State-of-the-art microelectrodes for in vivo voltammetry

Monoamine and motor responses to cocaine are co-deficient in the Fawn-Hooded depressed animal model

The Fawn-Hooded (FH) genetic animal model of depression continues to be of interest because the FH model has limited biochemical and immune function. The FH animal has an inherited trait, platelet storage pool deficiency (PSPD), an hemorrhagic disorder that is also a component of Chediak-Higashi syndrome (CHS). CHS is a pyrogenic infectious childhood disease; few patients live past the age of 20. Our hypothesis was that FH animals may exhibit different monoamine and motor responses to cocaine versus the Sprague-Dawley (SD) "normal" animal strain, which does not have the FH trait. Therefore, selective neuromolecular imaging (NMI) of the monoamines, dopamine (DA) and 5-HT within nucleus accumbens (NAcc) of behaving male FH versus SD rats was performed in vivo with BRODERICK PROBE sensors and a semiderivative voltammetric circuit. Each animal was placed in a faraday chamber and electrochemical signals were detected via a mercury commutator and flexible cable. Baseline values for neurotransmitters and behavior were derived during the last half-hour of habituation behavior. Release of DA and 5-HT was detected selectively, at separate oxidation potentials, within seconds, before and after intraperitoneal administration of the psychostimulant, cocaine (10 mg/kg). At the same time, frequencies of ambulations and central ambulations were separately monitored with infrared photobeams, which surrounded the faraday chamber. Data were compared by ANOVA analysis followed by Tukey's post hoc test. The data showed that (1) DA release in NAcc of behaving FH animals did not respond to cocaine; neither first hour nor second hour values significantly differed from baseline (both hours, p>0.05), whereas SD animals exhibited a significant increase in cocaine-induced DA release in NAcc (both hours, p<0.001). The ability for acute cocaine to increase DA release in NAcc was significantly greater in SD than in FH animals (p<0.001). (2) 5-HT release in NAcc of behaving FH animals was not significantly increased by cocaine (both hours, p>0.05), whereas 5-HT release in NAcc of SD animals was significantly increased after cocaine (both hours, p<0.001). The ability for acute cocaine to increase 5-HT release was significantly greater in SD than in FH animals (p<0.001). (3) Ambulations in the FH strain were modestly, yet significantly, enhanced after cocaine during both hours of study (p<0.05, p<0.001, respectively) as were ambulations in the SD strain. Nonetheless, the ability for acute cocaine to increase ambulations was significantly greater in SD than in FH animals in the first hour (p<0.001). (4) Central ambulations in the FH strain was not affected by cocaine (both hours, p>0.05), whereas SD animals showed a significant increase in central ambulatory activity in both hours of the cocaine study (p<0.001). The ability for acute cocaine to increase central ambulations was significantly greater in SD than in FH animals (p<0.001). Thus, this is the first study to determine in vivo the neurochemical response to acute cocaine in the behaving FH animal. Moreover, this is the first study to determine in vivo and simultaneously the neurochemical and behavioral response to acute cocaine in the FH strain in comparison with SD animals, a "normal" strain. Remarkable deficiencies in the ability for acute cocaine to alter neurochemistry and behavior in animals with the FH trait are shown. These studies emphasize the need to look differentially at cocaine effects in biochemically and immune-compromised subjects versus "normal" subjects.

Cocaine acts on accumbens monoamines and locomotor behavior via a 5-HT2A/2C receptor mechanism as shown by ketanserin: 24-h follow-up studies

It is well known that cocaine's psychomotor stimulant properties derive from enhanced monoamines via synaptic transporter/reuptake inhibition and release mechanisms. However, to further understand mechanisms of action for cocaine, which may be receptor-related, ketanserin, a selective 5-HT(2A/2C) antagonist was used to ascertain a possible mediation for 5-HT(2A//2C) receptors in the monoamine and behavioral responses to cocaine. The studies were performed in the freely moving and behaving animal with In Vivo Microvoltammetry. Miniature carbon sensors, BRODERICK PROBE microelectrodes detected dopamine (DA) and serotonin (5-HT) concentrations in Nucleus Accumbens (NAcc) of male, Sprague-Dawley laboratory rats in separate signals and within seconds while at the same time, locomotor behavior was monitored with infrared photobeams. Synaptic release of each monoamine was detected because separate studies showed that the depolarization blocker, gamma-butyrolactone (gamma BL), decreased steady-state values [Pharmacol. Biochem. Behav. 40 (1991) 969]. Acute studies (Day 1) were performed; the animals received single injection of drug(s) in the faradaic behavioral chamber after a stable baseline during habituation behavior was achieved. After completion of the study, the animals were returned to their home cages. Subacute studies (Day 2) were also performed; these took place 24 h later in the faradaic behavioral chamber; same animal control was used and no further drug was administered. Day 2 data were compared to baseline (habituation data) on Day 1. Results showed that (1) Acute administration of Cocaine (10 mg/kg, i.p.) (N=5) increased DA and 5-HT release above baseline (p<0.001) while locomotion was also increased above baseline (p<0.001). (2) In Subacute studies in the cocaine group, when no further drug was administered, DA release decreased (p<0.001) and decreases in 5-HT release also occurred throughout the time course (p<0.05). Locomotor behavior increased above baseline and showed a trend toward statistical significance (p<0.07). (3) Acute administration of Ketanserin/Cocaine (3 mg/kg s.c. and 10 mg/kg i.p., respectively) (N=6) showed that ketanserin antagonized DA and 5-HT release (p<0.001), while locomotion was antagonized as well (p<0.001). (4) In Subacute studies, in the ketanserin/cocaine group, when no further drug was administered, DA decreased (p<0.001), but 5-HT increased (p<0.001), while locomotor activity increased above baseline and a trend toward statistical significance was seen (p<0.07). Additional saline controls were without effect (p>0.05). In summary, Acute studies showed that cocaine produced its psychostimulant responses on monoamines and behavior and ketanserin antagonized these responses, likely via a 5-HT(2A/2C) receptor mediation. Presynaptic and postsynaptic responses were not distinguished, suggesting, in addition, a role for 5-HT-ergic modulation of DA, likely DA(2) postsynaptic modulation Subacute cocaine studies showed that on Day 2, deficiencies in monoamines occurred, reflecting cocaine withdrawal mechanisms neurochemically, while locomotor behavior did not show such dramatic deficiencies. Indeed, behavior increased above baseline. Moreover, ketanserin reversed 5-HT-related and not DA-related cocaine monoamine responses, while locomotion continued to be insignificantly increased above baseline as was seen in the Subacute cocaine group. The data suggest that presynaptic 5-HT(2A/2C) receptor mechanisms may be important during withdrawal from single injection of cocaine.

