Role of the paleostriatum in species-typical display behavior of the lizard (Anolis carolinensis)

Neural control of reproduction in reptiles

Reptiles display considerable diversity in reproductive behavior, making them great models to study the neuroendocrine control of reproductive behavior. Many reptile species are seasonally breeding, such that they become reproductively active during their breeding season and regress to a nonreproductive state during their nonbreeding season, with this transition often prompted by environmental cues. In this review, we will focus on summarizing the neural and neuroendocrine mechanisms controlling reproductive behavior. Three major areas of the brain are involved in reproductive behavior: the preoptic area (POA), amygdala, and ventromedial hypothalamus (VMH). The POA and VMH are sexually dimorphic areas, regulating behaviors in males and females respectively, and all three areas display seasonal plasticity. Lesions to these areas disrupt the onset and maintenance of reproductive behaviors, but the exact roles of these regions vary between sexes and species. Different hormones influence these regions to elicit seasonal transitions. Circulating testosterone (T) and estradiol (E2) peak during the breeding season and their influence on reproduction is well-documented across vertebrates. The conversion of T into E2 and 5α-dihydrotestosterone can also affect behavior. Melatonin and corticosterone have generally inhibitory effects on reproductive behavior, while serotonin and other neurohormones seem to stimulate it. In general, there is relatively little information on the neuroendocrine control of reproduction in reptiles compared to other vertebrate groups. This review highlights areas that should be considered for future areas of research.

Dynamic influences on the neural encoding of social valence

Social signals can serve as potent emotional triggers with powerful impacts on processes from cognition to valence processing. How are social signals dynamically and flexibly associated with positive or negative valence? How do our past social experiences and present social standing shape our motivation to seek or avoid social contact? We discuss a model in which social attributes, social history, social memory, social rank and social isolation can flexibly influence valence assignment to social stimuli, termed here as 'social valence'. We emphasize how the brain encodes each of these four factors and highlight the neural circuits and mechanisms that play a part in the perception of social attributes, social memory and social rank, as well as how these factors affect valence systems associated with social stimuli. We highlight the impact of social isolation, dissecting the neural and behavioural mechanisms that mediate the effects of acute versus prolonged periods of social isolation. Importantly, we discuss conceptual models that may account for the potential shift in valence of social stimuli from positive to negative as the period of isolation extends in time. Collectively, this Review identifies factors that control the formation and attribution of social valence - integrating diverse areas of research and emphasizing their unique contributions to the categorization of social stimuli as positive or negative.

Neural systems that facilitate the representation of social rank

Across species, animals organize into social dominance hierarchies that serve to decrease aggression and facilitate survival of the group. Neuroscientists have adopted several model organisms to study dominance hierarchies in the laboratory setting, including fish, reptiles, rodents and primates. We review recent literature across species that sheds light onto how the brain represents social rank to guide socially appropriate behaviour within a dominance hierarchy. First, we discuss how the brain responds to social status signals. Then, we discuss social approach and avoidance learning mechanisms that we propose could drive rank-appropriate behaviour. Lastly, we discuss how the brain represents memories of individuals (social memory) and how this may support the maintenance of unique individual relationships within a social group. This article is part of the theme issue 'The centennial of the pecking order: current state and future prospects for the study of dominance hierarchies'.

Hurricane Irma induces divergent behavioral and hormonal impacts on an urban and forest population of invasive Anolis lizards: evidence for an urban resilience hypothesis

Hurricanes can have both profound short-term effects on animal populations and serve as long-term drivers of evolutionary change. Animals inhabiting varying habitats may differ in their response to hurricane impacts. Increasing evidence suggests that animals from urban areas exhibit different behavioral and physiological traits compared to rural counterparts, including attenuated hormonal stress responses and a lowered propensity for flight behavior. A unique opportunity was presented when Hurricane Irma hit Florida on 10 September 2017 and interrupted a study of invasive brown anoles (Anolis sagrei) at an urban and a forest. Using data collected before and after Hurricane Irma, we documented that forest anoles exhibited a greater avoidance of people and more male territorial behavior for a longer period of time following the hurricane. Post-hurricane both populations increased corticosterone concentrations post-capture stress, but urban anoles recovered 2 weeks faster than forest conspecifics. A dexamethasone suppression experiment suggested that these population differences were the result of forest anoles having a less effective negative feedback regulating corticosterone secretion. In the brain, forest anoles had higher corticosterone concentrations within the amygdala and parts of the cortex associated with stress than urban lizards. One explanation may be Hurricane Irma brought flooding and debris that altered the landscape leading to behavioral instability, and urban lizards already exhibited ecological adjustments that permitted a more rapid recovery (i.e. the ‘urban resilience’ hypothesis). Testing if urban animals are more resilient to natural disasters can inform conservationists interested in understanding their role in facilitating invasive species expansion and what their increasing presence may indicate for animal populations.

Putting the "Biology" Back into "Neurobiology": The Strength of Diversity in Animal Model Systems for Neuroscience Research

Current trends in neuroscience research have moved toward a reliance on rodent animal models to study most aspects of brain function. Such laboratory-reared animals are highly inbred, have been disengaged from their natural environments for generations and appear to be of limited predictive value for successful clinical outcomes. In this Perspective article, we argue that research on a rich diversity of animal model systems is fundamental to new discoveries in evolutionarily conserved core physiological and molecular mechanisms that are the foundation of human brain function. Analysis of neural circuits across phyla will reveal general computational solutions that form the basis for adaptive behavioral responses. Further, we stress that development of ethoexperimental approaches to improve our understanding of behavioral nuance will help to realign our research strategies with therapeutic goals and improve the translational validity of specific animal models. Finally, we suggest that neuroscience has a role in environmental conservation of habitat and fauna that will preserve and protect the ecological settings that drive species-specific behavioral adaptations. A rich biodiversity will enhance our understanding of human brain function and lead in unpredicted directions for development of therapeutic treatments for neurological disorders.

