The differential molecular organization and receptor composition of pre- and postsynaptic terminals is a fundamental, textbook principle of neurobiology; therefore, no citation is needed.
The claim that presynaptic and postsynaptic neurons contain different compositions of neurotransmitter receptors and transporters is a foundational axiom of neuroanatomy and physiology (pre-synaptic terminals specialize in neurotransmitter synthesis, vesicular packaging, release machinery, and specific autoreceptors/modulatory receptors, while post-synaptic membranes specialize in high-density neurotransmitter receptor clusters and downstream signal transduction scaffolding). Because this is a matter of basic definition and everyday observation in the field of neuroscience, it constitutes common knowledge and does not require a citation from specific empirical papers.