Studies of somatostatin-induced barrel rotation in rats

Advanced progress of vestibular compensation in vestibular neural networks

Vestibular compensation is the natural process of recovery that occurs with acute peripheral vestibular lesion. Here, we summarize the current understanding of the mechanisms underlying vestibular compensation, focusing on the role of the medial vestibular nucleus (MVN), the central hub of the vestibular system, and its associated neural networks. The disruption of neural activity balance between the bilateral MVNs underlies the vestibular symptoms after unilateral vestibular damage, and this balance disruption can be partially reversed by the mutual inhibitory projections between the bilateral MVNs, and their top-down regulation by other brain regions via different neurotransmitters. However, the detailed mechanism of how MVN is involved in vestibular compensation and regulated remains largely unknown. A deeper understanding of the vestibular neural network and the neurotransmitter systems involved in vestibular compensation holds promise for improving treatment outcomes and developing more effective interventions for vestibular disorders.

Somatostatin, a negative-regulator of central leptin action in the rat hypothalamus

Leptin-responsive neurons of the hypothalamus constitute a heterogeneous population expressing a vast array of different neuropeptides and neurotransmitters, some of which participate in the regulation of hunger and satiety. Here we report that somatostatin modulates the efficacy of leptin-signalling in the rat hypothalamus. Using a two-pulse paradigm at 30-min intervals, we delivered somatostatin or somatostatin receptor subtype-selective agonists in combination with leptin into the lateral cerebral ventricle of stereotaxically cannulated rats. To monitor the effect of somatostatin on the leptin-signalling pathway, we quantified changes in the leptin-mediated activation of STAT3, the signal transducer and activator of transcription 3. Successive administration of somatostatin and leptin diminished the level of STAT3-phosphorylation and nuclear STAT3 translocation in the ventromedial and dorsomedial hypothalamic nuclei, the lateral hypothalamic area, and the arcuate nucleus by about 40% compared to leptin administration alone. Furthermore, application of subtype-selective somatostatin receptor agonists suggests that the observed reduction in leptin-responsiveness is predominantly mediated by the sst3 receptor-subtype, followed by sst1 and sst2. In addition, the intensity of the negative-regulatory effect of somatostatin on leptin-signalling displayed regional differences for the three receptor-subtypes involved. Addressing the functional consequences of the diminished leptin-signalling, behavioural analyses showed that centrally applied somatostatin counteracts the leptin-mediated suppression of food intake. These results suggest that the pleiotropic effector somatostatin also plays a role in the central regulation of energy homeostasis.

The growth hormone axis and cognition: empirical results and integrated theory derived from giant transgenic mice

Sleep is required for the consolidation of memory for complex tasks, and elements of the growth-hormone (GH) axis may regulate sleep. The GH axis also up-regulates protein synthesis, which is required for memory consolidation. Transgenic rat GH mice (TRGHM) express plasma GH at levels 100-300 times normal and sleep 3.4 h longer (30%) than their normal siblings. Consequently, we hypothesized that they might show superior ability to learn a complex task (8-choice radial maze); 47% of the TRGHM learned the task before any normal mice. All 17 TRGHM learned the task, but 33% of the 18 normal mice learned little. TRGHM learned the task significantly faster than normal mice (p < 0.05) and made half as many errors in doing so, even when the normal nonlearners were excluded from the analysis. Whereas normal mice expressed a linear learning curve, TRGHM showed exponentially declining error rates. The contribution of the GH axis to cognition is conspicuously sparse in literature syntheses of knowledge concerning neuroendocrine mechanisms of learning and memory. This paper synthesizes the crucial role of major components of the GH axis in brain functioning into a holistic framework, integrating learning, sleep, free radicals, aging, and neurodegenerative diseases. TRGHM show both enhanced learning in youth and accelerated aging. Thus, they may provide a powerful new probe for use in gaining an understanding of aspects of central nervous system functioning, which is highly relevant to human health.