The scientific contributions of Paul D. MacLean (1913-2007)

Paul D. MacLean, a leading brain scientist of the 20th century, died on December 26, 2007. We review his life as a scientist and highlight some of his most important research contributions.

Steroid hormones alter neuroanatomy and aggression independently in the tree lizard

Steroid hormones effect changes in both neuroanatomy and aggressive behavior in animals of various taxa. However, whether changes in neuroanatomy directly underlie changes in aggression is unknown. We investigate this relationship among steroid hormones, neuroanatomy, and aggression in a free-living vertebrate with a relatively simple nervous system, the tree lizard (Urosaurus ornatus). Weiss and Moore [1] manipulated testosterone and progesterone levels in adult male tree lizards and found that both hormones facilitated aggressive behavior toward a conspecific. In this study, we examined the brains of a subset of these animals to determine whether changes in limbic morphology were associated with hormone-induced changes in aggressive behavior. Specifically, we tested the hypothesis that testosterone and/or progesterone cause changes in neural morphology that are necessary for the expression of testosterone's effects on aggressive behavior. We found that both hormones increased aggression; however, only testosterone induced changes in neuroanatomy. Testosterone increased the size of both the amygdala and nucleus sphericus. However, we could detect no individual correlations between neuroanatomy and aggression levels suggesting that the observed large-scale changes in neuroanatomy are not precisely reflective of changes in mechanisms underlying aggression.

Social experience organizes parallel networks in sensory and limbic forebrain

Successful social behavior can directly influence an individual's reproductive success. Therefore, many organisms readily modify social behavior based on past experience. The neural changes induced by social experience, however, remain to be fully elucidated. We hypothesize that social modulation of neural systems not only occurs at the level of individual nuclei, but also of functional networks, and their relationships with behavior. We used the green anole lizard (Anolis carolinensis), which displays stereotyped, visually triggered social behaviors particularly suitable for comparisons of multiple functional networks in a social context, to test whether repeated aggressive interactions modify behavior and metabolic activity in limbic-hypothalamic and sensory forebrain regions, assessed by quantitative cytochrome oxidase (a slowly accumulating endogenous metabolic marker) histochemistry. We found that aggressive interactions potentiate aggressive behavior, induce changes in activities of individual nuclei, and organize context-specific functional neural networks. Surprisingly, this experiential effect is not only present in a limbic-hypothalamic network, but also extends to a sensory forebrain network directly relevant to the behavioral expression. Our results suggest that social experience modulates organisms' social behavior via modifying sensory and limbic neural systems in parallel both at the levels of individual regions and networks, potentially biasing perceptual as well as limbic processing.

Steroid hormone mediation of limbic brain plasticity and aggression in free-living tree lizards, Urosaurus ornatus

The neural mechanisms by which steroid hormones regulate aggression are unclear. Although testosterone and its metabolites are involved in both the regulation of aggression and the maintenance of neural morphology, it is unknown whether these changes are functionally related. We addressed the hypothesis that parallel changes in steroid levels and brain volumes are involved in the regulation of adult aggression. We examined the relationships between seasonal hormone changes, aggressive behavior, and the volumes of limbic brain regions in free-living male and female tree lizards (Urosaurus ornatus). The brain nuclei that we examined included the lateral septum (LS), preoptic area (POA), amygdala (AMY), and ventromedial hypothalamus (VMH). We showed that the volumes of the POA and AMY in males and the POA in females vary with season. However, reproductive state (and thus hormonal state) was incompletely predictive of these seasonal changes in males and completely unrelated to changes in females. We also detected male-biased dimorphisms in volume of the POA, AMY, and a dorsolateral subnucleus of the VMH but did not detect a dimorphism between alternate male morphological phenotypes. Finally, we showed that circulating testosterone levels were higher in males exhibiting higher frequency and intensity of aggressive display to a conspecific, though brain nucleus volumes were unrelated to behavior. Our findings fail to support our hypothesis and suggest instead that plasma testosterone level covaries with aggression level and in a limited capacity with brain nucleus volumes but that these are largely unrelated relationships.

Glucocorticoid interaction with aggression in non-mammalian vertebrates: reciprocal action

Socially aggressive interaction is stressful, and as such, glucocorticoids are typically secreted during aggressive interaction in a variety of vertebrates, which may both potentiate and inhibit aggression. The behavioral relationship between corticosterone and/or cortisol in non-mammalian (as well as mammalian) vertebrates is dependent on timing, magnitude, context, and coordination of physiological and behavioral responses. Chronically elevated plasma glucocorticoids reliably inhibit aggressive behavior, consistent with an evolutionarily adaptive behavioral strategy among subordinate and submissive individuals. Acute elevation of plasma glucocorticoids may either promote an actively aggressive response via action in specialized local regions of the brain such as the anterior hypothalamus, or is permissive to escalated aggression and/or activity. Although the permissive effect of glucocorticoids on aggression does not suggest an active role for the hormone, the corticosteroids may be necessary for full expression of aggressive behavior, as in the lizard Anolis carolinensis. These effects suggest that short-term stress may generally be best counteracted by an actively aggressive response, at least for socially dominant proactive individuals. An acute and active response may be evolutionarily maladaptive under chronic, uncontrollable and unpredictable circumstances. It appears that subordinate reactive individuals often produce compulsorily chronic responses that inhibit aggression and promote submissive behavior.

