Effect of electroconvulsive shock on the content of thyrotropin-releasing hormone in rat brain

Thyrotropin-releasing hormone d,l polylactide nanoparticles (TRH-NPs) protect against glutamate toxicity in vitro and kindling development in vivo

Thyrotropin-releasing hormone (TRH) is reported to have anticonvulsant effects in animal seizure models and certain intractable epileptic patients. However, its duration of action is limited by rapid tissue metabolism and the blood brain barrier. Direct nose-brain delivery of neuropeptides in sustained-release biodegradable nanoparticles (NPs) is a promising mode of therapy for enhancing CNS bioavailability. Bioactivity/neuroprotection of d,l polylactide nanoparticles containing TRH was assessed against glutamate toxicity in cultured rat fetal hippocampal neurons. Subsequently, we utilized the kindling model of temporal lobe epilepsy to determine if intranasal administration of nanoparticles containing TRH (TRH-NPs) could inhibit kindling development. Animals received daily treatments of either blank (control) or TRH-NPs for 7 days before initiation of kindling. On day 8 and each day thereafter until either fully kindled or until day 20, the animals received daily treatments before receiving a kindling stimulus 3 h later. Afterdischarge duration (ADD) was assessed via electroencephalographs recorded from electrodes in the basolateral amygdalae and behavioral seizure stereotypy was simultaneously recorded digitally. Intranasal application of TRH-NPs resulted in a significant reduction in seizure ADD as kindling progressed, while the number of stimulations required to reach stage V seizures and to become permanently kindled was significantly greater in TRH-NP-treated subjects. Additionally, delay to clonus was significantly prolonged while clonus duration was reduced indicating a less severe seizure in TRH-NP-treated subjects. Our results provide proof of principle that intranasal delivery of sustained-release TRH-NPs may be neuroprotective and can be utilized to suppress seizures and perhaps epileptogenesis.

Attenuation of kindled seizures by intranasal delivery of neuropeptide-loaded nanoparticles

Thyrotropin-releasing hormone (TRH; Protirelin), an endogenous neuropeptide, is known to have anticonvulsant effects in animal seizure models and certain intractable epileptic patients. Its duration of action, however, is limited by rapid tissue metabolism and the blood-brain barrier. Direct nose-to-brain delivery of neuropeptides in sustained-release biodegradable nanoparticles (NPs) is a promising mode of therapy for enhancing CNS neuropeptide bioavailability. To provide proof of principle for this delivery approach, we used the kindling model of temporal lobe epilepsy to show that 1) TRH-loaded copolymer microdisks implanted in a seizure focus can attenuate kindling development in terms of behavioral stage, afterdischarge duration (ADD), and clonus duration; 2) intranasal administration of an unprotected TRH analog can acutely suppress fully kindled seizures in a concentration-dependent manner in terms of ADD and seizure stage; and 3) intranasal administration of polylactide nanoparticles (PLA-NPs) containing TRH (TRH-NPs) can impede kindling development in terms of behavioral stage, ADD, and clonus duration. Additionally, we used intranasal delivery of fluorescent dye-loaded PLA-NPs in rats and application of dye-loaded or dye-attached NPs to cortical neurons in culture to demonstrate NP uptake and distribution over time in vivo and in vitro respectively. Also, a nanoparticle immunostaining method was developed as a procedure for directly visualizing the tissue level and distribution of neuropeptide-loaded nanoparticles. Collectively, the data provide proof of concept for intranasal delivery of TRH-NPs as a viable means to 1) suppress seizures and perhaps epileptogenesis and 2) become the lead compound for intranasal anticonvulsant nanoparticle therapeutics.

Intranasal delivery of a thyrotropin-releasing hormone analog attenuates seizures in the amygdala-kindled rat

PURPOSE

Thyrotropin-releasing hormone (TRH) is known to have anticonvulsant effects in several animal seizure models and is efficacious in treating patients with certain intractable epilepsies. However, the duration of TRH's action is limited due to low bioavailability and difficulty penetrating the blood-brain barrier (BBB). Since direct nose to brain delivery of therapeutic compounds may provide a means for overcoming these barriers, we utilized the kindling model of temporal lobe epilepsy to determine if intranasal administration of a TRH analog, 3-methyl-histidine TRH (3Me-H TRH), could significantly inhibit various seizure parameters.

METHODS

Kindling was accomplished using a 1s train of 60 Hz biphasic square wave (200 microA peak to peak) administered daily to the basolateral amygdala until the animal was fully kindled. Afterdischarge duration (ADD) was assessed via electroencephalographs (EEGs) recorded bilaterally from bipolar electrodes in the basolateral amygdala and behavioral seizure severity (stage I-V) was simultaneously recorded digitally. Kindled subjects received 3Me-H TRH (10(-9), 10(-8), 10(-7) M) intranasally 60 and 30 min prior to amygdala stimulation. The ADD and seizure stage was compared to control kindled animals receiving physiological saline intranasally.

RESULTS

Intranasal application of 3Me-H TRH resulted in a concentration-dependent reduction in total seizure ADD. Additionally, the analog had significant concentration-dependent effects on behavioral stages I through IV (partial) and stage V (generalized) seizures. However, 3Me-H TRH significantly reduced clonus duration only at the highest concentration.

DISCUSSION

The results indicate that intranasal delivery of TRH/analogs may be a viable means to suppress temporal lobe seizures and perhaps other seizure disorders.

