Functional synaptogenesis and the rat pineal gland: A pharmacological investigation

Abstract

Pineal glands obtained from rats of different ages were incubated in vitro with drugs known to specifically alter pre- or postsynaptic noradrenergic neurotransmission to determine when during development nerve terminal or receptor mediated control of glandular N-acetyltransferase (NAT) activity might reach functional maturation. Basal daytime NAT activity measured in vitro was lowest in fetal rats, increased dramatically by the day of birth, peaked at 10 days postnatally, and subsequently declined to near adult levels by 25 days of age. Drugs (isoproterenol, norepinephrine, or propranolol) known to influence pineal gland NAT activity by acting directly on pinealocyte postsynaptic beta-noradrenoceptors produced comparable changes in enzyme activity at all ages studied, although larger doses of the receptor agonist were required in fetal animals to elevate NAT activity. In contrast, in vitro incubation with indirect acting drugs (amphetamine or 1-dopa) which require functional presynaptic nerve terminals to exert their pharmacological effects, failed to increase pineal gland NAT activity until early in postnatal life. Hence, postsynaptic beta-noradrenoceptors may function to control pineal gland NAT activity prior to the time when the presynaptic sympathetic neurons innervating the gland attain maturational status.

Light affects neonatal rat pineal gland N-acetyltransferase activity by an extra-retinal mechanism

“…Since neonatal rats are ectothermic for the first few weeks of life (Hill, 1947;Lytle and Keil, 1974), and neonatal hypothermia causes elevations in pineal gland NAT activity (Torres et al, 1989), all animals were kept at 35 ~ (nest temperature) on a medical heating pad which subsequently maintained their body temperatures at approximately 34-35 ~ Rectal temperatures were measured at the end of the 4 hr period of dark or light exposure by means of a lubricated thermocouple (Model BAT-12) inserted ~ 1 cm beyond the anal sphincter. Shortly thereafter intact or enucleated pups were decapitated and pineal glands were rapidly excised and frozen at -70 ~ until assayed for NAT activity using a modification (Altar et al, 1983) of the method of Deguchi and Axelrod (1972). Data were analyzed by analysis of variance tests followed by post hoc comparisons using Student's t-tests.…”

Pineal Gland Free Amino Acids and Indoles During Postnatal Development of the Rat: Correlations in Individual Glands

“…The peak that occurred in nighttime levels of NAS in 10-day-old pups may simply reflect day-to-day variability in the phase of the rhythm. However, a dramatic rise in pineal NAT activity and plasma melatonin has been reported to occur at 10 days of age [Altar et al, 1983;Murakami et al, 19891. The age-related decline in tryptophan is associated with the rise in 5HT, although substrate utilization is probably not the only mechanism.…”

Pinealocyte synaptic ribbons and neuroendocrine function

“…Multiple pair-wise comparisons indicated that this effect of age on NAS was the result of elevated nighttime levels in 10-day-old animals ( Fig. 12b) reflecting the dramatic increase in the pineal N-acetyltransferase enzyme which has been reported to occur at 10 days of age (Altar et al, 1983).…”