Electroconvulsive seizures increase levels of pGlu-Glu-Pro-NH2 (EEP) in rat brain

Ketamine modulates TRH and TRH-like peptide turnover in brain and peripheral tissues of male rats

Major depression is the largest single healthcare burden with treatments of slow onset and often limited efficacy. Ketamine, a NMDA antagonist used extensively as a pediatric and veterinary anesthetic, has recently been shown to be a rapid acting antidepressant, making it a potential lifesaver for suicidal patients. Side effects and risk of abuse limit the chronic use of ketamine. More complete understanding of the neurobiochemical mechanisms of ketamine should lead to safer alternatives. Some of the physiological and pharmacological actions of ketamine are consistent with increased synthesis and release of TRH (pGlu-His-Pro-NH2), and TRH-like peptides (pGlu-X-Pro-NH2) where "X" can be any amino acid residue. Moreover, TRH-like peptides are themselves potential therapeutic agents for the treatment of major depression, anxiety, bipolar disorder, epilepsy, Alzheimer's and Parkinson's diseases. For these reasons, male Sprague-Dawley rats were anesthetized with 162 mg/kg ip ketamine and then infused intranasally with 20 μl of sterile saline containing either 0 or 5 mg/ml Glu-TRH. One, 2 or 4h later, the brain levels of TRH and TRH-like peptides were measured in various brain regions and peripheral tissues. At 1h in brain following ketamine only, the levels of TRH and TRH-like peptides were significantly increased in 52 instances (due to increased biosynthesis and/or decreased release) or decreased in five instances. These changes, listed by brain region in order of decreasing number of significant increases (↑) and/or decreases (↓), were: hypothalamus (9↑); piriform cortex (8↑); entorhinal cortex (7↑); nucleus accumbens (7↑); posterior cingulate (5↑); striatum (4↑); frontal cortex (2↑,3↓); amygdala (3↑); medulla oblongata (1↑,2↓); cerebellum (2↑); hippocampus (2↑); anterior cingulate (2↑). The corresponding changes in peripheral tissues were: adrenals (8↑); epididymis (4↑); testis (1↑,3↓); pancreas (1↑); prostate (1↑). We conclude that TRH and TRH-like peptides may be downstream mediators of the rapid antidepressant actions of ketamine.

Rapid modulation of TRH and TRH-like peptide release in rat brain and peripheral tissues by ghrelin and 3-TRP-ghrelin

Ghrelin is not only a modulator of feeding and energy expenditure but also regulates reproductive functions, CNS development and mood. Obesity and major depression are growing public health concerns which may derive, in part, from dysregulation of ghrelin feedback at brain regions regulating feeding and mood. We and others have previously reported that thyrotropin-releasing hormone (TRH, pGlu-His-Pro-NH(2)) and TRH-like peptides (pGlu-X-Pro-NH(2), where "X" can be any amino acid residue) have neuroprotective, antidepressant, anti-epileptic, analeptic, anti-ataxic, and anorectic properties. For this reason male Sprague-Dawley rats were injected ip with 0.1mg/kg rat ghrelin or 0.9mg/kg 3-Trp-rat ghrelin. Twelve brain regions: cerebellum, medulla oblongata, anterior cingulate, posterior cingulate, frontal cortex, nucleus accumbens, hypothalamus, entorhinal cortex, hippocampus, striatum, amygdala, piriform cortex and 5 peripheral tissues (adrenals, testes, epididymis, pancreas and prostate) were analyzed. Rapid and profound decreases in TRH and TRH-like peptide levels (increased release) occurred throughout brain and peripheral tissues following ip ghrelin. Because ghrelin is rapidly deacylated in vivo we also studied 3-Trp-ghrelin which cannot be deacylated. Significant increases in TRH and TRH-like peptide levels following 3-Trp-ghrelin, relative to those after ghrelin were observed in all brain regions except posterior cingulate and all peripheral tissues except prostate and testis. The rapid stimulation of TRH and TRH-like peptide release by ghrelin in contrast with the inhibition of such release by 3-Trp-TRH is consistent with TRH and TRH-like peptides modulating the downstream effects of both ghrelin and unacylated ghrelin.

