Medial amygdaloid suppression of predatory attack behavior in the cat: I Role of a substance P pathway from the medial amygdala to the medial hypothalamus

Substance P in the medial amygdala regulates aggressive behaviors in male mice

Behavioral and clinical studies have revealed a critical role of substance P (SP) in aggression; however, the neural circuit mechanisms underlying SP and aggression remain elusive. Here, we show that tachykinin-expressing neurons in the medial amygdala (MeATac1 neurons) are activated during aggressive behaviors in male mice. We identified MeATac1 neurons as a key mediator of aggression and found that MeATac1→ventrolateral part of the ventromedial hypothalamic nucleus (VMHvl) projections are critical to the regulation of aggression. Moreover, SP/neurokinin-1 receptor (NK-1R) signaling in the VMHvl modulates aggressive behaviors in male mice. SP/NK-1R signaling regulates aggression by influencing glutamate transmission in neurons in the VMHvl. In summary, these findings place SP as a key node in aggression circuits.

Mapping the neurocircuitry of impulsive aggression through the pharmacologic review of anti-impulsive aggressive agents

Impulsive aggression, in contradistinction to premeditated aggression in humans or predatory aggression in animals, corresponds to defensive aggression in animal models. At the core of the neurocircuitry of impulsive aggression, from murine to feline to human species, it is the medial amygdala-mediobasal hypothalamus-dorsal periaqueductal gray pathway. Here, we update current knowledge on the neurocircuitry of impulsive aggression by placing the neurocircuitry and its neurophysiological substrates into the top-down/bottom-up hypothesis of impulsive aggression. We then reverse the neurotranslational approach, which applies neuroscience to developing therapeutic drugs, and apply current understanding of potential mechanisms of anti-impulsive aggression agents to further clarify, at least heuristically and hypothetically, the dynamic biochemical components of the neurocircuitry of impulsive aggression. To do this, we searched the medical literature for studies attempting to clarify the neurobiological and neurochemical effects of the five most widely studied anti-impulsive aggressive agents, particularly as they pertain to the top-down/bottom-up hypothesis. Multiple different mechanisms are discussed, all of which fitting in the hypothesis by way of either promoting the "top-down" part (i.e., enhancing inhibitory neurotransmitters), or suppressing the "bottom-up" part (i.e., decreasing excitatory neurotransmitters). The hypothesis appears consistent with the current psychopharmacological understanding of these agents, as well as to account for the likely multifactorial etiology of the condition. Limitations of the hypothesis and future directions are finally discussed.

Mechanisms Responsible for Genetic Hypertension in Schlager BPH/2 Mice

It has been 45 years since Gunther Schlager used a cross breeding program in mice to develop inbred strains with high, normal, and low blood pressure (BPH/2, BPN/3, and BPL/1 respectively). Thus, it is timely to gather together the studies that have characterized and explored the mechanisms associated with the hypertension to take stock of exactly what is known and what remains to be determined. Growing evidence supports the notion that the mechanism of hypertension in BPH/2 mice is predominantly neurogenic with some of the early studies showing aberrant brain noradrenaline levels in BPH/2 compared with BPN/3. Analysis of the adrenal gland using microarray suggested an association with the activity of the sympathetic nervous system. Indeed, in support of this, there is a larger depressor response to ganglion blockade, which reduced blood pressure in BPH/2 mice to the same level as BPN/3 mice. Greater renal tyrosine hydroxylase staining and greater renal noradrenaline levels in BPH/2 mice suggest sympathetic hyperinnervation of the kidney. Renal denervation markedly reduced the blood pressure in BPH/2 but not BPN/3 mice, confirming the importance of renal sympathetic nervous activity contributing to the hypertension. Further, there is an important contribution to the hypertension from miR-181a and renal renin in this strain. BPH/2 mice also display greater neuronal activity of amygdalo-hypothalamic cardiovascular regulatory regions. Lesions of the medial nucleus of the amygdala reduced the hypertension in BPH/2 mice and abolished the strain difference in the effect of ganglion blockade, suggesting a sympathetic mechanism. Further studies suggest that aberrant GABAergic inhibition may play a role since BPH/2 mice have low GABA_A receptor δ, α4 and β2 subunit mRNA expression in the hypothalamus, which are predominantly involved in promoting tonic neuronal inhibition. Allopregnanolone, an allosteric modulator of GABA_A receptors, which increase the expression of these subunits in the amygdala and hypothalamus, is shown to reduce the hypertension and sympathetic nervous system contribution in BPH/2 mice. Thus far, evidence suggests that BPH/2 mice have aberrant GABAergic inhibition, which drives neuronal overactivity within amygdalo-hypothalamic brain regions. This overactivity is responsible for the greater sympathetic contribution to the hypertension in BPH/2 mice, thus making this an ideal model of neurogenic hypertension.

