Increased synapsin I expression in cerebral malaria

Abstract

Synapsin I is a neuronal phosphoprotein contained in the synaptic vesicles of mammalian central and peripheral nervous systems. It regulates both neurotransmitter release and synaptic formation. Variations in synapsin I expression in the brain have been reported to cause brain malfunction. In severe malaria, neurological complications, such as convulsion, delirium and coma, suggest abnormalities in the release of neurotransmitters. This study evaluated synapsin I expression in cerebral malaria (CM). An immunohistochemical method was used to study the semi-quantitative and qualitative expression of synapsin I in the brain of CM patients (10 cases) who died with Plasmodium falciparum, compared with non-cerebral malaria (NCM) (4 cases), and control brain tissues (5). Synapsin I was expressed in the gray matter of the cerebral cortex and the molecular layer of the cerebellum, as a diffusely dense precipitate pattern in the neuropil, with no immunoreactivity in the neurons, neuronal dendrites, glial cells, endothelial cells, and Purkinje cells. The findings were similarly demonstrated in CM, NCM, and control brain tissues. However, in the granular layer of the cerebellum, a significant increase in synapsin I expression was observed in the granule cells, and the glomerular synaptic complex, from the CM group, compared with the NCM, and control brain tissues (all P < 0.05). Parasitemia showed a positive correlation with synapsin I expression in the granule cells (on admission: Spearman's ρ = 0.600, P = 0.023) (before death: Spearman's ρ = 0.678, P = 0.008), and glomerular synaptic complex (before death: Spearman's ρ = 0.571, P = 0.033). It was hypothesized that CM causes pre-synaptic excitation and eventually activation of synapsin I, leading to increased neurotransmitter release. Synapsin I inhibitor should be investigated further as a target for a therapeutic intervention to alleviate neurological symptoms in severe malaria.

Keywords: Malaria; Plasmodium falciparum; cerebral malaria; immunohistochemistry; synapsin I.

Figure 1

Histopathologic changes of the brain in CM. Representative images showing petechial hemorrhages (arrowheads) in the cerebral cortex (A) (200 ×), and sequestration of PRBCs (arrows) in the cerebral blood vessels (BV) (B) (400 ×). Hematoxylin and eosin stain.

Figure 2

Synapsin I expression in the cerebral cortex, illustrating strong immunostaining in the gray matter (GM), and no staining in the white matter (WM) (A) (400 ×). At higher magnification (B), the junction between gray and white matter is shown. In the pyramidal cell layer (C), neuropil (Np) shows dispersed, strong immunostaining for synapsin I, while immunostaining is absent from the neurons (arrows), dendrites (asterisks), glial cells (arrowheads), and blood vessels (BV) (avidin-biotin peroxidase complex technique).

Figure 3

Synapsin I expression in the gray matter of the cerebellar cortex. Similar immunoexpression in the molecular layer (ML), and Purkinje cell layer (PL) was demonstrated in the control (A), NCM (B), and CM (C) brain tissues. Strong and diffused immunostaining was seen in the ML, while Purkinje cells failed to express synapsin I protein (asterisks). The granule cells in the granular layer (GL) shows increased in immuno-positive cells in CM (C), compared to NCM (B) and control brain (A) tissues. Increased synapsin I expression was seen in glomerular synaptic complex (arrows) in CM (C). Parasitized red blood cells (arrowhead) are seen in a blood vessel (C). All images are 400 × magnification. Bar = 20 µm. (avidin-biotin alkaline phosphatase complex technique).

Figure 4

Synapsin I expression in the granular layer of the cerebellar cortex. The granular cells in the control (A) and NCM (B) groups show few immunopositive cells compared to CM (C) brain tissues (arrowheads). Increased synapsin I expression in the glomeruli synaptic complex (arrows) was demonstrated in the CM (C). All images are 1,000 × magnification, Bar = 10 µm (avidin-biotin alkaline phosphatase complex technique).

Figure 5

Comparative findings of synapsin I expression in the cerebellum, showing a significant increase in immune-reactivity against synapsin I antibody for granule cells (A) and glomerular synaptic complex (B) in CM group. (*-P < 0.001, **-P < 0.002, NS- not significant).

Figure 6

Correlations between parasitemia and synapsin I expression in the granule cells (A), and glomerular synaptic complex (B) of the cerebellum.