Rat dopaminergic function in the retina during aging

The neurobiological effects of senescence on dopaminergic system: A comprehensive review

Over time, the body undergoes a natural, multifactorial, and ongoing process named senescence, which induces changes at the molecular, cellular, and micro-anatomical levels in many body systems. The brain, being a highly complex organ, is particularly affected by this process, potentially impairing its numerous functions. The brain relies on chemical messengers known as neurotransmitters to function properly, with dopamine being one of the most crucial. This catecholamine is responsible for a broad range of critical roles in the central nervous system, including movement, learning, cognition, motivation, emotion, reward, hormonal release, memory consolidation, visual performance, sexual drive, modulation of circadian rhythms, and brain development. In the present review, we thoroughly examine the impact of senescence on the dopaminergic system, with a primary focus on the classic delimitations of the dopaminergic nuclei from A8 to A17. We provide in-depth information about their anatomy and function, particularly addressing how senescence affects each of these nuclei.

Variations of dopamine, serotonin, and amino acid concentrations in Noda epileptic rat (NER) retina

Noda epileptic rats (NER) exhibit frequent spontaneous tonic-clonic convulsions which represent a valuable model of human epilepsy. If implication of brain neurotransmitters was largely reported, little is known about retina. However, it has been reported that human epilepsy syndrome varies not only with the location of seizure foci but also according to rhythmic patterns, for which retina has a major role in the transmission of external light-dark cycle information. The purpose of this work was to evaluate dopamine (DA), DA metabolites, serotonin (5-HT), and amino acid [glutamate, aspartate, glycine, gamma aminobutyric acid (GABA), and taurine] level variations in retina from NER, at two different nycthemeral periods (11 a.m. and 11 p.m.) and at different ages (2, 6, and 12 months). In NER, retinal dopaminergic function was decreased as soon as 2 months, whereas GABA levels were increased, even if no differences among the different ages could be distinguished. These variations were associated to a slight increase in 5-HT. Other amino acids tested were not affected by epilepsy, whereas taurine decreased with aging in NER as well as in control rats. Retinal 5-HT occurs principally as a precursor of melatonin (MEL). A triangular interaction may be hypothesized: MEL could decrease DA synthesis or release by enhancing GABA activity. Taken together, these results suggest that the retinal physiology is affected by the epileptic status and that information transmitted from retina to the brain should be affected by epilepsy in NER.

Retinal cholinergic and dopaminergic deficits of aged rats are improved following treatment with GM1 ganglioside

Selected cholinergic and dopaminergic markers were compared in the retina of aged (20-22-months-old) and young (3-months-old) rats before and after treatment with GM1 ganglioside. The dopaminergic markers, tyrosine hydroxylase, aromatic L-amino acid decarboxylase, dopamine, 3,4-dihydroxyphenylacetic acid and homovanillic acid were comparable in the young and aged animals and GM1 treatment did not alter them. In contrast, mazindol binding, a marker for the dopamine transporter, was diminished in the aged retina and treatment with GM1 restored binding to values found in the young animals. The cholinergic markers choline acetyltransferase and hemicholinium-3 binding, a marker for the high-affinity choline transport, were depressed in aged rats and GM1 corrected the deficits.

Effects of melatonin and light on porphyrin synthesis in the bovine retina, pigment epithelium and choroid

The quantity of porphyrin synthesized in the presence of 10(-3) M delta-aminolevulinic acid (ALA) is several times higher in the bovine pigment epithelium than in the retina. Synthesis in the retina was found to be increased by illumination, whereas synthesis in the pigment epithelium was decreased if the whole anatomical unit (retina-pigment epithelium-choroid) was cultivated together. The quantity of porphyrin synthesized in the presence of 10(-3) M ALA or 10(-6) M melatonin was different when the pigment epithelium and retina were separated. The combination 10(-3) M ALA with 10(-6) M melatonin inhibited retinal porphyrin synthesis after green light adaptation, while in the pigment epithelium green light adaptation induced porphyrin synthesis. It is postulated that the light-sensitive porphyrin-haeme synthesis of the retina-pigment epithelium-choroid functional unit may serve and modulate the synthesis of guanylate cyclase for cGMP.