The role of central and medial amygdala in normal and abnormal aggression: A review of classical approaches

The involvement of the amygdala in aggression is supported by overwhelming evidence. Frequently, however, the amygdala is studied as a whole, despite its complex internal organization. To reveal the role of various subdivisions, here we review the involvement of the central and medial amygdala in male rivalry aggression, maternal aggression, predatory aggression, and models of abnormal aggression where violent behavior is associated with increased or decreased arousal. We conclude that: (1) rivalry aggression is controlled by the medial amygdala; (2) predatory aggression is controlled by the central amygdala; (3) hypoarousal-associated violent aggression recruits both nuclei, (4) a specific upregulation of the medial amygdala was observed in hyperarousal-driven aggression. These patterns of amygdala activation were used to build four alternative models of the aggression circuitry, each being specific to particular forms of aggression. The separate study of the roles of amygdala subdivisions may not only improve our understanding of aggressive behavior, but also the differential control of aggression and violent behaviors of various types, including those associated with various psychopathologies.

Inhibition of substance P-induced defensive behavior via neurokinin-1 receptor antagonism in the central and medial but not basolateral nuclei of the amygdala in male Wistar rats

RATIONALE

The production of unconditioned defensive behaviors has been related to the amygdala, a key component of the encephalic aversion system. Microinjection of the neuropeptide substance P (SP) in the amygdala elicits defensive behaviors via the activation of type 1 neurokinin (NK-1) receptors. However, no studies have investigated whether intra-amygdala SP/NK-1 mechanisms can elicit other types of defensive responses, such as antinociception and ultrasonic vocalizations (USVs).

METHODS

The present study investigated the effects of SP-induced activation of the neurokininergic system in three main nuclei of the amygdala-basolateral (BLA), central (CeA), and medial (MeA) nuclei-in rats that were subjected to the elevated plus maze (EPM), tail-flick test, and USV recording. The effects of SP in these amygdaloid nuclei were challenged with combined injections of the NK-1 receptor antagonist spantide.

RESULTS

The present study showed that SP injections in the CeA and MeA but not BLA exerted anxiogenic-like effects. In contrast to the CeA, the anxiogenic-like effects of SP in the MeA were not dependent on NK-1 mechanisms. In the tail-flick test, SP microinjections produced antinociceptive effects only in the MeA through NK-1 receptor activation. No USV emissions were detected after the SP microinjections.

CONCLUSIONS

The present study showed that NK-1 receptors in the CeA and MeA but not BLA are involved in defensive reactions to conditions of fear. The present results may provide a better understanding of the neurochemical mediation of fear states.

Cerebrospinal fluid substance P-like immunoreactivity correlates with aggression in personality disordered subjects

BACKGROUND

Neurochemical studies have pointed to a modulatory role in human aggression for a variety of central neurotransmitters; some seem to play an inhibitory role, whereas others seem to play a facilitory role in the modulation of aggression. Laboratory animal studies of substance P suggest a facilitory role for this undecapeptide in the modulation of aggression, but no studies of substance P have yet been reported with regard to human aggression.

