Antiaggressive and motor effects of haloperidol show different temporal patterns in the development of tolerance

The study of the temporal course of tolerance development was used as a means to separate different aspects of the action of haloperidol on social behavior. Agonistic behavior was studied in isolated male mice that confronted standard opponents (anosmic and grouped conspecifics) in a neutral area. The aggressive and motor behaviors of the experimental animals were evaluated 30 min or 24 h either after a single injection of haloperidol (0.4 mg/kg) or following the last of a series of 15 or 30 injections. When animals were evaluated 30 min after the haloperidol injection, no tolerance to the antiaggressive effects was evident. The action on immobility, on the contrary, showed a clear tolerance development with repeated drug administration, both with 15 and 30 injections. When evaluated 24 h after the last injection, tolerance to the antiaggressive effects developed with repeated injections. Increased immobility was never found in the tests carried out after 24 h, not even in the single injection group. The clear divergence found in the temporal courses of tolerance to haloperidol in its antiaggressive and motor effects suggests that these actions are mediated through different neurophysiological mechanisms. A parallel with extrapyramidal and therapeutic effects is discussed.

Offense produced by chemical stimulation of the anterior hypothalamus of the rat

Offense behavior, including bite-and-kick attack, was obtained by microinjections of picrotoxin into the anterior hypothalamus of the rat. This is the first time that it has been possible to obtain offense by chemical stimulation of the brain, and the localization is more precise than that obtained with electrical stimulation. Mounting behavior and mounting by the opponent were also obtained from the anterior hypothalamus, the former corresponding to results obtained by previous studies using electrical stimulation. Other behaviors obtained from the hypothalamus included locomotion and circling, social and self-grooming, upright posture and boxing, digging, feeding, and leaping.

Effects of corticosterone on social behavior of male lizards

Adrenal corticoid release is a major component of the stress response which can affect many body functions including behavior. The purpose of our studies was to examine the effects of corticosterone (B) on both the agonistic and courtship components of social behavior in male side-blotched lizards (Uta stansburiana). Of particular interest was the effect of B on plasma testosterone (T), a hormone known to influence aggression, and the importance of this action on the behavioral effects of B. Experiments included either castrated males, hormone (either B, T, or B + T)-implanted intact males, or sham males. Behavioral observations were recorded when these males were challenged with "immigrant" males; measurement of plasma steroids confirmed the efficacy of implants in elevating B and T. Castration, B implantation, and combined B and T implantation significantly reduced aggressive behavior to varying degrees, while T implants in intact animals had no effect. B implants significantly decreased plasma T levels (from 1.87 to 0.33 ng/ml), but this decrease was not essential for the inhibitory effect of B on aggression since B + T implantation also reduced aggression, even though plasma T was elevated above normal (67.6 ng/ml). In contrast, B implantation did not affect male courtship and copulatory behavior when males were presented with estrogenized females. These results suggest that the effect of B on social behavior is not through just a single route, that of decreasing plasma T, and that B can affect various intra- and intersexual behaviors differently.

Influence of combined estradiol and testosterone implants on the aggressiveness of nonaggressive female rats

Female rats that had been cohabiting with a sterile male or with another female for 6 weeks were tested for aggression toward an unfamiliar female once each week for 3 weeks. Females that were not aggressive as a result of cohabitation with a sterile male were ovariectomized. Half were implanted with a Silastic tube containing estradiol (1 mm long hormone-filled space) and a tube containing testosterone (5 mm long hormone-filled space). The other half were implanted with empty tubes. All females that had been cohabiting with another female were ovariectomized and implanted with an estradiol- and a testosterone-filled tube. Three additional weekly tests of aggression were given beginning 1 week postoperatively. Females given hormone replacement displayed only a slight increase in aggression postoperatively. Females not given hormone replacement declined in aggressiveness. These results indicate that hormone replacement levels sufficient to maintain aggression in highly aggressive females following ovariectomy are not sufficient to produce a high level of aggression in females that have not become aggressive following cohabitation with a sterile male or that have been cohabiting with another female.

