Enhanced nucleus accumbens dopamine and plasma corticosterone stress responses in adult rats with neonatal excitotoxic lesions to the medial prefrontal cortex

Corticotropin releasing factor (CRF) receptor signaling in the central nervous system: new molecular targets

Corticotropin-releasing factor (CRF) and the related urocortin peptides mediate behavioral, cognitive, autonomic, neuroendocrine and immunologic responses to aversive stimuli by activating CRF(1) or CRF(2) receptors in the central nervous system and anterior pituitary. Markers of hyperactive central CRF systems, including CRF hypersecretion and abnormal hypothalamic-pituitary-adrenal axis functioning, have been identified in subpopulations of patients with anxiety, stress and depressive disorders. Because CRF receptors are rapidly desensitized in the presence of high agonist concentrations, CRF hypersecretion alone may be insufficient to account for the enhanced CRF neurotransmission observed in these patients. Concomitant dysregulation of mechanisms stringently controlling magnitude and duration of CRF receptor signaling also may contribute to this phenomenon. While it is well established that the CRF(1) receptor mediates many anxiety- and depression-like behaviors as well as HPA axis stress responses, CRF(2) receptor functions are not well understood at present. One hypothesis holds that CRF(1) receptor activation initiates fear and anxiety-like responses, while CRF(2) receptor activation re-establishes homeostasis by counteracting the aversive effects of CRF(1) receptor signaling. An alternative hypothesis posits that CRF(1) and CRF(2) receptors contribute to opposite defensive modes, with CRF(1) receptors mediating active defensive responses triggered by escapable stressors, and CRF(2) receptors mediating anxiety- and depression-like responses induced by inescapable, uncontrollable stressors. CRF(1) receptor antagonists are being developed as novel treatments for affective and stress disorders. If it is confirmed that the CRF(2) receptor contributes importantly to anxiety and depression, the development of small molecule CRF(2) receptor antagonists would be therapeutically useful.

A Microdialysis Profile of Dynorphin A1-8 Release in the Rat Nucleus Accumbens Following Alcohol Administration

BACKGROUND

Pharmacological studies have implicated the endogenous opioid system in mediating alcohol intake. Other evidence has shown that alcohol administration can influence endorphinergic and enkephalinergic activity, while very few studies have examined its effect on dynorphinergic systems. The aim of the present study was to investigate the effect of alcohol administration or a mechanical stressor on extracellular levels of dynorphin A(1-8) in the rat nucleus accumbens-a brain region that plays a significant role in the processes underlying reinforcement and stress.

METHODS

Male Sprague-Dawley rats were implanted with a microdialysis probe aimed at the shell region of the nucleus accumbens. Artificial cerebrospinal fluid was pumped at a rate of 1.5 microL/min in awake and freely moving animals and the dialysate was collected at 30-minute intervals. In one experiment, following a baseline period, rats were injected intraperitoneally with either physiological saline or 1 of 3 doses of alcohol, 0.8, 1.6, or 3.2 g ethanol/kg body weight. In a second experiment, following a baseline period, rats were applied a clothespin to the base of their tail for 20 minutes. The levels of dynorphin A(1-8) in the dialysate were analyzed with solid-phase radioimmunoassay.

RESULTS

Relative to saline-treated controls, an alcohol dose of 1.6 and 3.2 g/kg caused a transient increase in the extracellular levels of dynorphin A(1-8) in the first 30 minutes of alcohol administration. However, the effect resulting from the high 3.2 g/kg dose was far more pronounced and more significant than with the moderate dose. There was no effect of tail pinch on dynorphin A(1-8) levels in the nucleus accumbens.

CONCLUSIONS

In this experiment, a very high dose of alcohol was especially capable of stimulating dynorphin A(1-8) release in the nucleus accumbens. Dynorphin release in the accumbens has been previously associated with aversive stimuli and may thus reflect a system underlying the aversive properties of high-dose alcohol administration. However, the lack of effect of tail-pinch stress in the present study suggests that dynorphin A(1-8) is not released in response to all forms of stressful/aversive stimuli.

[Dreaming and schizophrenia: a common neurobiological background?]

Normal waking mentation is the outcome of the combined action of both electrophysiological and neurochemical antagonistic and complementary activating and inhibitory influences occurring mainly in the cerebral cortex. The chemical ones are supported principally by acetylcholine, and noradrenaline and serotonin, respectively. During rapid eye movement (REM) sleep, the monoaminergic silence - except dopaminergic ongoing activity - disrupts this equilibrium and seems to be responsible for disturbances of mental activity characteristic of dreaming. This imbalance could cause disconnectivity of cortical areas, failure of latent inhibition and possibly the concomitant prefrontal dorsolateral deactivation. Moreover, the decrease of prefrontal dopaminergic functioning could explain the loss of reflectiveness in this sleep stage. All these phenomena are also encountered in schizophrenia. The psychotic-like mentation of dreaming (hallucinations, delusions, bizarre thought processes) could result from the disinhibition of dopamine influence in the nucleus accumbens by the noradrenergic and serotonergic local silence and/or the lifting of glutamate influence from the prefrontal cortex and hippocampus. We hypothesize that, during REM sleep, the increase of dopamine and the decrease of glutamate release observed in nucleus accumbens reach the threshold values at which psychotic disturbances arise during wakefulness. Whatever the precise mechanism, it seems that the functional state of the prefrontal cortex and nucleus accumbens is the same during dreaming sleep stage and in schizophrenia. The convergent psychological, electrophysiological, tomographic, pharmacological and neurochemical criteria of REM sleep and schizophrenia suggest that this sleep stage could become a good neurobiological model of this psychiatric disease.

Blockade of presynaptic voltage-gated calcium channels in the medial prefrontal cortex of neonatal rats leads to post-pubertal alterations in locomotor behavior

Although the etiology of neurodevelopmental mental disorders remains obscure, converging lines of evidence using animal modeling suggest a critical role for activity-dependent neurodevelopmental processes during neonatal life. Here, we report the behavioral effects of a novel technique designed to induce targeted, transient disruption of activity-dependent processes in early development via reduction of calcium-mediated neurotransmitter release. We examined the post-pubertal behavioral effects of neonatal (postnatal day 7) medial prefrontal cortex infusion of either vehicle or N-type and P/Q-type presynaptic voltage-dependent calcium channel blockers (omega-conotoxins MVIIA and MVIIC respectively; 6.8 and 45 pmol infused respectively) in rat pups. In a test of amphetamine-induced behavioral sensitization, neonatal omega-conotoxin MVIIA treatment significantly increased locomotion following repeated amphetamine injections (1.5 mg/kg i.p.) and significantly decreased locomotion following repeated saline injections relative to animals treated neonatally with vehicle. However, there was no effect of conotoxin treatment on the long-term expression of amphetamine sensitization. Neonatal treatment with omega-conotoxins had no effect on the other behaviors assayed, namely, acoustic startle response, prepulse inhibition of startle, novelty- and amphetamine-induced (1.5 mg/kg i.p.) locomotion, and anxiety-like behavior in the elevated plus-maze. These data confirm that transient, region-specific disruption of synaptic transmission during early development can have long-term effects on behaviors relevant to neurodevelopmental mental disorders.

Mesocortical dopamine and HPA axis regulation: Role of laterality and early environment

The infralimbic (IL) cortex is importantly involved in regulating behavioral and physiological responses to stress, including those of the hypothalamic-pituitary-adrenal (HPA) axis. The mesocortical dopamine (DA) system is an important afferent modulator of this region, is highly stress sensitive and frequently shows functional hemispheric asymmetry. Postnatal handling stimulation facilitates development of cortical asymmetry and is also associated with optimal HPA axis regulation. The present study examines the poorly understood role of the mesocortical DA system in regulating HPA axis function in adult rats which were handled (H) or nonhandled (NH) postnatally. In the first experiment, unilateral intra-IL cortex injection of the DA (D1/D2) antagonist alpha-flupenthixol into either hemisphere significantly exaggerated the restraint stress-induced increases in plasma adrenocorticotrophic hormone and corticosterone in NH rats. In H rats, the same effect was lateralized to the right IL cortex. In a second experiment, post mortem neurochemical analysis of DAergic measures in the IL cortex was conducted in H and NH animals following either acute or repeated (5 times) restraint stress. DAergic measures in the right IL cortex were significantly correlated with reduced stress hormone activation in both H and NH rats, especially in repeatedly restrained rats. However, while H rats showed a significant rightward shift in DA metabolism with repeated stress experience, NH rats shifted DA metabolism to the left. It is suggested that, during stress, mesocortical DA release normally acts in an adaptive, negative feedback capacity preventing excessive HPA activation and, with repeated stress, the right IL cortex is particularly important in this capacity. As well, the selective enhancement of DA metabolism in the right IL cortex of H rats may underlie, in part, their typically superior ability to adapt to stress and constrain HPA activity.