Sequential super-stereotypy of an instinctive fixed action pattern in hyper-dopaminergic mutant mice: a model of obsessive compulsive disorder and Tourette's

BACKGROUND

Excessive sequential stereotypy of behavioral patterns (sequential super-stereotypy) in Tourette's syndrome and obsessive compulsive disorder (OCD) is thought to involve dysfunction in nigrostriatal dopamine systems. In sequential super-stereotypy, patients become trapped in overly rigid sequential patterns of action, language, or thought. Some instinctive behavioral patterns of animals, such as the syntactic grooming chain pattern of rodents, have sufficiently complex and stereotyped serial structure to detect potential production of overly-rigid sequential patterns. A syntactic grooming chain is a fixed action pattern that serially links up to 25 grooming movements into 4 predictable phases that follow 1 syntactic rule. New mutant mouse models allow gene-based manipulation of brain function relevant to sequential patterns, but no current animal model of spontaneous OCD-like behaviors has so far been reported to exhibit sequential super-stereotypy in the sense of a whole complex serial pattern that becomes stronger and excessively rigid. Here we used a hyper-dopaminergic mutant mouse to examine whether an OCD-like behavioral sequence in animals shows sequential super-stereotypy. Knockdown mutation of the dopamine transporter gene (DAT) causes extracellular dopamine levels in the neostriatum of these adult mutant mice to rise to 170% of wild-type control levels.

RESULTS

We found that the serial pattern of this instinctive behavioral sequence becomes strengthened as an entire entity in hyper-dopaminergic mutants, and more resistant to interruption. Hyper-dopaminergic mutant mice have stronger and more rigid syntactic grooming chain patterns than wild-type control mice. Mutants showed sequential super-stereotypy in the sense of having more stereotyped and predictable syntactic grooming sequences, and were also more likely to resist disruption of the pattern en route, by returning after a disruption to complete the pattern from the appropriate point in the sequence. By contrast, wild-type mice exhibited weaker forms of the fixed action pattern, and often failed to complete the full sequence.

CONCLUSIONS

Sequential super-stereotypy occurs in the complex fixed action patterns of hyper-dopaminergic mutant mice. Elucidation of the basis for sequential super-stereotypy of instinctive behavior in DAT knockdown mutant mice may offer insights into neural mechanisms of overly-rigid sequences of action or thought in human patients with disorders such as Tourette's or OCD.

Serotonergic response to social stress and artificial social sign stimuli during paired interactions between male Anolis carolinensis

Serotonergic activity is influenced by social status and manipulation of social signals. In the lizard Anolis carolinensis, eyespot formation, i.e. darkening of postorbital skin from green to black, appears during stressful and agonistic situations, forming first in males that become dominant. To assess the effect of eyespots on central serotonergic activity during social interaction, males were paired by weight and painted postorbitally with green or black paint. Manipulation of eyespot color influenced social interactions and status. All males that viewed an opponent with black painted eyespots became subordinate. In these subordinate animals, serotonergic activity was elevated in hippocampus, striatum, nucleus accumbens and locus ceruleus. In contrast, males that viewed opponents with hidden eyespots (painted green) and became dominant had increased serotonergic activity in hypothalamus, medial amygdala and raphé. Pre-painted eyespots produced results that distinguish dominant and subordinate relationships based on serotonergic activity not previously seen in unmanipulated pairs. Results from experiments using pairs are similar to those using mirrors for medial amygdala and locus ceruleus, but not hippocampus, nucleus accumbens or raphé. Decreased hypothalamic serotonin was associated with increased aggressive behavior. These results, when compared with previous studies, suggest some flexibility in central serotonergic systems, which may shape dominant and subordinate rank acquisition, and appear to be influenced by the completion of social role formation. Furthermore, social status and central serotonergic activity was influenced by a visual cue, the presence or absence of postorbital eyespots on an opponent.

Basal ganglia systems in ritualistic social displays: reptiles and humans; function and illness

Complex, situation-specific territorial maintenance routines are similar across living terrestrial vertebrates (=amniotes). Decades ago, Paul MacLean et al., at the Laboratory of Brain Evolution and Behavior of the National Institute of Mental Health, postulated that these are evolutionarily conserved behaviors whose expression is mediated by the similarly conserved amniote basal ganglia and related brain systems (BG systems). Therefore, they undertook studies in nonhuman primates and in small social lizards (the common green anole, Anolis carolinensis) to examine this idea. MacLean et al. also postulated that when BG systems misfunction in humans, behavioral abnormalities result, some of them under the rubric of psychiatric illnesses. Obsessive-compulsive disorder (OCD) was singled out as one likely candidate. In the last dozen years, functional brain imaging studies of OCD patients have validated the contention that this is, in fact, a condition involving dysfunctioning BG systems. Inspired by the MacLean group's original investigations, my colleagues and I have now applied related functional imaging techniques in naturalistic experiments using Anolis to better understand BG systems' roles in the mediation of complex behavioral routines in healthy amniotes. Here, I will review this functional imaging work in primates (man, and a little in monkey) and in lizards. I believe the literature not only supports MacLean et al.'s contentions about BG systems and behavior in general, but also validates Paul MacLean's life-long contention that human behavioral medicine can profit from a broad comparative approach.