Neonatal capsaicin exposure affects isolation-induced aggressive behavior and hypothalamic substance P levels of adult male mice (Mus musculus)

Subcutaneous administration of capsaicin (50 mg/kg) at Postnatal Days 2 and 5 exerted long-term effects on isolation-induced aggressive behavior of adult mice (Mus musculus) of the CD-1 strain. Isolated capsaicin-treated mice (scored during a 10-min session) showed the highest frequency and the longest duration of total attacks, attacks, rattling, and offensive upright posture when compared with nonisolated capsaicin-treated subjects and both isolated and nonisolated vehicle control animals. Hypothalamic Substance P (SP) was assessed by radioimmunoassay. Capsaicin treatment significantly lowered hypothalamic SP content in both isolated and nonisolated mice. Moreover, individual scores of isolated capsaicin-treated subjects showed a significant correlation between SP depletion and expression of offensive upright posture. Isolation per se was revealed to play an important role in depleting SP from the hypothalamus.

Morphine attenuates ultrasonic vocalization during agonistic encounters in adult male rats

Ultrasonic vocalizations (USV) in rats may communicate "affective" states during pain, sex and aggression. This proposal was evaluated in an experiment with adult male Long-Evans rats during agonistic encounters; specifically, morphine and naltrexone effects were studied on different types of USV by intruder rats exposed to resident attacks and to "threat of attacks" (i.e., intruder residing within the home cage of the resident but prevented from physical contact by a wire mesh cage). Intruders readily emitted USV during agonistic encounters. These calls consisted primarily of two distinct distributions of pure tone whistles: 0.3-3 s, 19-32 kHz ("low") calls and 0.02-0.3 s, 32-64 kHz ("high") calls. Sonographic analysis revealed a considerable repertoire of frequency modulated calls. Different types of vocalizations proved to be differentially sensitive to the opiate treatments: morphine (1-10 mg/kg SC) dose-dependently decreased the rate, duration and pitch of both low and high frequency USV during the threat of attack; this decrease in rate and duration measures was naltrexone-reversible (0.1 mg/kg IP). Interestingly, audible vocalizations were also emitted but were unaffected by morphine in this dose range. Concomitant with the decrease in USV after morphine was a dose-dependent decrease in rearing, walking and nasal contact behavior with increases in submissive crouch behavior and tail flick analgesia. The decreases in rate and duration of both low and high USV and the pitch of specific frequency modulated calls after morphine administration may reflect an attenuation of affective aspects of pain, and the many characteristics of US (rate, duration, pitch, frequency modulation, pre-and suffix attributes and temporal structure) point to potentially diverse functions.(ABSTRACT TRUNCATED AT 250 WORDS)

Agonistic behavior and its cardiovascular components elicited by microinjection of L-glutamic acid into the basal midbrain of the toad Bufo paracnemis

Microinjection of L-glutamic acid into the basal midbrain of the toad Bufo paracnemis induced a series of responses linked to antipredator behavior such as flight, backward locomotion and defensive postures. Furthermore, alerting/orientation occurred in 20% of the animals, a behavior which is probably important for the animal to achieve the above responses. Locomotion occurred in 18% of the toads. The existence of a mesencephalic premotor control for locomotion in these animals is discussed comparatively. All responses were accompanied by changes in arterial pressure, heart rate and intrabuccal pressure. In some animals which exhibited backward locomotion responses, defensive postures and alerting/orientation, bradycardia or cardiac arrest occurred, with no appreciable changes in arterial pressure. This fact is discussed on the basis of studies which have shown the occurrence of similar alterations in situations of fear in other vertebrates. Autonomic changes without other responses occurred in 16% of the animals. Flight behavior was usually observed as a consequence of stimulation of sites located in the anterodorsal tegmental nucleus and lateral portions of the midbrain tegmentum. In contrast, locomotion was obtained by stimulating basal sites of the tegmentum located in the anteroventral nucleus and in the reticular formation lateral to it. Sites related to the remaining behaviors were located more diffusely in the basal midbrain.

