Activity Of Catecholaminergic Neurons Research Articles

Milk consumption and bone mass

Neuronal metabolic activity was studied by in vivo electrochemistry in two brain areas of the anesthetized rat: the nucleus reticularis lateralis (NRL) region of the ventrolateral medulla oblongata - site of the hypotensive action of clonidine-like imidazolines - and the locus coeruleus (LC), which is involved in the sedative effect of these drugs. Hypotensive doses of i.v. rilmenidine (0.3 and 1.5 mg/kg), which is structurally related to clonidine, induced a dose-related inhibition of the metabolic activity of catecholaminergic neurons in the NRL region whereas higher doses (50-fold) were required to inhibit the activity of the catecholaminergic neurons in the locus coeruleus. On the other hand azepexole, another centrally acting antihypertensive drug that is not structurally related to the imidazolines failed to inhibit the neuronal metabolic activity of the RNL region when administered i.v. in hypotensive doses (1 mg/kg). Taken together, these findings suggest that the central hypotensive action of clonidine-like drugs requires the imidazoline structure or pharmacologically compatible compounds like rilmenidine. Our results also show that rilmenidine is twice as selective as clonidine for the NRL region, which contains imidazoline-preferring receptors, compared with the LC, which contains mainly α2-adrenoceptors. In conclusion, this study provides a functional confirmation of the dissociation between the therapeutic (hypotensive) and untoward (sedative) effects of rilmenidine.

Neurochemical evidence that 5-hydroxytryptaminergic neurons tonically inhibit noradrenergic neurons terminating in the hypothalamus

The medial zona incerta (MZI) and dorsomedial nucleus of the hypothalamus (DMN), which contain cell bodies and terminals of incertohypothalamic dopaminergic (DA) neurons, are densely innervated by both noradrenergic (NE) and 5-hydroxytryptaminergic (5-HT) neurons. In view of emerging anatomical and pharmacological evidence suggesting possible interactions between 5-HT and catecholaminergic neurons, the effects of experimental procedures that inhibit or disrupt 5-HT neurons on the activities of catecholaminergic neurons terminating in these regions were examined in the present study. Catecholaminergic neuronal activity was estimated by measuring catecholamine synthesis (accumulation of 3,4-dihydroxyphenylalanine [DOPA] after administration of a decar☐ylase inhibitor) and metabolism (concentrations of the dopamine metabolite 3,4-dihydroxyphenylacetic acid (DOPAC) and the norepinephrine metabolite 3-methoxy-4-hydroxyphenyleneglycol (MHPG) in the MZI and DMN of both male and female rats. Inhibition of 5-HT neurons following administration of the 5-HT 1A autoreceptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) increasedthe accumulation of DOPA in the DMN and the concentrations of DOPAC in the MZI and DMN, indicating an activation of catecholaminergic neurons in these regions. Concentrations of MHPG were increased in the MZI and DMN by 8-OH-DPAT or 5,7-dihydroxytryptamine-induced lesions of 5-HT neurons, revealing that NE neurons terminating in these regions were activated following procedures that decrease 5-HT neuronal function. Following destruction of NE neurons projecting to the MZI and DMN, 8-OH-DPAT no longer increased DOPAC concentrations in these brain regions. Taken together, these results reveal that 5-HT neurons tonically inhibit the activity of NE neurons terminating in the MZI and DMN, but do not influence the activity of incertohypothalamic DA neurons.

Activation of brainstem catecholaminergic neurons by conditioned and unconditioned aversive stimuli as revealed by c-Fos immunoreactivity

In an attempt to define areas of the brain that respond to stressors and influence immune function, we have previously identified stress-induced, c-Fos-immunoreactive areas of the diencephalon. We found that c-Fos was strongly expressed in cells of the paraventricular nuclei (some of which contain corticotropin-releasing hormone (CRH) and other hypothalamic areas directly associated with autonomic function. To further characterize the presumptive pathways mediating stress-induced immune alterations, including the assessment of brainstem catecholaminergic neuron involvement, the induction of c-Fos immunoreactivity was examined in the brainstems of rats exposed to conditioned and unconditioned, immunomodulating stimuli. In response to electric footshock (the unconditioned stimulus (US)), c-Fos immunoreactivity was strongly induced in the noradrenergic neurons of the locus ceruleus (A6), the nucleus of the solitary tract (A2/C2), the ventral lateral medulla (A1/C1), A5, and A7, as well as in unidentified neurons of the dorsal and ventral subdivisions of the periqueductal gray (PAG), and in the serotonergic neurons of the dorsal raphe nuclei. Conditioned animals re-exposed to the conditioned stimulus showed c-Fos induction in these same areas but to a lesser degree. Control animals exposed only to the conditioning stimulus (CS) (electronic tone) in the absence of the US, expressed very little, if any, c-Fos activity in the above loci except for a small degree of baseline expression in the PAG. These results further confirm the role of autonomic and endocrine pathways as mediators of the stress response and will help to more fully characterize the pathways of stress-induced immune alteration.

