the increase in tissue concentration of tyrosine hydroxylase (TH) elicited by a single administration of RU 24722 could modify the catecholaminergic reactivity of neuronal processes present in the rostrolateral part of the pericerulean area (r-lPCA) in response to tail pinch. Catecholaminergic activity was monitored by measuring in vivo the concentration of dopamine metabolite 3,4-dihydroxyphenylacetic acid (DOPAC) using microdialysis coupled to HPLC detection. In this study, the microdialysis probe was implanted at a sufficient distance from the lateral border of rostral nucleus locus ceruleus (LC) to avoid a large contribution of the noradrenergic cell bodies in the measurements performed. We first evidenced that DOPAC measured in the r-lPCA indicated the functional state of catecholaminergic metabolism in neuronal processes (dendrites and fibers) laying in this region. We also showed that the enhancement of TH protein concentration in the r-lPCA following RU 24722 treatment supported an increased in vivo catecholaminergic metabolism in this region. Furthermore, catecholaminergic metabolism response to tail pinch was potentiated in animals with greater TH tissue concentration. Thus, our study reveals that the modulation of both TH concentration and catecholaminergic metabolism in the r-lPCA may be critical in the functioning of cells and neuronal elements present in this region, notably in adaptive responses to noxious stimuli.

Imidazoline2 (I2) receptor- and alpha2-adrenoceptor-mediated modulation of hypothalamic-pituitary-adrenal axis activity in control and acute restraint stressed rats

Central noradrenaline regulates the activity of the hypothalamic-pituitary-adrenal (HPA) axis and the neuroendocrine response to stress. alpha2-adrenoceptors and imidazoline2 (I2) receptors modulate the activity of the central noradrenergic system. The present set of experiments investigated the role of alpha2-adrenoceptors and I2 receptors in the regulation of HPA axis activity under basal conditions and during exposure to the acute psychological stress of restraint. Three separate experiments were carried out in which rats were given an i.p. injection of either saline vehicle, the combined alpha2-adrenoceptor antagonist and I2 receptor ligand idazoxan (10 mg/kg), the selective I2 receptor ligand BU224 (2.5 or 10 mg/kg) or the selective alpha2-adrenoceptor antagonist RX821002 (2.5 mg/kg) with or without restraint stress. Drugs were administered immediately prior to restraint of 60 min duration. Blood was sampled pre-injection, 30, 60 and 240 min post-injection and plasma corticosterone was measured by radioimmunoassay. In experiment 1, idazoxan increased plasma corticosterone levels in naive animals and potentiated the corticosterone response to acute restraint stress. In experiment 2, BU224 administration increased plasma corticosterone levels in a dose-related manner in naive rats. The results of experiment 3 indicated that RX821002 also elevated plasma corticosterone levels in naive rats, however, only BU224 potentiated the corticosterone response to restraint stress. These studies suggest that both alpha2-adrenoceptors and I2 receptors play a role in modulating basal HPA axis activity and that I2 receptors may play a more important role than alpha2-adrenoceptors in modulating the HPA axis response to the acute psychological stress of restraint.

In vivo monitoring of evoked noradrenaline release in the rat anteroventral thalamic nucleus by continuous amperometry

Continuous amperometry coupled with untreated carbon-fibre electrodes was used in anaesthetized rats to measure the noradrenaline release evoked in the anteroventral thalamic nucleus by electrical stimulation of the dorsal noradrenergic bundle. As expected, the variations in the oxidation current detected in the anteroventral thalamic nucleus exhibited the characteristics of the in vivo noradrenaline release. They were closely correlated with stimulation and consistent with the anatomy of the noradrenergic system involved. They were abolished by the ejection of tetrodotoxin in the vicinity of the carbon-fibre electrode, diminished by clonidine, an alpha-2 agonist, and restored by yohimbine, an alpha-2 antagonist. Furthermore, the time course of these variations was dramatically increased by desipramine, a specific noradrenaline reuptake blocker. In contrast, neither dopamine nor serotonin reuptake blockers, nor the monoamine oxidase inhibitor pargyline were able to alter them. The main advantage of the present approach is its excellent time resolution. We show here for the first time that after single pulse stimulation, noradrenaline is released and eliminated in 118 milliseconds, this time lapse corresponding to the maximal period beyond which subsequent noradrenaline releases could not add up. These observations are in good agreement with the physiological relationship previously observed between impulse flow and noradrenaline overflow.