Clozapine and cocaine effects on dopamine and serotonin release in nucleus accumbens during psychostimulant behavior and withdrawal

There is an increasing awareness that a psychosis, similar to that of schizophrenic psychosis, can be derived from cocaine addiction. Thus, the prototypical atypical antipsychotic medication, clozapine, a 5-HT(2)/DA(2) antagonist, was studied for its effects on cocaine-induced dopamine (DA) and serotonin (5-HT) release in nucleus accumbens (NAcc) of behaving male Sprague-Dawley laboratory rats with In Vivo Microvoltammetry, while animals' locomotor (forward ambulations), an A(10) behavior, was monitored at the same time with infrared photobeams. Release mechanisms for monoamines were determined by using a depolarization blocker, gamma-butyrolactone (gammaBL). BRODERICK PROBE microelectrodes selectively detected release of DA and 5-HT within seconds and sequentially in A(10) nerve terminals, NAcc. Acute and subacute studies were performed for each treatment group. Acute studies are defined as single injection of drug(s) after a stable baseline of each monoamine and locomotor behavior has been achieved. Subacute studies are defined as 24-h follow-up studies on each monoamine and locomotor behavior, in the same animal at which time, no further drug was administered. Results showed that (1) acute administration of cocaine (10 mg/kg ip) (n=5) significantly increased both DA and 5-HT release above baseline (P<.001) while locomotion was also significantly increased above baseline (P<.001). In subacute studies, DA release decreased significantly below baseline (P<.001) and significant decreases in 5-HT release occurred at the 15-min mark and at each time point during the second part of the hour (P<.05); the maximum decrease in 5-HT was 40% below baseline. Locomotor behavior, on the other hand, increased significantly above baseline (P<.05). (2) Acute administration of clozapine/cocaine (20 and 10 mg/kg ip, respectively; n=6) produced a significant block of the cocaine-induced increase in DA (P<.001) and 5-HT release (P<.001). Cocaine-induced locomotion was blocked simultaneously with each monoamine by clozapine as well (P<.001). In subacute studies, DA release continued to be blocked presumably via clozapine by exhibiting a statistically significant decrease (P<.001), but 5-HT release increased significantly (P<.001), while cocaine-induced locomotor activity also continued to be antagonized by clozapine, i.e., locomotor activity exhibited no difference from baseline (P>.05). In summary, acute studies (a) support previous data from this laboratory and others that cocaine acts as a stimulant on the monoamines, DA and 5-HT and on locomotor behavior as well and (b) show that clozapine, 5-HT(2)/DA(2) antagonist, blocked enhanced DA, 5-HT and psychomotor stimulant behavior induced by cocaine. Subacute studies (a) suggest that withdrawal responses occurred in the cocaine group, based on recorded deficiencies in monoamine neurotransmitters (b) show that withdrawal effects in the cocaine group likely presynaptic, were distinguished from locomotor behavior, classically known to be mediated postsynaptically, and finally, (c) suggest that clozapine, with longer lived pharmacokinetic properties, reversed 5-HT cocaine-related withdrawal effects, but was unable to reverse DA cocaine-related withdrawal responses. Taken together with data from this laboratory, in which the 5-HT(2A/2C) antagonist, ketanserin, affected cocaine neurochemistry in much the same way as did clozapine, a mediation by either separate or combined 5-HT(2A/2C) receptors for these clozapine/cocaine interactions, is suggested. Further studies, designed to tease out the responses of selective 5-HT(2A) and 5-HT(2C) receptor compounds to cocaine and clozapine/cocaine, are underway.