Sociality, stress, and the corpus striatum of the green anolis lizard

The green anolis lizard, Anolis carolinensis, is a uniquely convenient species with great potential for providing insights about the causes and consequences of social behavior from an evolutionary perspective. In this species, social interactions are mediated by visual displays in which specific units of behavior are combined in various ways to communicate several more-or-less specific messages. Two related research programs that utilize this species converge in provocative ways to provide insight into this phenomenon. The first program is centered on the basal ganglia, now known to be crucial to the expression of aggressive territoriality in this species, and the second research program examines the way the physiological stress response is involved in aggression and its subsequent adaptive outcomes. Both the neural and the neuroendocrine systems affect the progress of social interactions as well as the subsequent social dominance relationships when combatants subsequently live together. Further, because body color depends almost exclusively on the stress response, skin color provides a unique in situ bioassay of otherwise inaccessible information about the animal's internal state. The fullest understanding of the physiological ethology of this model species will depend on an interdisciplinary approach that considers both proximate (physiological) and ultimate (evolutionary) causes of displays. Questions thus arising include how the nervous system controls and assembles the specific units of behavior-motor patterns and autonomic reflexes-into displays that are adaptive in specific contexts.

Temporal patterns of limbic monoamine and plasma corticosterone response during social stress

Dominant and subordinate males respond differently to the stress of social interaction. After an hour of social interaction, subordinate male Anolis carolinensis have elevated serotonergic activity in hippocampus, but dominant males do not. In other species, and using other stressors, the activation of hippocampal serotonergic activity is much more rapid than one hour. To elucidate early stress responsiveness, adult male A. carolinensis were divided into four groups: isolated controls, and pairs of males sampled after 10, 20 or 40 minutes of aggressive interaction. Development of dominant-subordinate relationships was determined by behavior and by the celerity of eyespot darkening. Serotonergic activity in the hippocampus, nucleus accumbens and amygdala was elevated rapidly and equally in both dominant and subordinate males, as were plasma corticosterone concentrations. Serotonergic activity remained elevated through 40 minutes in hippocampus and nucleus accumbens. Only subordinate males had elevated corticosterone levels at 40 minutes. Social status does not impede socially induced stress responses. Rather, rapid regulation of serotonergic stress responses appears to be a mediating factor in determining both behavioral output and social status. Temporal expressions of monoaminergic and endocrine stress responses are distinctive between males of dominant and subordinate social status. Such temporal patterns of transmitter and glucocorticoid activity may reflect neurocircuitry adaptations that result in behavior modified to fit social status.

Brain mediation of Anolis social dominance displays. I. Differential basal ganglia activation

Ritualistic displays of aggressive intent are important social signals, often obviating physically dangerous engagement. To date, however, brain regions mediating such behaviors are not established. Here we used male Anolis carolinensis together with an in vivo 14C-2-deoxyglucose method to determine patterns of brain activation during elicitation of this animal's dominance displays vs. other behaviors. By patching one eye regional brain activation in the hemisphere receiving display-evocative visual stimuli ('seeing' side) was compared to activity in the contralateral brain that did not see specific stimuli ('patched' side); this was quantitated as the ratio of seeing/patched activity for brain regions of interest. Lone males displaying dominantly to mirrors activated dorsolateral basal ganglia (BG) in the seeing, compared to the patched hemisphere; this was not seen in various non-displaying controls. Degree of dorsolateral BG activation also correlated with a measure of dominant display activity, but not with locomotion. In socially stable pairs, displaying dominants showed similar activation of dorsolateral BG, but deactivated ventromedial BG; non-dominant cagemates displaying submissively had the opposite pattern. When cohabiting peacefully without displaying, paired dominants' and subordinates' brain activity patterns were similar to each other. Thus, different BG subsystems seem involved in dominant vs. submissive display behaviors. Given similarities in both social displays and BG organization, homologous brain systems might have similar functions in members of other amniote classes, including primates.

Mammal-like striatal functions in Anolis. I. Distribution of serotonin receptor subtypes, and absence of striosome and matrix organization

Serotonin (5-HT) 5-HT(2A) and 5-HT(2C) receptors are thought to play important roles in the mammalian striatum. As basal ganglia functions in general are thought highly conserved among amniotes, we decided to use in situ autoradiographic methods to determine the occurrence and distribution of pharmacologically mammal-like 5-HT(2A) and 5-HT(2C) receptors in the lizard, Anolis carolinensis, with particular attention to the striatum. We also determined the distributions of 5-HT(1A), 5-HT(1B/D), 5 HT(3), and 5-HT(uptake) receptors for comparison. All 5-HT receptors examined showed pharmacological binding specificity, and forebrain binding density distributions that resembled those reported for mammals. Anolis 5 HT(2A/C) and 5-HT(1A) site distributions were similar in both in vivo and ex vivo binding experiments. 5-HT(2A & C) receptors occur in both high and low affinity states, the former having preferential affinity for (125)I-(+/-)-2,5-dimethoxy-4-iodo-amphetamine hydrochloride ((125)I-DOI). In mammals (125)I-DOI binding shows a patchy density distribution in the striatum, being more dense in striosomes than in surrounding matrix. There was no evidence of any such patchy density of (125)I-DOI binding in the anole striatum, however. As a further indication that anoles do not possess a striosome and matrix striatal organization, neither (3)H-naloxone binding nor histochemical staining for acetylcholinesterase activity (AChE) were patchy. AChE did show a band-like striatal distribution, however, similar to that seen in birds.