Behavioural effects of neonatal lesions of the medial prefrontal cortex and subchronic pubertal treatment with phencyclidine of adult rats

According to the neurodevelopmental hypothesis of schizophrenia, early brain damage renders the brain vulnerable to adverse effects during puberty, which precipitate the disease in young adults. Animal models can be used to test this hypothesis. We investigated the potentially independent or interactive effects of neonatal (postnatal day 7) excitotoxic lesions of the rat medial prefrontal cortex (mPFC) and subchronic pubertal phencyclidine (PCP)-treatment on adult rat behaviour. Sham-lesioned (vehicle-injection) and naive (unoperated) rats served as controls. On postnatal days 42-48 rats were systemically injected with 5 mg/kg PCP or vehicle twice daily. Behavioural testing started at postnatal day 70. Rats were tested for locomotor activity (open field), anxiety (elevated plus maze), social behaviour (conditioned place preference for cage-mates), reward-related operant behaviour [progressive ratio (PR)] and spatial learning (four-arm baited eight-arm radial maze task). Nissl-stained sections revealed considerable regeneration of much of the lesioned tissue in the mPFC, however, with disturbed cytoarchitecture. Locomotor activity was increased by neonatal lesions but reduced after pubertal PCP-treatment. Neonatal lesions alone increased operant behaviour in the PR-test and reduced anxiety in the elevated plus maze. In contrast, PCP-treatment disturbed social behaviour while neonatal lesions had no effect. Different aspects of leaning and memory in the radial maze task were independently disturbed after neonatal lesions and PCP-treatment. Neonatal lesions and pubertal PCP-treatment differentially affected adult rat behaviour and no interactions were found.

The dreaming sleep stage: A new neurobiological model of schizophrenia?

The rapid eye movement dreaming sleep stage and schizophrenia are both characterized by common intracerebral disconnections, disturbed responsiveness and sensory deafferentation processes. Moreover, in both states, there is dorsolateral prefrontal deactivation as shown by the decrease of blood flow. Finally, identical pharmacological and neurochemical variations are observed for acetylcholine, dopamine, noradrenaline, serotonin and glutamate concentrations. Consequently, rapid eye movement sleep could become a useful new neurobiological model of this mental disease since more functional than current rat models using stimulation, lesion or drugs.

Programming effects of antenatal dexamethasone in the developing mesolimbic pathways

Elevated glucocorticoids, during pregnancy, alter emotionality and increase propensity to drug abuse later in life, albeit through substrates and mechanisms are largely unknown. In this study, we examined whether antenatal glucocorticoid exposure induces enduring structural changes in the nucleus accumbens (NAcc), an important relay point in the reward limbic circuitry. To this end, rat dams were exposed to the synthetic glucocorticoid dexamethasone (DEX) on days 18 and 19 of gestation, and stereological tools were used to assess the total volume of, and neuronal numbers in, the NAcc, as well as the density of mesencephalic dopaminergic inputs from the ventral tegmental area (VTA) to the NAcc in their adult offspring. Further, we used measures of bromodeoxyuridine incorporation into NAcc cells to examine whether DEX-induced effects on cell proliferation represent another mechanism through which glucocorticoids alter the structure of mesolimbic pathways and might influence addictive behavior. Our studies show that exposure to DEX during late gestation results in significantly reduced volumes and cell numbers in the NAcc. The latter measure correlated strongly with a reduced rate of cell proliferation in DEX-exposed animals. Moreover, the treatment resulted in a decreased number of cells expressing tyrosine hydroxylase in the VTA and an impoverished dopaminergic innervation of the NAcc. These observations, which identify glucocorticoid-sensitive structures and neurochemical targets within the developing "reward pathway," pave way for future studies designed to understand how early life events can predispose individuals for developing drug dependence in adolescent and adult life.

Behavioral and morphological alterations following neonatal excitotoxic lesions of the medial prefrontal cortex in rats

The prefrontal cortex (PFC) is essential for executive functions in mammals. Damage of the developing PFC may partly be compensated over time, but may also lead to structural and functional deficits due to neurodevelopmental disturbances. The present study investigated the effects of excitotoxic lesions of the medial PFC (mPFC) in neonatal rats on brain morphology, myelination and behavior. Neonatal lesions were induced with ibotenate on postnatal day (pd) 7 and all animals were tested pre- and postpubertally for prepulse inhibition (PPI) of the acoustic startle reflex (ASR), locomotor activity and food preference. Furthermore, adult rats were tested for apomorphine sensitivity of PPI and for their performance in a progressive ratio operant response task. Neonatally lesioned animals showed a reduced volume of the mPFC, enlarged ventricles and a deficient myelination in some projection areas of the mPFC, including the thalamus, hippocampus, nucleus accumbens (NAC) and amygdala. PPI was enhanced in lesioned rats when tested as juveniles, but PPI-deficits induced by the dopamine receptor agonist apomorphine were exacerbated in adult rats after neonatal mPFC lesion. Furthermore, the break point in a progressive ratio task was lower in lesioned animals, whereas the total number of lever presses was initially increased, indicating an impulsive response of rats for food reward under a progressive ratio schedule after neonatal mPFC lesion. No effects were found on food preference and open field performance. These data support the hypothesis that neonatal mPFC lesions lead to disruptions of neurodevelopmental processes in a cortico-limbic-striatal network, which are manifested in adult animals as morphological and behavioral disturbances.

A detailed characterization of loud noise stress: Intensity analysis of hypothalamo-pituitary-adrenocortical axis and brain activation

The present studies were undertaken to help determine the putative neural circuits mediating activation of the hypothalamo-pituitary-adrenocortical (HPA) axis and the release of adrenocorticotropin hormone (ACTH) and corticosterone in response to the perceived threat of loud noise. This experiment involved placing rats in acoustic chambers overnight to avoid any handling and context changes prior to noise exposure, which was done for 30 min (between 9:00 and 10:00 am) at intensities of 80, 85, 90, 95, 100, 105, and 110 dBA in different groups (n = 8), and included a background condition (60 dBA ambient noise). This manipulation produced a noise-intensity-related increase in plasma ACTH and corticosterone levels, with levels beginning to rise at approximately 85 dBA. c-fos mRNA induction was very low in the brains of the control and 80 dBA groups, but several brain regions displayed a noise-intensity-related induction. Of these, several forebrain regions displayed c-fos mRNA induction highly correlated (r > 0.70) with that observed in the paraventricular hypothalamic nucleus and plasma ACTH levels. These regions included the ventrolateral septum, the anteroventral subiculum, several preoptic nuclei, the anterior bed nucleus of the stria terminalis (BNST), the anterior paraventricular nucleus of the thalamus, and the medial subdivision of the medial geniculate body. Together with prior findings with audiogenic stress, the present results suggest that either or both the anterior BNST or the lateral septum is ideally situated to trigger HPA axis activation by stimuli that are potentially threatening.

A prospective 3-year longitudinal study of cognitive predictors of relapse in first-episode schizophrenic patients

BACKGROUND

Cognitive predictors of relapse have been extensively explored only in few long term longitudinal studies of first-episode schizophrenia.

METHOD

This study prospectively followed 93 patients with first-episode schizophrenia, schizophreniform disorder, and schizoaffective disorder for 3 years after their first-episode illness. Cognitive domains including verbal intelligence, verbal and visual memory, verbal fluency, and Wisconsin Card Sorting Test performance were investigated as potential predictors of relapse.

RESULTS

We found that by the first year 21% patients had relapsed, by the second year 33% had relapsed, and by the third year 40% had relapsed. There was a significant difference in the relapse rate between patients with good adherence and patients with poor adherence to medication regimes. A multiple logistic regression analysis revealed that after controlling for medication adherence, perseverative error in the Wisconsin Card Sorting Test was the only cognitive function that significantly predict relapse with an odds ratio of 2.4.

CONCLUSIONS

Cognitive flexibility in set shifting is related to tendency towards relapse in first-episode schizophrenic patients. Other cognitive factors appear not to be related to relapse. Possible mechanisms included the link between prefrontal dysfunction and sub-cortical dopamine system stability, as well as the effects of executive dysfunction on insight impairment and adherence behavior.

Studying Toxicants as Single Chemicals: Does this Strategy Adequately Identify Neurotoxic Risk?

