Neuropeptides: anticonvulsant and convulsant mechanisms in epileptic model systems and in humans.

Neuropeptides represent a new class of compounds with important implications for the understanding of the mechanisms and treatment of epileptic disorders. Several systems of peptide modulators--in particular the opioid-like peptides, vasopressin, somatostatin, thyrotropin-releasing hormone (TRH) and ACTH--have partially demonstrated endogenous roles in some forms of epilepsy. Seizures and stressful situations may release endogenous opioid peptides and mediate postictal depression and postictal seizure refractoriness. Vasopressin is believed to increase susceptibility to convulsions and may be involved in the pathogenesis of febrile convulsions. Derangements in TRH regulation may lower thresholds for seizure expression by regulating arousal systems; however, some TRH analogs have proven to be effective anticonvulsants. Long-term alterations in somatostatin regulation could be components of focal epilepsies. ACTH is particularly useful in the treatment of infantile spasms. Pharmacological effects of these and other peptides have potentials for defining new classes of anticonvulsants. Cholecystokinin (CCK) and its analogs, the opioid peptides beta-endorphin and FK33824, TRH analogs, and several dipeptides exhibit potent anticonvulsant properties in chemical, electroshock, and genetic model screens. Convulsant actions of CRF, somatostatin, TRH, vasopressin, and high doses of endorphin or enkephalins may provide new tools to study regulatory mechanisms of cerebral excitability. The enkephalin epileptogenic effect is being developed as a predictive tool for new anti-petit mal anticonvulsants. Advances in molecular biology have identified the genes of particular peptide families. A concept has developed that the large propeptide precursors, coded by these genes, whose processing leads to functional peptide formation and release, regulate peptidergic humoral responses to external stimuli. This idea may have particular application in the understanding of the genetic basis of some seizure states. Techniques for amplification of mRNA expression have identified specific neuronal proteins and peptides. Knowledge of protein and propeptide structural cleavage sites has suggested previously unknown candidates for modular systems in epileptic states. Technological advances in automated peptide sequencing and synthesis have allowed the development of metabolically resistant analogs and antagonist peptides. The anticonvulsant potencies of CCK, TRH, and opioid peptides have been defined more clearly with these methods.(ABSTRACT TRUNCATED AT 400 WORDS)

Similar anticonvulsant, but unique, behavioural effects of opioid agonists in the seizure-sensitive Mongolian gerbil.

Opioid agonists were used to investigate the modulation of seizures mediated by mu, kappa and delta opiate receptors in the seizure-sensitive Mongolian gerbil. Morphine (1.0-25 mg/kg, s.c.) were used as prototypic agonists for mu, kappa and delta opiate receptors. Each opioid decreased the incidence and severity of the seizure as compared to control values. The anticonvulsant effects of morphine (10 mg/kg, s.c.) and ketocyclazocine (0.5 mg/kg, s.c.) were reversed by naloxone (1.0 mg/kg, s.c.), while the anticonvulsant effects of N-allylnormetazocine (2 mg/kg, s.c.) were not significantly changed by naloxone. Additionally, abnormal behavior was observed following administration of the opioids. Morphine (10 mg/kg, s.c.) produced excitation and hyperresponsiveness with intermittent cataleptic-like states. Ketocyclazocine (10 mg/kg, s.c.) predominantly produced a stuporous, immobile state, accompanied by some loss of posture. N-allylnormetazocine (10 mg/kg, s.c.) produced ataxia and stereotypic side-to-side head nodding . Naloxone was able to reverse the behavioral effects produced by morphine and ketocyclazocine but not those produced by N-allylnormetazocine. The data presented are consistent with earlier studies which demonstrated the anticonvulsant effects of beta-endorphin in the gerbil. This study further suggests that opioids have a protective role against seizure activity in the gerbil and the opioid anticonvulsant effect is not specific to one type of opioid agonist.

Neuropeptides: a role as endogenous mediators or modulators of epileptic phenomena.

