Effect of excitotoxic lesions of the neonatal ventral hippocampus on the immobility response in rats

Neurochemical anatomy of dorsal and tonic immobility responses

The dorsal immobility response (DIR) and the tonic immobility response (TIR) are cutaneo-motor reflexes typically triggered when a prey is seized. The neurochemical basis of the DIR appears to pass through the basal ganglia via dopaminergic fibers, while the neurochemical basis of the TIR appears to include a circuit comprising the amygdala, the periaqueductal gray (PAG), the dorsal raphe, and the nucleus magnus raphe (NMR) via glutamatergic, serotonergic, cholinergic, GABAergic, and opioid fibers. For the DIR, the basal ganglia also seem to be involved in regard to estradiol, while for the TIR, the HPA axis appears involved at the level of the amygdala and the oral pontine reticular nucleus.

Corticosterone microinjected into nucleus pontis oralis increases tonic immobility in rats

Tonic immobility (TI) is also known as "immobility response", "immobility reflex", "animal hypnosis", etc. It is an innate antipredatory behavior characterized by an absence of movement, varying degrees of muscular activity, and a relative unresponsiveness to external stimuli. Experimentally, TI is commonly produced by manually forcing an animal into an inverted position and restraining it in that position until the animal becomes immobile. Part of the neural mechanism(s) of TI involves the medullo-pontine reticular formation, with influence from other components of the brain, notably the limbic system. It has been observed that TI is more prolonged in stressed animals, and systemic injection of corticosterone (CORT) also potentiates this behavior. At present, the anatomical brain regions involved in the CORT modulation of TI are unknown. Thus, our study was made to determine if some pontine areas could be targets for the modulation of TI by CORT. A unilateral nucleus pontis oralis (PnO) microinjection of 1 μL of CORT (0.05 μg/1 μL) in rats resulted in clear behavioral responses. The animals had an increased duration of TI caused by clamping the neck (in this induction, besides of body inversion and restraint, there is also clamping the neck), with an enhancement in open-field motor activity, which were prevented by pretreatment injection into PnO with 1 μL of the mineralocorticoid-receptor antagonist spironolactone (0.5 μg/1 μL) or 1 μL of the glucocorticoid-receptor antagonist mifepristone (0.5 μg/1 μL). In contrast, these behavioral changes were not seen when CORT (0.05 μg/1 μL) was microinjected into medial lemniscus area or paramedian raphe. Our data support the idea that, in stressful situations, glucocorticoids released from adrenals of the prey reach the PnO to produce a hyper arousal state, which in turn can prolong the duration of TI.

PLC-beta1 knockout mice as a model of disrupted cortical development and plasticity: behavioral endophenotypes and dysregulation of RGS4 gene expression

The complexity of the genetics underlying schizophrenia is highlighted by the multitude of molecular pathways that have been reported to be disrupted in the disorder including muscarinic, serotonergic, and glutamatergic signaling systems. It is of interest, therefore, that phospholipase C-beta1 (PLC-beta1) acts as a point of convergence for these pathways during cortical development and plasticity. These signaling pathways, furthermore, are susceptible to modulation by RGS4, one of the more promising candidate genes for schizophrenia. PLC-beta1 knockout mice were behaviorally assessed on tests including fear conditioning, elevated plus maze, and the Y maze. In situ hybridization was used to assess RGS4 expression. We found that PLC-beta1 knockout mice display abnormal anxiety profiles on some, but not all measures assessed, including decreased anxiety on the elevated plus maze. We also show memory impairment and a complete absence of acquisition of hippocampal-dependent fear conditioning. Furthermore, at a molecular level, we demonstrate dramatic changes in expression of RGS4 mRNA in selective regions of the PLC-beta1 knockout mouse brain, particularly the CA1 region of the hippocampus. These results validate the utility of the PLC-beta1 knockout mouse as a model of schizophrenia, including molecular and cellular evidence for disrupted cortical maturation and associated behavioral endophenotypes.

Neuroendocrine responses to a cold pressor stimulus in polydipsic hyponatremic and in matched schizophrenic patients

Schizophrenia, many believe, reflects an enhanced vulnerability to psychological stress. Controlled exposure to stressors, however, has produced inconclusive results, particularly with regards to neurohormones. Some of the variability may be attributable to the nature and psychological significance of the stimulus and failure to control physiologic confounds. In addition, it is possible that the heterogeneity of schizophrenia is an important factor. In a carefully designed study and in a controlled setting, we measured the neuroendocrine response of eight polydipsic hyponatremic (PHS), seven polydipsic normonatremic (PNS), and nine nonpolydipsic normonatremic (NNS) (ie normal water balance) schizophrenic in-patients as well as 12 healthy controls (HC) to two different stressors: one of which appears to influence neuroendocrine secretion through its psychological (cold pressor) and the other (upright posture) through its systemic actions. Subjects in the three psychiatric groups were stabilized and acclimated to the research setting, and all received saline to normalize plasma osmolality. Following the cold pressor, plasma adrenocorticotropin and cortisol levels showed a more prolonged rise in PHS patients relative to PNS patients. NNS patients, in contrast, exhibited blunted responses relative to both of the polydipsic groups and the HC. Peak vasopressin responses were also greater in PHS and blunted in NNS patients. Responses to the postural stimulus were similar across patient groups. These findings provide a mechanism for life threatening water intoxication in schizophrenia; help to reconcile conflicting findings of stress responsiveness in schizophrenia; and potentially identify a discrete patient subset with enhanced vulnerability to psychological stress.