Developmental Brain Research, 51 (1990) 45-61 45 Elsevier BRESD 50994 Morphometrical and microdensitometrical studies on peptide tyrosine hydroxylase-like immunoreactivities in the forebrain prenatally exposed to methylazoxymethanol acetate Michele Zoli 1, Emilio Merlo Pich 1, Mauro Cimino 2, Gabriella Lombardelli 2, Guido Peruzzi 2, Kjell Fuxe 3, Luigi F. Agnati 1 and Flaminio Cattabeni 2 ~ Institute of Human Physiology, University of Modena, Modena (Italy), 21nstitute of Pharmacology and Pharmacognosy, University o Urbino, Urbino (Italy) and 3Department of Histology and Neurobiology, Karolinska Institutet, Stockholm (Sweden) (Accepted 13 June 1989) Key words: Methylazoxymethanol acetate; Neuropeptide; Immunocytochemistry; Computer-assisted image analysis; Microencep Methylazoxymethanol acetate (MAM Ac) injected into pregnant rats at a dose of 25 mg/kg at gestational day 15 causes micro to an atrophy of various telencephalic areas, mainly neocortex, hippocampus and basal ganglia. Previous studies demonstrated various neurochemical markers of classical transmitter systems in these regions. The present paper deals with changes in peptid hydroxylase (TH)-containing neurons in MAM Ac-induced microcephaly using immunocytochemistry coupled with computer-assisted morphometry and microdensitometry. No change in the number of vasoactive intestinal polypeptide (VIP)-immunoreactive n neocortex and neuropeptide Y (NPY)-immunoreactive neurons in the nucleus caudatus-putamen was found whereas cholecysto and NPY-immunoreactive neurons in the neocortex and CCK- and VIP-immunoreactive neurons in the hippocampus were d reduction of the latter peptide containing neuronal populations led to a maintained density of cells in MAM Ae-exposed rats, due reduction of the overall mass of these regions. TH immunoreactivity was found to be unchanged in the basal ganglia, and cerebral cortex in agreement with previous reports on noradrenaline cortical system after MAM Ac exposure. The presen heterogeneous vulnerability of different peptide immunoreactive neuronal populations to MAM Ac exposure. The sparing NPY-immunoreactive neurons may be due to their late development in the neocortex and striatum, respectively. The hypothesis i that cortical VIP interneurons can develop independent of marked alterations in the intrinsic circuitry of the cortical region INTRODUCTION Methylazoxymethanol acetate ( M A M Ac), injected into pregnant rats during a particular period of gestation, can cause a dose-dependent microcephaly together with a relatively maintained body weight 24'69. The cytotoxic effect of M A M Ac exposure is due to the antimitotic action of the molecule based on the methylation of D N A and R N A bases 58. After exposure to M A M Ac on gestational day 15, the most affected regions of the central nervous system (CNS) are the cerebral cortex and the hippocampal formation, while other telencephalic regions such as striatum show a less pronounced alter- ation. Histological examinations of the cerebral cortex and hippocampus from exposed rats grown to adulthood revealed hypoplasia and cytoarchitectonic abnor- malities 18"4°. The rest of the CNS is only slightly altered at doses up to 25 mg/kg 32. Previous neurochemical studies carried out both at the cortical and striatal levels showed that prenatal exposure to M A M Ac leads to increased concentration of nor- adrenaline, acetylcholine, dopamine and serotonin con- tents in the cerebral cortex and of monoamines in the striatum, whereas the total amount per region was unchanged or slightly reduced 11'33~4~'43"4s. In contrast, no changes in the concentration of presynaptic markersof y-aminobutyric acid ( G A B A ) and glutamic acid neurons in the cerebral cortex 4° and of acetylcholine and G A B A neurons in the striatum were found in M A M Ac-exposed animals, whereas total amounts per region were greatly reduced 11. Although there is a large number of reports describing the effects of M A M Ac exposure on classical neurotransmitters, few data are available on the fate of neuropeptides 15. In spite of the fact that M A M Ac-exposed rats show no gross behavioural deficit, impairments of various behav- ioural parameters such as general hyperactivity 14 and various cognitive deficits 8"61'66 have been described. However, these behavioural abnormalities have not been satisfactorily correlated to any specific neuroanatomical or neurochemical alterations. In the present paper the effects of M A M Ac exposure Correspondence: L.F. Agnati, Institute of Human Physiology, University of Modena, Via Campi 287, 41100 Modena, Italy. 0165-3806/90/$03.50 © 1990 Elsevier Science Publishers B.V. (Biomedical Division)