Effect of thyrotropin releasing hormone (TRH) on acetylcholine release from different brain areas investigated by microdialysis

Intracerebroventricular administration of TRH Agonist, RX-77368 alleviates visceral pain induced by colorectal distension in rats

Thyrotropin-releasing hormone (TRH) acts centrally to exert pleiotropic actions independently from its endocrine function, including antinociceptive effects against somatic pain in rodents. Whether exogenous or endogenous activation of TRH signaling in the brain modulates visceral pain is unknown. Adult male Sprague-Dawley rats received an intracerebroventricular (ICV) injection of the stable TRH analog, RX-77368 (10, 30 and 100 ng/rat) or saline (5 µl) or were semi-restrained and exposed to cold (4°C) for 45 min. The visceromotor response (VMR) to graded phasic colorectal distensions (CRD) was monitored using non-invasive intracolonic pressure manometry. Naloxone (1 mg/kg) was injected subcutaneously 10 min before ICV RX-77368 or saline. Fecal pellet output was monitored for 1 h after ICV injection. RX-77368 ICV (10, 30 and 100 ng/rat) reduced significantly the VMR by 56.7%, 67.1% and 81.1% at 40 mmHg and by 30.3%, 58.9% and 87.4% at 60 mmHg respectively vs ICV saline. Naloxone reduced RX-77368 (30 and 100 ng, ICV) analgesic response by 51% and 28% at 40 mmHg and by 30% and 33% at 60 mmHg respectively, but had no effect per se. The visceral analgesia was mimicked by the acute exposure to cold. At the doses of 30 and 100 ng, ICV RX-77368 induced defecation within 30 min. These data established the antinociceptive action of RX-77368 injected ICV in a model of visceral pain induced by colonic distension through recruitment of both opioid and non-opioid dependent mechanisms.

Thyroid dysfunction and Alzheimer's disease, a vicious circle

Recently, research into the link between thyroid dysfunction and Alzheimer's disease (AD) remains a current topic of interest. Previous research has primarily concentrated on examining the impact of thyroid dysfunction on the risk of developing AD, or solely explored the mechanisms of interaction between hypothyroidism and AD, a comprehensive analysis of the mechanisms linking thyroid dysfunction, including hyperthyroidism and hypothyroidism, to Alzheimer's disease (AD) still require further elucidation. Therefore, the aim of this review is to offer a thorough and comprehensive explanation of the potential mechanisms underlying the causal relationship between thyroid dysfunction and AD, highlighting the existence of a vicious circle. The effect of thyroid dysfunction on AD includes neuron death, impaired synaptic plasticity and memory, misfolded protein deposition, oxidative stress, and diffuse and global neurochemical disturbances. Conversely, AD can also contribute to thyroid dysfunction by affecting the stress repair response and disrupting pathways involved in thyroid hormone (TH) production, transport, and activation. Furthermore, this review briefly discusses the role and significance of utilizing the thyroid as a therapeutic target for cognitive recovery in AD. By exploring potential mechanisms and therapeutic avenues, this research contributes to our understanding and management of this devastating neurodegenerative disease.

TRH and NPY Interact to Regulate Dynamic Changes in Energy Balance in the Male Zebra Finch

In contrast to mammals, birds have a higher basal metabolic rate and undertake wide range of energy-demanding activities. As a consequence, food deprivation for birds, even for a short period, poses major energy challenge. The energy-regulating hypothalamic homeostatic mechanisms, although extensively studied in mammals, are far from clear in the case of birds. We focus on the interplay between neuropeptide Y (NPY) and thyrotropin-releasing hormone (TRH), 2 of the most important hypothalamic signaling agents, in modulating the energy balance in a bird model, the zebra finch, Taeniopygia guttata. TRH neurons were confined to a few nuclei in the preoptic area and hypothalamus, and fibers widely distributed. The majority of TRH neurons in the hypothalamic paraventricular nucleus (PVN) whose axons terminate in median eminence were contacted by NPY-containing axons. Compared to fed animals, fasting significantly reduced body weight, PVN pro-TRH messenger RNA (mRNA) and TRH immunoreactivity, but increased NPY mRNA and NPY immunoreactivity in the infundibular nucleus (IN, avian homologue of mammalian arcuate nucleus) and PVN. Refeeding for a short duration restored PVN pro-TRH and IN NPY mRNA, and PVN NPY innervation to fed levels. Compared to control tissues, treatment of the hypothalamic superfused slices with NPY or an NPY-Y1 receptor agonist significantly reduced TRH immunoreactivity, a response blocked by treatment with a Y1-receptor antagonist. We describe a detailed neuroanatomical map of TRH-equipped elements, identify new TRH-producing neuronal groups in the avian brain, and demonstrate rapid restoration of the fasting-induced suppression of PVN TRH following refeeding. We further show that NPY via Y1 receptors may regulate PVN TRH neurons to control energy balance in T. guttata.

Established Stem Cell Model of Spinal Muscular Atrophy Is Applicable in the Evaluation of the Efficacy of Thyrotropin-Releasing Hormone Analog

Spinal muscular atrophy (SMA) is an autosomal recessive neuromuscular disorder characterized by the degeneration of spinal motor neurons. This disease is mainly caused by mutation or deletion of the survival motor neuron 1 (SMN1) gene. Currently, no effective treatment is available, and only symptomatic treatment can be provided. Our purpose in the present study was to establish a human SMA-derived induced pluripotent stem cell (SMA-iPSC) disease model and assay a therapeutic drug in preparation for the development of a novel treatment of SMA. We generated iPSCs from the skin fibroblasts of a patient with SMA and confirmed that they were pluripotent and undifferentiated. The neural differentiation of SMA-iPSCs shortened the dendrite and axon length and increased the apoptosis of the spinal motor neurons. In addition, we found activated astrocytes in differentiated SMA-iPSCs. Using this model, we confirmed that treatment with the thyrotropin-releasing hormone (TRH) analog, 5-oxo-l-prolyl-l-histidyl-l-prolinamide, which had marginal effects in clinical trials, increases the SMN protein level. This increase was mediated through the transcriptional activation of the SMN2 gene and inhibition of glycogen synthase kinase-3β activity. Finally, the TRH analog treatment resulted in dendrite and axon development of spinal motor neurons in differentiated SMA-iPSCs. These results suggest that this human in vitro disease model stimulates SMA pathology and reveal the potential efficacy of TRH analog treatment for SMA. Therefore, we can screen novel therapeutic drugs such as TRH for SMA easily and effectively using the human SMA-iPSC model. Significance: Platelet-derived growth factor (PDGF) has recently been reported to produce the greatest increase in survival motor neuron protein levels by inhibiting glycogen synthase kinase (GSK)-3β; however, motor neurons lack PDGF receptors. A human in vitro spinal muscular atrophy-derived induced pluripotent stem cell model was established, which showed that the thyrotropin releasing hormone (TRH) analog promoted transcriptional activation of the SMN2 gene and inhibition of GSK-3β activity, resulting in the increase and stabilization of the SMN protein and axon elongation of spinal motor neurons. These results reveal the potential efficacy of TRH analog treatment for SMA.