Effects of angiotensin II on behavioral responses of defensive burying paradigm in rats

The effects of angiotensin II (ATII) administered intracerebroventricularly in male Wistar rats in doses of 0.1, 0.5, and 1.0 micrograms, as well as of ATII (1.0 micrograms) + saralasin (SAR, an analog ATII) (5.0 micrograms), on behavioral responses of the defensive burying paradigm were studied. ATII-treated animals displayed significantly less defensive burying behavior (less time spent in defensive burying and less frequent burying than in vehicle-treated rats) in a dose-dependent manner. SAR at a dose of 5 micrograms did not affect burying behavior significantly; it also did not modify the inhibition effects of ATII on behavioral responses of the defensive burying test. These results provide evidence that ATII can exert anxiolytic actions on central transmitter systems mediating conditioned fear-related behaviors (i.e., defensive burying). The present study suggests that the defensive burying animal model is a rather sensitive test fulfilling the pharmacological criteria of dose-dependent sensitivity for studying the central effects of neuropeptides (e.g., ATII).

Intrinsic and extrinsic influences on play fighting in rats: effects of dominance, partner's playfulness, temperament and neonatal exposure to testosterone propionate

Play fighting is a frequent activity of juvenile rats and appears to show marked variability amongst individuals in that some rats play a great deal and others very little. This study attempted to identify some of the factors involved in producing this individual variability. The major influence over an individual's frequency of play as a juvenile was found to be the frequency of play by the partner. That is, play appears to be contagious, in that a high playing animal stimulates its partner to play frequently as well. In male juveniles, but seemingly not in female juveniles, the subsequent adult status of one partner as dominant influences the subordinate-to-be to initiate more playful contacts. In addition to these extrinsic influences, however, there appear to be intrinsic factors that influence whether an individual is a high or low playing animal. One intrinsic factor appears to be 'boldness', so that bolder animals tend to initiate more playful contacts. Higher players tend to be more susceptible to the stereotypy-inducing effects of the dopamine agonist, apomorphine, and tend to be more dependent upon the playful activity of the partner to maintain their own high levels of play. Both of these characteristics are consistent with other studies comparing bold and timid rats. Boldness, however, only seems to influence how much play a rat will exhibit, not how much play it is capable of exhibiting. Neonatal testosterone augmentation increases juvenile play fighting but not apomorphine susceptibility, suggesting that a high player need not be a bold animal. The total frequency of play an individual is capable of initiating appears to depend upon perinatal exposure to androgens. Boldness and the playfulness of the partner appear to modulate the expression of this hormonally set value.

Defense reaction elicited by microinjection of kainic acid into the medial hypothalamus of the rat: antagonism by a GABAA receptor agonist

Electrical stimulation of either the midbrain central gray or the medial hypothalamus induces a defense reaction in the rat, characterized mainly by increased locomotion, rearing, and leaping. However, microinjection of the excitatory amino acid glutamate was effective only in the former region. Because excitatory amino acids do not depolarize axons of passage, it was suggested that the hypothalamus is devoid of soma/dendrites of neurons commanding the defense reaction. In the present study, we show that a subtoxic dose (60 pmol) of another excitatory amino acid, kainic acid, injected into the medial hypothalamus significantly enhanced locomotion and rearing of Wistar rats systematically observed in an open field. Similar behavioral changes have been reported following microinjection of drugs impairing GABAergic neurotransmission. Local pretreatment with the GABAA receptor agonist THIP (2 nmol) blocked the effect of kainic acid. Therefore, the medial hypothalamus of the rat seems to contain a population of neuronal cell bodies commanding the defense reaction, which is activated by excitatory amino acids and tonically inhibited by GABAergic fibers.

