Effect of monoamines on field potentials in the suprachiasmatic nucleus of slices of hypothalamus of the rat evoked by stimulation of the optic nerve

The effects of the application of serotonin, histamine, noradrenaline and dopamine to the bath on field potentials in the suprachiasmatic nucleus evoked by stimulation of the optic nerve were studied using a hypothalamic slice. Stimulation of the contralateral optic nerve evoked fast positive and late large negative waves in the suprachiasmatic nucleus. The monoamines produced a dose dependent suppression of the amplitude of the negative wave but did not affect that of the positive waves, and the order of potency was serotonin greater than noradrenaline greater than dopamine greater than or equal to histamine. The negative wave was suppressed by phenylephrine (0.1-10 microM) in a dose-dependent manner, whereas it was unaffected by isoproterenol (0.1-10 microM). The suppression of the negative wave produced by the application of histamine and noradrenaline was antagonized by the H1-receptor antagonist, diphenhydramine and the alpha 1-receptor antagonists, phenoxybenzamine and phentolamine. Therefore, the suppression of the negative wave by histamine and noradrenaline was mediated by the H1-receptor and alpha 1-receptor, respectively. The present study indicates that monoamines may play an inhibitory role in the regulation of neurotransmission in the retinohypothalamic pathway to the suprachiasmatic nucleus.

[Electroencephalographic effects of 450191-S and its metabolites in rabbits with chronic electrode implants]

Electroencephalographic (EEG) effects of 450191-S and its metabolites were investigated in unanesthetized rabbits with chronic electrode implants, and they were compared with those of nitrazepam and estazolam. 450191-S at doses of 0.1-0.5 mg/kg, i.v., induced a drowsy pattern of spontaneous EEG: high voltage slow waves and spindle bursts increased in the cortex and amygdala, while the hippocampal theta rhythm was desynchronized. In addition, low voltage fast waves appeared particularly in the cortical EEG. The EEG arousal response to auditory stimulation and to electric stimulation of the mesencephalic reticular formation, posterior hypothalamus and centromedian thalamus was markedly suppressed by 450191-S. The photic driving response elicited by a flash light in the visual cortex was significantly suppressed by 450191-S. 450191-S showed no significant effect on the recruiting response. The EEG effects of nitrazepam were qualitatively similar but less potent and shorter in duration of action than those of 450191-S. The effects of estazolam were approximately as potent as those of 450191-S, but its duration of action was much shorter than that of 450191-S. 450191-S was more potent than nitrazepam and approximately equipotent to estazolam in suppressing hippocampal and amygdaloid after-discharges. The EEG effects of M-1 and M-2 were similar to those of 450191-S in both qualitative and quantitative aspects. The effects of M-A were quantitatively similar but less potent and shorter in duration of action than those of 450191-S.

Effects of dibutyryl cyclic adenosine monophosphate and dibutyryl cyclic guanosine monophosphate on neuron activity of suprachiasmatic nucleus in rat hypothalamic slice preparation

In order to elucidate the role of cyclic nucleotides in the suprachiasmatic nucleus, we examined the effect of dibutyryl cyclic AMP (c-AMP) and dibutyryl cyclic GMP (c-GMP) on single neuronal activity of the suprachiasmatic nucleus of the rat. A hypothalamic slice about 300 micron thick, including the suprachiasmatic nucleus, was cut coronally using a vibratome. By means of bath- as well as iontophoretic application, c-AMP and c-GMP caused mainly an inhibition and facilitation in suprachiasmatic neuronal activity, respectively. The present results suggest that c-AMP and c-GMP play an important role in regulation of suprachiasmatic neuronal activity as a second messenger and that these two nucleotides may function as a reciprocal messenger.