Acute and subacute effects of risperidone and cocaine on accumbens dopamine and serotonin release using in vivo microvoltammetry on line with open-field behavior

In vivo microvoltammetry was used to detect dopamine (DA) and serotonin (5-HT) release from nucleus accumbens (NAcc) of freely moving, male, Sprague-Dawley laboratory rats, while animals' locomotor (forward ambulations) and stereotypic behavior (fine movements of sniffing and grooming) were monitored at the same time with infrared photobeams. Monoamine release mechanisms were determined by using a depolarization blocker (gamma-butyrolactone, gamma BL). Miniature carbon sensors (BRODERICK PROBES microelectrodes) smaller than a human hair were used in conjunction with a semidifferential electrochemical circuit to detect release of each monoamine in separate signals and within seconds. The purpose was to evaluate the neuropharmacology of the 5-HT(2)/DA(2) antagonist risperidone in its current therapeutic role as an atypical antipsychotic medication as well as in its potential role as pharmacotherapy for cocaine psychosis and withdrawal symptoms. Acute (single drug dose) and subacute (24-h follow-up studies in the same animal, no drug administration) studies were performed for each treatment group. The hypothesis for the present studies is derived from a growing body of evidence that cocaine-induced psychosis and schizophrenic psychosis share similar neurochemical and behavioral manifestations. Results showed that (1) Acute administration of risperidone (2 mg/kg sc) significantly increased DA and 5-HT release in NAcc above baseline (habituation) values (P<.001) while locomotion and stereotypy were virtually unaffected. In subacute studies, DA release did not differ from baseline (P>.05), whereas 5-HT release was significantly increased above baseline (P<.001). Locomotion increased over baseline but not to a significant degree, while stereotypy was significantly increased above baseline (P<.05). (2) Acute administration of cocaine (10 mg/kg ip) significantly increased both DA and 5-HT release above baseline (P<.001), while locomotion and stereotypy were significantly increased over baseline (P<.001). In subacute studies, DA decreased significantly below baseline (P<.001) and significant decreases in 5-HT release occurred at 15, 20, 50 and 55 min (P<.05). Behavior increased above baseline but did not reach a statistically significant degree. (3) Acute administration of risperidone/cocaine (2 mg/kg sc and 10 mg/kg ip, respectively) showed a significant block of the cocaine-induced increase in DA release in the first hour (P<.001) and 5-HT release in both hours of study (P<.001). Cocaine-induced locomotion and stereotypy were blocked simultaneously with the monoamines (P<.001). In subacute studies, DA and 5-HT release returned to baseline while locomotion and stereotypy increased insignificantly above baseline. Thus, (a) these studies were able to tease out pharmacologically the critical differences between presynaptic and postsynaptic responses to drug treatment(s) and these differences may lead to more effective therapies for schizophrenic and/or cocaine psychosis. (b) Taken together with other data, these acute studies suggest that risperidone may possibly act via inhibition of presynaptic autoreceptors to produce the observed increases in accumbens DA and 5-HT release, whereas cocaine may be acting at least in part via serotoninergic modulation of DA postsynaptically. The subacute data suggest that pharmacokinetics may play a role in risperidone's action and that neuroadaptation may play a role in the mechanism of action of cocaine. Finally, the ability of risperidone to block cocaine-induced psychostimulant neurochemistry and behavior during acute studies while diminishing the withdrawal symptoms of cocaine during subacute studies suggests that risperidone may be a viable pharmacotherapy for cocaine psychosis and withdrawal.

Interleukin 1alpha alters hippocampal serotonin and norepinephrine release during open-field behavior in Sprague-Dawley animals: differences from the Fawn-Hooded animal model of depression

Detection of two biogenic amine neurotransmitters, serotonin (5-HT) and norepinephrine (NE) within the CA1 region of the hippocampus (HPC) of behaving male laboratory animals (Rattus norvegicus), was performed with miniature carbon sensors (BRODERICK PROBES) and in vivo semidifferential microvoltammetry after acute administration of the soluble immune factor, human recombinant, interleukin (IL) 1alpha (10 and 100 ng/kg i.p.). Two animal models were compared, i.e., (a) the Sprague-Dawley (SD) model, a strain neither biochemically nor immune-challenged and (b) the Fawn-Hooded (FH) model, a biochemically (5-HT-deficient) and immune-challenged animal. Open-field behaviors, locomotion (ambulations) and stereotypy (fine movements of sniffing and grooming) were monitored with infrared photobeams while 5-HT and NE were selectively and separately detected within seconds in real time. Subchronic studies were performed in the same animals 24 h later at which time no further drug was administered. Results from acute treatment studies showed that IL-1alpha altered HPC monoamines and behavior viz-a-viz habituation values (baseline) in the SD strain differently from those in the FH strain as follows: (1) although 5-HT release was significantly increased within CA1 region of HPC in both SD and FH strains (P<.0001), the extent of the HPC 5-HT increase in the 5-HT-deficient FH strain was significantly less than that of the SD strain at both doses (P<.0001). The subchronic studies showed that 5-HT release within the HPC in the SD strain significantly increased (135%) over drug treatment values (P<.001), whereas HPC 5-HT release in the FH strain remained the same as that seen in the acute drug treatment studies; the difference between strains for the subchronic study was also statistically significant (P<.01). (2) IL-1alpha significantly decreased HPC NE release in the SD strain (P<.0004) while IL-1alpha decreased HPC NE release in the FH strain only at the 10-ng/kg dose (P<.001); at the 100-ng/kg dose in the FH strain, NE rebounded towards baseline and increased 15% above baseline reaching statistical significance (P<.05). Subchronic studies in the SD strain showed a further decreased NE signal to 38% below baseline (P<.0001), whereas subchronic studies in the FH strain showed a significant increase in NE release (P<.02). The difference between strains in the subchronic NE studies was significant (P<.001). (3) Ambulations were increased after IL-1alpha administration in acute studies in both the SD and the FH strains, but the increase did not reach statistical significance, whereas in the subchronic studies, both strains exhibited significant increases as revealed by post hoc analyses (P<.05). There was a statistically significant difference between strains in acute studies (P<.001), whereas no significant differences between models were seen in ambulation behavior in subchronic studies. (4) Fine movements increased over baseline after IL-1alpha administration in both animal models in acute studies, however, results did not reach statistical significance, likely due to the episodic effect of IL-1alpha on movement behavior in both the SD and the FH strains. However, the SD strain showed a significant increase in fine movement behavior during the subchronic studies (P<.02). Significant differences in fine movements between animal models were not observed either acutely or in subchronic studies. In summary, the data show that immune modulation by IL-1alpha affects HPC neurochemistry and behavior in SD versus FH animal models differently and/or to different degrees. The data show that while the FH animal model is subsensitive to 5-HT agonists, 5-HT function can be stimulated. Comparison of genetically diverse animal models provides a reliable means to identify and discern cytokine-induced depressive versus stressor properties. Selective sensor technology provides a powerful tool as movement behavior is monitored and interpreted as a function of monoamine neurotransmission.

