Monoamine activity in anterior hypothalamus of guinea pig pups separated from their mothers.

Brief isolation in a novel environment increased the ratios of 3-methoxy-4-hydroxyphenylethylene glycol to norepinephrine (MHPG:NE) and dihydroxyphenylacetic acid to dopamine (DOPAC:DA) in the anterior hypothalamus of 44 guinea pig pups. Ratios were significantly elevated after 90 min of isolation and for MHPG:NE, after 30 min of isolation; changes were due to increases in MHPG and DOPAC. Home cage isolation produced no change in any measure of catecholamine activity. No changes in levels of serotonin or its metabolite were observed. In Exp 1, resting levels of NE and DOPAC:DA were predictive of the rate of separation-induced vocalization. Maternal separation in the context of novelty increases hypothalamic NE and DA activity; however, both isolation and novelty are required because neither maternal separation in the home cage nor exposure to a novel cage together with the mother had any discernible effect. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Central dopamine turnover in guinea pig pups during separation from their mothers in a novel environment.

Guinea pig pups that were separated from their mothers and placed into a novel environment for 90 min showed an increase in dopamine (DA) turnover (ratio of metabolites to DA) in the septum compared with undisturbed baseline controls. Pups placed into the novel environment with their mothers exhibited an intermediate level of DA turnover. After 24 hr of separation in the novel environment, pups' DA turnover in the septum had returned to the baseline level. DA turnover in the caudate nucleus was unaffected by these procedures. Also, turnover in both septum and caudate nucleus when pups were not separated was positively correlated with the number of vocalizations emitted during 30 min of separation. These results closely parallel findings in separated monkeys and indicate that the guinea pig represents a useful rodent model for studying such effects. That elevated DA turnover during separation occurred in the septum suggests involvement of the mesolimbic system. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Affiliative vocalizations in infant rhesus macaques (Macaca mulatta).

In Exp 1, infant rhesus monkeys were separated and then reunited with mothers, united with a male, or placed into an empty cage. Infants girned more when with mothers or the male than when alone. Girns declined over time when infants were united with the male. Coo rates were high when the infant was alone or with the male. Shrieks, barks, and fear-related behavior were higher with the male. In Exp 2, the vocalizations of infants were examined during separation when alone or when mothers or a male were in the same room. Infants cooed more when mothers or a male were present. Cooing increased over time, with a greater increase in the mothers' presence. Girns were given to both mothers and males, but more were given to mothers. Coos and girns are both affiliative vocalizations but are differentially modulated as infants cease cooing when they receive contact comfort. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Nonedible material elicits chewing and reduces the plasma corticosterone response during novelty exposure in mice.

Mice placed into novel cages showed elevations of plasma levels of corticosterone. This response was of greater magnitude when the more novel of two cages was used. When mice had a piece of aluminum foil or cardboard available in the novel cages, they avidly chewed these substances. In the high novelty cage, the presence of either foil or cardboard reduced the magnitude of the plasma corticosterone response at 30 and 60 min. Mice exposed to novel cages for 30 min on each of 6 consecutive days showed a decline in chewing across days, although chewing still occurred during the last exposure. The plasma corticosterone response increased from the first to the sixth day of exposure, although the availability of foil in the high novelty cage reduced this response across days. The availability of a highly palatable food (peanut butter chips) evoked little chewing in the high novelty cage and had no effect on the plasma corticosterone response at 60 min. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Proinflammatory activity and the sensitization of depressive-like behavior during maternal separation.