METHODS

Basal lumbar cerebrospinal fluid samples were obtained from 38 physically healthy subjects with personality disorder (PD) and substance P-like immunoreactivity was measured and correlated with measures of aggression and impulsivity.

RESULTS

The cerebrospinal fluid substance P-like immunoreactivity levels were directly correlated with a composite measure of aggression and, more specifically, with Buss-Durkee Aggression. No correlation was seen with any measure of impulsivity or of general dimensions of personality.

CONCLUSIONS

These data suggest a direct relationship between central nervous system substance P containing neural circuits and aggression in human subjects. This finding adds to the complex picture of the central neuromodulatory role of impulsive aggression in human subjects.

Blood pressure variations real-time reflect the conditioned fear learning and memory

The conditioned fear learning and memory occurs when a neutral conditioned stimulus (CS) is paired with an aversive unconditioned stimulus (US). This process is critically dependent on the amygdala and inevitably involves blood pressure (BP) alterations. We hypothesized that BP variations could instantaneously reveal individual steps during conditioned fear learning and memory. An implanted telemetric probe was used to monitor the BP real-time in rats during training and testing sessions of the fear-potentiated startle. Our results showed that (i) the conditioned fear learning during the training sessions was reflected by light (CS)-induced rapid BP elevations and by electric shock (US)-evoked sympathetic tone elevations; (ii) these two BP-related parameters were not only negatively correlated with each other but also coupled to each other in the training session trials; (iii) both parameters closely predicted the performance of fear-potentiated startle on the next day; and (iv) although local blocking of one of the two fear-conditioned pathways in the training session partially inhibited fear learning, the fear memory retrieval still used both pathways. Altogether, real-time blood pressure variations faithfully revealed the critical steps involved in conditioned fear learning and memory, and our results supported a coupling between the cued learning and the post-shock calmness.

Neurokinin-1 receptor deletion modulates behavioural and neurochemical alterations in an animal model of depression

The substance P/NK1 receptor system plays an important role in the regulation of stress and emotional responding and as such had been implicated in the pathophysiology of anxiety and depression. The present study investigated whether alterations in the substance P/NK1 receptor system in brain areas which regulate emotional responding accompany the depressive behavioural phenotype observed in the olfactory bulbectomised (OB) mouse. The effect of NK1 receptor deletion on behavioural responding and monoamine levels in discrete brain regions of the OB model, were also examined. Substance P levels in the frontal cortex and NK1 receptor expression in the amygdala and hippocampus were enhanced following olfactory bulbectomy. Although NK1 receptor knockout (NK1-/-) mice did not exhibit altered behavioural responding in the open field test, noradrenaline levels were enhanced in the frontal cortex, amygdala and hippocampus, as were serotonin levels in the frontal cortex. Locomotor activity and exploratory behaviour were enhanced in wild type OB mice, indicative of a depressive-like phenotype, an effect attenuated in NK1-/- mice. Bulbectomy induced a decrease in noradrenaline and 5-HIAA in the frontal cortex and an increase in serotonin in the amygdala, effects attenuated in OB NK1-/- mice. The present studies indicate that alterations in substance P/NK1 receptor system underlie, at least in part, the behavioural and monoaminergic changes in this animal model of depression.

The involvement of substance P in the induction of aggressive behavior

Aggression is a complex social behavior that involves a similarly complex neurochemical background. The involvement of substance P (SP) and its potent tachykinin receptor (NK1) in the induction of both defensive rage and predatory attack appears to be a consistent finding. However, an overall understanding of the nature of the SP involvement in the induction of aggressive behavior has not yet been fully achieved. The aim of this review is to summarize and present the current knowledge with regards to the role of SP in the induction of aggressive behavior and to synopsize: (a) its biochemical profile, and (b) the exact anatomical circuits through which it mediates all types of aggressive behavior. Future studies should seriously consider the potential use of this knowledge in their quest for the treatment of mood and anxiety disorders.