Evaluation of the inhibition of choline uptake in synaptosomes by capillary electrophoresis with electrochemical detection

A direct method for evaluating choline uptake by the high-affinity choline transport system in synaptosomes was developed using capillary electrophoresis (CE) with electrochemical (EC) detection. On-column EC detection of choline and the internal standard, butyrylcholine, was accomplished with a 25 microm platinum electrode modified with the enzymes, choline oxidase and acetylcholinesterase. Choline uptake was evaluated as a function of choline concentration and a KM value of 1.7 microM was determined. The method was also used to evaluate a new class of redox affinity inhibitors of choline transport. In particular, the effectiveness of 3-[(trimethylammonio)methyl]catechol (TMC) as an inhibitor of choline uptake was examined independently and relative to the inhibition of the well-known inhibitor of choline transport, hemicholinium-3. The IC50 and KI for TMC were determined to be 30 microM and 14 microM, respectively. The combination of the selectivity and sensitivity afforded by CEEC provides a relatively straightforward approach for monitoring choline transport in synaptosomes.

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.

Monoamine neurotransmitters in resected hippocampal subparcellations from neocortical and mesial temporal lobe epilepsy patients: in situ microvoltammetric studies

It is known that epilepsy patients diagnosed with neocortical temporal lobe epilepsy (NTLE), differ from those diagnosed with mesial temporal lobe epilepsy (MTLE), e.g., in hippocampal (HPC) pathology. In the present studies, we tested the hypothesis that NTLE and MTLE subtypes of human epilepsy might differ in regards to their HPC monoamine neurochemistry. Monoamine neurotransmitters were studied in separate signals and within s with semiderivative microvoltammetry, used in combination with stearate indicator, Ag-AgCl reference and stainless steel auxiliary microelectrodes. Anterior HPC specimens from the patients' epileptogenic zone, defined by electrocorticography, were resected neurosurgically from 13 consecutive patients with intractable temporal lobe epilepsy. Four patients were diagnosed with NTLE and nine with MTLE. The criteria for the diagnosis of NTLE versus MTLE was absence versus presence of HPC sclerosis, respectively, based on MRI examination of resected tissue. In addition, NTLE patients demonstrated seizure onset in anterolateral temporal neocortex on electroencephalography (EEG). HPC subparcellations studied were: (a) Granular Cells of the Dentate Gyrus (DG), (b) Polymorphic Layer of DG and (c) Pyramidal Layer: subfields, CA1 and CA2. Dopamine (DA), serotonin (5-HT), norepinephrine (NE) and ascorbic acid (AA) (co-factor in DA to NE synthesis), exhibited separate and characteristic half-wave potentials in millivolts. Each half-wave potential, i.e., the potential at which maximum current was generated, was experimentally established in vitro. Concentrations of neurotransmitters found in HPC subparcellations were interpolated from calibration curves derived in vitro from electrochemical detection of monoamines and AA in saline phosphate buffer. Significant differences between subtypes in concentration of monoamines were analyzed by the Mann Whitney rank sum test and those differences in probability distribution of monoamines were analyzed by the Fisher Exact test; in each case, P<0.01 was the criteria selected for determining statistical significance. DA concentrations were higher in NTLE compared with MTLE in each HPC subparcellation [P=0.037, 0.024 and 0.007, respectively (P<0.01)] and DA occurred more frequently in NTLE in the Pyramidal Layer [P=0.077 (P<0.01)]. AA was present in one NTLE patient. NE concentrations were higher in MTLE vs. NTLE in each subparcellation [P=0.012, 0.067 and 0.07, respectively (P<0.01)] and NE occurred more frequently in MTLE in Granular Cells of DG and Pyramidal Layer [P=0.052 and 0.014, respectively (P<0.01)]. In MTLE, NE concentrations in the CA1 subfield of the Pyramidal Layer were decreased vs. the CA2 subfield [P=0.063 (P<0.01)]. Serotonin was found in every HPC subparcellation of each subtype but 5-HT concentrations were higher in NTLE vs. MTLE in the Granular Cells of DG and the Pyramidal Layer (CA1 subfield) [P=0.076 and 0.095, respectively (P<0.01)]. Thus, this preliminary study showed that marked differences in HPC monoamine neurochemistry occurred in NTLE patients as compared with MTLE patients.

