Axon-Sparing Lesions of the Hypothalamic Paraventricular Nucleus Abolish Gonadal Responses to Photoperiod in Male Syrian Hamsters

Intrahypothalamic injections of the excitotoxin N-methyl-D, L-aspartic acid (NMA) that destroyed the parvocellular regions of the paraventricular nucleus (PVN) prevented gonadal regression in male hamsters (Mesocricetus auratus) kept in short days (LD 6: 18). After 17 weeks in short days, these NMA-injected animals had large, functional gonads and displayed all components of male sexual behavior. These findings confirm that neurons of the PVN are part of the pathway that mediates photoperiodism in hamsters.