Endogenous prostaglandins in gastric alkaline response in the rat stomach after damage

A role of endogenous prostaglandins in gastric alkaline response (an increase of luminal pH) and functional recovery was investigated in the rat stomach after damage with acidified taurocholate (TC, 20 mM) or aspirin (ASA, 40 mM). Exposure of the stomach to TC or ASA similarly produced a transmucosal potential difference (PD) reduction and enhancement of H+ backdiffusion. The PD was restored gradually with time, and this process was much faster in the case of TC compared with ASA. After exposure to TC, acid secretion ceased and bicarbonate (0.5-1 mu eq/10 min) appeared in the lumen, whereas acid secretion persisted in the stomach exposed to ASA. However, in the presence of cimetidine (8 mg . kg-1 . h-1), these two agents produced a similar degree of luminal alkalinization (approximately 1 mu eq/10 min of HCO3-). Pretreatment with indomethacin (5 mg/kg, sc) significantly inhibited luminal alkalinization and PD recovery seen after exposure to TC. Concurrent administration of 16,16-dimethyl prostaglandin E2 (3 micrograms/kg, sc) antagonized the effects of indomethacin in stomachs exposed to TC and also unmasked luminal alkalinization and expedited the PD recovery in stomachs exposed to ASA. The levels of PGE2 and 6-keto-PGF1 alpha in the corpus mucosa were significantly increased in stomachs exposed to TC, but decreased in those exposed to ASA. These results indicate that luminal alkalinization of the stomach after damage with TC results from both an inhibition of acid secretion caused by endogenous prostaglandins and an increased appearance of HCO-3, and may play a role in functional recovery of the damaged mucosa. Gastric alkalinization seems to be a common phenomenon after exposure to mucosal damaging agents unless they have an inhibitory effect on prostaglandin biosynthesis.

Changes in brain catecholamine levels following olfactory bulbectomy and the effect of acute and chronic administration of desipramine in rats

Bilateral olfactory bulbectomy of the rat caused marked changes of noradrenaline level in several brain regions accompanied with the development of mouse-killing behavior (muricide). Noradrenaline level increased in the medial amygdala, ventromedial and lateral hypothalamus in muricidal olfactory bulbectomized rats (OB rats) but not in non-muricidal OB rats, while dopamine level decreased in the lateral hypothalamus in muricidal OB rats. Acute administrations of desipramine not only suppressed muricide of OB rats but normalized noradrenaline change in ventromedial hypothalamus and dopamine change in lateral hypothalamus. Chronic administration of desipramine also suppressed muricide and normalized noradrenaline changes in ventromedial and lateral hypothalamus and medial amygdala. These findings suggest that the increase in noradrenaline levels in the medial amygdala, ventromedial and lateral hypothalamus may be important for the induction of muricide in OB rats, and muricide was suppressed by desipramine in accordance with the normalization of increased noradrenaline levels, and that the change in dopaminergic function in the lateral hypothalamus may also be important for this muricide.

An important role of the central amygdaloid nucleus and mammillary body in the mediation of conflict behavior in rats

The present study was designed to elucidate the functional role of central amygdaloid nucleus (ACE) and mammillary body (MB) in the mediation of behavioral suppression using rat conflict punishment procedure. Lesion of ACE produced a significant and long-lasting increase in the punished responding during the experimental period. Rats with lesion of MB also showed a significant increase in the punished response 10-14 days after brain lesioning. These results demonstrated the important role of ACE and MB in the mediation of behavioral suppression such as conflict behavior.

Influence of excitatory amino acid receptor antagonists and of baclofen on synaptic transmission in the optic nerve to the suprachiasmatic nucleus in slices of rat hypothalamus