Visible sympathetic activity as a social signal in Anolis carolinensis: changes in aggression and plasma catecholamines

Darkening of postorbital skin in Anolis carolinensis occurs during stressful situations and is stimulated by sympathetic activation of beta(2)-adrenergic receptors via adrenal catecholamines. This eyespot forms more rapidly in dominant males during social interaction. Eyespot darkening (green to black) appears to function as a social signal communicating sympathetic activation and limiting aggressive interaction. To assess the value of the eyespot as a social signal, males were painted postorbitally with green, black, or red paint. Each male was exposed to a mirror following acclimation to the cage. The total number of aggressive displays toward the mirror image was greatest when eyespots were masked by green paint. In contrast, black or red artificial eyespots, regardless of size, inhibited biting behavior toward the mirror image. The most aggressive males, those who saw a reflected opponent with no eyespot (hidden with green paint), had significantly higher levels of all plasma catecholamines. These results suggest that A. carolinensis use information from the eyespot to assess their opponent's readiness to fight and thereby determine whether to be aggressive. Darkened eyespots are capable of inhibiting aggression, whereas aggressive displays from an opponent in the mirror without darkened eyespots do not. Darkened eyespots reflect rapid changes in plasma NE, DA, and Epi that may signal dominant social status.

Hemispheric control of territorial aggression in Anolis carolinensis: effects of mild stress

Previous work has demonstrated that the brain of Anolis carolinensis is functionally split, in that the left and right eyes project predominantly to the contralateral hemisphere, and as there are minimal connections between the left and right hemispheres. Using this model, the current experiment examined the effect of mild acute stress on hemispheric regulation of territorial aggression. Thirteen adult male Anolis were paired with an antagonistic males, and eye use and behavioral responses were repeatedly measured during 3 minute behavioral trials. Trials were conducted either after exposure to mild stress, produced by handling the subject, or without stress, and they were run either in the subject's home cage or in a cage foreign to the subject. Left eye preference for aggressive movements was found during the trials run in the non-stressed conditions (p < 0.05). Conversely, stressed subjects showed a reduction in left eye/right hemisphere mediated aggressive movements relative to the non-stressed subjects but no changes in right eye/left hemisphere aggression. This effect was independent of whether or not the subject was in its home or a foreign cage. No laterality in aggressive responding was found when the subjects were placed in separate cages with visual contact. These findings suggest that territorial aggression in Anolis is preferentially initiated and processed by the left eye/right hemisphere but is subject to right-hemispheric inhibition following exposure to acute mild stress.

Monoaminergic activities of limbic regions are elevated during aggression: influence of sympathetic social signaling

A visual social signal inhibiting aggression is coincident with limiting serotonergic and noradrenergic activity in subiculum, hippocampus, nucleus accumbens, medial amygdala, but not lateral amygdala, septum, and hypothalamus. Darkening of postorbital skin in the lizard Anolis carolinensis is stimulated by sympathetic activation of beta(2)-adrenergic receptors via adrenal catecholamines, and occurs more rapidly in dominant males during social interaction. Eyespot darkening functions as a social signal limiting aggressive interaction. To assess the effect of this social signal on telencephalic activity of monoamines, males were painted postorbitally with green or black paint, and exposed to a mirror. Serotonergic and noradrenergic turnover, as estimated by ratios of catabolite to transmitter, were elevated in the subiculum, hippocampus, nucleus accumbens, and medial amygdala of animals in which the eyespots were masked by green paint. Conversely, dopaminergic activity in these brain regions was lower in males with hidden eyespots (painted green). Hiding the eyespot evoked significantly increased aggressive activity toward the mirror image. Furthermore, changes in monoaminergic turnover were coincident with altered aggressive behavior, suggesting a relationship between them. Changes of monoaminergic activity were not observed in the septum, lateral amygdala, or hypothalamus, when males with eyespots permanently marked (black) were compared with those with eyespots hidden (painted green). Stimulated (serotonergic and noradrenergic) or inhibited (dopaminergic) activity due to social signal and aggression are confined to regions of the brain similarly activated during social stress, and do not constitute a generalized activation of monoaminergic systems.

Serotonergic responses to corticosterone and testosterone in the limbic system

Glucocorticoids secreted peripherally during stressful events act on central monoaminergic systems. In particular, serotonergic mediation of social behavior, such as aggression and reproduction, may be affected by glucocorticoids. This study was undertaken to determine if systemically administered corticosterone would rapidly affect central monoaminergic activity. Male Anolis carolinensis (N = 8 each group) were injected intraperitoneally with 10 or 100 micrograms corticosterone, 10 micrograms testosterone, or saline. Twenty minutes after treatment, brains were rapidly dissected and frozen and then microdissected (punch diameter 300 microm) and analyzed by high-performance liquid chromatography. Serotonergic turnover (estimated by 5-hydroxyindoleacetic acid/serotonin) in the hippocampus and medial amygdala was significantly enhanced by systemic corticosterone. Both of these regions of the brain have been associated with social stress. Testosterone also enhanced turnover in the hippocampus. The effect of corticosterone and testosterone may be to modulate socially induced differences in serotonergic response. Rapid, but short-lived, glucocorticoid stimulation of serotonin release suggests a possible mechanism for mediation of changing social behavioral events.