Neuroglialpharmacology: myelination as a shared mechanism of action of psychotropic treatments

Current psychiatric diagnostic schema segregate symptom clusters into discrete entities, however, large proportions of patients suffer from comorbid conditions that fit neither diagnostic nor therapeutic schema. Similarly, psychotropic treatments ranging from lithium and antipsychotics to serotonin reuptake inhibitors (SSRIs) and acetylcholinesterase inhibitors have been shown to be efficacious in a wide spectrum of psychiatric disorders ranging from autism, schizophrenia (SZ), depression, and bipolar disorder (BD) to Alzheimer's disease (AD). This apparent lack of specificity suggests that psychiatric symptoms as well as treatments may share aspects of pathophysiology and mechanisms of action that defy current symptom-based diagnostic and neuron-based therapeutic schema. A myelin-centered model of human brain function can help integrate these incongruities and provide novel insights into disease etiologies and treatment mechanisms. Available data are integrated herein to suggest that widely used psychotropic treatments ranging from antipsychotics and antidepressants to lithium and electroconvulsive therapy share complex signaling pathways such as Akt and glycogen synthase kinase-3 (GSK3) that affect myelination, its plasticity, and repair. These signaling pathways respond to neurotransmitters, neurotrophins, hormones, and nutrition, underlie intricate neuroglial communications, and may substantially contribute to the mechanisms of action and wide spectra of efficacy of current therapeutics by promoting myelination. Imaging and genetic technologies make it possible to safely and non-invasively test these hypotheses directly in humans and can help guide clinical trial efforts designed to correct myelination abnormalities. Such efforts may provide insights into novel avenues for treatment and prevention of some of the most prevalent and devastating human diseases.

Rapid modulation of TRH and TRH-like peptide release in rat brain and peripheral tissues by leptin

Leptin is not only a feedback modulator of feeding and energy expenditure but also regulates reproductive functions, CNS development and mood. Obesity and major depression are growing public health concerns which may derive, in part, from disregulation of leptin feedback at the level of the hypothalamic feeding centers and mood regulators within the limbic system. Identifying downstream mediators of leptin action may provide therapeutic opportunities. We and others have previously reported that thyrotropin-releasing hormone (TRH, pGlu-His-Pro-NH(2)) and TRH-like peptides (pGlu-X-Pro-NH(2), where "X" can be any amino acid residue) have neuroprotective, antidepressant, anti-epileptic, analeptic, anti-ataxic, and anorectic properties. For this reason, young, adult male Sprague-Dawley rats were injected ip with 1mg/kg rat leptin and peptide and protein levels were measured in brain and peripheral tissues at 0, 0.5, 1 and 2h later. Eleven brain regions: pyriform cortex (PYR), entorhinal cortex (ENT), cerebellum (CBL), nucleus accumbens (NA), frontal cortex (FCX), amygdala (AY), posterior cingulate (PCNG), striatum (STR), hippocampus (HC), medulla oblongata (MED) and anterior cingulate (ACNG) and five peripheral tissues (adrenals, testes, epididymis, pancreas and prostate) were analyzed. TRH and six TRH-like peptide levels in STR fell by 0.5h consistent with leptin-induced release of these peptides: STR (7 downward arrow). Significant changes in TRH and TRH-like peptide levels for other brain regions were: CBL (5 downward arrow), ENT (5 downward arrow), HC (4 downward arrow), AY (4 downward arrow), FCX (3 downward arrow), and ACNG (1 downward arrow). The rapid modulation of TRH and TRH-like peptide release combined with their similarity in behavioral, neuroendocrine, immunomodulatory, metabolic and steroidogenic effects to that of leptin is consistent with these peptides participating in downstream signaling.

Rapid modulation of TRH and TRH-like peptide release in rat brain, pancreas, and testis by a GSK-3beta inhibitor

