Randall J. Lee

Increased enkephalin and dynorphin immunoreactivity in the hippocampus of seizure sensitive Mongolian gerbils.

Radioimmunochemistry (RIA) and immunocytochemistry (ICC) were used to measure proenkephalin and prodynorphin peptides in the brain of a genetic model of epilepsy, the seizure-sensitive (SS) Mongolian gerbil. Brain levels of both [Met5]- or [Leu5]-enkephalin (ME-LI) and dynorphin A1-8 and dynorphin A1-17 (DN-LI) like immunoreactivity were increased in the hippocampal region of the SS gerbil. However, ME-LI and DN-LI did not follow the same patterns. ME-LI was significantly increased in the SS gerbils (post-seizure) compared to SR gerbils while ME-LI in SS (preseizure) gerbils was not significantly different from SR gerbils. DN-LI was significantly increased in the hippocampal region of both SS (preseizure) and SS (postseizure) gerbils compared to SR gerbils. These results strongly imply differences in the regulation of proenkephalin and prodynorphin metabolism in the Mongolian gerbil. The differences in metabolic regulation may signal fundamentally different roles of these opioid peptides in the modulation of seizure activity in this animal.

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.

Opioid receptor alterations in a genetic model of generalized epilepsy

Autoradiography was used to examine opioid receptor binding in the Mongolian gerbil, a genetic model of the epilepsies. Coronal brain sections of seizure-resistant (SR) and seizure-sensitive (SS) (both pre- and post-seizure conditions) gerbils were labeled with [3H]dihydromorphine. SS (pre-seizure) gerbils demonstrated overall greater brain opioid binding when compared to SR animals. The periaqueductal gray, substantia nigra and medial geniculate body were specific areas in SS (pre-seizure) gerbils which demonstrated highly significant increases in opioid binding compared to SR animals (% increase vs SR were 98%, 91.3% and 42.9%, respectively). Scatchard analysis demonstrated that the increase in opioid binding was due to an increase in the total number of receptors without a significant change in receptor affinity (i.e. periaqueductal gray area: total number of binding sites was 12.7 (SR) and 18.0 fmol/mg tissue (SS pre-seizure), while Kd values were 4.0 (SR) and 4.0 mM (SS pre-seizure). Opioid binding was also increased in the SS (post-seizure) animals when compared to SR animals, especially in the substantia nigra. However, when compared to SS (pre-seizure) gerbils, there was a general but not significant, decrease in opioid binding in SS post-seizure gerbils. The increased opioid binding in the SS (pre-seizure) gerbil compared to SR gerbils could reflect an up-regulation due to a deficit in endogenous ligand (e.g. a deficit in synthesis or decreased release) which could underlie the seizure diathesis in the gerbil.

The effects of the acute administration of phencyclidine hydrochloride (PCP) on the release of corticosterone, growth hormone and prolactin in the rat☆

There is little information on the neuroendocrine effects of PCP. The present study examined the effects of the acute subcutaneous administration of PCP on serum levels of corticosterone, growth hormone and prolactin in the male rat. PCP increased serum levels of corticosterone, decreased serum levels of prolactin and failed to affect growth hormone levels. The results indicate that, like other drugs of abuse, PCP alters neuroendocrine function.

The effect of spontaneous seizures on pentylenetetrazole and maximum electroshock induced seizures in the Mongolian gerbil

The seizure sensitive Mongolian gerbil, a genetic model of epilepsy, has been used to investigate the effects of prior spontaneous seizures on the threshold for pentylenetetrazole (PTZ) and maximum electroshock (MES) induced convulsions. In animals which had spontaneous epileptic seizures prior to testing the threshold for PTZ induced convulsions was raised compared to non-seized animals. This inhibitory effect of a spontaneous seizure was not observed for MES convulsions. Pretreatment with naltrexone, an opioid antagonist, attenuated the post-ictal inhibitory effect on PTZ induced convulsions. It is concluded that a spontaneous seizure in the epileptic gerbil leads to non-specific post-ictal inhibition of seizure sensitivity. Endogenous opioids may exert a modulatory action in mediating this phenomenon.

Anticonvulsant effect of muscimol injected into the thalamus of spontaneously epileptic Mongolian gerbils

Injections of muscimol (12.5 or 25 ng bilaterally), a GABAA agonist, into the posterior nuclei of the thalamus suppressed generalized convulsive seizures in the spontaneously epileptic Mongolian gerbil. This anticonvulsant effect was dose-dependent and was reversed by picrotoxin (10 ng bilaterally), a GABAA antagonist. Bilateral intrathalamic injections of 1-baclofen (50 ng), an agonist of the GABAB receptor, were ineffective in suppressing seizures in this model. These results suggest that GABAergic transmission within the thalamus is involved in the control or the genesis of some generalized convulsive seizures.

Cold acclimation and resistance to ethanol-induced hypothermia

The fall in core temperature induced by a fixed dose of ethanol (1 g x kg-1 i.p.) was an exponential function of the ambient temperature over the range 0-18 degrees C. In rats acclimated to 4 degrees C for 7 days the dose response curve relating the fall in body temperature to ethanol was markedly attenuated. The hypothermic effect of ethanol declined exponentially over 20 days of exposure to 4 degrees C and by the 20th day the fall was no greater than in saline injected controls. Blood ethanol concentrations were similar in acclimated and non-acclimated rats indicating that pharmacokinetic factors do not account for the altered responses. Although the time course of the development of resistance to the hypothermic effect of ethanol parallels that of cold acclimation to 4 degrees C, and the development of non-shivering thermogenesis, the attenuated drug effect does not appear to be due to the altered metabolic activity of brown adipose tissue. It is suggested that the modulation of the effect of ethanol in lowering the thermoregulatory set point results from central nervous system adaptation to the environmental thermal stress.

The Spontaneously Epileptic Mongolian Gerbil

The Mongolian gerbil (Meriones unguiculatus) was first described to the western scientific community by Milne-Edwards (1867). The species was introduced to the United States in 1954 by Schwentker (see Schwentker, 1972) and these animals formed the basis of the colony developed by Tumblebrook Farms, West Brookfield, Massachusetts, currently the major breeders and suppliers. Gerbils were first bred at UCLA by Rich in 1967 (Rich, 1968). Abnormal behaviors were soon noted in some of the animals and were recognized as epileptiform in nature by Loskota, who decided to study the gerbil as a model of the epilepsies; this research subsequently constituted the basis of his dissertation for the degree of doctor of philosophy at UCLA (Loskota, 1974).

Opiate receptor binding in the brain of the seizure sensitive Mongolian gerbil ( Meriones unguiculatus )

Opiate receptor binding was studied in seizure sensitive (SS) and seizure resistant (SR) strains of the Mongolian gerbil. Cryostat sections of the brain were labeled with [3H]-dihydromorphine, subjected to autoradiography and analysed by microdensitometry. SS gerbils, prior to seizure induction, demonstrated overall greater brain opiate binding when compared to SR animals. Immediately following a seizure, binding in the interpeduncular nucleus fell to levels found in SR animals. The increased opiate binding in the SS (pre-seizure) compared to SR gerbils could reflect a deficit of endogenous ligand which could underlie the seizure diathesis in the gerbil.