Gene profiling the response to kainic acid induced seizures

Kainic acid activates non-N-methyl-d-aspartate (NMDA) glutamate receptors where it increases synaptic activity resulting in seizures, neurodegeneration, and remodeling. We performed microarray analysis on rat hippocampal tissue following kainic acid treatment in order to study the signaling mechanisms underlying these diverse processes in an attempt to increase our current understanding of mechanisms contributing to such fundamental processes as neuronal protection and neuronal plasticity. The kainic acid-treated rats used in our array experiments demonstrated severe seizure behavior that was also accompanied by neuronal degeneration which is suggested by fluoro-jade B staining and anti-caspase-3 immunohistochemistry. The gene profile revealed 36 novel kainic acid regulated genes along with additional genes previously reported. The functional roles of these novel genes are discussed. These genes mainly have roles in transcription and to a lesser extent have roles in cell death, extracellular matrix remodeling, cell cycle progression, neuroprotection, angiogenesis, and synaptic signaling. Gene regulation was confirmed via quantitative real time polymerase chain reaction and in situ hybridization.

Thyroxine-induced hypermotor seizure

Thyroxine-induced epilepsy is a very rare condition occurring in epileptic patients. Here we report a boy with thyroxine-induced hypermotor seizure (HMS) following thyroxine administration for his central hypothyroidism secondary to surgery and cranial radiation for his brain tumor. After 3 years seizure-free period, he had repeated HMS, seven to eight attacks per day, after initiation L-thyroxine treatment. Following reduction of the daily thyroxine dose, his seizures decreased in frequency. To our knowledge, this is the first reported case of HMS associated with L-thyroxine administration.

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.

Acute ethanol administration induces changes in TRH and proenkephalin expression in hypothalamic and limbic regions of rat brain

Thyrotropin releasing hormone (TRH) present in several brain areas has been proposed as a neuromodulator. Its administration produces opposite effects to those observed with acute ethanol consumption. Opioid peptides, in contrast, have been proposed to mediate some of the effects of alcohol intoxication. We measured TRH content and the levels of its mRNA in hypothalamic and limbic zones 1-24 h after acute ethanol injection. We report here fast and transient changes in the content of TRH and its mRNA in these areas. The levels of proenkephalin mRNA varied differently from those of proTRH mRNA, depending on the time and region studied. Wistar rats were administered one dose of ethanol (intraperitoneal, 3 g/kg body weight) and brains dissected in hypothalamus, hippocampus, amygdala, n. accumbens and frontal cortex, for TRH quantification by radioimmunoassay or for proTRH mRNA measurement by RT-PCR. After 1 h injection, TRH levels were increased in hippocampus and decreased in n. accumbens; after 4 h, it decreased in the hypothalamus, frontal cortex and amygdala, recovering to control values in all regions at 24 h. ProTRH mRNA levels increased at 1 h post-injection in total hypothalamus and hippocampus, while they decreased in the frontal cortex. The effect of ethanol was also studied in primary culture of hypothalamic cells; a fast and transient increase in proTRH mRNA was observed at 1 h of incubation (0.001% final ethanol concentration). Changes in the mRNA levels of proTRH and proenkephalin were quantified by in situ hybridization in rats administered ethanol intragastrically (2.5 g/kg). Opposite alterations were observed for these two mRNAs in hippocampus and frontal cortex, while in n. accumbens and the paraventricular nucleus of the hypothalamus, both mRNA levels were increased but with different kinetics. These results give support for TRH and enkephalin neurons as targets of ethanol and, as possible mediators of some of its observed behavioral effects.

Effects of pentylenetetrazole-induced kindling on thyrotropin-releasing hormone biosynthesis and receptors in rat brain

It has been postulated that changes in thyrotropin-releasing hormone biosynthesis may be involved in the mechanism of kindling--an animal model of epileptogenesis. To test this hypothesis, a time-course study was carried out to investigate the effects of pentylenetetrazole kindling (40 mg/kg i.p., daily for eight days) on the expression of gene coding for preprothyrotropin-releasing hormone, the thyrotropin-releasing hormone tissue level and thyrotropin-releasing hormone receptor parameters in rat brain. As shown by an in situ hybridization study, a single, convulsant dose of pentylenetetrazole (70 mg/kg i.p.) increased the preprothyrotropin-releasing hormone messenger RNA level in the dentate gyrus of the hippocampal formation and piriform cortex after 3 h and, to a greater extent, after 24 h. Those changes were accompanied with increases in the thyrotropin-releasing hormone level in the striatum, hippocampus, amygdala and piriform cortex. Seven days after single pentylenetetrazole administration, the thyrotropin-releasing hormone level was still significantly elevated in the piriform cortex and striatum. Acute pentylenetetrazole decreased the density (Bmax) of thyrotropin-releasing hormone receptors in the striatum after 3 and 24 h, and increased that density in the piriform cortex and amygdala after 24 h and seven days, respectively. The thyrotropin-releasing hormone receptor affinity (Kd) was decreased in the striatum and increased in the amygdala after only 3 h. Kindled rats showed a moderate increase in the preprothyrotropin-releasing hormone messenger RNA content in the dentate gyrus of the hippocampal formation and piriform cortex after 3 and 24 h; however, a significant decrease in those parameters was found after 14 days. After 3 and 24 h, pentylenetetrazole kindling also elevated the thyrotropin-releasing hormone content in the hippocampus, piriform cortex, and striatum (in the latter structure after 24 h only), whereas in the septum the thyrotropin-releasing hormone level was decreased. After seven days, the thyrotropin-releasing hormone level was still elevated in the hippocampus and piriform cortex of kindled rats, but after 14 days it was significantly lowered in the hippocampus. The kindled rats also showed a significant decrease in the density (Bmax) of thyrotropin-releasing hormone receptors in the striatum (after 24 h, seven and 14 days), and an increase in the piriform cortex (after seven days). The thyrotropin-releasing hormone receptor affinity (Kd) value was increased in the hippocampus after seven and 14 days, and in the piriform cortex after seven days. These results indicate that pentylenetetrazole kindling induces long-lasting alterations in the thyrotropin-releasing hormone biosynthesis and thyrotropin-releasing hormone receptor affinity in discrete regions of rat brain. These region-specific changes, in particular down-regulation of the thyrotropin-releasing hormone biosynthesis in the hippocampus, may be involved in chronic neuronal hyperexcitability associated with kindling.