Barrel rotation evoked by intracerebroventricular injection of somatostatin and arginine-vasopressin is accompanied by the induction of c-fos gene expression in the granular cells of rat cerebellum

Intracerebroventricular (i.c.v.) injection of somatostatin (SS) or arginine-vasopressin (AVP) elicits barrel rotation (BR) in rats. To identify the potential neuron structures involved in this characteristic behavior, the regional expression of the c-fos gene in rat brain after i.c.v. injection of SS (10 micrograms) or AVP (1 micrograms) was examined by hybridization histochemistry. The c-fos expression could serve as a marker of neuronal activity and/or neural transmission. Following SS-induced BR, c-fos gene expression was observed in the lingula, uvula, nodulus, simplex, centralis, and culmen of the cerebellum, while following AVP-induced BR, c-fos gene expression was observed in the first four of the above-mentioned regions of the cerebellum, but not in the centralis or culmen. In these regions, the c-fos mRNA signals were observed on the granular layer. Expression of the c-fos gene was immediately and transiently induced and was not observed in rats in which BR was not evoked after SS or AVP injection. In both control rats and SS- or AVP-injected rats, the c-fos gene expression was induced in the piriform cortex and the flocculus of the cerebellum. The findings suggest that BR is a manifestation of behavior induced by massive transsynaptic activation of the granular cells in the cerebellum.

Toxic effects of somatostatin in the cerebellum and vestibular nuclei: multiple sites of action

This study demonstrates that somatostatin (SRIF), an endogenous peptide in vestibular nuclei and cerebellum, can produce both a dose-dependent death of Purkinje cells in distinct sagittal regions of cerebellar cortex and vascular infarcts centered selectively in the inferior vestibular nucleus. Alert, adult male rats were given a 5 microliters intracerebroventricular (i.c.v.) bolus of either SRIF alone (20 or 40 micrograms) or a combined dose of SRIF plus either arginine-vasopressin (AVP, 1 micrograms) or an AVP V1 antagonist, (1-(beta-mercapto-beta,beta-cyclopentamethylene propionic acid), 2-(O-methyl)-tyrosine)-arginine 8-vasopressin (mcAVP, 1 micrograms), through an implanted cannula. After a 4-5 day survival, the brains were stained with the cupric-silver selective degeneration method. Two types of dose-dependent lesions were observed in the cerebellar and vestibular nuclei of these animals: degeneration of Purkinje cell responses in the cerebellar cortex and vascular infarcts in vestibular nuclei. These toxic responses were unaffected by application of AVP or mcAVP; hence, they can be attributed to actions of SRIF. The distribution of Purkinje cell degeneration varied with the SRIF dose in different cerebellar regions. Purkinje cell responses in lobules I-III were equivalent at both SRIF doses, and degeneration in the copula pyramis, paraflocculus and paramedian lobule emerged at the higher SRIF dose. Purkinje cells in the medial aspect of lobules IX-X had an intermediate sensitivity to SRIF intoxication. Degenerating Purkinje cells tended to be arranged in parasagittal bands in each region, suggesting parasagittal zonal variations in susceptibility to SRIF intoxication. By contrast, infarctions in the vestibular nuclei only appeared at the higher SRIF dose. These infarcts could be unilateral or bilateral and always involved the inferior vestibular nucleus at the level of the caudal margin of the acoustic tubercle; they often extended into the medial and lateral vestibular nuclei. The infarcts had a necrotic core that was infiltrated by non-neuronal elements. Thus, they appear to reflect a direct or neurally-mediated vascular response to the peptide.

Barrel rotation in rats induced by SMS 201-995: suppression by ceruletide

Intracerebroventricular administration of SMS 201-995 (5 micrograms/rat), a somatostatin analogue, induced barrel rotation in rats. Pretreatment with ceruletide (40 micrograms/100 g b. wt., IP) 3 days or 7 days prior to the injection of SMS 201-995 significantly inhibited the response rate of barrel rotation induced by SMS 201-995, but not that induced by arginine-vasopressin (1 microgram/rat, ICV). The suppressive effect of ceruletide on barrel rotation could be partially countered by MK-329, a selective peripheral CCK (CCK-A) receptor antagonist. Desulfated cerulein did not affect the barrel rotation induced by SMS 201-995. These findings suggest that ceruletide specifically suppresses the barrel rotation evoked by SMS 201-995 in a long-lasting manner possibly acting through CCK-A receptor.

