c-fos immunoreactivity in the brain following electrical or chemical stimulation of the medial hypothalamus of freely moving rats

Hypothalamic Supramammillary Control of Cognition and Motivation

The supramammillary nucleus (SuM) is a small region in the ventromedial posterior hypothalamus. The SuM has been relatively understudied with much of the prior focus being on its connection with septo-hippocampal circuitry. Thus, most studies conducted until the 21st century examined its role in hippocampal processes, such as theta rhythm and learning/memory. In recent years, the SuM has been "rediscovered" as a crucial hub for several behavioral and cognitive processes, including reward-seeking, exploration, and social memory. Additionally, it has been shown to play significant roles in hippocampal plasticity and adult neurogenesis. This review highlights findings from recent studies using cutting-edge systems neuroscience tools that have shed light on these fascinating roles for the SuM.

Activation of Brainstem Neurons During Mesencephalic Locomotor Region-Evoked Locomotion in the Cat

The distribution of locomotor-activated neurons in the brainstem of the cat was studied by c-Fos immunohistochemistry in combination with antibody-based cellular phenotyping following electrical stimulation of the mesencephalic locomotor region (MLR) – the anatomical constituents of which remain debated today, primarily between the cuneiform (CnF) and the pedunculopontine tegmental nuclei (PPT). Effective MLR sites were co-extensive with the CnF nucleus. Animals subject to the locomotor task showed abundant Fos labeling in the CnF, parabrachial nuclei of the subcuneiform region, periaqueductal gray, locus ceruleus (LC)/subceruleus (SubC), Kölliker–Fuse, magnocellular and lateral tegmental fields, raphe, and the parapyramidal region. Labeled neurons were more abundant on the side of stimulation. In some animals, Fos-labeled cells were also observed in the ventral tegmental area, medial and intermediate vestibular nuclei, dorsal motor nucleus of the vagus, n. tractus solitarii, and retrofacial nucleus in the ventrolateral medulla. Many neurons in the reticular formation were innervated by serotonergic fibers. Numerous locomotor-activated neurons in the parabrachial nuclei and LC/SubC/Kölliker–Fuse were noradrenergic. Few cholinergic neurons within the PPT stained for Fos. In the medulla, serotonergic neurons within the parapyramidal region and the nucleus raphe magnus were positive for Fos. Control animals, not subject to locomotion, showed few Fos-labeled neurons in these areas. The current study provides positive evidence for a role for the CnF in the initiation of locomotion while providing little evidence for the participation of the PPT. The results also show that MLR-evoked locomotion involves the parallel activation of reticular and monoaminergic neurons in the pons/medulla, and provides the anatomical and functional basis for spinal monoamine release during evoked locomotion. Lastly, the results indicate that vestibular, cardiovascular, and respiratory centers are centrally activated during MLR-evoked locomotion. Altogether, the results show a complex pattern of neuromodulatory influences of brainstem neurons by electrical activation of the MLR.

Modulation of experimental arthritis by vagal sensory and central brain stimulation

Articular inflammation is a major clinical burden in multiple inflammatory diseases, especially in rheumatoid arthritis. Biological anti-rheumatic drug therapies are expensive and increase the risk of systemic immunosuppression, infections, and malignancies. Here, we report that vagus nerve stimulation controls arthritic joint inflammation by inducing local regulation of innate immune response. Most of the previous studies of neuromodulation focused on vagal regulation of inflammation via the efferent peripheral pathway toward the viscera. Here, we report that vagal stimulation modulates arthritic joint inflammation through a novel "afferent" pathway mediated by the locus coeruleus (LC) of the central nervous system. Afferent vagal stimulation activates two sympatho-excitatory brain areas: the paraventricular hypothalamic nucleus (PVN) and the LC. The integrity of the LC, but not that of the PVN, is critical for vagal control of arthritic joint inflammation. Afferent vagal stimulation suppresses articular inflammation in the ipsilateral, but not in the contralateral knee to the hemispheric LC lesion. Central stimulation is followed by subsequent activation of joint sympathetic nerve terminals inducing articular norepinephrine release. Selective adrenergic beta-blockers prevent the effects of articular norepinephrine and thereby abrogate vagal control of arthritic joint inflammation. These results reveals a novel neuro-immune brain map with afferent vagal signals controlling side-specific articular inflammation through specific inflammatory-processing brain centers and joint sympathetic innervations.

5-HT1A and 5-HT2A receptor control of a panic-like defensive response in the rat dorsomedial hypothalamic nucleus

The dorsomedial nucleus of the hypothalamus (DMH) has long been implicated in the genesis/regulation of escape, a panic-related defensive behavior. In the dorsal periaqueductal gray matter (dPAG), another key panic-associated area, serotonin, through the activation of 5-HT1A and 5-HT2A receptors, exerts an inhibitory role on escape expression. This panicolytic-like effect is facilitated by chronic treatment with clinically effective antipanic drugs such as fluoxetine and imipramine. It is still unclear whether serotonin within the DMH plays a similar regulatory action. The results showed that intra-DMH injection of the 5-HT1A receptor agonist 8-OH-DPAT, the preferential 5-HT2A receptor agonist DOI, but not the 5-HT2C agonist MK-212, inhibited the escape reaction of male Wistar rats evoked by electrical stimulation of the DMH. Local microinjection of the 5-HT1A antagonist WAY-100635 or the preferential 5-HT2A antagonist ketanserin was ineffective. Whereas chronic (21 days) systemic treatment with imipramine potentiated the anti-escape effect of both 8-OH-DPAT and DOI, repeated administration of fluoxetine enhanced the effect of the latter agonist. The results indicate that 5-HT1A and 5-HT2A receptors within the DMH play a phasic inhibitory role upon escape expression, as previously reported in the dPAG. Facilitation of 5-HT-mediated neurotransmission in the DMH may be implicated in the mode of action of antipanic drugs.