Effects of substance P in the amygdala, ventromedial hypothalamus, and periaqueductal gray on fear-potentiated startle

The neural pathways through which substance P (SP) influences fear and anxiety are poorly understood. However, the amygdala, a brain area repeatedly implicated in fear and anxiety processes, is known to contain large numbers of SP-containing neurons and SP receptors. Several studies have implicated SP neurotransmission within the amygdala in anxiety processes. In the present study, we evaluated the effects of site-specific infusions of an SP receptor antagonist, GR 82334, on conditioned fear responses using the fear-potentiated startle paradigm. GR 82334 infusion into the basolateral (BLA) or the medial (MeA) nuclei of the amygdala, but not into the central nucleus of the amygdala (CeA), dose dependently reduced fear-potentiated startle. Similar effects were obtained with GR 82334 infusion into the ventromedial nucleus of the hypothalamus (VMH), to which the MeA projects, and into the rostral dorsolateral periaqueductal gray (PAG), to which the VMH projects, but not into the deep layers of the superior colliculus/deep mesencephalic nucleus (dSC/DpMe), an output of the CeA previously shown to be important for fear-potentiated startle. Consistent with previous findings, infusion of the AMPA receptor antagonist, NBQX, into the dSC/DpMe, but not into the PAG, did disrupt fear-potentiated startle. These findings suggest that multiple outputs from the amygdala play a critical role in fear-potentiated startle and that SP plays a critical, probably modulatory role, in the MeA to VMH to PAG to the startle pathway based on these and data from others.

Differential effects of NK1 receptors in the midbrain periaqueductal gray upon defensive rage and predatory attack in the cat

This study utilized anatomical and behavioral-pharmacological methods to determine the role of NK(1)-Substance P receptors in the midbrain periaqueductal gray (PAG) in defensive rage behavior in cats. For behavioral pharmacological experiments, monopolar stimulating electrodes were implanted in the medial hypothalamus for elicitation of defensive rage behavior and cannula-electrodes were implanted in the PAG for microinjections of receptor compounds. Microinjections of the NMDA antagonist, AP-7 (2 nmol), into the dorsal PAG blocked defensive rage elicited by medial hypothalamic stimulation, thus establishing the PAG as a synaptic region that receives hypothalamic inputs linked to defensive rage behavior. Microinjections of the NK(1) agonist, GR73632, into the same injection sites facilitated defensive rage in a dose-dependent manner, and also induced spontaneous hissing in five cats. The effects of GR73632 were reduced by pretreatment of the PAG with the NK(1) antagonist, GR82334 (16 nmol), microinjected into the same sites. Microinjections of GR73632 (8 nmol) into the PAG also suppressed predatory attack elicited by stimulation of the lateral hypothalamus. Immunohistochemical methods utilized to detect Substance P and Fos immunoreactivity revealed that neurons in the PAG activated after defensive rage-inducing medial hypothalamic stimulation lie in the same region as Substance-P-immunoreactive processes. Fos immunoreactivity was highest in the dorsomedial aspect of the rostral PAG after medial hypothalamic stimulation. Cats that were unstimulated or that exhibited predatory attack after lateral hypothalamic stimulation had low c-fos expression levels in the PAG. Substance P immunoreactivity was high throughout the dorsal PAG. The results indicate that NK(1) receptors in the PAG potentiate defensive rage and suppress predatory aggression in the cat.