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.

I. Serotonin (5-HT) within dopamine reward circuits signals open-field behavior. II. Basis for 5-HT--DA interaction in cocaine dysfunctional behavior

Light microscopic immunocytochemical studies, using a sensitive silver intensification procedure, show that dopamine (DA) and serotonin (5-HT) axons terminate on neurons in the nucleus accumbens (NAcc) (A10) terminals and also in dorsal striatum (DSTr) (A9) terminals. The data demonstrate a prominent endogenous anatomic interaction at these distal presynaptic sites between the neurotransmitters 5-HT and DA; the pattern of the 5-HT-DA interaction differs between A10 and A9 terminals. Moreover, in distinction to the variance shown anatomically between 5-HT--DA interactions at distal A9 and A10 sites, the 5-HT--DA interactions at the level of DA somatodendrites, the proximal site, are similar, i.e. 5-HT terminals in the midbrain tegmentum are profuse and have a massive overlap with DA neurons in both ventral tegmental area (VTA) and substantia nigra pars compacta (SNpc). We suggest with reference to the DA neurons of A10 and A9 pathways, inclusive of somatodendrites (sites of proximal presynaptic interactions in the midbrain) and axons (sites of distal presynaptic interactions), that 5-HT--DA interactions in A10 terminals are more likely to exceed those in the DStr arrangement. Furthermore, our neuroanatomic data show that axonally released DA at A10 terminals may originate from proximal 5-HT somatodendrites, i.e. dorsal raphe (DR) or the proximal DA somatodendrites, VTA. In vivo microvoltammetric studies were done with highly sensitive temporal and spatial resolution; the studies demonstrate basal (endogenous) real time 5-HT release at distal A10 and distal A9 terminal fields and real time 5-HT release at proximal A10 VTA somatodendrites. In vivo microvoltammetric studies were performed concurrently and on line with studies of DA release, also at distal A10 and distal A9 terminal fields and at proximal A10 somatodendrites. Serotonin release was detected in a separate voltammetric peak from the DA voltammetric peak. The electrochemical signal for 5-HT release was detected within 10-12 s and that for DA release within 12-15 s, after each biogenic amine diffused through the synaptic environment onto the microelectrode surface. The electrochemical signal for 5-HT and a separate electrochemical signal for DA are detected on the same voltammogram within 22-27 s; each electrochemical signal represents current changes in picoamperes, within seconds of detection time. The amplitude of each electrochemical signal reflects the changes in diffusion of each biogenic amine to the microelectrode surface. Each neurotransmitter has a distinct potential at which oxidation occurs; this results in a recording which has a distinct peak for a specific neurotransmitter. The concentration of each neurotransmitter within the synaptic environment is directly related to the electrochemical signal detected via the Cottrell equation. Voltammograms were recorded every 5 min. At the time that basal 5-HT release and basal DA release were recorded within same animal control, open-field behavioral studies were performed, also concurrently, by infrared photocell beams. The frequency of each behavioral parameter was monitored every 100 ms; the number of behavioral events, were summated every 5 min during the time course of study. Thus, the detection of neurotransmitters occurs in real time, while simultaneously monitoring the animal's behavior by infrared photocell beams. The results from the in vivo microvoltammetric and behavioral data from this study show that basal 5-HT release at distal A10 and A9 terminals dramatically increased with DA release. Moreover, each increase in basal 5-HT release, at both A10 and at A9 terminal fields occurred consistently and at the same time as each increase in open-field locomotion and stereotypy occurred naturally during the animal's exploration in a novel chamber. Thus, the terminology 'synchronous and simultaneous' describes aptly the correlation between 5-HT release at distal A10 and A9 terminal fields and open-field locomo

Ibogaine modulates cocaine responses which are altered due to environmental habituation: in vivo microvoltammetric and behavioral studies

Ibogaine, a serotonergic (5-HTergic) indole alkaloid, was studied for cocaine modulatory effects on four parameters of behavior by computerized infrared photocell beam detection. The behavioral parameters were: a) locomotor activity (ambulations), b) rearing, c) stereotypy (fine movements, primarily grooming), and d) agoraphobia [(thigmotaxis) a natural tendency to avoid the center of the behavioral chamber]. With each behavioral data point, dopamine (DA) release, and serotonin (5-HT) release were detected within seconds in nucleus accumbens (NAcc) of the same behaving male Sprague-Dawley rats, using in vivo electrochemistry (voltammetry). Ibogaine was administered (40 mg/kg IP) for 4 consecutive days. Importantly, the DAergic and the 5-HTergic responses to (SC) cocaine and two behavioral responses, ambulations and central ambulations, were reduced in intensity due to extended time spent in the novel behavioral chamber (habituated). Rearing and fine movement patterns were not habituated. The results show that ibogaine downmodulated the (SC) cocaine-induced increase in NAcc DA release (p < 0.0001) and potentiated the (SC) cocaine-induced decrease in NAcc 5-HT release (p < 0.0001). Concurrently, ibogaine downmodulated cocaine-induced ambulation (p < 0.0001) and central ambulation behavior (p < 0.0001). On the other hand, the behavioral parameters that did not exhibit habituation, i.e., rearing behavior and fine movement behavior, were not downmodulated by ibogaine (p < 0.1558) (p < 0.3763), respectively. Furthermore, ibogaine itself did not significantly alter NAcc DA release over the 2-h period studied (p < 0.9113) although individual time points were significantly affected bidirectionally. Concurrently ibogaine significantly increased 5-HT release (p < 0.0155). Behaviorally, ibogaine appears to be a weak psychostimulant. The data show a critical modulatory role for 5-HT in ibogaine-cocaine interactions. Also elucidated as critical is the efficacy of ibogaine when the response to (SC) cocaine is decreased due to the habituation of the animals to their environment.

