Denervation hypersensitivity occurs when a presynaptic neuron dies and results in what?

Denervation hypersensitivity refers to the phenomenon where, after the injury or death of a presynaptic neuron, the postsynaptic receptors become more sensitive to the neurotransmitters that are still available. When a neuron that typically releases neurotransmitters is damaged, the postsynaptic neuron may experience a reduction in the overall neurotransmitter activity. In response to this reduction, the postsynaptic receptors can undergo changes that lead to an increased sensitivity, allowing them to respond more vigorously to lower levels of neurotransmitter, if present. This is a compensatory mechanism that increases the likelihood that the remaining neurotransmitters will elicit a sufficient response despite the loss of the presynaptic neuron.

Understanding this concept is essential in the context of stroke rehabilitation, as it illustrates a biological response that can impact recovery and the degree of responsiveness in neural circuits. The other options present different outcomes that do not align with the definition of denervation hypersensitivity. For instance, reduction in neurotransmitter release would occur as a result of presynaptic neuron death, while formation of new synaptic connections and decreased axonal growth are separate processes that do not directly describe the increased sensitivity of postsynaptic receptors.