Ability of cipramil to correct conditioned passive avoidance in ovariectomized female rats

The ability of cypramil, a selective inhibitor of serotonin re-uptake, to modify the cognitive performance was studied in ovariectomized female rats with passive avoidance paradigm and in the open-field test. It was found that cypramil in combination with estradiol restored the formation and retention of the passive avoidance performance. In addition, cypramil improved the emotional component of behavior in the open-field test.     

Antidepressant effect of L-tryptophan in male rats with dysbalance thyreoid hormones

The activity of L-tryptophan was studied on young male rats in depressive state caused by thyreoid hormone dysbalance. The immobilization time in the Porsolt forced swim test in thyreoidectomized rats was significantly increased in comparison to the intact control. The replacement therapy with triiodothyronin (T3) reduced the level of depressed behavior to the initial value. Chronic administration of L-tryptophan significantly decreased the total immobilization time in all the test groups, irrespective of the hormonal state. However, the effect of L-tryptophan was more pronounced in T3-treated rats.     

Comparative study of the antidepressant and anxiolytic activity of fluoxetine and tianeptine

The activity of fluoxetine (prozac) and tianeptine (coaxil) was studied in outbred male rats under Porsolt and S. Nomura modified forced swim tests. The antidepressant effect of tianeptine was much more pronounced that that of fluoxetine. In the conflict situation test, fluoxetine produced anxiogenic action. In contrast, tianeptine decreased (albeit not reliably) the anxiety. In combination with bicuculline (GABAA receptor blocker), the anxiolytic action was more pronounced for both antidepressants, which was manifested by a significant increase in the number of punished water takes. A neural network explaining the observed behavior is proposed, which includes GABA-ergic intemeurons inhibiting serotonin release from serotoninergic terminals.     

Antidepressant and memory affecting influence of estrogen and venlafaxine in ovariectomized rats

The experiments presented in this paper aimed to investigate whether estrogen level changes in oviariectomized rats (OVX) may lead to depression and memory disorders, and whether the effects of such changes may be reversible following administration of a new antidepressant, venlafaxine (CAS 9930-78-4, VEN, Efectin). The Porsolt forced swimming test and Morris water maze test were carried out on female Wistar rats after ovariectomy and in sham-ovariectomized rats. VEN 20 mg/kg was administered orally 30 min before the tests for the period of 14 days. Estradiol (17beta-estradiol benzoate, CAS 50-28-2, E2) administration (5 microg E2/0.2 ml sesame oil s.c.) was started 24 h after ovariectomy and was continued for 14 days--each dose was administered 180 min before the test. In the immobility test, which reflects antidepressant drug activity, it was found that VEN shortened immobility time (IT) after the 1st, 7th and 14th administration (days 1, 7, 14, respectively) in ovariectomized rats, whereas in the control group (sham-ovariectomized rats) VEN exerted antidepressant action only after single administration (day 1) and after 7 days of administration. E2 significantly reduced immobility behaviour both after single and chronic treatment in ovariectomized rats. After joint administration of VEN and E2 potentiation of the antidepressant activity of VEN could be observed in both groups except for concurrent administration of VEN and E2 after 14 days in sham-ovariectomized rats. VEN improved the spatial memory in the Morris water maze test, whereas E2 did not affect the memory of the tested animals. Joint administration of VEN and E2 maintained the memory improving effect induced by VEN. The regulatory role of the steroid hormone and the new antidepressant drug (VEN) in antidepressant activity and memory function could be related to the interactions between noradrenergic and serotoninergic systems.     

Prenatal stress decreases glycogen synthase kinase-3 phosphorylation in the rat frontal cortex