A heuristic model of mental depression derived from basic and applied research on thyrotropin-releasing hormone

Recent clinical reports have shown that intrathecal administration of thyrotropin-releasing hormone (TRH) can induce 2 to 3 day remissions of major depression more reliably than i.v. administration. Although clinically impractical, these remissions are rapid, occur within hours, and they survive at least one night's sleep. TRH and related peptides have regulatory effects in the limbic forebrain. Electroconvulsive shock (ECS) in rats induces synthesis of TRH in multiple subcortical limbic and frontal cortical regions, which are known in humans to be involved in both depression and in sleep. The increases in TRH and related peptides are regionally specific. The quantitative TRH increases in individual limbic regions have been correlated with the amount of forced-swimming done by the individual animal after ECS. Intraperitoneal TRH also gives a positive response in this test, as do all effective antidepressants. This article provides a heuristic framework for interdisciplinary neuroscientific study of the interrelated fields of depression and sleep, with a focus on TRH. Preclinical data suggest that glutamatergic, subcortical limbic circuits contain TRH and related peptides as inhibitory cotransmitters that may normally restrain glutamatergic hyperactivity. It is suggested that, in depression, pathologically overdriven glutamatergic circuits escape inhibitory regulation by TRH. This escape is especially pronounced during rapid eye movement (REM) sleep, and these phenomena may explain the prolonged latency of antidepressant treatment.

Brain thyrotropin-releasing hormone content varies through amygdaloid kindling development according to afterdischarge frequency and propagation

PURPOSE

Thyrotropin-releasing hormone (TRH), present in extra hypothalamic brain areas, has been proposed to have neuromodulatory functions and to be susceptible to change by electrical stimulation paradigms. We measured TRH concentrations of several brain areas during kindling development before its establishment and determined whether the changes detected in TRH levels were related to the behavioral stages of kindling, the number of stimulations required to reach these stages and, with the electrophysiological parameters characteristic of this paradigm (amygdaloid afterdischarge (AD) frequency, duration, and propagation).

METHODS

Male Wistar rats were implanted stereotaxically with indwelling bipolar electrodes in the basolateral nucleus of the amygdala and with two stainless-steel electrodes epidurally in frontal cortex. Amygdaloid kindling was induced by daily electrical stimulation; AD frequency and duration were recorded and analyzed throughout the development of kindling. TRH was extracted from several regions and quantified by radioimmunoassay (RIA).

RESULTS

Modifications in TRH concentrations were detected, depending on the region assayed, from stage II of kindling. A positive correlation was noted between the levels of TRH and the frequency and propagation of AD, but not with the number of stimulations. The rate of change in TRH concentration in relation to AD frequency or duration was highest in frontal cortex followed by hippocampus and amygdala.

CONCLUSIONS

A graded response was noted in the increase in TRH concentration dependent on the increase of AD frequency and propagation. The rate of response correlated with the region's epileptogenic susceptibility.

The effects of single and repeated morphine administration on the level of thyrotropin-releasing hormone and its receptors in the rat brain

Effects of single (20 mg/kg i.p.), and repeated morphine (increasing doses: from 20 to 100 mg/kg/day i.p., twice daily for 10 days) administration on the thyrotropin-releasing hormone (TRH) level and TRH receptors in discrete brain regions of the rat were investigated. As shown by a specific radioimmunoassay, a single dose of morphine increased the TRH level in the septum only. At 2 h after the last dose of repeated morphine, no significant changes in the TRH level were observed. At 72 h after the last morphine injection, the TRH level was increased in the striatum and hippocampus, but remained unchanged in the nucleus accumbens and septum. A radioreceptor assay showed that acute morphine had no effect on the density or affinity of TRH receptors in the brain regions studied. In contrast, repeated morphine increased the Kd of TRH receptors in the striatum at 2 h (by ca 42%) and 72 h (by ca 26%), and in the nucleus accumbens at 72 h (by ca 26%) after the last drug injection. At 2 h after the last morphine injection, the Bmax of TRH receptors was decreased in the nucleus accumbens (by ca 41%) and unchanged in other structures, whereas at 72 h it was elevated by ca 27% and 49% in the striatum and hippocampus, respectively. The above results indicate that repeated but not acute administration of morphine leads to long-lasting, region-specific changes in both the TRH level and receptors.

Changes in TRH and its degrading enzyme pyroglutamyl peptidase II, during the development of amygdaloid kindling

Pyroglutamyl peptidase II (PPII) is a neuronal ectoenzyme responsible for thyrotropin releasing hormone (TRH) degradation at the synaptic cleft. PPII, heterogeneously distributed in different brain regions and adenohypophysis, is regulated under various endocrine conditions where TRH is involved in thyrotropin or prolactin regulation but only at the adenohypophyseal level. TRH can downregulate PPII activity in cultured adenohypophyseal cells. TRH present in extrahypothalamic brain areas has been postulated to serve as a neuromodulator and levels of this peptide increase in amygdala, hippocampus and cortex after electrical stimulation (kindling or electroshock). To study whether brain PPII could be regulated in conditions that stimulate TRHergic neurons, TRH and PPII activity were determined during the development of amygdaloid kindling in the rat. TRH levels increased from stage II to V in amygdala and hippocampus in the ipsi- and contralateral side to stimulation. In n. accumbens a decrease, compared to sham was observed at stage II, but levels raised through stage V. In contrast, PPII activity was increased at stage II, in amygdala of both sides and in hipppocampus, frontal cortex, n. accumbens and hypothalamus of the contralateral side; levels decreased at stage V to sham values in most structures (except amygdala and hippocampus where the activity was 30% below controls). These results suggest that PPII activity in the central nervous system can be regulated in conditions known to affect TRHergic neurons.

