Somatostatin-like immunoreactivity (SLI) in cisternal cerebrospinal fluid of rats kindled by pentylenetetrazol

Cysteamine pre-treatment reduces pentylenetetrazol-induced plasticity and epileptiform discharge in the CA1 region of rat hippocampal slices

The effects of prior treatment of cysteamine, a somatostatin inhibitor, on pentylenetetrazol (PTZ) induced epileptic and plastic changes in CA1 excitability were examined. Population spikes were evoked by activation of Schaffer collaterals with a range of stimulation intensities. Changes in the population spike and epileptiform amplitudes were used as indices to quantify the effects of PTZ exposure in the control and cysteamine pre-treated slices. Cysteamine pre-treatment decreased baseline CA1 population spike amplitude following high intensity stimulation of Schaffer collaterals. Following PTZ application directly to the slices, cysteamine diminished the increased population spike and epileptiform amplitudes which were normally observed following collateral stimulation. Magnesium-free medium induced epileptiform activity was also significantly reduced with cysteamine pre-treatment. It is concluded that somatostatin may be involved in PTZ-induced epileptic and plastic changes in CA1 excitability.

Brain somatostatin: a candidate inhibitory role in seizures and epileptogenesis

Recent evidence shows that neuropeptide expression in the CNS is markedly affected by seizure activity, particularly in the limbic system. Changes in neuropeptides in specific neuronal populations depend on the type and intensity of seizures and on their chronic sequelae (i.e. neurodegeneration and spontaneous convulsions). This paper reviews the effects of seizures on somatostatin-containing neurons, somatostatin mRNA and immunoreactivity, the release of this peptide and its receptor subtypes in the CNS. Differences between kindling and status epilepticus in rats are emphasized and discussed in the light of an inhibitory role of somatostatin on hippocampal excitability. Pharmacological studies show that somatostatin affects electrophysiological properties of neurons, modulates classical neurotransmission and has anticonvulsant properties in experimental models of seizures. This peptidergic system may be an interesting target for pharmacological attempts to control pathological hyperactivity in neurons, thus providing new directions for the development of novel anticonvulsant treatments.

Somatostatin mRNA in the hippocampal formation following electroconvulsive shock in the rat

The effect of electroshock on the brain levels of somatostatin mRNA were evaluated by in situ hybridization using a selective oligonucleotide probe. Rats were submitted to single or repeated (7 days, one session for each day) sessions of electroshock. There was a marked increase of the expression of somatostatin mRNA in the hippocampal formation, mostly in the multiform layer of the hilus of the dentate gyrus, following repeated but not single electroshock. Our findings show that repeated ECS is associated with increase in the synthesis of somatostatin. The results also support previous data indicating that the hippocampal formation is selectively affected by the treatment.

Somatostatin concentrations in cerebrospinal fluid and brain tissue of patients with refractory epilepsy

The somatostatin concentrations of cerebrospinal fluid (CSF) and brain tissue in 16 refractory epileptic patients were measured simultaneously by a radioimmunoassay (RIA) method. An increased level of somatostatin was found in the epileptic foci of cerebral cortex, determined by the cortical EEG. There were significant differences among the epileptic foci (75.58 +/- 6.58 pg/mg wet wt, +/- SEM), nonfocal tissues (37.04 +/- 6.55 pg/mg), and normal tissues of control patients (47.69 +/- 10.12 pg/mg), p < 0.001 and p < 0.05, respectively. The somatostatin concentrations of CSF in 11 epileptic patients were determined before (257.78 +/- 19.11 pg/mL) and after (178.36 +/- 8.78 pg/mL) the removal of epileptic focal area, and a dramatic decrease of the CSF somatostatin concentration after operation was detected (p < 0.01). We also found that the somatostatin level of cerebral scar induced by head injury in cases of posttraumatic epilepsy was highest (106.39 +/- 12.41 pg/mg). The results suggested that the surgical removal of the epileptic focal area in refractory epileptic patients may reduce the increased central somatostatin level, which could play an important part in the pathophysiological process of refractory epilepsy.