It has been postulated that hyperactive glycogen synthase kinase-3 (GSK-3) is an important factor in the pathogenesis of depression, and that this enzyme also contributes to the mechanism of antidepressant drug action. In the present study, we investigated the effect of prenatal stress (an animal model of depression) and long-term treatment with antidepressant drugs on the concentration of GSK-3β and its main regulating protein kinase B (PKB, Akt). The concentration of GSK-3β, its inactive form (phospho-Ser9-GSK-3β), and the amounts of active (phospho-Akt) and total Akt were determined in the hippocampus and frontal cortex in rats. In order to verify our animal model of depression, immobility time in the forced swim test (Porsolt test) was also determined.We found that prenatally stressed rats display a high level of immobility in the Porsolt test and chronic treatment with imipramine, fluoxetine, mirtazapine and tianeptine normalize this change. Western blot analysis demonstrated that GSK-3β levels were significantly elevated in the frontal cortex, but not in the hippocampus, of prenatally stressed rats. The concentration of its non-active form (phospho-Ser9-GSK-3β) was decreased only in the former brain structure. No changes were found in the amounts of active (phospho-Akt) and total Akt in both studied brain structures. Chronic treatment with antidepressant drugs diminished stress-induced alterations in GSK-3β and phospho-GSK-3β levels in the frontal cortex, but had no effect on the concentration of these enzymes in the hippocampus. Moreover, levels of Akt and phospho-Akt in all experimental groups remained unchanged. Since our animal model of depression is connected with hyperactivity of the HPA axis, our results suggest that GSK-3β is an important intracellular target for maladaptive glucocorticoid action on frontal cortex neurons and in antidepressant drug effects. Furthermore, the influence of stress and antidepressant drugs on GSK-3β does not appear to impact the kinase activity of Akt.     

Influence of aripiprazole on the antidepressant, anxiolytic and cognitive functions of rats

Recent research has suggested that cognitive disorders are a persistent trait of mental illnesses such as schizophrenia. Cognitive deficits in the course of schizophrenia may be due to the disease and/or drug therapy, especially with old-generation drugs. Several clinical experiments have indicated the beneficial effects of new-generation antipsychotics on cognitive processes in patients treated for mental disorders. Aripiprazole is a new, atypical antipsychotic with a unique mechanism of action, which may have positive effects on cognitive functions. The aim of this study was to investigate the effects of aripiprazole on spatial memory in the Morris water maze and antidepressant activity in the Porsolt test. In addition, we examined whether aripiprazole had any side effects in the chimney test. The behavioral tests showed that aripiprazole improved spatial memory in rats and had antidepressant and anxiolytic effects after a single treatment; however, aripiprazole impaired motor coordination after repeated administration. We concluded that aripiprazole could be an effective antipsychotic for the treatment of patients with schizophrenia or bipolar disorder who have associated anxiety and cognitive deficits.     

5-Hydroxytryptamine1A receptor agonists in animal models of depression and anxiety.

The effects of different doses of buspirone, 3-dipropyl-amino-5-hydrochromar (NDO 008) and 8-hydroxydipropyl-aminotetralin (8-OH-DPAT) (administered intraperitoneally) were studied in tests of anxiolytic and antidepressant action in rats. These tests included the elavated plus maze test, the forced swim test, stress-induced suppression of open-field behavior, and the differential-reinforcement-of-low-rates-of-behaviour-72 sec (DRL 72 s) test. Buspirone (0.125 mg/kg) and NDO 008 (1.0 to 2.0 mg/kg) produced anxiolytic activity in the elevated plus maze, whereas 8-OH-DPAT did not in the doses employed. All three compounds increased activity in the forced swim test, although buspirone did so at a lower dose than NDO 008 and 8-OH-DPAT. In the stress-induced suppression test of open field activity all three compounds induced an antidepressant-like effect at different doses dependent on whether footshock (stressor) was presented 24 hr before or just prior to the open-field test. All three compounds even caused some reduction of activity in the non-shocked rats. 8-OH-DPAT (1.0 mg/kg) produced a significant and reliable increase in the Reinforcement/Response rate quotient in the DRL 72s test. These diverse results may provide an indication of potential clinical efficacy of the 5-HT1A agonists in the treatment of anxiety and depression.     

5-Hydroxytryptamine1A Receptor Agonists in Animal Models of Depression and Anxiety

Abstract: The effects of different doses of buspirone, 3-dipropyl-amino-5-hydrochromar (NDO 008) and 8-hydroxydipropyl-aminotetralin (8-OH-DPAT) (administered intraperitoneally) were studied in tests of anxiolytic and antidepressant action in rats. These tests included the elevated plus maze test, the forced swim test, stress-induced suppression of open-field behavior, and the differential-reinforcement-of-low-rates-of-behaviour-72 sec (DRL 72 s) test. Buspirone (0.125 mg/kg) and NDO 008 (1.0 to 2.0 mg/kg) produced anxiolytic activity in the elevated plus maze, whereas 8-OH-DPAT did not in the doses employed. All three compounds increased activity in the forced swim test, although buspirone did so at a lower dose than NDO 008 and 8-OH-DPAT. In the stress-induced suppression test of open field activity all three compounds induced an antidepressant-like effect at different doses dependent on whether footshock (stressor) was presented 24 hr before or just prior to the open-field test. All three compounds even caused some reduction of activity in the non-shocked rats. 8-OH-DPAT (1.0 mg/kg) produced a significant and reliable increase in the Reinforcement/Response rate quotient in the DRL 72s test. These diverse results may provide an indication of potential clinical efficacy of the 5-HT_1A agonists in the treatment of anxiety and depression.     