Antidepressants have been shown to be neuroprotective and able to reverse damage to glia and neurons. Thyrotropin-releasing hormone (TRH) is an endogenous antidepressant-like neuropeptide that reduces the expression of glycogen synthase kinase-3beta (GSK-3beta), an enzyme that hyperphosphorylates tau and is implicated in bipolar disorder, diabetes and Alzheimer's disease. In order to understand the potential role of GSK-3beta in the modulation of depression by TRH and TRH-like peptides and the therapeutic potential of GSK-3beta inhibitors for neuropsychiatric and metabolic diseases, young adult male Sprague-Dawley (SD) rats were (a) injected ip with 1.8mg/kg of GSK-3beta inhibitor VIII (GSKI) and sacrificed 0, 2, 4, 6, and 8h later or (b) injected with 0, 0.018, 0.18 or 1.8mg/kg GSKI and bled 4h later. Levels of TRH and TRH-like peptides were measured in various brain regions involved in mood regulation, pancreas and reproductive tissues. Large, 3-15-fold, increases of TRH and TRH-like peptide levels in cerebellum, for example, as well as other brain regions were noted at 2 and 4h. In contrast, a nearly complete loss of TRH and TRH-like peptides from testis within 2h and pancreas by 4h following GSKI injection was observed. We have previously reported similar acute effects of corticosterone in brain and peripheral tissues. Incubation of a decapsulated rat testis with either GSKI or corticosterone accelerated release of TRH, and TRH-like peptides. Glucocorticoids, via inhibition of GSK3-beta activity, may thus be involved in the inhibition of TRH and TRH-like peptide release in brain, thereby contributing to the depressogenic effect of this class of steroids. Corticosterone-induced acceleration of release of these peptides from testis may contribute to the decline in reproductive function and redirection of energy needed during life-threatening emergencies. These contrasting effects of glucocorticoid on peptide release appear to be mediated by GSK-3beta.

Evidence for interplay between thyrotropin-releasing hormone (TRH) and its structural analogue pGlu-Glu-Pro-NH2 ([Glu2]TRH) in the brain: an in vivo microdialysis study

Local perfusion of pGlu-Glu-Pro-NH2, an endogenous peptide structurally related to thyrotropine-releasing hormone (TRH), via in vivo microdialysis into the rat hippocampus did not change the basal level of extracellular acetylcholine. However, co-perfusion of pGlu-Glu-Pro-NH2 with TRH in equimolar concentrations yielded a significant attenuation of TRH-induced acetylcholine release. The results have supported the study's hypothesis that pGlu-Glu-Pro-NH2 opposes the cholinergic effect of TRH in the mammalian central nervous system. The enantiomer pGlu-d-Glu-Pro-NH2 affected neither basal extracellular nor TRH-induced increase of acetylcholine levels.

Circadian rhythms of TRH-like peptide levels in rat brain

This is the first report of diurnal variations in the levels of thyrotropin-releasing hormone-like peptides (pGlu-X-Pro-NH(2), where "X" can be any amino acid residue) in brain regions involved in mood regulation. These peptides have neuroprotective and antidepressant-like properties that may help stabilize chronobiologic systems that are often abnormal in neuropsychiatric disease. We hypothesized that diurnal fluctuations in the levels of these neuropeptides are components of the chronobiologic regulation of autonomic, behavioral and emotional states. Optimal use of these potentially therapeutic agents will benefit from an understanding of their response to, and effect on, normal vegetative, activity and sleep patterns, and the corresponding disordered patterns of mental illness. For these reasons, 16 male, 200 g, Sprague-Dawley rats were maintained for 4 weeks in a stable 12 h lights on, 12 h lights off photoperiod. Levels of TRH and TRH-like peptides were measured at 3.0 h, 10.5 h, 13.5 h and 21.0 h, where the subjective midnight was 0.0 h, by a combination of HPLC and RIA. Highly significant changes in TRH-like peptide levels were observed in the striatum, posterior cingulate, cerebellum, pyriform cortex, nucleus accumbens and medulla oblongata. TRH-like peptide levels, in general, were highly correlated with changes in TRH concentration, within and between brain regions, and may be colocalized in large glutamatergic neurons innervating the rat limbic system. We conclude that TRH-like peptides may be important components of chronobiologic systems involved in maintaining autonomic, behavioral and mood equilibria.

