Teiichiro Tonoue

Inhibition of shock-elicited ultrasonic vocalization by opioid peptides in the rat: A psychotropic effect

Following three series of electric footshocks (10 shocks/day), one out of three rats in most cages were brought to emit ultrasonic vocalization for several minutes after a single shock. The characteristics of shock-elicited ultrasound were pure tone pulses of a frequency between 22 and 28 kHz, with duration longer than 300 msec. The same type of ultrasound is produced by subordinate male rats during agonistic behavior. The intracerebroventricular injection of beta-endorphin, dynorphin, methionine-enkephalin or leucine-enkephalin attenuated the shock-elicited ultrasonic vocalization. Psychotropic drugs such as diazepam and chlorpromazine also attenuated the shock-elicited ultrasonic vocalization. A test utilizing ultrasonic vocalization in rodents can provide useful data for studying the psychotropic properties of neuropeptides.

Neuropeptides as central integrators of autonomic nerve activity: effects of TRH, SRIF, VIP and bombesin on gastric and adrenal nerves.

The nerve activity of the gastric ramus of the splanchnic (sympathetic) nerve, gastric ramus of the vagus, adrenal ramus of the splanchnic nerve and the superior laryngeal nerve (laryngeal ramus of vagus) were assessed before and after i.c.v. injection of neuropeptides in the rat. TRH stimulated the vagal branch but attenuated the sympathetic outflow to the stomach. In contrast, the sympathetic outflow to the adrenal was enhanced by TRH. SRIF suppressed the activity of all the nerves studied. VIP did not affect the sympathetic outflow to the stomach while suppressing the gastric branch of the vagus. The adrenal sympathetic branch as well as the superior laryngeal nerve was stimulated by VIP. Bombesin suppressed both vagal and sympathetic outflow to the stomach but markedly stimulated the laryngeal branch of the vagus. The adrenal sympathetic nerve was either stimulated or attenuated slightly by bombesin. These results indicate that centrally administered neuropeptides produce reactions specific for each nerve.

Sex difference in ultrasound distress call by rat pups.

Ontogenic changes in ultrasound production by isolated rat pups were compared in male and female pups of litters of various sex compositions. In both sexes, the peak of emission of sound around 50 kHz was on days 4-5, while 40 kHz sound production peaked on days 6-7. By days 4-5 each pulse is an inverted V-shape with frequencies between 40 and 55 kHz. At the peak of sound production, pulses with a slight downsweep from 40-45 kHz were prominent, and in the preweaning period, pulses of a relatively stable frequency of 35-40 kHz were emitted. There was a general tendency for sound pulses of female pups to be of short duration compared with those of male pups. The ontogenic changes in the ultrasonic distress call are less variable throughout all female pups of litters consisting of 2, 4, 6 or 8 female pups in a litter of 8. In contrast to this, it was found that male pups emit ultrasound more vigorously than female pups from days 2-3 to days 12-13 when male and female pups coexisted in the same litter. The activity of sound production of male pups which had no female littermates was similar to that of female pups. These findings suggest that the interaction of some kind between male and female pups produces the sex differences in the ultrasonic distress calls as early as several days after birth in the rat.

Effect of intracerebroventricular administration of thyrotropin-releasing hormone upon the electroenteromyogram of rat duodenum.

Electroenteromyographic activity (EMG) of the duodenum was recorded in pentobarbital-anesthetized rats. TRH intraventricularly administered to rats produced changes in EMG such as increased amplitude, decreased frequency of slow waves and the association of bursts of spike potentials with nearly every cycle of the basal electric rhythm (BER). The effect was selectively prompt and marked in the EMG of proximal duodenum. The response was abolished by vagotomy or atropine injection and no response was elicited in the neonatally 6-OHDA-treated rat. Hypophysectomy, cord-transection or acute i.v. injection of 6-OHDA did not block the response. In the brain, TRH seems to stimulate the neuronal system controlling the vagus efferents involved in the regulation of the duodenal enteric nervous system which in turn modulates the myogenic excitability of the duodenum.

Effects of Thyrotropin-Releasing Hormone (TRH) on the isolated small intestine and taenia coli of the guinea pig

Thyrotropin-releasing hormone (TRH) produced a contraction in the isolated segment of duodenum and taenia coli of the guinea-pig (pA2, 8.0 and 8.9). TRH induced a contraction, a relaxation, or a contraction followed by relaxation in the jejunum and ileum. All the responses to TRH of the small intestine and the taenia coli were abolished in the presence of tetrodotoxin but not affected by hexamethonium. The contractile response to TRH of the small intestine was abolished and replaced by a relaxation in the presence of hyoscine. This relaxant response was not affected by guanethidine. The taenial response to TRH was partially inhibited by either hyoscine or methysergide and markedly diminished by the two together. These findings indicate that TRH acts on the myenteric neurons of the small intestine and taenia coli of the guinea pig. The contractile response of small intestine is likely to be induced through cholinergic nerves while cholinergic, serotonergic and unidentified excitatory neurons seem to be involved in the taenial response. These neurogenic actions of TRH on the guinea-pig intestine are in contrast with the myogenic natur of the response to TRH in the duodenum of the rat.