Mechanism of triazolo-benzodiazepine and benzodiazepine action in anxiety and depression: behavioral studies with concomitant in vivo CA1 hippocampal norepinephrine and serotonin release detection in the behaving animal

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 CA1 region of hippocampus in the freely moving and behaving, male, Sprague Dawley laboratory rat. 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. 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 CA1 region of hippocampus in the freely moving and behaving rat. 4. Adinazolam initially increased NE release and then decreased NE release in CA1 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. 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. 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.

Alprazolam, diazepam, yohimbine, clonidine: in vivo CA1 hippocampal norepinephrine and serotonin release profiles under chloral hydrate anesthesia

1. Although the GABA-A receptor complex has been the main focus of anti-anxiety therapy, the neural interaction in the septohippocampal circuit between GABA-A and the neurotransmitter, 5-HT, compels a study of the monoamine, 5-HT, in anxiety as well. 2. Neurochemistry for anxiety is also intimately involved with the neurotransmitter, NE. Indeed, 5-HT is a component of the dorsal ascending noradrenergic bundle and both neurotransmitters, NE and 5-HT, have been implicated in clinical depression. 3. In vivo microvoltammetric studies were performed using miniature carbon based sensors to detect NE release and concurrent 5-HT release, with 2 separate neural electrochemical signals, within CA1 region of hippocampus, in the chloral hydrate anesthetized rat. 4. Time course studies showed that both the triazolobenzodiazepine (TBZD), alprazolam, and the benzodiazepine (BZD), diazepam, decreased hippocampal NE release. 5. The in vivo and on line neurochemical profile of hippocampal 5-HT release for alprazolam differed from that of diazepam, i.e. alprazolam increased hippocampal 5-HT release, whereas diazepam decreased hippocampal 5-HT release. 6. Time course studies showed that the alpha 2-adrenergic antagonist, yohimbine, an anxiogenic agent, increased both NE and 5-HT release in CA1 region of hippocampus; the alpha 2-adrenergic agonist, clonidine, decreased NE release and increased 5-HT release in the same region. 7. Neither the profile for the TBZD, alprazolam, nor that of the BZD, diazepam, mimicked the neurochemical profile for the anxiogenic agent, yohimbine; the neurochemical profile for the TBZD, alprazolam, was similar to that of the alpha 2-adrenergic agonist, clonidine. 8. Interestingly, alprazolam's hippocampal 5-HT/NE interaction is similar to clonidine's 5-HT/NE action at alpha 2-adrenergic autoreceptors, resulting in enhanced 5-HT release. 9. Enhanced 5-HT release in hippocampus, exhibited by the atypical TBZD, alprazolam, and not by the typical BZD, diazepam, may be an underlying mechanism for the antidepressant activity exhibited by alprazolam.

The role of alpha-2 adrenoceptors in the regulation of oxytocin neurones in the suckled rat

The role of alpha-2 adrenoceptors in the milk-ejection reflex was investigated by making electrophysiological recordings from oxytocin neurones in the supraoptic nucleus of urethane-anaesthetised rats. Systemic administration of the alpha-2 adrenoceptor antagonist. Idazoxan (0.5 mg/kg, i.v.), temporarily suppressed OT cell bursting activity, while having no consistent action on basal neuronal activity. Clonidine (25 micrograms/kg, i.v.) caused an immediate increase in the frequency and amplitude of oxytocin cell bursting, coincident with a fall in basal activity. A higher dose of clonidine (50 micrograms/kg, i.v.), inhibited both bursting and basal activity. These results indicate that alpha-2 adrenoceptors are essential for the normal functioning of the milk-ejection reflex and may be involved in the facilitatory and inhibitory regulation of suckling-evoked bursting in oxytocin neurones.