Regulation of 60-kDa heat shock protein expression by systemic stress and 5-hydroxytryptamine in rat colonic mucosa

Bowel dysfunction such as irritable bowel syndrome caused by stress is well described. Previous reports suggest that 5-hydroxytryptamine (5-HT) mediates alteration of bowel motility. In this study, the effects of water-immersion stress and the administration of 5-HT on the expression of a 60-kDa heat shock protein (HSP60) in rat colonic mucosa were investigated. The effect of YM-060, a 5-hydroxytryptamine 3 (5-HT3) receptor antagonist, on the expression of this protein was also studied. Water-immersion stress and the administration of 5-HT induced synthesis of HSP60 in rat colonic mucosa. The induction of HSP60 and the number of defecations were clearly inhibited by the oral administration of YM-060. Our results suggest that the induction of HSP60 in rat colonic mucosa by water-immersion stress may be associated with gastrointestinal motility mediated by 5-HT, especially via 5-HT3 receptors.

TRH gene products are implicated in the antidepressant mechanisms of seizures

1. After a series of electroconvulsive seizures, levels of TRH-Gly (the immediate precursor of TRH) in four limbic regions correlate significantly and highly with increased swimming in the forced-swim test model of antidepressant efficacy. Only in hippocampus did TRH itself correlate with swimming. 2. After ECS, limbic forebrain regions differ in the relationship of TRH to its precursor peptides. This probably results from differences in the coordination of induction of TRH-processing enzymes, as well as differences in the level of prepro-TRH following seizures. 3. Sprague-Dawley rats that are partially kindled with corneal stimulation swim less in the forced-swim test, opposite to the effect seen with antidepressant agents. 4. Pyriform cortex is unique among the four limbic regions examined in showing decreased amounts of the TRH precursor following swim/stress. 5. Combining ECS with the forced-swim test of antidepressant effects creates a useful model for studying the involvement of TRH and its precursor peptides in both the antidepressant and anticonvulsant effects of controlled therapeutic seizures in the treatment of major depressive disorders. Regional differences between the effects of pinnate and corneal ECS on peptides and behavior support the idea that corneal ECS is a better model than pinnate ECS for human bitemporal ECT. 6. Together with recent results in other laboratories, our results suggest that a series of generalized seizures results in prolonged and increased release and action of TRH in limbic forebrain.

Identification of a cortical site for stress-induced cardiovascular dysfunction

The evidence indicating that the insular cortex is a likely candidate to mediate stress-induced cardiovascular responses is reviewed. Both neuroanatomical and electrophysiological investigations demonstrate that the insular cortex receives an organized representation of visceral information. In addition, the insular cortex also receives highly processed association cortex information. The insular cortex is also highly interconnected with many subcortical limbic and autonomic regions. This combination of sensory input and limbic/autonomic connectivity would be necessary to permit the insular cortex to be a critical site for the integration of emotional and autonomic responses. Stimulation of the insular cortex elicits specific cardiovascular and autonomic responses from discrete sites. Phasic stimulation entrained to the cardiac cycle is even capable of causing severe arrhythmias. The efferent pathways and some of the neurotransmitter mechanisms have determined. It appears that the lateral hypothalamic area is the primary site of synapse for responses originating in the insular cortex and this information is relayed by NMDA glutamatergic receptors and modulated by neuropeptides including neuropeptide Y, neurotensin, leu-enkephalin and dynorphin. Finally, a rat stroke model, which includes the insular cortex in the infarct region indicates that disruption of the insula can produce substantial cardiac and autonomic abnormalities, which might be similar to those produced by stress. Some of the chronic neurochemical changes, including increases in opioids, neuropeptide Y and neurotensin in the central nucleus of the amygdala, which might be mediating these cardiovascular disturbances, have been determined.

Thyrotropin-releasing hormone release is enhanced in hippocampal slices after electroconvulsive shock

Hippocampal thyrotropin-releasing hormone (TRH) release was examined after seizures were induced by electroconvulsive shock (ECS). Rat hippocampal slices taken 12, 24, or 48 h after 3 days of alternate-day ECS treatment or sham-ECS treatment were stimulated with potassium with or without calcium in a superfusion system containing in-line charcoal adsorbent to concentrate TRH. Released TRH and tissue TRH were measured by radioimmunoassay. The TRH content of hippocampal slices was increased fivefold over sham-ECS levels 12, 24, and 48 h after ECS, but this was not associated with an increase in basal TRH release. Potassium-stimulated TRH release was significantly elevated over basal release 12, 24, and 48 h after ECS. Potassium-stimulated calcium-dependent TRH release increased linearly after ECS, reaching its highest level 48 h after seizure. Thus, although enhanced calcium-dependent TRH release was associated with elevated tissue levels, this relationship was not proportional in that tissue TRH was elevated to the same extent at all times after ECS, whereas potassium-evoked calcium-dependent TRH release increased gradually over time after seizure. These results suggest that postictal elevations in TRH are associated with an enhanced capacity for release that develops as a result of a time-dependent shift of TRH from a storage compartment ot a readily releasable pool. The observed elevation in stimulated TRH release may be relevant to seizure-induced modulation of TRH receptors in vivo.

