Effects of Decerebration on Toad

ABSTRACT

The brain is the most important part of an organism’s body. It is the one that receives all information from different stimuli and controls the movement of body parts. But for sudden stimuli that needs a quick response, spinal cord reflexes happened. The effect of decerebration on a toad (Bufo marinus) will cause its inability to move, but it still responded to stimuli because of certain reflexes which were not mediated by the brain. The intact toad’s response to certain stimuli was first observed. The same toad was decerebrated and took the same procedure. The result showed that the decerebrated frog still performed its withdrawal reflex on acetic acid, righting (toad on its back), croaking and swimming reflex and only failed two reflexes. Thus even if an organism was decerebrated, it can still responds on certain stimuli though reflexes.

INTRODUCTION

Amphibians are one of members of the group of vertebrate animals characterized by their ability to exploit both aquatic and terrestrial habitats ( Encyclopædia Britannica, 2012).They respire through their skin, gills and lungs, has closed circulatory system, cold blooded and have a well-develop brain (Evangelista and Malonzo, 2006). Toads, frogs and salamanders are classified as amphibians. Class Amphibia, like other classes of phylum Chordata, has a nervous system that developed from an embryonic nerve cord. It is divided into three divisions: the central nervous system, the peripheral nervous system and the autonomic nervous system (Reyes, 2013). The central nervous system consists of the brain and spinal cord, both derived from the embryonic neural tube. Both are surrounded by protective membranes called the meninges, and both float in a crystal-clear cerebrospinal fluid.

The brain is encased in a bony vault, the neurocranium, and integrates sensory information and directs motor responses; in higher vertebrates it is also the centre of learning (Encyclopædia Britannica, 2012). The spinal cord runs down the center of the back and is connected to the brain. It is protected by the vertebral column composed of individual vertebrae and extend about 43 cm from the base of the brain to an inch or below the last rib. It brings impulses to and from the brain. It also communicates with and receives information from the rest of the body through 31 pairs of spinal nerves and without the interaction with the brain, handles reflexes. (Evangelista and Malonzo). Reflexes, on the other hand, are immediate response to some stimuli, which come involuntary and is often not mediated by the higher center of the brain. Impulses enter the spinal cord through the dorsal root.

Once in the spinal cord, electrical signals synapse with interneurons, which in turn transmit impulses to motor neurons and into the effector organs (Ocampo and Reyes). An organism can response to a certain stimuli even if its brain is damaged or slightly destroyed through the spinal cord reflex. This shows that even if the toad( Bufo marinus)was decerebrated (only the brain was destroyed or damaged ), it can withdraw its limbs as the effect of acetic acid , maintain its proper posture , croak and swim because the spinal cord is still intact and can make reflexes. This study was conducted in RoomA-137, Institute of Biological Sciences, UP Los Banos on September 2013.

MATERIALS AND METHODS
A toad, a blunt object, water basin, acetic acid/ HCl and a dissecting kit were used in the experiment. The following procedures were done: probing a blunt object close to the toads’ eye, dropping of a small amount of acetic acid on its hand, allowing it to jump, placing the toad on its back, stroking the belly and placing it in a water basin and allowing it to swim. The observation on the normal (intact) toad was first done. After the observations were recorded, the same toad was double pithed using a dissecting kit leaving its spinal cord still in contact. The same experiment was also done to the decerebrated toad and the observations were recorded. A table showing the responses of an intact and decerebrated toad to different stimuli was made.

RESULTS AND DISCUSSION
Results showed that a decerebrated toad can still responds to certain stimuli even if its brain is severely damage or destroyed. The toad can still withdraw its hand due to the effect of acetic acid placed on it, bring back to its normal position, can still croak and swim in water. The effect of the decerebration can be seen on its inability to blink when a blunt object was probed close to one of its eyes and its inability to jump anymore (Table 1). The responses that were done by the decerebrated toad to certain stimuli is called spinal cord reflexes. Reflex is an involuntary response to a stimulus by the animal organism. In its simplest form, it consists of the stimulation of an afferent nerve through a sense organ, or receptor, followed by transmission of the stimulus, usually through a nerve center, to an efferent motor nerve, resulting in action of a muscle or gland, called the effector. In most reflex action, however, the stimulus passes through one or more intermediate nerve cells, which modify and direct its action, sometimes to the extent of involving the muscular activity of the entire organism. (Kanouse, 2007)

Table 1. The responses of intact and decerebrated toad to different stimuli. Stimulus
Response*

Intact
Decerebrated
A Blunt probe
(Blinking Reflex)
+
–
B Acetic acid or HCl
(Withdrawal reflex)
+
+
C Jumping Reflex

+
–
D Toad on its bacl
(Righting Reflex)
+
+
E Stroking to belly
(Croaking Reflex)
+
+
F Swimming Reflex
+
+
* +: positive, – : negative
The result of this experiment showed that spinal cord reflexes are important in an organism especially in its quick response to sudden stimuli. It also showed that decerebrated toads can still responds to certain stimuli through reflexes.

SUMMARY AND CONCLUSION
The effects of decerebration on toad (Bufo marinus) in accordance to its responses to different stimuli were determined. Intact and derebrated toad almost have the same responses except for the blinking and jumping reflex. The experiment also showed that the brain is not the only one who controls the movement of an organism particularly on sudden stimuli, the spinal cord also does through the reflexes. Therefore, even if an organism was decerebrated, it can still responds on certain stimuli though reflexes.

LITERATURE CITED
Amphibian. (2012). Encyclopædia Britannica. Encyclopædia Britannica Ultimate Reference Suite. Chicago: Encyclopædia Britannica. Brain. (2012). Encyclopædia Britannica. Encyclopædia Britannica Ultimate Reference Suite. Chicago: Encyclopædia Britannica. Evangelista, E.V. and E.R Malonzo. 2006. Science in Today’s World: Biology. Quezon City: Sibs Publishing House, Inc. pp. 110,252-253. Kanouse, D. “Reflex.” Microsoft® Student 2009 [DVD].
Redmond, WA: Microsoft Corporation, 2008. Ocampo, P.P and R.C Reyes. General Zoology: Laboratory Manual in Introductory Zoology. UPLB: Institute of Biological Sciences.pp.56-57. Reyes, R.C. 2013. Lecture Syllabus in General Zoology. UPLB: Institute of Biological Sciences.pp.70.