Voltammetric determination of dopamine in the presence of ascorbic acid at over-oxidized polypyrrole-indigo carmine film-coated electrodes

Over-oxidized polypyrrole films doped with indigo carmine (PPy-IC) offer substantial improvements in voltammetric sensitivity and selectivity towards dopamine. This polymer coating attenuates the voltammetric response of ascorbic acid while the oxidation peak current of dopamine is enhanced by over one order of magnitude compared with that at the bare electrode. The high sensitivity and selectivity for dopamine appears to be mainly due to the charge discrimination and the analyte accumulation. The detection limit is dependent on both film thickness and preconcentration time. At a 0.25 micron thick PPy-IC film-coated electrode, for a 2 min preconcentration time, the detection limit is 10(-8) mol l-1, over two orders of magnitude lower than at a bare glassy carbon electrode. The concomitant ascorbic acid shows no interference although its concentration is as high as 0.1 mmol l-1. The effects of various experimental parameters on the voltammetric response of dopamine were also investigated. The attractive permselective and preconcentrating properties of the PPy-IC films make them valuable for in vivo electrochemistry.

In vivo electrochemical studies of gradient effects of (SC) cocaine on dopamine and serotonin release in dorsal striatum of conscious rats

Cocaine (20 mg/kg) was administered subcutaneously (SC) to conscious male Sprague-Dawley rats after exploration in a novel chamber. (SC) cocaine was studied for its influence on in vivo dopamine (DA) and serotonin (5-HT) release in dorsal striatum (STr), with a further study of an anterior-posterior dorsal subdivision in a range of +/- 400 microns. Semiderivative voltammetry, a circuit for in vivo electrochemical biotechnologies, was used in combination with a stearate microelectrode to concurrently detect in separate electrochemical signals the electroactive species for DA and 5-HT in dorsal STr. The temporal resolution for detection was in the order of seconds. Concomitantly, cocaine-induced psychostimulant behaviors were studied with infrared photo beam detection. Psychostimulant behaviors classically thought to depend on DA--that is, hyperactivity (increased locomotor activity or ambulations), rearing, and finally stereotypy (fine movements of grooming and head bob)--and a 5-HT-ergic behavior, central ambulations, were monitored. The results showed that (SC) cocaine significantly (p < 0.0001) increased DA release in dorsal STr, whereas the overall effect of (SC) cocaine on 5-HT release was a significant increase (p < 0.0001) followed by an overall small (13%) but statistically significant decrease (p < 0.05). A dramatic cocaine-induced gradient effect on 5-HT release was seen in anterior-posterior dorsal STr, where 5-HT release was significantly (p < 0.0001) increased throughout the entire time period of study. Classically DA-dependent behaviors were significantly and positively correlated with increased DA release in dorsal STr and anterior-posterior dorsal STr (p < 0.001) in the 4-h period of study. However, 5-HT release after cocaine in the anterior-posterior dorsal STr was significantly and positively correlated with the classically DA-dependent behaviors as well (p < 0.001), implicating a role for 5-HT in the effectuation of cocaine-induced psychostimulant behavior. Generally, the 5-HT-ergic response to cocaine was enhanced before the DA-ergic response. Therefore, the data show that 5-HT as well as DA plays a role in the underlying mechanism of action of cocaine in dorsal STr. The data suggest that 5-HT may play a compensatory or adaptive role in the modulation of cocaine-induced nigrostriatal DA-ergic regulation.

Increase of catecholamine content in the extracellular space of the rat's brain cortex during spreading depression wave as determined by voltammetry

The effect of chemically initiated (KCl) spreading cortical depression on catecholamine content in the extracellular cortical space was examined using voltammetry technique in chloralhydrate-anaesthetized rats. Correlation between alterations in catechol-oxidative current (CA.OC) and the time-course of the slow potential (SP) change (one of the chief features of the spreading depression) showed that spreading depression wave was accompanied by the significant increase in CA.OC content (up to 158 +/- 43%, mean +/- S.D., P < 0.001). The rise of the negative SP preceded significant CA.OC increase by 20 +/- 8 s. This fact provides the evidence that catecholamine overflow cannot participate in triggering spreading depression wave; nevertheless it can be an important link of the spreading depression mechanism.