TRH-like antidepressant peptide, pyroglutamyltyroslyprolineamide, occurs in rat brain

We have previously reported the occurrence of pGlu-Glu-Pro-NH(2)(Glu-TRH, EEP), Val-TRH, Tyr-TRH, Leu-TRH, Phe-TRH, and Trp-TRH in rat brain using a combination of HPLC and radioimmunoassays with antibodies that cross-react with the general structure pGlu-X-Pro-NH(2) where 'X' maybe any amino acid residue (Peptides 2004; 25 : 647). This new family of TRH-like peptides, along with TRH (pGlu-His-Pro-NH(2)), has neuroprotective, anticonvulsant, antidepressant, euphoric, anti-amnesic, and analeptic effects. We now report that a combination of affinity chromatography using a rabbit antibody specific for Tyr-TRH and Phe-TRH, along with HPLC and tandem mass spectrometry operating in the multiple reaction monitoring (MRM) mode, provide conclusive evidence for the presence of Tyr-TRH in rat brain. Furthermore, synthetic Tyr-TRH is active in the Porsolt Swim Test suggesting that it is a fourth member of this family of in vivo neuroregulatory agents that have psychopharmacotherapeutic properties.

Prodrugs to enhance central nervous system effects of the TRH-like peptide pGlu-Glu-Pro-NH2

Potential prodrugs for the TRH-like tripeptide pGlu-Glu-Pro-NH(2) were synthesized either by esterifying the Glu side-chain of the parent peptide in solution with alcohols in the presence of resin-bound dicyclohexylcarbodiimide or by solid-phase peptide chemistry. Affinities of these ester prodrugs to lipid membranes as predictors of the transport across the blood-brain barrier were compared by immobilized artificial membrane chromatography, and prodrug activation was tested in the brain tissue of experimental animals. Esters of pGlu-Glu-Pro-NH(2) with long-chain primary alcohols emerged as potentially useful prodrugs to improve the central nervous system activity of pGlu-Glu-Pro-NH(2) upon systemic administration, as revealed by the enhancement of analeptic activity in mice.

Lithium modulates expression of TRH receptors and TRH-related peptides in rat brain

Lithium is an established mood stabilizer and neuroprotective agent frequently used in the treatment of bipolar disorder and as an adjuvant in drug-resistant unipolar depression. The mechanisms underlying both the therapeutic efficacy of lithium and the exacerbation of symptoms following rapid withdrawal are not understood. From previous studies showing antidepressant and neuroprotective activities of thyrotropin releasing hormone (TRH) and TRH-related neuropeptides we hypothesized that lithium may have substantial effects on the expression and secretion of these peptides and/or their receptors in various rat brain regions involved in the regulation of mood. Chronic lithium effect on TRH receptor binding studies: The effect of 1 and 2 weeks of dietary lithium on [(3)H]3-Me-His-TRH binding to plasma membranes of nucleus accumbens, amygdala and pituitary of young adult male Wistar and the endogenously 'depressed' Wistar Kyoto (WKY) rats was measured by the method of Burt and Taylor [Burt, D.R., Taylor, R.L., Endocrinology 106 (1980) 1416-1423]. Acute, chronic and withdrawal effect of lithium on TRH and TRH-like peptide levels in young, adult male Sprague-Dawley rats: Rats were divided into four lithium treatment groups. Control animals received a standard laboratory rodent chow. The acute group received a single i.p. injection of 1.5 milli-equivalents of LiCl 2 h prior to killing. The chronic and withdrawal groups received standard rodent chow containing 1.7 g/kg LiCl for 2 weeks. Withdrawal rats were returned to standard chow 48 h prior to killing while the chronic animals continued on the LiCl diet. TRH, TRH-Gly (pGlu-His-Pro-Gly, a TRH precursor), EEP (pGlu-Glu-Pro-NH(2), a TRH-like peptide with antidepressant activity) and Ps4 (a prepro-TRH-derived TRH-enhancing decapeptide) immunoreactivity (IR) were measured in 13 brain regions. The remaining samples were pooled and fractionated by high-pressure liquid chromatography followed by EEP radioimmunoassay. Chronic lithium treatment increased [(3)H]3Me-TRH binding in the nucleus accumbens and amygdala about two-fold in both Wistar and WKY rats but no change was observed in pituitary binding. The most widespread changes in TRH and TRH-related peptide levels were observed in the withdrawal group compared to the controls. The direction of change for the total IR was consistent for all TRH-IR and TRH-related peptide-IR within a given tissue. For example, withdrawal increased all peptide levels in the pyriform cortex and striatum but decreased these levels in the anterior cingulate and lateral cerebellum. Both acute injection and chronic treatment with LiCl decreased TRH and TRH-related peptide levels in the entorhinal cortex. Acute injection and withdrawal both increased EEP-IR in striatum by more than two-fold. The acute effects are most likely due to changes in the release of these peptides since 2 h is not sufficient time for alterations in peptide biosynthesis. Chronic treatment increased levels of pGlu-Phe-Pro-NH(2) levels in hippocampus, pGlu-Leu-Pro-NH(2), and peak '2' in septum by more than four-fold. The present results are consistent with a component role for TRH and related peptides in the mood-altering effects of lithium administration and withdrawal frequently observed during treatment for depression and bipolar disorder.

