Developmental Brain Research, 74 (1993) l 11 - 116 [ 11 © 1993 Elsevier Science Publishers B.V. All rights reserved 0165-38(/6/93/$06.00 BRESD 51654 Hippocampal y-aminobutyric acid and benzodiazepine receptors after early phenobarbital exposure Chaim G. Pick a,b, Abraham Weizman c, Fuad Fares d, Moshe Gavish d, Baruch I. Kanner ~ and Joseph Yanai ~' '~ The Melvin A. and Eleanor Ross Laboratory for Studies in Neural Birth Defi'cts, Department of Anatomy and Emhryoh~gy, The ftehrew Unit'ersity-Hadassah Medical School, Jerusalem (Israel), h Department of Anatomy and Anthropology, Saekler Fa~uhy q( Medicine Tel-At'it' University, Ramat At, ic, Tel At,it" (Israel), ~' The Felsenstein Medical Research Center (FMRC), Gehah Psychiatric Hospital, Beilinson Medical ('enter Petah-Tiqt'a and Sackler Faculty of Medicine Tel-At'it, Unit:ersity, Ramat At'it, Tel Atit' (Israel), ,I Rappaport Family htstitute tor Research in the Medical Sciences Department of Pharmacolo~©', Faculty of Medicine, Technion-lsrael Institute of Technology, Ha!]it (Israel) and " Department q[ Medical Biochemistry The Hebrew Unit'ersity-Hadassah Medical School, Jerusalem (ls'rael) (Accepted 26 January 19931 Key words: Early exposure; y-Aminobutyric acid uptake; y-Aminobutyric acid receptor; Benzodiazepine receptor; Hippocampus; Phenoharbilal Mice were exposed to phenobarbital (PhB) prenatally (PreB offspring) by feeding their mothers 3 g/kg PhB in milled food on gestation days 9-18, or neonatally by directly injecting pups of intact mothers with daily dose of 50 mg PhB on postnatal days 2-21 (NeoB offspring). At age 22 or 50 days, the offspring were tested for y-aminobutyric acid (GABA) up take in the hippocampus and in the rest of the brain. In addition, [3H]muscimol and [3H]flunitrazepam binding in the hippocampus and cortex were measured in the offspring at age 22 and 511 days. Long-term decrease in GABA uptake was found in the NeoB group. A 23%, decrease was found in 22-day-old mice (P < 0.001) and a 22% decrease in 50-day-old mice (P < 0.05). In addition, there was a 22% decrease in GABA uptake in the brain of 22-day-old PreB mice ( P < I).ll5). An increase of 52% in [3H]muscimol binding (P < 0.0011 and 45% (P < 0.001) in [3H]flunitrazepam binding were measured in the hippocampus in the 22-day-old NeoB mice; no differences were found in affinity. The differences were short-term and could no kruger be detected at age 50 days. No differences were found in the cortex; unlike NeoB, PreB mice did not differ from controls. The results suggest uprcgulation ~ff the GABAergic system in early PhB exposed mice. INTRODUCTION Studies on possible alterations in the y-aminobu- tyric acid (GABA) innervations after early exposure to phenobarbital are particularly relevant since barbitu- rates interact with the GABA/benzodiazepinc (Bz)/chloride ion channel complex ~H2. Similar to ben- zodiazepines, the barbiturates modulate GABA-recep- tor chloride channel regulation at the cellular level as assayed by electrophysiological or radioactive ion tracer techniques ~3. Barbiturates are widely used as anticonvulsant drugs for neonatal febrile convulsions and as a prophylaxis for neonatal hyperbilirubinemia ~. Their pharmacologi- cal effects are similar to those of the benzodiazepines, apart from the fact that in high doses they cause a more profound depression of the central nervous sys- t e m ~3. Early exposure to PhB induces changes in the devel- oping brain. These changes include morphological, pharmacological and behavioral deficits ml'~. One of the areas extensively studied is the hippocampus. Previous work showed neuronal deficits in the hippocampus, after both prenatal and neonatal administration >'2t'. Changes in neurotransmittcr systems that innervate the hippocampus were round after early exposure to PhB; for instance, reduction in the number of nora- drencrgic cells in the locus coeruleus 2~ and deficits in cholinergic neurotransmission v't724. In addition to this, impairment in spontaneous alternation, eight-arm and Morris mazes performance, behaviors which may bc linked to a large degree with hippocampal functioning, were found after early exposure to PhB 14A>LT. Since barbiturates are active at the GABA/BZ re- ceptor/chloride ion channel complex, it was assumed that early exposure to barbiturates can affect this sys- Correspondence." Ch.G, Pick, Department of Anatomy and Anthropology, Sackler School of Medicine, Tel-Aviv University. Ramat Aviv 6t1978. Israel. Fax: (972) (3) 6408287. Bitnet:ANAT03(~t CCSG.TAU.AC.IL.