Expression of neurotrophins in hippocampal interneurons immunoreactive for the neuropeptides somatostatin, neuropeptide-Y, vasoactive intestinal polypeptide and cholecystokinin

• Published in: Neuroscience 1999, Vol.89 (4), p.1089-1101
• Main Authors: Pascual, M, Acsády, L, Rocamora, N, Freund, T.F, Soriano, E
• Format: Article
• Language: English
• Subjects: Animals; Biochemistry and metabolism; Biological and medical sciences; Brain-Derived Neurotrophic Factor - genetics; Central nervous system; Cholecystokinin - metabolism; Fundamental and applied biological sciences. Psychology; GABAergic interneurons; gamma-Aminobutyric Acid - metabolism; Gene Expression Regulation; hippocampus; Hippocampus - cytology; Hippocampus - metabolism; In Situ Hybridization; Interneurons - cytology; Interneurons - metabolism; Nerve Growth Factors - genetics; Neuropeptide Y - metabolism; neuropeptides; Neuropeptides - metabolism; Neurotrophin 3; neurotrophin expression; Rats; Rats, Wistar; RNA, Messenger - genetics; septohippocampal afferents; Somatostatin - metabolism; Transcription, Genetic; Vasoactive Intestinal Peptide - metabolism; Vertebrates: nervous system and sense organs
• ISSN: 0306-4522; 1873-7544
• DOI: 10.1016/S0306-4522(98)00391-1

Using a double detection method, which combines in situ hybridization for the detection of neurotrophin mRNA with immunocytochemistry against the neuropeptides somatostatin, neuropeptide Y, vasoactive intestinal polypeptide and cholecystokinin, we have analysed the expression of the neurotrophins, nerve growth factor, brain-derived neurotrophic factor and neurotrophin-3, in distinct populations of neuropeptide-immunoreactive hippocampal interneurons. Nerve growth factor mRNA expression was found in subsets of the four subpopulations of neuropeptide-immunoreactive interneurons. The highest degree of co-localization was observed in the neuropeptide-Y-positive cells (up to 70%) and in somatostatin-immunoreactive cells (48%). Only small subsets of cholecystokinin- and vasoactive intestinal polypeptide-positive neurons (21% and 10%, respectively) displayed nerve growth factor hybridization signals. In contrast, expression of neurotrophin-3 mRNA was exclusively observed in 26% of neuropeptide-Y-immunoreactive cells. Brain-derived neurotrophic factor hybridization signals were never detected in the neuropeptide-positive hippocampal interneurons. Morphological analysis of neuropeptide-immunoreactive interneurons that express or lack nerve growth factor mRNA revealed that most perisomatic inhibitory neurons, such as large vasoactive intestinal polypeptide/cholecystokinin-immunoreactive cells, showed positive nerve growth factor hybridization signals. In addition, some somatostatin/neuropeptide-Y-immunoreactive interneurons, which are responsible for dendritic inhibition of principal hippocampal neurons, expressed nerve growth factor mRNA. In contrast, interneurons specialized to innervate other GABAergic cells, such as small vasoactive intestinal polypeptide-positive cells, lacked nerve growth factor expression. All these data indicate that expression of neurotrophins is differentially regulated in functionally distinct classes of hippocampal interneurons immunoreactive for neuropeptides. We also analysed whether neuropeptide-immunoreactive interneurons expressing neurotrophins were targets of the GABAergic septohippocampal pathway. We used a triple detection method, combining anterograde tracing of this connection, with in situ hybridization for the detection of neurotrophin mRNA, and immunocytochemistry against neuropeptides. Our data showed that the four populations of hippocampal interneurons studied (somatostatin, neuropeptide-Y, vasoactive intestinal polypept