Despite the fact that virtually all chemicals exposure of humans are to mixtures, and that these mixed exposures occur in the context of numerous other risk modifiers, our current understanding of human health risks is based almost entirely on the evaluation of chemicals studied in isolation. This paper describes findings from our collaborative studies that prompt questions about these approaches in the context of neurotoxicology. The first section describes studies investigating the interactions of maternal Pb exposure with maternal stress. Examined across a range of outcome measures, it shows that maternal Pb can modulate the effects of maternal stress, and, conversely, stress modifies the effects of Pb. Further, effects of Pb+stress could be detected in the absence of an effect of either risk factor alone, and, moreover, the profile of effects of Pb alone differs notably from that of Pb+stress. Collectively, interactions were not systematic, but differed by brain region, gender and outcome measure. A second section describes outcomes of studies examining combined exposures to the pesticides paraquat (PQ) and maneb (MB) during development which likewise reveal potentiated effects of combined exposures. They also demonstrate examples of both progressive and cumulative neurotoxicity, including a marked vulnerability following gestational exposure to MB, to the effects of PQ, a pesticide with no structural relationship to MB. The ability of current hazard identification and risk assessment approaches to adequately identify and encompass such effects remains an important unanswered question. One consideration proposed for further evaluating potential interactions that may be of significance for the nervous system is based on a multi-hit hypothesis. It hypothesizes that the brain may readily compensate for the effects of an individual chemical itself acting on a particular target system, but when multiple target or functional sites within that one system are attacked by different mechanisms (i.e., multiple chemical exposures or chemical exposures combined with other risk factors), homeostatic capabilities may be restricted, thereby leading to sustained or cumulative damage.

Comparative behavioral changes in postpubertal rats after neonatal excitotoxic lesions of the ventral hippocampus and the prefrontal cortex

The neonatal ventral hippocampal (nVH) and the neonatal prefrontal cortex (nPFC) lesions in rats have been used as models to test the hypothesis that early neurodevelopmental abnormalities lead to behavioral changes putatively linked to schizophrenia. We investigated the role of the nVH and the nPFC lesions on behavioral characteristics related to locomotor behaviors, social interaction, and grooming. Bilateral ibotenic acid lesions of the VH, the PFC, or both were made in neonatal Sprague-Dawley rats (postnatal day 7, P7) and their behaviors studied at P35 and P60. No significant differences in any of the behaviors were observed between sham animals and rats with ibotenic acid lesions at P35. Postpubertally (at P60), the spontaneous locomotor activity of nVH-lesioned rats was significantly enhanced compared to the sham controls; however, this hyperactivity was reversed by nVH and nPFC double lesions. Neonatal PFC lesion alone did not alter spontaneous activity, although a trend of increased activity was observed. The duration of grooming was significantly decreased in rats with neonatal lesions of the VH. Similar to the data on locomotion, nVH plus nPFC lesion normalized the grooming behavior. Lesion of the PFC alone was without any significant effect on grooming behavior. Neonatal VH-lesioned animals spent less time in active social interaction, and this effect persisted even in nVH plus nPFC-lesioned animals. By itself, nPFC lesion did not alter social behavior. These data suggest that subtle developmental aberrations within PFC caused by nVH lesions, rather than the lesion of PFC itself, may contribute to some of the behavioral changes seen in the nVH-lesioned rats.

Alterations in behavioral responses to a cholinergic agonist in post-pubertal rats with neonatal ventral hippocampal lesions: relationship to changes in muscarinic receptor levels

Excitotoxic neonatal ventral hippocampal (NVH) lesion in rats is considered as a putative animal model of schizophrenia as lesioned animals show characteristic post-pubertal emergence of neurochemical and behavioral abnormalities analogous to some of those seen in this disease. Converging evidence points to the involvement of central cholinergic system in this neuropsychiatric disorder, and our previous studies have suggested that cholinergic neurotransmission may be altered in post-pubertal NVH lesioned rats. We investigated here muscarinic receptor reactivity in NVH lesioned animals by measuring the effects of the muscarinic receptor agonist oxotremorine on physiological responses known to be modulated by these receptors such as body temperature, salivation, tremor, pain, and prepulse inhibition of the acoustic startle (PPI). Quantitative receptor autoradiography revealed that post-pubertal NVH lesioned animals display increased levels of [3H]pirenzepine/M1-like and [3H]AFDX-384/M2-like receptor binding sites in the striatum, nucleus accumbens, and in subareas of the dorsal hippocampus. Moreover, in response to the systemic administration of oxotremorine (0.25 mg/kg), post-pubertal NVH lesioned rats exhibited increases in salivation and tremor, and a greater reduction in body temperature compared to sham control animals. Increases in the hot-plate latency were also observed suggesting enhanced antinociceptive effects of oxotremorine in post-pubertal NVH lesioned animals. Finally, oxotremorine (0.1 and 0.25 mg/kg) disrupted PPI in post-pubertal sham control rats while the muscarinic receptor antagonist biperiden (0.5 and 1.0 mg/kg) normalized this behavior in NVH lesioned rats. Taken together, these findings reveal that post-pubertal NVH lesioned rats display enhanced muscarinic receptor responsiveness, which may relate to some behavioral abnormalities reported in this animal model.

Medial prefrontal cortex control of the paraventricular hypothalamic nucleus response to psychological stress: possible role of the bed nucleus of the stria terminalis

The medial prefrontal cortex (mPFC) has been strongly implicated in control of the paraventricular nucleus of the hypothalamus (PVN) response to stress. Because of the paucity of direct projections from the mPFC to the PVN, we sought to investigate possible brain regions that might act as a relay between the two during psychological stress. Bilateral ibotenic acid lesions of the rat mPFC enhanced the number of Fos-immunoreactive cells seen in the PVN after exposure to the psychological stressor, air puff. Altered neuronal recruitment was seen in only one of the candidate relay populations examined, the ventral bed nucleus of the stria terminalis (vBNST). Furthermore, bilateral ibotenic acid lesions of the BNST caused a significant attenuation of the PVN response to air puff. To better characterize the structural relationships between the mPFC and PVN, retrograde tracing studies were conducted examining Fos expression in cells retrogradely labeled with cholera toxin b subunit (CTb) from the PVN and the BNST. Results obtained were consistent with an important role for both the mPFC and BNST in the mpPVN CRF cell response to air puff. We suggest a set of connections whereby a direct PVN projection from the ipsilateral vBNST is involved in the mpPVN response to air puff and this may, in turn, be modulated by an indirect projection from the mPFC to the BNST.

Choice of lard, but not total lard calories, damps adrenocorticotropin responses to restraint

Although rats given the choice of eating high-density calories as concentrated sucrose solutions or lard exhibit reduced responsivity in the hypothalamo-pituitary-adrenal axis, rats fed high-fat diets have normal or augmented responses to stressors. To resolve this apparent discrepancy, we compared in adult male rats the effects of 7-d feeding with lard + chow (choice) to feeding a 50% lard-chow mixture (no-choice) and to chow only. Rats with choice composed diets with 50-60% total calories from lard. Rats were exposed to 30 min of restraint on d 7. In the choice group, there was a robust inhibition of ACTH and corticosterone responses to restraint compared with chow or no-choice groups. Total caloric intake was less with choice than no-choice. Fat depot weights and body weight gain were similar in the high-fat groups. Leptin concentrations were equal but insulin was higher in the choice group. We conclude the following: 1) choice of eating high-density calories strongly damps hypothalamo-pituitary-adrenal responses to stress; without choice, high-density diet is ineffective; and 2) insulin may signal metabolic well-being, and may act through hypothalamic sites to reduce caloric intake but through forebrain sites to damp stress responses.

Deficient social and play behavior in juvenile and adult rats after neonatal cortical lesion: effects of chronic pubertal cannabinoid treatment

The aim of the present study was to investigate the effects of neonatal excitotoxic lesions of the medial prefrontal cortex (mPFC) on social play, social behavior unrelated to play, and self-grooming in juvenile and adult rats. We additionally examined the behavioral effects of chronic pubertal treatment with the cannabinoid agonist WIN 55,212-2 (WIN) in order to test the hypothesis that early lesions render the brain vulnerable to cannabinoid intake in later life. Neonatal mPFC lesions and pubertal WIN treatment disrupted social play, social behavior, and self-grooming in juvenile and adult rats. Additionally, we observed more social play behaviors during light cycle in WIN-treated than in vehicle-treated rats. Notably, the combination of surgery and WIN treatment disrupted social behavior in lesioned and sham-lesioned rats. The present data indicate that the mPFC is important for adequate juvenile response selection in the context of social play and might be involved in the development of adult social and nonsocial behavior. Moreover, our data add further evidence for an involvement of the cannabinoid system in anxiety and social behavior. Additive effects of neonatal surgery-induced stress or cortical lesions in combination with pubertal cannabinoid administration are also shown. The disturbances of social and nonsocial behavior in rats are comparable to symptoms of early frontal cortex damage, as well as neurodevelopmental disorders in humans, such as schizophrenia and autism. Therefore, we propose the combination of neonatal cortical lesions with chronic cannabinoid administration during puberty as an animal model for studying neuronal mechanisms of impaired social functioning in neuropsychiatric disorders.