Comparison of the effects of trimebutine and YM114 (KAE-393), a novel 5-HT3 receptor antagonist, on stress-induced defecation

YM114 (KAE-393), (R)-5-[(2,3-dihydro-1-indolyl)carbonyl]-4,5,6,7- tetrahydro-1H-benzimidazole hydrochloride, is a derivative of YM060, a potent 5-HT3 receptor antagonist. We investigated the effects of YM114 on 5-HT3 receptors, both in vitro and in vivo, and on bowel dysfunction induced by restraint stress, 5-HT and thyrotropin-releasing hormone (TRH), and compared them with the effect of trimebutine. YM114 dose dependently inhibited the reduction in heart rate induced by 5-HT (30 micrograms/kg i.v.) in rats (ED50 = 0.31 micrograms/kg i.v.), and the potency of YM114 was almost the same as that of the racemate. The S-form of YM114 also inhibited 5-HT-induced bradycardia, but 1350 times less potent than the R-form. YM114 and its S-form inhibited [3H]GR65630 binding to N1E-115 cell membranes in a concentration-dependent manner with Ki values of 0.341 and 616 nM, respectively, showing the isomeric activity ratio (R-/S-form) of YM114 to be much greater (1800). YM114 antagonized 5-HT-induced depolarization of the nodose ganglion (EC50 = 1.39 nM). Trimebutine (1 mg/kg i.v.) failed to inhibit 5-HT-induced bradycardia, implying that it does not possess 5-HT3 receptor antagonistic activity. YM114 significantly and dose dependently prevented restraint stress-, 5-HT- and TRH-induced increases in fecal pellet output, and restraint stress- and 5-HT-induced diarrhea in rats and mice (ED50 = 6.9, 72.5, 154.6, 9.7 and 52.4 micrograms/kg p.o., respectively). Trimebutine significantly prevented stress- and 5-HT-induced diarrhea (ED50 = 29.4 and 87.3 mg/kg p.o., respectively), but only partially affected stress-, 5-HT- and TRH-induced increases in fecal pellet output. Thus, YM114 is a potent and stereoselective 5-HT3 receptor antagonist with much greater protective effects against stress-induced defecation than trimebutine.

Distribution of thyrotropin-releasing hormone binding sites: autoradiographic study in infant and adult human hippocampal formation

The rostrocaudal distribution of thyrotropin-releasing hormone (TRH) binding sites was studied in the human hippocampus. Cryostat sections of the right and left hippocampi from 6 infants (2 h to 5 months of age) and 11 adults (24 to 92 years) were subjected to in vitro quantitative autoradiography using [3H]MeTRH as a ligand. A single class of high affinity [3H]MeTRH binding sites with an apparent dissociation constant in the nanomolar range has been shown both in the infant and the adult. The maximal number of these sites was higher in the infant. No significant difference was observed between the general patterns of the right and the left hippocampi when taking postmortem delay and age as parameters. The highest concentrations of [3H]MeTRH binding sites were localized in the uncinate gyrus, the uncal subiculum and in the whole length of the molecular layer of the dentate gyrus. The lowest densities were present in the ventral subiculum. The major difference observed between the infant and the adult appeared in the molecular layer of the dentate gyrus where the densities were two-fold higher in infants (189 +/- 6 versus 88 +/- 2 fmol/mg of tissue). The only marked difference in the distribution was localized in the caudal part of the body where no specific labeling was found in the presubiculum of the infant.

Thyrotropin-releasing hormone gene expression and receptors are differentially modified in limbic foci by seizures

Previous studies using two seizure paradigms, electroconvulsive shock and kindling, suggested potential sites of endogenous thyrotropin-releasing hormone (TRH) action in specific epileptogenic areas. We studied TRH gene expression and TRH receptors in rat limbic areas using the kindling model of epilepsy. Immunoassayable TRH increased 4- to 20-fold over control levels in specific subregions of the hippocampus 24 hours after a single stage 5 seizure. Concurrently, TRH receptor binding was significantly reduced in hippocampal (23-39%) and amygdaloid (21-22%) membranes. Dramatic temporal and spatial changes in prepro-TRH messenger RNA were visualized by in situ hybridization histochemistry in the hippocampal dentate gyrus, the piriform cortex, and the amygdala. Peak hybridization occurred 6 and 12 hours postictally in these loci and returned toward basal levels by 24 hours. These results are consistent with the hypothesis that TRH may have an important role in the pathophysiology epilepsy by modulating excitatory processes.

Some regional anatomical relationships of TRH to 5-HT in rat limbic forebrain

It is now a recognized principle that various neuropeptides are neuronally co-localized with biogenic amine or aminoacid neurotransmitters. In the rat CNS it has previously been shown that TRH is co-localized with 5-HT (and also with substance P) in cell bodies of the posterior raphe that project to the spinal cord. Although TRH cell bodies are known to be widely distributed throughout the forebrain there is no other known co-localization with 5-HT. In this study we further specify the forebrain there is no other known co-localization with 5-HT. In this study we further specify the anatomical relationship of TRH with 5-HT by use of surgical and neurotoxic lesioning with reference to limbic forebrain regions wherein TRH is greatly increased following seizures. In groups of rats, the fimbria-fornix was lesioned alone, or combined with a lesion of the dorsal perforant path or the ventral perforant path. There was a sham lesioned control group. Additional groups were lesioned with 5,7 dihydroxytryptamine, 100 micrograms i.v.t., 45 min. after i.p. desipramine, 25 mg/kg. All rats were sacrificed three weeks after lesions. Indoleamines were determined by HPLC in left anterior cortex, left pyriform/olfactory cortex, left dorsal hippocampus and left ventral hippocampus. TRH was determined by specific RIA in the corresponding right brain regions. The modal n was 7 rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Neural adaptation in response to chronic imipramine and electroconvulsive shock: evidence for separate mechanisms

The effects of chronic imipramine and electroconvulsive shock alone or combined were assessed on rat brain beta-adrenoceptors and serotonin2 (5-HT2) receptors and on dynorphin and thyrotropin releasing hormone (TRH) levels. These treatments resulted in regionally discrete and treatment-specific patterns of change in beta-adrenoceptor and 5-HT2 receptor density and in TRH and dynorphin levels. Electroconvulsive shock eliminated the serotonergic component of hippocampal DHA binding, suggesting an effect of this treatment on 5-HT1 receptors. The effects of combined electroconvulsive shock and imipramine treatments on cortical 5-HT2 and beta-adrenoceptor density appeared to be the additive sum of the individual treatment effects. No treatment interaction was observed on hippocampal 5-HT2 and beta-adrenoceptors, except after day 2. No treatment interaction on peptide content was observed at any time. These results demonstrate independent anatomical specificity for the effects of electroconvulsive shock and imipramine and provide evidence that the mechanisms responsible for their antidepressant actions differ.

