Neuronal Uptake of Monoclonal Anti‐Vasopressin Antibodies in vivo and Relationship with the Physiological Status of Vasopressin Neurosecretory Cells

Mouse monoclonal anti-vasopressin antibody was injected just above one hypothalamic paraventricular nucleus of the rat brain. Immunocytochemistry and morphometric analysis showed that the antibody was taken up by neurons with the size and stereotaxic distribution of vasopressin-producing neurons. Labelled neurons were counted with an electronic image analyser. When the rats were deprived of drinking water for 48 h before injection, specific uptake was significantly increased in the caudal part of the nucleus. Conversely, rehydration following dehydration or chronic treatment with 1-deamino-8-D-arginine vasopressin significantly decreased neuronal uptake, mainly in the rostral subdivision of the nucleus. By contrast, bilateral adrenalectomy performed 2 weeks before injection did not modify the number of labelled magnocellular neurons, though the accumulation of injected antibody in the external layer of the median eminence indirectly demonstrated the stimulation of antibody uptake by parvocellular vasopressin neurons. The number of labelled neurons was therefore directly related to the physiological state of the vasopressin-producing neurons. Further investigations will have to be performed to prove that the immunological targeting of peptidergic neurons offers a new tool to act in vivo on central neurons.