High sensitivity measurement of brain catechols and indoles in vivo using electrochemically treated carbon-fiber electrodes

The combination of electrochemically treated carbon-fiber electrodes with DPV, DNPV or DPA represents a wide range of possibilities. As shown in this review, the choice of treatment and measurement technique depends on the purpose. As regards in vivo monitoring of 5-HIAA or DOPAC from very small brain nuclei, electrochemically treated carbon-fiber electrodes appear very potent and inexpensive. The main limitation of the established electrochemical techniques, including those discussed here, is that the unequivocal measurement of the basal extracellular neurotransmitter level cannot be achieved unless animals are treated with pargyline. On the other hand, this monitoring is feasible with in vivo dialysis. Therefore, electrochemical techniques, on the one hand, and in vivo dialysis, on the other hand, present different advantages. The former are much more potent than the latter in two respects. First, due to the much smaller size of the sensor, electrochemical techniques are more suitable for studying small brain nuclei. Second, since electrochemical techniques exhibit a better temporal resolution, they are recommended for investigating the relationship between impulse flow and neurotransmitter release. However, when high anatomical or temporal resolution is not required, in vivo dialysis is more suitable for recording the basal monoamine release.

In vivo microdialysis of noradrenaline overflow: effects of alpha-adrenoceptor agonists and antagonists measured by cumulative concentration-response curves

1. The purpose of the present study was to compare the effects of several alpha-adrenoceptor agonists and antagonists on cerebral cortical overflow of endogenous noradrenaline (NA) in freely moving rats. One or two days after the implantation of transcerebral dialysis tubes in the frontoparietal cortex, extracellular NA levels were monitored on-line with high performance liquid chromatography and electrochemical detection. The drugs were applied locally via the dialysis membrane, and effects on NA overflow were determined in cumulative concentration-response curves. 2. The average basal cortical NA overflow of all experiments was 0.25 pg min-1. The alpha 2-adrenoceptor agonists caused a concentration-dependent decrease in NA levels. UK-14,304 was the most potent and B-HT 933 the least potent agonist. The maximal decrease in NA overflow was to 10-15% of control levels after UK-14,304 or moxonidine, to 30% after clonidine and to 50% after B-HT 933 administration. Continuous activation of the presynaptic alpha 2-adrenoceptor with 10(-6) M UK-14,304 caused a decrease in NA levels to 40-50% of basal levels. This decrease was reached within 1 h and remained stable for the entire 3 h measurement period. The alpha 1-adrenoceptor agonists, phenylephrine and methoxamine, induced an increase in NA levels to 225% and 300%, respectively, at a concentration of 10(-3) M. 3. Local application of alpha 2-adrenoceptor antagonists caused an increase in NA levels, with idazoxan being more potent than piperoxan. Yohimbine did not cause any significant change. 4. All drugs used in these in vivo experiments had in vitro recoveries across the dialysis membrane between 10 and 20%. 5. We conclude that microdialysis with local drug application is suitable for the comparison of the pharmacological effects of drugs with affinity for alpha-adrenoceptors on cortical NA overflow in vivo,provided that the passage across the membrane is equal for the different drugs.

Principles of voltammetry and microelectrode surface states

In vivo voltammetry is approaching the end of its second decade as a technique to explore extracellular concentrations in the brain. The issues of selectivity and sensitivity, which caused considerable discussion and confusion in the early 1980s, are now resolved. It is clear that in vivo voltammetry and dialysis are complimentary tools to understand neurotransmitter dynamics. The two chief advantages of voltammetry compared to dialysis, improved temporal resolution and reduced tissue damage, make this technique exceptionally well suited for providing information which is complementary to that obtained by single-unit recording and is uniquely capable of providing information on the short-term regulation of extracellular levels of biogenic amines.