The effect of venlafaxine on behaviour, body weight and striatal monoamine levels on sleep-deprived female rats

Partial sleep deprivation is clinically associated with fatigue, depressive symptoms and reduced memory. Previously, it has been demonstrated that venlafaxine, an atypical antidepressant, increases the levels of noradrenaline and serotonin in rat hippocampus. The aim of this study was to evaluate the effects of venlafaxine on depression, anxiety, locomotor activity and memory in a model of REM sleep (REMs) deprivation in rats. We have also studied the influence of venlafaxine on monoamine levels in the striatum. Six groups of animals (N=20 each) were treated with saline or venlafaxine (1 or 10 mg/kg) during 10 days, submitted or not to REMs deprivation and studied with the forced swimming test of Porsolt (STP), plus-maze, passive avoidance and open-field tests right after sleep deprivation. Animals were also studied for passive avoidance 24 h later (rebound period). Brain samples for monoamine measurements were collected either immediately after REMs deprivation or after 24 h. Both REMs deprivation and venlafaxine showed an antidepressant effect. An anxiolytic effect was also observed after REMs deprivation. Previous treatment with venlafaxine blocked the antidepressant and anxiolytic effects of REMs deprivation. REMs deprivation alone and treatment with venlafaxine 10 mg/kg increased locomotor activity, and this effect was inhibited by venlafaxine in REMs deprived rats. Both venlafaxine treatment and REMs deprivation induced weight loss. Venlafaxine treatment, but not REMs deprivation, induced an increase in striatal dopamine (DA) levels. The combination of REMs deprivation and venlafaxine treatment was associated with an increase in serotonin turnover 24 h after rebound sleep. In this study, venlafaxine treatment hindered most behavioral effects of REMs deprivation and was associated with an interference on dopamine and serotonin systems in the striatum.     

Concomitant use of carbamazepine and olanzapine and the effect on some behavioral functions in rats

As shown in clinical studies, combinations of first generation normothymics (carbamazepine - CBZ) with atypical neuroleptics (olanzapine - OLA) lead to improvements in approximately half of patients treated for relapses of bipolar affective disease. Our previous studies have shown OLA to have an antidepressant effect when administered at a dose of 0.5 mg/kg only upon single administration; the effect did not last throughout chronic administration, whereas CBZ administered at a dose of 30 mg/kg showed an antidepressant effect only after 7 days of administration. As shown in our previous studies, both OLA and CBZ improve memory in rats but only after chronic administration. The improved antidepressant effect of many drugs, including OLA and CBZ used in combined therapy - as observed in our clinic - as well as confirmed evidence of OLA's and CBZ's positive effects on cognitive functions in humans and animals substantiated commencement of research on defining the effect of combined administration of OLA and CBZ on sedation (tested in a locomotor activity test), antidepressant effect (Porsolt test) and spatial memory (Morris test) in animals. The tests were performed on male Wistar rats. It was found that in combined administration of CBZ and OLA for 7 and 14 days, OLA would completely prevent the CBZ's sedative effect. With combined administration of CBZ and OLA, both as a single dose and after prolonged treatment for 7 days, a significant reduction in immobility time was observed. Combined administration of CBZ and OLA did not improve memory in rats that received these drugs in a single dose, whereas statistically significant differences were observed in the chronic experiments. It can be assumed that the observed effects of combined administration of CBZ and OLA may be due to the pharmacokinetic interactions, but further studies are necessary to confirm these assumptions.     

