Hypothalamic grafts induce the recovery of lordosis in female hamsters with lesions of the ventromedial hypothalamus.

Previous studies have documented the ability of neural grafts to stimulate the recovery of lordosis from neurochemical deficits. However, it was unclear if grafts also could reverse deficits in lordosis caused by lesions at critical points in the neural circuit controlling this response. To address this question, female hamsters were subjected to unilateral lesions of the ventromedial hypothalamus (VMN), a structure well known for its mediation of hormonal effects on lordosis. The effects of these lesions were described by noting the ability of manual stimulation of one flank to reinstate a deteriorating lordosis response. Consistent with past results, unilateral VMN lesions decreased responsiveness to stimulation of just the contralateral flank. Females showing such lateralized decrements then received control treatments or implants into the lesioned area of basal hypothalamic tissue from a neonatal male or female hamster. Approximately 1 month later, tests of lordosis reinstatement by ipsi- or contralateral manual stimuli were repeated. Whereas lateralized decrements in responsiveness persisted in control subjects, implants of tissue from male or female neonates led to reliable improvements in lordosis, reversing the lesion-induced decrease in contralateral responsiveness. The mechanism responsible for this change is unclear, but could involve an elevation in a lordosis-facilitating neuromodulator. Alternatively, it could depend on the reinforcement or replacement of neural circuits for lordosis, possibly including those that connect the two VMNs with each other or with the periaqueductal gray of the midbrain.