Effects of somatostatin and anti-somatostatin serum on picrotoxin-kindled seizures

The effects of somatostatin, administered into different areas of the brain were studied in preliminary picrotoxin-kindled rats. The injection of somatostatin into the lateral ventrical of the brain (i.c.v.) (1.8 nmol), the hippocampus (0.6 nmol) or the amygdala (0.6 nmol), resulted in a decrease in the severity of the picrotoxin-induced convulsions. Application of the peptide into the caudate-putamen or the substantia nigra reticulata did not alter the behavioural manifestations of the kindled seizures. The local injection of anti-somatostatin serum (1:5) into the hippocampus increased the severity of the kindled convulsions and blocked the anticonvulsive effect of somatostatin, given intraventricularly. Local administration of anti-somatostatin serum into the amygdala did not alter the kindled seizures and did not abolish the anticonvulsive action of somatostatin given intraventricularly. It is concluded that somatostatin could take part in endogenous control of seizures through a suppressant influence on limbic structures; the hippocampus could be a specific site for the antiepileptic action of somatostatin.

Vigabatrin pre-treatment prevents hilar somatostatin cell loss and the development of interictal spiking activity following sustained simulation of the perforant path

Somatostatin-containing neurons in the hilus of the dentate gyrus are known to be exceptionally vulnerable in experimental models of epilepsy, as well as in human temporal lobe epilepsy. The position of these cells in the circuitry of the dentate gyrus is ideal for gating the activation evoked by afferents from the entorhinal cortex. In the present study we have shown that the loss of hilar somatostatin-containing neurons, and the development of interictal spiking activity induced by sustained perforant pathway stimulation can be prevented by high doses (500 mg/kg), but not by low doses (100 mg/kg) of vigabatrin, an irreversible inhibitor of GABA-transaminase.

Repeated electroconvulsive shock increases glial fibrillary acidic protein, ornithine decarboxylase, somatostatin and cholecystokinin immunoreactivities in the hippocampal formation of the rat

Rats were submitted to single or repeated (7 days, one session for each day) sessions of electroconvulsive shock. A computer-assisted morphometric and microdensitometric analysis of glial fibrillary acidic protein-, ornithine decarboxylase-, somatostatin- and cholecystokinin-like immunoreactivities was performed in the hippocampal formation and other brain areas. The results of the study showed a significant increase of the intensity of the immunostaining for glial fibrillary acidic protein, ornithine decarboxylase, somatostatin and cholecystokinin in the hippocampal formation and distinctively in the dentate gyrus following repeated, but not single, electroconvulsive shock. No significant change was found in the number of somatostatin- and cholecystokinin-like immunoreactive cell bodies in any hippocampal subregion and in the number of glial cells in the hilus of dentate gyrus in rats treated with single or repeated electroconvulsive shock. It is a distinct possibility that the observed increase in the content of the neuropeptides in the hippocampal formation reflects a compensatory response of the brain to seizure-inducing stimuli and that such an increase may play a role in the therapeutic effect of electroconvulsive shock.

Time-dependent pro- and anticonvulsant effects of cysteamine on the development and expression of amygdaloid kindled seizures

The time-dependent pro- and anticonvulsant effects of cysteamine, a depletor of somatostatin, were investigated on the development and expression of amygdaloid kindled seizures. Acute administration of cysteamine (25-400 mg/kg, i.p.) produced a dose-dependent potentiation of kindled seizures when evoked 4 h after the drug. However, the seizures initiated 1 day after drug administration were dose-dependently suppressed. Furthermore, elicitation of seizures 4 h after cysteamine enhanced its anticonvulsant effects at 1 day after the drug, causing a parallel left shift of the dose-response curve. Since it has been reported that somatostatin is released during generalized seizures, the seizures given 4 h after cysteamine may encourage the somatostatin depletion by cysteamine and thereby potentiate its later anticonvulsant effects. The repeated administration of cysteamine (100 mg/kg, i.p.) during kindling development strongly retarded the development of generalized seizures but not the development of focal seizures or of afterdischarges in the amygdala. In contrast to the acute experiments, kindling stimulation given 4 h after each cysteamine treatment did not augment the blocking effect on kindling development. These data indicate that chronic cysteamine treatment has a strong inhibitory effect on the development of amygdaloid kindling.

Somatostatin and epilepsy

Hippocampal neurons containing somatostatin have been shown to be vulnerable in some experimental models of epilepsy. In this report, we describe our recent findings about the seizure-related changes in somatostatin in brain tissue and cerebrospinal fluid (CSF) in experimental and human epilepsy. These data strengthen the view that the somatostatinergic system is affected in epilepsy.

