Summary
A study was performed to examine the effect of the intermittent long-term (20 min/h
daily during 3 consecutive days) electric stress (footshocks) on the hypothalamic
LHRH in anoestrous ewe. On the third day, immediately after the last stimulation,
the animals were decapitated and the hypothalami and pituitaries were taken for analysis
of LHRH and LH by immunocytochemistry; LHRH was also assayed by radioimmunoassay.
In the stressed animals the concentration of immunoreactive LHRH (IR-LHRH) and LHRH
analysed by radioimmunoassay (RI-LHRH) increased significantly in the median eminence
(ME) and the medial preoptic area (MPOA) when compared with the controls. Additionally,
IR-LHRH perikarya appeared in the MPOA of stressed animals, whereas they were not
seen in the controls. RI-LHRH in the medial basal hypothalamus (MBH) of stressed ewes
was markedly lower than in control ones. No significant differences in RI-LHRH concentration
were found in the septum between stressed and control ewes. The present study clearly
indicates that prolonged stressful stimuli modify LHRH concentration in the discrete
areas of the hypothalamus of the anoestrous ewe. It is suggested that these changes
are attributed mainly to an inhibition of LHRH release from the ME and a suppression
of LHRH transport along neural fibres within the hypothalamus.
Key words
Stress - LHRH - Hypothalamus - Ewe