Structural and functional evolution of the basal ganglia in vertebrates

While a basal ganglia with striatal and pallidal subdivisions is 1 clearly present in many extant anamniote species, this basal ganglia is cell sparse and receives only a relatively modest tegmental dopaminergic input and little if any cortical input. The major basal ganglia influence on motor functions in anamniotes appears to be exerted via output circuits to the tectum. In contrast, in modern mammals, birds, and reptiles (i.e., modern amniotes), the striatal and pallidal parts of the basal ganglia are very neuron-rich, both consist of the same basic populations of neurons in all amniotes, and the striatum receives abundant tegmental dopaminergic and cortical input. The functional circuitry of the basal ganglia also seems very similar in all amniotes, since the major basal ganglia influences on motor functions appear to be exerted via output circuits to both cerebral cortex and tectum in sauropsids (i.e., birds and reptiles) and mammals. The basal ganglia, output circuits to the cortex, however, appear to be considerably more developed in mammals than in birds and reptiles. The basal ganglia, thus, appears to have undergone a major elaboration during the evolutionary transition from amphibians to reptiles. This elaboration may have enabled amniotes to learn and/or execute a more sophisticated repertoire of behaviors and movements, and this ability may have been an important element of the successful adaptation of amniotes to a fully terrestrial habitat. The mammalian lineage appears, however, to have diverged somewhat from the sauropsid lineage with respect to the emergence of the cerebral cortex as the major target of the basal ganglia circuitry devoted to executing the basal ganglia-mediated control of movement.

Regional and temporal separation of serotonergic activity mediating social stress

Stressful aggressive interaction stimulates central serotonergic activation in telencephalon as well as brainstem. Social roles can be distinguished by monoamine activity following aggression. Pairs of male lizards, Anolis carolinensis, were allowed to fight and form dominant/subordinate relationships. In micropunched regions of telencephalon, the greatest serotonergic changes occur in subordinate males. In hippocampal cortex and nucleus accumbens, subordinate males have increased 5-hydroxyindoleacetic acid/serotonin at 1 h following the fight. In these areas the ratio gradually decreases over a week of cohabitation, as was previously reported for brainstem. Medial and lateral amygdala develop increased serotonergic activity more slowly, with the greatest increase being evident following a week of interaction. Turnover, serotonin and 5-hydroxyindoleacetic acid levels in amygdala escalate over the first week of interaction in subordinate males, and return to baseline by one month. In dominant males, the pattern is accelerated, with the most extensive serotonin system activity present at 1 h, then decreasing over a month. The patterns of serotonergic activation are so similar in hippocampus, nucleus accumbens and brainstem that a co-ordinated response may be involved in mediating short-term social stress and aggression. Similarly, medial and lateral amygdala exhibit corresponding, but delayed patterns in subordinate males, suggesting a co-ordinated response in these regions mediating longer-term stress responses. These data are consistent with rapid neuroendocrine stress modulation in dominant individuals, and delayed serotonergic activity changes in subordinate males.

Lateralized effects of ethanol on aggression and serotonergic systems in Anolis carolinensis

The lateralized effects of ethanol (ETOH) upon behavior and monoamine biochemistry in the lizard, Anolis carolinensis, were examined. Eight adult male anoles consumed solutions of 19% ethanol (ETOH) twice daily over the course of 18 days, while controls consumed water. ETOH decreased the use of the left eye/right hemisphere, but not the right eye/left hemisphere, during territorial aggression (p<0.05). During crossover (i.e., ETOH to water and vice versa) this effect was reversible and replicable. Biochemically, an asymmetry was observed in 5-HT levels in the raphe both in ETOH and controls. ETOH increased levels of serotonin (5-HT; p<0.05), and 5-HIAA/5-HT ratios (p<0.05) in the raphe; serotonin levels in several brain regions correlated with aggressive responses. These results suggest that ETOH boosts 5-HT levels in animals subchronically exposed to ETOH. They further suggest that asymmetry in endogenous 5-HT systems may account for the asymmetrical regulation of aggression generally, and may explain the behavioral effects of ETOH upon lateralized aggression.

Effects of serotonergic drugs on lateralized aggression and aggressive displays in Anolis carolinensis

Previous work demonstrated that the brains of many reptiles, including the American chameleon Anolis carolinensis (A. carolinensis), are functionally 'split'. Because the left eye in this species projects predominantly to the right hemisphere, and vice versa, inferences about lateralized brain functioning can be made in A. carolinensis by observation of eye use during behavioral encounters. Using this model, past work suggested that territorial aggression in Anolis is under the preferential control of the right hemisphere, and that acute stress or chronic alcohol exposure selectively reduces right hemisphere mediated territorial aggression. In addition, drugs which increase serotonin (5-HT) in the synaptic cleft inhibit aggressive responding in anoles in both hemispheres. The current experiment examined whether or not the administration of the serotonin agonists 8-hydroxy-2-(di-n-propylamine) tetralin (8-OHDPAT), quipazine, or meta-chlorophenylbiguanide (mCPBG) alter territorial aggression in Anolis. Nine adult socially isolated male A. carolinensis underwent a series of behavioral trials during which an antagonistic male was introduced into the cage. Once stable responding was initiated, all subjects were injected in a semi-randomized crossover manner with the following agents, (1) lactated Ringer's, (2) the 5-HT2 agonist quipazine (1.5 mg/kg and 3.0 mg/kg), (3) the 5-HT1 agonist 8-OHDPAT (83 mg/kg), and (4) the 5-HT3 agonist mCPBG (3.0 mg/kg and 9 mg/kg). Twenty minutes post injections, the male intruder was reintroduced into the subject's cage. Several behaviors were recorded, including: (1) the time to the first aggressive response, (2) the number of aggressive episodes mediated by the left eye or right eye, and (3) changes in skin color and posture. Aggressive responding was virtually eliminated in all subjects injected with 8-OHDPAT. On the other hand, one-way ANOVA found that both the 9 mg/kg dose of mCPBG (P=0.007), and the 3.0 mg/kg dose of quipazine (P=0.035), selectively decreased territorial aggression mediated by the left eye/right hemisphere compared to lactated Ringer's controls, but had no effect on aggression mediated by the right eye/left hemisphere. Although 8-OHDPAT inhibited aggression, injected subjects developed phenotypic displays of aggressive coloring/posturing, such as blackening of the eye spot and a raising of the neck crest. These results suggest that aggressive action can be differentiated from phenotypic displays that accompany aggression by a 5-HT1 agonist. They also indicate that there is an asymmetrical effect of 5-HT2/5-HT3 serotonin agonists on hemispheric mediation of aggression in this species.