Preclinical and clinical studies with somatostatin related to the central nervous system

1. The tetradecapeptide somatostatin (SS) has a widespread, uneven distribution within several organs including the central nervous system (CNS), with particularly high concentration in the hypothalamus. 2. The SS-related peptides (SS28, SS28(1-12), SS28(15-28)) are originated from the precursor pre-prosomatostatin. 3. SS is suggested to be involved in a large number of CNS functions, locomotion, sedation, excitation, catatonia, body temperature, feeding, nociception, paradoxical sleep, self-stimulation, seizure, learning and memory. 4. SS influences central neurochemical processes. 5. It is possible that SS is related to various neurological and psychiatric illnesses, like Huntington's disease, multiple sclerosis, Parkinson's disease, epilepsy, eating disorders, Alzheimer's disease, schizophrenia and major depressive illness.

Effects of somatostatin-28 and some of its fragments and analogs on open-field behavior, barrel rotation, and shuttle box learning in rats

The effect of intracerebroventricular (ICV) administration of somatostatin-28 (SS-28) and some of its fragments, SS-28 (1-12), SS-28(15-28), and analogs, des-AA-(1,2,4,5,12,13)-(DTrp8)SS-14, ODT8-SS, and (DTrp8,DCys14)SS-14 were studied in different behavioral tests on rats. SS-28 (6.0 nM) decreased, SS-28(15-28) (0.6 nM) increased, and SS-28(15-28) (6.0 nM) decreased activity of the animals in an open-field test. SS-28(1-12) (0.6, 3.0, and 6.0 nM) did not influence this behavior. ODT8-SS (0.6, 3.0, and 6.0 nM) decreased activity of the rats, while (DTrp8,DCys14)SS-14 increased it, only at a high dose (6.0 nM). Similar results were obtained for barrel rotation, except that (DTrp8,DCys14)SS-14 even in high dose (12.0 nM) had no effect. In a shuttle-box learning paradigm, SS-28(15-28) (0.6 nM) facilitated, while SS-28(1-12) (0.6 nM) did not influence, the performance of the animals. These results suggest that the isomeric Cys(28) form of the SS-28(15-28) molecule may be crucial for the expression of the behavioral effects of these peptides.

Comparative studies of somatostatin-14 and some of its fragments on passive avoidance behavior, open field activity and on barrel rotation phenomenon in rats

Behavioral effects of somatostatin-14, and some of its fragments [somatostatin(3-8), somatostatin(9-14), somatostatin(7-10)] after intracerebroventricular (ICV) administration have been investigated in male rats. In a passive avoidance learning test, somatostatin-14 (0.6 nM) given immediately after the learning session increased the avoidance latency at 24 hr after the injection, when compared to a somatostatin(3-8) (0.6 nM)-treated group. However, compared to a saline-treated group, the peptides did not significantly influence the avoidance latency. Somatostatin-14 administered in higher dose (6.0 nM) decreased the avoidance latency compared to the saline-treated group, while its fragments did not influence it. In an open field behavioral test, immediately after the 24-hr passive avoidance test, 6 nM of somatostatin-14 decreased the rearing activity, while the fragments did not influence this behavior. Somatostatin-14 produced barrel rotation in a dose-related manner, but after the injection of a high dose of the peptide (12 nM) all of the animals died in cardiorespiratory failure (apnea, pulmonary oedema). The fragments did not produce barrel rotation.

Effects of cysteamine and pantethine on open-field behavior, hypothalamic catecholamine concentrations, and somatostatin-induced barrel rotation in rats

Cysteamine administered in a dose of 1.95 mM/kg subcutaneously (SC) markedly reduced several open-field behaviors (locomotion, rearing, grooming and defecation), while pantethine, administered in an equimolar dose, reduced the locomotion only. However, administered in a dose of 3.90 mM/kg (SC), pantethine also markedly reduced all open-field parameters. Cysteamine, and to less extent pantethine, reduced noradrenaline, and increased dopamine and DOPAC concentrations in the hypothalamus. It is discussed whether the lower potency of pantethine on open-field behaviors and hypothalamic catecholaminergic neurotransmission is connected with the limited activity of pantetheinase, the cysteamine-generating enzyme. Intracerebroventricularly (ICV) administered somatostatin did not influence the pantethine-induced (1.95 mM/kg SC) behavioral changes in the open-field test. It is possible that the peptide did not reach at the receptor sites in a sufficient concentration because of the reduced endogenous somatostatin content, or that the pantethine-induced noradrenaline depletion is connected with the ineffectiveness of somatostatin. Furthermore, pretreatment with cysteamine (1.95 mM/kg SC) or pantethine (1.95 mM/kg or 3.90 mM/kg SC) attenuated the somatostatin-induced (10 micrograms ICV) barrel rotation, suggesting that the level of endogenous somatostatin may play a role in the pathogenesis of this motor disturbance.