Elevated TRH levels in pyriform cortex after partial and fully generalized kindled seizures

In a previous study we reported significant elevations of TRH in neocortex, hippocampus and combined amygdala/pyriform cortex in rats 48 h after the last of a series of stage 5 kindled seizures. In the present study, to determine whether the increases in TRH were proportional to the intensity of the convulsions, and the degree of development of the kindling process, we compared the effects of partially kindled (stage 2) vs fully kindled (stage 5) seizures. As a further refinement, we examined separately the TRH responses in the pyriform, cingulate and frontal cortices. The responses were especially marked in the pyriform cortex, where TRH increased 7-fold after stage 5 kindled convulsions, compared with 2-fold increases after stage 2-3 seizures. Increases were seen in other cortical regions, as well, but only after stage 5 seizures. These findings are consistent with reports suggesting that the increases in brain TRH occurring after convulsions are aftereffects of the seizures, possibly representing homeostatic anticonvulsant responses, and that the pyriform cortex is a site that is uniquely activated by convulsions.

Repeated treatment with amitriptyline or electroconvulsive shock does not affect thyrotropin releasing hormone receptors in discrete rat brain structures

We studied the effect of repeated treatment with amitriptyline (10 mg/kg, p.o., twice daily for 14 days) or electroconvulsive shock (ECS) (once daily for 10 days) on the thyrotropin-releasing hormone (TRH) content and TRH receptors in the cerebral cortex, nucleus accumbens, striatum and septum of the rat. Repeated amitriptyline did not significantly affect the density or affinity of TRH receptors in the examined structures, but caused a marked increase in the TRH content in the striatum and nucleus accumbens. Long-term treatment with ECS reduced the density and affinity of TRH receptors in the septum only, but it increased the TRH concentration in the cerebral cortex and striatum. These results, together with the literature data, indicate that there is no simple relationship between the brain content (and release) of TRH and the functional sensitivity of TRH receptors on one hand, and the density of these receptors on the other.

Evidence for a role of brain thyrotropin-releasing hormone (TRH) on stress gastric lesion formation in rats

Specific polyclonal antibodies raised against synthetic thyrotropin-releasing hormone (TRH) infused intracerebroventricularly (ICV) significantly decreased gastric lesions induced by cold restraint stress. The antiulcer effect of immunologic blockade of brain TRH was specific. Normal rabbit serum or antibodies raised against somatostatin, alpha-MSH, Leu-enkephalin, gonadotropin-releasing hormone and atrial natriuretic factor were ineffective. These findings suggest that brain TRH may play an important role in experimental stress ulcer formation.

Systemic administration of kainic acid produces elevations in TRH in rat central nervous system

Several studies have suggested that the concentration of thyrotropin releasing hormone (TRH) in the central nervous system (CNS) is influenced by the level of CNS activation. Hibernation in the ground squirrel and estivation in the lungfish result in region-specific decreases in TRH concentrations. Repeated electroconvulsive shock (ECS) and amygdaloid kindling have been shown to result in elevations of TRH in limbic brain regions. In the present study, limbic seizures induced by systemic administration of kainic acid resulted in substantial increases in the TRH content of posterior cortex and of dorsal and ventral hippocampus, and in moderate elevations in anterior cortex, amygdala/piriform cortex and corpus striatum. Maximal elevations in TRH were observed 2-4 days after kainic acid administration, and by 14 days TRH levels were similar to control values, with the exception of the dorsal hippocampus, which exhibited more prolonged elevations in TRH levels. Prior exposure to limbic seizure activity attenuated the magnitude of TRH elevation in response to a second administration of kainic acid in the posterior cortex but in no other region. These results indicate that seizure-related processes or events influence TRH systems in the CNS. Neuronal populations involved in limbic seizure induced damage may be involved in the modulation of posterior cortical TRH levels.

The effect of repeated administration of antidepressant drugs on the thyrotropin-releasing hormone (TRH) content of rat brain structures

The present study investigated the effect of repeated treatment with the antidepressant drugs imipramine, amitryptyline, citalopram and mianserin (10 mg/kg PO, twice daily for 14 days) on levels of thyrotropin-releasing hormone (TRH) in several brain structures (cerebral cortex, amygdala + pyriform cortex, hippocampus, nucleus accumbens, striatum and hypothalamus) of the rat. Amitriptyline caused a marked increase in the TRH content in the striatum and nucleus accumbens. Citalopram and mianserin produced a smaller but significant increase in the TRH content in the striatum only, while imipramine did not significantly affect the TRH concentrations in any of the brain structures. None of the antidepressant drugs administered acutely significantly affected the TRH concentrations in the nucleus accumbens or the striatum. These results indicate that changes in brain TRH induced by antidepressant drugs are not related to their therapeutic activity.

The prolonged increase in thyrotropin-releasing hormone in rat limbic forebrain regions following electroconvulsive shock

We have previously demonstrated substantial increases in thyrotropin-releasing hormone (TRH) in specific regions of rat forebrain two days after single or repeated alternate-day electroconvulsive shock (ECS). To determine longer term effects of ECS-induced seizures on forebrain TRH content, we extended the time of the post-ECS observations to 6 and 12 days following 1 (ECS x 1) or 3 (ECS x 3) alternate-day ECS. Previous observations at 2 days post-ECS were confirmed except that hippocampal content of TRH was higher after ECS x 1. In pyriform cortex TRH remained elevated for 6 days after ECS x 1 and 3, and for 12 days after ECS x 3. In hippocampus TRH was elevated for 6 days after ECS x 1 and tended to remain elevated beyond 2 days after ECS x 3. In anterior cortex the increase persisted 6 days after ECS x 1 and 12 days after ECS x 3. These data show that convulsive seizures can induce sustained elevations of TRH beyond 48 h. This finding may be especially important in pyriform cortex and hippocampus where TRH may function as an endogenous anti-epileptic. Our data are also consistent with a possible role for TRH in affective regulation in the hippocampus, amygdala, pyriform and other cortical regions. Moreover, the present results further advance the analogy of the time-course of the TRH changes in rat to the course of the antidepressant response to electroconvulsive treatment in humans.