Contribution of catecholaminergic neurons of the dorsomedial and ventrolateral medulla oblongata to the hypotensive effect of clonidine in spontaneously hypertensive rats: in vivo voltammetric studies.

Our previous electrochemical studies in the normotensive Wistar-Kyoto (WKY) rat showed a positive correlation between the hypotensive effect of low doses of clonidine (2-10 micrograms/kg intravenously) and inhibition of the activity of catecholaminergic neurons within the brainstem, and that this action was mediated by imidazoline-preferring receptors. In the present study the possibility of a relationship between the centrally mediated hypotensive effect of clonidine and the metabolic activity of catecholaminergic neurons of the ventrolateral and dorsomedial medulla oblongata was investigated in pentobarbital-anaesthetized spontaneously hypertensive rats (SHR). Neuronal metabolic activity was monitored by in vivo electrochemistry in the nucleus reticularis lateralis region of the ventrolateral medulla and in the nucleus tractus solitarii region of the dorsomedial medulla oblongata. Hypotensive doses of intravenously administered clonidine (10 micrograms/kg) failed to inhibit the neuronal metabolic activity of the nucleus reticularis lateralis region; fivefold higher doses were required to inhibit these neurons. The low dose of clonidine (10 micrograms/kg) decreased the metabolic activity of the nucleus tractus solitarii region. Nevertheless, this effect did not appear to be correlated with a reduction in blood pressure and it was not attenuated by a prior central injection of idazoxan (5 nmol/kg intracisternally), which almost completely prevented the hypotensive and the neuronal inhibitory effects of clonidine in the nucleus reticularis lateralis region of the normotensive rat. Both the site and the mechanism of the central hypotensive action of clonidine in the SHR appear to be different from those in normotensive control WKY rats.

Selectivity of rilmenidine for the nucleus reticularis lateralis, a ventrolateral medullary structure containing imidazoline-preferring receptors

Neuronal metabolic activity was studied by in vivo electrochemistry in two brain areas of the anesthetized rat: the nucleus reticularis lateralis (NRL) region of the ventrolateral medulla oblongata - site of the hypotensive action of clonidine-like imidazolines - and the locus coeruleus (LC), which is involved in the sedative effect of these drugs. Hypotensive doses of i.v. rilmenidine (0.3 and 1.5 mg/kg), which is structurally related to clonidine, induced a dose-related inhibition of the metabolic activity of catecholaminergic neurons in the NRL region whereas higher doses (50-fold) were required to inhibit the activity of the catecholaminergic neurons in the locus coeruleus. On the other hand azepexole, another centrally acting antihypertensive drug that is not structurally related to the imidazolines failed to inhibit the neuronal metabolic activity of the RNL region when administered i.v. in hypotensive doses (1 mg/kg). Taken together, these findings suggest that the central hypotensive action of clonidine-like drugs requires the imidazoline structure or pharmacologically compatible compounds like rilmenidine. Our results also show that rilmenidine is twice as selective as clonidine for the NRL region, which contains imidazoline-preferring receptors, compared with the LC, which contains mainly α 2-adrenoceptors. In conclusion, this study provides a functional confirmation of the dissociation between the therapeutic (hypotensive) and untoward (sedative) effects of rilmenidine.