Electrical stimulation of the optic nerve evoked two positive waves with short latency, followed by a large negative wave in the suprachiasmatic nucleus of slices of hypothalamus of the rat. The latency to peak of the two positive waves and the large negative wave were 2.7 +/- 0.1, 6.1 +/- 0.1 and 10.3 +/- 0.5 msec, respectively. Only the large negative wave disappeared in low calcium Ca2+-high magnesium (Mg2+) Krebs solution and with the addition of tetrodotoxin (1 microM) all the waves disappeared. Baclofen inhibited the large negative wave in a dose-dependent manner but not the two positive waves. Excitatory amino acid antagonists also inhibited only the large negative wave, i.e. it was reduced to about 70% by 1 mM glutamic acid diethyl ester and to about 50% by both 1 mM 2-amino-4-phosphonobutyric acid and 1 mM DL-2-amino adipic acid. All waves were unaffected by 0.1 mM atropine, hexamethonium and curare. These results indicate that two positive waves, induced by stimulation of the optic nerve are attributed to nerve conduction and the large negative wave to the neurons of the suprachiasmatic nucleus, and that the neuronal pathway from the optic nerve to the suprachiasmatic nucleus may include aspartate and/or glutamate as an excitatory neurotransmitter.

Optic nerve stimulation-induced increase of release of 3H-glutamate and 3H-aspartate but not 3H-GABA from the suprachiasmatic nucleus in slices of rat hypothalamus

This study investigates the possibility of glutamate and/or aspartate as an excitatory transmitter in the retinohypothalamic fibers' terminal within the anterior hypothalamus, including the suprachiasmatic nucleus (SCN). We studied the release of 3H-Glu and 3H-Asp from the SCN of rat hypothalamic slices produced by optic nerve stimulation. Stimulation of the optic nerve released 3H-Glu, 3H-Asp but not 3H-GABA, while stimulation of the SCN released all three. These releases were suppressed in both Ca2+ free Krebs and tetrodotoxin (TTX) 1 microM containing Krebs. The present result with previous electrophysiological observations strongly suggest that glutamate and/or aspartate are included in this retinohypothalamic termination, while GABA is included in intrinsic and/or extrinsic neurons of the SCN, excluding the terminal of the retinohypothalamic fibers.

[Effects of misoprostol, (+/-)-methyl (11 alpha, 13E)-11, 16-dihydroxy-16-methyl-9-oxoprost-13-en-l-oate, on various gastric and duodenal lesions in rats]

Male Sprague-Dawley rats (230-280 g), either fasted for 15-24 hr or non-fasted prior to experiments, were used. Misoprostol (3-100 micrograms/kg, p.o.) dose-dependently inhibited the development of 150 mM HCl X aspirin (100 mg/kg)-, 150 mM HCl X 60% ethanol-, and aspirin (150 mg/kg)-induced gastric lesions. Misoprostol (30, 100 micrograms/kg, p.o.), given twice daily for 4 days, significantly inhibited prednisolone (50 mg/kg given once daily for 4 days)-induced gastric lesions. Misoprostol (30 or 2 X 300 micrograms/kg, p.o.) also significantly inhibited water-immersion stress (21 degrees C, 10 hr)-induced gastric lesions or mepirizole (200 mg/kg)-induced duodenal lesions, respectively. In contrast, misoprostol (30-300 micrograms/kg, p.o.) had no effects on indomethacin (25 mg/kg)- and mepirizole (200 mg/kg)-induced gastric lesions. Misoprostol (30 micrograms/kg, p.o.) had no effect on gastric secretion in pylorus-ligated preparations (4 hr), but it (100 or 300 micrograms/kg, p.o.) significantly increased the volume and pepsin output. Gastric motility, either normal or enhanced with indomethacin (25 mg/kg), was inhibited by misoprostol (30 or 300 micrograms/kg, p.o.). Misoprostol (30 micrograms/kg, i.d.) significantly stimulated duodenal HCO3- secretion. Mechanisms by which misoprostol inhibits various gastric lesions remain unknown. However, the stimulatory activity on duodenal HCO3- secretion appears to be involved in the preventive effect of misoprostol on the development of duodenal lesions. The effects of cimetidine and 16,16-dimethyl PGE2 were also studied and compared with those of misoprostol.

