Paraventricular Nucleus The hypothalamic paraventricular nucleus (PVN) contains premotor neurons that project from the parvocellular layer directly into the spinal cord.
These neurons have been shown to contain a variety of neurotransmitters: oxytocin, vasopressin, enkephalins, and dopamine. In rat models injection of a variety of neuromediators (oxytocin, glutamate, nitric oxide, dopamine agonists) into the PVN has been shown to elicit penile erection.
Additionally, in both rats and monkeys, stimulation of the PVN elicits erection. Lesion of the parvocellular layer of the PVN causes longer latencies and fewer noncontact erections in rats. Parvocellular PVN neurons have been shown to respond to stimulation of the dorsal nerve of the penis in rats, suggesting that the PVN may be a supraspinal reflex center for erections.viagra professional Canada
The PVN also receives input from the medial preoptic area (MPOA) suggesting that the PVN serves to integrate MPOA input before sending it downstream via autonomic pathways selectively activated within the PVN Medial Preoptic Area The MPOA of the hypothalamus is key to sexual behavior.
In rats and monkeys, MPOA stimulation elicits erection. In monkeys, increases in MPOA neuronal activity have been recorded during erection. Interestingly, MPOA lesions do not affect reflexive or noncontact erections.
All of this has led to debate as to the role of the MPOA in erectile function. The emerging theory is that the MPOA likely serves as an integration center of hormonal and sensory inputs for sexual behavior and redistributes these signals to the hypothalamic and brainstem structures thought to be more directly linked to erectile control, such as the PVN.
Other Supraspinal Centers Many other supraspinal areas have been shown in animal studies to be related to erectile function. In monkeys, isolated stimulation of the medial dorsal nucleus of the thalamus, ventral tegmental area, precallosal cingulate gyrus, and subcallosal and caudal gyrus led to erections.
Hippocampal stimulation in anesthetized rats increased intracavernous pressures as did desynchronization of the somatosensory cortex following cocaine administration. A center for descending the inhibition of spinal sexual reflexes has been localized to a group of neurons in the paragigantocellular reticular nucleus of the ventral medulla.
The exact role each supraspinal area plays in mediating erection is currently unclear. However, it is apparent that there are extensive interconnections between many supraspinal centers that contribute to descending pathways and exert powerful control, both inhibitory and excitatory, on the spinal responses driving erection.