Histaminergic modulation of nonspecific plasticity of the auditory system and differential gating

In the auditory system of the big brown bat (Eptesicus fuscus), paired conditioned tonal (CS) and unconditioned leg stimuli (US) for auditory fear conditioning elicit tone-specific plasticity represented by best-frequency (BF) shifts that are augmented by acetylcholine, whereas unpaired CS and US for pseudoconditioning elicit a small BF shift and prominent nonspecific plasticity at the same time. The latter represents the nonspecific augmentations of auditory responses accompanied by the broadening of frequency tuning and decrease in threshold. It is unknown which neuromodulators are important in evoking the nonspecific plasticity. We found that histamine (HA) and an HA3 receptor (HA3R) agonist (α-methyl-HA) decreased, but an HA3R antagonist (thioperamide) increased, cortical auditory responses; that the HA3R agonist applied to the primary auditory cortex before pseudoconditioning abolished the nonspecific augmentation in the cortex without affecting the small cortical BF shift; and that antagonists of acetylcholine, norepinephrine, dopamine, and serotonin receptors did not abolish the nonspecific augmentation elicited by pseudoconditioning. The histaminergic system plays an important role in eliciting the arousal and defensive behavior, possibly through nonspecific augmentation. Thus HA modulates the nonspecific augmentation, whereas acetylcholine amplifies the BF shifts. These two neuromodulators may mediate differential gating of cortical plasticity.

Glutamic acid decarboxylase 65 and 67 expression in the lateral septum is up-regulated in association with the postpartum period in mice

The postpartum period in mammals undergoes a variety of physiological adaptations, including metabolic, behavioral and neuroendocrine alterations. GABA signaling has been strongly linked to various emotional states, stress responses and offspring protection. However, whether GABA signaling may change in the lateral septum (LS), a core brain region for regulating behavioral, emotional and stress responses in postpartum mice has not previously been examined. In this study, we tested whether the expression of two isoforms of glutamic acid decarboxylase (GAD), GAD65 (GAD2) and GAD67 (GAD1), the rate-limiting enzyme for GABA synthesis, exhibits altered expression in postpartum mice relative to nonmaternal, virgin mice. Using microdissected septal tissue from virgin and age-matched postpartum females, quantitative real-time PCR and Western blotting were carried out to assess GAD mRNA and protein expression, respectively. We found both protein and mRNA expression of GAD67 in the whole septum was up-regulated in postpartum mice. By contrast, no significant difference in the whole septum was observed in GAD65 expression. We then conducted a finer level of analysis using smaller microdissections and found GAD67 to be significantly increased in rostral LS, but not in caudal LS or medial septum (MS). Further, GAD65 mRNA expression in rostral LS, but not in caudal LS or MS was also significantly elevated in postpartum mice. These findings suggest that an increased GABA production in rostral LS of the postpartum mice via elevated GAD65 and GAD67 expression may contribute to multiple alterations in behavioral and emotional states, and responses to stress that occur during the postpartum period. Given that rostral LS contains GABA neurons that are projection neurons or local interneurons, it still needs to be determined whether the function of elevated GABA is for local or distant action or both.

Brain circuits mediating baroreflex bradycardia inhibition in rats: an anatomical and functional link between the cuneiform nucleus and the periaqueductal grey

Defence responses triggered experimentally in rats by stimulation of the dorsomedial nucleus of the hypothalamus (DMH) and the dorsolateral periaqueductal grey matter (PAG) inhibit the cardiac baroreflex response (i.e. bradycardia). It has also been proposed that the midbrain cuneiform nucleus (CnF) is involved in active responses. Our aim was to identify the neurocircuitry involved in defence-induced baroreflex inhibition, with a particular focus on the link between DMH, CnF and dorsolateral PAG. Microinjection of the anterograde tracer Phaseolus vulgaris leucoaggutinin into the CnF revealed a dense projection to the dorsolateral PAG. Moreover, activation of neurons in the CnF induced increased expression of Fos protein in the dorsolateral PAG. Inhibition of neurons of the CnF or dorsolateral PAG prevented the inhibition of baroreflex bradycardia induced by DMH or CnF stimulation, respectively. These results provide a detailed description of the brain circuitry underlying acute baroreflex modulation by neurons of the DMH. Our data have shown for the first time that the CnF plays a key role in defence reaction-associated cardiovascular changes; its stimulation, from the DMH, activates the dorsolateral PAG, which, in turn, inhibits baroreflex bradycardia.

Withdrawal from methylphenidate increases neural reactivity of dorsal midbrain

Ritalin (methylphenidate hydrochloride, MP) is a non-amphetamine psychostimulant and is the drug of choice to treat children and adults diagnosed with the attention deficit hyperactivity disorder (ADHD). Several studies have demonstrated that rats treated with MP during early developmental stage exhibit alterations in anxiety-related processes such as an increased response to stressful stimuli and elevated plasma levels of corticosterone. Accordingly, the present study was designed to further characterize the neural and behavioral consequences of withdrawal from MP in adult rats and its influence on the neural reactivity of the dorsal midbrain. After initial exposure to an elevated plus-maze (EPM), brainstem neural activation, elicited by exposure to EPM aversive cues, was analyzed using a Fos-protein immunolabeling technique. Additional independent groups of animals were submitted to electrical stimulation of the dorsal column (DPAG) or the startle response procedure, in order to verify the influence of withdrawal from MP on the expression of unconditioned fear induced by DPAG activation and the effects of or withdrawal from MP on motor response, respectively. Our results provide new findings about the influence of MP treatment in adult rats, showing that, after a sudden MP treatment-break, increased anxiety, associated with the neural sensitization of anxiety-related regions, ensues.