Cocaine regulates TRH-related peptides in rat brain

Cocaine administration has previously been reported to alter the levels of prepro-TRH mRNA and TRH (pGlu-His-Pro-NH(2)) in the limbic system of rats (J. Neurochem. 60 (1993) 1151). We have now demonstrated that a previously unrecognized family of TRH-like peptides is involved in the actions of cocaine. We treated young adult male Sprague-Dawley rats (five per group, 250g body weight at sacrifice) for 2 weeks with either twice daily injections of saline (control group), twice daily injections of 15mg/kg cocaine until sacrifice (chronic group), single injection of 15mg/kg cocaine 2h prior to sacrifice (acute group) or chronic cocaine injections replaced by saline injections 72h prior to sacrifice (withdrawal group (WD)). Twelve different brain regions were dissected and immunoreactivity for TRH (TRH-IR), EEP (pGlu-Glu-Pro-NH(2); EEP-IR) and related peptides were measured by radioimmunoassay (RIA). High pressure liquid chromatography (HPLC) revealed that in many brain regions EEP-IR and TRH-IR consisted of a mixture of TRH, and other TRH-like peptides including EEP, pGlu-Val-Pro-NH(2) (Val(2)-TRH), pGlu-Tyr-Pro-NH(2) (Tyr(2)-TRH), pGlu-Leu-Pro-NH(2) (Leu(2)-TRH), and pGlu-Phe-Pro-NH(2) (Phe(2)-TRH). Following i.p. injection, these TRH-like peptides readily crossed the blood-brain barrier but cleared very slowly from brain tissues. Acute cocaine produced a 4.1-fold increase in Val(2)-TRH level in medulla while Val(2)-TRH and Tyr(2)-TRH, increased 6.2- and 2.9-fold, respectively in pyriform cortex PYR. TRH and Leu(2)-TRH, decreased 47 and 93%, respectively in the nucleus accumbens (AM) while other EEP-IR peaks decreased 50-100% consistent with the significant decrease in total EEP-IR in the AMs following acute cocaine treatment. Because 2h is too short a time to alter levels of neuropeptides via changes in the rate of biosynthesis, the acute cocaine-induced elevation or reduction in TRH and related peptides is most likely due to suppression or stimulation, respectively, of the corresponding peptide secretion rate. Because TRH and TRH-like peptides have antidepressant, analeptic and euphorigenic properties, we conclude that these endogenous substances are potential mediators of both the cocaine "high" and withdrawal symptoms.

Nutrition and brain function: a multidisciplinary virtual symposium

A few months ago, the Brazilian Society for Neuroscience and Behavior (SBNeC) promoted a "virtual symposium" (by Internet, under the coordination of R.C.A. Guedes) on "Nutrition and Brain Function". The discussions generated during that symposium originated the present text, which analyzes current topics on the theme, based on the multidisciplinary experience of the authors. The way the brain could be non-homogeneously affected by nutritional alterations, as well as questions like early malnutrition and the development of late obesity and hormone abnormalities were discussed. Also, topics like the role of essential fatty acids (EFAs) on brain development, increased seizure susceptibility and changes in different neurotransmitters and in cognitive performance in malnourished animals, as well as differences between overall changes in nutrient intake and excess or deficiency of specific nutrients (e.g. iodine deficiency) were analyzed. It was pointed out that different types of neurons, possibly in distinct brain structures, might be differently affected by nutritional manipulation, including not only lack-but also excess of nutrient intake. Such differences could help in explaining discrepancies between data on humans and in animals and so, could aid in determining the basic mechanisms underlying lesions or changes in brain function and behavior.