NK1 receptors in the medial hypothalamus potentiate defensive rage behavior elicited from the midbrain periaqueductal gray of the cat

Defensive rage in the cat occurs naturally in response to a threat and is also elicited by electrical or chemical stimulation over the rostro-caudal extent of the medial hypothalamus and dorsolateral aspect of the periaqueductal gray (PAG). This behavior is mediated over a descending projection from the hypothalamus to the midbrain PAG. The underlying hypothesis for the present study was that medial hypothalamic defensive rage neurons are excited in two ways: by NK(1) receptors and by an ascending input from the PAG. The first aspect of this hypothesis was tested by eliciting defensive rage by electrical stimulation of the PAG and then microinjecting a selective NK(1) agonist and antagonist into the hypothalamus. Microinjections of 16 or 12 nmol/0.25 microl of the NK(1) agonist, GR 73632, resulted in facilitation of defensive rage. These facilitatory effects were then blocked by pretreatment with the NK(1) antagonist, GR 82334. However, microinjections of GR 82334 alone had no effect. The second aspect of the hypothesis was tested by stimulating defensive rage sites in the PAG and using immunohistochemical methods to test for the presence of c-Fos in the hypothalamus. The results revealed the presence of c-Fos immunoreactivity in the medial but not lateral hypothalamus. Overall, the findings indicate that NK(1) receptors in the medial hypothalamus facilitate defensive rage elicited from PAG neurons whose axons project back to the medial hypothalamus. The likely ethological significance of the ascending input is that it allows for potentiation and prolongation of defensive rage in response to a threatening stimulus.

Effect of electrical stimulation of the baso-lateral amygdala nucleus on defensive burying shock probe test and elevated plus maze in rats

In the present report, the putative effect of a single electrical stimulation (75, 150 or 300 microA) to the baso-lateral amygdala (BLA) nucleus was assessed in shock probe defensive burying behavior test (DB) and elevated plus maze (EPM). These models have been used for measuring anxiety levels and screening putative anxiolytic compounds. A group of 28 rats were randomly divided for the following experimental conditions: Control-control, sham-operated, BLA stimulated groups: 75, 150 and 300 microA tested for DB. The cumulative defensive burying in a 15 min-test, the latency of burying, the number of shock received and the height of the bedding material in the probe were recorded. Another group of 28 individuals was also randomly distributed for the following experimental conditions: Control-control, sham-operated, BLA stimulated animals: 75, 150, 300 microA and tested in the EPM. The time the subjects spent in the open arms, the crosses and the faeces number excreted during the test were recorded. Decreased levels of defensive burying were observed in 75, 150 and 300 microA stimulated groups. The 150 and 300 microA groups reached statistical significance. The fact that 300 microA stimulated group showed statistically significant increase in the latency of defensive burying, in the number of shock received and decreased amount in bedding material suggests a sedative action of electrical stimulation. Increased time in the open arms and augmented number of crossings in 150 microA group was observed. No changes in the number of faeces were observed in any group. The evidence supported the notion of an inhibitory amygdaline mechanism triggered by sub-threshold electrical stimulation.

Repeated anabolic-androgenic steroid treatment during adolescence increases vasopressin V(1A) receptor binding in Syrian hamsters: correlation with offensive aggression

Repeated anabolic-androgenic steroid treatment during adolescence increases hypothalamic vasopressin and facilitates offensive aggression in male Syrian hamsters (Mesocricetus auratus). The current study investigated whether anabolic-androgenic steroid exposure during this developmental period influenced vasopressin V(1A) receptor binding activity in the hypothalamus and several other brain areas implicated in aggressive behavior in hamsters. To test this, adolescent male hamsters were administered anabolic steroids or sesame oil throughout adolescence, tested for offensive aggression, and examined for differences in vasopressin V(1A) receptor binding using in situ autoradiography. When compared with control animals, aggressive, adolescent anabolic steroid-treated hamsters showed significant increases (20-200%) in the intensity of vasopressin V(1A) receptor labeling in several aggression areas, including the ventrolateral hypothalamus, bed nucleus of the stria terminalis, and lateral septum. However, no significant differences in vasopressin V(1A) receptor labeling were found in other brain regions implicated in aggressive responding, most notably the lateral zone from the medial preoptic area to anterior hypothalamus and the corticomedial amygdala. These data suggest that adolescent anabolic steroid exposure may facilitate offensive aggression by increasing vasopressin V(1A) receptor binding in several key areas of the hamster brain.