Methimazole-induced hypothyroidism inhibits the panic-like behaviors produced by electrical stimulation of dorsal periaqueductal gray matter of rats

Conflicting clinical data on the relationship of panic disorder and thyroid diseases illustrate the need for a simpler approach using animal models. Defensive behaviors evoked by electrical or chemical stimulation of dorsal periaqueductal gray matter (DPAG) have been proposed as a model of panic attack. Therefore, the present study examined the effects of the anti-thyroid agent methimazole (MTZ) either on the panic-like behaviors induced by electrical stimulation of DPAG or the anxiety-like behaviors of rats exposed to the elevated plus-maze (EPM). Male Wistar rats bearing electrodes in the DPAG were stimulated with stepwise increased currents. Rats which displayed galloping at intensities below 60muA were retested following 5- and 10-day treatments with MTZ (0.6mg/kg/day, i.p.) or 10- and 15-day washout periods. MTZ effects on EPM performance were assessed in separate groups. MTZ-treated groups were compared to saline-treated controls. In other experiments, rats were similarly treated with MTZ and the blood was collected for hormone assays. The 10-day treatment with MTZ produced marked increases in the thresholds of exophthalmus (65%), immobility (75%), trotting (63%), galloping (56%), jumping (47%), defecation (114%) and micturition (85%). Effects outlasted the drug discontinuation. In contrast, MTZ had variable effects in the EPM, significantly increasing the open-arm exploration in 5-day treated and 10-day washout groups. Biochemical data revealed a small but significant decrease (13%) in free thyroxine in MTZ-treated groups. Although not significant, thyrotrophin levels showed a 111% increase following the 10-day treatment with MTZ. Selective attenuation by MTZ of DPAG-evoked defensive behaviors supports attenuation of panic attacks in hypothyroidism.

Tone-specific and nonspecific plasticity of inferior colliculus elicited by pseudo-conditioning: role of acetylcholine and auditory and somatosensory cortices

Experience-dependent plasticity in the central sensory systems depends on activation of both the sensory and neuromodulatory systems. Sensitization or nonspecific augmentation of central auditory neurons elicited by pseudo-conditioning with unpaired conditioning tonal (CS) and unconditioned electric leg (US) stimuli is quite different from tone-specific plasticity, called best frequency (BF) shifts, of the neurons elicited by auditory fear conditioning with paired CS and US. Therefore the neural circuits eliciting the nonspecific augmentation must be different from that eliciting the BF shifts. We first examined plastic changes in the response properties of collicular neurons of the big brown bat elicited by pseudo-conditioning and found that it elicited prominent nonspecific augmentation-an auditory response increase, a frequency-tuning broadening, and a threshold decreas-and that, in addition, it elicited a small short-lasting BF shift only when the CS frequency was 5 kHz lower than the BF of a recorded neuron. We examined the role of acetylcholine and the auditory and somatosensory cortices in these collicular changes. The development of the nonspecific augmentation was affected little by a muscarinic acetylcholine receptor antagonist applied to the inferior colliculus and by a GABA(A) receptor agonist applied to the auditory or somatosensory cortex. However, these drugs abolished the small short-lasting BF shift as they abolished the large long-lasting cortical and short-lasting collicular BF shifts elicited by the conditioning. These results indicate that, different from the BF shift, the nonspecific augmentation of the inferior colliculus depends on neither the cholinergic neuromodulator nor the auditory and somatosensory cortices.

Orexin neurons in the hypothalamus mediate cardiorespiratory responses induced by disinhibition of the amygdala and bed nucleus of the stria terminalis

We previously showed that the defense response elicited by stressors was attenuated in prepro-orexin knockout mice and in orexin neuron-ablated mice, and we proposed that orexin serves as a master switch within multiple efferent pathways that mediate the defense response. In this study we sought to determine whether excitation of the amygdala (AMG) or the bed nucleus of stria terminalis (BNST) activates orexin-containing neurons and whether those neurons are essential in eliciting cardiorespiratory responses to the stimulus. In urethane-anesthetized mice, the GABA-A receptor antagonist bicuculline was microinjected into the AMG or BNST and blood pressure, heart rate, and respiration were measured. Injection of bicuculline in either site induced long-lasting dose-dependent cardiorespiratory excitation in wild-type mice. In contrast, mice in which orexin neurons had been ablated demonstrated no such response after activation of the AMG and an attenuated response after activation of the BNST. Double immunohistochemical staining for orexin and c-Fos, an indicator of neural activation, revealed that an injection of bicuculline induced significantly larger numbers of orexin positive neurons that expressed c-Fos in the perifornical/dorsomedial hypothalamus (58.2+/-6.4% into AMG and 66.4+/-6.6% into BNST, n=3 each) than did vehicle (18.2+/-4.4% into AMG and 28.3+/-2.1% into BNST). Disinhibition to the BNST induced widespread expression of c-Fos not only in orexin-containing neurons but also other neurons in the hypothalamus. We conclude that orexin-containing neurons in the medial hypothalamus mediate at least a part of AMG- and BNST-induced cardiorespiratory responses.

Induction of Fos-immunoreactivity in the rat brain following disinhibition of the dorsomedial hypothalamus

Activation of neurons in the dorsomedial hypothalamus (DMH) appears to play an important role in signaling the excitation of brain regions responsible for experimental fever and for many of the physiological and behavioral changes seen in experimental stress or anxiety in rats. Here, we examined the effect of disinhibition of the DMH by unilateral microinjection of bicuculline methiodide (BMI) on Fos expression in selected regions of the brain that have been implicated in anxiety and responses to stress and fever in rats. Disinhibition of the DMH resulted in dramatic increases in local Fos expression and also increased the numbers of Fos-positive neurons in the lateral septal nucleus and in both the parvocellular and magnocellular subdivisions of the paraventricular nucleus, with greater increases ipsilateral to the injection site in the DMH. However, microinjection of BMI had no significant effect on Fos expression in the bed nucleus of the stria terminalis, another forebrain area implicated in stress and anxiety. In the brainstem, disinhibition of the DMH increased Fos expression in the nucleus tractus solitarius and the ventrolateral medulla bilaterally with greater increases again ipsilateral to the site of the microinjection, and also in the midline rostral raphe pallidus. Thus, disinhibition of neurons in the DMH in conscious rats results in increases in Fos expression in selected forebrain and brainstem regions that have been implicated in stress-induced physiological changes, anxiety, and experimental fever.