A cross-sectional study on thyroid status in North Indian elderly outpatients with dementia

BACKGROUND

Several population based studies have demonstrated an association between hypo-or hyperthyroidism and dementia in last two decades. As a consequence, thyroid stimulating hormone has become part of the screening laboratory test for dementia.

AIM

The aim of the present study was to evaluate the association between thyroid function and Alzheimer's disease (AD) and vascular dementia (VaD) and to determine the risk of AD and VaD in clinically euthyroid patients.

MATERIALS AND METHODS

A cross-sectional hospital based study was carried out in subjects diagnosed with AD/VaD and were assessed for thyroid status as routine screening test.

RESULTS

Free T3, free T4 and TSH were studied in 114 AD patients (mean age: 65 years), 35 VaD patients (mean age: 62 years) and 105 control subjects (mean age: 62 years). In AD group, TSH levels were significantly lower than controls (P = 0.00) and for each unit increase in TSH level, the odds of having dementia decreased by 37.1%. No such relation was seen in VaD.

CONCLUSION

The results suggest a consistent association of subclinical hyperthyroidism and AD.

The role of Thyrotropin Releasing Hormone in aging and neurodegenerative diseases

Thyrotropin releasing hormone (TRH) is primarily known as the central regulator of the hypothalamic-pituitary-thyroid (HPT) axis. However, TRH also exerts a variety of central nervous system effects independent from its activity in the HPT axis. With advancing age, decreases in TRH synthesis, expression, and activity have been demonstrated. Associated with this emerging evidence suggests that TRH is implicated in neurodegenerative diseases of aging, including Alzheimer's disease and Parkinson's disease. TRH and its synthetic analogs have been recognized as trophic factors in neurons of the diencephalon and spinal cord, and as neuroprotectants against oxidative stress, glutamate toxicity, caspase-induced cell death, DNA fragmentation, and inflammation. In this review, we will provide an overview of some of the roles of TRH, outside of the HPT axis, associated with pathological aging and neurodegeneration and we shall discuss the potential of TRH and TRH analogs for the treatment of neurodegenerative diseases.

Clinical review: The thyroid in mind: cognitive function and low thyrotropin in older people

CONTEXT

Several studies have reported an association between low serum TSH, or subclinical hyperthyroidism (SH), and dementia, but little emphasis has been placed on this field because not all studies have demonstrated the same association. We performed a detailed systematic review to assess the evidence available to support the association between these two conditions.

METHODS

We performed a systematic search through the PubMed, Embase (1996 to 2012 wk 4), Cochrane Library, and Medline (1996 to January wk 4, 2012) electronic databases using key search terms encompassing subclinical hyperthyroidism, TSH, dementia, and cognitive impairment.

RESULTS

This review examines the 23 studies that provide information about the association between SH or lower serum TSH within the reference range and cognition. Fourteen of these studies, including several well-designed and well-powered cross-sectional and longitudinal analyses, have shown a consistent finding of an association between SH with cognitive impairment or dementia.

CONCLUSION

There is a substantial body of evidence to support the association between SH and cognitive impairment, but there is no clear mechanistic explanation for these associations. Nor is there an indication that antithyroid treatment might ameliorate dementia. Larger and more detailed prospective longitudinal or randomized controlled trials are required to inform these important questions.

[Glu2]TRH dose-dependently attenuates TRH-evoked analeptic effect in mice

Thyrotropin-releasing hormone (TRH, pGlu-His-Pro-NH(2)) and the structurally related [Glu(2)]TRH (pGlu-Glu-Pro-NH(2)) are endogenous peptides with a plethora of actions in the central nervous system. Many centrally-mediated effects of TRH are shared with those of [Glu(2)]TRH, although the involvement of different receptors is presumed. The analeptic action is the best-known TRH-related central nervous system effect. While [Glu(2)]TRH itself is analeptic, its co-administration with TRH into mice produced a dose-dependent attenuation of TRH-evoked reversal of barbiturate-induced sleeping time. This finding is in agreement with our previous observations that [Glu(2)]TRH significantly attenuates TRH-induced hippocampal extracellular acetylcholine release. Taken together, [Glu(2)]TRH may be considered as a negative modulator for the cholinergic effect of TRH in the mouse brain.

Regulation of cortical acetylcholine release: insights from in vivo microdialysis studies

Acetylcholine release links the activity of presynaptic neurons with their postsynaptic targets and thus represents the intercellular correlate of cholinergic neurotransmission. Here, we review the regulation and functional significance of acetylcholine release in the mammalian cerebral cortex, with a particular emphasis on information derived from in vivo microdialysis studies over the past three decades. This information is integrated with anatomical and behavioral data to derive conclusions regarding the role of cortical cholinergic transmission in normal behavioral and how its dysregulation may contribute to cognitive correlates of several neuropsychiatric conditions. Some unresolved issues regarding the regulation and significance of cortical acetylcholine release and the promise of new methodology for advancing our knowledge in this area are also briefly discussed.

Structure–activity relationships of methoctramine-related polyamines as muscarinic antagonist: Effect of replacing the inner polymethylene chain with cyclic moieties

The aim of the present paper was to investigate the role of the octamethylene spacer of methoctramine (1) on the biological profile. Thus, this spacer was incorporated into a dianiline or dipiperidine moiety to determine whether flexibility and the basicity of the inner nitrogen atoms are important determinants of potency with respect to muscarinic receptors. The most potent compound was 4, which displayed, in the functional assays, a comparable potency at muscarinic M(2) receptors with respect to 1, and, in the binding assays, a loss of potency and selectivity toward muscarinic M(1) and M(3) receptor subtypes. Both compounds were endowed with antinociceptive activity. Furthermore, in microdialysis tests in rat parietal cortex, they enhanced acetylcholine release, most likely by antagonizing presynaptic muscarinic receptor subtypes.

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.