Endocannabinoid signaling negatively modulates stress-induced activation of the hypothalamic-pituitary-adrenal axis

Activation of the hypothalamic-pituitary-adrenal (HPA) axis is critical for the adaptation and survival of animals upon exposure to stressful stimuli, and data suggest that endocannabinoid (eCB) signaling modulates neuroendocrine function. We have explored the role of eCB signaling in the modulation of stress-induced HPA axis activation. Administration of the CB1 receptor antagonist/inverse agonist SR141716 (0.01, 0.1, 1, and 5 mg/kg, i.p.) to male mice produced a small, dose-dependent increase in the serum corticosterone (CORT) concentration. Despite this effect, the highest dose of SR141716 did not significantly increase neuronal activity within the paraventricular nucleus of the hypothalamus, as measured by the induction of Fos protein. Similarly, exposure of mice to 30 min of restraint increased serum CORT concentrations, but did not produce a consistent, statistically significant increase in Fos expression within the PVN. However, pretreatment of mice with SR141716 before restraint stress robustly potentiated restraint-induced CORT release and Fos expression within the PVN. Pretreatment of mice with either the CB1 receptor agonist CP55940, the eCB transport inhibitor AM404, or the fatty acid amide hydrolase inhibitor URB597 significantly decreased or eliminated restraint-induced CORT release. Upon exposure to acute restraint, hypothalamic 2-arachidonylglycerol content was reduced compared with the control value; however, after 5 d of restraint exposure (which resulted in an attenuated CORT response), the hypothalamic 2-arachidonylglycerol content was increased compared with the control value. These data indicate that eCB signaling negatively modulates HPA axis function in a context-dependent manner and suggest that pharmacological augmentation of eCB signaling could serve as a novel approach to the treatment of anxiety-related disorders.

Delayed onset of prepulse inhibition deficits following kainic acid treatment on postnatal day 7 in rats

Abnormal activity in corticolimbic circuits during development may be a predisposing factor for schizophrenia. Permanent or temporary lesions of limbic structures such as the ventral hippocampus and basolateral amygdala in rats on postnatal day (PND) 7 result in functional changes similar to some behavioural and cognitive signs of schizophrenia. The present experiments tested whether transient increases in the neural activity of corticolimbic circuits on PND 7 would result in similar behavioural changes. Long-Evans rats were treated with either kainic acid (KA, 1.5 mg/kg, i.p.) or saline on PND 7 and tested for prepulse inhibition (PPI) of the acoustic startle response and spontaneous locomotor activity both in a novel environment and following amphetamine treatment before puberty (PND 35) and in early adulthood (PND 56). In subgroups of animals PPI was also measured following apomorphine administration (0.2 mg/kg) and spatial learning and memory were tested in the water maze. Rats treated with KA were indistinguishable from saline-treated animals on PND 35. However, on PND 56, KA-treated animals showed a subtle consistent decrease in PPI relative to control animals, but did not show increased sensitivity to the disruptive effects of a low dose of apomorphine on PPI. Locomotor responses to novelty or amphetamine were not reliably altered in the KA-treated animals. KA- and saline-treated animals performed similarly in the water maze. These results support the hypothesis that neural hyperactivity on PND 7 in rats causes behavioural changes in early adulthood that resemble some symptoms of schizophrenia. These pharmacological data suggest that the changes are not mediated by postsynaptic alterations in mesolimbic dopamine transmission.

Medial prefrontal cortical integration of psychological stress in rats

The present study aimed to determine whether the medial prefrontal cortex (mPFC) (prelimbic and infralimbic regions) is implicated in the integration of a stress response. Sprague-Dawely rats were implanted with telemetry probes and guide cannulae so that either muscimol or vehicle could be administered locally within the mPFC or dorsomedial hypothalamus (DMH). The heart rate and blood pressure of rats was continuously recorded as either muscimol or vehicle was administered centrally and rats were either exposed to restraint stress or left alone in their home cages. After the stress challenge, or equivalent period, rats that had received intra-mPFC injections were processed for immunohistochemical detection of Fos throughout the neuraxis. Bilateral microinjection of muscimol into the mPFC had no effect upon either baseline cardiovascular parameters or restraint stress-induced tachycardia or pressor responses whereas, in the DMH, pretreatment with muscimol attenuated the cardiovascular stress response. Analysis of Fos expression throughout the CNS of nonstressed rats showed no effect of muscimol injections into the mPFC on baseline expression in the nuclei examined. In contrast, rats that had received muscimol injections into their mPFC and were subsequently restrained exhibited an increase in the number of Fos-positive cells in the DMH, medial amygdala, and medial nucleus tractus solitarius as compared to vehicle-injected rats that experienced restraint stress. These results indicate that, during acute psychological stress, the mPFC does not modulate the cardiovascular system in rats but does inhibit specific subcortical nuclei to exert control over aspects of an integrated response to a stressor.

Differential involvement of rat medial prefrontal cortex dopamine receptors in modulation of hypothalamic- pituitary-adrenal axis responses to different stressors

Recent investigations have implicated the medial prefrontal cortex (mPFC) in modulation of subcortical pathways that contribute to the generation of behavioural, autonomic and endocrine responses to stress. However, little is known of the mechanisms involved. One of the key neurotransmitters involved in mPFC function is dopamine, and we therefore aimed, in this investigation, to examine the role of mPFC dopamine in response to stress in Wistar rats. In this regard, we infused dopamine antagonists SCH23390 or sulpiride into the mPFC via retrodialysis. We then examined changes in numbers of cells expressing the c-fos immediate-early gene protein product, Fos, in subcortical neuronal populations associated with regulation of hypothalamic-pituitary-adrenal (HPA) axis stress responses in response to either of two stressors; systemic injection of interleukin-1 beta, or air puff. The D1 antagonist, SCH23390, and the D2 antagonist, sulpiride, both attenuated expression of Fos in the medial parvocellular hypothalamic paraventricular nucleus (mpPVN) corticotropin-releasing factor cells at the apex of the HPA axis, as well as in most extra-hypothalamic brain regions examined in response to interleukin-1 beta. By contrast, SCH23390 failed to affect Fos expression in response to air puff in any brain region examined, while sulpiride resulted in an attenuation of the air puff-induced response in only the mpPVN and the bed nucleus of the stria terminalis. These results indicate that the mPFC differentially processes the response to different stressors and that the two types of dopamine receptor may have different roles.

Effects of neonatal lesions of the medial prefrontal cortex on adult rat behaviour

While prefrontal lesions in rodents serve as models for frontal lobe syndromes, neonatal lesions are considered as models for disconnection syndromes, such as schizophrenia. We investigated the effect of neonatal lesions of the rat medial prefrontal cortex (mPFC) together with pubertal dexamethasone-challenge on adult rat behaviour and on apomorphine-induced behavioural changes. Adult lesions were used as controls. Rats with neonatal (postnatal day 7) or adult excitotoxic lesions or sham-lesions of the mPFC were tested 9 weeks after surgery. At postnatal day 49 one group of neonatal operated rats were systemically injected with the glucocorticoid receptor agonist dexamethasone (20 mg/kg), in order to simulate stress-induced glucocorticoid receptor activation. Working memory and perseveration was tested in T-maze tasks (continuous delayed alternation and reversal learning). Additionally, locomotor activity and prepulse inhibition (PPI) of startle was tested with and without apomorphine-treatment. Brain tissue damage was assessed using Nissl-staining and parvalbumine-immunocytochemistry. Pronounced thinning of the prelimbic-infralimbic subregion of the mPFC accompanied by altered cytoarchitecture and reduced number of parvalbumine-immunopositive neurones was found after neonatal lesions while adult lesions resulted in loss of neurones accompanied by gliosis. Neonatal lesions increased perseveration in the T-maze tasks and enhanced PPI, while adult lesions induced a working memory deficit. This differential behavioural outcome presumably reflects neurodevelopmentally induced alterations in neuronal circuits after neonatal lesions versus damage to mPFC alone after adult lesions. Dexamethasone-injection at day 49 did not alter behaviour in these tasks. Motor activity was not affected by neonatal or adult lesions but dexamethasone reduced apomorphine-induced hyperlocomotion.

