Divergent effects of acute and chronic monosodium l-glutamate treatment on the anterior and posterior parts of the arcuate nucleus

Young albino rats were injected with either single or repeated doses of 0.1–6.0 mg/g body weight of monosodium l-glutamate between the ages of 2 and 40 days. The smallest, single effective dose was 0.25 mg/g body weight administered during the first week of life. The sensitivity to monosodium l-glutamate decreased with age. Monosodium l-glutamate caused nuclear pyknosis and edematous swelling of neurons in the anterior part of the arcuate nucleus which is located at the level of the ventromedial nucleus. These effects resulted in a reduction of neurons in this region. All of the doses used were ineffective in producing necrosis or cell death in the posterior part of the arcuate nucleus which is found at the level of the premamillary nuclei. The number of neurons in the arcuate nucleus of control animals was 46,500 with a neuron/glia ratio of 1.22. The anterior part of the arcuate nuclus had 55% of the neurons.Adult animals with an 80–90% loss of neurons in the anterior part of arcuate nucleus showed marked adiposity, hypoactivity, decreased body length, tail automutilation and reduced endocrine organ weight. The histological appearance of the ovaries, testes and pituitary glands was normal. The sexual behavior of these rats was normal, but the females were not fertile.The results of this study indicate that monosodium l-glutamate has a regional effect on the arcuate nucleus. These data also indicate that the majority of the neurons in the anterior arcuate region do not play a definitive role in the basal regulation of gonadotrophic hormones.