Effect of antiepileptic drugs on somatostatin release in vitro

In the present study we investigated the effect of antiepileptic drugs on high potassium (50 mM) stimulated somatostatin release in rat cortical slices in a superfusion system. The somatostatin-like immunoreactivity (SLI) in superfusate was determined by radioimmunoassay. The antiepileptic drugs studied, vigabatrin, valproate, carbamazepine, phenobarbital, primidone, clonazepam and phenytoin were tested at a concentration range of 1-1000 microM). Of the drugs used vigabatrin had the most significant inhibitory effect on SLI release (IC50 = 240 microM). Vigabatrin also caused a concomitant, dose-dependent increase in superfusate gamma-amino butyric acid (GABA) level. A 30% decrease in the release of SLI followed incubation with valproate and carbamazepine, but only at high drug concentrations (1000 microM). Phenobarbital, primidone, clonazepam and phenytoin did not affect SLI release. Addition of GABA to superfusate caused a dose-dependent decrease in the amount of SLI release (IC50 = 56 microM). In conclusion, at low concentrations the antiepileptic drugs had only minor effects on SLI release. At higher concentrations, however, vigabatrin and valproate decreased the release of SLI, which may relate to their ability to elevate tissue levels of GABA.

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.

Somatostatin, neuropeptide Y, GABA and cholinergic enzymes in brain of pentylenetetrazol-kindled rats

We studied the effect of pentylenetetrazol (PTZ)-induced kindling (35 mg/kg, i.p., daily) on somatostatin-like immunoreactivity (SOM) with special attention to the duration of changes (rats were sacrificed either 10 days or 4 months after the development of kindling) and to transmitters or modulators related to somatostatin (neuropeptide Y (NPY), GABA, choline acetyltransferase (ChAT), acetylcholinesterase (AchE]. In rats sacrificed 10 days after the last kindled seizure, SOM was elevated in frontal cortex and striatum (p less than 0.01); NPY was elevated in frontal cortex, striatum and hippocampus (p less than 0.05) of kindled or prekindled rats (i.e., rats which were treated daily with PTZ but did not express three consecutive generalized seizures). ChAT activity was slightly decreased (p less than 0.05) in cortex. GABA levels and AchE activity were unchanged in kindled cortex. In rats sacrificed 4 months after the development of kindling none of the parameters analyzed differed from controls. The present study suggests that the cortical and striatal neurons containing SOM/NPY are affected by PTZ-kindling. The cortical cholinergic system is affected to a much smaller extent. The neuropeptide changes are not persistent, as is the lowered seizure threshold, so they are probably not involved in the maintainance of the latter.

Selective depression of GABA-mediated IPSPs by somatostatin in area CA1 of rabbit hippocampal slices

In area CA1 of hippocampus, a subpopulation of gamma-aminobutyric acid (GABA)-containing interneurons that make synaptic contacts on pyramidal cells also contains the neuropeptide, somatostatin. The effects of GABA and somatostatin on hippocampal pyramidal cells have been investigated separately, but it is not known whether an interaction occurs between these co-localized substances. We demonstrate that somatostatin has a potent inhibitory effect on GABA-mediated synaptic potentials which hyperpolarize pyramidal cells. This effect may be relevant to the well-documented epileptogenicity of the hippocampus, as well as the phenomenon of long-term potentiation, which is a well-studied example of synaptic plasticity.

Effect of cysteamine on somatostatin-like immunoreactivity in the amygdala-kindled rat brain

Previous studies have shown that a somatostatin-depleting drug, cysteamine (CYS), suppresses kindled seizures. However, no data is available concerning the levels of somatostatin-like immunoreactivity (SLI) in the kindled rat brain after CYS administration. In the present study, we used radioimmunoassay to measure SLI in the frontal cortex, amygdala + piriform cortex, hippocampus, striatum and hypothalamus: 1) in control rats, 2) in amygdala-kindled rats decapitated 14 days after the last stimulus, and 3) in amygdala-kindled rats decapitated 14 days after the last stimulus but treated either 11 days or 4) 4 hours before decapitation with CYS (100 mg/kg, subcutaneously). The results showed that, compared to controls, in kindled rats SLI was elevated both in the ipsi lateral (28%, p = 0.0372) and contralateral (17%, p = 0.0078) frontal cortex. Compared to kindled rats, CYS given 4 hours before decapitation decreased SLI in the frontal cortex (to 71%, p = 0.0066) and hippocampus (to 72%, p = 0.0027), but compared to the controls, only in the hippocampus. In rats given CYS 11 days before decapitation, SLI did not differ from either the controls or from the kindled rats. In conclusion, the somatostatinergic system is affected in amygdala-kindling; but the relationship of anatomical localization and the magnitude of CYS-induced decrease of SLI to elevated seizure threshold needs to be studied further.