Corticotropin-releasing factor receptors CRF1 and CRF2 exert both additive and opposing influences on defensive startle behavior

The corticotropin-releasing factor (CRF) receptors (CRF1 and CRF2) are crucial mediators of physiological and behavioral responses to stress. In animals, CRF1 appears to primarily mediate CRF-induced anxiety-like responses, but the role of CRF2 during stress is still unclear. Here we report the effects of CRF1 and CRF2 on the magnitude and plasticity of defensive startle responses in mice. Startle plasticity is measured by inhibition of startle by sensory stimuli, i.e., prepulse inhibition (PPI), and is disrupted in patients with panic or posttraumatic stress disorders in which CRF neurotransmission may be overactive. Pharmacological blockade of CRF1 reversed both CRF-induced increases in startle and CRF-induced deficits in PPI. CRF2 blockade attenuated high-dose but not low-dose CRF-induced increases in startle and reduced PPI. Conversely, activation of CRF2 enhanced PPI. CRF had no effect on startle and increased PPI in CRF1 knock-out mice. These data indicate that CRF receptors act in concert to increase the magnitude of defensive startle yet in opposition to regulate the flexibility of startle. These data support a new model of respective CRF receptor roles in stress-related behavior such that, although both receptors enhance the magnitude of defensive responses, CRF1 receptors contravene, whereas CRF2 receptors enhance, the impact of sensory information on defensive behavior. We hypothesize that excessive CRF1 activation combined with reduced CRF2 signaling may contribute to information processing deficits seen in panic and posttraumatic stress disorder patients and support CRF1-specific pharmacotherapy.

Brain inhibitory mechanisms involved in basic and higher integrated sleep processes

Brain function is supported by central activating processes that are significant during waking, decrease during slow wave sleep following waking and increase again during paradoxical sleep during which brain activation is as high as, or higher than, during waking in nearly all structures. However, inhibitory mechanisms are crucial for sleep onset. They were first identified by behavioral, neuroanatomical and electrophysiological criteria, then by pharmacological and neurochemical ones. During slow wave sleep, they are supported by GABAergic mechanisms located at midbrain, mesopontine and pontine levels but are induced and sustained by forebrain and hindbrain influences. GABAergic processes are also responsible for paradoxical sleep occurrence, particularly by suppression of noradrenaline and serotonin (5-HT) inhibition of paradoxical sleep-generating structures. Hindbrain and forebrain modulate these structures situated at the mesopontine level. For sleep mentation, the noradrenergic and serotonergic silence is thought, today, to be directly, or indirectly, responsible for dopamine predominance and glutamate decrease in the nucleus accumbens, which could be the background of the well-known psychotic-like mental activity of dreaming.

Neonatal medial prefrontal cortex lesion enhances the sensitivity of the mesoaccumbal dopamine system

Neurodevelopmental models of schizophrenia posit that early brain damage leads to dys- or misconnection effects possibly altering synaptic transmission in brain sites distal of the lesion. We tested the hypothesis that neonatal medial prefrontal cortex (mPFC) lesions affect the sensitivity of the mesoaccumbal dopamine (DA) system. Using extracellular single-unit recordings combined with systemic application of the DA agonist apomorphine, followed by the D2 receptor antagonist haloperidol or the D1 receptor antagonist SCH23390, we compared electrophysiological properties of nucleus accumbens core and shell neurons after bilateral excitotoxic lesions of mPFC induced at postnatal day 7 or in adult rats. Whereas animals with adult mPFC lesions showed an altered discharge pattern within the core region, neonatal mPFC lesions altered the discharge pattern within the shell region. Subcutaneous administration of apomorphine (4 mg/kg) reduced accumbal firing rate in 77% of all neurons. Onset and magnitude of apomorphine-induced inhibition of neuronal activity was faster and stronger in rats with neonatal but not adult mPFC lesions in both core and shell regions. Apomorphine-induced inhibition was partially reversed by 0.1 mg/kg haloperidol only in core region of neonatal lesioned rats. Apomorphine-induced excitation of neuronal activity (in 21% of all neurons) was reversed by the D1 receptor antagonist SCH23390 (0.1 mg/kg) in all excited neurons. These data support the hypothesis that neonatal but not adult lesions of mPFC alter cortico-striatal networks and suggest that disturbance of mPFC development leads to neurodevelopmental changes in mesoaccumbal DA system during adulthood.

Chronic behavioral stress induces apical dendritic reorganization in pyramidal neurons of the medial prefrontal cortex

Both the hippocampus and the medial prefrontal cortex (mPFC) play an important role in the negative feedback regulation of hypothalamic-pituitary-adrenal (HPA) activity during physiologic and behavioral stress. Moreover, chronic behavioral stress is known to affect the morphology of CA3c pyramidal neurons in the rat, by reducing total branch number and length of apical dendrites. In the present study, we investigated the effects of behavioral stress on the mPFC, using the repeated restraint stress paradigm. Animals were perfused after 21 days of daily restraint, and intracellular iontophoretic injections of Lucifer Yellow were carried out in pyramidal neurons of layer II/III of the anterior cingulate cortex and prelimbic area. Cellular reconstructions were performed on apical and basal dendrites of pyramidal neurons in layer II/III of the anterior cingulate and prelimbic cortices. We observed a significant reduction on the total length (20%) and branch numbers (17%) of apical dendrites, and no significant reduction in basal dendrites. These cellular changes may impair the capacity of the mPFC to suppress the response of the HPA axis to stress, and offer an experimental model of stress-induced neocortical reorganization that may provide a structural basis for the cognitive impairments observed in post-traumatic stress disorder.

Hemispheric asymmetry in stress processing in rat prefrontal cortex and the role of mesocortical dopamine

The prefrontal cortex (PFC) is known to play an important role not only in the regulation of emotion, but in the integration of affective states with appropriate modulation of autonomic and neuroendocrine stress regulatory systems. The present review highlights findings in the rat which helps to elucidate the complex nature of prefrontal involvement in emotion and stress regulation. The medial PFC is particularly important in this regard and while dorsomedial regions appear to play a suppressive role in such regulation, the ventromedial (particularly infralimbic) region appears to activate behavioral, neuroendocrine and sympathetic autonomic systems in response to stressful situations. This may be especially true of spontaneous stress-related behavior or physiological responses to relatively acute stressors. The role of the medial PFC is somewhat more complex in conditions involving learned adjustments to stressful situations, such as the extinction of conditioned fear responses, but it is clear that the medial PFC is important in incorporating stressful experience for future adaptive behavior. It is also suggested that mesocortical dopamine plays an important adaptive role in this region by preventing excessive behavioral and physiological stress reactivity. The rat brain shows substantial hemispheric specialization in many respects, and while the right PFC is normally dominant in the activation of stress-related systems, the left may play a role in countering this activation through processes of interhemispheric inhibition. This proposed basic template for the lateralization of stress regulatory systems is suggested to be associated with efficient stress and emotional self-regulation, and also to be shaped by both early postnatal experience and gender differences.

Anoxia at birth induced hyperresponsiveness to amphetamine and stress in postpubertal rats

Several evidences suggest that transient global anoxia after Caeraean section birth in rats produces behavioral changes related to dopaminergic transmission. However, all of the reports tested the behavioral changes in adult rats. Here we investigated the role of perinatal anoxia on behavioral paradigms related to dopamine (DA) such as novel environment, saline injection, D-amphetamine, apomorphine and stress-induced changes in locomotor activity at prepubertal and postpubertal ages. All these dimensions of behavior can be affected in schizophrenia. Caesarean section birth with or without an additional period of anoxia was performed in Sprague-Dawley rats and their behaviors were studied at P35 and P56, respectively. In addition, a third group of animals born vaginally served as control. No significant differences in saline injection and D-amphetamine-induced locomotion were observed when the three groups of rats at P35 were compared. However, stress-induced locomotor activity was significantly increased in the Caesarean birth plus anoxia at P35, while after puberty (at P56), saline injection, D-amphetamine and stress-induced locomotion were significantly enhanced in the Caesarean birth plus anoxia compared to its control groups. The data suggests that anoxia at birth mediates differently the functional development and maturation of DA behaviors in adult rats.