Mechanisms of antisecretory action of intragastric FPL-52694: a mast cell stabilizer in anesthetized rats

Mechanisms of antisecretory action of intragastric FPL-52694, a mast cell stabilizer, were investigated in anesthetized rats. In Schild's rat preparation, intravenous FPL-52694 (10 mg/kg) significantly suppressed acid secretion in response to only tetragastrin (20 micrograms/kg, i.v.) (42.1 +/- 19.4%), while intragastric application of FPL-52694 (100 mg/kg) for 30 min produced a marked, unequivocal inhibition (over 70%) in acid secretory responses to histamine (1 mg/kg, i.v.) and carbachol (2.5 micrograms/kg, i.v.) as well as tetragastrin. The inhibitory effect of intragastric FPL-52694 was confirmed in the lumen-perfused rats, where acid secretion (24-25 mumol/10 min) induced by intravenous infusion of histamine (8 mg/kg/h) was abolished for 1 h after exposure of the stomach for 30 min to this agent. Inhibition of histamine-stimulated acid secretion by intragastric FPL-52694 was much greater and lasted longer (2 h) as compared with xylocaine (4% solution), but significantly mitigated by pretreatment of the rats with subcutaneous administration of indomethacin (3 mg/kg). Furthermore, application of FPL-52694 but not of xylocaine to the stomach caused a reduction of transmucosal potential difference, an increase of luminal appearance of HCO-3 (1-2 mumol/10 min), and an enhancement of H+ back-diffusion, although no damage was appreciated in the mucosa. These results suggest that antisecretory action of intragastric FPL-52694 may involve local mechanisms such as neutralization of acid with HCO-3, a loss of acid due to H+ back-diffusion, and inhibition of acid production mediated by endogenous prostaglandins, but is not related to the local anesthetic activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibitory action of insulin on suprachiasmatic nucleus neurons in rat hypothalamic slice preparations

In order to elucidate a role of insulin on neurons in the suprachiasmatic nucleus (SCN) involved in the generation of circadian feeding behavior, we examined the effect of insulin on SCN neuronal activity at in vitro condition. Bath application of insulin (1-100 microU) mainly inhibited the SCN neuronal activity, and this inhibitory effect was still observed in a Ca2+-free Krebs solution. The present result strongly suggests that insulin directly inhibits SCN neurons and may explain an increase in food intake by insulin infusion into the SCN during the light period.

delta 9-Tetrahydrocannabinol elicited ipsilateral circling behavior in rats with unilateral nigral lesion

The present study was designed to examine the influence of delta 9-tetrahydrocannabinol (THC) on the central dopaminergic system using circling behavior. THC 5 mg/kg i.p. produced ipsilateral circling in rats with unilateral nigral lesion by 6-hydroxy-dopamine. THC-induced ipsilateral circling was completely antagonized by 0.2 mg/kg of haloperidol. These findings suggest that THC may cause a presynaptic stimulation of nigrostriatal dopaminergic neurons.

Influence of prednisolone on gastric alkaline response in rat stomach. A possible explanation for steroid-induced gastric lesion

Exposure of the rat stomach for 10 min to 1 M NaCl produced an increase of luminal pH (alkaline response) with a concomitant reduction of the transmucosal potential difference (PD) and an increased generation of mucosal prostaglandins of E2 and 6-keto F1 alpha. Prednisolone (3-50 mg/kg), given subcutaneously 4 hr before exposure to 1 M NaCl, dose-dependently inhibited alkaline response without affecting the PD reduction, and at 50 mg/kg completely prevented the increased production of mucosal prostaglandins after exposure to 1 M NaCl. The inhibitory effect of prednisolone on alkaline response was significantly antagonized by pretreatment with 16,16-dimethyl prostaglandin E2 (16,16-dmPGE2) (3 micrograms/kg) or cycloheximide (1.5 mg/kg). A repeated administration of prednisolone (3-50 mg/kg), once daily for 4 days, produced gastric lesions dose-dependently. At 50 mg/kg, gastric lesions appeared after administration of this drug for more than 2 days, and the inhibition of alkaline response caused by 1 M NaCl became more potent as the days of treatment increased. Either 16,16-dmPGE2 (10-100 micrograms/kg) or cycloheximide (1 or 3 mg/kg), given daily in two divided doses for 4 days, dose-dependently inhibited formation of gastric lesions in response to prednisolone (50 mg/kg). These results indicate that prednisolone inhibits gastric alkaline response caused by 1 M NaCl by reducing generation of endogenous prostaglandins. The weakened self-defense mechanisms caused by prednisolone may be involved in the pathogenesis of steroid-induced gastric lesions.