Effects of eltoprazine hydrochloride on reactivity to conspecific or novel odors and activity

Treatment with eltoprazine (DU 28853) increased the number of entries by male mice into compartments containing the odors of male and female conspecifics. This effect was most pronounced when odors were provided by previously defeated males. In contrast, the drug had no effect upon responsiveness to the odors of cinnamon and chocolate. The results suggest that eltoprazine may selectively increase reactivity to conspecific odors and that this effect is further enhanced by agonistic experience. Eltoprazine also substantially increased activity levels in all experiments. Since hyperactivity occurred both in the presence and absence of conspecific odors, however, the drug's effects on activity and olfaction seem to be largely independent. The results suggest that the aggression-modulating effects of eltoprazine, as well as other drugs, may be mediated in part by their effects on normal olfactory function.

Cocaine, social behavior, and alcohol-solution drinking in monkeys

Eight group-living male monkeys received cocaine (0 to 3.0 mg/kg) individually or as a group. Cocaine suppressed social affiliative behaviors, eating, and drinking (of both alcohol and control solutions). It induced bizarre stereotypies, hypervigilance, panic-like fleeing, enhancement and then suppression of locomotion, and a seizure. Cocaine had little effect on aggressiveness or sexual behavior. Proportion of time spent lying or sitting changed significantly. Cocaine produced severe behavioral abnormality in this social setting.

Alcohol and "bursts" of aggressive behavior: ethological analysis of individual differences in rats

A quantitative ethological analysis of rodent aggression was performed in order to characterize the aggression-heightening effects of alcohol in certain individuals. In dyadic confrontations, a resident rat pursues, threatens and attacks an intruder, who reacts with defensive, flight and submissive behaviors. The behavioral data from five series of experiments conducted from 1984 through 1989 were subjected to a lag sequential analysis that identified highly predictable sequences of aggressive behavior, and to interval analysis that delineated a burst pattern of aggressive behavior. These analyses revealed a distinct behavioral sequence of pursuit----sideways threat----attack bite----aggressive posture that occurs in bursts with an inter-event interval of less than 6.6 s. In the total population, alcohol heightened attack behavior at low acute doses (0.1, 0.3, 1.0 g/kg) in 47% of the animals (n = 44), suppressed reliably attack behavior in another 25% (0.1-3.0 g/kg; n = 23) and had unreliable effects in the remaining 28% (n = 24). The peak enhancement of aggressive behavior was seen over more than a log cycle of alcohol doses (0.1, 0.3 or 1.0 g/kg) in different individuals. In an additional group of rats (n = 20), individuals were identified according to whether or not acute low alcohol doses enhanced or suppressed the frequency of attack bites. In the subgroup of five rats who doubled their attack frequency upon acute alcohol challenge, this aggression-heightening effect was confirmed on repeated occasions. The aggression-heightening effects of alcohol were seen during the high-rate interactions in the initial phase of the confrontation and particularly during the lower level of fighting later on. Regardless of alcohol dose and subgroup, the highly predictable sequence of pursuit----sideways threat----attack bite----aggressive posture remained intact as long as the individual was able to fight. The present analysis identifies those individuals in whom low alcohol doses increase the frequency of attack behavior, the number of aggressive elements in bursts and particularly the "time in burst". Alcohol produces these changes without altering the latency to initiate aggressive behavior, the rate of aggressive behavior within a burst or the number of bursts in an encounter. Alcohol may lengthen aggressive bursts by preventing termination of longer aggressive sequences rather than by altering the initiation of this behavior.

Comparison of the effects of benzodiazepine and non-benzodiazepine anxiolytics on agonistic behavior in male mice

The present study investigated whether there is any difference between the effects of benzodiazepine and non-benzodiazepine anxiolytics on agonistic behavior in male mice, using an ethopharmacological technique. Agonistic behavior was evoked using a resident-intruder paradigm. The effects of four doses of the following drugs were assessed in either resident or intruder mice: diazepam (vehicle, 1, 2.5 and 5 mg/kg, p.o.) and tandospirone (vehicle, 2.5, 5 and 10 mg/kg, p.o.). Residents and intruders were drugged on alternate test days, and all animals received different sequences of each of the drug conditions according to a random schedule. The injection-test interval was 30 min. When a resident mice were treated with either diazepam or tandospirone, the frequency of attack bite was suppressed significantly in a dose-dependent manner. When intruder mice were treated with diazepam, attack bites by untreated residents were significantly increased, whereas tandospirone was ineffective. Although diazepam caused a significant decrease in both locomotion and rearing, tandospirone did not cause motor dysfunction. These evidence indicate that tandospirone, a 5-HT1A receptor agonist, has different pharmacological properties from diazepam.