D2-type dopaminergic receptors and anxiety-depression-like behavior in female rats

Results of a comparative study of the effects of chronic administration of the D2-receptor agonist quinperole (0.1 mg/kg, i.p.) and the D2-receptor antagonist sulpiride (10.0 mg/kg, i.p.) for 14 days on anxiety- and depressive-like behavior in key phases of the ovarian cycle in adult female rats are presented. The model of depression in rats was implemented in Porsolt test, while the anxiety level was assessed in the elevated plus maze test. It is established that the chronic administration of quinperole produced an anxiolytic action in female rats during diesrous, estrous and proestrous phases, but failed to modify depression-like behavior during the entire ovarian cycle. Sulpiride administration resulted in anxiogenic effect in all phases of the ovarian cycle. It was also found that sulpiride produced some modulation of depression-like behavior in connection to ovarian cycle phases, which was a prodepressive action at a moderate level of estrogens and an antidepressant effect at a reduced/enhanced level of estrogen. It is suggested that the extent of involvement of D2-receptors in the mechanisms of anxiety-depressive-like behavior can vary depending on alterations of the hormonal balance during the ovarian cycle. The data obtained are indicative of a close interaction between ovarian hormonal and dopaminergic systems of the brain involved in the mechanisms of anxiety and depression.     

Long-lasting effects of chronic chlorimipramine treatment of rats on exploratory activity on a hole-board, and on immobility in the forced swimming test

The study concerned the effects of acute and chronic clomipramine administration to male rats on exploratory activity in a novel environment (hole-board) and on immobility in the forced swimming test. Acute clomipramine administration did not alter either exploratory activity on a hole-board as measured 3 or 20 h after drug administration, or immobility in the forced swimming test as measured 20 h after drug administration. Approximately 20 h after the last injection of clomipramine, the rats chronically treated with the drug showed reduced exploratory activity on the hole-board. In contrast, chronic clomipramine treatment significantly increased the activity in the forced swimming test. The effects of the drug on exploratory and forced swimming activities persisted for 14 days after the cessation of clomipramine administration. These data indicate that chronic clomipramine administration exerted profound and long-lasting effects on central nervous system function. The long-lasting action of the drug on behaviour in the forced swimming test might explain the long-term beneficial effect of antidepressant drugs in counteracting behavioral depression.     

Novel aminopropiophenones as potential antidepressants

The atypical antidepressant drug bupropion and the psychostimulant drug methcathinone are both members of a chemical class known as aminopropiophenones. Differences in the psychoactive effects of these two drugs result from small variations in their chemical structures, but the relationship between chemical structure and psychoactivity has not been characterized. To investigate how structural modifications to aminopropiophenones affect antidepressant or stimulant activity, we synthesized several analogs of bupropion and methcathinone and tested the new compounds for antidepressant‐like or psychostimulant effects. The synthesized compounds are 2‐(methylamino)‐1‐(3‐bromophenyl)propan‐1‐one (3‐BMAP), 2‐(methylamino)‐1‐(4‐bromophenyl)propan‐1‐one (4‐BMAP), 2‐(iso‐propylamino)‐1‐phenylpropan‐1‐one (i‐PAP), and ‐(tert‐butylamino)‐1‐phenylpropan‐1‐one (t‐BAP). Bupropion, methcathinone, desipramine, and the newly‐synthesized aminopropiophenones were administered to rats for behavioral testing. We used the Porsolt swim test to assess antidepressant‐like activity and a locomotor activity assay to test for psychostimulant effects. All of the compounds displayed antidepressant‐like effects in the Porsolt swim test. Some compounds, including bupropion, increased locomotor activity at moderate‐to‐high doses. A halogenated analog of methcathinone, 4‐BMAP, increased swim time but did not stimulate locomotor activity, even at the highest dose tested. The data indicate that phenyl ring substitution or branched alkylamines can shift the psychopharmacological profile of aminopropiophenones from stimulant activity to antidepressant‐like activity. Several of the new drugs may be effective antidepressants in humans with fewer stimulant‐like side effects compared to bupropion. Drug Dev. Res. 60:252–260, 2003. © 2003 Wiley‐Liss, Inc.     