Brainstem areas activated by diazepam withdrawal as measured by Fos-protein immunoreactivity in rats

In the 1970s, chronic treatment with benzodiazepines was supposed not to cause dependence. However, by the end of the decade several reports showed that the interruption of a prolonged treatment with diazepam leads to a withdrawal syndrome characterized, among other symptoms, by an exaggerated level of anxiety. In laboratory animals, signs that oscillate from irritability to extreme fear-like behaviors and convulsions have also been reported. In recent years many studies have attempted to disclose the neural substrates responsible for the benzodiazepines withdrawal. However, they have focused on telencephalic structures such as the prefrontal cortex, nucleus accumbens and amygdala. In this study, we examined the Fos immunoreactivity in brain structures known to be implicated in the neural substrates of aversion in rats under spontaneous diazepam-withdrawal. We found that the same group of structures that originally modulate the defensive responses evoked by fear stimuli, including the dorso-medial hypothalamus, the superior and inferior colliculus and the dorsal periaqueductal gray, were most labeled following diazepam withdrawal. It is suggested that an enhanced neural activation of neural substrates of fear in the midbrain tectum may underlie the aversive state elicited in diazepam-withdrawn rats.

Differential activation of anterior and midline thalamic nuclei following retrieval of aversively motivated learning tasks

Two thalamic nuclear groups, the anterior thalamic nuclei (ATN) and midline and intralaminar thalamic complex (MITC) have connections to the prefrontal cortex, amygdala, hippocampus and accumbens that are important for learning and memory. However, the anatomical proximity between the ATN and MITC makes it difficult to reveal their roles in memory retrieval of aversive conditioned behavior. To address the issue, we explored the activation of the ATN and MITC, as represented by the expression of the immediate early gene c-fos, following either the retrieval of a conditioned taste aversion (CTA) induced by taste-LiCl pairing (visceral aversion) or of inhibitory avoidance (IA) induced by context-foot shock pairing (somatic aversion) in rats. The anterodorsal (AD) nucleus in the ATN was activated by foot shock and the recall of IA, but not by i.p. injection of LiCl or the recall of CTA. No significant elevation was observed in the other ATN following these treatments. Among nuclei of the MITC, the paraventricular thalamic nucleus (PVT) was activated by the delivery of shock or LiCl and by the recall of both CTA and IA, while the mediodorsal thalamus (MD) and central medial and intermediate thalamus (CM/IMD) were not. The innately aversive taste of quinine did not elevate c-fos expression in either the ATN or MITC. These results suggest that the PVT in the MITC is involved in the processing and retrieval of both taste-malaise and context-shock association tasks, while the AD in the ATN is involved in those of context-shock association only. The difference of the activity between the ATN and MITC demonstrates their functional and anatomical heterogeneity in neural substrates for aversive learning tasks.

Contribution of the ventromedial hypothalamus to generation of the affective dimension of pain

The ventromedial hypothalamus (VMH) is a core structure underlying the generation of affective behaviors to threats. The prototypical threat to an individual is exposure to a noxious stimulus and the dorsomedial division of the VMH (dmVMH) receives nociceptive input. The present study evaluated the contribution of the dmVMH to generation of the affective reaction to pain in rats. Noxious tailshock elicits from rats vocalization afterdischarges (VADs) that have distinct spectrographic characteristics and are a validated model of the affective reaction to pain. VAD-like vocalizations (vocalizations with the same spectral characteristics of VADs) were elicited by stimulation (electrical or chemical) of the dmVMH. Stimulation in the vicinity of the dmVMH was ineffective in eliciting VADs. Manipulation of GABA(A) neurochemistry within the dmVMH altered the threshold for elicitation of VADs by dmVMH stimulation or tailshock. Administration of the GABA(A) antagonist bicuculline or the GABA(A) agonist muscimol into the dmVMH lowered and elevated VAD thresholds, respectively. These treatments did not alter thresholds of other tailshock elicited responses (vocalizations during tailshock or spinal motor reflexes). Bicuculline and muscimol administered into the dmVMH also elevated and lowered the asymptotic level of fear conditioning supported by dmVMH stimulation or tailshock. These findings demonstrate that the dmVMH contributes to the processing of pain affect and that the affective dimension of pain belongs to a broader class of sensory experience that represents threat to the individual.

Unilateral electrical stimulation of the inferior colliculus of rats modifies the prepulse modulation of the startle response (PPI): effects of ketamine and diazepam

The magnitude of an acoustic startle response can be reduced by a weak stimulus presented immediately before the startle-eliciting noise. This phenomenon has been termed prepulse inhibition of the startle reaction (PPI). Previous studies indicated that the primary neural pathways mediating PPI belong to the brain stem and that the inferior colliculus (IC) was crucial. Its destruction reduced PPI. Stimulations applied to brain areas may be as deleterious as lesions. Therefore, we looked for the possibility of a brain stimulation applied to the IC during a PPI test to reduce also PPI. Rats were implanted with chronic electrodes, their tips being aimed at the IC. They were located within or close to the inter-colliculus nucleus. A train of stimulations was applied and PPI was tested alternately during and between periods of stimulation. As the most common method used to attenuate PPI consists in administrating drugs, for example ketamine, we also tested the effect of this drug. Another drug was also tested, diazepam, since it alters the functioning of the IC without any known effect on PPI. This allowed a comparative analysis of the neurobiological and the pharmacological effects. It appeared that the stimulation decreased PPI quantitatively as much as ketamine (6 mg/kg) without an effect of the basic startle reaction. These effects did not interfere with each other. Diazepam (1 mg/kg) did not modify PPI, neither under stimulation nor per se. Only for a very high dose (4 mg/kg), a sedative and myo-relaxant one the basic startle and PPI were altered.