The origins of cerebral asymmetry: a review of evidence of behavioural and brain lateralization in fishes, reptiles and amphibians

Early evidence for lateralization at a population and/or individual level in 'lower' vertebrates is reviewed. The lateralities include structural asymmetries in the epithalamus of several species of fish and amphibians, asymmetries in the location of both eyes on the same side of the head and of the dorsal/ventral crossing at optic-chiasma in flatfish, asymmetries in copulatory organs of several species of fishes, asymmetries in lung size and direction of coiling in reptiles, and asymmetrical distribution of scarring in whitefish. More recent data on functional lateralization at population level in lower vertebrates are also reviewed. These include: lateral asymmetries in the direction of turning during escape behaviour and in eye use in poeciliid fish; lateralization of pectoral stridulation sounds in catfish; neural lateralization for control of vocalization in the frogs; pawedness in toads; lateralization of courtship behaviour in newts; and lateralization of aggressive responses in lizards. Several cases of behavioural asymmetries at the individual level are also described, and possible relationships between lateralization at the individual level and fluctuating asymmetries arising from reduced heterozygosity are discussed. It is argued that the overall evidence now available supports the hypothesis of an early origin of brain lateralization in vertebrates.

Effects of alcohol consumption on lateralized aggression in Anolis carolinensis

Previous work has suggested that the lizard Anolis carolinensis, like many other reptiles, has a functionally split brain. Specifically, the left eye of this species projects primarily to the right hemisphere (and vice versa), there is no corpus callosum, and the physical placement of the eyes restricts their field(s) of vision to one region of hemispace. The current experiment used this preparation to examine the effect of alcohol administration and withdrawal on lateralized brain functioning during territorial aggression. Thirteen adult males were divided into control (CON) or alcohol (ETOH) groups. Baseline territorial aggression was assessed, following which ETOH subjects were then given twice daily solutions of 19% alcohol. After 19 days of ETOH consumption, territorial aggression was again assessed. Eye use during aggressive encounters was measured either following short periods (24 h) of alcohol withdrawal, or 90 m following alcohol consumption. Control subjects were found to have a predominance of left eye/right hemisphere-mediated aggressive responses, as has previously been reported. Alcohol withdrawn subjects were found to have a suppression of left eye/right hemisphere-mediated aggression. This reached statistical significance on several measures of aggression, including the number of dewlaps and headbob (P < 0.001) and the total number of aggressive responses (P = 0.001). Consumption of ETOH reversed this pattern and reinstated the normal pattern of left eye/right hemisphere dominance during aggression. Conversely, right eye/left hemisphere mediation of aggression was found to be increased, or not affected, during alcohol withdrawal, and to show no differences from CON following ETOH administration. Extrapolating from other recent findings in this species, these results suggest that the stress caused by ETOH withdrawal on the CNS may differentially effect the right hemisphere of the brain while having little effect on the left.

Behavioral changes in Anolis carolinensis following injection with fluoxetine

Eight adult male lizards of the genus and species Anolis carolinensis were used in this experiment. In order to induce aggressive responding, animals were caged separately and daily underwent pairing with another male, during which aggressive responses and changes in skin color were measured. After obtaining a baseline measure of aggressive responding, animals were injected either with fluoxetine or vehicle-controls in a cross-over design. Subjects were then exposed to five more days of (non drug) pairing with the intruder male, after which they underwent a second trial with fluoxetine/vehicle. Finally, two post-drug paired-trials were obtained. Fluoxetine injection significantly reduced the aggressive responding in the males while causing the postorbital eyespot to significantly darken. Subjects also showed increased aggressivity and skin-color reactivity subsequent to the two drug trials, although it is unclear if the fluoxetine, or non-specific factors of the injection paradigm, accounted for these changes. These results suggest that serotonergic CNS systems tonically regulate aggression in Anolis carolinesis, similar to that seen in many other species. They further suggest that eyespot-darkening and aggressive responding can be pharmacologically dissociated, implicating serotonin in the regulation of this phenomenon.

Efferent connections of the striatum and the nucleus accumbens in the lizard Gekko gecko

The efferent connections of the striatum and the nucleus accumbens of the lizard Gekko gecko were studied with the anterograde tracer Phaseolus vulgaris-leucoagglutinin (PHA-L). These structures were found to have segregated output systems. The striatum shows a major projection to the globus pallidus. Striatal fibers which are more caudally directed run through the lateral forebrain bundle and can be traced as far caudally as the pars reticularis of the substantia nigra where they exhibit many varicosities. Along its course, the lateral forebrain bundle issues fibers with varicosities to the anterior and posterior entopeduncular nuclei. The major recipient structure of the nucleus accumbens is the ventral pallidum. The nucleus accumbens, in addition, projects to the portion of the lateral hypothalamus in the path of the medial forebrain bundle and to the ventral tegmental area, which is its most caudal target. Subsequently, the same technique was used in an attempt to study the efferents of the globus pallidus and the ventral pallidum, the major recipient structures of the striatum and the nucleus accumbens. The globus pallidus was found to project to the rostral part of the suprapeduncular nucleus in the ventral thalamus and, in addition, may distribute fibers to the same structures as does the striatum. The ventral pallidum distributes fibers to the ventromedial thalamic nucleus. It probably also projects diffusely to the hypothalamus, the habenula, and the mesencephalic tegmentum.