Inhibition of tyrosine hydroxylase activity by methyl bromide exposure

Rats were exposed to methyl bromide gas (16–250 ppm) for 8 hr, and tyrosine hydroxylase (TH) activity in the striatum, hypothalamus, frontal cortex, midbrain, and medulla oblongata was measured in brain homogenates from exposed rats, and in vivo following administration of decarboxylase inhibitor. Exposure to methyl bromide dose-dependently inhibited both in vitro and in vivo TH activity. Of the five brain areas, TH activity in the hypothalamus was most sensitive to methyl bromide. The time course of enzyme inhibition after exposure was similar to those of decreases in catecholamine concentrations, locomotor activity change, and body temperature reported previously. These results suggest methyl bromide reduces catecholaminergic neuronal activity in the brain via inhibition of TH activity.

Changes in Convulsion Susceptibility of Lidocaine by Alteration of Brain Catecholaminergic Functions.

Influences of the manipulation of brain catecholaminergic neuronal activity on the incidence of lidocaine-induced convulsions in mice were studied and compared with those of pentylenetetrazol (PTZ)-induced convulsions. alpha-Methyl-p-tyrosine (alpha-MPT) decreased both brain noradrenaline (NA) and dopamine (DA) levels, and disulfiram decreased the NA level and increased the DA level. The incidence of lidocaine-induced convulsions was decreased by treatments with alpha-MPT and disulfiram, while that of PTZ was increased by either treatment. The incidence of lidocaine-induced convulsions was slightly, but not significantly increased by L-dihydroxyphenylalanine (L-DOPA), although the brain DA level was increased by L-DOPA. Methamphetamine and desipramine increased the incidences of lidocaine-induced convulsions. These results may suggest that brain catecholaminergic neurons, differing from their role in inhibiting control of PTZ-seizure, act to facilitate lidocaine-induced convulsions.

Catecholamines Mediate Nicotine-Induced Adrenocorticotropin Secretion via a-Adrenergic Receptors*

Previous studies determined that iv nicotine stimulates ACTH secretion by acting on sites accessible from the fourth ventricle (IV), rather than directly on CRF-containing neurons in the hypothalamus. Brainstem catecholaminergic cell groups, which are accessible from the IV, project to the hypothalamus and stimulate the secretion of CRF and ACTH. Therefore, these studies investigated the role of catecholamines in nicotine-stimulated ACTH secretion. Experiments with the catecholaminergic neurotoxin, 6-hydroxydopamine, demonstrate that the ACTH response to nicotine delivered iv (0.03 or 0.05 mg/kg body wt) or instilled into the IV (1 or 2.5 micrograms) was significantly reduced in lesioned animals (P less than 0.01). Selective inhibitors of epinephrine synthesis, SKF 64139 and 2,3-dichloro-alpha-methylbenzylamine (DCMB), significantly reduced (P less than 0.01) the ACTH response to 0.05 mg/kg body wt nicotine iv, without affecting median eminence CRF content. Because controversy exists about the effect of DCMB as an alpha 2 adrenoreceptor antagonist in vivo, this was examined by administering norepinephrine into the third ventricle after DCMB ip; DCMB significantly reduced the ACTH response to norepinephrine 0.2 micrograms (P less than 0.05) but not to 0.5 micrograms. To determine whether alpha 2 receptors are indeed involved in the ACTH response to nicotine, yohimbine, an alpha 2 antagonist, was injected into the third ventricle before nicotine injection into the IV. Yohimbine significantly reduced the ACTH response. Thus, the secretion of both hypothalamic epinephrine and, to some extent, norepinephrine is involved in the ACTH response to the activation of catecholaminergic neurons in the IV. Further investigation of the adrenergic receptor(s) involved compared the ACTH response to nicotine (1 microgram) instilled into the IV after prazocin (alpha 1 antagonist), or propranolol (beta antagonist) was injected into the third ventricle. Prazocin significantly reduced (P less than 0.05) the ACTH response, whereas propranolol was ineffective. Thus, both alpha 1 and alpha 2 receptors are involved in mediating the ACTH response to nicotine.

Tyrosine hydroxylase, tryptophan hydroxylase, biopterin, and neopterin in the brain of anorexia nervosa

The activities of tyrosine hydroxylase and tryptophan hydroxylase and contents of biopterin and neopterin were measured for the first time in various regions of human brain from a patient with anorexia nervosa (AN). In AN as compared with controls, tyrosine hydroxylase activity was markedly reduced in all brain regions analyzed, while tryptophan hydroxylase activity and biopterin content had a tendency to increase. Neopterin content did not change dramatically. The opposite changes of tyrosine hydroxylase and tryptophan hydroxylase suggest an imbalance between the activity of catecholaminergic neurons and that of serotonergic neurons, and may be related to pathogenesis of AN.