Regulation of affect by the lateral septum: implications for neuropsychiatry

Substantial evidence indicates that the lateral septum (LS) plays a critical role in regulating processes related to mood and motivation. This review presents findings from the basic neuroscience literature and from some clinically oriented research, drawing from behavioral, neuroanatomical, electrophysiological, and molecular studies in support of such a role, and articulates models and hypotheses intended to advance our understanding of these functions. Neuroanatomically, the LS is connected with numerous regions known to regulate affect, such as the hippocampus, amygdala, and hypothalamus. Through its connections with the mesocorticolimbic dopamine system, the LS regulates motivation, both by stimulating the activity of midbrain dopamine neurons and regulating the consequences of this activity on the ventral striatum. Evidence that LS function could impact processes related to schizophrenia and other psychotic spectrum disorders, such as alterations in LS function following administration of antipsychotics and psychotomimetics in animals, will also be presented. The LS can also diminish or enable fear responding when its neural activity is stimulated or inhibited, respectively, perhaps through its projections to the hypothalamus. It also regulates behavioral manifestations of depression, with antidepressants stimulating the activity of LS neurons, and depression-like phenotypes corresponding to blunted activity of LS neurons; serotonin likely plays a key role in modulating these functions by influencing the responsiveness of the LS to hippocampal input. In conclusion, a better understanding of the LS may provide important and useful information in the pursuit of better treatments for a wide range of psychiatric conditions typified by disregulation of affective functions.

The supramammillary area: its organization, functions and relationship to the hippocampus

The supramammillary area of the hypothalamus, although small in size, can have profound modulatory effects on the hippocampal formation and related temporal cortex. It can control hippocampal plasticity and also has recently been shown to contain cells that determine the frequency of hippocampal rhythmical slow activity (theta rhythm). We review here its organization and anatomical connections providing an atlas and a new nomenclature. We then review its functions particularly in relation to its links with the hippocampus. Much of its control of behaviour and its differential activation by specific classes of stimuli is consistent with a tight relationship with the hippocampus. However, its ascending connections involve not only caudal areas of the cortex with close links to the hippocampus but also reciprocal connections with more rostral areas such as the infralimbic and anterior cingulate cortices. These latter areas appear to be the most rostral part of a network that, via the medial septum, hippocampus and lateral septum, is topographically mapped into the hypothalamus. The supramammillary area is thus diffusely connected with areas that control emotion and cognition and receives more topographically specific return information from areas that control cognition while also receiving ascending information from brain stem areas involved in emotion. We suggest that it is a key part of a network that recursively transforms information to achieve integration of cognitive and emotional aspects of goal-directed behaviour.

The relevance of neuronal substrates of defense in the midbrain tectum to anxiety and stress: empirical and conceptual considerations

The medial hypothalamus, amygdala, and dorsal periaqueductal gray constitute the main neural substrates for the integration of aversive states in the brain. More recently, some regions of the mesencephalon, such as the superior and inferior colliculi have also been proposed as part of this system. In fact, fear-like behaviors often result when these sites are electrically or chemically stimulated. Both the behavioral and autonomic consequences of electrical stimulation of the mesencephalic tectum have been shown to be attenuated by minor tranquilizers, probably through enhancement of gamma-aminobutyric acid (GABA)-mediated neurotransmission, which exerts a tonic inhibitory control on the neural circuits responsible for the so-called defense behavior repertoire. Besides GABA, also 5-hydroxy tryptamine serotonin (5-HT), opioids, neuropeptides, histaminergic and excitatory amino acids have all been implicated in the regulation of anxiety-related behaviors induced by stimulation of midbrain tectum. Efforts have been made to characterize how these neurotransmitters interact with each other in the organization of these reactions to aversive stimulation. In this review, we summarize the evidence linking the brain's defense response systems to the concept of fear-anxiety. Furthermore, a case is made for the consideration of the relevance of this body of data to the search for the physiological underpinnings of depression and its consequences.

The role of the medial supramammillary nucleus in the control of hippocampal theta activity and behaviour in rats

The medial supramammillary nucleus (mSUM) controls the frequency of hippocampal theta activity, completely in anaethsetized rats and partially in free-moving rats. mSUM could therefore influence hippocampal contributions to cognition and emotion. Using chemical lesions of mSUM in rats, we tested whether mSUM is involved in controlling several hippocampal-dependent functions: (i) defensive behaviour (open field, fear conditioning); (ii) behavioural inhibition (fixed interval schedule, differential reinforcement of low rates schedule); and (iii) spatial learning (water maze). Theta frequency was measured in all these tasks. mSUM lesions produced a pattern of changes in motivated/emotional behaviours (hyperactivity in defensive and operant tasks) similar to the pattern produced by hippocampal lesions, but had no significant effect on spatial learning. mSUM lesion decreased theta frequency modestly (by approximately 0.4 Hz) in behaving rats if the amount of movement was unchanged. There was not always a parallel between changes in theta frequency and behaviour; behaviours changed despite unchanged theta in defensive tasks and learning changed little despite a lower frequency of theta in the water maze task. This suggests that mSUM function impacts on emotional behaviour more than cognition, and can modulate theta and behaviour independently.