Effects of small amygdaloid lesions on pancreatic exocrine secretion

To investigate the role of the amygdala in central regulation of pancreatic exocrine secretion, the effects of electrolytic lesions on pancreatic secretion were studied in rats. Small bilateral electrolytic lesions in amygdaloid body restricted to basolateral, medial and central nuclei were produced. Eight days after the lesions, bile-pancreatic juice was collected following anesthetization with urethane and chloralose. Basal secretion and secretion stimulated by exogenous pancreozymin and secretin were evaluated in terms of amylase output. In the group with basolateral nucleus lesions, both basal and stimulated secretion were significantly increased. After medial nucleus lesions, mean body weight was reduced to 59% of initial, and basal and stimulated secretion were significantly lower than in the control group and also significantly lower than in an unoperated group, whose mean body weight was reduced to the same level as that of the medially lesioned group by restricting daily food intake. After lesions of the central nucleus, basal secretion was significantly increased, while stimulated secretion was not affected. These results indicated that the amygdala is involved in regulating pancreatic exocrine secretion and that its various nuclei exert different effects.

[Behavioral and electroencephalographic effects of lormetazepam]

Behavioral and electroencephalographic effects of lormetazepam were investigated in rats, mice and rabbits, in comparison with those of diazepam, nitrazepam and flurazepam. Locomotor activity of mice in an open-field situation was decreased with large doses of lormetazepam and diazepam, while it was increased with nitrazepam and flurazepam. The anticonflict effect of lormetazepam in rats was much more potent than those of diazepam, nitrazepam and flurazepam. In suppressing the muricide of olfactory bulbectomized and raphe lesioned rats, lormetazepam was more potent than diazepam, nitrazepam and flurazepam. Lormetazepam, diazepam and flurazepam prevented both maximal electroshock and pentetrazol convulsions in mice, the effects on the latter being much more potent than those on the former. Lormetazepam was more potent than diazepam and flurazepam in potentiating thiopental-, ether- and ethanol anesthesia, impairing rotarod performance and in muscle relaxant activity. In conscious rabbits with chronically implanted electrodes, lormetazepam induced a drowsy EEG pattern and suppressed the EEG arousal responses not only to auditory stimulation but also to electrical stimulation of the midbrain reticular formation or hypothalamus. Lormetazepam also inhibited afterdischarges induced by electrical stimulation of the hippocampus and amygdala. These results indicate that lormetazepam has pharmacological properties characteristic of benzodiazepines and that the activity is more potent than those of diazepam, nitrazepam and flurazepam.

The role of central noradrenergic neurons in electroconvulsive shock-induced muricide inhibition in olfactory bulbectomized rats

In order to elucidate the role of central monoaminergic neurons in electroconvulsive shock (ECS)-induced muricide inhibition in the olfactory bulbectomized rat (OB rat), we examined the effect of chemical or electrical lesions of each monoamine-containing neuron on ECS-induced muricide inhibition. ECS-induced muricide inhibition was antagonized by 6-hydroxydopamine (6-OHDA) treatment and locus coeruleus lesions, while it was unaffected by desipramine + 6-OHDA, substantia nigra lesion, and desipramine + 5,7-dihydroxytryptamine. The present results strongly suggest that ECS-induced muricide inhibition of the OB rat is due to increased activity of the noradrenaline but not of dopamine and serotonin neurons.