Brain structures and neurotransmitters regulating aggression in cats: implications for human aggression

1. Violence and aggression are major public health problems. 2. The authors have used techniques of electrical brain stimulation, anatomical-immunohistochemical techniques, and behavioral pharmacology to investigate the neural systems and circuits underlying aggressive behavior in the cat. 3. The medial hypothalamus and midbrain periaqueductal gray are the most important structures mediating defensive rage behavior, and the perifornical lateral hypothalamus clearly mediates predatory attack behavior. The hippocampus, amygdala, bed nucleus of the stria terminalis, septal area, cingulate gyrus, and prefrontal cortex project to these structures directly or indirectly and thus can modulate the intensity of attack and rage. 4. Evidence suggests that several neurotransmitters facilitate defensive rage within the PAG and medial hypothalamus, including glutamate, Substance P, and cholecystokinin, and that opioid peptides suppress it; these effects usually depend on the subtype of receptor that is activated. 5. A key recent discovery was a GABAergic projection that may underlie the often-observed reciprocally inhibitory relationship between these two forms of aggression. 6. Recently, Substance P has come under scrutiny as a possible key neurotransmitter involved in defensive rage, and the mechanism by which it plays a role in aggression and rage is under investigation. 7. It is hoped that this line of research will provide a better understanding of the neural mechanisms and substrates regulating aggression and rage and thus establish a rational basis for treatment of disorders associated with these forms of aggression.

Induction of preprotachykinin-I and neurokinin-1 by adrenocorticotropin and prolactin. Implication for neuroendocrine-immune-hematopoietic axis

We studied the complex interactions within the neuroendocrine-immune-hematopoietic axis by determining a possible link among ACTH, PRL, PPT-I and the receptors for its peptides, NK-1 and NK-2. Indeed, ACTH and PRL induced the expression of PPT-I and NK-1 in human bone marrow stroma with no effect on NK-2. Consistent with a role for PPT-I in regulating the development of myeloid and erythroid progenitors, we found that ACTH and PRL, through NK-1 stimulated the proliferation of both types of progenitors. Induction of PPT-I was regulated at the transcriptional and post-transcriptional levels. The results showed that ACTH and PRL stimulated the proliferation of bone marrow progenitors, partly through PPT-I and NK-1 induction.

Intraventricular administration of substance p increases the dendritic arborisation and the synaptic surfaces of Purkinje cells in rat's cerebellum

Substance P was infused in the lateral ventricles of twenty Lewis rats for twenty days. On the twentieth day the animals were sacrificed and the cerebellar cortex was processed for electron microscopy. The ultrastructural morphometric analysis revealed that the Purkinje cell dendritic arborisation and the number of the synapses between the parallel fibres and the Purkinje cell dendritic spines were much higher than in control animals. Numerous unattached spines of the secondary and tertiary dendritic branches of the Purkinje cells were also seen in the molecular layer either free or surrounded by astrocytic sheath. The increased number of synapses between the Purkinje cell dendrites and the parallel fibres in the animals, which received substance P intraventricularly, in correlation to control animals, supports a neurotrophine-like activity of the substance P in the mammalian cerebellum, enforcing the pre-programmed capability of the Purkinje cells to develop new synaptic surfaces.