The distribution of fos immunoreactivity in rat brain following freezing and escape responses elicited by electrical stimulation of the inferior colliculus

Several sources of evidence indicate that the inferior colliculus also integrates acoustic information of an aversive nature besides its well-known role as a relay station for auditory pathways. Gradual increases of the electrical stimulation of this structure cause in a hierarchical manner alertness, freezing and escape behaviors. Independent groups of animals implanted with bipolar electrodes into the inferior colliculus received electrical stimulation at one of these aversive thresholds. Control animals were submitted to the same procedure but no current was applied. Next, analysis of Fos protein expression was used to map brain areas activated by the inferior colliculus stimulation at each aversive threshold and in the controls. Whereas alertness elicited by stimulation of the inferior colliculus did not cause any significant labeling in any structure studied in relation to the respective control, electrical stimulation applied at the freezing threshold increased Fos-like immunoreactivity in the central amygdaloid nucleus and entorhinal cortex. In contrast, escape response enhanced Fos-like immunoreactivity in the nucleus cuneiform and the dorsal periaqueductal gray matter of the mesencephalon. This evidence supports the notion that freezing and escape behaviors induced by electrical stimulation of the inferior colliculus activate different neural circuitries in the brain. Both defensive behaviors caused significant expression of c-fos in the frontal cortex, hippocampus and basolateral amygdaloid nucleus. This indistinct pattern of c-fos distribution may indicate a more general role for these structures in the modulation of fear-related behaviors. Therefore, the present data bring support to the notion that amygdala, dorsal hippocampus, entorhinal cortex, frontal cortex, dorsal periaqueductal gray matter and cuneiform nucleus altogether play a role in the integration of aversive states generated at the level of the inferior colliculus.

Effects of ibotenic acid lesions of the nucleus accumbens on paced mating behavior in the female rat

The present study investigated the role of the nucleus accumbens (NAcc) in paced mating behavior in female rats. A sexually receptive female rat will approach and withdraw from a sexually active male, thereby controlling the timing of the receipt of sexual stimulation (e.g., mounts, intromissions, ejaculations). In this study, ibotenic acid lesions in the NAcc core increased the likelihood that a female rat would withdraw from a male rat after a mount but did not affect contact return latency or sexual receptivity. Ibotenic acid lesions in the NAcc shell did not affect paced mating behavior or sexual receptivity. The results suggest that the NAcc core plays a role in suppressing withdrawal behavior in response to less intense mating stimulation.

Differential expression of Fos protein in the rat brain induced by performance of avoidance or escape in the elevated T-maze

Analysis of Fos protein expression was used to map brain areas activated by exposure of male Wistar rats to the elevated T-maze, an animal model of anxiety where tasks of inhibitory avoidance or one-way escape can be separately performed. The apparatus consists of three elevated arms--one enclosed and two open. In the inhibitory avoidance task--considered to represent learned fear--the time taken by rats to leave from the enclosed arm in three consecutive trials is measured. One-way escape task is measured by recording the time taken by animals to withdraw from the open arm and is thought to reflect innate fear. Control animals were placed three times at the end of the transversal arm of a T-maze composed of three enclosed arms and withdrawal latencies from this arm was similarly measured. Performance of avoidance task increased Fos-like immunoreactivity in the medial amygdaloid nucleus, in the anterior hypothalamic nucleus and in the median raphe nucleus. In contrast, performance of escape task enhanced Fos-like immunoreactivity in the basolateral amygdaloid nucleus and in the dorsal periaqueductal gray matter of the mesencephalon. Both behavioural tasks promoted an increase in Fos-like immunoreactivity in the paraventricular nucleus of the thalamus and in the dorsomedial hypothalamic nucleus. Therefore, the obtained results indicate that different sets of brain structures were, respectively, activated by inhibitory avoidance and one-way escape. This evidence supports the original hypothesis that two types of fear/anxiety are generated in the elevated T-maze.

Induction of Fos-like immunoreactivity in the ventral thalamus after electrical or chemical stimulation of various subcortical centres of rats

We have examined the patterns of Fos-like immunoreactivity in the ventral thalamus (thalamic reticular nucleus (Rt), zona incerta (ZI) and ventral lateral geniculate nucleus (LGv)) after electrical or chemical stimulation of nuclei in either the brainstem (midbrain reticular nucleus), basal forebrain (substantia innominata) or dorsal thalamus (parafascicular nucleus). Sprague-Dawley rats were anaesthetised with Halothane or Ketamil/Rompun and the above mentioned centres were stimulated either electrically or chemically (using kainic acid). Brains were then processed for Fos-like immunocytochemistry using standard methods. We detected no major differences in the labelling patterns after either electrical or chemical stimulation or after using Halothane or Ketamil/Rompun anaesthesia. After brainstem or dorsal thalamic stimulations, many Fos-like immunoreactive cells were seen within the rostral pole of the Rt, the dorsal sector of the ZI and the parvocellular lamina of the LGv. After basal forebrain stimulations, many Fos-like immunoreactive cells were seen in the rostral pole of the Rt and rostral sector of the ZI, but very few were apparent in the LGv. Overall, our results show that distinct groups of cells in the ventral thalamus show increased levels of Fos-like immunoreactivity after stimulation of different subcortical centres. These activated cells of the ventral thalamus, are in turn, in a position to influence particular thalamocortical pathways through their dorsal thalamic projections.

Immunohistochemical characterisation of Fos-positive cells in brainstem monoaminergic nuclei following intracranial self-stimulation of the medial forebrain bundle in the rat

Fos immunostaining was used as a marker of neuronal activity following intracranial self-stimulation (ICSS) of the medial forebrain bundle (MFB) in the rat, and was combined with immunostaining for tyrosine hydroxylase (TH), serotonin (5-HT), gamma-aminobutyric acid (GABA), or NR1 (one of the glutamate N-methyl- D-aspartate receptor subunits) for purposes of neurochemical identification. ICSS induced a significant but different degree of increase in the number of Fos-immunopositive (Fos+) cells in the six brainstem monoaminergic nuclei examined, which included the ventral tegmental area (VTA), substantia nigra pars compacta (SNc), dorsal raphe nucleus (DR), median raphe nucleus (MR), locus coeruleus (LC), and A7 noradrenaline cells. Densely labelled Fos+ cells were observed in the LC following ICSS, and many of these Fos+ cells were colocalized with TH. Similarly, many of Fos+ cells in the A7 and DR/MR were colocalized with TH and 5-HT, respectively. By contrast, a smaller number of Fos+ cells was detected in the VTA and SNc following the ICSS, and in these regions the majority of Fos+ cells were not colocalized with TH. Although results among regions quantitatively differed, the ICSS induced a significant increase in the number of double-labelled cells (GABA+/Fos+ or NR1+/Fos+) in all of the VTA, DR, and LC, in which the ICSS produced an ipsilaterally weighted increase in Fos-like immunoreactivity. These results suggest that ICSS of the MFB induces differential Fos expression within monoaminergic and GABAergic neurons in brainstem monoaminergic nuclei under modulation by glutamatergic afferents.

