Molecular examination of the endogenous opioid system in rhesus macaque monkeys with self-injurious behavior

Self-injurious behavior (SIB) can lead to serious injury and occurs in approximately 1%-4% of the adult population, with higher incidences in adolescent and institutionalized populations, as well as in children with developmental disorders such as Autism. SIB also spontaneously occurs in a low percentage of captive monkeys. Rhesus macaque (Macaca mulatta) monkeys are evolutionarily and physiologically similar to humans, share 93% genetic sequence similarity to humans, and have long been used as testing subjects for vaccine and clinical trials. Previous studies hypothesized that altered endogenous opioid expression occurs in the brains of individuals and animals that self-injure. We examined the regional mRNA expression of opioid signaling genes in sixteen rhesus macaques that exhibited SIB and eight sex- and age- matched controls. The brain regions examined are linked to reward reinforcement and stress adaptation including the hypothalamus, orbital frontal cortex, nucleus accumbens, hippocampus, caudate, and the amygdala. We found decreased μ-opioid receptor (OPRM1) in the amygdala of monkeys with SIB, and reduced prodynorphin (PDYN) in the hypothalamus. Our data suggest dysfunction in the regulation of opioid peptide precursors and calls for further investigation of the endogenous opioid system in SIB.

Modification of kynurenine pathway via inhibition of kynurenine hydroxylase attenuates surgical brain injury complications in a male rat model

Neurosurgical procedures result in surgically induced brain injury (SBI) that causes postoperative complications including brain edema and neuronal apoptosis in the surrounding brain tissue. SBI leads to the release of cytokines that indirectly cause the stimulation of kynurenine 3-monooxygenase (KMO) and the release of neurotoxic quinolinic acid (QUIN). This study tested a KMO inhibitor, RO 61-8048, to prevent postoperative brain edema and consequent neuronal apoptosis in an in vivo model of SBI. A rodent model of SBI was utilized which involves partial resection of the right frontal lobe. A total of 127 Sprague-Dawley male rats (weight 275-325 g) were randomly divided into the following groups: Sham surgical group, SBI, SBI + DMSO, SBI + RO 61-8048 (10 mg/kg), SBI + RO 61-8048 (40 mg/kg), and SBI + RO 61-8048 (40 mg/kg) + KAT II inhibitor PF-04859989 (5 mg/kg). RO 61-8048 was administered by intraperitoneal injection after SBI. Postoperative assessment at different time points included brain water content (brain edema), neurological scoring, and western blot. SBI increased brain water content (ipsilateral frontal lobe), decreased neurological function, and increased apoptotic markers compared with sham animals. Treatment with RO 61-8048 (40 mg/kg) reduced brain water content and improved long-term neurological function after SBI. RO 61-8048 increased the expression of kynurenic acid while reducing QUIN and apoptotic markers in the surrounding brain tissue after SBI. These neuroprotective effects were reversed by PF-04859989. This study suggests KMO inhibition via RO 61-8048 as a potential postoperative therapy following neurosurgical procedures.

Differential innervation within a transverse plane of spinal gray matter by sensorimotor cortices, with special reference to the somatosensory cortices

The corticospinal (CS) neurons projecting to the cervical cord distribute not only in motor-related cortical areas, but also in somatosensory areas, including the primary somatosensory cortex (S1). The exact functions of these widely distributed CS neurons are largely unknown, however. In this study, we injected mice with adeno-associated virus encoding membrane-binding fluorescent proteins to investigate the distribution of axons from CS neurons in different regions within a broad cortical area. We found that CS axons from the primary motor cortex (M1), the rostral part of S1 (S1r), and the caudal part of S1 (S1c) differentially project to specific compartments within the spinal gray matter of the seventh cervical cord segment: (a) M1 projects mainly to intermediate and ventral areas, (b) S1r to the mediodorsal area, and (c) S1c to the dorsolateral area. We also found that the projection from S1r, which corresponds to the forelimb area, largely overlaps the cutaneous afferent terminals from the forepaw (hand) in the dorsal horn, and we detected a similar relation between S1c and the trunk. Our findings suggest the existence of considerably fine somatotopic compartments within the dorsal horn that process somatosensation and descending information, which is provided mainly by S1 CS neurons and contribute to delicate control of sensory information in generation of movement.

Primate neocortex development and evolution: Conserved versus evolved folding

The neocortex, the seat of higher cognitive functions, exhibits a key feature across mammalian species-a highly variable degree of folding. Within the neocortex, two distinct subtypes of cortical areas can be distinguished, the isocortex and the proisocortex. Here, we have compared specific spatiotemporal aspects of folding between the proisocortex and the isocortex in 13 primates, including human, chimpanzee, and various Old World and New World monkeys. We find that folding at the boundaries of the dorsal isocortex and the proisocortex, which gives rise to the cingulate sulcus (CiS) and the lateral fissure (LF), is conserved across the primates studied and is therefore referred to as conserved folding. In contrast, the degree of folding within the dorsal isocortex exhibits huge variation across these primates, indicating that this folding, which gives rise to gyri and sulci, is subject to major changes during primate evolution. We therefore refer to the folding within the dorsal isocortex as evolved folding. Comparison of fetal neocortex development in long-tailed macaque and human reveals that the onset of conserved folding precedes the onset of evolved folding. Moreover, the analysis of infant human neocortex exhibiting lissencephaly, a developmental malformation thought to be mainly due to abnormal neuronal migration, shows that the evolved folding is perturbed more than the conserved folding. Taken together, our study presents a two-step model of folding that pertains to primate neocortex development and evolution. Specifically, our data imply that the conserved folding and the evolved folding constitute two distinct, sequential events.

Mediolateral and dorsoventral projection patterns of cutaneous afferents within transverse planes of the mouse spinal dorsal horn

The central projection patterns of cutaneous afferents from the forelimb and shoulder of mice were studied in the spinal dorsal horn after intracutaneous injection of AlexaFluor 488-conjugated and/or 594-conjugated cholera toxin subunit B (CTB). Based on their dermatomes, the following eight skin regions are thought to be innervated by spinal nerves from the sixth to eighth cervical spinal nerve roots: the dorsal surface of the shoulder, brachium, proximal forearm, distal forearm, hand, palmar surface of the second and third digits, and palm. The termination areas of afferents from the dorsal surface of the shoulder and forearm were narrow, distributed in a dorsoventral direction, and aligned in order from lateral to medial within the sixth to eighth cervical dorsal horns. By contrast, the termination areas of the palmar surface of the second and third digits largely overlapped. We also injected CTB into the dorsal surface of the hindlimb and pelvic regions. Skin regions there are thought to be innervated by nerves from the third to fifth lumbar spinal nerve roots. The observed projection patterns in the lumbar dorsal horn were similar to the cervical patterns. Injection of a mixture of CTB and wheat-germ agglutinin-conjugated horseradish peroxidase (WGA-HRP), which are thought to label Aβ and Aδ/C fibers, respectively, showed segregated termination areas of CTB- and WGA-HRP-labeled afferents. Moreover, alignment of the termination areas was in the dorsoventral direction. These results suggest there is fine somatotopic (mediolateral axis) and modality-specific (dorsoventral axis) organization within the spinal dorsal horn.