Neurokinin-1 expression and co-localization with glutamate and GABA in the hypothalamus of the cat

Recent behavioral studies using pharmacological techniques have demonstrated that the high affinity substance P (SP) receptor, neurokinin-1 receptor (NK-1), in the medial hypothalamus could be important in mediating defensive rage behavior in the cat. These observations prompted us to use molecular techniques to determine the distribution of NK-1 in the hypothalamus and in other regions of the forebrain relevant to the control of rage behavior. We cloned a 650 bp fragment of the cat NK-1 cDNA. Partial DNA sequence analyses of this fragment indicate 90% homology with the human cDNA. By in situ hybridization (ISH), we showed that NK-1 mRNA was localized in the cytoplasm but not nuclei of cat forebrain neurons. Furthermore, NK-1 mRNA was co-localized in neurons that displayed positive immunolabeling for glutamate or GABA. Moderate labeling was visualized in the anterior medial hypothalamus which receives significant SP input via the stria terminalis from the medial amygdala. Strong labeling was also observed in the basal amygdaloid complex. The functional significance of this labeling pattern is suggested from the observation that both the medial and basal complex of amygdala serve as powerful modulators of defensive rage behavior. Weaker labeling was seen over the posterior medial and lateral hypothalamus. The distribution of NK-1 in the hypothalamus was matched by that of SP-immunoreactive axons and pre-terminals that were observed in the hypothalamus. The overall findings provide anatomical evidence to show that the high affinity SP receptor, NK-1, is linked to glutamate and GABA neurons in the anterior medial hypothalamus and further suggests its likely role in the regulation of feline aggression.

Neuropharmacology of brain-stimulation-evoked aggression

Evidence is reviewed concerning the brain areas and neurotransmitters involved in aggressive behavior in the cat and rodent. In the cat, two distinct neural circuits involving the hypothalamus and PAG subserve two different kinds of aggression: defensive rage and predatory (quiet-biting) attack. The roles played by the neurotransmitters serotonin, GABA, glutamate, opioids, cholecystokinin, substance P, norepinephrine, dopamine, and acetylcholine in the modulation and expression of aggression are discussed. For the rat, a single area, largely coincident with the intermediate hypothalamic area, is crucial for the expression of attack; variations in the rat attack response in natural settings are due largely to environmental variables. Experimental evidence emphasizing the roles of serotonin and GABA in modulating hypothalamically evoked attack in the rat is discussed. It is concluded that significant progress has been made concerning our knowledge of the circuitry underlying the neural basis of aggression. Although new and important insights have been made concerning neurotransmitter regulation of aggressive behavior, wide gaps in our knowledge remain.

Neuroimmunomodulation via limbic structures--the neuroanatomy of psychoimmunology

During the last 20 years, mutual communications between the immune, the endocrine and the nervous systems have been defined on the basis of physiological, cellular, and molecular data. Nevertheless, a major problem in the new discipline "Psychoneuroimmunology" is that controversial data and differences in the interpretation of the results make it difficult to obtain a comprehensive overview of the implications of immunoneuroendocrine interactions in the maintenance of physiological homeostasis, as well as in the initiation and the course of pathological conditions within these systems. In this article, we will first discuss the afferent pathways by which immune cells may affect CNS functions and, conversely, how neural tissues can influence the peripheral immune response. We will then review recent data, which emphasize the (patho)physiological roles of hippocampal-amygdala structures and the nucleus accumbens in neuroimmunomodulation. Neuronal activity within the hippocampal formation, the amygdaloid body, and the ventral parts of the basal ganglia has been examined most thoroughly in studies on neuroendocrine, autonomic and cognitive functions, or at the level of emotional and psychomotor behaviors. The interplay of these limbic structures with components of the immune system and vice versa, however, is still less defined. We will attempt to review and discuss this area of research taking into account recent evidences for neuroendocrine immunoregulation via limbic neuronal systems, as well as the influence of cytokines on synaptic transmission, neuronal growth and survival in these brain regions. Finally, the role of limbic structures in stress responses and conditioning of immune reactivity will be commented. Based on these data, we propose new directions of future research.