When guinea pig pups are isolated for a few hours in a novel environment, they exhibit a distinctive passive behavioral response that appears to be mediated by proinflammatory activity. Recently, we observed that pups separated on two consecutive days show an enhanced (sensitized) passive response on the second day. In Experiment 1, pups receiving intracerebroventricular infusion of 50 ng of the anti-inflammatory cytokine interleukin-10 prior to a first separation failed to show a sensitized behavioral response to separation the next day. In Experiment 2, pups separated on Days 1 and 2, or just 2, showed an increase in passive responding during separation on Day 5. Pups injected with the bacterial antigen lipopolysacchride (LPS; 75 μg/kg body weight, intraperitoneal) prior to separation on Day 1 showed an increase in passive behavior several days later not shown by pups injected with saline prior to Day 1 separation. However, injection of LPS without separation on the first day did not enhance responding during an initial separation on the second day. These results suggest that immune activation is necessary, but not sufficient, to account for the sensitization of passive behavior of isolated guinea pig pups the following day, that boosting proinflammatory activity during an initial separation may promote sensitization several days later, and that the sensitized response persists for at least several days. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Development of selective social buffering of the plasma cortisol response in laboratory-reared male guinea pigs (Cavia porcellus).

The authors examined the effect of different classes of females on the plasma cortisol response of male guinea pigs (Cavia porcellus) from shortly after weaning through full adulthood. Males housed under standard laboratory conditions with artificial harems of 2 unrelated females of similar age were tested at 4 age ranges (~Days 40, 120, 180, and 240). At each age range, males were placed into a novel environment for 2 hr on 4 separate occasions: while alone, with 1 female cage mate, with the other female cage mate, or with an unfamiliar female. Relative preference for the 2 female cage mates was determined from observations in the home cage. Puberty was estimated by plasma testosterone levels. At the 3 youngest ages, the more preferred, less preferred, and unfamiliar females did not differentially reduce the plasma cortisol response. At 240 days of age, only the presence of the more preferred female was able to significantly reduce cortisol levels. These results demonstrate a very selective social buffering effect on the plasma cortisol response in a nonmonogamous species. This effect emerges well after sexual maturity and can be observed under standard laboratory housing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Intermale fighting affected by home-cage odors of male and female mice.

Conducted 3 experiments to test the hypothesis that male mice can produce an aggression-inhibitory or facilitory odor under varying conditions of social stimulation. In Exp I, 25 male fighter mice fought 25 castrated opponents more vigorously in soiled home cages of either single or stable groups of male mice than they did in clean cages. Fighting was also stimulated in cages briefly occupied by other pairs of fighting mice. It is concluded that the release of aggression-promoting home-cage odors by male mice is not necessarily a consequence of social instability and that they are of urinary, rather than preputial, origin. In Exp II (with 21 fresh Ss) and Exp. III (with 30 Ss from Exp I), odors deposited by either single or groups of female mice greatly reduced fighting, indicating that their urinary aggression-inhibiting pheromone is effective after deposition upon the home environment. Testosterone propionate implants abolished the females' inhibitory pheromone and did so independently of their enlarged preputial glands. (20 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Behavioral and hormonal responses to separation in infant rhesus monkeys and mothers.

Examined the effects of social stimuli on behavioral and physiological responses in 9 infant rhesus monkeys, 8 Ss at 4–6 mo (Exp I) and 7 of the original Ss and an additional S at age 8–10 mo (Exp II). Infants and mothers were removed from the social group and housed as dyads. Following this period, infants were removed and separated under 4 counterbalanced conditions: (a) totally isolated—placed in a holding cage for 24 hrs; (b) mother present, no contact—housed in a single cage in view of their mother, no contact; (c) mother present, contact—similar to above, with mother in proximity to the infant; and (d) peer present—separated but in proximity to a peer. In Exp I, infants rarely vocalized when totally isolated but showed high rates of vocalization in the presence of the mother, both with and without contact. In the mother-present conditions, they failed to show a plasma cortisol response. In contrast, totally isolated infants showed a significant elevation in plasma cortisol. In Exp II, these infants were separated for 3 days under 2 conditions: mother present and totally isolated. Results support and extend the findings of Exp I, indicating that age was not a factor in modulating response to separation. (20 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Behavioral and physiological responses to maternal separation in squirrel monkeys (Saimiri sciureus).