Role of TRH receptors as possible mediators of analeptic actions of TRH-like peptides

A large family of TRH-like peptides in the limbic region of rat brain including pGlu-Glu-Pro-NH(2) (EEP), pGlu-Val-Pro-NH(2) (Val(2)-TRH), Leu(2)-TRH, Phe(2)-TRH and Tyr(2)-TRH has recently been discovered. TRH (pGlu-His-Pro-NH(2)) has antidepressant, neuroprotective, analeptic, anticonvulsant, antiamnesic and euphoric properties, and other TRH-like peptides such as EEP exert several of these effects. A new TRH receptor (TRHR2) has been reported which is highly expressed in regions of rat brain that regulate attention and learning, arousal, sleep and processing of sensory information. The TRHR1 predominates in limbic structures involved in regulation of mood and in pituitary. This study examined the possibility that some of the newly discovered TRH-like peptides bind with high affinity to TRHR2, and that this receptor acts as the transducer for some of the CNS effects of this new class of neuropeptides. EEP, Val(2)-TRH and Leu(2)-TRH were analeptics, like TRH, but Phe(2)-TRH and Tyr(2)-TRH were not. The affinity and efficacy of TRH-like peptides for TRHR1 and TRHR2 were measured in HEK293 cells stably expressing these receptors. The IC(50) values of TRH-like peptides for displacement of [3H]TRH from TRHR2 were TRH<<<(Leu(2)-, Phe(2)-TRH)<(Gln(2)-, Ser(2)-TRH)<<(Val(2)-, Tyr(2)-, Arg(2)-, Thr(2)-, and Glu(2)-TRH). The IC(50) for Leu(2)-TRH was about 100 times that for TRH. When tested at the calculated IC(50) values, TRH-like peptides stimulated calcium responses in cells expressing TRHR1 and TRHR2, indicating that the peptides act as weak agonists at both receptors. These results indicate that TRHR1 and TRHR2 do not mediate the behavioral effects of TRH-like peptides.

In vitro neuroprotection against glutamate-induced toxicity by pGlu-Glu-Pro-NH(2) (EEP)

EEP is a tripeptide structurally similar to thyrotropin releasing hormone (TRH) and, like TRH, it is found in the mammalian brain. TRH has been found to increase in brain regions after seizures and to be neuroprotective. EEP has also been shown to increase in brain regions following seizure activity. We therefore sought to determine whether the similarities between these two peptides might be extended to include neuroprotection. Both TRH and EEP were found to be neuroprotective in vitro against an excitotoxic insult. Interestingly, the two tripeptides appeared to have different mechanisms of action. Even though EEP was as much as four times more neuroprotective than TRH, its ability to reduce glutamate-stimulated increases in intraneuronal Ca(2+) was about half that of TRH.

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.

Regulation of TRH and TRH-related peptides in rat brain by thyroid and steroid hormones

To investigate the possibility that TRH (pGlu-His-Pro-NH(2)) and EEP (pGlu-Glu-Pro-NH(2)) contribute to the behavioral and mood changes attending hypothyroidism, hyperthyroidism and hypogonadism, we have treated young, adult, male Sprague-Dawley rats (5/group, 250 g bw at time of sacrifice) for one week with either daily ip injections of saline, 5 microg T(4), 3 mg PTU or castration. Immunoreactivity for TRH (TRH-IR), TRH-Gly (pGlu-His-Pro-Gly, a TRH precursor), EEP and Ps4 (prepro-TRH-derived TRH-enhancing peptide) was measured in 8 brain regions by RIA. Castration reduced the Ps4-IR levels in hippocampus by 80%. High pressure liquid chromatography revealed that in many brain regions EEP-IR and TRH-IR consisted of a mixture of TRH and other TRH-like peptides including EEP, Val(2)-TRH, Tyr(2)-TRH, Leu(2)-TRH and Phe(2)-TRH. Transition from the hyperthyroid to the hypothyroid state increased the Val(2)-TRH and Tyr(2)-TRH levels in the accumbens by 10-fold and 15-fold, respectively, and the corresponding ratios for the pyriform cortex increased 9-fold and 12-fold, respectively. Hypothyroidism and castration reduced the levels of TRH and the majority of other TRH-like peptides in the entorhinal cortex. This is the first report that thyroid and steroid hormones alter the levels of TRH, prepro-TRH-derived peptides, and a newly discovered array of TRH-like neuropeptides in limbic brain regions.