As more small peptidergic components of the central nervous system are isolated, their role in disease states is being investigated. Several of these neuropeptides, especially the opioidlike peptides, adrenocorticotropic hormone, and some hypothalamic releasing factors, have been found to alter neuronal excitability. This finding has led to the proposal that these peptides may play a role in the pathogenesis of the epilepsies. We tested this hypothesis in a genetic model of epilepsy. At nontoxic doses, several exogenously administered peptides had anticonvulsant properties, while others were proconvulsant. The most potent anticonvulsant was the opioidlike peptide beta-endorphin. Its effect was similar to that of the opioid alkaloids. Using the potent antagonist naloxone hydrochloride to block possible endogenous opioid-like peptides, we found no effects on seizures in naive animals. Naloxone did alter postictal events, however, by partially blocking the postictal refractoriness to further seizures. We speculate that one possible role for the endogenous opioid peptides may be to limit the spread of seizures or to modulate postictal susceptibility to further seizures. Naloxone was effective in this model only after stressful situations occurred that modified the seizures and presumably induced a release of endogenous opioidlike peptides. Support for this hypothesis from other epilepsy models is discussed. Other peptidergic systems may also be active in various epileptic models, and the current understanding of their roles is reviewed.

Opioid peptides and seizures in the spontaneously epileptic Mongolian gerbil.

The naturally epileptic Mongolian gerbil was used to investigate the epileptogenic properties of beta-endorphin, dynorphin, met-enkephalin and morphine. The results indicate that opioid induced "seizures" are different from naturally spontaneous seizures in the gerbil in respect to EEG recording and motor behavior. Evidence for a protective role in preventing seizures is also presented.

Modulation of spontaneous seizures in the mongolian gerbil: effects of beta-endorphin.

Intraventricular injection of beta-endorphin (0.1-3 micrograms) into gerbils from the UCLA seizure sensitive strain reduced the incidence and severity of spontaneous epileptiform seizures, both the motor manifestations and the preceding high voltage focal spiking and accompanying seizure activity in the cortical EEG. This "'anticonvulsant" effect of beta-endorphin was prevented by prior administration of naloxone (1 mg . kg-1 IP). These findings suggest that the endogenous opioid peptide may be involved in the normal suppression of the epileptic diathesis in these animals during the interictal periods.

Hippocampal neuron density and seizures in the Mongolian gerbil.

Mongolian gerbils of the seizure-sensitive strain exhibit epileptic seizures in relation to changes in the environment, a characteristic which has been increased to about 100% by inbreeding. The seizures vary from animal to animal but are rather stable in the individual animal, which makes it possible to study the neuron densities in the hippocampus of the gerbil in relation to seizure type and seizure intensity. Five groups of gerbils with seizures ranging from minor movements and motor arrest to intense generalized convulsions were investigated with a quantitative method including cell counting by light microscope and estimation of possible brain shrinkage, as well as determination of nucleoli and nuclei diameters. The cell densities were determined in different areas of the pyramidal cells of the hippocampus (H-fields). The study discloses a reduction of cell densities in fields H2 and H3 in relation to intense generalized convulsions. It is suggested that the reduction in cell density in field H2 is a result of seizure activity, whereas the field H3 cell loss can be the result of both the hypoxia and the seizure activity.

Association of waking episodes with menopausal hot flushes.

To examine the possible relationship between the occurrence of menopausal hot flushes and waking episodes, a study was conducted of nine postmenopausal women with severe hot flushes and five asymptomatic premenopausal women. Measurement of simultaneous changes of finger temperature and skin resistance over the sternum was used as an objective marker of hot flushes. During cumulative sleep 47 objectively measured hot flushes occurred, and 45 were associated with a waking episode measured by polygraphic techniques. In eight of nine subjects, a significant correlation was observed between the occurrence of hot flushes and waking episodes. A similar association was not observed in premenopausal subjects. Estrogen administered to symptomatic patients resulted in significant reductions of both hot flushes and waking episodes. These data suggest the menopausal flushes are associated with a chronic sleep disturbance, and both can be improved by estrogen therapy.

Thermoregulatory mechanisms and ethanol hypothermia.