The TRH neuron: a hypothalamic integrator of energy metabolism

Thyrotropin-releasing hormone (TRH) has an important role in the regulation of energy homeostasis not only through effects on thyroid function orchestrated through hypophysiotropic neurons in the hypothalamic paraventricular nucleus (PVN), but also through central effects on feeding behavior, thermogenesis, locomotor activation and autonomic regulation. Hypophysiotropic TRH neurons are located in the medial and periventricular parvocellular subdivisions of the PVN and receive direct monosynaptic projections from two, separate, populations of leptin-responsive neurons in the hypothalamic arcuate nucleus containing either alpha-melanocyte-stimulating hormone (alpha-MSH) and cocaine- and amphetamine-regulated transcript (CART), peptides that promote weight loss and increase energy expenditure, or neuropeptide Y (NPY) and agouti-related protein (AGRP), peptides that promote weight gain and reduce energy expenditure. During fasting, the reduction in TRH mRNA in hypophysiotropic neurons mediated by suppression of alpha-MSH/CART simultaneously with an increase in NPY/AGRP gene expression in arcuate nucleus neurons contributes to the fall in circulating thyroid hormone levels, presumably by increasing the sensitivity of the TRH gene to negative feedback inhibition by thyroid hormone. Endotoxin administration, however, has the paradoxical effect of increasing circulating levels of leptin and melanocortin signaling and CART gene expression in arcuate nucleus neurons, but inhibiting TRH gene expression in hypophysiotropic neurons. This may be explained by an overriding inhibitory effect of endotoxin to increase type 2 iodothyroine deiodinase (D2) in a population of specialized glial cells, tanycytes, located in the base and infralateral walls of the third ventricle. By increasing the conversion of T4 into T3, tanycytes may increase local tissue concenetrations of thyroid hormone, and thereby induce a state of local tissue hyperthyroidism in the region of hypophysisotrophic TRH neurons. Other regions of the brain may also serve as metabolic sensors for hypophysiostropic TRH neurons including the ventrolateral medulla and dorsomedial nucleus of the hypothalamus that have direct monosynaptic projections to the PVN. TRH also exerts a number of effects within the central nervous system that may contribute to the regulation of energy homeostasis. Included are an increase in core body temperature mediated through neurons in the anterior hypothalamic-preoptic area that coordinate a variety of autonomic responses; arousal and locomotor activation through cholinergic and dopaminergic mechanisms on the septum and nucleus accumbens, respectively; and regulation of the cephalic phase of digestion. While the latter responses are largely mediated through cholinergic mechanisms via TRH neurons in the brainstem medullary raphe and dorsal motor nucleus of the vagus, effects of TRH on autonomic loci in the hypothalamic PVN may also be important. Contrary to the actions of T3 to increase appetite, TRH has central effects to reduce food intake in normal, fasting and stressed animals. The precise locus where TRH mediates this response is unknown. However, evidence that an anatomically separate population of nonhypophysiotropic TRH neurons in the anterior parvocellular subdivision of the PVN is integrated into the leptin regulatory control system by the same arcuate nucleus neuronal populations that innervate hypophysiotropic TRH neurons, raises the possibility that anterior parvocellular TRH neurons may be involved, possibly through interactions with the limbic nervous system.

Central nervous system effects of thyrotropin-releasing hormone and its analogues: opportunities and perspectives for drug discovery and development

Besides its well-known endocrine role in the thyroid system, thyrotropin-releasing hormone (L-pyroglutamyl-L-histidyl-L-prolinamide) has been long recognized as a modulatory neuropeptide. After a brief overview of the extrahypothalamic and receptor distribution, and of the neurophysiological, neuropharmacological and neurochemical effects of this tripeptide, this review discusses efforts devoted to enhance therapeutically beneficial central nervous system effects via structural modifications of the endogenous peptide. An enormous array of maladies affecting the brain and the spinal cord has been a potential target for therapeutic interventions involving agents derived from thyrotropin-releasing hormone as a molecular lead. Successful development of several centrally active analogues and recent accounts of efforts aimed at improving metabolic stability, selectivity and bioavailability are highlighted.

Multiple injections of thyrotropin releasing hormone fail to reverse learning and memory deficits in rats with lesions of the nucleus basalis of meynert

The learning and memory enhancing effects of thyrotropin releasing hormone (TRH) was examined in an animal model of Alzheimer's disease. Adult rats were prepared with either sham surgeries or cholinergic lesions of the nucleus basalis of Meynert (nbM). Subjects were injected (ip) with one of three doses of TRH (0, 5, 10 mg/kg) starting on the day of surgery and continuing once every other day for a total of four injections. Performance (four trials/day for 4 days, 30 m inter-trial interval) in a Morris water maze was assessed one week after the last TRH injection (i.e., 2 weeks postoperatively). Latency to find the hidden platform served as the dependent variable. Results indicated that damage to the nbM impaired task performance in that animals with nbM lesions generally required more time to find the platform and showed less trial-to-trial improvement. Treatment with TRH failed to reverse this lesion-induced deficit. These results suggest that multiple injections of TRH do not provide residual protection against the deleterious effects on learning and memory produced by cholinergic lesions of the basal forebrain. Other doses and administration parameters, however, need to be studied in order to determine the generalizability of these findings.

Neuropharmacodynamic evaluation of the centrally active thyrotropin-releasing hormone analogue [Leu2]TRH and its chemical brain-targeting system

The centrally active thyrotropin-releasing hormone (TRH) analogue pGlu-Leu-Pro-NH(2) ([Leu(2)]TRH) showed a significant increase in the extracellular acetylcholine concentration during its perfusion to the hippocampus in rats, and this effect was manifested upon the delivery of the analogue in much smaller quantities compared to TRH when measured by in vivo intracranial microdialysis. The neuropharmacodynamic efficacy of [Leu(2)]TRH upon intravenous administration was augmented by the use of a brain-targeting derivative in which the progenitor sequence of the mature peptide was embedded in a molecular architecture that promoted enhanced brain delivery, retention and in situ generation of the pharmacologically active molecule. Compared to the unmodified peptide, the targeting system significantly improved the cumulative effect of the treatment on extracellular acetylcholine levels in rats.

S 17092: a prolyl endopeptidase inhibitor as a potential therapeutic drug for memory impairment. Preclinical and clinical studies

Any treatment that could positively modulate central neuropeptides levels would provide a promising therapeutic approach to the treatment of cognitive deficits associated with aging and/or neurodegenerative diseases. Therefore, based on the activity in rodents, S 17092 (2S,3aS,7aS)-1][(R,R)-2-phenylcyclopropyl]carbonyl]-2-[(thiazolidin-3-yl)carbonyl]octahydro-1H-indole) has been selected as a potent inhibitor of cerebral prolyl-endopeptidase (PEP). By retarding the degradation of neuroactive peptides, S 17092 was successfully used in a variety of memory tasks. These tasks explored short-term, long-term, reference and working memory in aged mice, as well as in rodents and monkeys with chemically induced amnesia or spontaneous memory deficits. S 17092 has also been safely administered to humans, and showed a clear peripheral expression of its mechanism of action through its inhibitory effect upon PEP activity in plasma. S 17092 exhibited central effects, as evidenced by EEG recording in healthy volunteers, and could improve a delayed verbal memory task. Collectively, the preclinical and clinical effects of S 17092 have suggested a promising role for this compound as an agent for the treatment of cognitive disorders associated with cerebral aging.

