Neurotoxic lesions of the paraventriculo-spinal projection block the nocturnal rise in pineal melatonin synthesis in the Syrian hamster

The paraventriculo-spinal projection of the Syrian hamster was characterized by retrograde labelling of neuronal perikarya in the paraventricular nucleus of the hypothalamus (PVN) following injection of True blue tracer into the intermediolateral cell column of the thoracic spinal cord. Injection of the excitatory neurotoxin, N-methyl- d,l-aspartic acid into the region of the PVN spared magnocellular neurones and fibres of passage but destroyed parvocellular neurones of the paraventriculo-spinal pathway. Hamsters bearing complete bilateral lesions of the parvocellular PVN failed to show the typical nocturnal increase in pineal melatonin content. These data indicate the importance of the paraventriculo-spinal projection in the central control of pineal melatonin synthesis.