Diazepam and endorphin independently inhibit ultrasonic distress calls in rats

Ultrasonic distress calls elicited in male rats by footshock under inescapable conditions were suppressed by diazepam. The suppression was blocked by pretreatment with Ro15-1788 or CGS8216, selective benzodiazepine receptor antagonists, while an opiate antagonist naloxone failed to modify the effect of diazepam. In contrast, naloxone antagonized but Ro15-1788 and CGS8216 did not antagonize beta-endorphin which also suppressed the ultrasonic vocalization. These findings suggest that benzodiazepine and opioid receptors may contribute separately to antianxiety activity.

Evidence that endogenous thyrotropin-releasing hormone (TRH) may control vagal efferents to thyroid gland: neural inhibition by central administration of TRH antiserum

The intracerebroventricular (i.c.v.) injection of rabbit antiserum to thyrotropin-releasing hormone (TRH) to the urethane anesthetized rat inhibited the spontaneous electrical discharge of the superior laryngeal nerve (n.sl). On the other hand, the i.c.v. injection of rabbit antiserum to somatostatin (SRIF) failed to influence the nerve activity whereas SRIF itself is capable of inhibiting the n.sl activity. These findings suggest that TRH in the brain takes a role continuously in regulating the neural activity while SRIF is involved in the neuronal circuits as an agent for the down regulation of the autonomic nervous system.

Stimulation by thyrotropin-releasing hormone of vagal outflow to the thyroid gland.

An intracerebroventricular (i.c.v.) injection of TRH to the urethane anesthetized rat stimulates the activity of the superior laryngeal nerve (n.sl) which is a vagal ramus terminating at the thyroid gland and adjacent muscles. The response to TRH, a tonic increase in the n.sl outflow, was dose dependent in the 0.005-5.0 micrograms/100 g B.W. range. In contrast to this, methionine-enkephalin (ENK), neurotensin (NT) and somatostatin (SRIF) (5 micrograms/100 g, i.c.v.) all caused a transient decrease in n.sl activity. SRIF showed the highest attenuating effect when injected alone and was capable of diminishing the increased activity produced by a prior injection of TRH. ENK and NT failed to affect the TRH-induced increased activity. When injected concomitantly with TRH, SRIF blocked the response to TRH while ENK and NT both failed to affect the response to TRH. Pretreatment with triiodothyronine for 5 days strongly inhibited the response of the n.sl outflow to TRH. On the other hand, pretreatment with atropine, haloperidol, propranolol, phenoxybenzamine and p-chlorophenylalanine failed to block the stimulating effect of TRH although the response was diminished by some antagonists. It therefore seemed that TRH transmission is involved in central stimulation and SRIF is antagonistic in this regulation of n.sl outflow to the thyroid gland.

Myogenic receptivity for Met-enkephalin in the rat duodenum: Comparison with the guinea-pig duodenum

Met-enkephalin (ENK) induced a dose-dependent transient relaxation in vitro in the rat duodenum while morphine neither induced a response nor affected the response to ENK. The response was not blocked by tetrodotoxin but was abolished by naloxone. The response of guinea-pig duodenum to ENK was either relaxation or pulsatile contractions depending on the dose and was abolished by tetrodotoxin.

Neonatal damage to neocortex abolishes the anxiolytic action of diazepam in adult rats

A neonatal cerebral cortical lesion was made in rats and the effects of diazepam on ultrasonic isolation calls in pups and footshock-elicited ultrasonic distress calls in young adult rats were assessed. There was no indication that the cortical lesion influenced the production of the ultrasonic distress calls in either pups or adults. Diazepam attenuated the ultrasonic isolation calls in all the pups with and without cortical lesion, and the distress calls in normal adult rats. However, diazepam failed to exert the effect in rats which received a neonatal cortical lesion. 8-Hydroxy-2-(di-n-propylamino)tetralin hydrobromide (8-OH-DPAT), another anxiolytic, was effective to diminish the distress calls even in the adult rats which had had the neonatal damage to the cortex. These findings indicate that the intact cerebral cortex is not always required for production of ultrasonic distress calls; however, the development of the neuronal mechanism involving benzodiazepine receptors to inhibit the ultrasonic expression of anxiety or fear in adult rats is dependent on the integrity of the cerebral cortex.