Changes in catecholamine metabolism in the rostral ventrolateral medulla following halothane and nitroprusside-induced hypotension: an in vivo electrochemical study

The objective was to observe changes in rostral ventrolateral medulla (RVLM) catecholamine metabolism using in vivo voltammetry following induced hypotension with halothane or nitroprusside (SNP). Rats anesthetized (halothane, metocurine) and ventilated were stereotaxically implanted with carbon microelectrodes in the RVLM. The catechol oxidation current (CA·OC, % baseline) was used as an index of RVLM catecholaminergic metabolism. Groups of rats (n = 5) were given (A) halothane 0.75% for 60 min; (B) halothane 2.75% plus phenylephrine infusion to maintain mean arterial pressure (MAP) for 30 min, then halothane 0.75% for 30 min; (C) halothane (2.5–3.0%) for 30 min (MAP60 ± 5mmHg) then halothane 0.75% for 30 min; (D)halothane 0.75% and sodium nitroprusside (SNP) for 30 min (MAP60 ± 5mmHg), then halothane 0.75% for 30 min. Halothane 0.75% produced no significant change in CA·OC or MAP (A), while halothane 2.5–3.0% produced a significant decrease in MAP and a symmetrical significant increase in CA·OC (ANOVA,P < 0.5). This increase peaked at 30 min (180 ± 28%) and reached110 ± 9% baseline at 60 min. The halothane and phenylephrine combination produced no significant change in CA·OC or MAP during the 30 min exposure (B). SNP (D) produced a significant increase in CA·OC (peak 48 min,224 ± 35%) which remained elevated at 60 min (198 ± 32%). Thus, the induced hypotension produced activation of RVLM catecholaminergic neurons. SNP induced a prolonged significant increase in RVLM catecholamine metabolism which may relate to rebound hypertension following use of this drug.

Short‐ and Long‐Term Alterations of Gene Expression in Limbic Structures by Repeated Electroconvulsive‐Induced Seizures

Rats were submitted to a series of 10 daily electroconvulsive shocks (ECS). A first group of animals was killed 1 day after the last seizure and a second group 30 days later. Tyrosine hydroxylase (TH) activity was measured using an in vitro assay in the nucleus caudatus, anterior cortex, amygdala, substantia nigra, ventral tegmental area, and locus ceruleus. The mRNA corresponding to this enzyme (TH-mRNA) was evaluated using a cDNA probe at the cellular level in the ventral tegmental area, substantia nigra, and locus ceruleus. Met-enkephalin (MET)-immunoreactivity and the mRNA coding for the preproenkephalin (PPE-mRNA) were assayed in striatum and the central nucleus of the amygdala. The day after the last ECS an increase of TH activity was observed in the ventral tegmental area, locus ceruleus, and substantia nigra in parallel with a similar increase in the amygdala and striatum; in the anterior cortex TH activity remained unchanged. TH-mRNA was increased in the locus ceruleus, evidencing the presence in this structure of a genomic activation. The amounts of MET and PPE-mRNA were unaffected in the striatum but increased in the amygdala. Thirty days after the last ECS we observed a decrease of TH activity in the amygdala and of TH-mRNA amount in the ventral tegmental area. In the locus ceruleus TH-mRNA remained higher in treated animals than in controls whereas TH activity returned to control levels. These results demonstrate that a series of ECS induces an initial increase of the activity of mesoamygdaloid catecholaminergic neurons followed by a sustained decrease through alterations of TH gene expression which could mediate the clinical effect of the treatment.

Age-associated alterations in catecholaminergic concentrations, neuronal activity, and α1 receptor densities in female rats

The density of α 1-adrenergic receptors and catecholamine concentrations and neuronal activity were assessed in selected estrogen-responsive regions of the hypothalamus and pineal glands. The results of this study demonstrate that the densities of α 1-adrenergic receptors and norepinephrine and epinephrine concentrations and activity rate constants are altered in aged rats. The direction and extent of the change depend on the specific brain region and reproductive state of the animals. No widespread decline with increased age was observed in any of the parameters measured.

Pattern of catecholamine release in the nucleus tractus solitarii of the cat.