Application of in vivo microdialysis to the study of cholinergic systems

The application of in vivo microdialysis to the study of acetylcholine (ACh) release has contributed greatly to our understanding of cholinergic brain systems. This article reviews standard experimental procedures for dialysis probe selection and implantation, perfusion parameters, neurochemical detection, and data analysis as they relate to microdialysis assessments of cholinergic function. Particular attention is focused on the unique methodological considerations that arise when in vivo microdialysis is dedicated expressly to the recovery and measurement of ACh as opposed to other neurotransmitters. Limitations of the microdialysis technique are discussed, as well as methodological adaptations that may prove useful in overcoming these limitations. This is followed by an overview of recent studies in which the application of in vivo microdialysis has been used to characterize the basic pharmacology and physiology of cholinergic neurons. Finally, the usefulness of the microdialysis approach for testing hypotheses regarding the cholinergic systems' involvement in cognitive processes is examined. It can be concluded that, in addition to being a versatile and practical method for studying the neurochemistry of cholinergic brain systems, in vivo microdialysis represents a valuable tool in our efforts to better comprehend ACh's underlying role in a variety of behavioral processes.

Molecular simplification of 1,4-diazabicyclo[4.3.0]nonan-9-ones gives piperazine derivatives that maintain high nootropic activity

Several 4-substituted 1-acylpiperazines, obtained by molecular simplification of 4-substituted 1,4-diazabicyclo[4.3.0]nonan-9-ones, have been synthesized and tested in vivo on the mouse passive avoidance test, to evaluate their nootropic activity. The results show that, apparently, an N-acylpiperazine group can mimic the 2-pyrrolidinone ring of 1,4-diazabicyclo[4.3.0]nonan-9-one, as the compounds of the new series maintain high nootropic activity. Moreover molecular simplification produces more clear-cut structure-activity relationships with respect to the parent series. The mechanism of action also appears to be similar in the two series. In fact, although the molecular mechanism remains to be elucidated, the most potent compound of each class (DM232 and 13, DM235) is able to increase acetylcholine release in rat brain. Piperazine derivatives represent a new class of nootropic drugs with an in vivo pharmacological profile very similar to that of piracetam, showing much higher potency with respect to the reference compound. Among the compounds studied, 13 (DM235) shows outstanding potency, being active at a dose of 0.001 mg kg(-1) sc.

Further evidence for a dissociation between different forms of mnemonic expressions in a mouse model of age-related cognitive decline: effects of tacrine and S 17092, a novel prolyl endopeptidase inhibitor

It has been demonstrated previously on the radial maze that the emergence of an age-related mnemonic impairment is critically dependent on the form which the discrimination problems took. Hence, when the arms were presented one by one (i.e., successive go-no-go discrimination), both adult and aged mice learned to distinguish between positive (baited) and negative (unbaited) arms readily, as evidenced by their increased readiness to enter positive relative to negative arms (i.e., by a differential in arm-entry latencies). A selective impairment in the aged mice was seen when these arms were presented subsequently as pairs, such that the mice were confronted with an explicit choice (i.e., simultaneous 2-choice discrimination). When discriminative performance was measured by the differential run speed between positive and negative arms, aged mice were also impaired. This was particularly pronounced in the 2-choice discrimination condition. We examined the effects of tacrine (3mg/kg, subcutaneously) or S 17092 (10mg/kg, orally) in aged mice on the three behavioral indices of this 2-stage spatial discrimination paradigm. The results indicated that: (1) Tacrine, but not S 17092, enhanced the acquisition of go-no-go discrimination as reflected in arm-entry latencies; (2) both drugs improved choice accuracy in simultaneous discrimination, although the effect of tacrine was less striking and, in particular, far from statistical significance in the very first 2-choice responses; and (3) neither drugs significantly affected run-speed performance. We conclude further that the specific patterns of drug effects on the three indices of discriminative performance might suggest that each index is associated with a distinct form of mnemonic expression relying on separate neural systems.

Effect of JTP-2942, a novel thyrotropin-releasing hormone analog, on motor deficits after chronic focal cerebral ischemia in rats

To investigate the chronic effects of a novel thyrotropin-releasing hormone analog, JTP-2942 (N(alpha)-[(1S, 2R)-2-methyl-4-oxocyclopentylcarbonyl]-L-histidyl-L-prolinamide monohydrate), on behavioral changes after stroke, the authors examined its effects on motor and neurologic deficits using a middle cerebral artery (MCA) occlusion model in rats. A left MCA was permanently occluded at a proximal site. From 1 week after occlusion, JTP-2942 was intravenously administered once a day for 4 weeks. Sensorimotor performance was evaluated weekly for 10 weeks after the occlusion. The ability of the rat to maintain its body position on an inclined plane and neurologic examination based on hemiparesis and abnormal posture were examined. After all behavioral examinations were completed, the degree of shrinkage of the left hemisphere was measured. The ability of MCA-occluded rats to maintain body position on an inclined plane in the left-headed position was significantly lower than that of sham-operated rats throughout the test period. JTP-2942 gradually improved this deficit dose dependently, and a dose of 0.03 mg/kg of JTP-2942 significantly improved performance to the levels of the sham-operated rats. Neurologic deficits were also observed in MCA-occluded rats. JTP-2942 also significantly improved these deficits dose dependently. On the other hand, CDP-choline (500 mg/kg, administered intravenously), a therapeutic agent for the disturbance of consciousness and hemiparesis after stroke, improved neurologic deficits but did not affect the motor deficits measured using the inclined plane. It is noteworthy that the effects of JTP-2942 on these deficits were observed 4 weeks after cessation of drug administration. Furthermore, there was no difference in the degree of shrinkage of the cerebrum among the MCA-occluded groups. In the present study, long-lasting improving effects of JTP-2942 on the impairment of motor and neurologic functions were observed in rats with MCA occlusion, which continued after cessation of drug administration and which were not attributable to a reduction in ipsilateral cerebral shrinkage. It is considered that the effect of JTP-2942 on functional recovery is attributable to the activation of substitutive functions such as neuronal reconstruction. These pharmacologic properties of JTP-2942 may be of interest for the treatment of patients with motor and neurologic deficits during the chronic or subacute phase of stroke.