Neonatal handling and gender modulate brain monoamines and plasma corticosterone levels following repeated stressors in adulthood

Neonatal handling affects the response to repeated stress in a sexually dimorphic manner. In order to elucidate the mechanisms underlying these gender-dependent effects, we investigated the consequences of neonatal androgenization and handling on adult stress reactivity by determining: (a) immobility time during repeated forced swimming, (b) plasma corticosterone levels, and (c) brain serotonin and dopamine levels and turnover after either repeated forced swimming, or repeated forced swimming followed by repeated restraint stress. In neonatally androgenized females, immobility time was lower in the handled than in the non-handled rats, a pattern resembling that of the males, suggesting that the sexually dimorphic effect of handling on immobility time can be attributed to the organizational effects of testosterone. No differences were found between androgenized females and females injected neonatally with vehicle, indicating that the gender differences in circulating corticosterone are not due to the organizational effects of testosterone. The stress of a neonatal injection interacted with neonatal handling resulting in lower plasma corticosterone and hypothalamic dopamine and serotonin levels in the neonatally injected handled animals following repeated forced swimming. The serotonergic system appears to be sensitive to both the organizational actions of testosterone and the effects of handling, since handled androgenized females had higher serotonin levels and decreased turnover following repeated forced swimming stress, compared to those injected neonatally with vehicle. Handling resulted in increased hypothalamic and striatal serotonin levels in both males and females following repeated forced swimming. Our results reveal that handling has gender-dependent effects on adult hypothalamic-pituitary-adrenal axis and brain monoaminergic system reactivity to stress and that these effects can be attributed to both the organizational and activational effects of gonadal hormones.

Role of catecholaminergic inputs to the medial prefrontal cortex in local and subcortical expression of Fos after psychological stress

A wide variety of stressors elicit Fos expression in the medial prefrontal cortex (mPFC). No direct attempts, however, have been made to determine the role of the inputs that drive this response. We examined the effects of lesions of mPFC catecholamine terminals on local expression of Fos after exposure to air puff, a stimulus that in the rat acts as an acute psychological stressor. We also examined the effects of these lesions on Fos expression in a variety of subcortical neuronal populations implicated in the control of adrenocortical activation, one classic hallmark of the stress response. Lesions of the mPFC that were restricted to dopaminergic terminals significantly reduced numbers of Fos-immunoreactive (Fos-IR) cells seen in the mPFC after air puff, but had no significant effect on stress-induced Fos expression in the subcortical structures examined. Lesions of the mPFC that affected both dopaminergic and noradrenergic terminals also reduced numbers of Fos-IR cells observed in the mPFC after air puff. Additionally, these lesions resulted in a significant reduction in stress-induced Fos-IR in the ventral bed nucleus of the stria terminalis. These results demonstrate a role for catecholaminergic inputs to the mPFC, in the generation of both local and subcortical responses to psychological stress.

What the rodent prefrontal cortex can teach us about attention-deficit/hyperactivity disorder: the critical role of early developmental events on prefrontal function

The present review surveys a broad range of findings on the functions of the rodent prefrontal cortex (PFC) in the context of the known pathophysiology of attention-deficit/hyperactivity disorder (ADHD). An overview of clinical findings concludes that dysfunction of the right PFC plays a critical role in ADHD and that a number of early developmental factors conspire to increase the risk of the disorder. Rodent studies are described which go far in explaining how the core processes which are deficient in ADHD are mediated by the PFC and that the mesocortical dopamine (DA) system plays a central role in modulating these functions. These studies also demonstrate a surprising degree of cerebral lateralization of prefrontal function in the rat. Importantly, the PFC is highly vulnerable to a wide variety of early developmental insults, which parallel the known risk factors for ADHD. It is suggested that the regulation of physiological and behavioral arousal is a fundamental role of the PFC, upon which many "higher" prefrontal functions are dependent or at least influenced. These right hemispheric arousal systems, of which the mesocortical DA system is a component, are greatly affected by early adverse events, both peri- and postnatally. Abnormal development, particularly of the right PFC and its DAergic afferents, is suggested to contribute directly to the core deficits of ADHD through dysregulation of the right frontostriatal system.

Decreased dendritic spine density on prefrontal cortical and hippocampal pyramidal neurons in postweaning social isolation rats

The effects of postweaning social isolation (pwSI) on the morphology of the pyramidal neurons from the medial part of the prefrontal cortex (mPFC) and hippocampus were investigated in rats. The animals were weaned on day 21 postnatal (P21) and isolated 8 weeks. After the isolation period, locomotor activity was evaluated through 60 min in the locomotor activity chambers and the animals were sacrificed by overdoses of sodium pentobarbital and perfused intracardially with 0.9% saline solution. The brains were removed, processed by the Golgi-Cox stain and analyzed by the Sholl method. The locomotor activity in the novel environment from the isolated rats was increased with respect to the controls. The dendritic morphology clearly showed that the pwSI animals presented a decrease in dendritic length of pyramidal cells from the CA1 of the hippocampus without changes in the pyramidal neurons of the mPFC. However, the density of dendritic spines was decreased in the pyramidal cells from mPFC and Hippocampus. In addition, the Sholl analyses showed that pwSI produced a decrease in the number of sholl intersections compared with the control group only in the hippocampus region. The present results suggest that pwSI may in part affect the dendritic morphology in the limbic structures such as mPFC and hippocampus that are implicated in schizophrenia.

Mother's voice "buffers" separation-induced receptor changes in the prefrontal cortex of octodon degus

Although the potential vulnerability of the postnatally developing brain toward adverse environmental influences is generally recognized, relatively little is known about the basic mechanisms involved. The plasticity and adaptability of the postnatally developing brain in response to adverse emotional experiences was analyzed in the South American Octodon degus. Our study revealed that repeated brief separation from the parents and exposure to an unfamiliar environment induces an up-regulation of dopamine (D1) and 5-hydroxytrytamine (5HT1(A))-receptor density in the precentral medial, anterior cingulate, prelimbic and infralimbic cortices in female pups. No significant changes of gamma aminobutyric acid (GABA(A)) receptor density were found in deprived animals of both genders. The acoustic presence of the mother during parental separation suppressed the D1-receptor up-regulation as well as the 5-HT1(A)-receptor up-regulation, again only in the female pups. These results demonstrate that that early adverse emotional experience alters aminergic function within the prefrontal cortex in the female but not the male brain. The mother's voice, a powerful emotional signal, can protect the developing cortex from separation-induced receptor changes.

Central mechanisms of stress integration: hierarchical circuitry controlling hypothalamo-pituitary-adrenocortical responsiveness

Appropriate regulatory control of the hypothalamo-pituitary-adrenocortical stress axis is essential to health and survival. The following review documents the principle extrinsic and intrinsic mechanisms responsible for regulating stress-responsive CRH neurons of the hypothalamic paraventricular nucleus, which summate excitatory and inhibitory inputs into a net secretory signal at the pituitary gland. Regions that directly innervate these neurons are primed to relay sensory information, including visceral afferents, nociceptors and circumventricular organs, thereby promoting 'reactive' corticosteroid responses to emergent homeostatic challenges. Indirect inputs from the limbic-associated structures are capable of activating these same cells in the absence of frank physiological challenges; such 'anticipatory' signals regulate glucocorticoid release under conditions in which physical challenges may be predicted, either by innate programs or conditioned stimuli. Importantly, 'anticipatory' circuits are integrated with neural pathways subserving 'reactive' responses at multiple levels. The resultant hierarchical organization of stress-responsive neurocircuitries is capable of comparing information from multiple limbic sources with internally generated and peripherally sensed information, thereby tuning the relative activity of the adrenal cortex. Imbalances among these limbic pathways and homeostatic sensors are likely to underlie hypothalamo-pituitary-adrenocortical dysfunction associated with numerous disease processes.

Schizophrenia: from phenomenology to neurobiology

Schizophrenia is a common and debilitating illness, characterized by chronic psychotic symptoms and psychosocial impairment that exact considerable human and economic costs. The literature in electronic databases as well as citations and major articles are reviewed with respect to the phenomenology, pathology, treatment, genetics and neurobiology of schizophrenia. Although studied extensively from a clinical, psychological, biological and genetic perspective, our expanding knowledge of schizophrenia provides only an incomplete understanding of this complex disorder. Recent advances in neuroscience have allowed the confirmation or refutation of earlier findings in schizophrenia, and permit useful comparisons between the different levels of organization from which the illness has been studied. Schizophrenia is defined as a clinical syndrome that may include a collection of diseases that share a common presentation. Genetic factors are the most important in the etiology of the disease, with unknown environmental factors potentially modulating the expression of symptoms. Schizophrenia is a complex genetic disorder in which many genes may be implicated, with the possibility of gene-gene interactions and a diversity of genetic causes in different families or populations. A neurodevelopmental rather than degenerative process has received more empirical support as a general explanation of the pathophysiology, although simple dichotomies are not particularly helpful in such a complicated disease. Structural brain changes are present in vivo and post-mortem, with both histopathological and imaging studies in overall agreement that the temporal and frontal lobes of the cerebral cortex are the most affected. Functional imaging, neuropsychological testing and clinical observation are also generally consistent in demonstrating deficits in cognitive ability that correlate with abnormalities in the areas of the brain with structural abnormalities. The dopamine and other neurotransmitter systems are certainly involved in the treatment or modulation of psychotic symptoms. These broad findings represent the distillation of a large body of disparate data, but firm and specific findings are sparse, and much about schizophrenia remains unknown.