The mechanisms underlying the hypothermic effect of ethanol have been investigated in rats. At an ambient temperature of 26 degrees C, at which tail skin blood flow will normally be expected to play a role in regulating core temperature, no change in tail cutaneous temperature occurred during the period in which the core temperature was falling after administration of ethanol. As the drug effect waned tail skin temperature fell below the initial temperature as the hypothermia was corrected. This last observation confirms earlier results indicating a shift in the thermoregulatory set point after administration of ethanol. There was no significant change in oxygen consumption related to the ethanol induced fall in core temperature so decreased heat production would not appear to be a factor in the thermal imbalance. Neither was there any change in respiratory rate or minute volume to account for an increase in convective or evaporative heat loss via the lungs. From these results it is not clear by what mechanism the ethanol induced lowering of the set point leads to a fall in core temperature. Other avenues of heat loss, for example from other cutaneous surfaces, and further detailed thermal balance studies will be needed to resolve this problem.

Objective techniques for the assessment of postmenopausal hot flashes.

The present study was undertaken to evaluate objective methods of monitoring postmenopausal hot flashes. Continuous recordings of finger and core temperature and sternal skin conductance were carried out in 8 postmenopausal and 4 premenopausal women. Four postmenopausal patients were studied a second time following 30 days of daily oral administration of ethinyl estradiol 0.05 mg. One hundred twenty flashes were subjectively noted and recorded during 104 hours of study in the postmenopausal women. Eighty-two, 98, and 81% of subjective flashes were associated with changes in finger temperature, skin conductance, and core temperature, respectively. The rate of occurrence and magnitude of changes of physiologic markers were significantly greater (P less than .01) in postmenopausal than premenopausal women. Estrogen replacement therapy not only eliminated the subjective sensations but also significantly reduced (P less than .02) the frequency and magnitude of the changes in physiologic function measured by finger temperature. Measurement of skin conductance changes was the single most sensitive and specific indicator of hot flashes. The simultaneous change of both skin conductance and finger temperature, although less sensitive, was a very specific indicator of a hot flash. These results support the concept that the measurement of physiologic changes can be used to assess objectively the occurrence of this symptom complex.

Monitoring the pathophysiological correlates of post-menopausal hot flushes.

Clinical assessment of the severity and frequency of post-menopausal hot flushes can be made objectively by measuring the associated changes in skin conductance and skin and core temperature. Such measurements provide a more reliable index of the response to therapy than does subjective reporting which has been employed in the past. The design and use of a working analyzer is presented that is sufficiently simple, rugged, safe and portable to be used under normal clinical conditions to provide a permanent record of the attacks.

Postmenopausal hot flushes: a disorder of thermoregulation.

The changes in cutaneous and body temperature and cutaneous conductance during hot flushes in eight postmenopausal women were studied. The vasomotor changes occurred approx. 45 sec after the patients experienced the initial subjective symptoms of the attacks. The rise in skin conductance appeared to be a more reliable index of the flushing episode than did the change in skin temperature. On the basis of the changes recorded it is suggested that the hot flush syndrome may represent a specific thermoregulatory disorder rather than being due to a non-specific central autonomic discharge. The episodes may be triggered by a neuroendocrine imbalance following the disruption of ovarian function and fall in estrogen production. In assessing the frequency and severity of hot flushes, and the effects of treatment, objective measurements of skin and core temperature and skin conductance should replace subjective criteria.

Ethanol-induced hypothermia in the rat.

Ethanol (0.5-3.2g x kg-1 i.p.) caused a dose-dependent fall in body temperature in rats. A dose of 1.5g x kg-1 i.p. led to a fall of 1.6 +/- 0.20 degrees C over 60 min at an environmental temperature of 18 +/- 1 degrees C. There was no evidence of acute tolerance when the hypothermic response was elicited by the same dose of ethanol (0.7--20.0g x kg-1 i.p.) 24 h later; indeed the second response was consistently, although not significantly, greater than the first. Behavioral thermoregulatory studies indicated that the fall in temperature after ethanol is due, at least in part, to a downward setting in the thermoregulatory set point. These results suggest that the rat may be a suitable animal model for a study of accidental hypothermia following ethanol ingestion and exposure to low environmental temperatures.