Effect of N-methyl-D-aspartate on motor activity and in vivo adenosine striatal outflow in the rat

It has been previously found that the systemic administration of low doses of N-methyl-D-aspartate (NMDA) in mice induces motor depression. The effects of the systemic administration of different doses of NMDA (10, 30 and 60 mg/kg s.c.) on the motor activity and on the in vivo extracellular levels of adenosine in the striatum was studied in Sprague-Dawley rats. The adenosine concentration in samples of perfusate was determined 24 h after implantation of a transverse microdialysis probe. At 30 and 60 mg/kg, but not 10 mg/kg, NMDA induced both a significant motor depression (motility and rearing) and a significant increase in the striatal extracellular levels of adenosine. Both the motor depression and the changes in the extracellular levels of adenosine were only evident during the first 30 min after NMDA administration. The non-competitive NMDA receptor antagonist MK-801 (0.1 mg/kg s.c.) completely counteracted the effects of NMDA (30 mg/kg s.c.) on motor activity (motility) and on the striatal extracellular levels of adenosine. The correlation between the behavioural and the biochemical data strongly support the hypothesis that adenosine release in the striatum is a main mechanism responsible for the motor depressant effects produced by the systemic administration of NMDA.

Involvement of nicotinergic mechanisms in thyrotropin-releasing hormone-induced neurologic recovery after concussive head injury in the mouse

A behavioral study was performed in an attempt to understand the neuronal mechanisms involved in the thyrotropin-releasing hormone (TRH)-induced improvement of consciousness after concussive head injury in the mouse. Intravenous administration of TRH dose dependently shortened the duration of unconsciousness after concussion in the mouse (ED50 = 3.2 mg/kg). The improvement of recovery evoked by TRH (3 mg/kg i.v.) after concussion was not affected by i.p. pretreatment with N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine, alpha-methyl-para-tyrosine, p-chlorophenylalanine, scopolamine or methylscopolamine. However, mecamylamine or hexamethonium i.p. pretreatment completely inhibited the TRH-induced improvement of outcome in traumatic brain injury. The results imply that TRH-induced improvement of recovery after concussion is not associated with increased activity of monoaminergic neurons in the brain. These results suggest that the inhibitory effect of TRH upon unconsciousness after concussion in mice is mainly produced by activation of central cholinergic systems via nicotinic receptors whereas muscarinic receptors seem to be not implicated.

Effect of subchronic treatment with metrifonate and tacrine on brain cholinergic function in aged F344 rats

The effects of 21-day treatment with the acetylcholinesterase inhibitors metrifonate (80 mg kg(-1) per os (p.o.)) and tacrine (3 mg kg(-1) p.o.), twice daily, on cortical and hippocampal cholinergic systems were investigated in aged rats (24-26 months). Extracellular acetylcholine levels were measured by transversal microdialysis in vivo; choline acetyltransferase and acetylcholinesterase activities were measured ex vivo by means of radiometric methods. Basal cortical and hippocampal extracellular acetylcholine levels, measured 18 h after the last metrifonate treatment, were about 15 and two folds higher, respectively, than in control and tacrine-treated rats. A challenge with metrifonate further increased cortical and hippocampal acetylcholine levels by about three and four times, respectively. Basal extracellular acetylcholine levels, measured 18 h after the last treatment with tacrine were not statistically different from those of the control rats. A challenge with tacrine increased cortical and hippocampal extracellular acetylcholine levels by about four and two times. A 75% inhibition of cholinesterase activity was found 18 h after the last metrifonate administration, while only a 15% inhibition was detectable 18 h after the last tacrine administration. The challenge with metrifonate or tacrine resulted in 90 and 80% cholinesterase inhibition, respectively. These results demonstrate that in aging rats a subchronic treatment with metrifonate results in a long-lasting, cholinesterase inhibition, and a persistent increase in acetylcholine extracellular levels which compensate for the age-associated cholinergic hypofunction. Metrifonate is therefore a potentially useful agent for the cholinergic deficit accompanying Alzheimer's disease.

JTP-2942, a novel thyrotropin-releasing hormone analogue, protects against spinal motor neuron degeneration in the wobbler mouse

JTP-2942, a novel thyrotropin-releasing hormone (TRH) analogue, exhibits a strong acetylcholine release-enhancing effect in the rat hippocampus and frontal cortex. This molecule has a more powerful and prolonged action on cholinergic neurons than TRH. Here we studied whether JTP-2942 treatment can ameliorate motor dysfunction and spinal motor neuron degeneration in the wobbler mouse. After clinical diagnosis at postnatal age 3-4 weeks, wobbler mice received intraperitoneal injections of JTP-2942 (2 mg/kg per day) for 4 weeks (long-term treatment) or 2 weeks (short-term treatment), TRH (50 mg/kg per day) for 4 weeks or vehicle in a blind fashion. Compared with the vehicle, long-term administration of JTP-2942 potentiated grip strength, attenuated muscle contractures in the forelimbs, reduced denervation muscle atrophy and protected spinal motor neurons. After cessation of JTP-2942 (short-term treatment), motor dysfunction deteriorated rapidly. Symptomatic and neuropathological progression were not retarded in mice that received TRH or short-term JTP-2942 treatment. Our results indicate that JTP-2942 may have therapeutic potential for lower motor neuron disease or motor neuropathy.

An update on the CNS actions of TRH and its analogs

This brief review will discuss the recent literature on several of the central actions of TRH and its analogs. The most prominent of these actions include: (1) the arousal or analeptic effect in drug narcotized animals or in concussion models; (2) the reversal of cognitive deficits produced by various drugs or procedures, and (3) the improvement of several neurological deficits produced in animal models of spinal and/or cerebellar injury. The mediation of these TRH effects by neurotransmitters is discussed. While little has been published on the human neuropsychopharmacology of TRH, and especially of its analogs, the future holds considerable therapeutic promise for these interesting drugs.

Effect of the subchronic treatment with the acetylcholinesterase inhibitor heptastigmine on central cholinergic transmission and memory impairment in aged rats

The effect of subchronic administration of the acetylcholinesterase (AChE) inhibitor heptastigmine (HEP 0.6 mg/kg s.c. daily for 15 days) was investigated on cortical extracellular acetylcholine (ACh) levels and on memory function in aged male rats (26 months old at the beginning of the experiments) using microdialysis and behavioural techniques. Twenty-four hours after the last treatment, cortical ACh levels were significantly higher in rats subchronically treated with HEP than in rats treated with saline and AChE activity was still inhibited in cortex, hippocampus and striatum. The injection of a challenge dose of HEP (0.6 mg/kg s.c.) 24 h after the last treatment produced a faster and a more sustained increase of ACh in the cortex of subchronically treated rats compared to those repeatedly injected with saline. However, the maximum increase of ACh levels after injection of the challenge was comparable in both groups. In an object recognition test in which the pretest and test phase were spaced by 45 days, HEP prevented the deterioration of spatial memory occurring during this period, but had no effect on non-spatial memory. The present results suggest that moderate inhibition of brain AChE is able to maintain high levels of cortical extracellular ACh in aged rats and that this increase matches facilitatory effect of HEP on spatial memory.