Long-term increase in striatal thyrotropin-releasing hormone receptor binding caused by amygdaloid kindling

Our previous finding that intracerebroventricular (i.c.v.) administration of both thyrotropin-releasing hormone (TRH) and its analogue, gamma-butyrolactone-gamma-carbonyl-L-histidyl-L-prolinamide citrate (DN-1417), suppressed seizure development of amygdaloid (AM) kindling and kindled AM seizures leads to a new hypothesis that endogenous TRH may be an antiepileptic substance in the brain. In this study, we examined postictal chronological changes in both immunoreactive TRH (IR-TRH) and TRH receptor binding activity in discrete brain regions of AM-kindled rats to study the relationship of the brain TRH system to kindling-induced seizure susceptibility. AM-kindled rats were decapitated 30 min, 24 h, 48 h, 7 days, and 21 days after the last kindled convulsion. IR-TRH increased markedly in the AM/pyriform cortex and hippocampus 24 and 48 h after the last convulsion, and returned to the control (unstimulated, sham-operated) value within 3 weeks after the convulsions ended. In contrast, a significant increase in the striatal TRH binding sites was evident 24 h after the cessation of convulsions which lasted 21 days. A lasting change in the striatal TRH neural system may be related to kindling-induced seizure susceptibility.

Mechanism of action of ECT in major depressive disorders: a neuroendocrine interpretation

Electroconvulsive therapy (ECT) is often efficacious in severe depression, and it is occasionally used in the treatment of schizophrenia. The mechanism of action of ECT is still poorly understood. We evaluated thyroid-stimulating hormone (TSH) and prolactin responses to thyrotropin-releasing hormone (TRH) after a first ECT and at the end of a series of seven ECTs in eight unipolar depressed patients with blunted basal TSH/TRH response, eight unipolar depressed patients with normal TSH/TRH response, and eight schizophrenic patients. The hormone patterns obtained after the first ECT showed an increase in prolactin and a decrease in TSH in all groups of patients, suggesting a nonspecific response. At the end of the therapeutic course, TSH responses increased in both groups of depressed patients, and the elevation was more relevant in depressed patients with normal TSH/TRH. Our data suggest that the mechanism of action of ECT becomes more specific when it is performed chronically and differs according to the organic substrate underlying different mental disorders. Moreover, an aminergic activation in the two groups of depressed patients seems to take place.

Effects of ECT on the TRH stimulation test

The prognostic value of the TRH stimulation test was evaluated in 23 inpatients with major depressive disorder before and after a trial of ECT. In contrast to previous reports, the peak TSH response to TRH was significantly decreased after treatment compared with before treatment. This effect was consistent across individuals and subgroups (responders/nonresponders; unilateral/bilateral ECT). The particular ECT technique used in the study may account for the discrepancies between these findings and those previously reported by other authors.

Effects of electroconvulsive therapy (ECT) on thyroid function parameters

Serum concentrations of thyroxine, triiodothyronine, TSH and prolactin were measured in 10 patients with affective disorders receiving ECT. Samples were drawn at -15 min, 0, +30 min, +60 min and +3 hr after ECT. A significant increase in both prolactin and TSH was observed 30 min after ECT. A small but significant decrease in triiodothyronine but no change in thyroxine was found in all post-ECT samples. The increase in TSH may be caused by an anti-dopaminergic effect of ECT at either the pituitary or the hypothalamic level.

Change in brain thyrotropin-releasing hormone (TRH) mechanism of amygdaloid kindled rats

We reported previously that DN-1417, a potent analog of thyrotropin-releasing hormone (TRH), suppressed both the progression of amygdaloid (AM) kindling and AM kindled seizure. To study a functional role of the cerebral TRH mechanism in AM kindling, immunoreactive TRH (IR-TRH) and specific TRH receptor binding were examined in the rat brains kindled from the left AM. The IR-TRH concentration elevated significantly in the amygdala plus piriform cortex and the hippocampus 24 and 48 hours after the AM kindled convulsion. Such an elevation of IR-TRH was not found 7 days after the last convulsion, indicating that the elevation of IR-TRH was a transient change seen after the AM kindled convulsion. By contrast, the specific TRH receptor binding in the striatum increased 48 hours, 7 and 21 days after the AM kindled convulsion. This indicates that the increase of the specific TRH binding in the striatum was a long-lasting change. The present study suggests that the change in the striatal TRH receptors may be associated with a long-lasting seizure susceptibility of AM kindled rats.

Endogenous anticonvulsant substances

Epileptic seizures will normally arrest abruptly and spontaneously, and the brain will remain refractory to further seizures for some time thereafter. This paper reviews the possible mechanisms underlying this seizure arrest and refractoriness. The data suggests that neuronal fatigue is not involved in either of these processes, whereas the role of ions and excitatory systems are unclear. Rather, seizure arrest and refractoriness may come about by the seizure-induced release and/or activity of multiple endogenous anticonvulsant substances. The spontaneous arrest of the seizure may involve the purine adenosine, in addition to other unknown mechanisms. Seizure refractoriness involves multiple systems, the most important of which, on the available evidence, are prostaglandins and opioid peptides and possibly benzodiazepine systems, although other neuropeptides and the purines may also be involved. The implications of these conclusions to anti-epileptic drug development and status epilepticus are discussed.