Medial prefrontal cortex suppression of the hypothalamic-pituitary-adrenal axis response to a physical stressor, systemic delivery of interleukin-1beta

Previous studies have shown that the medial prefrontal cortex can suppress the hypothalamic-pituitary-adrenal axis response to stress. However, this effect appears to vary with the type of stressor. Furthermore, the absence of direct projections between the medial prefrontal cortex and corticotropin-releasing factor cells at the apex of the hypothalamic-pituitary-adrenal axis suggest that other brain regions must act as a relay when this inhibitory mechanism is activated. In the present study, we first established that electrolytic lesions involving the prelimbic and infralimbic medial prefrontal cortex increased plasma adrenocorticotropic hormone levels seen in response to a physical stressor, the systemic delivery of interleukin-1beta. However, medial prefrontal cortex lesions did not alter plasma adrenocorticotropic hormone levels seen in response to a psychological stressor, noise. To identify brain regions that might mediate the effect of medial prefrontal cortex lesions on hypothalamic-pituitary-adrenal axis responses to systemic interleukin-1beta, we next mapped the effects of similar lesions on interleukin-1beta-induced Fos expression in regions previously shown to regulate the hypothalamic-pituitary-adrenal axis response to this stressor. It was found that medial prefrontal cortex lesions reduced the number of Fos-positive cells in the ventral aspect of the bed nucleus of the stria terminalis. However, the final experiment, which involved combining retrograde tracing with Fos immunolabelling, revealed that bed nucleus of the stria terminalis-projecting medial prefrontal cortex neurons were largely separate from medial prefrontal cortex neurons recruited by systemic interleukin-1beta, an outcome that is difficult to reconcile with a simple medial prefrontal cortex-bed nucleus of the stria terminalis-corticotropin-releasing factor cell control circuit.

The neurobiological consequences of early stress and childhood maltreatment

Early severe stress and maltreatment produces a cascade of neurobiological events that have the potential to cause enduring changes in brain development. These changes occur on multiple levels, from neurohumoral (especially the hypothalamic-pituitary-adrenal [HPA] axis) to structural and functional. The major structural consequences of early stress include reduced size of the mid-portions of the corpus callosum and attenuated development of the left neocortex, hippocampus, and amygdala. Major functional consequences include increased electrical irritability in limbic structures and reduced functional activity of the cerebellar vermis. There are also gender differences in vulnerability and functional consequences. The neurobiological sequelae of early stress and maltreatment may play a significant role in the emergence of psychiatric disorders during development.

Effects of neonatal handling on basal and stress-induced monoamine levels in the male and female rat brain

Neonatal handling has pervasive effects on the rat brain leading to increased ability to cope with and adapt to stressful stimuli. We determined the effects of neonatal handling on the dopaminergic and serotonergic system, in the male and female rat brain, under basal conditions before and after puberty and after short- and long-term forced swimming stress. Exposure of animals to neonatal handling resulted in sex-dependent changes in the concentration and turnover of monoamines in the different brain areas. In the prepubertal brain, the effect of neonatal handling was manifested as an increase in dopamine turnover in the females, particularly in the hypothalamus, an increase in serotonin levels and a decrease in its turnover in all three brain regions examined of both males and females. Certain of the handling-induced effects observed in the prepubertal brain were reversed in the postpubertal animals. Thus, in the postpubertal brain, the handling-induced changes in serotonin levels and its turnover observed in both sexes before puberty were abolished. On the other hand, the handling-induced increase in hypothalamic dopamine turnover was maintained. After exposure to short-term stress, the effect of handling was manifested on one hand as decreased striatal dopamine levels in the females, and decreased dopamine turnover in the hypothalamus of both males and females, and on the other, as increased serotonin levels in the hypothalamus. After exposure to long-term stress, handled females had decreased dopamine turnover in the hypothalamus and the striatum, but there was no effect of handling on the serotonergic system. Our results provide some neurobiological evidence supporting the determinant role of the mother-infant relationship in the development of psychopathology. Neonatal handling, which modifies normal mother-pup interactions, results in alterations in brain dopaminergic and serotonergic systems, both of which are involved in the etiopathogenesis of major psychoses. Exposure to either short- or long-term stress in adult life results in sex-dependent changes in brain monoamines, which are affected by handling thus making coping more efficient and rendering the stressful stimulus less noxious.

Pretreatment with corticosterone attenuates the nucleus accumbens dopamine response but not the stimulant response to cocaine in rats

It has been suggested that stress, via corticosterone secretion, can modulate some of the behavioural responses to cocaine. In particular, we have demonstrated that daily exposure to electric footshock stress or daily pretreatment with corticosterone shifts the ascending limb of the dose-response curve for the acquisition of cocaine self-administration upwards and to the left. It has been suggested that this corticosterone-induced increase in sensitivity to low doses of cocaine is associated with an enhancement of dopaminergic neurotransmission. The present study was designed to test this hypothesis. Adult male rats were pretreated with corticosterone (2.0 mg/kg intraperitoneally) 15 min prior to an injection of cocaine (5.0, 10.0 or 20.0 mg/kg intraperitoneally), and motor activity and extracellular dopamine concentrations in the nucleus accumbens were monitored. Cocaine administration resulted in dose-related increases in motor activity that were unaffected by pretreatment with corticosterone. However, rather than augmenting cocaine-induced increases in dopamine in the nucleus accumbens, corticosterone pretreatment actually caused attenuation at the two highest doses of cocaine tested. These data suggest dissociation between locomotor activation and nucleus accumbens dopamine responses to cocaine, and indicate that other brain regions and/or mechanisms may be involved in the changes in sensitivity to cocaine induced by corticosterone.

Functional subsets of serotonergic neurones: implications for control of the hypothalamic-pituitary-adrenal axis

Serotonergic systems play an important role in the regulation of behavioural, autonomic and endocrine responses to stressful stimuli. This includes modulation of both the hypothalamic-pituitary-adrenal (HPA) axis and the hypothalamic-spinal-adrenal (HSA) axis, which converge at the level of the adrenal cortex to regulate glucocorticoid secretion. Paradoxically, serotonin can either facilitate or inhibit HPA axis activity and stress-related physiological or behavioural responses. A detailed analysis of the brainstem raphé complex and its ascending projections reveals that facilitatory and inhibitory effects of serotonergic systems on glucocorticoid secretion may be due to influences of topographically organized and functionally diverse serotonergic systems. (i) A serotonergic system arising from the middle and caudal dorsal raphé nucleus and projecting to a distributed central autonomic control system and a lateral 'emotional motor system'. Evidence suggests that serotonin can sensitize this subcortical circuit associated with autonomic arousal, anxiety and conditioned fear. (ii) A serotonergic system arising from the median raphé nucleus and projecting extensively and selectively to a ventral subiculum projection system. Evidence suggests that serotonin facilitates this limbic circuit associated with inhibition of ultradian, circadian and stress-induced activity of both the HPA axis and the HSA axis. These new perspectives, based on functional anatomical considerations, provide a hypothetical framework for investigating the role of serotonergic systems in the modulation of ultradian, circadian and stress-induced neuroendocrine function.

Neonatal prefrontal cortex lesion using CO2 laser technique

Prefrontal cortex (PFC) is a large area of the brain and its neonatal lesion with ibotenic or kainic acid is used to study the early abnormalities in neurodevelopment that lead to behavioral changes linked to schizophrenia. However, these exitotoxic drugs produce a large and asymmetric damage in the PFC. We produced the bilateral lesions of the dorsal part of the PFC of neonatal Sprague-Dawley rats (postnatal day 7, P7) at the anteroposterior +2.5 mm and mediolateral +/-0.4 coordinates by the new laser technique that employ the confined radiation of the CO(2) laser in the pulsed mode. The laser was used because its coherent radiation can be focused in a very small spot and as small as of several tens of micrometers in diameters. The CO(2) laser radiation is strongly absorbed by water that is present in any soft tissue. Thereafter, the configuration of the heated zone and, consequently, that of the lesion does not depend on the morphological non-homogeneity of particular structures. We obtained the symmetric, conical in shape and small-size bilateral lesions of the PFC. The size of the lesion depended on the beam spot-size and could be as small as several dozens of micrometers in diameter. Our data suggests that the laser technique will be used for the anatomical-functional studies of the PFC in the brain.