The neuropeptide TRH has a minor effect on the enzymatic activity of acetylcholinesterase in vitro

The neuropeptide thyrotropin-releasing hormone (TRH) elicits a variety of physiological effects of which some are due to cholinergic mechanisms. TRH modulates in vivo the effects of compounds affecting acetylcholinesterase (AChE). In the present study the in vitro effects of TRH on the activity of AChE were explored. TRH has no effect at physiologically relevant concentrations. At unphysiologically high concentrations (>5 mM) a slight inhibition was found. This was noticed also when the enzyme was exposed to the amide-free tripeptide analog p-Glu-His-Pro. We conclude that any cholinergic effect of TRH observed in vivo is unlikely to be due to a direct interaction of the peptide with AChE.

Effects of thyrotrophin-releasing hormone tartrate and its sustained release formulation on cerebral glucose metabolism in aged rats

The effects of a sustained release formulation of thyrotrophin-releasing hormone (TRH) over two weeks (TRH-SR, 10 or 50 mg kg-1, equivalent to 0.56 or 2.80 mg kg-1 free TRH, respectively) and repeated treatment with TRH tartrate (TRH-T, 0.3, 1.0 or 3.0 mg kg-1, equivalent to 0.2, 0.7 or 2.0 mg kg-1 free TRH, respectively) on the rate of local cerebral glucose utilization (LCGU) were investigated using the quantitative autoradiographic 2-deoxy-[14C]D-glucose method in various brain regions of aged rats. In aged rats (28 months old), the LCGU was significantly reduced as compared with young adult rats (3 months old), while treatment with TRH-SR ameliorated the reduction of the LCGU in a dose-dependent manner. The brain regions ameliorated by TRH-SR were the auditory cortex, septal nucleus, substantia nigra, cerebellar cortex and cerebellar nucleus. In contrast, once-daily repeated treatment over one week with TRH-T at a dose of 0.3 mg kg-1 (equivalent to 50 mg kg-1 of TRH-SR) had no effect on the reduced LCGU in various brain regions in aged rats (27 months old), whereas treatment with a higher dose of TRH-T (0.7 or 2.0 mg kg-1 free TRH) significantly ameliorated the reduction. The comparison of the ameliorating potencies between TRH-T and TRH-SR indicated that TRH-SR had a potency about 7 times greater than TRH-T.

Effect of neuropeptides on cognitive function

Recent evidence indicates that, in addition to the involvement of cholinergic and other neurotransmitter systems, various neuropeptides that occur in cortical and subcortical brain regions have a role in cognitive behavior. This evidence results largely from behavioral studies in rodents and other animals, following peptide administration and only in a very few cases from similar studies in human subjects. Several neuropeptides studied appear to enhance or produce changes conducive to improvement in cognitive performance and these include vasopressin, corticotrophin-releasing hormone (CRH), somatostatin, substance P, neuropeptide Y, and thyrotrophin-releasing hormone (TRH), while one peptide, galanin, has been reported to inhibit cognitive processes. Of those neuropeptides that improve performance, only TRH has been shown recently to attenuate the memory impairment of human subjects and Alzheimer patients treated with an anticholinergic drug, and this review describes a series of complimentary studies in adult and aged rodents that contribute to our understanding of the possible mechanisms involved in the role of TRH in cognition.

Effect of metrifonate on extracellular brain acetylcholine and object recognition in aged rats

The effects of metrifonate were investigated in 4-6- and 22-24-month-old rats. Extracellular acetylcholine levels were measured by transversal microdialysis in vivo. Baseline extracellular acetylcholine levels in the cerebral cortex and hippocampus were 42% and 60% lower, respectively, in old than in young rats. Old rats did not discriminate between familiar and novel objects. In old rats, metrifonate (80 mg/kg p.o.) brought about 85% inhibition of cholinesterase activity in the cortex and hippocampus, a 4-fold increase in extracellular acetylcholine levels in the cortex only, and restored object recognition. In young rats, metrifonate caused 75% cholinesterase inhibition in the cerebral cortex and hippocampus, a 2-fold increase in cortical and hippocampal extracellular acetylcholine levels, and no effect on object recognition. The slight cholinesterase inhibition following metrifonate (30 mg/kg) in aged rats had no effect on cortical acetylcholine levels and object recognition. In conclusion, metrifonate may improve the age-associated cholinergic hypofunction and cognitive impairment.

Stereoselective increase in cholinergic transmission by R-(+)-hyoscyamine

R-(+)-hyoscyamine, the dextro enantiomer of atropine, has been shown to amplify cholinergic transmission. R-(+)-hyoscyamine, unlike S-(-)-hyoscyamine, was able to increase acetylcholine release both in vitro and in vivo at a range of concentrations (10(-14) to 10(-12) M) and doses (5 microg/kg i.p.) which were inadequate for blocking muscarinic receptors. The increase over control values in ACh release was 15.9 +/- 2.1% in in vitro experiments performed in rat phrenic nerve-hemidiaphragm preparations (n = 6), and 63.3 + 16.3% in cortical microdialysis performed in free-moving rats (n = 5). The maximum ACh release was reached 60 min after R-(+)-hyoscyamine administration in in vivo experiments. At the same doses and concentrations, R-(+)-hyoscyamine was also able to elicit: antinociception of a cholinergic type (55.6-112.7% depending on the test used); complete prevention of scopolamine- and dicyclomine-induced amnesia; potentiation of muscular contractions electrically evoked in isolated guinea-pig ileum (16.7 +/- 3.6%) and in rat phrenic nerve-hemidiaphragm (19.9 +/- 3.2%) preparations. Antinociception was performed using the hot-plate and acetic acid abdominal constriction tests in mice, and the paw pressure test in rats, while prevention of induced amnesia was evaluated in mice using the passive-avoidance test. The respective affinities (pA2) for R-(+)- and S-(-)-hyoscyamine vs M1 (rabbit vas deferens), M2 (rat atrium) and M3 (rat ileum) receptor subtypes were as follows: 7.05 +/- 0.05/9.33 +/- 0.03 for M1; 7.25 +/- 0.04/8.95 +/- 0.01 for M2; 6.88 +/- 0.05/9.04 +/- 0.03 for M3. The respective pKi values for R-(+)- and S-(-)-hyoscyamine vs the five human muscarinic receptor subtypes expressed in Chinese hamster oocytes (CHO-K1) were as follows: 8.21 +/- 0.07/9.48 +/- 0.18 for m1; 7.89 +/- 0.06/9.45 +/- 0.31 for m2; 8.06 +/- 0.18/9.30 +/- 0.19 for m3; 8.35 +/- 0.11/9.55 +/- 0.13 for m4; 8.17 +/- 0.08/9.24 +/- 0.30 for m5.

