H. Elliott Albers

The regulation of social recognition, social communication and aggression: Vasopressin in the social behavior neural network

Neuropeptides in the arginine vasotocin/arginine vasopressin (AVT/AVP) family play a major role in the regulation of social behavior by their actions in the brain. In mammals, AVP is found within a circuit of recriprocally connected limbic structures that form the social behavior neural network. This review examines the role played by AVP within this network in controlling social processes that are critical for the formation and maintenance of social relationships: social recognition, social communication and aggression. Studies in a number of mammalian species indicate that AVP and AVP V1a receptors are ideally suited to regulate the expression of social processes because of their plasticity in response to factors that influence social behavior. The pattern of AVP innervation and V1a receptors across the social behavior neural network may determine the potential range and intensity of social responses that individuals display in different social situations. Although fundamental information on how social behavior is wired in the brain is still lacking, it is clear that different social behaviors can be influenced by the actions of AVP in the same region of the network and that AVP can act within multiple regions of this network to regulate the expression of individual social behaviors. The existing data suggest that AVP can influence social behavior by modulating the interpretation of sensory information, by influencing decision making and by triggering complex motor outputs. This article is part of a Special Issue entitled Oxytocin, Vasopressin, and Social Behavior.

Neuropeptide Y microinjected into the suprachiasmatic region phase shifts circadian rhythms in constant darkness.

The geniculohypothalamic tract (GHT) is a projection from the intergeniculate leaflet to the suprachiasmatic nucleus (SCN). The GHT exhibits neuropeptide Y (NPY) immunoreactivity and appears to communicate photic information to the SCN. Microinjection of NPY into the SCN has been found to phase shift circadian rhythms of hamsters housed in constant light in a manner similar to the phase shifts produced by pulses of darkness or triazolam injections. In the present study, NPY was injected into the SCN of Syrian hamsters housed in constant darkness and was found to produce phase shifts similar to those seen in hamsters housed in constant light. Microinjections were not followed by wheel running during the subjective day (the time when NPY microinjections are followed by significant phase advances). These data suggest that NPY produces phase shifts by some mechanism other than by inducing wheel running or by inhibiting the response of SCN neurons to light and supports a role for NPY in nonphotic shifting of the circadian clock.

Scent marking and the maintenance of dominant/subordinate status in male golden hamsters.

Since it is thought that flank marking communicates dominance status, experiments were designed to look at changes in aggression and flank marking behaviors in pairs of male hamsters with intact flank glands (Experiment One) or when one (Experiment Two) or both (Experiment Three) members of a pair had their flank glands surgically removed. In Experiment One the dominant members of twelve pairs of hamsters had a mean daily frequency of flank marks that was over two-fold greater than their subordinate partners, F(1,11) = 17.59, p less than 0.001. Over the course of five consecutive daily tests there was a significant decrease in the aggression index of both the dominant, t(44) = 4.49, p less than 0.01, and subordinate, t(44) = 3.33, p less than 0.01, hamsters. Accompanying the decrease in aggression was a significant increase in the flank marking of both dominant, t(44) = 7.8, p less than 0.01, and subordinate, t(44) = 3.59, p less than 0.01, hamsters. In Experiment Two, six out of eleven flank glandectomized hamsters were dominant over their sham operated partners while the remaining five were subordinate. Unlike Experiment One there was no significant difference in the flank marking between dominant and subordinate hamsters, in fact, in seven pairs the subordinate hamsters flank marked more than their dominant partners. In Experiment Three both hamsters had their flank glands removed, and as in Experiment Two, there was no significant difference in flank marking between dominant and subordinate hamsters, neither was there any significant change in their aggression and flank marking behaviors over the course of the five test periods.(ABSTRACT TRUNCATED AT 250 WORDS)

Distribution of hypocretin-(orexin) immunoreactivity in the central nervous system of Syrian hamsters (Mesocricetus auratus).

