Thoracic and lumbar splanchnic nerves carry:

postsynaptic sympathetic fibers from the sympathetic trunk to their target organs.
presynaptic sympathetic fibers from the lumbar segments of the spinal cord to the sympathetic trunk.
postsynaptic sympathetic fibers from the prevertebral ganglia to their target organs.
presynaptic sympathetic fibers to their target organs where they synapse.
presynaptic sympathetic fibers from the sympathetic trunk to the prevertebral ganglia where they synapse.