Qualitative and quantitative analysis of muscarinic acetylcholine receptors in the piebald lethal mouse model of Hirschsprung's disease

Cholinergic innervation in the aganglionic bowel of the piebald lethal mouse model of Hirschsprung's disease was investigated by analysis of muscarinic acetylcholine receptors before and after administration of hexamethonium. After hexamethonium administration in the normal rectum, the maximum specific binding (Bmax) of [3H]quinuclidinyl benzilate increased from 196.6 to 346.2 fmol/mg protein without affecting the dissociation constant. This increase of muscarinic acetylcholine receptors was associated with a decrease in the 50% effective dose (ED50) of contractile response to oxotremorine from 3.8 X 10(-7) M to 6.5 X 10(-8) M. In the aganglionic rectum, hexamethonium administration did not change the Bmax (166.4 fmol/mg protein) or dissociation constant value. The ED50 of contractile response to acetylcholine and oxotremorine (4.3 X 10(-8) M, 6.5 X 10(-8) M) was lower than that in the normal rectum (1.9 X 10(-7) M, 2.0 X 10(-7) M), but it was not changed by hexamethonium. It is concluded that cholinergic innervation is congenitally absent in the aganglionic rectum in piebald lethal mice.

Effects of psychotropic drugs on discrimination conditioning in olfactory bulbectomized rats

In the acquisition process of discrimination avoidance conditioning, bilateral olfactory bulbectomized rats showed poor discrimination conditioning since both the avoidance responses to positive conditioned stimuli (CS) and the incorrect responses to negative CS increased. The effects of various psychotropic drugs upon this poor discrimination conditioning were examined. Chlordiazepoxide 5 mg/kg, IP, produced an increase in the avoidance responses with simultaneous decrease in the incorrect responses, thus making the discrimination possible. Chlorpromazine 2 mg/kg, IP, worsened the discrimination by decreasing both the avoidance and incorrect responses as compared with saline-treated rats. Amitriptyline 10 mg/kg, IP, decreased the incorrect responses without affecting the avoidance responses, thus making the discrimination possible. Methamphetamine 0.5 mg/kg, IP, increased both the avoidance and incorrect responses resulting in poor discrimination conditioning. From these results, it was found that the poor discrimination conditioning of O.B. rats was improved by psychotropic drugs like chlordiazepoxide and amitriptyline.

Effect of L-glutamate, injected into the posterior hypothalamus, on blood pressure and heart rate in unanesthetized and unrestrained rats

In unanesthetized and unrestrained rats, microinjection of L-glutamate into the posterior hypothalamus produced hypertension and tachycardia. These cardiovascular responses were mostly accompanied with behavioral excitation such as searching the cage, rearing and sniffing. The cardiovascular responses elicited by L-glutamate were attenuated by prior injection with propranolol and hexamethonium but not with glutamate diethylester, phentolamine and atropine. The behavioral responses to L-glutamate were suppressed by propranolol, hexamethonium and phentolamine. These results suggest that catecholaminergic and/or cholinergic systems in the posterior hypothalamus may be involved in the mediation of the cardiovascular and behavioral responses induced by L-glutamate.

Effects of chronic LiCl and RbCl on muricide induced by midbrain raphe lesions in rats

Midbrain raphe lesions in rats (raphe rats) induce aggressive behavior including muricide. A single administration of LiCl (Li) 100 mg/kg to raphe rats produced only 25% of muricide inhibition. However, the inhibitory effect of muricide in raphe rats significantly increased from the 5th day following repeated administration of Li. Chronic Li also inhibited muricide in olfactory bulbectomized (OB) rats. The inhibition of muricide lasted until the next day to some extent. In this point, the effect of Li on muricide is similar to that of antidepressants, but not of neuroleptics. On the contrary, RbCl (Rb) showed a tendency to induce muricide. The single re-administration of Li 100 mg/kg on the withdrawal on the 7th day after repeated administration for 14 days showed a significant inhibition of muricide in raphe rats, unlike that in OB rats. Li also showed a partial prophylactic effect on muricide when Li 100 mg/kg was administered for 1 week before raphe lesions. These results suggest that raphe rats may serve not only as an experimental model of depression, but also as that of manic illness.

