PirB regulates asymmetries in hippocampal circuitry

The left-right side-specific endocrine signaling in the effects of brain lesions: questioning of the neurological dogma

Each cerebral hemisphere is functionally connected to the contralateral side of the body through the decussating neural tracts. The crossed neural pathways set a basis for contralateral effects of brain injury such hemiparesis and hemiplegia as it has been already noted by Hippocrates. Recent studies demonstrated that, in addition to neural mechanisms, the contralateral effects of brain lesions are mediated through the humoral pathway by neurohormones that produce either the left or right side-specific effects. The side-specific humoral signaling defines whether the left or right limbs are affected after a unilateral brain injury. The hormonal signals are released by the pituitary gland and may operate through their receptors that are lateralized in the spinal cord and involved in the side-specific control of symmetric neurocircuits innervating the left and right limbs. Identification of features and a proportion of neurological deficits transmitted by neurohormonal signals vs. those mediated by neural pathways is essential for better understanding of mechanisms of brain trauma and stroke and development of new therapies. In a biological context, the left–right side-specific neuroendocrine signaling may be fundamental for the control of the left- and right-sided processes in bilaterally symmetric animals.

Molecular and cellular basis of left-right asymmetry in vertebrates

Although the human body appears superficially symmetrical with regard to the left-right (L-R) axis, most visceral organs are asymmetric in terms of their size, shape, or position. Such morphological asymmetries of visceral organs, which are essential for their proper function, are under the control of a genetic pathway that operates in the developing embryo. In many vertebrates including mammals, the breaking of L-R symmetry occurs at a structure known as the L-R organizer (LRO) located at the midline of the developing embryo. This symmetry breaking is followed by transfer of an active form of the signaling molecule Nodal from the LRO to the lateral plate mesoderm (LPM) on the left side, which results in asymmetric expression of Nodal (a left-side determinant) in the left LPM. Finally, L-R asymmetric morphogenesis of visceral organs is induced by Nodal-Pitx2 signaling. This review will describe our current understanding of the mechanisms that underlie the generation of L-R asymmetry in vertebrates, with a focus on mice.

Predominant synaptic potentiation and activation in the right central amygdala are independent of bilateral parabrachial activation in the hemilateral trigeminal inflammatory pain model of rats

Nociceptive signals originating in the periphery are conveyed to the brain through specific afferent and ascending pathways. The spino-(trigemino-)parabrachio-amygdaloid pathway is one of the principal pathways mediating signals from nociception-specific ascending neurons to the central amygdala, a limbic structure involved in aversive signal-associated emotional responses, including the emotional aspects of pain. Recent studies suggest that the right and left central amygdala play distinct roles in the regulation of nociceptive responses. Using a latent formalin inflammatory pain model of the rat, we analyzed the right-left differences in synaptic potentiation at the synapses formed between the fibers from the lateral parabrachial nucleus and central amygdala neurons as well as those in the c-Fos expression in the lateral parabrachial nucleus, central amygdala, and the basolateral/lateral amygdala after formalin injection to either the right or left side of the rat upper lip. Although the single-sided formalin injection caused a significant bilateral increase in c-Fos-expressing neurons in the lateral parabrachial nucleus with slight projection-side dependence, the increase in the amplitude of postsynaptic excitatory currents and the number of c-Fos-expressing neurons in the central amygdala occurred predominantly on the right side regardless of the side of the inflammation. Although there was no significant correlation in the number of c-Fos-expressing neurons between the lateral parabrachial nucleus and central amygdala in the formalin-injected animals, these numbers were significantly correlated between the basolateral amygdala and central amygdala. It is thus concluded that the lateral parabrachial nucleus-central amygdala synaptic potentiation reported in various pain models is not a simple Hebbian plasticity in which raised inputs from the lateral parabrachial nucleus cause lateral parabrachial nucleus-central amygdala potentiation but rather an integrative and adaptive response involving specific mechanisms in the right central amygdala.

Propofol Alters Long Non-Coding RNA Profiles in the Neonatal Mouse Hippocampus: Implication of Novel Mechanisms in Anesthetic-Induced Developmental Neurotoxicity

BACKGROUND

Propofol induces acute neurotoxicity (e.g., neuroapoptosis) followed by impairment of long-term memory and learning in animals. However, underlying mechanisms remain largely unknown. Long non-coding RNAs (lncRNAs) are found to participate in various pathological processes. We hypothesized that lncRNA profile and the associated signaling pathways were altered, and these changes might be related to the neurotoxicity observed in the neonatal mouse hippocampus following propofol exposure.

METHODS

In this laboratory experiment, 7-day-old mice were exposed to a subanesthetic dose of propofol for 3 hours, with 4 animals per group. Hippocampal tissues were harvested 3 hours after propofol administration. Neuroapoptosis was analyzed based on caspase 3 activity using a colorimetric assay. A microarray was performed to investigate the profiles of 35,923 lncRNAs and 24,881 messenger RNAs (mRNAs). Representative differentially expressed lncRNAs and mRNAs were validated using reverse transcription quantitative polymerase chain reaction. All mRNAs dysregulated by propofol and the 50 top-ranked, significantly dysregulated lncRNAs were subject to bioinformatics analysis for exploring the potential mechanisms and signaling network of propofol-induced neurotoxicity.

RESULTS

Propofol induced neuroapoptosis in the hippocampus, with differential expression of 159 lncRNAs and 100 mRNAs (fold change ± 2.0, P< 0.05). Bioinformatics analysis demonstrated that these lncRNAs and their associated mRNAs might participate in neurodegenerative pathways (e.g., calcium handling, apoptosis, autophagy, and synaptogenesis).

CONCLUSION

This novel report emphasizes that propofol alters profiles of lncRNAs, mRNAs, and their cooperative signaling network, which provides novel insights into molecular mechanisms of anesthetic-induced developmental neurodegeneration and preventive targets against the neurotoxicity.