The release of endogenous dopamine, noradrenaline and adrenaline was studied in the nucleus tractus solitarii (subnucleus medialis) of anaesthetized cats. Two push-pull cannulae were inserted into the right and left nuclei tractus solitarii which were simultaneously superfused with artificial cerebrospinal fluid. The release of the neurotransmitters was determined in the superfusates which were continuously collected in 10 min or 2.5 min time periods for 6 h or 2 h, respectively. Collection of the superfusates in time periods of 10 min showed that the release rates of endogenous dopamine, noradrenaline and adrenaline varied rhythmically according to an ultradian rhythm, the time interval between 2 adjacent phases of high release rate being approximately 1 h. Some of the phases of high release rates of the three endogenous catecholamines timely coincided with each other. Collection of the perfusates in time periods of 2.5 min revealed the existence of additional oscillations with a frequency of about 1 cycle/10 min for dopamine, noradrenaline and adrenaline. The findings suggest that catecholamines are released in the nucleus tractus solitarii according to an ultradian rhythm with low (1 cycle per h) and high (1 cycle per 10 min) frequencies, which might reflect the activity of catecholaminergic neurons in this brain structure.

Effect of low doses of gamma-hydroxybutyric acid on serotonin, noradrenaline, and dopamine concentrations in rat brain areas

The effects of intraperitoneal administration of gamma-hydroxybutyric acid (GHB) on biogenic amine levels in hemispheres, hypothalamus, midbrain, and medulla-pons, and on tryptophan in serum and brain, were studied. One hour after GHB administration (50 and 100 mg/kg) significant increases of dopamine concentration were observed in the hemispheres with both doses and in the hypothalamus with the higher dose, but a significant decrease of noradrenaline in the hypothalamus. No significant changes of serotonin metabolism were observed. These results indicate that low doses of GHB selectively affect the catecholaminergic neuronal activity.

Differential effects of experimentally induced blood pressure changes on the release of catecholamines in hypothalamic and limbic areas of rats

The effects of longer lasting blood pressure changes on the release of endogenous catecholamines (CA) in limbic and hypothalamic areas were studied in anaesthetized rats. For this purpose the central nucleus of the amygdala (AC), ventral hippocampus (VH) and medial hypothalamus (MH) were simultaneously superfused through push-pull cannulae with artificial cerebrospinal fluid and the release of the endogenous catecholamines dopamine (DA), noradrenaline (NA) and adrenaline (A) was determined before and after blood pressure manipulations. A fall in blood pressure elicited by the ganglionic blocking agent chlorisondamine resulted in different changes of the various CA release patterns in AC. Short lasting increased CA release rates as compared to prehypotension levels could be observed in the hippocampus. The activity of catecholaminergic neurons in MH remained unchanged. A rise in arterial blood pressure induced by intravenous injection of tramazoline did not change the release rates of DA in all 3 brain areas studied. In hippocampus, NA levels in the superfusates decreased initially during hypertension but returned to normal values 40 min after drug injection. In the late phase of hypertension increased rates of release of NA in the amygdala and of A in the hypothalamus could be observed. The different patterns in the release of CA suggest that DA, NA and A are differentially implicated in the regulation of experimentally induced blood pressure changes.

Simultaneous determination of catechols in thalamic slices with liquid chromatography/electrochemistry

A method was developed for the simultaneous determination of dopamine (DA), epinephrine (E), norepinephrine (NE), 3,4-dihydroxyphenylacetic acid (DOPAC) and 3-methoxy-4-hydroxyphenylglycol (MHPG), as well as L-3,4-dihydroxyphenylalanine (L-DOPA) with liquid chromatography (LC) using electrochemical (EC) detection. With a ODS column and a mobile phase consisting of a sodium acetate-citrate with heptasulfonic acid, this method was applied on simultaneous determination of chatechols released from thalamic slices of ddY mouse. The pretreatment of the bathing medium required only centrifugation, and the supernatant was injected directly into the LCEC system. The high potassium stimulation of catecholaminergically innervated thalamic slices led to increase in the levels of DA, NE, DOPAC and MHPG, especially of NE, but not that of L-DOPA itself. In the present study, we designed to make simultaneous determination of catechols released from thalamic slices for estimation of the physiological status of catecholaminergic neuronal activity.

Behavioral and biochemical studies of dopamine receptor sensitivity in differentially housed mice.