[Behavioral pharmacology of amantadine with special references to the effect on abnormal behavior in mice and rats]

Behavioral effects of amantadine, especially on abnormal behavior in mice and rats, were reevaluated, in comparison with those of tricyclic antidepressants, methamphetamine and L-DOPA. 1) Amantadine at 10 approximately 50 mg/kg, i.p., tended to decrease ambulation and rearing in rats and mice. The drug at 50 mg/kg, i.p., caused piloerection and hyperirritability and at doses over 80 mg/kg, i.p., it impaired coordinated motor activity in rats. 2) Amantadine inhibited methamphetamine-induced hyperactivity, but apomorphine-induced stereotyped behavior was unaffected in rats. 3) Amantadine was equipotent to imipramine in suppressing haloperidol-induced catalepsy in rats, but L-DOPA was without effect. On the other hand, amantadine was 40 and 400 times as potent as imipramine and L-DOPA, respectively, in suppressing delta 9-tetrahydrocannabinol (THC)-induced catalepsy in rats. 4) Amantadine was as potent as imipramine in suppressing the muricide of olfactory bulbectomized rats, but was 3.5, 8.8 and 225.5 times as potent as methamphetamine, imipramine and L-DOPA, respectively, in inhibiting THC-induced reversible muricide in rats. 5) Amantadine at 50 mg/kg did not elicit circling behavior in the rat with unilateral nigral lesion induced by 6-hydroxydopamine. 6) Amantadine at high doses caused irritable aggression characterized by squealing in rats pretreated with intraventricular 6-hydroxydopamine. The most important characteristic of amantadine is its prominent effect suppressing the THC-induced catalepsy and muricide. This may be a reflection of the feature of amantadine activating the dopaminergic as well as the serotonergic systems.

Role of the amygdala in the hippocampal kindling effect of rats

In the present experiment, the role of the amygdala in the formation of the hippocampal kindling effect was investigated in rats with chronic electrode implants. The number of trials required for the establishment of hippocampal kindling was significantly shortened by either ipsilateral or bilateral amygdaloid lesions. The high amplitude spike waves in the frontal cortex and reticular formation appeared earlier in the amygdaloid lesioned rats than in the sham lesioned rats. It is suggested that the amygdala has an inhibitory effect on the development of the hippocampal kindling effect. On the other hand, either the ipsilateral or bilateral amygdaloid lesions after the establishment of hippocampal kindling inhibited the induction of generalized convulsion by hippocampal stimulation. Three and 8 repeated daily stimulations were needed to reestablish the hippocampal kindling effect after the ipsilateral and bilateral amygdaloid lesions, respectively. These results do not coincide with the above-mentioned results indicating that the amygdala has an inhibitory role in the formation of hippocampal kindling. It is suggested that the neuronal circuits involved in the formation of hippocampal kindling in the amygdaloid lesioned rats are different from those in the intact rats.

Differential effects of electroconvulsive shock on four models of experimentally-induced aggression in rats

The effects of electroconvulsive shock (ECS) on the hyperemotionality and muricide in olfactory bulbectomized rats (OB rat) were compared with those in spontaneous killer rats (SP rat), raphe lesioned rats (Raphe rat) and delta 9-tetrahydrocannabinol treated rats (THC rat). Single and chronic treatment of ECS inhibited the muricide and attack response to a rod, but did not affect the struggle response to handling and flight response to air blowing. Muricide was markedly inhibited by ECS in OB and SP rats, and was moderately inhibited in THC rats, while it was slightly inhibited in Raphe rats. The present result indicates that muricide of OB rats is a useful model for evaluating antidepressant drugs as this behavior is markedly inhibited by ECS in OB rats. Furthermore, it is suggested that the effect of ECS on muricide is different depending upon the methods to induce muricide, although muricide itself seems to be behaviorally similar.