This study extends an examination of the behavioral and pituitary-adrenal responses of infant squirrel monkeys (Saimiri sciureus) separated from their mothers under different environmental conditions to another physiological system by measuring the metabolites of the central monoamines found in the cerebrospinal fluid (CSF). This study included spectrographic examination of the vocalizations emitted by the infant during separation. Infants were separated from their mothers for 24 hr under 3 conditions: Home, infant remained in his home cage after removal of mother; adjacent, infant was placed in a cage adjacent to its mother; and total, infant was totally isolated. The behavioral results indicated that the number of calls emitted differed with condition (adjacent?>?total?>?home), and the peak frequency of the calls and number of multiple calls was greatest in the total condition. Plasma cortisol elevations after separation differentiated the conditions of separation (total?>?adjacent?>?home?>?base). The elevations in the CSF catecholamine metabolites (3-methoxy-4-hydroxyphenylglycol and homovanillic acid) were also sensitive to the conditions of separation (total?>?adjacent?>?base). These results are discussed in the context of coping theory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Mother-infant separation in the java monkey (Macaca irus).

Studied the behavior of 8 7-8 mo. old Java monkeys separated from their mothers and reunited after 3 wk. Infant playing and related behaviors decreased during separation. Presence of a conspecific unfamiliar adult female mother-substitute did not alleviate the debilitating effects of separation. During reunion, Ss responded differentially to their own mothers regardless of whether they were returned to original or spatially-reoriented home cages. Most behaviors returned to preseparation levels, but the mother-infant relationship was intensified. Separation effects were not attributable to traumatic forceful removal of mothers, since 4 controls separated and immediately returned were minimally affected. Species differences in reaction to maternal separation are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Responses of virgin mice, and of maternal females, to normal and caesarian-section delivered pups.

Conducted 2 experiments in which Porton strain mouse pups were presented to a total of 100 male and female adult Porton mice. Significantly more mothers and virgin females retrieved pups to the nest than did virgin males. More virgin females than males licked pups, built nests, and assumed lactation posture. Differences were significant even if males that attacked pups were excluded from consideration. Latencies to 1st appearance of maternal activities were higher than reported by most other workers. Possible genetic strain differences in the response of virgin mice to pups are discussed. In Exp II pups delivered by caesarian section with placentas attached were used. More mothers than either virgin males or females cleaned and accepted pups, indicating that pup cleaning may be controlled by factors different from those influencing other maternal activities. (17 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of 6-hydroxydopamine lesions of the nucleus accumbens septi and olfactory tubercle on feeding, locomotor activity, and amphetamine anorexia in the rat.

In Exp I with 24 male albino Wistar rats, bilateral 6-hydroxydopamine lesions of the nucleus accumbens septi (NAS) and olfactory tubercle (OT) caused enhanced intake of wet mash in 23-hr-food-deprived Ss tested in photocell activity cages during restricted 30-min sessions. This mild hyperphagia was accompanied by a significant hypoactivity in the group with NAS/OT lesions. No hyperphagia was observed during a prolonged 120-min test session or in free-feeding tests conducted in the home cage. Anorexia induced by dextroamphetamine (.5 and 1.5 mg/kg) was unaltered by the lesion, although the locomotor stimulant action of the drug was attenuated. Results of Exp II, with 36 Ss, show that the NAS/OT lesion also enhanced food intake in the photocell cages during 30-min sessions with dry food pellets but that food-associated drinking was concomitantly reduced. Results are consistent with the hypothesis that the behavioral changes caused by mesolimbic neuron destruction result in part from an inability to switch from one behavioral activity to another. (29 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

An investigation of the effects of maternal separation and novelty on central mechanisms mediating pituitary-adrenal activity in infant guinea pigs (Cavia porcellus).