Antidepressant properties of rotigotine in experimental models of depression

Limited clinical data are available on the use of dopamine agonists for the control of motor function and also for the treatment of depression. This study was performed to evaluate the potential effects of the dopamine receptor agonist rotigotine in rat models of anxiety and depression. After repeated administration at doses of 0.05, 0.5, 1, and 5 mg/kg, rotigotine increased spontaneous motor activity at the 5 mg/kg dose after 3-5 days of treatment. At lower doses, the drug had no effect on locomotor activity. After a single administration, rotigotine had no anxiolytic activity in rats during the elevated plus-maze test or the Geller-Seifter conflict test. In the behavioral despair test (also known as the forced swim test), the 5 mg/kg dose of rotigotine enhanced the mobility of rats. Rotigotine (0.5, 1, and 5 mg/kg/day for 5 days) reversed the active avoidance deficit of helpless rats in the learned helplessness test, as shown by a significant decrease in escape failures after 3 to 4 days (0.5 mg/kg/day), 5 days (1 mg/kg/day), and 3 to 5 days (5 mg/kg/day) of treatment. During open-field testing of rats subjected to olfactory bulbectomy and given a 14-day schedule of rotigotine (0.3 mg/kg every 2 days), hyperactivity reversed according to a U-shaped dose-response curve. These results suggest that rotigotine may have antidepressant properties at doses of 1 mg/kg and lower. Potential effects at doses of 5 mg/kg and higher may be masked by an effect of the compound whereby general locomotor activity is enhanced.     

Potential Antidepressive Properties of Amantadine,Memantine and Bifemelane

Abstract: The effects of amantadine, its dimethyl derivative, memantine and the chemically unrelated compound bifemelane were tested for antidepressant activity. Reserpine-induced hypothermia and the forced swim test (Porsolt test) were selected for this purpose. In the former test amantadine and bifemelane but not memantine were effective. In the forced swim test all three agents produced antidepressive-like activity (decreased immobility time), but in case of bifemelane it was less pronounced. The effect in the forced swim test was specific i.e. it was apparently not the result of an increase in general activity as evidenced by control experiments in the open field. The mechanism of amantadine and memantine action may involve indirect dopaminomimetic activity resulting from the blockade of NMDA receptors. However in reserpine-induced hypothermia this explanation is not valid considering the lack of effect of memantine and positive action of amantadine. Hence, amantadine may have an additional central sympathomimetic action that memantine is lacking. Bifemelane antidepressant-like activity might be attributed to an enhancement of noradrenergic transmission. We suggested that amantadine and bifemelane could be particularly useful therapeutically when depressive symptoms are present in patients suffering from Parkinson's disease and dementia.     

Effect of 8-OH-DPAT on the depressive behavior and monoamine metabolism in the hippocampus of ovariectomized rats

The influence of the chronic administration of the 5-HT1A receptor agonist 8-OH-DPAT (0.05 mg/kg, s.c.) and the 5-HT1A receptor antagonist NAN-190 (0.1 mg/kg, i.p.) alone or in combination with 17beta-estradiol (0.5 microg per animal, i.m.) for 14 days on the depression behavior and the monoamine level in hippocampus has been studied in adult ovariectomized (OVX) female rats. The model of depression in rats was realized under the Porsolt test conditions. The levels of monoamine and its metabolites were determined using HPLC. It was established that the chronic administration of 8-OH-DPAT alone produces an antidepressant effect in OVX rats. The chronic administration of 8-OH-DPAT in combination with 17beta-estradiol potentiated the antidepressant action of both preparations. The antidepressant effect of 8-OH-DPAT in OVX rats was correlated with the restoration of noradrenergic, serotoninergic, and dopaminergic neurotransmission in the hippocampus. The obtained data are indicative of a close interaction between the ovarian hormonal system and the cerebral serotoninergic system in the realization of depression mechanisms.     

Effects of antagonists of 1A and 2A/2C subtypes of serotonin receptors on the depressive behavior and expression of c-Fos protein in hypothalamus of ovariectomized rats

We have studied the influence of a chronic administration of the 5-HT(2A/2C) receptor antagonist ketanserin (0.1 mg/kg, i.p.) and the 5-HT(1A) receptor antagonist NAN-190 (0.1 mg/kg, i.p.) alone or in combinations with 17beta-estradiol (0.5 mg per animal, i.m.) for 14 days on the depressive behavior and expression of c-Fos protein in the paraventricular nucleus of hypothalamus in adult ovariectomized (OVX) female rats. The depression in rats was modeled by the Porsolt test. The c-Fos protein expression in the paraventricular nucleus of hypothalamus was determined using immunohistochemical techniques. In the Porsolt test, 17beta-estradiol in OVX rats reduced the immobilization time to some extent. Ketanserin alone significantly decreased the immobilization time in OVX rats. The chronic administration of ketanserin in combination with 17beta-estradiol in OVX females potentiated the antidepressant effect of ketanserin. At the same time, ketanserin administration led to a significant decrease in the level of c-Fos protein in the hypothalamus in OVX rats as compared to the intact control. These results are indicative of a substantial interaction between the ovarian hormonal system and the serotoninergic brain system involved the mechanisms of depression.     