Ethopharmacological studies on the effects of antihormones on rodent agonistic behavior with especial emphasis on progesterone

The effects of a range of antiandrogens and antiestrogens on conflict behaviors in laboratory rats and mice are reassessed in the light of recent studies applying ethophamacological analyses (recording the full spectrum of behaviors) to such investigations. It is argued that any antihostility properties of the antiandrogen cyproterone acetate are largely a consequence of indirect actions on odor communication, whereas antiestrogens (e.g., tamoxifen and CI 680) seem to have more fundamental motivational effects in addition to communicatory actions. A detailed example of the approach is provided in which progesterone (which can be antiandrogenic) is given to rats paired in different ways. The type of pairing has a very substantial effect on the actions seen after treatment, and the ethopharmacological approach generates a better picture of antihormone effect than traditional psychopharmacological tests.

Serotonergic modulation of footshock induced aggression in paired rats

Footshock induced aggression (FIA) was induced in paired rats and three paradigms of aggressive behaviour were recorded, namely, latency to fight (LF), total period of physical contact (TPP) and cumulative aggression scores (CAS). The effects of increasing or decreasing central serotonergic activity, by using a number of pharmacological agents with well defined effects on rat brain serotonin, were investigated on FIA and on FIA augmented by apomorphine, a dopamine receptor agonist. The results show that centrally administered serotonin, the serotonin precursor, 5-hydroxytryptophan administered with clorgyline, a selective MAO A inhibitor, quipazine, a serotonin receptor agonist, and fluoxetine, a selective inhibitor of neuronal re-uptake of serotonin, attenuated all paradigms of FIA and apomorphine induced potentiation of FIA. On the contrary, the other re-uptake inhibitor used, citalopram, appeared to have a dual effect and decreased LF and CAS, while increasing TPP. The serotonin synthesis inhibitor, p-chlorophenylalanine and the selective serotonin receptor (5-HT2) antagonist, ketanserin, augmented all paradigms of FIA per se and apomorphine induced augmentation of FIA. However, the other serotonin receptor antagonist used, metergoline, which blocks both 5-HT1 and 5-HT2 receptor subtypes, attenuated FIA per se but decreased only CAS in apomorphine induced increase in FIA. The data confirm the inhibitory effect of the central serotonergic system on aggressive behaviour and the inverse relationship existing between it and the central dopaminergic system in the modulation of FIA, as has also been confirmed in earlier biochemical investigations from this laboratory. The data has been discussed in the light of existing knowledge on serotonin receptor subtypes and the presence of modulatory serotonergic heteroreceptors on central dopaminergic neurones.

Behavioural differences between artificially selected aggressive and non-aggressive mice: response to apomorphine

The present study reports a first attempt to unravel the neurochemical background that underlies the difference in behavioural profiles between aggressive and non-aggressive male mice. For this purpose two bidirectionally selected lines for attack latency (SAL and LAL) were used. In pursuit of Cools'9 approach, the susceptibility of individuals of both selection lines to the dopamine agonist apomorphine was measured. The apomorphine was injected subcutaneously at dose levels of 2.5 and 5.0 mg/kg. Apomorphine is considered to stimulate the dopamine receptors in the telencephalon and induces stereotyped behaviour. The responsivity to apomorphine can be rated as a total stereotypy-score. SAL (aggressive) mice showed a significantly greater enhancement of stereotyped behaviour in response to apomorphine than LAL (non-aggressive) mice. In addition, it was demonstrated that this difference is of a quantitative rather than qualitative character. Pharmacokinetic variation between the two lines could be ruled out as cause of the difference. Hence, it was concluded that SAL mice are more sensitive to apomorphine than LAL males, which provides evidence for a difference in the dopaminergic system between the two selection lines. It was suggested that this difference underlies the difference in flexibility in behaviour between aggressive and non-aggressive male mice.