Benzodiazepines in schizophrenia: prefrontal cortex atrophy predicts clinical response to alprazolam augmentation

Benzodiazepines augment clinical responses to neuroleptics in some, but not all, treatment-refractory schizophrenic patients; however the biological predictors of response have remained unclear. Since patients with prefrontal cortex (PFC) volume loss demonstrate exaggerated subcortical dopamine responses to stress, and since benzodiazepines curtail stress-induced subcortical dopamine release in PFC-lesioned animals, we reasoned that patients with PFC volume loss might show preferential clinical responses to benzodiazepine augmentation. Five patients, who were participating in a larger four-week double-blind study of alprazolam augmentation of neuroleptics in treatment-resistant or partially treatment-resistant schizophrenia, had brain MRI scans prior to entry into the study. MRI scans were morphometrically analyzed to yield estimates of PFC grey and white matter volumes and PFC cerebrospinal fluid (CSF) volume, and these were correlated with clinical responses to alprazolam augmentation. PFC grey matter volume (adjusted for overall cranial capacity) was significantly correlated (r = 0.96, p < 0.01), in the predicted direction, with alprazolam-associated changes in total Brief Psychiatric Rating Scale ratings. PFC volume loss may represent a biological marker for benzodiazepine responsivity in schizophrenia, although the present findings are considered preliminary because of the small sample size. Mechanistic considerations and suggestions for future research are discussed.

The stress-vulnerability hypothesis in psychotic disorders: focus on the stress response systems

The vulnerabilty stress model is an intriguing concept to look into the etiology of psychotic disorders and, in particular, into the "nature nurture" principle. That stress affects a vulnerable nature may be obvious, but its mechanism is not well understood, and many questions remain to be answered, let alone how to define "vulnerability". The present review tries to focus on the core issues of the vulnerability stress concept--identifying vulnerability, the way stress interferes with it, and the possiblilities of modulating their interaction. Attention is drawn to the biologic stress response systems, the autonomic nervous system (ANS), the hypothalamic pituitary adrenal (HPA) system, and the immune system, and highlights the plasticity of the HPA system as the mediator of adaptation.

Developmental neurobiology of childhood stress and trauma

Severe early stress and maltreatment produces a cascade of events that have the potential to alter brain development. The first stage of the cascade involves the stress-induced programming of the glucocorticoid, noradrenergic, and vasopressin-oxytocin stress response systems to augment stress responses. These neurohumors then produce effects on neurogenesis, synaptic overproduction and pruning, and myelination during specific sensitive periods. Major consequences include reduced size of the mid-portions of the corpus callosum; attenuated development of the left neocortex, hippocampus, and amygdala along with abnormal frontotemporal electrical activity; and reduced functional activity of the cerebellar vermis. These alterations, in turn, provide the neurobiological framework through which early abuse increases the risk of developing post-traumatic stress disorder (PTSD), depression, symptoms of attention-deficit/hyperactivity, borderline personality disorder, dissociative identity disorder, and substance abuse.

Behavioral effects of excitotoxic lesions of ventral medial prefrontal cortex in the rat are hemisphere-dependent

The ventral region of the medial prefrontal cortex (mPFC) is highly sensitive to stressful inputs and implicated in a variety of behaviors. Studies have also demonstrated numerous functional hemispheric asymmetries within this brain area of the rat. The present study examines the effects of ibotenic acid or sham lesions targeting the left, right or bilateral infralimbic cortex, on a variety of behaviors. Lesions (which destroyed infralimbic and ventral prelimbic cortex) were without effect on acquisition or reversal of a spatial learning task in the Morris water maze. Similarly unaffected were spontaneous and amphetamine-induced locomotor activity and sensitization, and prepulse inhibition of the acoustic startle response. In contrast, lesions significantly affected behavior in the elevated plus maze, as right-lesioned animals spent more time exploring the open arms of the maze than shams or left-lesioned rats, while not differing in closed arm entries. As well, in a simple taste aversion paradigm, right-lesioned rats drank significantly more of a sweetened milk/quinine solution than shams and left-lesioned rats, despite not differing in consumption of sweetened milk alone. The anxiolytic effects of right, but not left lesions of ventral mPFC, parallel the asymmetrical suppression of physiological stress responses previously reported for similar lesions. It is suggested that the right ventral mPFC plays a primary role in optimizing cautious and adaptive behavior in potentially threatening situations.

Prefrontal cortical regulation of hypothalamic-pituitary-adrenal function in the rat and implications for psychopathology: side matters

In recent years, dysfunction of hypothalamic-pituitary-adrenal (HPA) axis function has been implicated in a wide variety of psychiatric conditions. The importance of this system in responding to and coping with stress is well documented, and the integrity of such systems is of obvious significance to good mental health. The prefrontal cortex (PFC) is also heavily implicated in numerous psychopathological conditions. There is thus a growing interest in the potential role the PFC might play in regulating HPA function, and whether abnormalities of these systems are linked. The present paper reviews a number of recent animal studies which have attempted to elucidate the role of the PFC in regulation of HPA axis function, and how these systems may interact. It is concluded that the PFC is involved both in activating HPA responses to stress and in the negative feedback regulation of this system. Cerebral laterality is an important feature of this regulation, with the right PFC being most directly linked to stress-regulatory systems. On this basis, a number of parallels are drawn to the human literature, where asymmetrical disturbances in PFC activity may help explain associated patterns of HPA dysfunction.

Maturation of extinction behavior in infant rats: large-scale regional interactions with medial prefrontal cortex, orbitofrontal cortex, and anterior cingulate cortex

The ability to express a behavior during the postnatal period may be related to developmental changes in the recruitment of particular neural systems. Here, we show that developmental changes in the functional interactions involving three cortical regions (the medial prefrontal cortex, orbitofrontal cortex, and anterior cingulate cortex) are associated with maturation of extinction behavior in infant rats. Postnatal day 17 (P17) and P12 pups were trained in a straight-alley runway on an alternating schedule of reward and nonreward [patterned single alternation (PSA)] or on a pseudorandom schedule of partial reinforcement (PRF); the pups were then injected with fluorodeoxyglucose (FDG) and shifted to continuous nonreward (extinction). Handled control groups exposed to the same training environment but not trained on a particular schedule were included. Among P17 pups, extinction proceeded faster in PSA pups relative to PRF pups. No differences were found between P12 groups. FDG uptake, an index of acute changes in functional activity, was quantified in the three cortical regions and 27 other brain regions of interest. A multivariate covariance analysis, seed partial least squares, revealed that functional relationships involving the three cortical regions and large-scale systems of regions throughout the rostrocaudal extent of the brain changed with training in P17 pups. The cortical regions were primarily uncoupled in the younger group. The data suggest that functional maturation of the frontal cortical regions and their interactions with other brain systems are related to the maturational shift in behavior.

Perinatal distress leads to lateralized medial prefrontal cortical dopamine hypofunction in adult rats

Obstetric complications involving anoxia or prolonged hypoxia are suspected to increase the risk for such mental disorders as schizophrenia and attention deficit-hyperactivity disorder. In previous studies, we reported evidence of enhanced nucleus accumbens (NAcc) dopamine (DA) function in adult rats subjected to intrauterine anoxia during cesarean (C) section birth. In the present study, we used voltammetry and monoamine-sensitive electrodes to investigate the possibility that this functional hyperactivity of the meso-NAcc system is attributable to a loss of inhibitory control from the medial prefrontal cortex (PFC). We monitored the DA responses to repeated once-daily stress in the right or left PFC of adult male rats born vaginally (VAG) or by C-section, either with (C + 15) or without (C + 0) an additional 15 min of intrauterine anoxia. In C + 15 animals, we observed a pronounced and persistent blunting of stress-induced DA release in the right PFC but not in the left; with repeated testing, a similar pattern of dampened right PFC DA stress responses emerged in C + 0 animals. In addition, C + 15 animals were spontaneously more active than VAG and C + 0 animals and displayed an increase in PFC DA transporter density that was also lateralized to the right hemisphere. There was no evidence, however, that PFC D(1) and D(2) receptor levels differed between birth groups or hemisphere. These findings suggest a mechanism by which perinatal complications involving anoxia might contribute to the etiology of mental disorders that have been linked to disturbances in central DA transmission and lateralized PFC dysfunction.