Inhibition of the LH Surge by Restraint Stress in Cyclic Rats: Studies on the Role of GABAA and GABAB Receptors

There is evidence that stress can alter the activity in the brain of gamma-aminobutyricacid (GABA), a neurotransmitter that has been implicated in the regulation of LH secretion. In the present study the role of GABA in the restraint stress-induced inhibition of the LH surge was investigated in the intact cyclic rat. Intracerebroventricular (icv) administration of the GABAA receptor agonist muscimol (0.1, 0.5 or 1 μg) 5 min before the presumed onset of the pro-oestrous LH surge (at 0900 h) caused a dose dependent suppression of the surge. A single dose of the GABAB receptor agonist baclofen (1 μg; icv) injected at 0855 h postponed the onset of the LH surge, and repeated injections at 0855 and 1130 h suppressed the surge. These data indicate that GABA-ergic activity in the brain can inhibit the LH surge in the cyclic rat via GABAA and GABAB receptors. Pro-oestrous rats were subjected to 5 hrs of restraint starting at 0855 h. Pretreatment with the GABAA receptor antagonist bicuculine (1 μg; icv) at 0840, 0940 and 1040 h or pretreatment with the GABAB receptor antagonist phaclofen (10 μg; icv) at 0840 h were ineffective in preventing the restraint-induced inhibition of the LH surge. The results suggest that GABAA and GABAB receptors are not involved in the inhibitory effect of restraint stress on the LH surge.     

Alzheimer's disease patients' cognitive status and course years prior to symptom recognition

This is a prospective examination of the cognitive performance and cognitive course of persons in an asymptomatic "preclinical" phase who eventually developed Alzheimer's disease (AD). We compared performances on the Mayo Cognitive Factor Scales (MCFS) of 20 persons in a neurologically normal cohort who subsequently developed AD to the performances of 60 persons who remained free of dementia symptoms. For the AD patients, exams occurred prior to the appearance of dementia symptoms (an average of 4.2 and 1.5 years prior to symptom onset). Results reveal strong group differences on learning and retention, with eventual AD patients scoring lower than controls years prior to reporting symptoms of the disease. There was no significant interaction effect (group x testing session) for memory retention, suggesting that memory decline in this preclinical period may be too slow to be a useful indicator of future AD. A significant interaction (but no group effect) was seen for verbal comprehension.     

Alzheimer's Disease Patients' Cognitive Status and Course Years Prior to Symptom Recognition

This is a prospective examination of the cognitive performance and cognitive course of persons in an asymptomatic “preclinical” phase who eventually developed Alzheimer's disease (AD). We compared performances on the Mayo Cognitive Factor Scales (MCFS) of 20 persons in a neurologically normal cohort who subsequently developed AD to the performances of 60 persons who remained free of dementia symptoms. For the AD patients, exams occurred prior to the appearance of dementia symptoms (an average of 4.2 and 1.5 years prior to symptom onset). Results reveal strong group differences on learning and retention, with eventual AD patients scoring lower than controls years prior to reporting symptoms of the disease. There was no significant interaction effect (group × testing session) for memory retention, suggesting that memory decline in this preclinical period may be too slow to be a useful indicator of future AD. A significant interaction (but no group effect) was seen for verbal comprehension.