Neuroendocrine mechanisms of stress ulceration: focus on thyrotropin-releasing hormone (TRH)

It is generally accepted that stress ulceration, a multifactorial or pluricausal gastrointestinal disorder, may be the result of mechanistic interrelationships between mucosal, vascular, hormonal and neurogenic factors. The relative importance of each of these independent mechanisms remains unclear. This minireview represents an attempt to interpret many recent studies on certain neurogenic mechanisms and to integrate these observations into the existing body of knowledge. A variety of in vitro techniques and animal models to manipulate actual structures, organ systems, and certain well-defined hormonal influences have been utilized. The peripheral studies have followed, for the most part, the established observation that the stomach is under reciprocal control by sympathetic inhibitory and parasympathetic excitatory autonomic fibers. As a result, several autonomic adrenergic neurotransmitter substances have been found to promote mucosal resistance. Some of these include dopamine, epinephrine, and norepinephrine. Others in contrast, appear to promote vulnerability of the mucosa, and of these, the most well-studied include acetylcholine and histamine.

Association between regularly occurring complex partial seizures and thyroid function parameters

A 28-year-old man with regularly occurring clusters of complex partial seizures was studied over a total of 224 days. His seizure periods lasted 2-4 days and occurred at intervals of 5-6 weeks. Several parameters were studied. The most striking finding was an increase in the serum concentration of thyroxine prior to and during the seizure periods. The concentrations of urine catecholamines and serum cortisol also varied with the seizure periods, but these hormones increased after the seizure periods had begun. To determine if there is a general 4-6-week rhythm in thyroid hormone concentrations, 12 weekly blood samples from 10 healthy male students were analyzed. No rhythmicity was found.

Changes in TRH immunoreactivity in spinal cord after experimental spinal injury

Concentrations of immunoreactive TRH (TRH-ir) in rat spinal cord were examined after traumatic injury. TRH-ir was significantly increased at the injury site (thoracic region) and rostral areas (cervical region), and significantly decreased below the injury site. Changes were delayed and time-dependent. Since TRH may serve as an excitatory neurotransmitter within the spinal cord, these changes may contribute to the functional alterations observed after spinal injury.

Involvement of thyrotropin-releasing hormone (TRH) neural system of the brain in pentylenetetrazol-induced seizures

In order to study the relationship between pentylenetetrazol (PTZ)-induced seizures and the thyrotropin-releasing hormone (TRH) neural system, immunoreactive TRH (IR-TRH) and TRH receptor binding activity were determined in discrete regions of the rat brain before as well as 40 s (immediately before seizures), 150 s (during seizures) and 24 h after an intraperitoneal injection of PTZ (75 mg/kg). IR-TRH markedly increased in the septum 40 and 150 s after the injection, and also in the hippocampus and the thalamus-midbrain region 40 and 150 s after the injection, respectively. However, no significant changes were observed in the TRH receptor binding before, during or after the seizures, suggesting that the increased IR-TRH was not released into the synaptic cleft. This speculation was supported by the dose-dependent inhibition of PTZ-induced generalized seizures by the pre-treatment with TRH or its analogue DN-1417 into the cerebral ventricle.

Intraventricular 6-hydroxydopamine increases thyrotropin-releasing hormone (TRH) content in regions of rat brain

Rats were given intraventricular (ivt) injections of various doses (50-400 micrograms, hydrobromide salt) of 6-hydroxydopamine (6-OHDA) and killed 1, 3 or 6 days later. Brains were removed, dissected into 11 regions, and the thyrotropin-releasing hormone (TRH) content of each region was measured by radioimmunoassay. 6-OHDA (400 micrograms) caused significant elevations in the TRH content of 6 regions: olfactory bulb, anterior cortex, brainstem, posterior cortex, hippocampus, and amygdala-piriform cortex. The magnitude of these increases ranged from 59% in olfactory bulb to 497% in hippocampus and was, in all cases, greatest at 3 days. These results suggest that the TRH content of certain brain regions may be regulated by catecholamine neurotransmitters.

Seizures and thyrotropin-releasing hormone (TRH) neural system in the rat brain

In order to study the relationship between seizures and the thyrotropin-releasing hormone (TRH) neural system, immunoreactive TRH (IR-TRH) and TRH receptor binding activity were determined by pentylenetetrazol (PTZ)-induced seizures and amygdaloid (AM) kindling. IR-TRH markedly increased in the septum 40 and 150 seconds after the PTZ injection. A significant increase in the IR-TRH concentrations was also noted in the hippocampus and thalamus/midbrain 40 and 150 seconds after the PTZ injection, respectively. However, no significant changes were observed in the TRH receptor binding before, during or after the PTZ-induced seizures. In addition, a lasting change in the striatal TRH receptors after AM kindling as well as a transient IR-TRH increase in the limbic structures were seen 48 hours after Am-kindled convulsions. TRH and its analog (DN-1417) inhibited PTZ-induced generalized seizures dose-dependently. These findings indicate the involvement of the TRH neural system in seizure mechanisms, and suggest that endogenous TRH may be an antiepileptic substance in the brain.

Effects of subconvulsive and repeated electroconvulsive shock on thyrotropin-releasing hormone in rat brain

Male Sprague-Dawley rats were given a single electroconvulsive shock (ECS) on alternate days and sacrificed 48 hrs after 1, 3, or 5 seizures. The content of TRH in hippocampus, pyriform cortex and amygdala was increased 2.5-fold, 5.4-fold and 4.3-fold respectively, 48 hrs. after 3 alternate-day electroconvulsive shocks (ECS) and remained unchanged after 2 additional shocks. Pyriform cortex exhibited a significant intermediate increase (1.7-fold) after only 1 ECS. In a second study, rats were sacrificed 48 hrs after a series of 5 alternate-day ECS vs. subconvulsive shocks (SCS). SCS had no significant effect in these same regions, but was seen to alter TRH in striatum. These results provide an interesting parallel to several aspects of clinical electroconvulsive treatment (ECT) of depression. Together with other findings, these data suggest also, that endogenous TRH may play a role in the modulation of convulsive seizures.