Gyroxin, a toxin from the venom of Crotalus durissus terrificus, is a thrombin-like enzyme

We report a simple method for the isolation of gyroxin, a protein from the venom of the South American rattlesnake Crotalus durissus terrificus. The intravenous injection of gyroxin into mice produces temporary episodes characterized by opisthotonos and rotations around the long axis of the animal. We found gyroxin to be a glycoprotein with thrombin-like and esterase activities. Gyroxin loses its ability to produce the gyroxin syndrome, its thrombin-like activity and its esterase activity with heat, dithiothreitol, phenylmethylsulfonyl fluoride or diisopropylfluorophosphate. We also report that three other thrombin-like enzymes, crotalase from the eastern diamondback rattlesnake (Crotalus adamanteus), ancrod from the Malayan pit viper (Agkistrodon rhodostoma) and a thrombin-like enzyme from the Central American rattlesnake (Crotalus durissus durissus), produce the gyroxin syndrome in mice. These enzymes may work by releasing neuroactive peptides from endogenous precursors.

Excessive grooming induced by somatostatin or its analog SMS 201-995

Intracerebroventricular (i.c.v.) administration of somatostatin or SMS 201-995 induces excessive grooming behavior in rats. The grooming inducing effect of somatostatin is rather weak, as doses of 300 ng or less did not result in increased total grooming scores. In contrast a dose of 10 ng SMS 201-995 already significantly increased the total grooming scores. However, doses of 100 ng and more did not further increase the total grooming scores reached with a 50 ng dose of this peptide. Systemic administration of SMS 201-995 in doses up to 900 micrograms did not result in excessive grooming behavior. The patterns of excessive grooming induced by i.c.v. SMS 201-995 and somatostatin were characterized by a predominant display of scratching. Since peptide-induced scratching is mainly due to activation of opiate receptor systems it is suggested that opiate receptors are involved in the behavioral response to SMS 201-995 and somatostatin administration. This suggestion is further supported by the suppressive effect of naloxone on excessive grooming induced by these peptides. Haloperidol and neurotensin also suppress the excessive grooming induced by somatostatin but not that induced by SMS 201-995. Finally, tolerance developed to the grooming-inducing effect of SMS 201-995 and somatostatin. In addition there was cross tolerance between somatostatin and SMS 201-995.

Barrel rotation in rats induced by intracerebroventricular bradykinin antagonists

Intracerebroventricular (ICV) administration of bradykinin (BK) analogs containing the substitution DPhe7 produced extreme postural distortions within 2-4 min after injection, eventually causing rats to spin repeatedly around their longitudinal axis. This behavior, called barrel rotation, has been previously reported following ICV administration of several other neuropeptides. Episodes lasted 5-20 min; two deaths occurred at high doses, but no other long-term effects were observed. The quantal ED50 of the prototype compound B4162 (DArg0, Thi5,8 DPhe7BK), was 14.9 nmole; all seven other DPhe7 analogs tested elicited a positive response at 20 nmole. Among analogs not containing DPhe7, only BK elicited any activity (20% response rate), and only at 100 nmoles. Structure-activity considerations indicate that this behavior is not mediated by classical kinin receptors. The response rate to 20 nmole B4162 (81%) did not significantly change after pretreatment with ICV BK (100 nmoles), or IP atropine, haloperidol or phenytoin; whereas pretreatment with ICV captopril and muscimol and IP naloxone, diazepam and phenobarbital all significantly inhibited the response. A GABAergic mechanism may be involved in this peptide behavior.