Real time detection of acute (IP) cocaine-enhanced dopamine and serotonin release in ventrolateral nucleus accumbens of the behaving Norway rat

Cocaine (10 mg/kg), administered intraperitoneal (IP), was studied for its effects on dopamine (DA) and serotonin (5-HT) release in ventrolateral nucleus accumbens (vlNAcc) of conscious and behaving male, virus-free, Sprague-Dawley rats with in vivo electrochemistry (voltammetry). Miniature stearate probes detected DA and 5-HT release, on line and within a temporal resolution of seconds. Psychostimulant behaviors, in the form of four behavioral components (i.e., the classically DA-dependent behaviors of locomotor activity [ambulations], rearing, and stereotypy, and a 5-HT-ergic behavior, central ambulations) were studied concurrently with infrared photobeam detection. The results show that (IP) cocaine significantly increased vlNAcc DA release (p < 0.0001) and 5-HT release (p < 0.0012). Each of the four parameters of cocaine-induced psychostimulant behavior was concurrently and significantly increased as well (ambulations: p < 0.0001); rearing p < 0.0008; stereotypy: p < 0.0004; central ambulations: p < 0.0082). Moreover, exactly coincident data points for DA and 5-HT release occurred 10 and 40 min after (IP) cocaine administration. Cocaine-induced DA and 5-HT release were highly and positively correlated during the first hour of study (p < 0.01). As expected, increased DA release in vlNAcc after cocaine administration was significantly and positively correlated with classically DA-dependent behaviors (first- and second-hour effects) (p < 0.01) and with the 5-HT-ergic behavior, central ambulations (p < 0.01). Also, cocaine-induced 5-HT release was significantly and positively correlated with 5-HT behavior (p < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Distinguishing effects of cocaine i.v. and SC on mesoaccumbens dopamineand serotonin release with chloral hydrate anesthesia

The effect of i.v. cocaine (0.5 and 1.0 mg/kg) was studied on synaptic concentrations of dopamine (DA) and serotonin [5-hydroxytryptamine (5-HT)] in the mesoaccumbens nerve terminal, the nucleus accumbens (NAcc), in chloral hydrate-anesthetized, male Sprague-Dawley rats (Rattus norvegicus) with in vivo electrochemistry (voltammetry). In further in vivo voltammetric studies, the effects of SC cocaine on synaptic concentrations of DA and 5-HT were studied in the chloral hydrate-anesthetized paradigm in two neuroanatomic substrates, NAcc and mesoaccumbens somatodendrites, the ventral tegmental area (VTA-A10), in a dose-response fashion (10, 20, and 40 mg/kg) in six separate studies. Moreover, in two additional in vivo voltammetric studies, again using the chloral hydrate-anesthetized paradigm, the impulse flow blocker, gamma-butyrolactone (gamma-BL) (750 mg/kg, IP), was studied alone and in combination with SC cocaine (20 mg/kg) to determine whether or not cocaine can act by presynaptic releasing mechanisms for DA and 5-HT. The results show that IV cocaine concurrently and significantly increased DA and 5-HT release in the NAcc (p < 0.001, p < 0.0005, respectively) at both doses tested. Moreover, IV cocaine effects on DA and 5-HT release were significantly and positively correlated (p < 0.01). On the other hand, SC cocaine concurrently and significantly decreased DA and 5-HT release in NAcc (p < 0.0001) and VTA (p < 0.0001) at each separate dose tested. SC cocaine effects on DA and 5-HT release were significantly and positively correlated across dose and neuroanatomic substrate (p < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Cholecystokinin antagonists inhibit in vivo voltammetric signals generated by KCl-induced slow wave depolarization in rat caudate

The effect of sulfated cholecystokinin octapeptide (CCK-8S) on the generation of slow wave depolarisation in the rat caudate-putamen (CPu) was studied using in vivo voltammetry. Pressure-ejection of 50 microM CCK-8S into the CPu induced voltammetric signals recorded at widely spaced Nafion-coated carbon fiber microelectrodes. Based on the in vitro selectivity properties of the electrodes, the signals were predominantly due to increases in extracellular concentrations of dopamine (DA). The similar propagation rates of the signals induced by CCK-8S and 100 mM KCl suggests that the CCK-8S-induced signals represent a slow wave depolarization (SWD). Since the CPu was refractory to a second CCK-8S stimulus, the effects of CCK antagonists on DA signals associated with 100 mM KCl-induced SWD were evaluated. Proglumide (4-64 mg/kg) and lorglumide (20-640 micrograms/kg), administered intravenously, decreased KCl-induced DA signals in the CPu in a dose-dependent manner. The antagonistic effect of lorglumide on the KCl-induced signals was partly reversed 130 min after drug administration. The generation of a SWD by CCK-8S and the inhibitory effects of CCK-8S antagonists on KCl-induced signals suggest that the susceptibility of the CPu to KCl-induced SWD may be enhanced by CCK-8S.

Cocaine's colocalized effects on synaptic serotonin and dopamine in ventral tegmentum in a reinforcement paradigm

The effect of subcutaneous (SC) cocaine (20 mg/kg) on synaptic concentrations of the biogenic amines, dopamine (DA), and serotonin (5-HT) in Ventral Tegmental Area, (VTA-[A10]) was studied in freely moving and behaving rats (rattus norvegicus) with in vivo voltammetry (in vivo electrochemistry). The actual detection of the biogenic amines was on-line and within a temporal resolution of seconds. Simultaneously, the psychostimulant behavior induced by cocaine was studied by infrared photocell beam detection. The results show that cocaine concurrently and significantly increased synaptic concentrations of DA (p less than 0.0001) and 5-HT (p less than 0.004) in VTA. Serotonin changes were accompanied by a notable oscillatory pattern. Importantly, DA and 5-HT changes in VTA were significantly and positively correlated (p less than 0.01). Moreover, psychostimulant behaviors induced by cocaine were significantly increased over control values (p less than 0.0001). Psychostimulant behaviors were significantly correlated with concurrently changing synaptic concentrations of DA (p less than 0.01) and also with 5-HT to a lesser degree. Additionally, behavioral data indicate that cocaine may exhibit an anxiolytic effect during acute administration because agoraphobic behavior, as shown by increased central ambulatory behavior, was dramatically reduced by cocaine. Summarily, the present findings show that cocaine increased synaptic concentrations of DA in VTA, an action that is correlated with cocaine-induced psychostimulant behavior. The DA-ergic effect appears to be tonically maintained. Furthermore, new findings demonstrate a colocalized, cocaine induced 5-HT-ergic effect in VTA, which keeps pace with cocaine-induced alterations in DA-ergic neurotransmission. Thus, 5-HT may be a relay or a gating mechanism for a DA reward signalling pathway for cocaine.