In mammalian species in which the young exhibit a strong filial attachment (e.g., monkeys, guinea pigs), numerous studies have shown that even brief separation from the attachment figure potently elevates circulating concentrations of glucocorticoids and adrenocorticotropic hormone (ACTH). However, effects of separation on central regulation of this stress response are not known. Therefore, we investigated central mechanisms mediating pituitary-adrenal activation during maternal separation and novelty exposure in guinea pig (Cavia porcellus) pups. Corticotropin-releasing factor (CRF) mRNA expression in the hypothalamic paraventricular nucleus (PVN), and plasma cortisol and ACTH levels, were elevated only during separation in a novel environment. C-Fos activity was elevated in the medial amygdala (MeA) and reduced in the bed nucleus of the stria terminalis (BNST) during novelty exposure, regardless of separation. On the other hand, c-Fos activity was elevated in the PVN during separation, regardless of novelty exposure. These results demonstrate independent and combined effects of separation and novelty in regions of the guinea pig CNS that regulate pituitary-adrenal activity. Moreover, they suggest that a pathway from MeA to BNST to PVN mediates responses to novelty in the guinea pig pup, as in the adult rat, though inputs from other cell populations appear required to fully account for the HPA activity observed here. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sensory control of maternal aggression in Rattus norvegicus..

Three experiments, with nulliparous Wistar rats, investigated the effects of restricted pup exposure and male exposure on maternal aggression and the incidence of olfactory exploration of an intruder by the mother rat. It was found that a decline in maternal aggression occurred when the litter was placed in a glass flask while remaining in the home cage. In contrast, maternal aggression persisted following placement of the pups in a nylon mesh bag. The pups did not vocalize while in the mesh bags, suggesting that olfactory cues from the offspring constitute a critical element in the maintenance of maternal aggression in the rat. It has been suggested that the odor not only of the pups but also of the intruder may contribute to eliciting aggressive behavior in lactating rodents. In line with this proposal, it was found that mother rats spent about one-third of the time preceding the 1st attack sniffing the body of the intruder. In contrast to findings in mice, housing of the prospective intruder behind a double wire mesh partition in the lactating female's home cage failed to reduce her aggressiveness toward him. Rats may require more intimate contact with an individual than do mice for the aggression-reducing effect of familiarization to be observed. (30 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Ultrasonic vocalizations are elicited from rat pups in the home cage by pentylenetetrazol and U50,488, but not naltrexone.

Although isolated rat pups emit ultrasonic vocalizations (USVs), those kept warm and undisturbed in the home cage with their littermates seldom do. Drugs were administered to 10-day-old Wistar rat pups in the home cage to determine whether pharmacological agents can elicit USVs in this familiar environment. Ss were injected with U50,488, a highly selective kappa opioid agonist; pentylenetetrazol (PTZ), an anxiogenic drug that binds at the GABA-benzodiazepine receptor complex; or naltrexone (NLX), an opiate receptor blocker, and then were returned to their littermates in the home cage. U50,488 increased USV and activity levels, lowered body temperature, and disrupted contact with littermates. PTZ raised activity levels but had a smaller effect on vocalization rates and did not alter temperature or contact with littermates. Behavioral measures and body temperature were unchanged by NLX. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Potentiation of isolation-induced vocalization by brief exposure of rat pups to maternal cues

Since their discovery in 1956, the highest rates of ultrasonic vocalization (USV) have been recorded from infant rats when first isolated in an unfamiliar place. We now report that peak USV rates can be doubled by allowing test pups a brief initial period of contact with their anesthetized dam (1-10 min) in the test chamber before isolating the pup by her removal. Potentiation of the isolation response was specific to the dam, for it failed to occur following initial contact with a group of 4 warm, anesthetized littermates. Control experiments showed that potentiation could not be attributed to thermal contrast, experimenter handling, general behavioral activation, novelty of maternal cues, or nursing deprivation. Furthermore, it did not occur when pups were taken for isolation testing directly from prolonged contact with their anesthetized dam in the home cage. Potentiation may be understood in terms of the communicative role of the pups' call and/or prior learning contingencies within the mother-infant interaction.     

Ingestion of a novel flavor before exposure to pups injected with lithium chloride produces a taste aversion in mother rats (Rattus norvegicus).