Capsaicin affects aggressive behavior, but not hot plate responding, of adult male mice

Adult male mice of albino Swiss-derived CD-1 strain were used to assess the effects of capsaicin (a powerful agent that produces a marked depletion of the undecapeptide substance P) on both intraspecific aggressive behavior (induced by 8 weeks of individual housing) and pain sensitivity. Capsaicin was given SC, 48 h before behavioral testing. Aggressive behavior, scored during a 5-min session under red light, was significantly enhanced by capsaicin treatment (50 or 100 microliters of a 7.5 mg/ml solution). In fact, Total Aggressive Episodes, Attacks, and Upright Offensive Posture were significantly higher in the two capsaicin-treated groups, while Latency to the first Attack was decreased, when compared to both vehicle or unhandled controls. A concomitant decrease in Submissive Postures and Flee was also evident in capsaicin mice. Hot plate testing (55 +/- 0.1 degrees C, cutoff time 30 s), carried out on nonisolated mice, did not reveal any difference among the two capsaicin groups (same doses) and vehicle or unhandled controls.

Behavioral and neuroendocrine response to psychosocial stress in male rats: the effects of the 5-HT 1A agonist ipsapirone

The effect of the 5-HT 1A agonist ipsapirone on the behavior, plasma catecholamine, and corticosterone levels was studied in male Wistar rats during the psychosocial stress of confrontation with a confined dominant opponent 24 hr after defeat. The effect of the drug was also studied during a predefeat confrontation with the confined (would-be dominant) rat. Blood samples were withdrawn via a permanent heart catheter. The drug (5 mg/kg, ip) or vehicle was given 30 min before transportation to the experimental room. Ipsapirone had no major effects on the plasma hormone concentrations and had no influence upon the behavioral response to the confined rat. At the postdefeat test ipsapirone led to a significant increase of immobility, whereas both rearing and time spent sniffing the cage were diminished. Postdefeat psychosocial stress resulted in an increase of the hormone, particularly catecholamine levels. These responses were further elevated by the drug. The presence of high corticosterone levels in the home cage after postdefeat ipsapirone treatment leads to the hypothesis that postsynaptic 5-HT 1A receptor hypersensitivity develops after the social stress of defeat.

Prolonged estrogen-progesterone treatment of nonpregnant ovariectomized rats: factors stimulating home-cage and maternal aggression and short-latency maternal behavior

A 16-day treatment of nonpregnant, ovariectomized rats using 5-mm Silastic implants of estradiol (E), daily injections of 4 mg of progesterone (P), and terminal injections of 5 micrograms/kg of estradiol benzoate (EB) to provide a pregnancy-like pattern of hormone exposure, stimulates (a) home-cage aggression toward unfamiliar intruder rats, (b) short-latency maternal behavior when the females are exposed continuously to pups, and (c) maternal aggression after maternal care has been initiated. Preliminary experiments examined the persistence of stimulation of aggression by the 16-day treatment in the absence of exposure to pups eliciting maternal care, and whether an abbreviated, 1-week treatment stimulates aggression equally. Subsequent experiments examined the importance of the elements of the treatment (E implants, P injections, EB injection), and whether prolonging exposure to P or E would alter its behavioral effects. The full 16-day E/P/EB treatment stimulated higher levels of home-cage and maternal aggression, and shorter maternal behavior latencies than abbreviated and partial treatments. E in combination with P or EB significantly raised home-cage aggression, whereas P alone was without effect. Administering P for 2 additional days attenuated reductions in maternal behavior latencies by E/P/EB, but did not reduce home-cage or maternal aggressiveness. Continuous exposure to E throughout testing did not affect any dependent variable. Comparing these findings to earlier data and reports suggests that hormone exposure for 2 weeks or more, and provision of P levels approaching those of pregnancy are important to the effects of the E/P/EB treatment on aggression.

