Neurochem. Int. Vol. 21, No. 2, pp. 223-228, 1992 0197-0186/92 $5.00+0.00 Printed in Great Britain.All rightsreserved Copyright© 1992PergamonPressLtd BRAIN PHOSPHATIDIC ACID AND POLYPHOSPHOINOSITIDE FORMATION IN A BROKEN CELL PREPARATION: REGIONAL DISTRIBUTION AND THE EFFECT OF AGE J. BOTHMER, M. MARKERINK and J. JOLLES* Department of Neuropsychology and Psychobiology, University of Limburg, P.O. Box 616, 6200 MD Maastricht, The Netherlands (Received 13 November 1991 ; accepted 10 January 1992) Abstract--The effect of age on phosphate incorporation into phosphatidylinositol 4-phosphate (PIP), phosphatidylinositol4,5-bisphosphate (PIP2) and phosphatidic acid (PA) was studied. Lysed crude synap- tosomal fractions of different brain regions of 3-month-old and 32-month-old Brown Norway rats were used. The brain regions tested were the hippocampus, frontal cortex, occipital/parietal cortex, entorhinal/pyriformal cortex, striatum/septum, thalamus and hypothalamus. The individual specific phos- phorylating activities were unevenly distributed within the brain of Brown Norway rats. Strikingly, the distribution of phosphate incorporation into PIP2 was opposite from that of phosphate incorporation into PA. Phosphate incorporation into PA decreased (-15%) with age in almost all brain regions tested, whereas phosphate incorporation into PIP2 decreased with age only in the frontal cortex (-20%) and in the hypothalamus (-8%). The effects of age may reflect a deterioration of phosphoinositide metabolism, with its function in signal transduction coupled to receptors via G-proteins, in the brain regions involved. In addition, there was an age related decrease in protein content and total phospholipid phosphorus content of lysed crude synaptosomal preparations of all brain regions. The high correlation between the changes in these parameters may be indicative of a decrease in the number or size of synaptosomes with age in the brain regions involved. Phosphatidylinositol and its phosphorylated con- geners phosphatidylinositol 4-monophosphate (PIP) and phosphatidylinositol 4,5-bisphosphate (PIP2) play an important role in signal transduction. PIP2 is thought to be hydrolysed by phospholipase C into the second messengers inositol trisphosphate and diacyl- glycerol (DAG) after receptor stimulation (Abdel- Latif, 1986; Berridge, 1987). Recently, receptor-stimulated phosphoinositide hy- drolysis was found to be increased in the hippo- campus of old rats after muscarinic M1 receptor stimulation (Tandon et al., 1991) and in the brain cortex of old rats after alpha-1 adrenoceptor and muscarinic M1 receptor stimulation (Nalepa et aL, 1989). This increased responsiveness in senescence could be a compensatory mechanism for neuronal cell death and reduced levels of transmitters (Tandon et al., 1991). Protein phosphorylation, which is the final pathway in the action of transmitters and hor- mones at the neuronal level, is also affected in aging * Author to whom all correspondence should be addressed. (Magnoni et al., 1991). Cyclic AMP-dependent pro- tein kinase and protein kinase C have been reported to be modified during aging in various cerebral areas. These changes may involve either enzyme activity or substrate availability (Magnoni et al., 1991). However, hardly anything is known about possible changes in the conversions of brain phospho- inositides, other than receptor stimulated hydrolysis, with aging. This aspect of phosphoinositide metab- olism is also essential for the conversion of extra- cellular signals into biological responses. The DAG- kinase activity in pig brain (Kanoh et al., 1983) appears to be regulated by its phospholipid micro- environment. PI-kinase and PIP-kinase in rat brain, which are partially attached to the plasma mem- brane (Stubbs et al., 1988), are probably also influ- enced by their phospholipid microenvironment. This phospholipid microenvironment changes during aging by way of an increased cholesterol/phospholipid ratio, which results in a more viscous membrane (Rouser et al., 1972). Changes in lipid fluidity can influence synaptic transmission processes, ligand- receptor binding properties, and the dynamics of 223