A series of experiments investigated the ability of Sprague-Dawley mother rats to learn aversions to novel flavors ingested prior to the illness of their pups. In Exp I, 24 mothers learned to avoid a novel flavored solution ingested prior to the illness of their nursing litters. Exp II was designed to investigate the extent to which any adult rat is capable of such learning: 16 nonlactating multiparous females learned aversions to novel flavors ingested prior to exposure to pups injected with LiCl, whereas 16 nonlactating nulliparous females and 16 males did not learn these aversions. Several possible reasons for differences in this learning ability are discussed. In Exps III and IV, the nature of the UCS for these aversions was investigated. Visual, auditory, and taste cues associated with the lithium-injected pups did not mediate the aversions. Evidence suggests that olfactory characteristics of the lithium-injected pups mediated the flavor aversions in the present experiments. These olfactory cues did not appear to be general stress signals but instead were likely specific cues for gastrointestinal discomfort. Results are discussed in terms of classical conditioning and also of their adaptive significance for both mother and offspring. (63 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Odor modulation of ventral scent gland marking in the Mongolian gerbil.

In an experiment with 18 male and 18 female Mongolian gerbils, gerbil odors were allowed to accumulate in individual home cages for several months to provide stable olfactory stimuli that might modulate the number of ventral scent gland marks produced by the Ss. Male marking levels for most test conditions were 2–3 times larger than those in females, although, the relative patterns of responsiveness to particular odors were similar in both sexes. The number of scent marks in home cages was significantly smaller than the number obtained in clean cages. Marking levels in the home cages of other Ss were substantially higher than those seen in the test S's own cage and were maximal in the home cages of other males. Behaviorally receptive females marked at significantly higher levels in home, clean, and conspecific cages than did nonreceptive females. Conspecific urine odors, especially those from females, increased marking levels significantly over those obtained in home cages. In males, home cage marking was significantly enhanced by the presence of a female. Both sexes showed significant reductions in marking levels in another's cage if the resident was present. Results suggest that scent-marking like other olfactory guided behaviors and odor preferences, is context-specific. (36 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Evidence for a transitional period for development of persistence in infant rats.

Conducted 4 experiments with a total of 188 rat pups to test the hypothesis that rat pups can learn persistence at age 11 days but cannot express this learning in their behavior until they are a few days older. Exp I used a space-trial procedure to investigate the relative reinforcing effects of milk suckling, dry suckling, and contact without suckling at ages 11 and 14 days. Exp II used the Exp I procedure, manipulating schedule of reward at 2 ages and under 2 of the reward conditions. Exp III manipulated the dry suckling reward schedule in 11- and 14-day-old pups. Exp IV manipulated partial and continuous reinforcement on Day 11 but tested for persistence on Day 14. Results suggest the existence of a traditional period in neonatal rats for the learning of persistence. Partial reinforcement training with suckling on an anesthetized dam as reward induced greater persistence in extinction of the approach response than did continuous reinforcement in rat pups 14 days old but not in 11-day-old pups. Other aspects of this period of development are discussed. (26 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Role of the infraorbital nerve in retrieving behavior in lactating rats.

Studied the acute effect of perioral anesthesia on retrieval of pups in primiparous Wistar rats. Injecting lidocaine into the mystacial pads of Ss rendered the snout insensitive to touch and abolished Ss' ability to retrieve. In Exp I, injecting the drug into masseter muscles or ip did not render the snout anaptic or abolish retrieval, indicating that the effect of intramystacial lidocaine treatment could not be attributed to systemic toxicity or to the drug's spreading from mystacial pads to affect masseter muscles. In Exp II, cutting the infraorbital nerves produced temporary retrieval impairment that was indistinguishable from that produced by intramystacial lidocaine. The deficit was not due to postoperative debilitation. Infraorbital section did not interfere with the ability to locate and consume a piece of cheese. Cutting the facial nerves abolished vibrissal movement but did not disrupt retrieval. In Exp III, the possibility was tested that infraorbital deafferentation has a profound effect on retrieval because anaptic dams, in their initial attempts at picking up pups, elicit distress vocalizations from offspring. Ss injected with lidocaine in the mystacial pads failed to retrieve pups that had been anesthetized to abolish distress vocalizations. Thus, pup-produced vocalizations are not responsible for the retrieval impairment exhibited by anaptic mothers. (33 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)