Figure 1.
PRV-614/MC4R-GFP double-labeled neurons in the spinal cord.
Images A1, B1, C1 were taken from an animal after injections of PRV-614. A1 showed neurons infected with PRV-614, which send transsynaptic projections to the gastrocnemius muscle; B1 showed MC4R-GFP positive neurons in the spinal cord; C1 showed overlaid images of A1 plus B1. Images A2, B2, C2 amplified views of A1, B1, C1, respectively. Arrows indicate double-labeled neurons. In contrast to the IML, we didn't detect PRV-614 labeled neurons in the VH in spinally transected mice. IML, the intermediolateral cell column; DH, Dorsal horn; VH, ventral horn. Scale bars, 50 µm.
Figure 2.
PRV-614/MC4R-GFP double-labeled neurons in the periaqueductal gray.
Images A1, B1, C1 were taken from an animal after injections of PRV-614. A1 showed neurons infected with PRV-614, which send transsynaptic projections to the gastrocnemius muscle; B1 showed MC4R-GFP positive neurons in the periaqueductal gray; C1 showed overlaid images of A1 plus B1. Images A2–C2 amplified views of A1–C1, respectively. aq, aqueduct; PAG, periaqueductal gray. Arrows indicate double-labeled neurons. Scale bars, 50 µm.
Figure 3.
PRV-614/MC4R-GFP double-labeled neurons in the motor cortex.
The red box in the top drawing indicates the approximate location from which the images were digitized. Images A–C were taken from an animal after injections of PRV-614. Image A showed neurons infected with PRV-614, which send transsynaptic projections to the gastrocnemius muscle; Image B showed MC4R-GFP positive neurons in the motor cortex; Image C showed overlaid images of A plus B. Arrows indicate double-labeled neurons. Scale bars, 50 µm. A drawing was taken from Ilan A. Kerman (J Neurosci 2006).
Figure 4.
Summary diagram showed that the melanocortin-sympathetic pathway between the motor cortex and gastrocnemius muscle.
Motor cortex, PAG and spinal cord are all participated in the modulation of the muscle activities. It is speculated that neurons within the motor cortex may send projections to PAG, which in turn projects to the IML sympathetic preganglionic neurons, which control gastrocnemius muscle activity by melanocortin-sympathetic signals. IML, intermediolateral column; MC, motor cortex; MC4R, the melanocortin-4 receptor; PAG, periaqueductal gray; PRV-614, pseudorabies virus-614. Some drawings were taken from HB Xiang (Brain 2013).