Barrel rotation and prostration by vasopressin and nicotine in the vestibular cerebellum

The aim of this study was to determine whether the primary sites for the action of vasopressin and nicotine in producing barrel rotation and prostration in rats were located in the modular cerebellum, i.e., lobule X. When arginine vasopressin was administered into either the fourth ventricles or directly into the nodular cerebellum via chronically implanted cannulae, the rats displayed intermittent barrel rotation and clonic convulsions. The administration of nicotine into the same areas resulted in prostration, atonia and, occasionally, clonic convulsions. A few days after the nodular cerebellum was lesioned with kainic acid, the motor disturbances resulting from either agent were virtually abolished. Histologic studies revealed that kainic acid had destroyed Purkinje and other large neurons, but had left the granular neurons relatively intact. The administration of procaine into either the fourth ventricles or nodular cerebellum blocked the behavioral responses of either vasopressin or nicotine given into the fourth ventricles. It was concluded that the nodular cerebellum is a primary site for the motor disturbances produced by vasopressin and nicotine.

The effects of cysteamine on dopamine-mediated behaviors: evidence for dopamine-somatostatin interactions in the striatum

The effects of prior treatment with cysteamine, a drug which appears to deplete selectively the neuropeptide somatostatin, on apomorphine-induced stereotypy and amphetamine-induced locomotor activity and conditioned place preferences were investigated. Twelve hours following systemic cysteamine injections apomorphine-induced stereotypy was attenuated and striatal somatostatin levels were reduced by half. Systemic cysteamine also decreased the motor stimulant effects of amphetamine, without influencing the rewarding properties as determined by the conditioned place preference procedure. Direct injections of cysteamine into the nucleus accumbens also decreased the locomotor response to amphetamine, and produced a local reduction in somatostatin levels in the accumbens. Cysteamine did not appear to alter monoamine turnover in the striatum after either systemic or intra-accumbens injections. These results suggest that somatostatin in the nucleus accumbens and caudate-putamen modulates the motor, but not the reinforcing properties of dopaminergic drugs, possibly via an action postsynaptic to dopamine-releasing terminals. Furthermore, it is evident from these results that cysteamine is an important tool with which to study the central actions of somatostatin.

Effects of bombesin on behavior

This report describes the influence of bombesin on the gross behavior of goldfish, frogs, mice, rats, guinea pigs, rabbits, chicks, pigeons and monkeys. Goldfish, frogs, chicks and pigeons were overtly unaffected by bombesin given centrally and/or peripherally. Mice, rats, guinea pigs, rabbits and monkeys responded quickly to intracerebroventricular (i.c.v.) and/or intrathecal (i.th.) administration of bombesin by displaying a range of behaviors suggestive of altered skin sensation. In mice, bombesin was essentially equipotent as a scratch inducer by i.c.v. and i.th. routes (A50 = 0.010-0.019 microgram) but 6800 times less potent i.p. In rats, bombesin-induced grooming and scratching behaviors were shown to be qualitatively different from those associated with ACTH-(1-24) and thyrotropin releasing hormone. Spantide and [D-Arg1, D-Pro2, D-Trp7,9, Leu11]substance P (both at 0.20, 0.50 and 0.80 microgram i.c.v.), two proposed bombesin receptor antagonists, did not markedly influence bombesin-induced scratching or hypothermia in rats.

Abnormal behavioural changes associated with vasopressin-induced barrel rotations

Arginine-8-vasopressin (AVP) was injected into the cerebral ventricles of rats in order to characterize the dose-response relations of the convulsant actions of AVP and to obtain a detailed description of other acute behavioural effects. The incidence of barrel rotations, a violent and apparently uncontrolled motor activity during which rats rotate about their long axis, was found to be dose dependent, with a threshold of between 1 and 10 ng per rat. Other behavioural effects of AVP including immobility, titubation, ataxia, backward walking, and inhibition of exploratory activities and of grooming were seen at doses as low as 100 pg. These behavioural effects occurred within 9 min after injection, and thus have the same time course as barrel rotations. These acute actions of AVP may be significant in interpreting the effects of AVP on cognitive processes and memory and should also be taken into consideration in the clinical use of AVP as an anti-amnestic.