Electroconvulsive seizures modulate levels of thyrotropin releasing hormone and related peptides in rat hypothalamus, cingulate and lateral cerebellum

We have studied the neuroanatomic extent of electroconvulsive (ECS)-responsive prepro-TRH and TRH-related gene expression and its possible interaction with forced swimming. Young adult male Wistar rats were treated in a 2x2 Latin square protocol of swimming, no swimming, three daily ECS or sham ECS. Sixteen different brain regions were dissected and immunoreactivity measured for TRH (pGlu-His-Pro-NH(2)); TRH-Gly, a TRH precursor; Ps4, a prepro-TRH-derived TRH-enhancing decapeptide, and EEP (pGlu-Glu-Pro-NH(2)). ECS, in addition to elevating TRH-immunoreactivity (TRH-IR), TRH-Gly-IR, Ps4-IR and EEP-IR levels in the limbic regions, as we have previously reported, also significantly increased Ps4-IR levels in hypothalamus, posterior cingulate and lateral cerebellum, and increased TRH-Gly-IR levels in hypothalamus. Interestingly, the combination of ECS and swimming significantly reduced the levels of TRH-Gly-IR in the anterior cingulate compared to the sham ECS-no swim group. The combined use of high-pressure liquid chromatography and the EEP radioimmunoassay (RIA) revealed that pGlu-Tyr-Pro-NH(2) and/or pGlu-Phe-Pro-NH(2) occur in amygdala, anterior cingulate, frontal cortex, entorhinal cortex, lateral cerebellum and striatum and make a substantial contribution to the EEP-IR and TRH-IR. We conclude that ECS can alter the expression and secretion of TRH-related peptides in the hypothalamus, cingulate and lateral cerebellum. Such effects have not previously been reported in these limbic and extra-limbic regions which are increasingly implicated in the autonomic, behavioral and volitional changes which accompany severe depression and its treatment.

Antidepressants: past, present and future

Since the discovery of first antidepressants in mid-1950's, the field has been intensively studied. Several new classes of compounds emerged and several hypotheses on the mechanism of their action were proposed. The novel antidepressants are either selective and reversible monoamine oxidase inhibitors, (e.g., moclobemide), or selective serotonin reuptake inhibitors (e.g., citalopram or paroxetine), or serotonin and noradrenaline reuptake inhibitors (e.g. , venlafaxine). Recently neuropeptides (e.g., thyrotropin-releasing hormone,TRH) or antagonists of neuropeptide receptors (e.g., tachykinin NK(1) receptor) undergo clinical tests. Several hypotheses proposed the predominant involvement of one or few neurotransmitter receptors in the mechanism of antidepressant action, but it is now assumed that several distinct receptor mechanisms' trigger different but converging intracellular signal cascades that activate transcription factors, which, in turn, promote the expression of genes encoding for proteins, that play a crucial role in restoring of neuronal functions involved in mood regulation.

Characterization of neutral TRH-like peptides in mammary gland, mammary tumors and milk

Three pyroglutamylpeptide amides, pGlu-Glu-Pro amide, pGlu-Phe-Pro amide and pGlu-Gln-Pro amide, with similar structures to thyrotropin-releasing hormone (TRH), have been identified previously in the male reproductive system. We report here that rat and human mammary gland contain neutral TRH-immunoreactive peptides which are not retained on cation or anion exchange chromatography and that similar peptides occur in the milk of rat, cow, ewe and sow. The TRH-like peptides in lyophilized milk from the cow were purified by gel exclusion chromatography, mini-column cation exchange chromatography and reversed phase high performance liquid chromatography (HPLC) and the chromatographed peptides were located by TRH radioimmunoassay (RIA). In each chromatographic system the major TRH-immunoreactive peptide from cow milk exhibited identical behavior to pGlu-Phe-Pro amide; in addition there were two minor TRH-immunoreactive components. The possible physiological role of the TRH-like peptides in the mammary gland is discussed. In a series of patients with breast carcinoma, mammary tumor tissue was shown to contain approximately four times more TRH-like peptide than normal mammary tissue from the same patient, raising the possibility that the TRH-like peptides may be implicated in tumor development.