Alpha 2-adrenoceptor modulation of A1 noradrenergic neuron input to supraoptic vasopressin cells

The A1 noradrenaline (NA) cell group of the caudal medulla provides a direct excitatory input to supraoptic nucleus (SON) vasopressin (VP) cells. We have now investigated the possibility that NA released from A1 terminals acts presynaptically to modulate A1 input to VP cells. Initial experiments done in pentobarbitone anaesthetized rats established that SON application of NA excited VP cells but also depressed their response to activation of the A1 input. Moreover, the latter effect was mimicked by the alpha 2-adrenoceptor agonist clonidine and antagonised by intravenous administration of the alpha 2-adrenoceptor antagonist yohimbine. Further studies showed that yohimbine also prevented the relative decline in synaptic excitation of VP cells normally observed as A1 activation frequency increases. These data are consistent with the proposal that NA, released from the SON terminals of A1 NA cells, acts via alpha 2-adrenoceptors to depress A1 transmitter release and thus A1 influence on VP cells.

Real-time monitoring of electrically stimulated norepinephrine release in rat thalamus: I. Resolution of transmitter and metabolite signal components

Electrical stimulation of an ascending path of the locus ceruleus-norepinephrine system was used to elicit release of norepinephrine at noradrenergic terminal fields of the rat thalamus. Overflow into the extracellular fluid space was measured by fast in vivo chronoamperometry. At pretreated carbon fibers, the electrochemical signal consists of a sharp peak of approximately 20-30 s duration followed by a slower, plateau-like decay to baseline. The peak, characterized by a variety of pharmacological manipulations and dialysis perfusion, is primarily due to norepinephrine. The plateau was shown to correspond to metabolite efflux of 3,4-dihydroxy-phenylacetic acid. By varying the degree of electrochemical pretreatment, the response time and sensitivity of the fibers can be tuned to follow the entire signal or to select the separate components for detailed evaluation. This approach can be used to provide new information on the spatial and temporal characteristics of stimulated neurotransmitter release.

Alpha 2- and beta-adrenergic stimulation of corticosterone secretion in rats

Bilateral injection of 6-hydroxydopamine into the medial forebrain bundle (MFB) significantly decreased monoamine concentrations in the hypothalamus. The noradrenaline and serotonin content of the paraventricular nucleus (PVN) was also significantly reduced. These drastic decreases in neurotransmitter concentration did not alter basal secretion of corticosterone. Isoproterenol, a beta-adrenoceptor agonist (1 mg/kg, i.p.), significantly stimulated corticosterone release in saline and MFB lesioned rats. This stimulation did not differ significantly between the two groups. Clonidine, an alpha 2-adrenoceptor agonist, injected either intraperitoneally or intracerebrally just dorsal to the PVN, caused a dose-dependent increase in corticosterone secretion. The stimulation of corticosterone release by clonidine (250 micrograms/kg, i.p.) was antagonised by the selective alpha 2-adrenoceptor antagonist, yohimbine (1 mg/kg, i.p.) and significantly reduced by the MFB lesion. These results suggest that corticosterone secretion is stimulated by activation of alpha 2-adrenoceptors which occur on noradrenergic nerve terminals in the PVN.

In vivo noradrenaline release evoked in the anteroventral thalamic nucleus by locus coeruleus activation: an electrochemical study

The anteroventral thalamic nucleus is innervated by noradrenergic terminals exclusively originating in the locus coeruleus, a densely packed cell group located in the dorsotegmental part of the pons. In urethane-anaesthetized rats, electrical stimulations of locus coeruleus axons (dorsal noradrenergic bundle; 14 Hz, 20 s) evoked a rapid increase in the signal (catechol oxidation current) measured within the anteroventral thalamic nucleus by the use of carbon fibre electrodes combined with electrochemistry. This effect was reproducible and immediately reversible. Evoked changes in this current were found to be due to oxidation of noradrenaline released from terminals. The amplitude of the evoked noradrenaline release varied non-linearly with the frequency of stimulation. We investigated the influence of locus coeruleus activation on noradrenaline release measured in the anteroventral thalamic nucleus every second by means of differential pulse amperometry: (i) chemical activation of locus coeruleus by local injection of glutamate (0.2-0.8 nmol) immediately and consistently evoked noradrenaline release in a dose-dependent manner; and (ii) peripheral stimulation of the sciatic nerve (20 s)--known to enhance the firing rate of locus coeruleus neurons-evoked a noradrenaline release similar to that produced by a stimulation of the dorsal noradrenergic bundle at 8-10 Hz. Pharmacological and kinetic characteristics of the noradrenaline release were the same for central or peripheral stimulation of locus coeruleus neurons. Our results indicate that in vivo electrochemistry, because of its sensitivity and its high space and time resolution, is well suited for studies of evoked noradrenaline release from locus coeruleus terminals. This approach allowed us to describe the characteristics of central noradrenaline release evoked by central and peripheral stimulations of short duration. In particular, we observed a very close relationship between impulse flow and evoked noradrenaline release.