Effect of cysteamine on levels of somatostatin-like immunoreactivity and catecholamines and on electroencephalogram in the rat brain

Cysteamine (CYS) is known to be a quite specific depletor of somatostatin in the rat brain. In the present study we investigated the effect of CYS (100 mg/kg, 300 mg/kg, subcutaneously) on levels of somatostatin-like immunoreactivity (SLI) in the brain and cerebrospinal fluid, on catecholamines in the cortex, and on spectral cortical electroencephalogram (EEG) of rat. SLI was decreased in both the cortex and the striatum (p less than 0.05) of CYS-treated rats, but no change was seen in SLI of CSF. Cortical levels of dopamine, noradrenaline and homovanillic acid were decreased (p less than 0.05) following administration of either dose of CYS. In EEG, during mobility both the frontal and occipital peak (Fp) and mean (Fm) frequencies were slowed (p less than 0.05). Frontally, the amplitude of the frequency bands 1.5-3Hz and 3-5Hz was increased (p less than 0.05). During immobility the Fp and Fm were also slowed. In frequency bands of 3-5Hz, 5-10Hz and 10-20Hz the amplitude was decreased (p less than 0.05), indicating that, in addition to theta frequency, the low voltage fast activity is also affected by CYS. According to our results, both the cortical intrinsic neurons containing somatostatin and also the ascending catecholaminergic systems are affected after the single administration of CYS concomittantly with, but not necessarily related to, changes in different frequency bands in EEG.

Amygdaloid kindling of rats increases preprosomatostatin mRNA and somatostatin without affecting glutamic acid decarboxylase (GAD) mRNA or GAD

The levels of preprosomatostatin (preproSS) mRNA, somatostatin-like immunoactivity (SS-LI) (also known as somatotropin-release inhibitory factor, or SRIF), glutamic acid decarboxylase (GAD) activity and GAD mRNA were determined in several brain regions of amygdaloid-kindled rats. SS mRNA and SS increased in the cortex and striatum, while only SS increased in the hippocampus. No changes were detected in either GAD activity or GAD mRNA in any brain region. The data suggest that somatostatin may be one of the factors involved in the chain of events leading to kindled seizures.

Cysteamine normalizes cerebral somatostatin level and binding in pentylenetetrazol-kindled rats

Rats were kindled by intraperitoneal injection of pentylenetetrazol (PTZ) (30 mg/Kg) every 48 h. Once kindled, some of the animals received a single injection of cysteamine (200 mg/Kg). Somatostatin-like immunoreactivity (SLI) and 125 I-Tyr11-somatostatin binding were measured in the frontoparietal cortex and hippocampus of the two experimental groups and the control rats. After PTZ kindling the following was observed: 1) SLI content was increased in the two areas; 2) Somatostatin receptor affinity decreased in the frontoparietal cortex and was unaltered in the hippocampus; 3) The number of somatostatin receptors decreased in the hippocampus and was unaltered in the frontoparietal cortex. Cysteamine, an agent which depletes brain somatostatin and suppresses kindled seizures in PTZ-treated rats, reversed the altered SLI levels and binding in these rats.

Myoclonus inducing and seizure modifying effect of cysteamine on cortical and amygdaloid kindled rats

The effect of the somatostatin depleting substance, cysteamine (100 mg/kg, i.p.), on cortical and amygdaloid kindled seizures was investigated. Cysteamine was tested after the establishment of amygdaloid kindling (AM group) and at two different developmental stages of cortical kindling, namely 'focal-cortical' (FC group) and 'cortico-generalized' seizures (CG group). In control, non-kindled, sham operated animals, cysteamine did not induce any spike activity or myoclonus. However, in all kindled groups clustered spike bursting appeared in the cortex within 5-15 min of the injection. The kindled bursting appeared in the cortex within 5-15 min of the injection. The kindled rats exhibited myoclonic jerks at 10 to 30 min after cysteamine injection, which coincided with the cortical spikes, and continued for about 40 min. In contrast, relatively small amounts of spiking were observed in the amygdala and this did not correlate with the myoclonus. At 4 h after cysteamine injection, the motor seizure and afterdischarge durations of the kindled seizure were prolonged in all kindled groups compared with preinjection levels. However, 24 h later the motor seizure duration and the afterdischarge duration were markedly reduced from the preinjection level in the AM and the CG groups and the tonic seizure component was suppressed in the FC group. This inhibitory effect on seizure activity lasted several days and gradually disappeared. These modifying effects of cysteamine were more marked in cortical kindled, than in amygdaloid kindled animals. The results suggest that the cortex is more sensitive to the effect of cysteamine on kindled seizures involves two phases. The first of these effect of cysteamine on kindled seizures involves two phases.(ABSTRACT TRUNCATED AT 250 WORDS)