Differential effects of ethanol on feline rage and predatory attack behavior: an underlying neural mechanism

Previous studies have shown that, at certain dose levels, ethanol can exert a powerful, facilitatory effect on aggressive behavior in both animals and humans. In the cat, however, it was discovered that ethanol differentially alters two forms of aggression that are common to this species. Defensive rage behavior is significantly enhanced, whereas predatory attack behavior is suppressed by ethanol administration. One possible mechanism governing alcohol's potentiation of defensive rage behavior is that it acts on the descending pathway from the medial hypothalamus to the midbrain periaqueductal gray (PAG)-an essential pathway for the expression of defensive rage behavior that uses excitatory amino acids as a neurotransmitter. This hypothesis is supported by the finding that the excitatory effects of alcohol on defensive rage behavior are blocked by administration of the N-methyl-D-aspartate antagonist alpha-2-amino-7-phosphoheptanoic acid (AP-7) when microinjected into the periaqueductal gray, a primary neuronal target of descending fibers from the medial hypothalamus that mediate the expression of defensive rage behavior. Thus, the present study establishes for the first time a specific component of the neural circuit for defensive rage behavior over which the potentiating effects of ethanol are mediated.

Medial amygdaloid suppression of predatory attack behavior in the cat: II. Role of a GABAergic pathway from the medial to the lateral hypothalamus

The medial amygdala is known to powerfully suppress predatory attack behavior elicited by electrical stimulation of the lateral hypothalamus of the cat. In the preceding paper, it was shown that the initial limb of a pathway subserving suppression of predatory attack from the medial amygdala to the lateral hypothalamus projects to the ventromedial hypothalamus and its functions are mediated by substance P. The present study tested the hypothesis that the second limb of the pathway subserving medial amygdaloid suppression of predatory attack behavior projects from the medial to lateral hypothalamus and its functions are mediated by GABA. Cannula electrodes were implanted into the lateral hypothalamus for elicitation of predatory attack behavior as well as for the microinfusion of GABA compounds. Monopolar stimulating electrodes were implanted into sites within the medial amygdala from which subseizure levels of stimulation could suppress predatory attack behavior. Initially, the effects of dual stimulation of the medial amygdala and lateral hypothalamus upon response latencies for predatory attack were compared with single stimulation of the lateral hypothalamus alone. Dual stimulation was shown to significantly suppress predatory attack elicited from the lateral hypothalamus. Then, the GABAA receptor antagonist, bicuculline, was microinjected into sites within the lateral hypothalamus from which predatory attack was elicited in doses of 0.015, 0.075 and 0.15 nmol and paired trials of single and dual stimulation were again repeated in a manner identical to that applied prior to drug administration. Drug infusion produced a blockade of medial amygdaloid suppression of predatory attack in a time- and dose-dependent manner. Conversely, microinfusions of the GABAA receptor agonist, muscimol (10, 25 and 50 pmol), into the same lateral hypothalamic 'attack' site in the absence of medial amygdaloid stimulation suppressed predatory attack, thus simulating the effects of medial amygdaloid stimulation. Furthermore, pretreatment with bicuculline microinjected into the lateral hypothalamus blocked the suppressive effects of substance P, that was infused into the ventromedial hypothalamus, upon predatory attack. Receptor autoradiography demonstrated the presence of high affinity binding for GABAA receptors in the lateral hypothalamus. A combination of immunocytochemical and retrograde axonal tract tracing procedures, in which Fluoro-Gold was microinjected into the lateral hypothalamic attack sites, revealed the presence of populations of neurons labeled for both Fluoro-Gold and GABA in the ventromedial hypothalamus. These findings provide new evidence for the existence of a pathway from the medial to lateral hypothalamus whose functions are mediated by GABA. Thus, the overall findings provide support for the view that the pathway from the medial amygdala to the lateral hypothalamus underlying suppression of predatory attack behavior involves a two-neuronal arc: the first neuron projects from the medial amygdala to the medial hypothalamus and its functions are mediated by substance P: the second neuron involves a GABAergic pathway originating in the ventromedial hypothalamus and which projects to the lateral hypothalamus.