Does rilmenidine act in vivo on central α2-adrenoceptors modulating noradrenaline release?

Noradrenaline release evoked by electrical stimulation was recorded in the rat hypothalamus by in vivo electrochemistry. Rilmenidine (0.3-10 mg kg-1 i.v.) did not diminish this evoked release while clonidine induced a dose-dependent decrease. These results further suggest that the antihypertensive action of rilmenidine is not mediated by central alpha 2-adrenoceptors and might explain why, unlike clonidine, rilmenidine does not have sedative effects.

Adinazolam affects biogenic amine release in hippocampal CA1 neuronal circuitry

The new triazolobenzodiazepine, adinazolam, which has dual anxiolytic and antidepressant activities, was studied for its effects on hippocampal CA1 norepinephrine and serotonin release in chloral hydrate-anesthetized rats, with in vivo voltammetry. Norepinephrine signals were further characterized in vivo by the detection of a significantly increased norepinephrine signal (mean = 25.8%) (p less than 0.003) after intraperitoneal administration of the alpha 2 adrenoreceptor antagonist, yohimbine, and by the detection of a significantly decreased norepinephrine signal (mean = 20.1%) (p less than 0.037) after intraperitoneal administration of the alpha 2 adrenoreceptor agonist, clonidine. Time course studies showed that the anxiolytic-antidepressant drug adinazolam (10 mg/kg IP) significantly decreased hippocampal norepinephrine release (mean = 26.2%) (p less than 0.007). The norepinephrine signal was further significantly decreased by adinazolam (mean = 16.4%) (p less than 0.009) after an additional 2 mg/kg IP injection. Serotonin release, which was detected with norepinephrine in sequence, was also significantly decreased by adinazolam (10 mg/kg IP) (mean = 22.4%) (p less than 0.002). The supplemental dose of adinazolam (2 mg/kg IP), however, did not significantly alter serotonin release any further (p less than 0.307). The findings show that the mechanism of action of adinazolam occurs simultaneously on presynaptic release mechanisms for norepinephrine and for serotonin in CA1 region of hippocampus. These findings implicate that noradrenergic and serotonergic release mechanisms may be responsible in part for the dual anxiolytic-antidepressant efficacy of adinazolam.

5-HT1A agonists uncouple noradrenergic somatodendritic impulse flow and terminal release

Both noradrenergic (NE) and serotonergic (5-HT) systems have been implicated in anxiety and depression, as well as in the therapeutic actions of drugs treating these conditions. We have used microelectrode recordings of nerve cell impulse frequencies and in vivo voltammetric recordings of monoamine release to evaluate effects of the arylpiperazine 5-HT1A anxiolytics, buspirone and ipsapirone. Both buspirone and ipsapirone significantly depressed 5-HT neuronal firing rates in dorsal raphe (DR), but significantly increased NE neuronal firing rates in locus coeruleus (LC). In CA1 region of hippocampus, both buspirone and ipsapirone significantly depressed NE release with potencies greater than those required for the significant depression of 5-HT release. It is concluded that, contrary to the belief that the 5-HT1A arylpiperazines act primarily through 5-HT mechanisms, alterations in NE function may be critically important for their therapeutic effects, just as is the case for the benzodiazepine anxiolytics and the tricyclic antidepressants.