Behavioral and heart rate effects of infusing kainic acid into the dorsal midbrain during early development in the...

The dorsal midbrain including the periaqueductal gray (PAG) is involved in the control of threat-induced vocalizations and other behavioral and autonomic defensive responses in adult animals. Little is known of its function early in life. The present study examined the ability of kainate receptor stimulation in these midbrain areas to trigger behavioral and physiological responses during the first three postnatal weeks in the rat. Kainate (0.03-0.3 nmol) was infused into the dorsal midbrain of postnatal day 7 (P7), P14 and P21 rat pups. At P7, subjects exhibited only a brief period of locomotor activation immediately following infusion of kainate. There were no changes in the heart rate or in any other behavioral measures, including their production of ultrasonic vocalizations. At P14, kainate induced adult-typical escape behaviors consisting of running and jumping, increases in the duration of time spent immobile, and increases in heart rate. At P21, subjects given kainate exhibited escape behavior coupled with elevated heart rate and immobility coupled with decreased heart rate. P14 and P21 subjects produced only small, non-significant increases in their production of ultrasonic vocalizations. These results indicate that kainate receptor stimulation in the dorsal midbrain does not mediate most adult-typical, threat-induced responses until sometime during the second postnatal week in the rat.