Intracerebroventricular administration of neuropeptide Y affects parameters of dopamine, glutamate and GABA activities in the rat striatum

The effects of intracerebroventricular (ICV) injection of neuropeptide Y (NPY) on parameters of dopamine (DA), glutamate (Glu) and gamma-aminobutyric acid (GABA) activities were investigated in the rat striatum. NPY (1.17-4.70 nmol) induced a dose-dependent increase in the striatal endogenous DA release monitored in freely moving animals by means of a voltammetric method. Maximal increase was observed about one hour after the peptide injection. This result is consistent with the hypothesis that NPY may influence striatal DA turnover in a facilitatory manner by activating DA release. DA, DOPAC, Glu and GABA endogenous contents as well as 3H-Glu and 3H-GABA synaptosomal high affinity uptakes were examined one hour after NPY ICV administration at the same dose range in chloral hydrate-anesthetized animals. Depending on the NPY dose injected, opposite changes in Glu uptake were observed, suggesting that NPY has a bimodal influence on glutamatergic transmission. The Glu uptake rate increased markedly at 1.17 nmol NPY and decreased at 4.70 nmol, which may reflect an activation and an inhibition of the striatal Glu transmission, respectively. In parallel, the GABA uptake was found to decrease slightly at the higher doses of NPY tested, whereas no significant alteration of the striatal concentrations of either DA, DOPAC, Glu or GABA was observed. These results indicate that NPY may be involved in regulating the activity of nigral dopaminergic and cortical glutamatergic afferent pathways and that of intrinsic GABA neurons in the rat striatum.

Cocaine: on-line analysis of an accumbens amine neural basis for psychomotor behavior

Dose-response studies on subcutaneous cocaine were done to ascertain its effects in nucleus accumbens in dopaminergic and serotonergic neuronal circuitry in the behaving rat with in vivo voltammetry. Simultaneously, and at each dose of cocaine, unconditioned psychomotor stimulant behavior induced by cocaine was studied in terms of multiple concurrent measures of spontaneous behavior and by activity pattern analysis, a study of spatial patterns of locomotion. Time course studies showed that the neurochemical effects of cocaine (10, 20, and 40 mg/kg SC) significantly (p less than 0.0001) increased accumbens synaptic concentrations of dopamine (DA) and concurrently and significantly (p less than 0.0001) decreased accumbens synaptic concentrations of serotonin (5-HT) in a dose response manner. Simultaneous behavioral time course studies showed that cocaine (10, 20, and 40 mg/kg SC) significantly (p less than 0.0001) increased ambulations (locomotor activity), fine movements (stereotypic movements of sniffing and grooming) and rearing behavior, while significantly decreasing agoraphobic behavior, as measured by a statistically significant increase in central ambulations (p less than 0.0001). The high dose of cocaine (40 mg/kg SC) significantly increased fine movements over those produced by the lower doses of cocaine (p less than 0.0002). One import of the findings is that the DA and 5-HT biogenic amine response occurs in a behavioral paradigm of psychomotor stimulation, which is a known measure of reinforcement. Another is that the biogenic amines DA and 5-HT are affected by cocaine in this reinforcement paradigm with exactly opposite directionality. Finally, acute cocaine administration is shown to produce a dose response inhibition of agoraphobia (fear), which is highly correlated (p = .983, p less than 0.01) with the opposing effects of cocaine on the accumbens biogenic amines, DA and 5-HT.

In vivo voltammetric studies on release mechanisms for cocaine with gamma-butyrolactone

The effect of cocaine (20 mg/kg SC) on presynaptic mechanisms of release for dopamine (DA) and for serotonin (5-HT) was studied in nucleus accumbens of unrestrained rats (Rattus norvegicus). The studies were done by assaying synaptic concentrations of DA and 5-HT in the presence of the neuronal impulse flow inhibitor, gamma-butyrolactone (gamma-BL). The results were compared with cocaine effects on accumbens DA and 5-HT in the freely moving rat, without gamma-BL treatment. A neurochemical time course profile showed that the cocaine-induced increase in accumbens synaptic concentrations of DA was significantly blocked (p less than 0.0001) after DA impulse flow was significantly inhibited (p less than 0.0038) by gamma-BL (35.8%). The neurochemical time course profile concurrently showed that the cocaine-induced decrease in accumbens synaptic concentrations of 5-HT was significantly blocked (p less than 0.0004) after impulse flow was significantly inhibited (p less than 0.025) by gamma-BL (50.6%). The findings show that cocaine's effects on synaptic concentrations for DA and for 5-HT in accumbens are dependent on neuronal impulse flow. The findings indicate that presynaptic releasing mechanisms, which may be different for DA vis-à-vis 5-HT, play a role in the mechanism of action of cocaine.

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.