Reptilian behavioural patterns in childhood autism

Childhood autism may be caused by damage to three phylogenetically distinct regions of the brain, or their major pathways and connections. Injury to the neocortex results in loss of language and cognitive function, while injury to the limbic cortex results in autistic withdrawal and abolition of play behaviour. Injury to the more primitive striatal complex, mammalian counterpart of the brain of reptiles, results in a bizarre and truncated form of stereotyped and ritualistic behaviour. The causes of brain injury in childhood autism could be those common in the perinatal period including cerebral anoxia, haemorrhage, phenylketonuria, neurolipidoses , meningitis, toxoplasmosis, and congenital rubella. All these conditions have previously been shown to be associated with childhood autism.

Role of the amygdala in the reproductive and aggressive behavior of the lizard, Anolis carolinensis

Thirteen male green anole lizards were lesioned in the ventromedial nucleus (VMN) of the posterior dorsal ventricular ridge ("amygdala") and/or the paleostriatum (PS) to determine the influence of these structures on assertion and challenge displays addressed to male intruders, or courtship displays and copulatory neckgrip directed toward females. Lesions that affected both VMN and PS reduced or eliminated both challenge and courtship displays as well as the neckgrip, a crucial component in courtship. Subjects with lesions limited to VMN had assertion and challenge left unimpaired but courtship was reduced and neckgrip eliminated in most subjects. A lesion restricted to PS caused a significant deficit in challenge while other measures were unaffected. These data indicate that the VMN is involved in reproductive function in the green anole lizard.

The effects of lesions of telencephalic visual structures on visual discriminative performance in turtles (Chrysemys picta picta)

Ascending thalamotelencephalic visual pathways that terminate in specific telencephalic regions have been described in all reptiles studied. Although the anatomical data suggests that such telencephalic regions may play a role in visual processing in reptiles, few behavioral data are available. In the present study, the effects of destruction of either the core nucleus (CN) of the dorsal ventricular ridge (telencephalic terminus of the tectothalamofugal pathway) or the dorsal cortex (telencephalic terminus of the retinothalamofugal pathway) on visual discriminative performance in the turtle were examined. Following extensive bilateral destruction of the CN, turtles were severely impaired in their performance of both a simultaneous pattern discrimination and a simultaneous visual intensity discrimination. The extent of the discriminative impairment was found to be specifically correlated with the amount of CN damage. In contrast to the effects of CN lesions, lesions of the dorsal cortex had no evident effect on the performance of either a simultaneous pattern discrimination or a simultaneous visual intensity discrimination. The present results suggest that, as in birds and mammals, telencephalic visual areas play an important role in visual functions in reptiles. As in at least some birds (such as pigeons), the telencephalic terminus of the tectothalamofugal visual pathway appears to play a larger, or at least more readily measurable, role in visual discrimination than does the telencephalic terminus of the retinothalamofugal pathway.

A forebrain atlas and stereotaxic technique for the lizard, Anolis carolinensis

A forebrain atlas and stereotaxic neurosurgical techniques were developed for use in anatomical and behavioral experiments on the green anolis lizard (Anolis carolinensis). Green anoles are convenient and robust experimental subjects with a rich behavioral repertoire, the social components of which are partly under hormonal control. The technique and atlas were devised to conduct neuroethological investigations of the effect of lesions on species-typical display behavior. The atlas consists of 12 transverse sections from an average size adult male. The figures (4-15) are based on Nissl material and supplemented with fiber-stained material from adjacent sections. They appear at the end of the article. Limitations on the accuracy of stereotaxic coordinates are discussed and tables of correlative nomenclature for principal telencephalic and diencephalic nuclei are provided.

Species-typical behavior of hamsters deprived from birth of the neocortex

Hamsters deprived from birth of the neocortex developed normally and displayed the usual hamster-typical behavioral patterns. With the additional concurrent destruction of midline limbic convolutions (cingulate and underlying dorsal hippocampal), there were deficits in maternal behavior and a lack of development of play behavior. These findings demonstrate in a rodent (i) that the striatal complex and limbic system, along with the remaining neuraxis, are sufficient for giving expression to a wide range of unlearned forms of species-typical behavior and (ii) that midline limbic structures are required for the expression of play behavior and the integrated performance of maternal behavior.

The effects of extensive forebrain lesions on visual discriminative performance in turtles (Chrysemys picta picta)

Though anatomical research has demonstrated major ascending telecephalically directed visual channels in reptiles, little behavioral research has examined reptilian forebrain visual functions. The present study reports the effects of extensive forebrain lesions, involving either severe destruction of dorsal thalamus or disruption of the fibers of the lateral forebrain bundle (by lesions of the basolateral telecephalon), upon visual discriminative performance in the turtle. Such lesions, which extensively damage the ascending visual pathways, rendered turtles incapable of relearning preoperatively acquired visual discriminative problems. The magnitude of the visual impairments observed following such forebrain lesions suggest a major role on the part of the forebrain in visual processing in reptiles.