The differential effects of post-session administration of amineptine and imipramine on memory processes in mice

The effects of post-trial administration of amineptine, a dopaminergic antidepressant drug, were compared with those of memory-facilitating (strychnine, piracetam) or impairing drugs (phenobarbital, imipramine) on an experimental model of memory. Mice were given two sessions in open-field test and the decrease in activity at the second session (habituation) served as an index of retention. The good retention observed with a 1-day inter-session interval was impaired by post-session administration of phenobarbital (10 mg/kg i.p.) or imipramine (5.0 mg/kg i.p.). The poor retention observed with a 5-day inter-session interval was enhanced by post-session administration of strychnine (0.20 mg/kg i.p.), piracetam (1000 mg/kg i.p.) and amineptine (10 mg/kg i.p.). These findings show that different profiles of cognitive and psychomotor effects were produced by imipramine and amineptine. Amineptine, lacking sedative and anticholinergic properties which are characteristic of imipramine, interferes positively with learning and memory, in a manner similar to piracetam and strychnine.     

Fluoxetine-induced increases in open-field habituation in the olfactory bulbectomized rat depend on test aversiveness but not on anxiety

Little is known regarding the functional processes underlying the treatment efficacy of antidepressant drugs. Given the close association between stress, anxiety and depression, distinguishing the common and disparate features of these processes may contribute to our current understanding. Using the olfactory bulbectomized (OBX) rat, an animal model sensitive to a variety of antidepressant drugs, this study examined the effects of chronic fluoxetine administration on open-field behavior under different conditions of stressfulness (luminance) and compared the fluoxetine effects to those evoked by the anxiolytic lorazepam. Sham-operated and OBX rats received 21 daily injections of fluoxetine (10 mg/kg), one or seven injections of lorazepam (0.1 and 0.5 mg/kg) or vehicle prior to testing in the open field or plus maze. Time series data were collected and fit with exponential regression models to estimate behavioral reactivity, habituation and residual rate of responding. Relative to sham controls, OBX rats displayed increased locomotor activity in the high luminance open field but showed decreased activity in the lower luminance open field. Time series analysis revealed that while sham animals showed increased habituation in the high compared to lower luminance open field, OBX rats did not significantly modify their responding between the two conditions. Chronic fluoxetine treatment invoked rectifying effects in OBX animals only in the high luminance open field by increasing the rate of habituation. Both acute and subchronic administration of lorazepam also reduced OBX hyperactivity but did so only by decreasing the residual rate of responding. As expected, lorazepam administration significantly increased the ratio of open-to-total arm activity in the elevated plus maze. These findings suggest that OBX responding in the open field may be maladaptive, reflecting an inability to modify behavior appropriately in certain environmental contexts. Chronic antidepressant treatment enhances habituation of OBX animals only under more stressful or aversive conditions and appears to do so in a manner temporally distinct from anxiolytic treatment.     

Antidepressant effects of thyrotropin-releasing hormone analogues using a rodent model of depression

The antidepressant potential of two naturally occurring analogues of thyrotropin-releasing hormone (TRH), pGLU-GLU-PRO-NH2 (EEP) and pGLU-PHE-PRO-NH2 (EFP), were examined using a rodent model of antidepressant efficacy. The Porsolt Swim Test was used to assay the antidepressant properties of these two peptides. Both analogues of TRH produced significant antidepressant effects, with EEP producing the stronger response. No effect of EEP upon triiodothyronine (T3) was observed at the dosage used. EFP, which has previously been demonstrated to crossreact with the TRH receptor, significantly increased serum T3. Since an effect upon T3 was only observed in the weaker of the two compounds, these data suggest that the behavioral effect of EEP was not secondary to stimulation of thyroid hormone. Additionally, the differential behavioral response to the two compounds suggests a degree of sequence specificity in the ability of TRH-like tripeptides to produce an antidepressant effect.