Group housed and individually housed mice were compared in (1) the motor activity responses to direct and indirect dopamine (DA) agonists, (2) in vivo presynaptic autoreceptor sensitivity and (3) in vitro binding of 3H-spiperone. Relative to group housed mice, individually housed mice showed an increased motor activity response to amphetamine, 1.25 and 0.625 mg/kg. Using two in vivo measures of presynaptic DA receptor sensitivity, the antagonism of spontaneous locomotor activity and the antagonism of dihydroxyphenylalanine (DOPA) accumulation by apomorphine (APO), individually housed mice showed greater activity counts and higher DOPA accumulations than group housed mice. Levels of tyrosine were significantly greater in individually housed mice. Significant effects of housing were also noted with the motor activity response to APO, 0.075-0.300 mg/kg, following pretreatment with reserpine, an in vivo measure of postsynaptic receptor sensitivity. However, there was no effect of housing on the number or affinity of 3H-spiperone binding sites in the striatum. These results are discussed in terms of the presynaptic activity of catecholaminergic neurons and the postsynaptic receptor sensitivity to APO in individually housed mice.

Differential effects of d-amphetamine and scopolamine on the ontogeny of rearing

Although rearing is ontogenetically an important behavior, very little is known about the neural bases of rearing. The role development of catecholaminergic and cholinergic neurons play in the ontogeny of rearing was investigated by examining rearing in infant, adolescent, and adult rats following various doses of d-amphetamine (an indirectly acting catecholaminergic agonist) and scopolamine (a cholinergic muscarinic receptor antagonist). d-Amphetamine increased rearing in infants but not in adolescents and adults. These findings suggest that activation of catecholaminergic neurons increases rearing in infants but not in adolescents or adults. Scopolamine increased rearing in adolescents and adults but not in infants, indicating that blocking transmission of cholinergic neurons increases rearing in only older rats.

Serotonergic-catecholaminergic interactions and foot shock-induced jumping behavior in rats

The role of serotonergic neurons in foot shock-induced jumping behavior was evaluated by studying the effects of serotonin agonists and depletors under conditions of increasing activity of catecholaminergic neurons by combining different shock intensities with methamphetamine or clonidine pretreatment. Low shock (40 V) jumping was suppressed by three different kinds of serotonergic agonists: 5-hydroxytryptophan (50 and 100 mg/kg), 5-methoxydimethyltryptamine (1 and 5 mg/kg) and clomipramine (5 mg/kg) but these drugs did not suppress high shock (60 V) jumping. A depletor of brain serotonin, p-chlorophenylalanine (200 mg/kg), failed to affect the jumping induced by both shock intensities. The inhibitory effect of serotonergic agonists on low shock jumping was abolished by pretreatment with methamphetamine (1 mg/kg) or clonidine (100 μg/kg). Furthermore, 5-methoxydimethyltryptamine (5 mg/kg), a serotonergic postsynaptic receptor stimulant, potentiated high shock jumping in rats pretreated with methamphetamine (3 and 5 mg/kg). The results indicated that activation of serotonergic neurons has a differential effect on jumping behavior ranging from inhibitory to facilitatory, depending upon the increasing activity of catecholaminergic neurons.

FORMATION OF PHYSICAL DEPENDENCE ON BARBITURATES AND CEREBRAL MONOAMINES

The effects of cerebral monoamine-related substances during the course of formation of barbital (B) dependence were studied in male S.D. rats by the B-admixed food method. The monoamine-related substances, p-chlorophenylalanine (PCPA), tranylcypromine (Tcp), a-methyl-p-tyrosine (a-MT), methamphetamine (MA) and reserpine were administered during each B treatment period, except in the control group that was fed a food admixed with B only. All groups were examined for B withdrawal signs during each of 2 B withdrawal periods. Compared with the control group, B withdrawal signs tended to be mild in the PCPA-treated group, remained similar in the Tcp-treated group, were severe in the α-MT-treated group, very mild in the MA-treated group, and very severe in the reserpine-treated group. These findings suggested B withdrawal signs may tend to be reduced in severity if the activity of catecholaminergic neurons is kept elevated during the course of formation of physical dependence on B, and they suggested that acquirement of tolerance to and formation of dependence on barbiturates tend to be reduced under a condition of reduced cerebral 5-HT activity.