Age-related changes in neurotensin content and receptors in various rat brain areas

Neurotensin receptor levels as a function of brain aging and cognitive performance in the Morris water maze task in the rat

The present study evaluated whether neurotensin (NT) binding sites were altered in the aged rat brain and if these alterations were related to the cognitive status of the animal. Aged (24-25 months old) Long-Evans rats were behaviorally screened using the Morris water maze task and were classified as either aged, cognitively impaired (AI) or cognitively unimpaired (AU) based on their relative performances in the task compared to young control (Y) animals. Decreases in specific [125I]NT binding were observed in the hippocampal formation, namely the dentate gyrus (DG), as well as in the septum and hypothalamus. Both aged groups also showed significant reductions in specific [125I]NT binding levels compared to the Y animals in the hippocampal CA3 sub-field, with the AI animals exhibiting the lowest levels. In the Substantia Nigra Zona Compacta (SNc) and the ventral tegmental area (VTA), specific [125I]NT binding was decreased as a function of age while binding in the paraventricular nucleus of the hypothalamus (PVNh) was decreased as a function of age and cognitive status. These alterations in the level of specific [125I] NT binding in the aged animals suggest decreases in NT receptor signaling as a function of age and potential involvement of NT-ergic systems in the etiology of age-related cognitive deficits.

Autoradiographic distribution of [3H]neurotensin receptors in the brains of superoxide dismutase transgenic mice

Superoxide dismutase (SOD) plays an important role in the protection of cells against the deleterious effects of free radicals by dismutating the toxic superoxide anion radical. Although oxygen-based radicals have been implicated in the process of aging and in neurodegenerative disorders such as Parkinson's disease, the contribution of these free radicals to the pathology of these entities has yet to be clarified. It is also not certain that increased levels of free radical scavenging enzymes would attenuate the molecular and cellular processes that lead to these pathological states. In order to assess the contribution of increased SOD gene dosage to the pathogenesis of Down's syndrome, transgenic mice have been constructed that overexpress the human CuZnSOD. We are also using this model to evaluate the role of free radicals in age-associated changes in brain neurotransmitters and their receptors. In the present study, transgenic mice and their nontransgenic littermates, aged 6 weeks and 21 months, were used in an autoradiographic receptor study of the distribution of brain neurotensin receptors. At 6 weeks of age, there were no significant differences between the two groups of mice in most brain regions. In addition, [3H]NT binding sites showed parallel age-related decreases in the majority of the areas examined in both groups. However, significant age-related decreases in the septum, the diagonal band of Broca, and in some subdivisions of the caudate-putamen were observed only in SOD-Tg mice. In contrast, significant age-related decreases in the core area of the nucleus accumbens and the dorsal aspect of the dentate gyrus of the hippocampus were seen only in non-Tg mice.(ABSTRACT TRUNCATED AT 250 WORDS)

Reduction of the amount of neurotensin retrogradely transported in dopaminergic neurons of senescent rats

It is now clearly established that fast anterograde axonal transport can be altered during ageing, both in the central and the peripheral nervous systems, but no information is yet available concerning the modifications of fast retrograde axonal transport during senescence. In the present paper, we report the changes occurring in the retrograde axonal transport of neurotensin in dopaminergic neurons of old rats. When iodinated neurotensin was injected into the striatum, a diminution of approximately 50% in the amount of the labelling measured in the ipsilateral substantia nigra was observed in senescent rats by comparison with young adult rats. Nevertheless, the rate of neurotensin transport was not modified. Our results clearly indicate that less neurotensin is transported from the nerve terminals towards the cell bodies in senescent rats which may have possible consequences for dopaminergic neurons.

Behavioral effects of neurotensin: operant responding and assessment of 'anhedonia'

Neurotensin and antipsychotic drugs share certain properties. This study investigates whether neurotensin and neuroleptics share the ability to produce 'anhedonia'. A dose-response curve for the effect of neurotensin on continuously reinforced behavior was obtained in Experiment 1. Centrally administered neurotensin reduced food-reinforced responding. Based on the results of Experiment 1, a dose of neurotensin (0.95 micrograms) was chosen which had minimal effects on food-reinforced operant responding. To test for anhedonia, repeated presentations of this dose were given. Because response rates did not decrease over repeated testing, no evidence for anhedonia was found.

Neurotensin in microdissected brain nuclei and in the pituitary of the lean and obese Zucker rats

Neurotensin (NT) is a tridecapeptide common to the gastrointestinal tract and central nervous system which suppresses food intake when centrally injected in various regions of the hypothalamus. We measured neurotensin levels in several microdissected brain nuclei as well as in the pituitary in 10 obese hyperphagic Zucker (fa/fa) rats, 9 heterozygous Fa/fa and 5 Fa/Fa lean rats. The greatest NT concentration and content were observed in the anterior lobe of the pituitary in the median eminence and in the lateral preoptic area (500 to 1000 pg/area, 3 to 5 ng/mg protein). NT was also detected in the median preoptic area, paraventricular (PVN), supraoptic, ventromedian nuclei (VMN) (about 250 pg/nucleus, 1.5 to 2 ng/mg protein). The smallest amounts were found in the suprachiasmatic (SCH) and accumbens nucleus (about 100 pg/nucleus, 1 ng/mg protein) and the peptide was absent in the cortex. NT content in the obese rat was significantly lower in all brain nuclei examined except the accumbens nucleus. This was most evident in the three nuclei involved in the regulation of feeding behaviour: PVN (276 +/- 38 (Fa/Fa) vs 188 +/- 15 (fa/fa) pg/nucleus, P less than 0.05), VMN (226, +/- 21 (Fa/Fa) vs 75 +/- 22 (fa/fa) pg/nucleus, P less than 0.001), and SCH (98 +/- 14 (Fa/Fa) vs 52 +/- 11 (fa/fa) pg/nucleus, P less than 0.05). There was no difference in the pituitary lobes between lean and obese rats.(ABSTRACT TRUNCATED AT 250 WORDS)