Changes in vascular endothelial growth factor (VEGF) induced by the Morris water maze task

Abstract

The present study was undertaken to evaluate the effects on hippocampal vascular endothelial growth factor (VEGF) levels in rats when they experience hippocampal-dependent spatial learning via the Morris water maze (MWM) task. Rats underwent one of two different versions of the MWM: weak or intensive. After one day of intensive training, a highly sensitive enzyme-linked immunosorbent assay (ELISA) was used to measure VEGF protein levels in the hippocampus, cortex, and serum, and higher levels were found in the trained group compared to a naive control group. VEGF levels also increased in rats that swam only for durations equal to the intensive training periods. In contrast, rats trained under the weaker MWM paradigm for five days showed a decrease in hippocampal VEGF protein level. Mimicking increases in neuronal VEGF in the hippocampus by direct infusion of VEGF into CA1 resulted in up-regulation of the phosphorylation of the cAMP response element-binding (CREB) protein and the Ca2+/calmodulin-dependent protein kinases II (CaMKII). These results suggest that VEGF may be a physiological parameter involved in learning procedures that include physical activity.

Fig. 1.

Effects of MWM on VEGF protein levels for a one-session-per-day procedure conducted for five consecutive days. (A) Acquisition curves for the weak version of the MWM hidden platform test. The latency in seconds is presented for each day. Each point represents the mean latency in sec ± SEM. (B) VEGF protein level in the hippocampus, cortex and serum detected by ELISA. Each point represents the mean ± SEM; n = 5–8 rats per group, ^*P < 0.05, ^**P < 0.01.

Fig. 2.

Effects of MWM on VEGF protein levels for a three-session-per-day procedure conducted for one day. (A) Acquisition curves for the intensive version of the MWM hidden platform test. The latency in seconds is presented for each day. Each point represents the mean latency in sec ± SEM. (B, C) VEGF protein level in the hippocampus, cortex, and serum detected by ELISA 2 h (B) and 24 h (C) after training. Each point represents the mean ± SEM; n = 5–8 rats per group, ^*P < 0.05, ^**P < 0.01.

Fig. 3.

VEGF mRNA expression in rats subjected to two MWM paradigms. (A) Representative RT-PCR. (B, C) Expression of VEGF and BDNF in MWM-trained rats (n = 4 naïve, n = 4 swim, n = 5 intensive MWM, n = 4 weak MWM; ^***P < 0.001 intensive MWM compared with swim). H, hippocampus; C, cortex.

Fig. 4.

Effects of stereotaxic VEGF treatment on protein levels in the CA1. (A) VEGF (50 ng/side) into was bilaterally injected into the hippocampal CA1 subregion in rats and immunohistochemistry was performed as described in the “Materials and Methods.” (B) VEGF increased p-CREB immunoreactivity in the pyramidal cells. (C) VEGF increased p-CaMKII immunoreactivity in the dendrites (arrow). Scale bar, 50 μm. (Graphs) Quantification of relative p-CREB and p-CaMKII levels in the hippocampal CA1 2 h after the injection of VEGF. ^*P < 0.05, ^**P < 0.01.