The hypocretins are peptides synthesized in neurons of the hypothalamus. Recent studies have suggested a role for these peptides in the regulation of sleep, feeding, and endocrine regulation. The distribution of hypocretin-immunoreactive cell bodies and fibers has been extensively described in rats, but not in other species. This study was designed to examine the distribution of hypocretin immunoreactivity in Syrian hamsters, as important differences in neuropeptide distribution between rats and hamsters have previously been demonstrated. Immunoreactive cell bodies were found primarily in the lateral hypothalamic area and the perifornical area, although a few hypocretin-positive cells were also located in the dorsomedial hypothalamus and the retrochiasmatic area. Fibers were distributed throughout the brain in a pattern similar to that seen in rats. The densest projections were found in the paraventricular nucleus of the thalamus, locus coeruleus, dorsal raphe, and lateroanterior hypothalamus. The innervation of the anterior hypothalamus may be of particular interest as similar cluster of immunoreactivity does not appear to be present in rats. Moderate levels of immunoreactivity could be seen throughout the hypothalamus, the lateral septum, bed nucleus of the stria terminalis, A5 noradrenergic area, and the midline thalamic nuclei. Hypocretin-immunoreactive fibers are present in all lamina of the spinal cord, with the greatest axon densities in lamina 1 and 10. The widespread distribution of hypocretin suggests its involvement in a wide variety of physiological and behavioral processes. Our results in hamsters indicate that the organization of the hypocretin system is strongly conserved across species, suggesting an important role for the peptide and its projections.

Microinjection of NMDA into the SCN region mimics the phase shifting effect of light in hamsters

Although there is considerable data that glutamate is the primary transducer of photic information to the circadian clock in the suprachiasmatic nucleus (SCN), the ability of glutamate to mimic the phase-shifting effects of light has yet to be demonstrated in vivo. In the present study, microinjections of the glutamate agonist NMDA directly into the SCN of Syrian hamsters induced significant phase delays at circadian time (CT) 13.5 and phase advances at CT 19. These results support the hypothesis that glutamate is the primary neurotransmitter responsible for the transduction of photic information to the SCN.

6 – Hormonal Basis of Social Conflict and Communication

Publisher Summary There is a substantial body of data on the interactions among hormones, reproductive behavior, and communicative behavior. However, significantly less is known about how hormones regulate social conflict and the communicative behaviors that are involved in influencing social relationships This chapter focuses on the hormonal regulation of social conflict and communication in Syrian (sometimes called golden) hamsters. Social behavior and its hormonal regulation have been studied in Syrian hamsters since the 1950s. Unlike many other species, both male and female hamsters are highly aggressive, and the behaviors engaged in during social conflict are readily observable and easily quantified. The severity of these encounters (in terms of bites or tissue damage) is usually quite low, and dominance relationships are often formed with relatively little overt aggression. These relationships are usually established very rapidly and remain stable over time. Hamsters also exhibit a variety of communicative behaviors that are easily quantified and that have been investigated extensively. As such, hamsters represent a comparatively simple animal model for the study of social conflict and communication.

Vasopressin (V1a) receptor binding, mRNA expression and transcriptional regulation by androgen in the Syrian hamster brain.

Arginine vasopressin plays an important role in the regulation of social behaviours in rodents. In the Syrian hamster, vasopressin injected directly into the brain stimulates scent marking and aggressive behaviour in a steroid dependent manner and is therefore a useful model for investigating steroid‐peptide–behaviour interactions. In this study, we used in situ hybridization and radioligand binding assays on adjacent sections of hamster brains to compare the relative distribution of vasopressin (V1a) receptor mRNA and V1a receptor binding. V1a receptor mRNA and binding are abundant in the lateral septum, bed nucleus of the stria terminalis, medial preoptic nucleus, anterodorsal thalamus and suprachiasmatic nucleus. Moderate receptor binding and low levels of receptor mRNA are present in the central nucleus of the amygdala and a lateral zone from the medial preoptic area through the anterior hypothalamus. V1a receptor mRNA is anatomically more restricted in several areas compared to the ligand binding pattern, which is consistent with significant spread of receptor protein along neuronal processes. Comparison of V1a receptor ligand binding and mRNA in intact, castrated, and castrated‐testosterone treated animals reveals that V1a receptors in the medial preoptic nucleus are regulated by androgen, most likely by an upregulation of V1a receptor gene expression in a cluster of neurones concentrated in the ventromedial part of this nucleus. This study confirms the presence of the V1a subtype of vasopressin receptors in behaviourally important regions of the hamster brain and suggests that transcriptional regulation by gonadal steroids may play a role in modulating behavioural sensitivity to vasopressin.