In vivo amino acid release from the striatum of aging rats: adenosine modulation

The release of glutamate, aspartate, GABA, and taurine from the striatum of young (3 months), mature (12 months), and old (22 months), freely moving male rats was investigated by using a microdialysis fiber inserted transversally in the striatum. In old rats basal extracellular glutamate and aspartate levels were decreased vs. young rats (-38 and -49%, respectively). GABA and taurine levels were unmodified by age. In the presence of the adenosine receptor antagonist 8-phenyltheophilline (8-pT) at the concentration of 50 microM, both K(+)-evoked releases of glutamate and aspartate were more than doubled in young, but not in mature and old rats. 8-pT at the concentration of 500 microM significantly decreased glutamate basal levels and K(+)-evoked aspartate release in old rats only. GABA and taurine releases were not affected by 8-pT at either dose. Our findings indicate a modified adenosine modulation on glutamate and aspartate release in aged rats, that could result from a change in the balance between A1 and A2a adenosine receptor density or an alteration of A1 and A2a receptor-effector coupling.

Effect of a novel prolyl endopeptidase inhibitor, JTP-4819, on spatial memory and central cholinergic neurons in aged rats

The effects of a novel prolyl endopeptidase inhibitor (PEP), (S)-2-[[(S)-2-(hydroxyacetyl)-1-pyrrolidinyl]carbonyl]-N-(phenylmethyl)- 1-pyrrolidinecar-boxamide (JTP-4819), on performance of the Morris water maze task and on central cholinergic function were investigated in aged rats. Spatial memory (escape latency, path length, and swimming speed to the platform) was impaired in aged rats performing the Morris water maze task when compared to young rats. Administration of JTP-4819 (1 mg/kg, p.o.) for 14 days improved this memory deficit in aged rats, as shown by the decrease in escape latency and path length. In addition, when JTP-4819 (at doses of 1 and 3 mg/kg, p.o.) was administered for 3 wk, it reversed the age-related increase of ChAT activity in the cerebral cortex and the decrease of 3H-choline uptake in the hippocampus. These data suggest that JTP-4819 ameliorates age-related impairment of spatial memory and partly reverses central cholinergic dysfunction, possibly due to the enhancement of neuropeptide function by inhibition of PEP mediated degradation of substance P, arginine-vasopressin, and thyrotropin-releasing hormone.

Alterations in local cerebral glucose metabolism and endogenous thyrotropin-releasing hormone levels in rolling mouse Nagoya and effect of thyrotropin-releasing hormone tartrate

To identify the brain region(s) responsible for the expression of ataxic gaits in an ataxic mutant mouse model, Rolling mouse Nagoya (RMN), changes in local cerebral glucose metabolism in various brain regions and the effect of thyrotropin-releasing hormone tartrate (TRH-T), together with alterations in endogenous thyrotropin-releasing hormone (TRH) levels in the brains of RMN, were investigated. Ataxic mice [RMN (rol/rol)] showed significant decreases in glucose metabolism in regions of the diencephalon: thalamic dorsomedial nucleus, lateral geniculate body and superior colliculus; brain stem: substantia nigra, raphe nucleus and vestibular nucleus; and cerebellar nucleus as compared with normal controls [RMN (+/+)]. When RMN (rol/rol) was treated with TRH-T (10 mg/kg, equivalent to 7 mg/kg free TRH), glucose metabolism was significantly increased in these regions. These results suggest that these regions may be responsible for ataxia. We also found that TRH levels in the cerebellum and brain stem of RMN (rol/rol) were significantly higher than those of RMN (+/+). These results suggest that ataxic symptoms in RMN (rol/rol) may relate to the abnormal metabolism of TRH and energy metabolism in the cerebellum and/or brain stem and that exogenously given TRH normalizes them.

Effect of a thyrotrophin-releasing hormone analogue, RX77368, on AMPA-induced septal-hippocampal lesioned rats in an operant delayed non-matching to position test

The aim of the present study was to determine the effect of a thyrotrophin-releasing hormone (TRH) analogue, RX77368, on performance of a working memory test, using a delayed non-matching to position (DNMTP) procedure, in (RS)-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-induced septal-hippocampal lesioned rats. Following a post-surgery recovery period, pretrained rats were tested once daily on DNMTP, 30 min post-administration of RX77368 (1.0 mg kg-1, i.p.) or saline. AMPA-induced lesions significantly reduced percent correct responses during the second week of testing. Comparison of percent correct responses between days 1 and 13 of testing showed that sham rats significantly improved DNMTP performance, whereas lesioned rats did not. RX77368 significantly reduced general locomotor activity in sham rats in activity boxes, but did not disrupt non-mnemonic measures, such as locomotion and motivation, in the DNMTP test. RX77368 increased percent correct responses in AMPA-lesioned rats on days 8-10 and 11-13. There was also a significant improvement in percent correct responses achieved between day 1 and 13 in RX77368-treated lesioned and sham rats. These results showed that: (i) septal-hippocampal lesioned rats did not improve over the testing period; and (ii) on test days when a significant impairment was present, RX77368 partially improved DNMTP performance.

A2 adenosine receptors: their presence and neuromodulatory role in the central nervous system

1. Adenosine is an endogenous neuromodulator that exerts its depressant effect on neurons by acting on the A1 adenosine receptor subtype. Excitatory actions of adenosine, mediated by the activation of the A2 adenosine receptor subtype, have also been shown in the central nervous system. 2. Adenosine A2a receptors are highly localized in the striatum, as demonstrated by the binding assay of the A2a selective agonist, CGS2680, and by analysis of the A2 receptor mRNA localization with in situ hybridization histochemistry. However, adenosine A2a, receptors, albeit at lower levels, are also localized in other brain regions, such as the cortex and the hippocampus. 3. In the striatum, adenosine A2a, receptors are implicated in the control of motor activity. Evidences exists of an antagonistic interaction between adenosine A2a and dopamine D2 receptors. 4. Utilizing selective agonists and antagonists for adenosine A2a receptors, their role in the modulation of the release of several neurotransmitters (acetylcholine, dopamine, glutamate, GABA) has been extensively studied in the brain (striatum, cortex, hippocampus). Controversial results have been obtained and, because the overall effect of endogenous adenosine in the brain is that of an inhibitory tonus, the physiological meaning of the excitatory A2 receptor remains to be clarified.

