Assesment of rat intracardiac neurons‘ morphology

Background: Researches show that intracardiac nerve plexus plays an important role in regulation of heart work. Different functional types of intracardiac neurons are heterogenous on their cytochemic, morphologic – bodies and processes – and electrophysiologic features. Although rat is used in experimental investigations quite often and intracardiac neurons of rat have already been assessed neurochemically, electrophysiologically and morphologically, there is still lack of information about it. In most of the scientists‘ works dimensions of the bodies of intracardiac rat neurons were measured and length and features of processes were not. To supplement the knowledge of neurons morphology of mammalian heart, we measured dimensions of neuronal bodies, axons and processes after intracellularly injecting neurons with Alexa Fluor 568 in situ. Aim of the study: To evaluate morphologic features of neurons of rat intracardiac nerve plexus using intracellular dye injection method. Objectives: 1. To inject intracellular dye Alexa Fluor 568 into chemically unfixed neurons in situ. To photograph injected neurons using serial optical sections and to analize data using AxioVision 4.7.2. 2. To measure dimensions of bodies of neurons, length of axons, length of processes and to group processes (excluding axons) by their length and starting point. Material and methods: Preparations of heart intracardiac nerve plexuses were obtained from adult rats. Neurons were injected intracellularly with Alexa Fluor 568 dye in situ using chemically unfixed micropreparations. Data of serial optical sections of dyed neurons were analyzed using fluorescent microscope and software AxioVision 4.7.2 Results: Most of measured rat heart neurons were round–shaped, having unsmooth surface of the body. The area of the body of neuron was 789 ± 275 µm2 on average and the area of the nucleus of neuron was 125 ± 38 µm2 on average, body area to nucleus area ratio was 6,4 ± 1,6 on average. There were 40% multipolar, 39,2% unipolar and 20,8% bipolar neurons. The axon length was 570 ± 438 µm on average, the total length of neuron processes‘ was 640 ± 485 µm on average. Conclusions: Most of rat intracardiac neurons are multipolar and unipolar. Most of the processes, excluding axon, start from the body of the neuron (apart from axon hillock). Total length of processes starting from axon hillock is similar to total length of processes starting from neuron body on average