Using c-Fos immunocytochemistry to identify forebrain regions that may inhibit maternal behavior in rats

Evidence indicates there is a neural system that inhibits maternal behavior in virgin rats. It has been suggested that pregnancy hormones promote the onset of maternal behavior by reducing the behavioral influence of this system. The authors used c-Fos immunocytochemistry to identify brain regions more activated by pup exposure in nonmaternal rats than in maternal rats. Previous experiments indicated that some of these regions, such as the posterodorsal medial amygdala and several medial hypothalamic sites, inhibit maternal behavior. For others, such as the ventral lateral septum, dorsal premammillary nucleus, and principal bed nucleus of the stria terminalis, this is the first indication that they could also inhibit maternal responding. These regions have previously been implicated in promoting defensive behaviors, consistent with the finding that nonmaternal rats actively avoid pups. These findings suggest the existence of a neural circuit through which pup exposure could promote defensive responses in virgin rats, and how pregnancy hormones could reduce such activity to stimulate maternal behavior.

Initiation of locomotion in mammals

Several "locomotor regions" of the mammalian brain stem can be stimulated, either electrically or chemically, to induce locomotion. Active cells labeled with c-fos within the mesencephalic locomotor region (MLR) have been found in the periaqueductal gray, the cuneiform nucleus, the pedunculopontine nucleus, and the locus coeruleus. Different subsets of these nuclei appear to be activated during locomotion produced in different behavioral contexts. The locomotor nuclei can be classified into areas associated with exploratory, appetitive, and defensive locomotion, in accordance with the proposal of Sinnamon (1993, Prog. Neurobiol. 41: 323-344). The interpretation of lesion studies designed to reveal areas of the brain essential for locomotion must be based on knowledge of the nuclei which become active in the specific locomotor task being tested. An argument is put forward in favor of the continued use of the term "mesencephalic locomotor region."

Differential expression of c-fos mRNA and Fos protein in the rat brain after restraint stress or pentylenetetrazol-induced seizures

1. c-fos mRNA expression and Fos protein expression were investigated by in situ hybridization and immunohistochemistry after 30 min of forced restraint stress or pentylenetetrazol (PTZ; 64 mg/kg, i.p.)-induced seizures. 2. Forced restraint stress and PTZ-induced seizures generated c-fos mRNA expression of distinct intensities, but in similar brain regions, including the hippocampus, the amygdala, the piriform cortex, the paraventricular hypothalamic nucleus, the habenula, and parts of the cerebral cortex. 3. The distribution of Fos-like immunoreactivity induced by stress or seizures only partially overlap. No Fos-like expression was found in the hippocampus or the habenula after restraint stress. Nevertheless, both areas presented Fos-like expression after PTZ-induced seizures. 4. Our results support the suggestion that immediate early gene expression in vivo may exhibit both region- and stimulus-specific expression.

Rewarding brain stimulation induces only sparse Fos-like immunoreactivity in dopaminergic neurons

In this study, c-fos immunohistochemistry was used to identify the brain regions activated by rewarding brain stimulation in rats. Rats had monopolar electrodes implanted in the medial forebrain bundle and were allocated to either a self-stimulation (n = 4), yoked stimulation (n = 4) or no stimulation (n = 6) group. In a single 1 h test session, each rat in the self-stimulation group made 1000 nose poke responses with each response followed by a 0.5 s train of brain stimulation. Rats in the yoked-stimulation group were paired with a partner in the self-stimulation group and received brain stimulation whenever their partner did. However, their nose poke responses did not trigger stimulation. This yoked procedure was thus used to identify any Fos-like immunoreactivity due to operant responding. Rats in the no stimulation group were placed in the same apparatus as the other rats but received no brain stimulation and were thus used to assess baseline Fos-like immunoreactivity. Results showed that stimulation increased Fos-like immunoreactivity in many areas of the brain in both the self-stimulation and yoked groups. The areas with the highest Fos-like immunoreactivity were ipsilateral to the electrode site and included the medial prefrontal cortex, lateral septum, nucleus accumbens (shell), the medial and lateral preoptic areas, bed nucleus of the stria terminalis, central amygdala, lateral habenula, dorsomedial hypothalamus, lateral hypothalamus and the anterior ventral tegmental area. Bilateral Fos-like immunoreactivity was evident in the nucleus accumbens core, paraventricular nucleus of the hypothalamus, the retrorubral fields and the locus coeruleus. A double-labelling procedure identifying both Fos and tyrosine hydroxylase was used to show that very few (< 5%) of the A10 dopamine cell bodies in the ventral tegmental area expressed Fos following brain stimulation. In contrast, most of the noradrenergic neurons of the locus coeruleus (A6), rubrospinal tract (A5) and pontine tegmental area (A7) were Fos positive. Overall, the results show that rewarding, brain stimulation induces Fos-like immunoreactivity in many forebrain regions but only sparsely in mesolimbic and mesocortical dopamine neurons. The similar patterns of Fos-like immunoreactivity seen in the self-stimulation and yoked-stimulation groups suggests that the operant responding for brain stimulation causes minimal Fos expression in itself.