Effect of TA-0910, a novel thyrotropin-releasing hormone analog, on in vivo acetylcholine release and turnover in rat brain

To examine the action of a novel thyrotropin-releasing hormone (TRH) analog, TA-0910 ((-)-N-[(S)-hexahydro-1-methyl-2,6-dioxo-4-pyrimidinylcarbonyl]-L- histidyl-L-prolinamide tetrahydrate), on the cerebral cholinergic systems, the release of acetylcholine (ACh) and choline in freely-moving rats and ACh accumulation in gamma-butyrolactone (GBL, a nerve impulse flow blocker)- and physostigmine-treated rats were examined. TA-0910 (0.1-1 mg/kg, i.p.) caused a marked dose-dependent increase in extracellular ACh levels and a decrease in choline levels in the hippocampus of freely moving rats. These effects were significantly stronger and longer-lasting than similar effects of TRH. TA-0910 (1, 3 mg/kg, i.p.) depressed the ACh accumulation in the cerebral cortex and hippocampus of GBL (1000 mg/kg, i.p.)-treated rats. Moreover, this analog (1, 3 mg/kg, i.p.) increased the accumulation rate of ACh in these regions in physostigmine (1 mg/kg, i.p.)-treated rats. TRH (30 mg/kg, i.p.) affected the ACh accumulation only in the hippocampus of the GBL-treated rats. These results suggest that TA-0910 not only enhances the release of ACh, but also accelerates the ACh turnover, i.e., ACh release and synthesis, at the cholinergic neuronal terminals in normal rats.

Chiral synthesis and pharmacological evaluation of the enantiomers of SM32, a new analgesic and cognition-enhancing agent

The enantiomers of 3-alpha-tropyl 2-(phenylthio)butyrate (SM32, 1) were prepared by chiral synthesis and tested for analgesic, cognition-enhancing, and ACh-releasing properties. They show enantioselectivity in some of the tests, the eutomer being related in configuration to R-(+)-hyoscyamine.

Synthesis and enantioselectivity of the enantiomers of PG9 and SM21, new potent analgesic and cognition-enhancing drugs

The enantiomers of two alpha-tropanyl esters, SM21 (1) and PG9 (2), derived from (+)-R-hyoscyamine, that act by increasing the central cholinergic tone, were obtained by esterification after resolution of the corresponding racemic acids [(-)-S-1, (-)-R-2 and (+)-S-2] and by stereospecific synthesis [(+)-R-1]. Their analgesic and cognition-enhancing activities were tested in mice and their ACh-releasing properties determined on rat parietal cortex. These compounds show enantioselectivity in analgesic and cognition-enhancing tests on mice, the eutomers being the isomers which possess the same spatial arrangement of the groups on the chiral atom as (+)-R hyoscyamine [(+)-R-SM21, (+)-S-PG9]. The ACh-releasing effect of the enantiomers of SM21 in rats is in agreement with the results in mice, while PG9 enantiomers do not show any appreciable enantioselectivity in this test. On the basis of the different effects of the 5-HT4 antagonist SDZ 205557 on analgesia induced by the enantiomers of 1 and 2 and by (+)-R-hyoscyamine and the alpha-tropanyl ester of 2-phenylpropionic acid 3, a mechanism of action is proposed for this class of compounds.

NS-3(CG3703), a TRH analog, ameliorates scopolamine-induced memory disruption in rats

The effects of a metabolically stable TRH analog, N-[[(3R, 6R)-6-methyl-5-oxo-3-thiomorpholinyl]carbonyl]-L-histidyl-L- prolinamide tetrahydrate (NS-3, CG3703) on the scopolamine-induced memory disruption in maze performance tests were investigated in rats. a) In the delayed nonmatching-to-sample (DNMS) task using a T-maze, NS-3 (0.3 mg/kg) produced a significant reversal of the marginal disruption of choice accuracy induced by scopolamine (0.3 mg/kg) at the short (5 s) and long (120, 480 s) interval delays. Physostigmine (0.5 mg/kg) produced a significant reversal only at a 5-s interval delay. b) In the eight-arm radial maze task, NS-3 (0.3 mg/kg) significantly reversed the deficit of choice accuracy induced by scopolamine (0.3 mg/kg), whereas neither TRH (3-30 mg/kg) nor physostigmine (0.1-1 mg/kg) had any effect. The consistent reversal of these maze-learning performances by NS-3, but not by TRH or physostigmine, may be due to its potent enhancement of cholinergic and noradrenergic neuronal activities.

Differential effects of amyloid peptides beta-(1-40) and beta-(25-35) injections into the rat nucleus basalis

The nucleus basalis of male Charles River Wistar rats was injected with 10 micrograms of the beta-amyloid peptides beta-(1-40) and beta-(25-35) and changes in the morphology of the lesioned area, the release of acetylcholine from the cortex, and in behavior were investigated. Injections of saline and a scrambled (25-35) peptide were used as controls. One week after lesioning, a Congo Red-positive deposit of aggregated material was found at the beta-peptides injection site, which lasted for about 21 days in the case of the beta-(25-35) peptide and at least two months for beta-(1-40). No deposit was detected after scrambled peptide injection. At one week post injection, an extensive glial reaction surrounded the injection site of all peptides and saline as well. Such a reaction was still present but rather attenuated after two months. A decrease in the number of cholinergic neurons was detected in the nucleus basalis after one week with all treatments except saline. After two months, a reduction in the number of choline acetyltransferase-immunopositive neurons was still detectable in the rats injected with beta-(1-40) but not in the beta-(25-35)-or scrambled-injected. The reduction in choline acetyltransferase immunoreactivity was closely paralleled by a decrease in basal acetylcholine release from the parietal cortex ipsilateral to the lesion. Disruption of object recognition was observed in the first weeks after beta-(25-35) peptide injection, whereas the beta-(1-40) peptide impaired the performance only two months after lesion. Rats with lesions induced by beta-peptides may be a useful animal model of amyloid deposition for investigation of the pathogenetic mechanisms leading to Alzheimer's disease.

NS-3 (CG3703), an analog of thyrotropin-releasing hormone, ameliorates cognitive impairment in rats

The effects of thyrotropin-releasing hormone (TRH) and its analog, N-[[(3R,6R)-6-methyl-5-oxo-thiomorpholinyl] carbonyl]-L-histidyl-L- prolinamide tetrahydrate (NS-3, CG3703) on disturbance of memory of a passive avoidance response (PAR) and an escape response in rats were investigated. NS-3 improved amnesia caused by scopolamine, electroconvulsive shock (ECS), and cycloheximide (CXM), but TRH improved only the ECS-induced amnesia. NS-3 reversed learning deficits caused by hypercapnia, but TRH had no effect. These differences in the effect between NS-3 and TRH may be due to their biological half-life in rat plasma. These results suggest that NS-3 possesses more potent antiamnestic effects than TRH in rats.