The effect of L-dopa upon in vitro dopamine release from the corpus striatum of young and old male rats

In the present experiments, we examined the effects of superfusion of L-DOPA upon in vitro dopamine (DA) release from the corpus striatum (CS) in young (2-4 months) and old (24 months) male rats. In Experiment I, responses to two successive increasing doses of L-DOPA (1.0 and 10 microM) indicated a clear age difference with DA release from CS of young rats significantly greater than that of old rats in response to the 10 microM dose of L-DOPA. Interestingly, CS fragments of young and old male rats responded marginally to the 1.0 microM L-DOPA infusion, and no significant differences between these two age groups were obtained. Since we have previously observed that the addition of naloxone to the superfusion medium restored the potassium stimulated DA release of old rats to that of young rats, in Experiment II, responses of CS tissue fragments of young and old rats superfused in medium with or without naloxone (100 microM) were tested with a single 10 microM L-DOPA infusion. The results of Experiment II indicated that the addition of naloxone to the superfusion medium did not alter the responses of CS tissue to L-DOPA in either young or old rats; however, the overall response of the young rats remained significantly greater than that of the old rats. Taken together, these results demonstrate a significant age-related decrement in the capacity of 10 microM L-DOPA to stimulate DA release from CS fragments.(ABSTRACT TRUNCATED AT 250 WORDS)

Age-related changes of RNA and lipid synthesis in vitro by retina and optic nerve of the rat

We examined the effects of age on RNA and lipid formation by whole retina and optic nerve in vitro. Male Wistar rats, aged 4, 12, and 24 mo, were used. From the results obtained the following conclusions may be drawn: 1. In assaying the lipid biosynthesis during aging, a striking difference between the retina and optic nerve clearly emerged; 2. In isolated retina, [3H]uridine incorporation into RNA was relatively constant at the three ages, whereas both [14C]palmitate and [3H]choline incorporation into lipids showed a substantial increase in rats at 24 mo of age compared with those at 4 mo; 3. In contrast, in the optic nerve of the oldest rats, compared with the youngest, a significant decrease of [14C]acetate and [14C]palmitate incorporation into acylglycerols, cerebrosides, and phospholipids was found. Each fatty acid precursor label was incorporated to a proportion that reflected the typical acyl group composition of individual lipids; 4. Following labeling of the optic nerve with [3H]choline, the specific radioactivity of choline-containing phospholipids was drastically decreased with increasing rat age; and 5. The incorporation of [2-3H]glycerol into optic nerve diacylglycerols, PtdEtn, and PtdIns declined with age, whereas no significant change took place in the incorporation into PtdCho. The results strongly support the concept that RNA metabolism of rat retina (most likely photoreceptor cell layer) is not altered during aging; on the contrary, phospholipid synthesis is stimulated in comparison with that of the optic nerve, for which a serious impairment was concomitantly observed. The physiological significance of these responses, and the mechanism by which retinal tissue is spared from the general age derangement of the nervous system, remain to be defined.

Changes in the mechanisms of hormone and neurotransmitter action during aging: current status of the role of receptor and post-receptor alterations. A review

Alterations in responsiveness to hormones and neurotransmitters during aging appear to be due to changes at both the receptor and post-receptor levels. Although many such observations have now been independently confirmed, disagreement over the extent and/or importance of receptor alterations exists in a number of cases. Receptors do not appear to change with age in certain systems, but only a few reports have actually been able to localize particular post-receptor alterations responsible for changes in response. This review attempts to catalogue studies in these areas which have been carried out to date, and discusses possible reasons for discrepancies as well as future research directions.