Effects of estrogen treatment on dominance relationships in cows

The effects of prolonged estrogen treatment were studied in two groups of eight ovariectomized heifers. In Group I, four animals were treated with increasing doses of estradiol benzoate (300 micrograms/day to 1.5 mg/day) for 180 days. In Group II, four animals were treated with 1.5 mg/day for 90 days. In each group the other four animals received the vehicle only. Ninety percent of the dominance relationships between treated and control animals was reversed. The delay was, nevertheless, longer than those observed previously following androgen treatment. As is the case following androgen treatment, changes in social rank could not be explained by an increase in aggressiveness by treated animals, but rather could be explained by a lowered reactivity to aggressions and perhaps by a decrease in fear reactions.

Dexamethasone can prevent stress-related litter deficits in the golden hamster

This study was designed to examine the effects of social subordination during early pregnancy in the golden hamster (Mesocricetus auratus). Primiparous females were mated to proven breeders and stressed during early pregnancy. Females were housed singly throughout gestation except for Days 4, 5, and 6 when they were paired for 10-min intervals three times each day with another female matched for age, weight, and day of pregnancy. Within each of the pairs, one female was consistently dominant to the other. Controls were exposed to a novel area instead of a conspecific. At parturition, all pups were counted, sexed, and weighed. There were no significant differences between control and dominant females' litter sizes and sex ratios. Subordinate females produced significantly smaller litters than control or dominant dams and significantly lower sex ratios than control dams. Subordinates produced fewer males than control or dominant dams, but there were no differences in the number of females produced. The entire experiment was repeated exactly except that females received a small dosage of dexamethasone in their drinking water on Days 3-7 of pregnancy. In this second group, there were no significant reductions in mean litter size, sex ratio, or pup weights among litters born to subordinate dams. These results suggest that subordinate dams produce smaller litters via selective resorption of males in utero and that the typical adrenal response to stress mediates this response.

Behavioral reactivity following 5-MeODMT administration in 5,7-DHT-pretreated killer rats

Grouped, nonkiller and killer animals were centrally injected either with vehicle or with 5,7-dihydroxytryptamine. After a period of 7-10 days, forepaw treading and hindlimb abduction were induced by 5-MeODMT administration in all sham and lesioned rats. As expected, behavioral supersensitivity was observed in grouped and nonkiller lesioned rats. A reduced increase in 5-MeODMT-induced behaviors was obtained in killer lesioned animals. 5-HT uptake studies showed a comparable reduction of 5-HT uptake within all the lesioned rats. This evidence suggests an altered capacity to promote adaptive changes on 5-HT sites in killer rats following the destruction of central serotonergic fibers.

The influence of an enkephalin derivative, DAGO, on the behavior and activity of neurons of the neocortex and hippocampus of rabbits during the development of defensive and inhibitory conditioned reflexes

After the administration of a morphine-like opiate, DAGO (D), in a dose of 250 micrograms/kg, a decrease was observed in the probability of movements of a rabbit in response to light flashes, the signal for a defensive reflex. The level of the background impulse activity of the neurons gradually decreased in the sensorimotor cortex and in the hippocampus, and did not change in the visual cortex. The decrease and the recovery of the responses of the neurons to the reinforcing stimulus (electrodermal stimulation of the limb) proceeded unidirectionally in all of the areas of the cortex studied, while there were substantial differences in the relationship to the cortical area studied and to the biological significance of the stimulus in the dynamics of the responses to the inhibitory and reinforced light flashes. The identification of the features of the systemic organization of the neurons during training with change in the properties of the reinforcement under the influence of the preparation under study is discussed, as well as the similarity of some features in the mechanisms of the development of internal inhibition in the defensive situation and of the properties of positive reinforcement.