Social stress in hamsters: defeat activates specific neurocircuits within the brain

During an agonistic encounter, subordinate male hamsters display defensive and submissive postures and show increased secretion of glucocorticoids, whereas dominant males do not. To determine whether specific neuronal pathways are activated during the behavioral and neuroendocrine responses of subordinate males, expression of c-fos mRNA within the brains of subordinate males was compared with the pattern in dominant males after fighting. After 1 week of handling, pairs of hamsters were either swapped between cages (handled control males), or were allowed to interact for 30 min [dominant (DOM) males and subordinate (SUB) males]. A second group of control animals that received no handling or social stimulation (unhandled control males) were also included. After testing, all animals were killed by decapitation, their brains were removed for c-fos in situ hybridization, and trunk blood was collected for analysis of plasma cortisol and corticosterone levels. Exposure of males to their partner's cage for 30 min resulted in increased expression of c-fos mRNA in multiple brain regions. In addition, fighting increased c-fos expression in the medial amygdaloid nucleus of both DOM and SUB males as well as having more selective effects. In DOM males, c-fos expression was elevated within the supraoptic nucleus of the hypothalamus. In SUB males, c-fos expression increased within a multitude of brain areas, including cingulate cortex, lateral septum, bed nucleus of the stria terminalis, medial preoptic area, several hypothalamic nuclei, central amygdaloid nucleus, amygdalohippocampal area, dorsal periaqueductal gray, dorsal raphe, cuneiform nucleus, and locus coeruleus. These findings are discussed in relation to neurocircuits associated with behavioral arousal and stress.

Severe reduction of rat defensive behavior to a predator by discrete hypothalamic chemical lesions

Nonspecific lesion and stimulation methods have suggested that the hypothalamus is critical for the expression of defensive behavior, although the organization of neural circuits mediating such behavior is unclear. In the rat hypothalamus, we found that increased Fos levels were restricted to specific cell groups following presentation of a stimulus (predator) known to elicit partly innate defensive responses. The dorsal premammillary nucleus showed the most striking increase in Fos levels, and cell body-specific chemical lesions therein virtually eliminated two major components of defensive behavior but increased exploratory behavior, suggesting that this caudal hypothalamic nucleus plays a critical role in the expression of behavioral responses sometimes critical for survival of the individual. We have previously shown that the Fos-responsive cell groups in the medial hypothalamus are interconnected in a neural system distinct from those mediating reproductive and ingestive behaviors.

Kainate microinjection into the dorsal raphe nucleus induces 5-HT release in the amygdala and periaqueductal gray

Earlier results obtained in one of our laboratories showed that microinjection into the dorsal raphe nucleus (DRN) of the excitatory amino acid kainic acid, the benzodiazepine (BZD) inverse agonist FG 7142, and the 5-HT1A receptor agonist 8-OHDPAT changed the behavior of rats in the elevated T-maze, an animal model of anxiety. The present study investigates biochemical correlates of these results in awake rats by measuring 5-HT release with in vivo microdialysis in two brain structures innervated by the DRN-the amygdala (Am) and the dorsal periaqueductal gray matter (DPAG)-that have been implicated in anxiety. Microinjection of kainic acid (60 pmol) into the DRN significantly increased 5-HT release in both the Am and the DPAG. In the DPAG, the increase was 14-fold higher with respect to the baseline and occurred only at the first sample, which was collected 30 min after the injection. In the Am, the increase was less pronounced (nearly fourfold) but persistent, lasting until the fourth sample, which was collected 120 min from the injection. FG 7142 (40 pmol) and 8-OH-DPAT (8 nmol) were ineffective. Because only intra-DRN kainate both increased inhibitory avoidance and decreased one-way escape in the elevated T-maze, the present behavioral results support the suggestion that 5-HT facilitates conditioned fear in the Am and inhibits unconditioned fear in the DPAG.

Clozapine and some other antipsychotic drugs may preferentially block the same subset of GABA(A) receptors

Selective blockade of a subset of GABA(A) receptors may be involved in the antipsychotic effects of Clozapine and several other antipsychotic drugs. Seven antipsychotic drugs, and 11 drugs classified as antidepressants that only partially reverse the inhibitory effect of 1 microM GABA on [35S]TBPS binding, do not yield additive reversal when tested pairwise with Clozapine, which also only partially reverses the inhibitory effect of GABA. This suggests that all of these antipsychotic/antidepressant drugs may block a common subset of GABA(A) receptors. DMCM and Ro 5-4864 are also partial reversers of GABA's inhibitory effect, but they yield additive reversals when tested pairwise with the antipsychotic/antidepressant drugs, and also with each other, suggesting that DMCM, Ro 5-4864, and the antipsychotic drugs define three heterogeneous subsets of GABA(A) receptors, with variable overlap, depending on the drug. Several potent ligands for benzodiazepine binding sites can block the GABA inhibitory effects of DMCM and Ro 5-4864, but with different patterns: the ligands generally blocked DMCM less potently, but more completely than Ro 5-4864. Ro 5-4864 was not blocked by Flumazenil or CGS-8216, ligands that potently blocked DMCM. Nine additional antipsychotic/antidepressant drugs, as well as Clozapine, and 7 "classical" GABA(A) receptor blockers, all of which reversed GABA nearly completely, when tested at lower concentrations that only reverse approximately 20-35%, yielded almost complete additivity when tested pairwise with DMCM or Ro 54864. Another convulsant benzodiazepine, KW-1937, a positional isomer of Brotizolam, fully reverses the inhibitory effect of 1 microM GABA. At a lower concentration yielding about 50% reversal, KW-1937 is completely additive with DMCM, but entirely nonadditive with Ro 5-4864. The 50% reversal obtained with KW-1937 was potently blocked by Triazolam, but with a plateau similar to that obtained with Ro 5-4864. The results with KW- 1937 suggest that its 50% reversal largely corresponds to the reversal obtained with Ro 5-4864, and that virtually all of the [35S]TBPS binding sites inhibited by 1 microM GABA are coupled to benzodiazepine binding sites. The fraction of GABA(A) receptors preferentially blocked by all the antipsychotic/antidepressant drugs, roughly 25% of the [35S]TBPS binding sites inhibited with 1 microM GABA, are sensitive to KW-1937, but not to DMCM or to Ro 5-4864.