Inhibition of vasopressin-stimulated flank marking behavior by V1-receptor antagonists

Flank marking, a form of olfactory communication displayed by hamsters, is dependent upon vasopressin-sensitive neurons in the anterior hypothalamus. In the present study two vasopressin type-1 (V1) receptor antagonists, d(CH2)5Tyr(Me)AVP and dPTyr(Me)AVP were tested for their ability to block flank marking stimulated by the microinjection of arginine vasopressin (AVP) into the anterior hypothalamus. Dose-response curves were established for AVP and flank marking in the presence or absence of different concentrations of each antagonist. DPTyr(Me)AVP was microinjected into the anterior hypothalamus 1 h before the microinjection of AVP while d(CH2)5Tyr(Me)AVP and AVP were prepared together and delivered as a single microinjection. This procedure was necessary because dPTyr(Me)AVP, but not d(CH2)5Tyr(Me)AVP, had agonist activity when initially injected into the anterior hypothalamus in concentrations ranging from 0.90-900 microM. The ED50 values (microM) for dPTyr(Me)AVP and AVP were 17.9 and 0.90, respectively. The initial agonist activity of dPTyr(Me)AVP was always followed by blocker activity. Both V1-receptor antagonists caused a dose-dependent decrease in AVP-stimulated flank marking. Maximal inhibition of AVP-stimulated flank marking was produced with approximately 1.0 mM of either antagonist. Both antagonists blocked AVP-stimulated flank marking behavior for over 12 h following their microinjection.

Role of vasopressin and oxytocin in the control of social behavior in Syrian hamsters(Mesocricetus auratus

Vasopressin (VP) and oxytocin (OT) play an important role in regulating social behavior in a variety of species as a result of their actions in the central nervous system. The following paper reviews the actions of VP and OT in controlling a range of social behaviors involved in communication, aggression and reproduction in the Syrian hamster. These data suggest that social and hormonal stimuli alter the expression of specific social behaviors by altering the release of, or the response to, VP and OT within key elements of the neural circuits controlling these behaviors.

Role of the suprachiasmatic nuclei in the circadian timing system of the squirrel monkey. I. The generation of rhythmicity

The circadian organization of squirrel monkey (Saimiri sciureus) drinking behavior was evaluated before and after the placement of radiofrequency lesions which completely destroyed the suprachiasmatic nuclei (SCN) in 4 monkeys and partially ablated the SCN in another 4 animals. In continuous illumination (LL: 600 lux) prior to surgery, each monkey had a precise free-running circadian rhythm of drinking behavior with a period of 25.31 +/- 0.21 h (means +/- S.E.M.). By 4-6 weeks following the lesions, the temporal organization of drinking behavior had become disrupted, but a statistically significant free-running circadian rhythm was still detectable by time series analyses. Subsequently, the circadian organization of drinking behavior in 7 out of 8 monkeys gradually decayed with either no statistically significant rhythmicity or only weak circadian and/or ultradian rhythmicity detected by time series analyses by 10-92 weeks post-lesion. The remaining animal which maintained a statistically reliable free-running rhythm in drinking behavior received the least damage (less than 50%) to the SCN. Despite the major alterations in the temporal patterning of behavior, the overall amount of drinking behavior per 24 h was unchanged. The SCN are thus essential for maintaining the circadian organization of squirrel monkey drinking behavior. However, the existence of residual circadian rhythmicity following SCN lesions and the gradual decay of circadian organization thereafter suggest that the SCN may coordinate the activity of circadian oscillators which lie outside its borders.